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°C and the crystallization temperature raising of 24°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.

The crystalline structures of polymorphic polymer not only are determined by the processing parameters but also could further evolve within the service period. In this work combining in-situ wide-angle X-ray diffraction and ex-situ differential scanning calorimetry, the stretching-induced crystallite evolution was studied for polymorphic polybutene-1 (PB) within a broad stretching temperature (T stretching) range of 30–115 °C. First of all, it was found that although the initial crystallites were in the most thermodynamically stable modification of the trigonal phase, the metastable but kinetically favored tetragonal phase was generated during stretching at the elevated temperatures because of crystallite melting and subsequent recrystallization. What is more interesting is that those stretching-generated amorphous fractions also have the possibility of recrystallizing into the trigonal form I′ when cooled to room temperature, depending on T stretching. These results demonstrate that the polymorphism selection occurs in the stretching-induced recrystallization, where form II might be generated during stretching at the elevated temperature and form I′ is obtained by cooling. The unusual re-appearance of the trigonal form I′ may be associated with the local confinement crystallization caused by the residual crystallites. The combination of structural evolution with mechanical response disclosed that the stretching-induced recrystallization requires macroscopic yielding to destroy the crystallite skeleton for melting. Furthermore, the increase of lamellar thickness decreases the amount of stretching-induced amorphous phase and increases the critical T stretching of recrystallization into forms II and I′. Based on the quantitative results, a threshold criterion of stretching-melted PB, which is crystallinity of around 12.6%, was identified to be required for recrystallization of the trigonal phase form I′ by cooling the stretched form I crystallites.

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The introduction of propylene co-units into butene/propylene random copolymers can accelerate the II–I phase transition and even induce the direct formation of trigonal form I′ from an amorphous melt.

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