Ultrafast Form II to I Transition of Isotactic Polybutene-1

Effect of Annealing Process and Molecular Weight on the Polymorphic Transformation from Form II to Form I of Poly(1-butene)

Poly(1-butene) (PB-1) resin has excellent mechanical properties, outstanding creep resistance, environmental stress crack resistance and other excellent properties. However, PB-1 resin experiences a crystal transformation for a period, which seriously affects the production efficiency and directly restricts its large-scale commercial production and application. The factors affecting the crystal transformation of PB-1 are mainly divided into external and internal factors. External factors include crystallization temperature, thermal history, nucleating agent, pressure, solvent induction, etc., and internal factors include chain length, copolymerization composition, isotacticity, its distribution, etc. In this study, to avoid the interference of molecular weight distribution on crystallization behavior, five PB-1 samples with narrow molecular weight distribution (between 1.09 and 1.44) and different molecular weights (from 23 to 710 k) were chosen to research the influence of temperature and time in the step-by-step annealing process and molecular weight on the crystal transformation by differential scanning calorimetry (DSC). When the total annealing time was the same, the step-by-step annealing process can significantly accelerate the rate of transformation from crystal form II to I. PB-1 samples with different molecular weights have the same dependence on annealing temperature, and the optimal nucleation temperature (i.e., low annealing temperature, T_l) and growth temperature (i.e., high annealing temperature, T_h) were -10 °C and 40 °C, respectively. At these two temperatures, the crystal form I obtained by step-by-step annealing had the highest content; other lower or higher annealing temperatures would reduce the rate of crystal transformation. When the annealing temperature was the same, crystal form I first increased with annealing time t_l, then gradually reached a plateau, but the time to reach a plateau was different. The crystalline form I contents of the samples with lower molecular weight increased linearly with annealing time t_h. However, the crystalline form I contents of the samples with higher molecular weight increased rapidly with annealing time t_h at the beginning, and then transformation speed from form II to form I slowed down, which implied that controlling T_l/t_l and T_h/t_h can tune the different contents of form I and form II. At the same T_l/t_l or T_h/t_h, with increasing molecular weight, the transformation speed from form II to form I via the step-by-step annealing process firstly increased and then slowed down due to the competition of the number of linked molecules and molecular chain mobility during crystallization. This study definitely provides an effective method for accelerating the transformation of poly(1-butene) crystal form, which not only has important academic significance, but also has vital industrial application.

Crystallization and phase transition of butene/propylene copolymers

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.

Crystallization Behavior of Isotactic Polybutene Blended with Polyethylene

In this work, the melt crystallization behavior and the solid phase transition of isotactic polybutene (PB) were studied in the polybutene/high-density polyethylene (PB/PE) blends covering the whole composition range. For the dynamic cooling crystallization, PE exhibits almost the same crystallization temperature in all blends, whereas PB exhibits a distinct non-monotonic dependence on the composition ratio. Combining the ex situ X-ray diffraction and in situ Fourier transform infrared spectroscope, it was demonstrated that during cooling at 10 °C/min, the presence of at least 70 wt% PE can induce the formation of form I' directly from the amorphous melt. The detailed relations of polymorphism with temperature were systematically investigated for the PB/PE blends. Different from the formation of the sole tetragonal phase with ≤50 wt% PE, the trigonal form I' could crystallize directly from amorphous melt with ≥60 wt% PE, which can be further enhanced by elevating the temperature of isothermal crystallization. Interestingly, the critical lowest temperature of obtaining pure form I' was 85 °C with 70 wt% PE and decreased to 80 °C as the PE fraction was increased to 80 wt%. On the other hand, the spontaneous phase transition from the kinetically favored form II into the thermodynamically stable form I was also explored with X-ray diffraction methods. It was found that at the room temperature, phase transition kinetics can be significantly accelerated by blending at least 70 wt% PE.

Crystal structures, crystallization and II-I transition behaviors of iPB-1 in iPB-1/UHMWPE blends - Part 1. Crystal structures and crystallization behaviors

Isotactic polybutene-1 (iPB-1) is of particular commercial interest due to its excellent mechanical performances. The form I polymorph is preferred in most industrial applications, while the form II is kinetically...

Chain dimension and crystallization temperature affect the – transition of isotactic polybutene-1

The molecular weight dependence of the II–I phase transformation shows significant differences between isothermally and non-isothermally crystallized iPB-1.

A new perspective to enhance the II–I transition of polybutene-1

The bottleneck for the application and potential utilization of polybutenene-1 (PB-1) with excellent physical and mechanical properties is its inevitable phase transition.

Role of conformation in crystal formation and transition of polybutene-1

Polymer conformation is the molecular basis underlying essentially all physical properties of polymers, and chain conformation and conformational energy play central roles in crystalline structure formations and structure transitions of polymers.