ON SEGMENTAL MOBILITY IN A COMPATIBLE POLY(ALPHA-METHYLSTYRENE)-BLOCK-POLYSTYRENE COPOLYMER

The segmental mobility in a compatible poly(alpha-methylstyrene)-block-polystyrene (P-alpha-MS-block-PS) copolymer was investigated, using solid-state nuclear magnetic resonance (NMR) spectroscopy. For the study, a series of P-alpha-MS-block-PS copolymers containing various amounts of P-alpha-MS (from 13 to 81 wt %) were synthesized via anionic polymerization. The results of differential scanning calorimetry (DSC) showed a very broad, single glass transition temperature (T(g)) for all block copolymers studied. However, measurements of the spin-lattice relaxation rate in the rotating frame (T1-rho-H) via cross polarization in NMR as a function of temperature indicate that the block copolymer has microheterogeneity at temperatures above the onset point of the glass transition but becomes homogeneous as the temperature approaches the midpoint of the glass transition. NMR spectroscopy indicates further that there is a distribution of segmental mobilities, with the PS and P-alpha-MS strongly influencing each other.X1111sciescopu