| 1. |
- Liu, H., et al.
(författare)
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Reaction of epoxy resin and hyperbranched polyacids
- 2000
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Ingår i: Journal of Polymer Science Part A. - : John Wiley & Sons Inc, New York, NY, United States. - 0887-624X .- 1099-0518. ; 38:24, s. 4457-4465
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Tidskriftsartikel (refereegranskat)abstract
- The condensation reaction between two different epoxy resins and a hyperbranched polyester (MAHP) [poly(allyloxy maleic acid-co-maleic anhydride)] was studied. We compared two kinds of diglycidyl ether bisphenol A type of epoxy resins with different molecular weights, that is, epoxy resin GY240 (M = 365 g/mol) and GT6064 (M = 1540 g/mol) in this reaction. The results showed a marked difference in their reaction pattern in terms of ability to form crosslinked polymer networks with MAHP. For the former low-molecular-weight epoxy resin, no crosslinking could be observed in good solvents such as THF or dioxane within the set of reaction conditions used in this study. Instead, polymers with epoxide functional degrees between 0.34 and 0.5 were formed. By contrast, the latter high-molecular-weight epoxy resin, GT6064, rapidly produced highly crosslinked materials with MAHP under the same reaction conditions. The spherical-shape model of hyperbranched polymer was applied to explain this difference in reaction behavior. Hence, we have postulated that low-molecular-weight epoxy resins such as GY240 are unable to crosslink the comparatively much bigger spherically shaped MAHP molecules. However, using high-molecular-weight epoxy resins greatly enhances the probability of crosslinking in this system. Computer simulations verified the spherical shape and condensed bond density of MAHP in good solvents, and submicron particle analysis showed that the average MAHP particle size was 9 nm in THF. Furthermore, the epoxy-functionalized polyesters were characterized by 1H NMR and FTIR, and the molecular weights and molecular-weight distributions were determined by size-exclusion chromatography.
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| 2. |
- Liu, Y., et al.
(författare)
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New segmented poly(ester-urethane)s from renewable resources
- 2001
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 39:5, s. 630-639
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Tidskriftsartikel (refereegranskat)abstract
- The physical and mechanical properties of aliphatic homopolyesters from monomers obtainable from renewable resources, namely, 1,3-propanediol and succinic acid, were improved by their combination with aromatic urethane segments capable of establishing strong intermolecular hydrogen bonds. Segmented poly(ester-urethane)s were synthesized from dihydroxy-terminated oligo(propylene succinate)s chain-extended with 4,4'-diisophenylmethane diisocyanate. The newly synthesized materials were exhaustively characterized by H-1 NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, dynamic mechanical analysis, and with respect to their main static mechanical properties, an Instron apparatus was used. The average repeat number of the hard segments, evaluated by NMR, ranged from 4 to 9, whereas that of the flexible segments was about 14. The degree of crystallinity, glass-transition temperature, melting point, tensile strength, elongation, and Young's modulus were influenced by the ratio between hard and soft segments of the segmented copolymer in a predictable way. The results demonstrated that poly(ester-urethane)s from 1,3-propanediol and succinic acid are promising thermoplastics.
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| 3. |
- Zhou, Qi, et al.
(författare)
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Synthesis and properties of O-2- 2-(2-methoxyethoxy) ethoxy acetyl cellulose
- 2001
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 39:3, s. 376-382
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Tidskriftsartikel (refereegranskat)abstract
- In this article, a series of O-2-[2-(2-methoxyethoxy)ethoxy] acetyl celluloses with different degree of substitution (DS) values was synthesized by a homogeneous reaction of cellulose with 2-[2-(2-methoxyethoxy)ethoxy] acetyl chloride in a 10% (w/w) dimethylacetamide/lithium chloride solution, combined with pyridine as the acid acceptor. The total DS values of the derivatives in anhydroglucose units was determined by H-1 and C-13 NMR spectra, and ranged from 0.4 to 3.0, depending on the amount of acid chloride in the reaction. The effects of the total DS values and the O-2-[2-(2-methoxyethoxy)ethoxy]acetyl acetyl substituent distribution on the solubility of the derivatives were investigated. The lowest limit of the DS value for water-soluble 0-2-[2-(2methoxyethoxy)ethoxy]acetyl cellulose was approximately 0.5, which is lower than that of methylcellulose. The amphiphilic derivatives with higher DS values than 1.7 exhibited a good solubility in both water and organic solvents, such as dimethyl sulfoxide, tetrahydrofuran, and chloroform. Sol-gel transition in aqueous solution was observed for the amphiphilic derivatives with a higher DS value than 1.7; the precipitation temperature (T-p) decreased as the DS value increased, showing that the derivatives are highly temperature sensitive. The thermal properties of the fully substituted derivative were measured using polarized microscopy, DSC, and X-ray diffraction; and are dis cussed in terms of phase transition of the sample derivatives.
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| 4. |
- Edlund, Ulrica, et al.
(författare)
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Morphology engineering of a novel poly(L-lactide)/poly(1,5-dioxepan-2-one) microsphere system for controlled drug delivery
- 2000
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 38:5, s. 786-796
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Tidskriftsartikel (refereegranskat)abstract
- Morphology is presented as a powerful tool to control the in vitro degradation and drug release characteristics of novel drug delivery microspheres prepared from homopolymer blends of 1,5-dioxepan-2-one, DXO, and L-lactide, L-LA. Their performance in this respect was compared to analogous P(L-LA-co-DXO) microspheres. Blends formed denser and less porous microspheres with a higher degree of matrix crystallinity than copolymers of corresponding L-LA:DXO composition. The morphology differences of blends and copolymers, further adjustable by means of component ratio, are shown to have a vital impact on the in vitro performance. Sustained drug delivery was obtained from both copolymers and blends. Molecular weight; loss was retarded and diffusion-mediated release was inhibited in the latter case, further delaying the release process. The effects of storage on the physicochemical properties of these systems were evaluated under desiccated and moist conditions for 5 months. Storage-induced physicochemical changes, such as matrix crystallization and molecular weight decrease, were accelerated at higher relative humidities. P(L-LA-co-DXO) demonstrated higher moisture sensitivity than a PLLA-PDXO blend of corresponding composition. The more crystalline and dense morphology of blend microspheres may thus be considered an improvement of the storage stability.
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| 5. |
- Edlund, Ulrica, et al.
(författare)
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Novel drug delivery microspheres from poly(1,5-dioxepan-2-one-co-L-lactide)
- 1999
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 37:12, s. 1877-1884
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Tidskriftsartikel (refereegranskat)abstract
- Novel microspheres from copolymers of 1,5-dioxepan-2-one (DXO) and L-lactide (L-LA) were prepared by oil-in-water solvent evaporation and oil-in-oil solvent removal. The two preparation techniques were evaluated for sphere formulation and incorporation of two different drugs. Sustained release of these therapeutic substances was obtained. The consequences of altering the DXO : LA ratio, preparation method, and drug hydrophilicity were explored and identified as factors governing sphere quality, in vitro degradation, and drug release characteristics. We show that these relationships provide a powerful means of controlling the microsphere performance.
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| 6. |
- Stridsberg, K., et al.
(författare)
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Controlled ring-opening polymerization of L-lactide and 1,5-dioxepan-2-one forming a triblock copolymer
- 2000
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 38:10, s. 1774-1784
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Tidskriftsartikel (refereegranskat)abstract
- Novel elastomeric A-B-A triblock copolymers were successfully synthesized in a new two-step process: controlled ring-opening polymerization of the cyclic etherester 1.5-dioxepan-2-one as the amorphous middle block (B-block) followed by addition and polymerization of the two semicrystalline L-lactide blocks (A-block). A 1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane initiator system was utilized and the reaction was performed in chloroform at 60 degrees C. A good control of the synthesis was obtained, resulting in well defined triblock copolymers. The molecular weight and chemical composition were easily adjusted by the monomer-to-initiator ratio. The triblock copolymers formed exhibited semicrystallinity up to a content of 1,5-dioxepan-2-one as high as 89% as determined by differential scanning calorimetry. WAXS investigation of the triblock copolymers showed a crystal structure similar to that of the pure poly(L-lactide).
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| 7. |
- Trollsas, M, et al.
(författare)
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Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters
- 1998
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 36, s. 2793-2798
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Tidskriftsartikel (refereegranskat)abstract
- Living ring opening polymerization of epsilon-caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of epsilon-caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case. (C) 1998 John Wiley & Sons, Inc.
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| 8. |
- Liu, H., et al.
(författare)
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Radical alternating copolymerization: A strategy for hyperbranched materials
- 2000
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Ingår i: Journal of Polymer Science Part A. - : John Wiley & Sons Inc, New York, NY, United States. - 0887-624X .- 1099-0518. ; 38:17, s. 3074-3085
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Tidskriftsartikel (refereegranskat)abstract
- Novel hyperbranched polymers were synthesized in a high yield without gelation through the free-radical alternating copolymerization of an AB/B′ (allyloxy maleic acid/maleic anhydride) system, in which group B and monomer B′ both could only alternately polymerize with group A. The arm number of the produced highly branched polymers was equal to the product of the linear chain length and the probability of pendent B groups being growing centers. The molecular weight of these novel hyperbranched polymers increased with increasing initiator concentration and prolonged polymerization times. The AB/B′ system, used as described, provides a new general methodology for highly branched and functional polymers.
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| 9. |
- Albertsson, Ann-Christine, et al.
(författare)
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Synthesis of core-shell structured carboxylated microparticles with a straightforward procedure and their evaluation as a polymer support
- 2005
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 43:23, s. 5889-5898
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Tidskriftsartikel (refereegranskat)abstract
- Poly(trimethylolpropane trimethacrylate) microspheres with a narrow size distribution were obtained by precipitation polymerization. They were subsequently modified by surface grafting with acrylic acid in a polar ethanol-water reaction medium, without stabilizer, yielding core-shell particles with diameters in the micrometer range. The resulting polymeric material was characterized by SEM and potentiometric titration, FTIR spectroscopy, and thermal analysis. It was shown that the particle characteristics (size, size distribution, and functionality) obtained by this straightforward procedure can be controlled by modifying the synthesis parameters (monomer concentration, agitation rate, and temperature). The high functionality, the chemical and physico-mechanical stability, as well as the possibility to control the performances of the resulting polymeric materials by synthesis allow its applications in various areas. Envisaging separation and catalysis domains, Cu(II), Cd(II), and Cr(III) uptake capacity from aqueous solutions was investigated under noncompetitive conditions as a function of synthesized particle functionality, time, and pH range. It was also found that the addition of the carboxylated. microparticles to polyethylene stabilized with alpha-tocopherol improved the thermo-oxidative behaviour of the polymeric material.
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| 10. |
- Andronova, Natalia, et al.
(författare)
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Fibrillar structure of resorbable microblock copolymers based on 1,5-dioxepan-2-one and epsilon-caprolactone
- 2003
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Ingår i: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 41:15, s. 2412-2423
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Tidskriftsartikel (refereegranskat)abstract
- The copolymerization of 1,5-dioxepan-2-one (DXO) and E-caprolactone, initiated by a five-membered cyclic tin alkoxide initiator, was performed in chloroform at 60 degreesC. Copolymers with different molar ratios of DXO (25, 40, and 60%) were synthesized and characterized. C-13 NMR spectroscopy of the carbonyl region revealed the formation of copolymers with a blocklike structure. Differential scanning calorimetry measurements showed that all the copolymers had a single glass transition between -57 and -49 degreesC and a melting temperature in the range of 30.1-47.7 degreesC, both of which were correlated with the amount of DXO. An increase in the amount of DXO led to an increase in the glass-transition temperature and to a decrease in the melting temperature. Dynamic mechanical thermal analysis measurements confirmed the results of the calorimetric analysis, showing a single sharp drop in the storage modulus in the temperature region corresponding to the glass transition. Tensile testing demonstrated good mechanical properties with a tensile strength of 27-39 MPa and an elongation at break of up to 1400%. The morphology of the copolymers was examined with polarized optical microscopy and atomic force microscopy; the films that crystallized from the melt showed a short fibrillar structure (with a length of 0.05-0.4 mum) in contrast to the untreated solution-cast films. (C) 2003 Wiley Periodicals, Inc.
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