Self-Nucelation Effect on Crystallization of Double Crystalline Polypropylene-b-Polybutene Block Copolymers

Self-nucleation effect of crystalline polymers originates from the intrinsic in-complete relaxation of crystallization-associated ordered structure and plays a crucial role in accelerating crystallization without adding the extra nucleating agents. In this work, the polypropylene-b-polybutene block copolymers are designed and synthesized with the sequential polymerization method. The in situ wide-angle X-ray diffraction characterization demonstrates that polybutene (PB) and polypropylene (PP) sequences are both crystallizable, which crystallize into the mixture of tetragonal and trigonal phases, and monoclinic phase, respectively. In the meanwhile, The PP sequences in block copolymers exhibit the self-nucleation effect similar to the homopolymer, of which the PP crystallization kinetics is accelerated with decreasing self-nucleation temperatures (T_s). Unexpectedly, this self-nucleation effect of PP blocks on PB crystallization exhibits a rather complex and non-monotonous dependence on T_s. It is interesting to see that as T_s is lowered to Domains II and III to largely accelerate crystallization of PP, PB crystallization is suppressed. However, as the further decreased T_s only anneals PP crystallites, the suppressed PB crystallization could recover. This complex self-nucleation on crystallization is interpreted by the constraint of evolved PP crystallites on PB sequences.