H. Kricheldorf, Gert Schwarz
Mar 1, 1983
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0
Influential Citations
70
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Quality indicators
Journal
Macromolecular Chemistry and Physics
Abstract
Poly(4-hydroxybenzoate) was prepared under a variety of reaction conditions. In addition to using the well-known monomers 4-acetoxybenzoic acid and phenyl 4-hydroxybenzoate, p-tolyl 4-hydroxybenzoate, 4-pivaloyloxybenzoic acid, and 4-trimethylsiloxybenzoyl chloride were also condensed. A new routine method for the determination of number average molecular weights (Mn) was developed, namely 1H NMR spectroscopic end-groups analysis of hydrolyzed poly-(4-hydroxybenzoate). By means of this technique, the relationships between monomer structure or reaction conditions, on the one hand, and the polymerization mechanism and polymer properties (e.g. Mn), on the other hand, were investigated. Whereas bulk condensations yield molecular weights of less than 10 000, polycondensations in solution may lead to values in the range of 20000 – 50000. The best results with respect to both yield and Mn were obtained with 4-acetoxybenzoic acid and 4-trimethylsiloxybenzoyl chloride. Regardless of the nature of the monomer, condensations in solution lead at first to precipitation of oligomer crystals with DP's in the range of 6–8. Due to intra- and intercrystalline transesterifications, chain growth continues in these oligomer crystals even in the absence of monomer or solvent. New reaction mechanisms are discussed. Depending on the nature of the monomer and the reaction conditions, poly(4-hydroxybenzoate) can adopt various crystal modifications. The thermal stability depends on both the degree of polymerization and crystal modifications.