Crystal Polymorphism of Isodimorphic Polyesters Tuned by cis- and trans-C=C Comonomer Units

Polymorphism is ubiquitous in polymer crystallization due to the diversified chain conformations and interchain packings in polymer crystals. Controlling chain conformation is effective in tailoring the crystal polymorphism of polymers, which, however, is challenging at the molecular level. Herein, we have synthesized poly(butylene adipate) (PBA)-based copolymers containing C=C units and demonstrated the important role of trans/cis-C=C units in tuning the chain conformation and crystal polymorphism of polymers. Both PBA-based trans- and cis-copolymers show isodimorphic crystallization behavior with the partial inclusion of C=C units in PBA crystals. The presence of trans-C=C units favors the formation of metastable beta-crystals of PBA and retards the beta-to-alpha crystal transition upon heating due to the highly conformational matching between trans-C=C units and beta-crystals. Conversely, the incorporation of cis-C=C units destroys the regularity of the trans conformation and favors the growth of alpha-crystals of PBA. This work has elucidated the crucial role of local chain conformation in the crystal polymorphism of polymers.

Automated summary

This study demonstrates the crucial role of trans and cis units in controlling chain conformation and crystal polymorphism of polymers, through the synthesis of copolymers containing C=C units.