| 1. |
- Percec, Virgil, et al.
(author)
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Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 degrees C
- 2006
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 128:43, s. 14156-14165
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Journal article (peer-reviewed)abstract
- Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an innersphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H2O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X-2 species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X-2 species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu2Se, Cu2Te, Cu2S, or Cu2O species, not by Cu(I) X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electronwithdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.
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| 2. |
- Stjerndahl, Anna, et al.
(author)
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Industrial utilization of tin-initiated resorbable polymers : synthesis on a large scale with a low amount of initiator residue
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:3, s. 937-940
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Journal article (peer-reviewed)abstract
- This article presents the successful large-batch synthesis of a resorbable polymer with a minimal amount of residual tin. Ring-opening polymerization of ε-caprolactone was performed in toluene, with a tin (IV) alkoxide as the initiator. A number of parameters were varied in order to study the polymerization with respect to the purity of solvent, batch size, and the residual amount of tin in the polymers. The synthesis of ε-caprolactone in undistilled toluene with 1-di-n-butyl-1-stanna-2,5-dioxacyclopentane as the initiator was successfully performed in batches of 5, 20, and 50 g with no differences in the final conversion, molecular weight, or molecular-weight distribution. The residual amount of tin was significantly reduced from over 1000 to 23 ppm. This study examines the industrial utility of the materials regarding the size and purity of the synthesis.
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| 3. |
- Stjerndahl, Anna, et al.
(author)
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Minimization of residual tin in the controlled Sn(II)octoate-catalyzed polymerization of ε-caprolactone
- 2008
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In: Journal of Biomedical Materials Research - Part A. - : Wiley. - 1549-3296 .- 1552-4965. ; 87A:4, s. 1086-1091
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Journal article (peer-reviewed)abstract
- By using less catalyst in the ring-opening polymerization of epsilon-caprolactone, a residual tin content of 5 ppm was reached without the need for additional purification. The initial amount of tin (II) 2-ethylhexanoate [Sn(Oct)(2)] was varied using catalyst:monomer ratios of 1:1000, 1:10,000, and 1:20,000. The impact on the final conversion, reaction control, average molecular weight, and polydispersity was studied. The amount of Sn(Oct)(2) could be significantly, reduced without influencing the reaction results. The residual amount of tin was reduced from 176 ppm with a catalyst:monomer ratio of 1:1000 in the polymer, to 5 ppm with the ratio 1:10,000. It was thus concluded that a catalyst:monomer ratio of 1:10,000 or lower is required to achieve a polymer with tin content Suitable for biomedical applications. The materials were also tested in a proliferation study with mesenchymal stem cells from mouse. Porous scaffolds were fabricated from the polymers, using a salt leaching technique, and the cell growth on the porous scaffolds as well as on homogeneous films was determined by light absorbance measurements. In this study, the cell proliferation results showed that cells could grow on all polymers with ail efficiency equal to or better than that on normal tissue Culture plastic.
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| 4. |
- Albertsson, Ann-Christine, et al.
(author)
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Controlled synthesis of star-shaped homo- and co-polymers of aliphatic polyesters
- 2006
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In: 7th International Biorelated Polymers Symposium. ; , s. 37-38
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Conference paper (peer-reviewed)abstract
- The challenges in finding a material with the proper characteristics for a given tissue engineering application are several. One solution is improving the ability to tailor the mechanical and physical properties along with the degradation profile of aliphatic polyesters, by for example alterations in their composition and architecture. In this study, well-defined star-shaped aliphatic polyesters constituted of four arms were synthesized. As a model system, L,L-lactide and a spirocyclic tin initiator was chosen and the affect of the solvent, temperature and monomer-to-initiator ratio on the number average molecular weight, the molecular weight distribution and the conversion of the polymers was shown. Consecutively, we proved that well-defined star-shaped block copolymers composed of 1,5-dioxepan-2-one and L,L-lactide with narrow molecular weight distributions and controlled block lengths can be synthesized using this system.
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| 5. |
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| 6. |
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| 7. |
- Finne Wistrand, Anna, et al.
(author)
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Resorbable Scaffolds from Three Different Techniques : Electrospun Fabrics, Salt-Leaching Porous Films, and Smooth Flat Surfaces
- 2008
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In: Macromolecular Bioscience. - : Wiley. - 1616-5187 .- 1616-5195. ; 8:10, s. 951-959
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Journal article (peer-reviewed)abstract
- Nanofibrous scaffolds of poly[(L-lactide)-co-(1,5-dioxepan-2-one)] generated by electrospinning have been compared with porous films obtained by solvent cast/salt leaching and homogeneous films. A comparison between the fibrous materials and the homogeneous solvent-cast films revelead that the surface of the nanofibers was more hydrophobic and that the nanofibers were degraded more rapidly in the presence of proteinase. It was obvious that the strain-to-break was reduced by the nanofiber formation, it decreased from 370% to 130% independent of fiber diameter. These values were however considerably higher than the strain-to-break of the solvent-cast/salt leaching scaffold. In addition, the nanofibrous material accelerated the adhesion and growth of the mesenchymal stem cell compared to the smooth material.
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| 8. |
- Finne Wistrand, Anna, et al.
(author)
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The use of polymer design in resorbable colloids
- 2006
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In: Annual review of materials research (Print). - : Annual Reviews. - 1531-7331 .- 1545-4118. ; 36, s. 369-395
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Research review (peer-reviewed)abstract
- During the past decade, researchers in the field of polymer chemistry have developed a wide range of very powerful procedures for constructing ever-more-sophisticated polymers. These methods subsequently have been used in suitable systems to solve specific medical problems. This is complicated, and many key factors such as mechanical properties, biocompatibility, biodegradation, stability, and degradation profile must be considered. Colloid particle systems can be used to solve many biomedical- and pharmaceutical-related problems, and it is expected that nanotechnology can be used to develop these materials, devices, and systems even further. For example, an injectible scaffold system with a defined release and degradation profile has huge potential for the repair and regeneration of damaged tissues. This short, nonexhaustive review presents examples of polymer architecture in resorbable particles that have been compared and tested in biomedical applications. We also discuss the design of polymers for core-shell structures.
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| 9. |
- Finne Wistrand, Anna, et al.
(author)
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Tuned mechanical properties achieved by varying polymer structure : Knowledge that generates new materials for tissue engineering
- 2007
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In: Chinese Journal of Polymer Science. - 0256-7679 .- 1439-6203. ; 25:2, s. 113-118
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Journal article (peer-reviewed)abstract
- By changing both the monomer composition and the polymer structure, we have varied the mechanical properties of resorbable polymers. The polymers were synthesized by ring-opening polymerization using L-lactide (LLA), epsilon-caprolactone (epsilon CL), trimethylene carbonate (TMC) and 1,5-dioxepan-2-one (DXO) as monomers. Well-defined triblock copolymers, microblock copolymers and networks have been evaluated, and comparisons between them show that it is possible to tune the mechanical properties. Triblock copolymers with an amorphous middle block of poly(1,5-dioxepan-2-one) (PDXO) and semi-crystalline end-blocks of poly(epsilon-caprolactone) (PCL) were stronger and had a higher strain at break than triblock copolymers with poly(L-lactide) (PLLA) as end-blocks. Polymers with both DXO and TMC in the amorphous middle-block and PLLA as end-blocks showed a lower stress at break, but the material gained elasticity, a property which is very valuable in tissue engineering. Mechanical properties of networks, synthesized by a novel method, containing PDXO and PCL are also presented. Although it is difficult to compare them with the uncross-linked polymers, this is an additional way to modify and widen the properties.
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| 10. |
- Numata, Keiji, et al.
(author)
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Branched poly(lactide) synthesized by enzymatic polymerization : effects of molecular branches and stereochernistry on enzymatic degradation and alkaline hydrolysis
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:10, s. 3115-3125
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Journal article (peer-reviewed)abstract
- In this article the effects of the number of molecular branches (chain ends) and the stereochemistry of poly(lactide)s (PLAs) on the enzymatic degradation and alkaline hydrolysis are studied. Various linear and branched PLAs were synthesized using lipase PS (Pseudomonas fluorescens)-catalyzed ring-opening polymerization (ROP) of lactide monomers having different stereochemistries (L-lactide, D-lactide, and D,L-lactide). Five different alcohols were used as initiators for the ROP, and the monomer-to-initiator molar feed ratio was varied from 10 to 100 and 1000 for each branch in the polymer architecture. The properties of branched PLAs that would affect the enzymatic and alkaline degradations, i.e., the glass transition temperature, the melting temperature, the melting enthalpy, and the advancing contact angle, were determined. The PLA films were degraded using proteinase K or 1.0 M NaOH solution, and the weight loss and changes in the number average molecular weight (M-n) of the polymer were studied during 12 h of degradation. The results suggest that an increase in the number of molecular branches of branched PLAs enhances its enzymatic degradability and alkali hydrolyzability. Moreover, the change in M-n of the branched poly(L-lactide) (PLLA) by alkaline hydrolysis indicated that the decrease in M-n was in the first place dependent on the number of molecular branches and thereafter on the length of the molecular branch of branched PLA. The branched PLLA, poly(D-lactide) (PDLA), and poly(D,L-lactide) (PDLLA) differed in weight loss and change in M-n of the PLA segment during the enzymatic degradation. It is suggested that the branched PDLLA was degraded preferentially by proteinase K.
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