Manipulating the Co-crystallization Behavior in Isomorphic Copolymers by Introducing a Third Monomeric Unit

Abstract

Isomorphism is a distinctive kind of co-crystallization behavior of random copolymers and provides opportunities to regulate the crystalline structure and performance without the loss of crystallinity. Though the intrinsic structural differentiation would induce variation of accommodation capacity in the co-crystal lattice for different co-monomeric units, subtle manipulation of isomorphism has not been realized yet. In this study, butylene adipate (BA) as the crystallizable unit is incorporated into an isomorphism system model of poly(butylene succinate-ran-butylene fumarate) (PBSF) to form the terpolymers of PBSFA, and the crystallization features are investigated. It is confirmed that part of BA (i.e., ≤20 mol %) does not hinder the isomorphism formation in the terpolymers of PBSFA but influences the accommodation capacities of the isomorphic counterparts of butylene succinate (BS) and butylene fumarate (BF). When BA with 10 mol % is copolymerized, the adoption of BS unit in isomorphism becomes less favorable in comparison to the biopolymers of PBSF, showing an increase of the defect Gibbs free energy for the co-crystal and a decrease of the accommodation ratio of BS. However, with a further lifting of the BA content to 20 mol %, the accommodation preference of BS and BF in the isomorphism lattice reverses, and BS turns into a favorable unit instead of BF. Such a transition of accommodation capacity might be due to the deterioration of intersegmental interaction caused by the third co-crystallizable unit of BA. This work directly reveals the differentiation of co-monomeric units in the isomorphic lattice and sheds light on the manipulation of isomorphism.