Crystallization and Phase Transition of 1-Butene Copolymers with Distinct Cyclic Co-Units

Comprehensive Summary The dimethylpyridylamidohafnium catalyst was used to synthesize 1-butene/cyclohexene and 1-butene/vinylcyclohexane random copolymers, which have extra six-membered cyclic co-units in main chain and side chain, respectively. For the obtained copolymers of different incorporations, the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry. Both of the incorporated cyclic co-units decrease the crystallization kinetics, but the presence of cyclohexene keeps the melting temperature of copolymers constant. Interestingly, the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature, as the content of co-units was increased. The 1-butene/vinylcyclohexane copolymer with 1.52 mol% co-units exhibits a rather strong memory effect with the broad Domain IIa width of 43 degrees C and the crystallization temperature raising of 24 degrees C. Furthermore, the transition of tetragonal phase into trigonal phase was also explored for different co-units and incorporations. It was found that both of the cyclohexene co-units and vinylcyclohexane co-units effectively slow down the kinetics of phase transition. However, the vinylcyclohexane co-units have a much higher efficiency in suppressing phase transition than the cyclohexene co-units, where 0.53 mol% vinylcyclohexane can completely stop phase transition within 1320 h. Considering the fact that copolymers with vinylcyclohexane co-units actually have lower glass transition temperatures, it was indicated that the suppression of phase transition is also largely influenced by the steric co-units in the side chain for the helical and positional adjustments, not only by the segmental mobility.