Diol sequencing in copolyesters

Abstract

Abstract Homogeneous condensation of a symmetrical diacyl monomer T with two symmetrical diols D 1 and D 2 has been studied under low‐temperature, nonequilibrium conditions, using the diol sequence in the product as a probe. For terephthalate copolyesters of diols such as bisphenol A and neopentyl glycol the alternation frequency f 12 has been related to the rate parameters by measurement [using nuclear magnetic resonance (NMR) and other methods] and calculation. It is usually assumed that all functionalities attached to the same residue have the same reactivity, that is, that all steps of type have the same specific rate; this assumption leads to a random , high‐molecular‐weight copolyester. If the diacyl species shows a large penultimate group effect, as in phosgene, chloroformate [see M. Matzner et al., Chem. Rev. , 64 , 645 (1964)], and phthalates, this assumption must be discarded. After simplification the alternation can be calculated exactly in terms of two parameters: r , the relative reactivity of the diacyl functionalities, and δ, the relative reactivity of the two diols. A nonrandom copolyester results only when neither r nor δ is unity. The maximum nonrandomness (for fixed r ) occurs when δ → ∞ (sequential reaction).