Crystallization and Relaxation Behavior of Partially Disentangled Poly(vinyl chloride) Prepared from Large Molecule Solvent Dioctyl Phthalate

Abstract

Poly(vinyl chloride) (PVC) samples for the conformation and structural relaxation studies were prepared by freeze-extracting the solutions in various solvents and with varying concentrations. The partially disentangled PVC samples could be obtained by freeze-extracting very dilute PVC/ tetrahydrofuran (THF) and PVC/dimethyl phthalate (DMP) solution (0.05 wt %), while the PVC sample remains in an entangled state after freeze-extracting the concentrated solutions in THF and in DMP. Surprisingly, the extent of interpenetration of PVC chain decreases, even in concentrated solution in dioctyl phthalate (DOP) (5 wt %), which is contrary to accepted theories. DSC and infrared spectroscopic studies showed that a higher ordered conformation could be achieved for the disentangled specimens recovered from concentrated solution in DOP than for the entangled samples prepared from THF and DMP. DSC heating curves showed strong and sharp endothermal peaks for the disentangled polymer after sub-T g annealing. The structural relaxation behavior of the disentangled PVC freeze-extracted from DOP solutions is more predominant, which is in good agreement with the modeling predictions. IntroductionIt is well-known 1 that atactic poly(vinyl chloride) (PVC) is a low crystalline polymer. Commercial PVC contains less than 10% crystalline segments. But this relatively low level of order has a surprisingly significant effect on both its processing and properties. As early as 1926, Flumiani 2 reported that the dispersion state of PVC in the solution could be influenced by temperature, the various heating period, the aging of the solution, the solvent itself, and even the method of preparation of different concentrations of the solution. Despite numerous studies 2-6 dealing with the gelation and aging process of PVC solutions, the mechanism of formation and the structure of PVC physical gel have still not been fully elucidated. It is generally accepted that the cross-links in these gels are tiny crystallites, although according to Guenet et al.,7 hydrogen bonding also plays an important role. Effects of polymerization temperature, 8 heat treatment, 9,10 and processing temperature 11 on crystalline of PVC have been investigated. However, until now, little has been done on the conformation and structural relaxation of PVC affected by solvent because of the complexity of the solvents applied.In our previous work, we prepared partially disentangled PVC samples by the freeze-extraction method from dilute PVC/THF solutions and found that the conformation and relaxation behavior of PVC depended strongly on the entanglements in polymers. 12 We also found that the molar volume of solvents plays an important role in the entanglement state of polymer in solution. 13-15 Therefore, it is necessary for us to explore the effect of solvent on the conformation of PVC. In this work, we selected a normal plasticizer DOP, which has large molar volume, as well as DMP and THF, as the solvents for PVC. Some attempts [16][17][18] have been made to study the extent of...

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