Miscibility studies in polymer-diluent blends and segmented block copolymers via high-resolution carbon-13 solid-state nuclear magnetic resonance spectroscopy

Abstract

Miscibility in blends and short-segmented block copolymers has been studied at the molecular level with the aid of high-resolution solid-state nuclear magnetic resonance (n.m.r.) spectroscopy. The spectroscopic results are in agreement with those from differential scanning calorimetry (d.s.c.). The blend of poly(methyl methacrylate) and 2,2′-dinitrobiphenyl is completely miscible. This is a consequence of near-neighbour interactions between diluent molecules and the pendant groups of the macromolecular chain. The polyether-polyester block copolymers (duPont's Hytrel copolymers) are incompletely phase-separated. Supporting evidence is derived from the observation of n.m.r. signals due to polyester segments dissolved in the polyether-rich mobile domains. As the overall polyester content of the copolymer is increased, molecular mobility in both the crystalline and amorphous domains becomes more restricted. This conclusion is based upon the effect of composition on the proton spin-lattice relaxation times in the rotating frame of reference. Finally, proton dipolar communication via spin diffusion within the soft segment becomes more efficient as the fraction of uncrystallized polyester segments in the polyether-rich domains increases.