Structural studies of pressure‐crystallized polymers. I. Heat treatment of oriented polymers under high pressure

Abstract

synopsisA convenient pressure apparatus was designed for crystallization of high polymers under hydrostatic pressure up to 5OOO atm. Melt crystallization as well as heat treatment under various temperatures and pressures was carried out on several polymers, and the effects of pressure on the molecular and crystal structures of the samples are discussed. Heat treatment of syndiotactic polypropylene under high pressure yields a new crystal modification rather than the previously known helii and planar zigzag modifications. Of the three modifications of poly(viny1idene fluoride), modification I11 was found as a high-pressure phase for specimens in the unoriented state, while modification I was obtained as the most stable one on heat treatment of oriented specimens under high pressure. Heat treatment under high pressure converts ordinary isotactic poly-4-methylpentene-1 with a lower density than the noncrystalline value, to a new crystal modification with higher density. As is reasonable, the dense modification is stable in a highpressure range. For these three cases, the orientation of specimens was found to remain unchanged during the transitions, which must therefore occur in the solid state.

Crystal Structures of Three Crystalline Forms of Poly(vinylidene fluoride)

“…An oriented specimen of form JI was prepared by drawing the melt-crystallized film at 150°C; draw ratio 400% (Figure l(b)). The specimens of form III were obtained by (1) heat treatment of unoriented form II under a high pressure (4000 atm, 285°C) 18 and also (2) precipitation from dimethyl sulfoxide solution. 6 • 11 (a) (b) Figure 1.…”

Melting and Crystallization of Poly(vinylidene fluoride) in the Blend with Poly(methyl methacrylate) under High Pressure

“…PMMA with a molecular weight 9.33 x 10 4 was purchased from Scientific Polymer Products Inc. The mixed powder of 3 g of PVF 2 and PMMA with the desired weight fraction was dissolved in N,N-dimethylformamide ( 100 cm 3 ) at 30oC in a laboratory dish. The solvent was completely evaporated in a vacuum vessel after exposure to flowing air for 5 days in a glass box.…”

“…In the present investigation, differential thermal analysis (DTA) of PVF 2 and PMMA blends was performed under high pressures up to 350 MPa. The effect of pressure on the melting and crystallization of PVF 2 in the blends was studied.…”

“…9 The melting temperature Tm of form II at atmospheric pressure is about 170oC and it changes with the content of head-to-taillinkage. PVF 2 and poly(methyl methacrylate) (PMMA) form a compatible mixture in the melt. 10 -13 The melting temperature of PVF 2 decreases with decreasing PVF 2 content in the blend.…”

A Review on Polymer Crystallization Theories

“…For instance, polyvinylidene difluoride [120,121], polytetrafluoroethylene [122], polychlorotrifluoroethylene [123], trans-1,4-polybutadiene [124][125][126][127], and polyethylene terephthalate [128][129][130].…”