Memory Effect of Crystallization in 1-Butene/α-olefin Copolymers

The macromolecular architecture is the crucial factor in determining the arrangement of the ordering structures, which, because of the multiscale feature, may exhibit distinct melting behaviors and induce the so-called memory effect to affect the following recrystallization. Until present, the correlation between the occurrence of memory effect and the intrinsic molecular structure is still far from the comprehensive understanding. In this work, four kinds of 1-butene/alpha-olefin random copolymers were designed and synthesized using the (pyridyl-amino) hafnium catalyst to introduce the different branches. The branch length was precisely controlled by the specific alpha-olefin comonomers, which include 1-hexene, 1-decene, 1-tetradecene, and 1-octadecene, while the branch density was tuned by the incorporation. As expected, the incorporation of alpha-olefin co-units to poly(1-butene) backbone decreases the non-isothermal crystallization kinetics and the degree of crystallinity. More interestingly, the resulting linear branch can induce the occurrence of memory effect and the threshold concentration of co-units (i.e., branch density) decreases with increasing the branch length. Based on the results of these 1-butene/alpha-olefin copolymers with designable branches, a direct correlation with the occurrence of memory effect and the fraction of amorphous region was established, which quantitatively indicates the degree of local segregation of the crystallized poly(1-butene) sequences by the alpha-olefin co-units.

Automated summary

The macromolecular architecture plays a crucial role in determining ordering structures and can induce the memory effect. By controlling branch length and density, the melting behavior and degree of crystallinity of copolymers can be adjusted.