Abstract
The crystallization behaviors of two copolymers of PVDF were studied, and the effect of copolymerized chains on the crystallization behavior was investigated. The results indicated that both copolymers had a lowered crystallization temperature and crystallinity. The crystallization rate was improved by the copolymer with symmetrical units in PVDF chains, but hindered by asymmetrical units, compared with the neat PVDF. The symmetrical units in PVDF chains favored the β-crystals with fiber-like structures. According to the solubility parameter rule, methyl salicylate (MS) can be chosen as a diluent for PVDF copolymers. Both diluted systems had liquid-liquid (L-L) regions in the phase diagrams, which was due to the lowered crystallization temperature.
Highlights
Poly(vinylidene fluoride) (PVDF), a semi-crystalline polymer with excellent physical and chemical properties and a good thermal stability, has been used in many applications [1]
Compared with a PVDF/methyl salicylate (MS) system [10], an obvious wide L-L phase separation region is observed, in which the monotectic point, φm [21], of PVDFc1 and PVDFc2 is around 50 wt% and 40 wt%, respectively
The effect of chain structure and membrane formation via the thermally-induced phase separation (TIPS) method was investigated in this work
Summary
Poly(vinylidene fluoride) (PVDF), a semi-crystalline polymer with excellent physical and chemical properties and a good thermal stability, has been used in many applications [1]. At least four known crystalline phases of PVDF, α, β, γ and δ, can be obtained, depending on the competition between the phase separation and the crystallization process [2] and the solvent evaporation rate when PVDF is crystallized from a solution [3,4]. This implies that when phase separation occurs, the kinetic parameters (including quenching temperatures, the time limit for each phase separation region) will play an important role in the ultimate membrane structure.
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