Interrelations Between Side Chain and Main Chain Packing in Different Crystal Modifications of Alkoxylated Polyesters

Interrelations between main chain and side chain packing are studied in a series of comb-like poly(1,4-phenylene-2,5-n-dialkyloxy terephthalate)s (PPAOTs) with C = 6–12 alkyl carbons per side chain by X-ray diffractometry. Two different polymorphic states, called modification A and modification B, are observed depending on thermal treatment and side chain length. For PPAOTs with short side chains (C ≤ 8), modification A is commonly observed. “As synthesized” (solution crystallized) PPAOTs with longer side chains (C ≥ 10) contain mostly modification B while modification A is growing during melt cooling. A solid–solid transition from modification B to modification A is observed above ≈70 °C for the decyl member (C = 10, PPDOT) while modification A converts under ambient conditions slowly to modification B. This indicates that modification B is thermodynamically stable at low temperature while modification A is stable at higher temperature. Crystallographic analysis shows that both modifications are characte...