Synthesis and characterization of high performance polymeric materials: poly(arylene ethers), polyamides, polyesters and liquid crystalline polyarylates

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Virginia Tech

Poly(arylene ether)s (PAEs) were synthesized via the silyl ether displacement route. Both AA, BB, and AB silylated monomers were prepared by partial or complete hydrolysis of the dihalide using potassium hydroxide in aqueous dimethyl sulfoxide followed by silylation with hexamethyl disilazane. Both linear and star-branched structures of PAEs were synthesized and this polymerization route allowed both random and block copolymers to be prepared. Triaryl phosphine oxide containing homo-& co-PAEs exhibited very high char yields, which suggested that these polymers were potentially flame-resistant materials. The AB type halogenophenols were also polymerized in the presence of diphenylsulfone as a diluent and potassium carbonate as a base at elevated temperatures.

Poly(ε-caprolactam) (Nylon 6) copolymers were prepared by the incorporation of controlled molecular weight poly(arylene ether sulfone) (PES) oligomer segments into the polymer backbone which were functionalized with carboxyl end groups. A hydrolytic melt polymerization process was used to copolymerize the oligomers with ε-caprolactam. Two series of the copolymers, with varying weight ratios and PES segment lengths, were investigated. Extensive characterization experiments including thermal analysis, mechanical property measurement, wide angle x-ray diffraction and dynamic mechanical analysis were performed to illustrate that the copolymers displayed a good balance of properties.

Hydrolytically stable triaryl phosphine oxide containing dicarboxylic acid monomers were synthesized and were chemically incorporated into the poly(hexamethylene adipamide) backbone to produce improved flame-resistant copolymers. The content of triaryl phosphine oxide comonomer in the melt synthesized copolymers was controlled from 0-30 mole%. The copolymers were melt crystallizable only at 10 and 20 mole% incorporation of the phosphine oxide comonomer. Cone calorimetric tests were employed to investigate the fundamental flame retardancy behavior of the copolymers. The tests were conducted in a constant heat environment (40 kW/m²). Significantly depressed heat release rates were observed for the copolymers containing phosphine oxide moiety. The results of the cone calorimetric tests and TGA data suggested that the triaryl phosphine oxide containing nylon 6,6 copolymers had improved flame resistance properties.

The triaryl phosphine oxide dicarboxylic methyl ester was also introduced into poly(ethylene terephthalate) via melt transesterification to produce copolymers which had increased char yields as the P(O) content increased. However, crystallinity was totally disrupted at 20 mole percent P(O) incorporation in compression molded specimen.

Novel star-branched liquid crystalline polyarylates (LCP) were made via melt acidolysis which were subsequently transformed to liquid crystalline foams by supersaturation of carbon dioxide followed by thermal blowing. It was found that the AB type monomers were essential to generate star shaped LCPs without crosslinking. The branching agents were necessary to control the molecular weights, disrupt crystallinity and to allow for higher gas uptake by the polymer matrix.