Phase Structure of Polyethylene and Other Crystalline Polymers by Solid-State 13C NMR

Abstract

Crystalline polymers generally comprise a variety of phase structures, including the crystalline and noncrystalline components. The noncrystalline component is thought to be in a supercooled state of the molten state of polymers, either in the rubbery or glassy state. The question is whether a somewhat ordered noncrystalline component exists or not, due to the coexistence with the crystalline component. Flory reported in 1949 that the boundary between the crystalline and amorphous regions of most long-chain molecules will not be well-defined as is typical of monomeric systems [1]. Subsequent theoretical analyses, involving several methods, have quantitatively established the existence of an interfacial region that comprises a transition phase from the crystalline to the amorphous phase [2 11]. Over the past few years, a variety of experimental methods have confirmed the expectation of such an interphase [12]. These methods involve broad-line 1H NMR [13 16] high-resolution solid-state 13C NMR [17 31] Raman spectroscopy [32 35], and small-angle X-ray and neutron scattering, among others [36 42].