CO2-Induced Phase Transition of Isotactic Poly-1-butene with Form III upon Heating

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.

Ab initio determination of crystal stability of di-p-tolyl disulfide

With the rapid growth of energy demand and the depletion of existing energy resources, the new materials with superior performances, low costs and environmental friendliness for energy production and storage are explored. Di-p-tolyl disulfide (p-Tol₂S₂) is a typical lubricating material, which has been applied in the field of energy storage. The conformational properties and phase transformations of p-Tol₂S₂ have been studied by pioneers, but their polymorphs and the polymorphism induced crystal structure changes require further analysis. In this study, we perform the crystal structural screening, prediction and optimization of p-Tol₂S₂ crystal with quantum mechanical calculations, i.e., density functional theory (DFT) and second-order Møller–Plesset perturbation (MP2) methods. A series of crystal structures with different molecular arrangements are generated based on the crystal structure screening. As compared to long-established lattice energy calculation, we take an advantage of using more accurate technique, which is Gibbs free energy calculation. It considers the effects of entropy and temperature to predict the crystal structures and energy landscape. By comparing the Gibbs free energies between predicted and experimental structures, we found that phase α is the most stable structure for p-Tol₂S₂ crystal at ambient temperature and standard atmospheric pressure. Furthermore, we provide an efficient method to discriminate different polymorphs that are otherwise difficult to be identified based on the Raman/IR spectra. The proposed work enable us to evaluate the quality of various crystal polymorphs rapidly.

Poly (1-butene-ran-ethylene) Monomodal Copolymers from Metallocene Catalysts: Structural and Morphological Differences with Increasing Ethylene Content

Samples of random poly(butene-ran-ethylene) copolymers produced with metallocene catalysts were studied in order to elucidate the different behaviors of this particular class of materials as a function of increasing ethylene (C2) content. The samples cooled down from the melt are semi-crystalline or amorphous and crystallize in different crystal modifications, depending on the amount of C2. Thermal analysis, X-ray diffraction, and microscopic techniques were used to follow the changes of the materials with aging time and to understand the structural and morphological behavior with the aim of highlighting possible peculiar properties, which may be of great interest in the application of such materials in the field of Hot Melt adhesives.

Thermal Analysis of Crystallization and Phase Transition in Novel Polyethylene Glycol Grafted Butene-1 Copolymers

Copolymerization is an effective strategy to regulate the molecular structure and tune crystalline structures. In this work, novel butene-1 copolymers with different polyethylene glycol (PEG) grafts (number-average molecular weight M_n = 750, 2000, and 4000 g/mol) were synthesized, for the first time introducing long-chain grafts to the polybutene-1 main chain. For these PEG-grafted copolymers, crystallization, melting, and phase transition behaviors were explored using differential scanning calorimetry. With respect to the linear homopolymer, the incorporation of a trimethylsilyl group decreases the cooling crystallization temperature (T_c), whereas the presence of the long PEG grafts unexpectedly elevates T_c. For isothermal crystallization, a critical temperature was found at 70 °C, below which all polyethylene glycol-grafted butene-1 (PB-PEG) copolymers have faster crystallization kinetics than polybutene-1 (PB). The subsequent melting process shows that for the identical crystallization temperature, generated PB-PEG crystallites always have lower melting temperatures than that of PB. Moreover, the II-I phase transition behavior of copolymers is also dependent on the length of PEG grafts. When form II, obtained from isothermal crystallization at 60 °C, was annealed at 25 °C, PB-PEG-750, with the shortest PEG grafts of M_n = 750 g/mol, could have the faster transition rate than PB. However, PB-PEG-750 exhibits a negative correlation between transition rate and crystallization temperature. Differently, in PB-PEG copolymers with PEG grafts M_n = 2000 and 4000 g/mol, transition rates rise with elevating crystallization temperature, which is similar with homopolymer PB. Therefore, the grafting of the PEG side chain provides the available method to tune phase transition without sacrificing crystallization capability in butene-1 copolymers.

Controlling crystal polymorphism of isotactic poly(1-butene) by incorporating long chain branches

Isotactic poly(1-butene) (iPB-1) is a high performance plastic with outstanding properties, such as flexibility, superior creep, environmental stress cracking and abrasive resistance. However, it exhibits a complex crystal polymorphism and polymorphic transformation behavior, which has limited its commercial development. In this paper, the incorporation of long chain branches (LCBs) causes coil contraction in the melt, which favors the direct melt-crystallization of form III that was generally crystallized from solutions and made of unconventional highly twined lamellae. Consequently, low-to-moderately branched iPB-1 samples as-crystallize from the melt into mixtures of form II and form III by compression-molding and fast cooling of the melt to room temperature, and the fraction of crystals of form III (fIII) increases with increasing concentration of LCBs, whereas highly branched samples can as-crystallize into pure form III with uniform crystal size distribution. The corresponding thermomechanical properties can be modified by controlling fIII.

Polymorphic Behavior and Phase Transition of Poly(1-Butene) and Its Copolymers

The properties of semicrystalline polymeric materials depend remarkably on their structures, especially for those exhibiting a polymorphic behavior. This offers an efficient way to tailor their properties through crystal engineering. For control of the crystal structure, and therefore the physical and mechanical properties, a full understanding of the polymorph selection of polymers under varied conditions is essential. This has stimulated a mass of research work on the polymorphic crystallization and related phase transformation. Considering that the isotactic poly(1-butene) (iPBu) exhibits pronounced polymorphs and complicated transition between different phases, the study on its crystallization and phase transformation has attracted considerable attention during the past decades. This review provides the context of the recent progresses made on the crystallization and phase transition behavior of iPBu. We first review the crystal structures of known crystal forms and then their formation conditions and influencing factors. In addition, the inevitable form II to form I spontaneous transition mechanism and the transformation kinetics is reviewed based on the existing research works, aiming for it to be useful for its processing in different phases and the further technical development of new methods for accelerating or even bypass its form II to form I transformation.

Direct fabrication of porous isotactic poly-1-butene with form I from the melt using CO2

The deformation of isotactic poly-1-butene (iPB-1) matrix, during the CO(2) -assisted foaming process, makes the iPB-1 melt crystallize into form I rather than form I', which crystallizes after annealing under high-pressure CO(2) without foaming. The result provides a new strategy to directly obtain porous iPB-1 with stable form I from iPB-1 melt.