Unusual Memory Effect of Crystallization Raised by 4-Phenyl-1-butene and 4-Anthryl-1-butene Comonomers in 1-Butene-Based Copolymers

A strong memory effect has been identified in copolymers even above the equilibrium melting temperature, which accelerates the subsequent recrystallization process. In this study, two series of novel 1-butene-based random copolymers were synthesized from two comonomers: 4-phenyl-1-butene (PhB) and 4-anthryl-1-butene (AnB). PhB and AnB introduced phenyl and anthryl groups, respectively, into the poly(1-butene) main chain. The occurrence and evolution of the memory effect were systematically explored in the presence of these designed counits via differential scanning calorimetry. The strong memory effect above the equilibrium melting temperature occurred in both copolymers, while their critical compositions of incorporation varied largely. The memory effect was triggered with the incorporated PhB counits up to 5.33 mol % for a fixed annealing period of 10 min. However, the incorporation of only 0.6 mol % of the sterically hindered large AnB counits induced a strong memory effect. A plot of the crystallization temperature as a function of the melt temperature (T_melt) showed a counterintuitive bell-shaped trend for AnB copolymers. The strength of the memory effect increased on extending the holding duration, contrary to the customary decaying behavior. Such a developed memory effect clearly explains the origin of the observed inversion of the crystallization rate over a broad temperature range.