New polymer syntheses. CIX. Biodegradable, alternating copolyesters of terephthalic acid, aliphatic dicarboxylic acids, and alkane diols

Copolyesters with an alternating sequence of terephthalic acid and aliphati c dicarboxylic acids were prepared with three different methods. First, dic arboxylic acid dichlorides were reacted with bis(2-hydroxyethyl)terephthala te (BHET) in refluxing 1,2-dichlorobenzene. Second, the same monomers were polycondensed at 0-20 degreesC in the presence of pyridine. Third, dicarbox ylic acid dichlorides and silylated BHET were polycondensed in bulk. Only t his third method gave satisfactory molecular weights. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the c opolyesters prepared by the pyridine and silyl methods might have contained considerable fractions of cyclic oligoesters and polyesters despite the ab sence of transesterification and backbiting processes. The alternating sequ ences and thermal properties were characterized with H-1 NMR spectroscopy a nd differential scanning calorimetry measurements, respectively. In agreeme nt with the alternating sequence, all copolyesters proved to be crystalline , but the crystallization was extremely slow [slower than that of poly(ethy lene terephthalate)]. A second series of alternating copolyesters was prepa red by the polycondensation of silylated bis(4-hydroxybutyl)terephthalate w ith various aliphatic dicarboxylic acid dichlorides. The resulting copolyes ters showed significantly higher rates of crystallization, and the melting temperatures were higher than those of the BHET-based copolyesters. (C) 200 1 John Wiley & Sons, Inc.