| 1. |
- Asplund, Basse, et al.
(författare)
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Variable Hard Segment Length in Poly(urethane urea) through Excess of Diisocyanate and Vapor Phase Addition of Water
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39, s. 4380-4385
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Tidskriftsartikel (refereegranskat)abstract
- Poly(urethane urea)s with hard segments derived only from diisocyanate linked via urea linkages were synthesized using a new and simple one-pot method. The creation of urea linkages were done via creating the amine in situ by adding water in vapor phase slowly and continuously. This synthesis method eliminates the tedious control to approach stoichiometry, is less sensitive to impurities, involves no intermediate isolation steps, and does not involve any chain extender. A study using a two-armed poly(-caprolactone) as soft segment and methyl 2,6-diisocyantohexanoate (LDI) as the hard segment was performed. The length of the hard segment was varied from 4.8 to 11.6 LDI units. Stress-strain measurements showed an increase in elastic modulus, 146 to 235 MPa, when increasing the hard segment length, while the elongation at break decreased, 980 to 548%. IR spectroscopy showed an increase in hydrogen bonding when increasing the hard segment length. The synthesis was also shown to be applicable to common diisocyanates such as HDI, TDI, and MDI.
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| 2. |
- Atthoff, Björn, et al.
(författare)
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Biodegradable Ionomers
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:11, s. 3907-3913
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Tidskriftsartikel (refereegranskat)abstract
- Several telechelic anionic or cationic ionomers were synthesized starting from poly(trimethylene carbonate) diols (PTMC) of different molecular weight, ranging from 1000 to 12 000 g/mol. In the synthesis of the anionomer, addition of sulfur trioxide trimethylene complex to the PTMC end-group hydroxyls and subsequent ion exchange afforded a disulfate monoester sodium salt. The cationomer was synthesized in two steps. Acylation of the PTMC diol using 4-chlorobuturyl chloride was followed by displacement of the alkyl chloride with trimethylamine to give a quaternary ammonium salt. These ionomers showed excellent swelling properties, up to around 500% in H2O, while the unfunctionlized PTMC did not swell at all. The lowest molecular weight ionomers were soluble in both water and chloroform. The physical properties of the ionomers were analyzed with oscillating rheological experiments. Interestingly, the ionomers displayed "rubbery plateau". The mechanical and swelling properties may be linked to phase separation resulting in ionic aggregates within the bulk, which may function as physical cross-links. At ambient temperatures, the PTMC starting material behaved like a highly viscous fluid, while the ionomers behaved as elastomers. In a hydrophilic environment, the ionomers displayed a surface rearrangement making the surface of the ionomer hydrophilic by allowing the ionic end groups to appear at the water ionomer interface. In air or vacuum all the ionic groups were found in the bulk of the material as analyzed by XPS or contact angle measurements. Finally, we showed that with the specific ionic groups it was possible to complex specific molecules to the ionomers.
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| 3. |
- Barrau, Sophie, et al.
(författare)
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Nanomorphology of Bulk Heterojunction Organic Solar Cells in 2D and 3D Correlated to Photovoltaic Performance
- 2009
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:13, s. 4646-4650
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Tidskriftsartikel (refereegranskat)abstract
- Control of the nanoscale morphology of the donor-acceptor material blends inorganic solar Cells is critical for optimizing the photovoltaic performances. The influence of intrinsic (acceptor materials) and extrinsic (donor:acceptor weight ratio, substrate, solvent) parameters was investigated, by atomic force microscopy (AFM) and electron tomography (ET), on the nanoscale phase separation of blends of a low-band-gap alternating polyfluorene copolymers (APFO-Green9) with [6,6]-phenyl-C-71-butyric acid methyl ester ([70]PCBM). The photovoltaic performances display an optimal efficiency for the device elaborated with a 1:3 APFO-Green polymer:[70][PCBM weight ratio and spin-coated from chloroform solution. The associated active layer morphology presents small phase-separated domains which is a good balance between as a large interfacial donor-acceptor area and Continuous paths of the donor and acceptor phases to the electrodes.
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| 4. |
- Benkoski, JJ, et al.
(författare)
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Light-activated desorption of photoactive polyelectrolytes from supported lipid bilayers
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:9, s. 3852-3860
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Tidskriftsartikel (refereegranskat)abstract
- Phospholipid vesicles and supported bilayers have emerged as a promising platform for the development of biorecognition devices. To expand the capabilities of such biochips, it becomes desirable to direct and control the assembly of lipid structures into more sophisticated architectures. As one step toward this goal, we demonstrate the photoregulated desorption of a new class of polymer from lipid bilayers. The neutral, hydrophobic polymer resides within the bilayer under mild pH and ambient conditions. However, it contains side groups that can undergo excited state proton transfer (ESPT). The polymer therefore behaves as a polyelectrolyte when exposed to IN light. With the ensuing increase in hydrophilicity, the molecule is spontaneously ejected from the bilayer. Quartz crystal microbalance measurements with dissipation monitoring (QCM-D) have recorded this process and have shown that a rapid buffer exchange during light exposure results in efficient removal of the polymer from the system. Three polymers were tested in all: a polyanion, a polyeation, and a polyzwitterion. A one-step approach to the synthesis of the monomer, performed under relatively mild reaction conditions, made it possible to synthesize each polymer in one step.
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| 5. |
- Bergenudd, Helena, et al.
(författare)
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Solvent Effects on ATRP of Oligo(ethylene glycol) Methacrylate. Exploring the Limits of Control
- 2009
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:9, s. 3302-3308
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Tidskriftsartikel (refereegranskat)abstract
- Five copper complexes in combination with six monomer-solvent mixtures have been used to investigate the solvent effects oil ATRP of oligo(ethylene glycol) methacrylate (OEGMA). The redox properties of the copper complexes in OEGMA-solvent mixtures and the apparent rate constants (k(p)(app)) for ATRP of OEGMA were correlated to the degree of control over the polymerizations. Based on this correlation, a general discussion of the limits of control in ATRIP is carried out. One of the key parameters for control in ATRP is the propagation rate constant, making the choice of monomer essential for the design of ail ATRP system. Also, the solvent effects oil the ATRP equilibrium constant (K-ATRP) affect the limit of control (i.e., the apparent rate constant above which control is lost). The choice of copper complex is also more important than the choice of solvent for the design of a well-controlled ATRP system.
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| 6. |
- Chen, Gaojian, et al.
(författare)
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A modular click approach to glycosylated polymeric beads : Design, synthesis and preliminary lectin, recognition studies
- 2007
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:21, s. 7513-7520
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Tidskriftsartikel (refereegranskat)abstract
- Covalent immobilization of a range of carbohydrate derivatives onto polymeric resin beads is described. Copper-catalyzed Huisgen [2 + 3] cycloaddition (often termed click chemistry) was used to graft mannose-containing azides to complementarily functionalized alkyne surfaces, namely (a) Wang resin or (b) Rasta particles consisting of a clickable alkyne polymer loose outer shell and a Wang resin inner core. For the second approach, Wang resin beads were first converted into immobilized living radical polymerization initiators with subsequent polymerization of trimethylsilanyl-protected propargyl methacrylate followed by deprotection with TBAF to yield the desired polyalkyne clickable scaffold. The appropriate (x-mannopyranoside azide was then clicked onto the bead to give a mannose functionalized Rasta resin. IR, gel-phase H-1 NMR, and elemental analysis have been used to characterize the modified resins. The binding abilities of these D-mannose-modified particles were subsequently tested using fluorescein-labeled Concanavalin A (Con A), a lectin that binds certain mannose-containing molecules. Preliminary results indicated that the novel glyco-hybrid materials presented in this work are able to efficiently recognize mannose-binding model lectins such as Con A, opening the way for their potential application in affinity chromatography, sensors, and other protein recognition/separation fields.
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| 7. |
- Cheun, H., et al.
(författare)
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Polarized optical absorption spectroscopy, NEXAFS, and GIXRD measurements of chain alignment in polyfluorene thin films
- 2008
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:17, s. 6463-6472
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Tidskriftsartikel (refereegranskat)abstract
- The uniaxial chain alignment of low molecular weight poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films cast atop rubbed polyimide templates is characterized by polarized optical absorption spectroscopy, carbon K near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and grazing incidence X-ray diffraction (GIXRD) in response to thermal annealing and increasing film thickness (ca. 15-150 nm). The highest overall levels of uniaxial alignment are obtained in the thinnest PF2/6 films. However, the orientation of chains at the top surface after thermal annealing is nearly thickness independent despite a large drop in the maximum optical dichroic ratio as the film thickness increases. The kinetics of chain alignment on heating are strongly film thickness dependent and only weakly correlated with a crossover to a nematic liquid crystal state. All told these data support a structural model in which there is a graded morphology such that the top and bottom surfaces exhibit appreciable planar, uniaxial alignment while the film interior includes a greater proportion of nomplanar (i.e., tilted) chains after thermal cycling. These inhomogeneities are likely to influence technologically important optical and transport properties.
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| 8. |
- Chronakis, IS, et al.
(författare)
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Generation of molecular recognition sites in electrospun polymer nanofibers via molecular imprinting
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:1, s. 357-361
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Tidskriftsartikel (refereegranskat)abstract
- A simple method for the formation of molecular recognition sites in polymer nanofibers was developed. Electrospun nanofibers were prepared from a Solution mixture of poly(ethylene terephthalate) (PET) and polyallylamine in the presence of a template molecule, 2,4-dichlorophenoxyacetic acid (2,4-D). The polyamine was used to provide functional groups that interact with the template during the electrospinning process, and PET acted as a major supporting matrix to ensure easy fiber formation and to minimize the conformational change of the polymers when the nanofibers were subjected to different solvent treatments. When the template was removed by solvent extraction, imprinted binding sites were left in the nanofiber materials that are capable of selectively rebinding the target molecule. The molecularly imprinted nanofibers were characterized by SEM, FT-IR, and radioligand binding analysis.
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| 9. |
- Colsenet, Roxane, et al.
(författare)
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Effect of casein concentration in suspensions and gels on poly(ethylene glycol)s NMR self-diffusion measurements
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:22, s. 9171-9179
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Tidskriftsartikel (refereegranskat)abstract
- PFG-NMR spectroscopy was used to study the diffusion of molecular probes (poly(ethylene glycol)s) in casein suspensions and gels in terms of the effects of probe molecular size (molecular mass between 1080 and 634 000 g/mol), casein concentrations (from 3.24 to 16.22 g/100 g), and effects of rennet coagulation. A strong dependency of diffusion on probe size was observed, both in casein suspensions and in gels: as the PEG size increased, the diffusion was reduced. This effect was more pronounced for higher casein concentrations. Changes in casein structure after addition of rennet increased the diffusion coefficient for 82 250 and 634 000 g/mol PEG. The PEG self-diffusion coefficients in casein gels were compared to the casein gel structures characterized by scanning electron microscopy. Assuming high internal micelle porosity, a diffusion model with two diffusion pathways, one outside and one inside the micelles, was used to explain the PEG diffusion in casein solutions and gels. The results were discussed in the context of variations in casein micelle voluminosity after renneting.
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| 10. |
- Colsenet, Roxane, et al.
(författare)
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Pulsed field gradient NMR study of poly(ethylene glycol) diffusion in whey protein solutions and gels
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:3, s. 1053-1059
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Tidskriftsartikel (refereegranskat)abstract
- PEG self-diffusion coefficients of poly(ethylene glycol)s (PEGs) (1080, 8500, and 82 250 g/mol) were measured by PFG-NMR spectroscopy in whey protein solutions and gels in relation to whey protein concentration effects (from 6.49 to 40.45 g/100 g) and whey protein heat denaturation effects (30 min at 70 degrees C). A strong dependency of diffusion on probe size was observed in both whey protein solutions and gels: as PEG size increased, diffusion was reduced. This effect was more pronounced for higher protein concentrations. Changes in whey structure after thermal aggregation increased the diffusion coefficient for all PEGs, particularly for the 8500 g/mol PEG. The PEG self-diffusion coefficients in whey protein gels were compared to the gel structures characterized by scanning electron microscopy. The results are discussed in relation to a reptation model and compared to PEG diffusion in casein micelle suspensions and gels.
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| 11. |
- Doherty, Walter J, et al.
(författare)
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Electrochemical copolymerization and spectroelectrochemical characterization of 3,4-ethylenedioxythiophene and 3,4-ethylenedioxythiophene-methanol copolymers on indium-tin oxide
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:13, s. 4418-4424
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Tidskriftsartikel (refereegranskat)abstract
- This work describes the electrochemical copolymerization and spectroelectrochemical characterization of 3,4-ethylenedioxythiophene (EDOT) with a commonly used EDOT derivative: 2,3-dihydrothieno[3,4b]-l,4-dioxyn-2-yl methanol (EDTM), on indium-tin oxide (ITO) electrodes, as a function of the EDTM/EDOT comonomer feed ratio. The potential of initial polymerization and the degree of optical contrast between reduced and oxidized states increased steadily with increasing proportions of EDTM. Reactivity ratios were determined by spectroscopic characterization of the copolymer film and by monitoring the depletion of monomer from the starting solution by liquid chromatography, following the formation of relatively thick PEDOT/PEDTM films. Average reactivity ratios of 1.5 ±0.2 and 0.4 ±0.3 were obtained for EDOT and EDTM, respectively, demonstrating preferential deposition of EDOT on ITO electrode surfaces. Significant differences were noted at low and high degrees of conversion, indicating changes in copolymer composition with film thickness. These results have real significance for the characterization of electron-transfer rates for the first monolayer of PEDOT/ PEDTM on ITO, determined by a new mode of potential-modulated attenuated total reflectance spectroelectrochemistry. © 2006 American Chemical Society.
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| 12. |
- Edgecombe, Samuel, et al.
(författare)
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Monte Carlo simulation of polyelectrolyte gels: Effects of polydispersity and topological defects
- 2007
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:10, s. 3868-3875
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Tidskriftsartikel (refereegranskat)abstract
- Volumes and other structural properties of polyelectrolyte gels in equilibrium with pure water have been determined by Monte Carlo simulations. The role of chain length polydispersity and topological network defects of four different networks with varying cross-linking density, monomer charge, and chain stiffness have been investigated. Generally, a chain length polydispersity reduced the gel volume, whereas the presence of chains with one end detached from the cross-linker (severed chains) led to an increased gel volume. Polyelectrolyte networks displayed the largest and uncharged polymer networks the smallest dependence on chain length polydispersity. The effect of severed chains was strongest for flexible polyelectrolyte gels and weakest for uncharged networks and stiff polyelectrolyte gels. Mechanical properties of uncharged and charged polymer gels were also investigated through uniaxially stretching and compared with theory.
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| 13. |
- Forsman, Jan, et al.
(författare)
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Surface forces at restricted equilibrium, in solutions containing finite or infinite semiflexible polymers
- 2007
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:23, s. 8396-8408
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Tidskriftsartikel (refereegranskat)abstract
- We use density functional theory to investigate how the presence of polymers influence the interactions between adsorbing or nonadsorbing flat surfaces, forming a slit geometry. The study is primarily made under "restricted equilibrium" conditions, i.e., below a threshold separation, the chains are allowed to equilibrate conformationally between the surfaces, but they are unable to diffuse into or out from the slit. This is believed to be a reasonable model for commonly encountered experimental situations, when the surfaces are large and adsorbing and the polymers are long. Using a recently presented density functional theory, we are able to compare predictions for chains of finite and infinite length. A major advantage of the infinite chain formulation is that it is a high resolution theory, and predictions from the finite length version will exactly approach the ones for infinite chains, when the degree of polymerization becomes large enough. Our study spans across a relatively large number of relevant system parameters, such as bulk concentration, surface adsorption strength, polymer length, and chain flexibility. The response in terms of the net surface interaction, to a change of a system parameter, is often nonmonotonic. We also make comparisons with predictions it full equilibrium, where the diffusion constraint has been relaxed. We give a specific example of how a diffusion-limited process can lead to hysteresis effects, similar to those observed in many surface force measurements. Finally, in a separate section of this work, we have included some direct experimental comparisons, demonstrating the relevance and applicability of restricted equilibrium conditions to "real world" scenarios. The computational power of the density functional approach is here highlighted, with calculations including semiflexible 20000-mers.
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| 14. |
- Forsman, Jan, et al.
(författare)
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Surface forces in solutions containing rigid polymers: Approaching the rod limit
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:3, s. 1269-1278
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper,(1) we investigated how the interaction between two adsorbing surfaces in a polymer solution responds to changes of the intrinsic stiffness of the polymer chains. We demonstrated that as the chain rigidity is increased, starting from the fully flexible limit, a free energy barrier develops. In this work, we shall continue our studies of semiflexible polymers but focus on the other extreme, where the stiffness is increased to the extent that the chains become rodlike. In this limit, the free energy barrier disappears and is replaced by a long-ranged attraction. A weak barrier at separations corresponding to the length of a fully stretched chain is, however, present. The approach to rodlike behavior is very slow at low polymer concentrations; i.e., rods will under these conditions behave in a manner which is qualitatively different from that of even extremely rigid semiflexible chains. At higher concentration, a slightly different picture emerges, since saturation effects will prevent an exceptionally strong adsorption of rods. Semiflexible polymers will then display reasonably "rodlike" behavior at a more moderate chain rigidity. Still, our results suggest that models of semiflexible chains as rods or cylinders should be treated with considerable caution, at least in terms of adsorption or surface force properties. Our results furthermore show that the results for explicit solvent models, adopted in our previous work, are in this case qualitatively reproduced by simpler models, where the solvent enters implicitly. The agreement across a range of different model systems, of which some are solved exactly, lends support to the qualitative conclusions drawn from our studies on these systems. Finally, we compare structural density functional predictions with corresponding simulation results. The predictions are accurate, except in the case of extremely stiff chains and rodlike chains. These display considerable ordering at the surfaces, a phenomenon that cannot be captured by the present density functional. This leads to a significant underestimation of the primary adsorption peak. However, comparisons between surface forces in rod solutions, as obtained from grand canonical simulations and density functional calculations, demonstrate that the ordering transitions have little influence on the surface interactions. This is because the surface interactions are governed by the free chains, which are not strongly adsorbed to any surface. We also show that the small quantitative effect that surface ordering does have on the surface forces, in principle, can be handled in an effective manner by a simple increase of the surface potential strength.
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| 15. |
- Forsman, Jan, et al.
(författare)
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Surface forces in solutions containing semiflexible polymers
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:3, s. 1261-1268
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Tidskriftsartikel (refereegranskat)abstract
- The influence of intrinsic chain stiffness on surface forces in solutions containing semiflexible polymers is investigated with density functional theory. The solvent is included explicitly, but comparisons are also made with exact results obtained with ideal chains, in the absence of solvent particles. We find that as the intrinsic stiffness increases, the polymers are at intermediate separations less able to form strong attractive bridges. This leads to a substantial free energy barrier. At short separations, bridging does dominate, resulting in an attractive interaction. However, the way in which the height of the free energy barrier responds to changes of the chain length, at a given stiffness, as well as on stiffness, for a given chain length, is nontrivial and not monotonic. There is furthermore a saturation effect, which at high monomer concentrations leads to a depletion interaction at intermediate separations. This amounts to a reversal of the mechanisms underlying the net interaction. That the density functional theory is accurate is verified by an excellent agreement between predicted structural properties and corresponding data obtained by simulations.
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| 16. |
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| 17. |
- Hakkarainen, Minna, et al.
(författare)
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ESI-MS reveals the influence of hydrophilicity and architecture on the water-soluble degradation product patterns of biodegradable homo- and copolyesters of 1,5-dioxepan-2-one and epsilon-caprolactone
- 2008
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:10, s. 3547-3554
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Tidskriftsartikel (refereegranskat)abstract
- The hydrolytic degradation process and degradation product patterns of biodegradable homo- and copolyesters of 1,5-dioxepan-2-one (DXO) and epsilon-caprolactone (CL) were monitored by electrospray ionization mass spectrometry (ESI-MS). The degradation product patterns were compared to mass loss, molecular weight changes, copolymer composition, and pH changes after various hydrolysis times. Water-soluble oligomers up to heptadecamer were identified after hydrolysis of hydrophilic PDXO, while only oligomers up to hexamer were detected after hydrolysis of the more hydrophobic PCL. The product pattern of DXO-CL-DXO triblock copolymer mainly consisted of DXO-based oligomers, whereas the CL/DXO multiblock copolymer degradation product pattern contained DXO and CL oligomers as well as oligomers containing both DXO and CL units. The DXO-rich oligomers, however, dominated the product patterns. ESI-MS gave valuable insights into the hydrolysis process of hydrophobic and hydrophilic polyesters and showed that hydrophilicity of the polymer as well as copolymer architecture both greatly influenced the water-soluble degradation product patterns.
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| 18. |
- Hedfors, Cecilia, et al.
(författare)
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Thiol end-functionalization of poly(epsilon-caprolactone), catalyzed by Candida antarctica lipase B
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:3, s. 647-649
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Tidskriftsartikel (refereegranskat)abstract
- The use of Candida antarctica Lipase B (CALB) chemoselective catalyst in the Thiol End-Functionalization of Poly(ε-caprolacetone) was discussed. Thiol-functionalization of poly(ε-caprolacetone)(PCL) was made by an initiation reaction catalyzed by CALB in bulk. 2-Mercaptoethanol (1) was used to initiate the enzyme-assisted ring opening polymerization of ε-caprolacetone(2) to give the desired thiol-functionalized polymer. The structure of the terminated PCL was confirmed by 13C nuclear magnetic resonance .
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| 19. |
- Iruthayaraj, Joseph, et al.
(författare)
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Adsorption of Low charge Density Polyelectrolyte Containing Poly(ethylene oxide) Side chains on Silica : Effects of Ionic strength and pH
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:14, s. 6152-6160
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption characteristics of a random copolymer of poly(ethylene oxide) monomethyl ether methacrylate and methacryloxyethyl trimethylammonium chloride (PEOMENIA:METAC) on silica were studied using stagnation point adsorption reflectometry (SPAR), quartz crystal microbalance with dissipation (QCM-D), and contact angle techniques. The PEOMEMA:METAC copolymer used in this study is a low charge density polyelectrolyte, with 2% of the monomer units carrying permanent positive charges and 98% containing poly(ethylene oxide) side chains that are approximately 45 repeating units long. The surface excess was determined as a function of pH and concentration of indifferent electrolyte. It was found that the presence of a small amount of 1: 1 electrolyte decreases the adsorbed amount significantly. Further, increasing the pH at a constant ionic strength, 10 mM, results in decreasing surface excess. It is suggested that the adsorption is realized via a combination of non-Coulomb interactions between the poly(ethylene oxide), PEO, grafts and protonated silanol groups at the silica-solution interface and an electrostatic interaction between the charged segments and the oppositely charged surface. Increasing pH and/or salt concentration results in progressive charging of the silica surface with the consequent decrease in affinity between silica and PEO, explaining the decrease in the adsorbed amount of the polymer.
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| 20. |
- Jaczewska, Justyna, et al.
(författare)
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Polymer vs Solvent Diagram of Film Structures Formed in Spin-Cast Poly(3-alkylthiophene) Blends
- 2008
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Ingår i: Macromolecules. - Washington : American Chemical Society. - 0024-9297 .- 1520-5835. ; 41, s. 4802-4810
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Tidskriftsartikel (refereegranskat)abstract
- A polymer vs solvent diagram of film structures, formed in polystyrene (PS) blends (1:1 w:w PS/PT) with poly(3-alkylthiophenes) PT [regioregular R-P3DDT, R-P3HT and regiorandom P3BT, P3DDT] spincoated onto oxidized silicon surfaces from various common solvents [p-xylene, toluene, chloroform, chlorobenzene, cyclohexanone] is presented. The structures were determined with microscopic techniques (atomic, AFM and lateral, LFM, force microscopy, fluorescent microscopy FM) and dynamic secondary ion mass spectrometry (dSIMS). The diagram, arranged according to the solubility parameter of the PTs and the solvents, exhibits three main structural classes: dewetting, lamellar, and lateral (quasi-2-dim) morphology. Decrease in PT solubility parameter δPT inhibits dewetting of polymer films. It induces also a transition from lamellar to lateral film structure. Increase in solvent solubility parameter δS has similar effects. Such behavior is related to the stability of transient homogeneous films and multilayers in the course of spin-casting. The role of δPT and δS is elucidated based on the stability analysis performed in terms of spreading coefficient (dependent on δPT) and effective interfacial tension of solvent-rich polymer phase (dependent on δS).
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| 21. |
- Jonkheijm, P, et al.
(författare)
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Control of film morphology by folding hydrogen-bonded oligo(p-phenylenevinylene) polymers in solution
- 2006
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 39:2, s. 784-788
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Tidskriftsartikel (refereegranskat)abstract
- The film morphology of pi-conjugated oligomers has been controlled by self-assembly in solution. To this end supramolecular hydrogen-bonded systems of oligo(p-phenylenevinylene) (OPV) carrying ureido-s-triazine hydrogen-bonding groups are used. Neutron scattering experiments in dodecane solutions show that columnar stacks are formed. Films with thicknesses on the order of 100 nm are made that have a supramolecular organization resembling the organization present in solution. Uniform rodlike morphological domains range over several hundreds of nanometers as shown by atomic force microscopy. The rodlike morphology of the OPVs was also preserved when blended with a C-60 derivative, producing stable photovoltaic devices.
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| 22. |
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| 23. |
- Kemerink, Martijn, et al.
(författare)
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Substitution and preparation effects on the molecular-scale morphology of PPV films
- 2005
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 38:18, s. 7784-7792
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Tidskriftsartikel (refereegranskat)abstract
- The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a function of the substitution pattern of the conjugated backbone. Moreover, the influence of concentration in the casting solution, annealing, the choice of solvent, and the role of defects are addressed. By using a recently developed scanning-probe technique, we are able to visualize individual polymer chains and aggregates on the surface of spin-cast films. We find that a symmetric substitution pattern strongly promotes interchain aggregation in the surface layer, whereas an unsymmetric pattern in some cases leads to intrachain or self-aggregation. The nature of these intrachain aggregates is further investigated using molecular dynamics simulations. The observed molecular morphologies can in most cases be qualitatively related to macroscopic electrooptical properties. Therefore, our results strongly suggest that the surface morphology may be regarded as indicative of the morphology of the entire film.
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| 24. |
- Kirsebom, Harald, et al.
(författare)
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Mechanism of Cryopolymerization: Diffusion-Controlled Polymerization in a Nonfrozen Microphase. An NMR Study
- 2009
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:14, s. 5208-5214
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Tidskriftsartikel (refereegranskat)abstract
- Polymerization of dimethylacrylamide (DMAAm) cross-linked with PEG diacrylate was studied using H-1 NMR both in situ in a semi frozen system and in a supercooled aqueous system. The amount of nonfrozen microphase, in which polymerization proceeds, is defined by the concentration of the starting monomers and the freezing temperature, which depends on the depression in freezing temperature caused by dissolved osmolytes. However, despite there being identical initial concentrations in the nonfrozen microphase, at a chosen temperature of -10 degrees C the cryopolymerization proceeded at different rates depending on the size of the nonfrozen microphase. Further studies of the conditions in the nonfrozen microphase were performed by using pulsed gradient spin echo (PGSE) to study the self-diffusion of solutes. Observations regarding the reaction rate were rationalized in terms of different degrees of long-range diffusion which was seen using PGSE. Cryopolymerization resulted in decreasing osmolyte concentration, and hence in gradual freezing of excess water as defined by the depression in freezing point caused by the remaining monomers. The NMR data provide a way of rationale predicting the effect of the monomer concentrations and freezing temperatures on the amount of nonfrozen microphase and its polymer concentration. These parameters define cryogel properties such as mechanical strength and porosity, which are evaluated using SEM and as flow resistance of cryogels.
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| 25. |
- Knaapila, Matti, et al.
(författare)
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Evidence for 21-helicity of poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl]
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:10, s. 3610-3614
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Tidskriftsartikel (refereegranskat)abstract
- The conformational state of the pi-conjugated polyfluorene poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] is reconsidered. Contrary to the general opinion, this helical polymer is shown to organize in a giant repeat consisting of 21 monomer units. The length of the unit cell of 16.97 nm is suggested.
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| 26. |
- Knaapila, Matti, et al.
(författare)
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Influence of side chain length on the self-assembly of hairy-rod poly(9,9-dialkylfluorene)s in the poor solvent methylcyclohexane
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:26, s. 9398-9405
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the phase behavior of poly(9,9-dihexylfluorene) (PF6), poly(9,9-diheptylfluorene) (PF7), poly(9,9-diocylfluorene) (PF8) poly(9,9-dinonylfluorene) (PF9), and poly(9,9-didecylfluorene) (PF10) in methylcyclohexane (MCH). After a heating-cooling cycle, in the 10-50 mg/mL. concentration range. PF6/ MCH. PF7/MCH. PF8/MCH, and PF9/MCH systems were found to be gel-like, while PF10/MCH appears less viscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10- 100 nm) sheetlike assemblies (thickness of 2-3 nm). The larger length scale Structures of these sheets show an odd-even dependence on the side chain (spacer) length: the PF6 and PF8 sheets are broader and thinner, whereas PF7 and PF9 sheets are thicker with a Putative double layer Structure. PF10 does not follow this sequence, and only part of the polymer is assembled into a sheetlike structure the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixtures also have lower length scale crystalline structures with an internal period corresponding to the periodicity observed in the solid-state P phase of PF8. Vestiges of crystalline domains are found for PF6 and PF7 but not for PF10. PF7/MCH. PF8/MCH, and PF9/MCH systems contain the conformational isomer C, of those chains observed in the ss phase, while this is not observed with other polymer/MCH systems.
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| 27. |
- Källrot, Niklas, et al.
(författare)
-
Dynamic study of single-chain adsorption and desorption
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:13, s. 4669-4679
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of adsorption and desorption of uncharged homopolymers have been investigated using a coarse-grained model comprised of a bead-spring chain and a planar surface. Brownian dynamics simulation has been used to examine the adsorption process for polymers released near the surface and with bulk properties as well as Monte Carlo simulations to explore equilibrium adsorption structures of the polymer. Systems with varying polymer contour length, polymer stiffness, and polymer-surface interaction potential have been considered. Investigations have been made on polymer extensions perpendicular and parallel to the surface and also characterized the adsorbed state in terms of loops, tails, and trains. After a diffusion of the polymer to the vicinity of the surface, three succeeding phases were identified: distortion, attachment, and relaxation phase. In the distortion phase, the polymer starts to experience the potential of the surface and becomes elongated perpendicular to the surface. In the attachment phase, the polymer makes direct contact with the surface and becomes contracted perpendicular to the surface and starts to spread on the surface. Finally, in the extended relaxation phase, the polymer continues to spread on the surface.
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| 28. |
- Källrot, Niklas, et al.
(författare)
-
Dynamics of Polymer Adsorption from Bulk Solution onto Planar Surfaces
- 2009
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:10, s. 3641-3649
-
Tidskriftsartikel (refereegranskat)abstract
- Polymer adsorption of uncharged homopolymers onto planar surfaces has been investigated by employing a coarse-grained bcad-spring polymer model using simulation techniques. Polymer solutions of two different densities and polymers of two different Contour lengths have been examined. The dynamics of the adsorption process appearing in systems composed of a polymer Solution placed near attractive. but initially polymer-free, surfaces were determined by Brownian dynamics simulations and equilibrium properties of corresponding systems by Monte Carlo simulations. The properties of the systems have been analyzed by monitoring the number of adsorbed polymers, bead density profiles, time and frequency of polymer attachments, spatial extension of polymers perpendicular and parallel to the surface, and configurational characteristics. Initially, the polymers diffuse toward the Surfaces, and at shorter distances the attractive Surface potential starts to pull the polymers toward the surface, making them slightly stretched perpendicular to the Surface. Thereafter, the polymers collapse onto the surface with multiple anchoring, and a slower relaxation increasing the extension of the polymers parallel to the Surfaces appears. Finally, at even longer times, and connected to the slow relaxation of the number of adsorbed polymers, the extension of the polymer coils parallel to the Surface is reduced. and the perpendicular extension is increased, with associated changes of the number of beads residing in tails, loop, and trains. The adsorption process becomes faster at decreasing polymer length and at increasing polymer density.
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| 29. |
- Limé, Fredrik, et al.
(författare)
-
Monodisperse Polymeric Particles by Photoinitiated Precipitation Polymerization
- 2007
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:6, s. 1962-1968
-
Tidskriftsartikel (refereegranskat)abstract
- Monodisperse polymer particles consisting of DVB and styrene-copoly-DVB were successfully synthesized by photoinitiated precipitation polymerization with 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator. A focused 150 W xenon short arc lamp was used to radiate the sample mixtures. The size of the particles ranged from 1.5 to 4 m and could be varied by changing the monomer concentration between 2 and 10% (v/v) and by means of the time of polymerization. By using photoinitiation instead of thermal initiation, it was possible to avoid coagulum and arrive at spherical particles with an exceptionally high monodispersity for particles of this size range (polydispersity index < 1.02) and with monomer loadings well above 5%.
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| 30. |
- Linse, Per, et al.
(författare)
-
Modeling of bottle-brush polymer adsorption onto mica and silica surfaces
- 2009
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:16, s. 6310-6318
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a series of charged bottle-brush polymers with side chains of constantlength on mica and silica surfaces is modeled using a lattice mean-field theory, and the predicted results are compared to corresponding experimental data. The bottle-brush polymers are modeled as being composed of two types of main-chain segments: charged segments and uncharged segments with an attached side chain. The composition variable X denotes the percentage of charged main-chain segments and ranges from X=0 (uncharged bottle-brush polymer) to X=100 (linear polyelectrolyte). The mica-like surface possesses a constant negative surface charge density and no special affinity, whereas the silica-like surface has a constant negative surface potential and a positive affinity for the side chains of the bottle-brush polymers. The model is able to reproduce a number of salient experimental features characterizing the adsorption of the bottle-brush polymers for the full range of the composition variable X on the two surfaces, and thereby quantifying the different nature of the two surfaces with respect to electrostatic properties and nonelectrostatic affinity for the polymer. In particular, the surface excess displays a maximum atX≈50 for the mica surface and at X≈10 for the silica surface. Moreover, the thickest adsorbed layer is obtained at X=10-25.
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| 31. |
- Ma, Weiming, et al.
(författare)
-
Free volume changes, crystallization, and crystal transition behavior of syndiotactic polystyrene in supercritical CO2 revealed by positron annihilation lifetime spectroscopy
- 2008
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:14, s. 5307-5312
-
Tidskriftsartikel (refereegranskat)abstract
- The free volume of syndiotactic polystyrene (sPS) conditioned in supercritical CO2 was investigated by using positron annihilation lifetime spectroscopy (PALS). Supercritical CO2 increased the free volume cavity size of amorphous sPS and made the formation of gamma crystal occur. The orthopositronium (o-Ps) intensity I-3 was correlated well with the crystallinity of gamma form sPS, revealed by its gradual decrease with the increase of crystallinity. Furthermore, the treatment atmosphere affected the crystallization behavior of amorphous sPS. The increased free volume cavity size of amorphous sPS treated in supercritical CO2 was larger than those treated in ambient air and supercritical N-2. Among these treatment conditions, supercritical CO2 increased the free volume size of amorphous sPS more effectively and thus resulted in the formation of gamma crystals. PALS measurements indicated that supercritical CO2 helped remaining a constant high free volume level of the amorphous parts of the semicrystalline sPS. Likely, the crystalline parts were also affected by the scCO(2) as a transition from the gamma form to the beta form was revealed at high temperatures by WAXD.
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| 32. |
- Makita, Naoko, et al.
(författare)
-
Conformational change of giant DNA with added salt as revealed by single molecular observation
- 2006
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:18, s. 6200-6206
-
Tidskriftsartikel (refereegranskat)abstract
- The structural change of individual giant double-stranded T4 DNA (165.6 kilobase pairs) molecules as a function of salt concentration was investigated by single molecular observation with fluorescence microscopy in a wide range of concentration of NaCl, 1 x 10(-6)-3 M. The measured long-axis length was transformed into a persistence length and subjected to a power-law analysis, which showed that the electrostatic contribution to the persistence length is inversely proportional to the square root of the salt concentration; i.e., it has a linear dependence on the screening length. This is interpreted as the behavior of a flexible chain with electrostatic excluded-volume interactions. Although double-stranded DNA is locally stiff, it displays flexibility when the contour length is much longer than the persistence length, as is the case for T4 DNA.
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| 33. |
- Malkoch, Michael, et al.
(författare)
-
Structurally diverse dendritic libraries : A highly efficient functionalization approach using Click chemistry
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:9, s. 3663-3678
-
Tidskriftsartikel (refereegranskat)abstract
- The high fidelity and efficiency of Click chemistry are exploited in the synthesis of a library of chain end functionalized dendritic macromolecules. In this example, the selectivity of the Cu-catalyzed [3 + 2 pi] cycloaddition reaction of azides with terminal acetylenes, coupled with mild reaction conditions, permits unprecedented functional group tolerance during the derivatization of dendrimeric and hyperbranched scaffolds. The resulting dendritic libraries are structurally diverse, encompassing a variety of backbones/surface functional groups, and are prepared in almost quantitative yields under very mild conditions. The robust and simple nature of this procedure, combined with its applicability to many aspects of polymer synthesis and materials chemistry, demonstrates an evolving synergy between advanced organic chemistry and functional materials.
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| 34. |
- Mindemark, Jonas, et al.
(författare)
-
End-Group-Catalyzed Ring-Opening Polymerization of Trimethylene Carbonate
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:10, s. 3515-3517
-
Tidskriftsartikel (refereegranskat)abstract
- A controlled self-catalyzed polymerization reaction yielding well-defined heterotelechelic polymer chains and eliminating low molecular weight catalyst residues in the final polymer product were analyzed by utilizing a ternary amine. The molecular weights were kept relatively low for end-group analysis by Nuclear Magnetic Resonance spectroscopy (NMR) and linear correlation between the degree of polarization and monomer were found. NMR results show that the polydispersities remained low at high monomer conversions and longer reaction times after full conversion led to a larger molecular weight distribution. The results also show that the ternary amine catalyst are attached to the growing polymer chains that is shown by a downfield shift from 2.44 to 2.56 ppm. The benzoic acid ester of the ternary amine is found to be potent catalyst of Ring-Opening Polymerization (ROP).
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| 35. |
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| 36. |
- Nilsson, Kristian, et al.
(författare)
-
Addition of Thiol-Containing Ligands to a Surface-Active Michael Acceptor
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:4, s. 901-908
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces the synthesis, characterization, surface properties, and reactions of maleic acid monoester end group functionalized polymers. Acylation using maleic acid anhydride of hydroxyl end groups present in either poly(ethylene glycol) (PEG) or poly(trimethylene carbonate) (PTMC) afforded the corresponding maleic acid monoester salts (PEGDM) or (PTMCM). Michael additions of ethanethiol or cysteine to the conjugated double bonds were performed in solution or at a polymer film−water interface. To further evaluate the reactivity and regioselectivity of the thiol addition to maleic acid monoester, a model compound, benzyl 6-hydroxyhexanoate, was used to aid a spectroscopic characterization. Film properties, evaluated with contact angle measurements, of PTMCM revealed surface-active properties of ionic maleic acid monoester salt. Further contact angle measurements showed that maleic acid monoesters present at the polymer−water interface could be reacted with the mercapto group in cysteine to give an amino acid decorated surface.
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| 37. |
- Nilsson, Markus, et al.
(författare)
-
Influence of polydispersity on the micellization of triblock copolymers investigated by pulsed field gradient nuclear magnetic resonance
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:23, s. 8250-8258
-
Tidskriftsartikel (refereegranskat)abstract
- The molecular motion in water of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer with the nominal composition EO97PO68EO97 (F127) was investigated with the aid of pulsed field gradient nuclear magnetic resonance (PFG NMR). The signal decays in the PFG experiments have been recorded for 1 wt % F127 in the temperature range from 288 to 313 K and in the concentration range 0.1-35 wt % at 298 K. Below the critical micellization temperature (cmt) or the critical micellization concentration (cmc), the PFG signal decays approximately linearly when the intensities are plotted on a logarithmic scale versus the experimentally relevant parameter. At the cmt or cmc, the signal decays are curved. The NMR data were processed using inverse Laplace transformation to obtain the distribution of self-diffusion coefficients, P(D). At 288 K for a I wt % solution, a narrow distribution was observed, while at 362 K a bimodal distribution was observed. This observation can be explained by the polydispersity of the polymer. It implies that, at a given temperature, only the more hydrophobic compound of F127 takes part in the aggregation process, while the more hydrophilic components diffuse as free nonassociated polymer. Increasing the temperature to 313 K resulted in a monomodal distribution, suggesting that all the polymers are aggregated. It is suggested that an ideal mixing model for the Pluronic micelles can explain the self-diffusion data. The NMR self-diffusion raw data were also analyzed with the COmponent REsolved (CORE; Stilbs, P.; Paulsen, K. Rev. Sci. Instrum. 1996, 67, 43804386) algorithm, resulting in spectra for free block copolymer and micellized block copolymer. With an increase in temperature, the intensity of the peaks for free block copolymer is reduced, whereas the intensity of the peaks for aggregated block copolymer. increases. The ratios between the size of the PEO and PPO blocks (mEO/nPO) show a marked increase in free polymer compared to the ratio observed in micellized polymer when the temperature is increased. The effect of added salts to a I wt % F 127 solution at 303 K was investigated to determine how the populations of free and micellized surfactant were changed on account of the ions present. Finally, the diffusion behavior of Pluronic F68 (EO76PO29EO76) at 35 wt % has been investigated from 298 to 313 K. Both the diffusion time and the time of the gradient have been varied. The data show that the diffusion is Gaussian in the temperature range.
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| 38. |
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| 39. |
- Nilsson, Svante, et al.
(författare)
-
Morphology and phase segregation of spin-casted films of polyfluorene/PCBM blends
- 2007
-
Ingår i: Macromolecules. - ACS : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:23, s. 8291-8301
-
Tidskriftsartikel (refereegranskat)abstract
- In this study the morphology of spin-casted films of polymers blended with [6,6]-phenyl C61-butyric acid methyl ester (PCBM) has been studied. It was found that the lateral structure formation in the films is favored by rapid solvent evaporation and strong polymer−PCBM repulsion. The formation of homogeneous films is favored by slow evaporation and weak polymer−PCBM repulsion. The effect of solvent evaporation rate is the opposite of what is found for spin-casting polymer−polymer blends. The results can be explained by the kinetics of phase separation and the phase behavior involving limited solubility and crystallization of PCBM.
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| 40. |
- Nyström, Andreas, et al.
(författare)
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Characterization of Poly(norbornene) Dendronized Polymers Prepared by Ring-Opening Metathesis Polymerization of Dendron Bearing Monomers
- 2006
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:21, s. 7241-7249
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and characterization of a series of first to fourth generation dendronized poly-(norbornene)s are presented. The monomers were synthesized in a divergent fashion from 5-norbornene-2-methanol, utilizing the acetonide protected anhydride of 2,2-bis(methylol)propionic acid. The norbornenyl bearing dendrons were polymerized by ring-opening metathesis polymerization, and it was found that the Grubbs' first generation catalyst resulted in polymers with lower polydispersity compared to the materials obtained when employing the second generation catalyst. Two series of first to fourth generation polymers were characterized by DSC, SEC, and dynamic rheological measurements. In addition, it was found that the fourth generation material could form regular, porous membranes and birefringent fibers. The membranes were characterized with atomic force and optical microscopy. The birefringent fibers were analyzed with X-ray diffraction, polarized FTIR, and polarized optical microscopy.
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| 41. |
- Ossipov, Dmitri A., et al.
(författare)
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Poly(vinyl alcohol) cross-linkers for in vivo injectable hydrogels
- 2008
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:11, s. 3971-3982
-
Tidskriftsartikel (refereegranskat)abstract
- New poly(vinyl alcohol) (PVA) derivatives containing different pendant chemoselective functionalities have been prepared for the in situ formation of hydrogels at physiological conditions. Particularly, incorporations of thiol, cysteine 1,2-aminothiol, and aminooxy side chains to PVA were performed for the first time by direct coupling of the protected nucleophilic functionalities to PVA's hydroxyl groups via carbamate linkages followed by acidic deprotection. In the second approach, PVA was first derivatized to a low degree (3%) with amino groups which were used to quantitatively react with different N-hydroxysuccinimide esters of carboxylic acids containing maleimide, a-iodoacetyl, or acrylate thiophilic functionalities. The utility of the amino-derivatized PVA was also demonstrated for further functionalization with semicarbazide terminated side chains. The ability of the new PVA derivatives to act as multifunctional cross-linking agents was examined in the course of in situ cross-linking reactions with hyaluronic acid carrying aldehyde groups. Use of multi functional PVA cross-linkers was shown to give short gelation times, i.e., within half a minute, which is critical for clinical applications. The hyaluronan hydrogels were enzymatically degradable as evidenced by the results of in vitro degradation by hyaluronidase. Moreover, these hydrogels were found to be nontoxic to human dermal fibroblasts. Hence, PVA-based multifunctional cross-linkers can extend the scope of in situ preparation and properties of hydrogel-based synthetic mimics of extracellular matrix as compared with well established bifunctional poly(ethylene glycol) analogs.
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| 42. |
- Pacios, I E, et al.
(författare)
-
Nanometric sieving of polymer coils by a lamellar liquid crystal: Surfactant AOT and polydimethylacrylamide
- 2005
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:5, s. 1949-1957
-
Tidskriftsartikel (refereegranskat)abstract
- The liquid crystal formed by surfactant AOT/water mixtures in its lamellar mesophase at a spacing between lamellae, d, equal to 8 nm, is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight in the range M-n= 2-20 x 10(3); the polymers are synthesized by living radical polymerization. The lowest molecular weights do not affect d significantly, indicating that the polymer coils penetrate inside the lamellar phase and dissolve in the water layers. With higher molecular weights, d decreases with added polymer, this decrease being stronger as the molecular weight of the polymer is higher, and the mixture becomes microheterogeneous. This indicates that the higher-molecular-weight polymers are segregated in a separate microphase that partially deswells the lamellae and that this segregation increases with the molecular weight of the polymer. The law, which governs the deswelling of lamella with added polymer, is deduced assuming that a fraction of each polymer can dissolve in the lamellar phase, while the rest of the polymer is segregated from it. This latter fraction is then obtained for each polymer simply by fitting to this law the experimental d as function of polymer concentration. It is proposed that the reason for this fractionation of polymer is that the lamellar structure acts as a grating which sieves the polymer coils according to their size relative to d, chains with molecular weight above a certain cutoff value, determined by d, being excluded from the interlamellar space. The fraction of chains excluded from the lamellae is calculated comparing the experimental molecular weight distributions (from SEC) of the polymers with the cutoff values determined by d. The results show that the polymer samples synthesized here cover the whole spectrum of behaviors, from almost total penetration to almost total exclusion. Both this method of cutting off the molecular weight distribution according to d and the other method of fitting d to the law for lamellar deswelling give similar results for the fraction of polymer that is segregated from the lamellae.
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| 43. |
- Parvole, Julien, et al.
(författare)
-
Polysulfones grafted with poly(vinylphosphonic acid) for highly proton conducting fuel cell membranes in the hydrated and nominally dry state
- 2008
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:11, s. 3893-3903
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanically strong and flexible membranes with very high local concentrations of immobilized proton-conducting phosphonic acid have been achieved by grafting poly(vinylphosphonic acid) side chains onto polysulfones. The graft copolymers were prepared by anionic polymerization of diethyl vinylphosphonate initiated from lithiated polysulfones, followed by quantitative cleavage of the ester functions. The resulting phosphonic acid units acted like monoprotic acids to indicate a high level of intramolecular interactions, and the phase-separated nature of the copolymers was shown by dual glass transitions. Fully polymeric membranes were conveniently cast from solution and showed high proton conductivities, e.g., 5 mS/cm under nominally dry conditions at 120 °C and up to 93 mS/cm under 100% relative humidity at the same temperature. The corresponding conductivities measured for Nafion 115 under the same conditions were 0.04 and 105 mS/cm, respectively. The former membranes furthermore showed high thermal stability with decomposition temperatures exceeding 300 °C under air. Additions of 2−5 wt % of a perfluorosulfonic acid polymer to the phosphonated membranes were found to reduce the water uptake significantly, thus improving the mechanical properties. The conductivity of these fully polymeric doped membranes was generally observed to be enhanced, or at least to remain at the same level, under both humidified and nominally dry conditions. The findings of this study demonstrate that phosphonated membranes with a proper macromolecular design may potentially show some important advantages in relation to the more commonly studied sulfonated membranes in fuel cell applications.
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| 44. |
- Patra, Michael, et al.
(författare)
-
Reorganization of nanopatterned polymer brushes by the AFM measurement process
- 2006
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:13, s. 4540-4546
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction between a nanopatterned polymer brush and a rigid pyramidal body representing an AFM tip has been investigated using molecular dynamics ( MD) simulation. The computed forces for varying position and penetration depth are systematically contrasted with the density and pressure tensor profiles of the unperturbed brush. For weak penetration of the AFM tip in the brush, we find that the force can quantitatively be computed from the properties of the unperturbed brush after folding with the geometry of the AFM tip. This steric effect leads to a force profile that is significantly wider than the physical brush. The structure of the perturbed brush has also been examined, and we show that for deep penetration of the AFM tip more than half of the force originates from the reorganization of the brush.
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| 45. |
- Perrin, Renaud, et al.
(författare)
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Nanostructured proton conducting polystyrene - poly(vinylphosphonic acid) block copolymers prepared via sequential anionic polymerizations
- 2009
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:14, s. 5146-5154
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(styrene-b-vinylphosphonic acid) diblock copolymers have been prepared via sequential anionic polymerization and evaluated as nanostructured polymer electrolytes. The ionic block copolymers were synthesized by first initiating the polymerization of styrene using n-butyllithium in tetrahydrofuran at −78 °C. 1,1-Diphenylethylene was then added to the living polystyryl anions before charging diethyl vinylphosphonate to polymerize the second block. The poly(diethyl phosphonate) block was subsequently completely hydrolyzed to obtain the poly(vinylphosphonic acid) block. Analysis by calorimetry showed two distinct glass transitions of the acidic copolymers, indicating phase separation between the two blocks. The glass transition temperature of the densely phosphonated blocks was strongly influenced by the formation of anhydride links through reversible self-condensation reactions at elevated temperatures. Studies of thin copolymer films by tapping mode atomic force microscopy revealed nanophase-separated morphologies with continuous phosphonated domains. In addition, the acidic block copolymers were found to self-assemble into spherical micellar nanoparticles which, in turn, formed branched arrays of supramolecular “necklace-like” chain structures. Block copolymers equilibrated at 25 °C and 98% relative humidity reached proton conductivities in the order of 30 mS/cm at 130 °C.
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| 46. |
- Persson, Christian, et al.
(författare)
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Intrinsically proton-conducting benzimidazole units tethered to polysiloxanes
- 2005
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:8, s. 3283-3289
-
Tidskriftsartikel (refereegranskat)abstract
- Polysiloxanes with pendant benzimidazole units have been prepared by free radical thiolene coupling reactions of 2-(2-benzimidazolyl)ethanethiol and vinyl-functional polysiloxanes. The latter polymers were prepared by anionic ring opening copolymerization of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclosiloxane and 1,3,5-hexamethyleyclosiloxane. Copolymers with different degrees of benzimidazole functionality were conveniently obtained by varying the monomer ratios. The coupling reaction was found to be very efficient, and the vinyl groups were completely consumed, as confirmed by NMR and FTIR spectroscopy. The glass transition temperature (T-g) of the benzimidazole functional copolymers increased dramatically with the benzimidazole content at low contents to reach a plateau value just above 50 degrees C at a content of approximately 33 mol% benzimidazole functional siloxane residues in the copolymer. Conductivity measurements carried out at 60 and 140 degrees C indicated that the level of polymer segmental mobility, and thus the Tg, was the most decisive parameter for the proton conductivity at low temperatures (60 C), while the benzimidazole concentration was more important at elevated temperatures (140 degrees C). A conductivity of 7 x 10(-6) S/cm was reached at 140 degrees C by a polysiloxane carrying 57 mol% benzimidazole-grafted siloxane residues under completely anhydrous conditions.
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| 47. |
- Piletsky, SA, et al.
(författare)
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Polymer cookery: Influence of polymerization time and different initiation conditions on performance of molecularly imprinted polymers
- 2005
-
Ingår i: Macromolecules. - : ACS American Chemical Society. - 0024-9297 .- 1520-5835. ; 38:4, s. 1410-1414
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Tidskriftsartikel (refereegranskat)abstract
- A set of polymers was imprinted with (-)-ephedrine using thermal and UV initiation. The performance of the synthesized materials was studied by HPLC. It was shown that the polymer morphology and enantioselective properties are dependent on the polymerization conditions and time of the reaction. The binding mechanism of synthesized polymers was studied using Vant Hoff analysis. The results of testing strongly indicate that the polymer receptor structure is shaped during the initial phase of polymer gelation. The present study shows the importance of controlling experimental conditions in the MIP synthesis and highlights potential problems expected during scaling up of MIP production.
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| 48. |
- Rangelov, Stanislav, et al.
(författare)
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Structural Polymorphism Exhibited by Polyglycidol-Based Analogues to Pluronic Copolymers in Aqueous Solution
- 2008
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:22, s. 8885-8894
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, nanostructures formed in water by a novel series of (G)n(PO)68(G)n triblock copolymers, where n = 18−135, and G and PO stand for glycidol and propylene oxide, respectively, are parametrized. The copolymers are considered analogues of Pluronic copolymers in which the flanking poly(ethylene oxide) (PEO) blocks are substituted by polyglycidol (PG). PG is structurally similar to PEO and differs in that each monomer unit bears a hydroxymethylene group. In composition, the copolymers are closest to the Pluronic series L121−F127. Dilute (but invariably above the critical aggregation concentration) aqueous solutions in the temperature interval 25−70 °C were investigated by means of dynamic and static light scattering, cryogenic transmission electron microscopy, and small-angle neutron scattering (SANS). In the temperature-composition continuum studied the novel copolymers exhibit rich structural polymorphism. Large compound particles as those observed earlier for related copolymers, small core-corona micelles, rods, and vesicles were detected and parametrized by combining light scattering and SANS. Upon heating, the simultaneous increase in both hydrophobicity of poly(propylene oxide) and hydrophilicity of PG cause counteracting effects that are reflected in appearance of maxima in the temperature dependence of aggregation numbers of the particles, variations in the density of the latter, and anomalous thermotropic transitions for some of the copolymers.
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| 49. |
- Simpson, Neil, et al.
(författare)
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Thiol-functionalized poly(omega-pentadecalactone) telechelics for semicrystalline polymer networks
- 2008
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 41:10, s. 3613-3619
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Tidskriftsartikel (refereegranskat)abstract
- Semicrystalline macromonomers based on poly(pentadecalactone), PPDL, have been synthesized by the lipase-catalyzed ring-opening of the otherwise chemically inert pentadecalactone monomer. The macromonomers were designed to have reactive thiols as end groups by the appropriate choice of initiator and chain terminator. The thiol functional macromonomers were then used together with ene monomers to give crosslinked thin films after irradiation in the molten state by UV light in the presence of a photoinitiator (Irgacure 65 1). Two different ene monomers were used, i.e., a tetrafunctional norbornene species and a trifunctional allyl ether maleate species, and resulted in semicrystalline cured films when cured with PPDL. An amorphous, commercially available, trifunctional thiol, trimethylolpropane tri(3-mercaptopropionate), TRIS, was also used for network formation in order to better understand the effect of crystallinity. All thiol-ene systems were found to be readily photopolymerised to high conversion. The PPDL-based networks were semicrystalline in the crosslinked state where the degree of crystallinity was found to depend on the nature of the cross-linker. Networks based on TRIS were found to be amorphous.
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| 50. |
- Srivastava, Rajiv, et al.
(författare)
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Enzyme-Catalyzed Ring-Opening Polymerization of Seven-Membered Ring Lactones Leading to Terminal-Functionalized and Triblock Polyesters
- 2006
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:1, s. 46-54
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Tidskriftsartikel (refereegranskat)abstract
- Terminal-functionalized polyesters and triblock polyesters were synthesized by lipase-CA-catalyzed ring-opening polymerization of seven-membered ring lactones, i.e., 1,5-dioxepan-2-one (DXO) and epsilon-caprolactone (CL), in the bulk in the presence of an appropriate alcohol that acts as an initiator. To introduce a double bond at the chain end, 4-pentene-2-ol was used to initiate the polymerization of the lactones. The unsaturation introduced at the chain end in this way is a useful approach for synthesizing comb polymers. Two different dihydroxyl compounds, viz. poly(caprolactone diol) and poly(ethylene glycol), were used as macro-initiators. Triblock copolymers were synthesized in this way, where the macro-initiator formed the middle block. Polymers having different degrees of polymerization were synthesized by varying the molar feed ratio of monomer to initiator. DXO and CL showed significant differences in reactivity toward lipase-CA-catalyzed polymerization initiated by different alcohols as initiators. The polymers were characterized by FTIR, NMR, SEC, optical microscopy, and DSC techniques.
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