New polymer syntheses .85. Telechelic, star-shaped and hyperbranched polyesters of beta-(4-hydroxyphenyl) propionic acid

The trimethylsilylester of beta-(4-acetoxyphenyl) propionic acid (APPA), which is easier to isolate than the free acid, was used as monomer for all polycondensations. Copolycondensations with small amounts of 4-tert-butylbenzoic acid or 4-tert-butylphenol acetate yielded oligo- and polyesters with two different endgroups. All oligoesters show a reversible first order phase transition between 240 and 265 degrees C yielding a solid mesophase upon heating. The formation of an isotropic melt occurs between 340 and 380 degrees C depending on the degree of polymerization (DP). The glass transition temperatures increased from 48-50 degrees C to values around 63-65 degrees C with increasing molecular weight. Copolycondensations with acetylated bisphenol-P yielded telechelic oligoesters with two identical endgroups. Four-armed star-shaped polyesters were prepared by copolycondensation of a tetraacetoxyspirobisindan. Since the bisphenol-P and the spirobisindane units are unfavourable for the crystallization, the crystallinity depends on the DP, and the solubility depends in turn on the crystallinity. Hyperbranched copolyesters were synthesized by copolycondensation of silylated APPA with silylated or free 3,5-bisacetoxybenzoic acid with variation of the molar ratio. The hyperbranched character of these copolyesters was demonstrated by their reluctance to crystallize and by C-13 n.m.r. spectroscopic sequence analyses. The T(g)s of these hyperbranched copolyesters follow almost exactly the Fox equation. G.p.c. measurements revealed number average molecular weights (M-n) up to 31 000 g mol(-1) (for the 1/1 copolyester) and M-w/M-n ratios in the range of 3.5-6.5. (C) 1997 Elsevier Science Ltd.