Abstract: A process for the production of terephthalic acid comprises subjecting polyalkylene terephthalate to hydrolysis using a ratio of water to polyalkylene terephthalate in the mixture prior to heating and carrying out the reaction under conditions such that, at the reaction temperature, a significant proportion of the terephthalic acid produced is in the solid phase. The degree of recrystallization necessary to recover the terephthalic acid produced is thereby reduced. The reaction can with advantage be carried out with alkylene glycol present in the mixture prior to hydrolysis.

Abstract: Copolymers of propylene and a non-conjugated diene or triene of the formula (I): CH.sub.2 =CH(CHR.sup.4).sub.n CR.sup.1 =CR.sup.2 R.sup.3, where R.sup.1 and R.sup.2 are hydrogen or alkyl, but are not both hydrogen; R.sup.3 is alkyl or alkenyl of the formula (II): --(CHR.sup.8).sub.m CR.sup.5 =CR.sup.6 R.sup.7, where R.sup.5 and R.sup.6 are as defined for R.sup.1 (above), but are not both hydrogen; R.sup.7 is alkyl; each R.sup.8 is as defined for R.sup.4 (below); and m is 1 to 5; R.sup.4 is hydrogen or alkyl especially methyl; and n is from 2 to 5, can be made using highly stereospecific Ziegler-Natta polymerisation catalysts. The copolymers have 99.9 to 60, particularly 99.5 to 85, mole % propylene residues and 0.1 to 40, particularly 0.5 to 15, mole % diene residues. The copolymers have unexpectedly low solubility in organic solvents such as xylene and can be cross-linked, vulcanised or cured to give polymers having improved high temperature performance.