Distinctive Polymorphism-like Isodimorphism in Poly(propylene succinate-ran-propylene fumarate)

Co-crystallization of different monomeric units fundamentally contributes to the versatile and tunable performance of random copolymers. At present, the crystallization manners of random binary copolymers have been divided into three categories: isomorphism, isodimorphism and comonomer exclusion. Each category, however, has its own advantages and disadvantages. Therefore, it is challenging to design and prepare random copolymer sharing the advantages of isomorphism and isodimorphism through a new co-crystallization manner beyond the ones already exist. On the basis of previous study on poly(alkylene succinate- ran -alkylene fumarate) whose co-crystallization can be extensively and finely regulated by simply varying the chemical structure of alkylene, random copolymers of poly(propylene succinate- ran -propylene fumarate) (PPSF) are synthesized using 1,3-propanediol as the diol source. The thermal properties and crystal structure of PPSF are investigated, and, intriguingly, it is proved that PPSF is an isodimorphism system while displays similar composition-dependent thermal properties and crystallinity as isomorphism. That is, PPSF exhibits a novel co-crystallization behavior that has rarely been discovered, which would combine the advantages of both isomorphism and isodimorphism. Consequently, PPSF could be termed as a new-type, special composition-dependent polymorphism. Besides, the altering of PPS-like to PPF-like crystal structure of PPSF when changing chain composition has been proved to originate from the shift of dominant inter-segment interaction from van der Waals forces to strong hydrogen-bonding interaction. This work enriches the co-crystallization manner of random copolymers, leading to more diverse performance design of polymer materials.