Viscoelastic and Thermal Behavior of Polyvinyl Chloride near the Glass Transition Temperature

Abstract

Viscoelastic and thermal behaviors of polyvinyl chloride (PVC) films prepared in different conditions were studied near the glass transition temperature (T_g). PVC films (degree of polymerization 800-1400) cooled slowly under pressing from melt to room temperature show two transitions at 58°C and 71°C in differential scanning calorimetry (DSC). Filmsprepared in the same way but having higher degree of polymerization (2200-2700) show only one transition. By the heat treatment at higher temperatures than T_g, the low temperature transition disappears and the high temperature transition shifts to the lower temperature.
Films cast from tetrahydrofuran solution show also two transitions at 55°C and 77°C. The low temperature peak in DSC of the solvent casting films is larger than that of melt pressing films. The peak of dynamic loss E'' corresponds to larger peak of DSC. So the viscoelasticity of PVCs prepared in different conditions shows the quite different behaviors.
PVC films swollen in various organic solvents and dried, were studied. Though the polymer is not crosslinked, the structures during swelling are fairly kept in solid state and its viscoelasticity is different from that of untreated or crosslinked polymer. The shapes and positions of two transitions in DSC changes according to the solvents used. It is suspected that bulkiness and entanglement of chain affect these behaviors.
PVC-styrene graft copolymer was prepared by Co⁶⁰ γ-ray irradiation and its properties were also examined. By the grafting and swelling during polymerization, PVC-styrene copolymer shows a complicated transition and it is separated into two components by the heat treatment.
These results suggest that the low temperature transition in DSC is due to the mobile short chain or bulky region made by the swelling or the grafting and entanglement of whole chain causes the large unusual endothermic peak of the transition.