Diluent effects on carbonate mobility in bisphenol-A polycarbonate in the solid state

Abstract

The effect of miscible low molecular weight additives on the mobility of the carbonate group in bisphenol-A polycarbonate (BPAPC) has been studied using n.m.r. and dielectric relaxation experiments in the solid state. Proton-enhanced dipolar-decoupled carbon-13 n.m.r. spectra of BPAPC, isotopically enriched at the carbonate position, are obtained without magic-angle sample spinning. The resolved chemical shift anisotropy allows study of nuclear spin relaxation for the carbonate groups in the polymer that have different orientations relative to the static magnetic field in the laboratory frame. The spin-lattice relaxation time in the rotating frame ( T 1 ϱ ) is measured at a motional-probe frequency of 50 kHz for the undiluted polymer and for BPAPC-diluent blends containing either dibutylphthalate or dinitrobiphenyl. The T 1 ϱ exhibits some dependence on orientation in all systems studied. In the blend containing dibutylphthalate (DBP), T 1 ϱ is decreased by a factor of two for all orientations of the carbonate group. This implies that DBP substantially increases the spectral density of 50 kHz motions in the carbonate region of the polymer at ambient temperature. In contrast, dinitrobiphenyl does not significantly alter the Fourier component of thermal fluctuations at 50 kHz. Dielectric relaxation measurements at 10 kHz reveal that the primary ( T g) and secondary (β) motional processes in BPAPC are affected by low molecular weight additives. An intermediate relaxation process appears in the temperature interval between the glass transition temperature ( T g) and the sub- T g β-relaxation ( T β ) in the polymer-diluent blends. The n.m.r. spin-lattice relaxation rate in the rotating frame, T −1 1 ϱ , correlates well with the relative magnitude of the dielectric dissipation factor (tan δ ε ) between T g and T β .