Influence of Solvent Type on Acceleration of Phase Transition from Phase II to Phase I of Polybutene-1 via Solvent Vapor Treatment

A series of isotactic polybutene-1 (PB-1) in phase II obtained via isothermal crystallization at 50 degrees C were treated with different solvent vapors. Wide-anlge X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques were used to evaluate such samples before and after treatment. Meanwhile, in situ XRD was used to study the phase transition process of PB-1 annealed in different solvent vapors. Solvents, except water and alcohol solvents, such as n-hexane, chloroform, 1, 2-dichloroethane, benzene, toluene, xylene, chlorobenzene, ethyl acetate, tetrahydrofuran, acetone have obvious accelerating effect on the phase transition process, which can shorten the phase transition time from more than 4-5 days under normal conditions to tens of minutes. Through in situ XRD characterization, it was found that during the solvent annealing process, the crystal form II of PB-1 disappeared while the crystal form I was formed. The entrance of solvents, which promotes the crystal form transformation, can be divided into two steps: adsorption and diffusion. Adsorption is affected by solubility parameters and polarity, while diffusion mainly depended on the geometric size of solvent molecules: a small size in any direction will lead to a faster spread and larger promotion effect. Through this research, we found that n-hexane or petroleum ether is an efficient and low-toxic solvent that accelerates the II-I phase transition of PB-1, and has good application prospects.