Thermoreversible gelation copolymer solutions

Lee DS, Shim MS, Kim SW, Lee H, Park I, Chang T. Novel thermoreversible gelation of biodegradable PLGA-block-PEO-block-PLGA triblock copolymers in aqueous solution. Macro-mol Rapid Commun 2001 22 587-592. 

Jeong B, Bae YH, Kim SW. Thermoreversible gelation of PEG-PLGA-PEG triblock copolymer aqueous solutions. Macromolecules 1999 32 7064-7069. 

Lee, JW Hua, FJ Lee, DS. Thermoreversible gelation of biodegradable poly(e-caprolaetone) and poly(ethylene glycol) multiblock copolymers in aqueous solutions. J Control Rel, 2001, 73, 315-327. 

Jeong, B Bae, YH Kim, SW. Thermoreversible Gelation of PEG-PLGA-PEG Triblock Copolymer Aqueous Solutions. Macromolecules, 1999, 32, 7064-7069. 

The crystallization of a homopolymer from dilute solution results in two distinct phases that can usually be separated by mechanical means. In contrast, when a random copolymer crystallizes from dilute solution this separation often cannot be made. The polymer molecule pervades the complete volume and the very highly fluid dilute solution is converted to a rigid medium of essentially infinite viscosity. This process is popularly termed thermoreversible gelation and is a manifestation of crystallization. Crystallization of random copolymers from dilute solution is not the only mechanism by which thermoreversible gelation can occur. It is, however, a very common occurrence. Other important gel forming mechanisms of polymers have been described.(268-270) Thermoreversible gels can also be formed by homopolymers, under appropriate conditions(270), and also by n-alkanes.(271)... 

Thermoreversible gelation, as a consequence of crystallization from dilute solutions of random copolymers has been observed in a variety of mixtures. These include, among others, poly(vinyl chloride) in dioctyl phthalate,(55) poly-(acrylonitrile) in dimethyl formamide,(56) nitrocellulose in ethyl alcohol,(272) methyl cellulose in water,(273) ethylene copolymers,(274) syndiotactic isotactic and atactic poly(styrene),(275-279) and random copolymers of ethylene terephtha-late with isophthalate.(280) Flory and Garrett (281) have shown that the classical thermoreversible gelation system, gelatin in water, is the result of a crystal-liquid transformation. The gelation or dissolution can be treated as a first-order phase transition. 

Thermoreversible gelation has been studied in o-xylene for syndiotactic poly(methyl methacrylate) based block copolymers. The dynamic properties of solutions and gels have been analyzed and discussed on the basis of scaling assumptions. At the gel point, where the loss angle tan 5c=G 7G is independent of the probing frequency, the samples obey the typical power law G ((o) G (co) o... 

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