Solid-state NMR study of the multiphase behavior of linear and cross-linked poly(1,3-dioxolane)

The multiphase behavior of poly(1,3-dioxolane) (polyDXL) in linear and network forms as a function of molecular weight and cross-link density of the samples was investigated by high-resolution solid-state C-13 NMR. The ability to introduce two acrylate end groups and to control the molecular weight of the polymer provided a unique way to synthesize polyDXL networks with molecular weights varying from 4000 to 9000 between the cross-links. Besides an elastomeric phase and a crystalline phase, the existence of a third phase with intermediate molecular mobility could be shown for cross-linked polyDXL. This could be realized by making use of different techniques, such as T-1 rho H studies at well-selected contact times and careful Lorentzian deconvolution of the acetal C-13 CP/MAS resonance lines. In these OCH2O resonances, the peak of the interphase is situated around 96 ppm, at about the same chemical shift as that of the elastomeric phase, but it has a broader bandwidth due to increased spin diffusion. The crystalline component having the broadest bandwidth is positioned around 93.4 ppm. While the introduction of cross-links clearly is attributed to the development of an interphase, T-1 rho H studies demonstrated that the limited molecular mobility of this phase is independent of the cross-link density of the samples. The presence of such a noncrystalline, immobile interphase between the crystalline and elastomeric regions could not be demonstrated for linear polyDXL with a molecular weight range of 4000-9000.