SOLID-STATE NMR-STUDY OF MISCIBILITY AND PHASE-SEPARATION IN BLENDS AND SEMIINTERPENETRATING NETWORKS OF C-13-LABELED POLY(STYRENE-CO-ACRYLONITRILE) AND POLY(STYRENE-CO-MALEIC ANHYDRIDE)

Site-directed isotopic enrichment and solid-state C-13 spin-diffusion NMR techniques were employed to characterize miscibility at the molecu lar level and phase separation in blends of amorphous polymers. Using 2D proton-driven spin-diffusion techniques on a mixture of C-13-labele d poly(styrene-co-maleic anhydride), [(CH2)-C-13,(CO)-C-13]SMA (27 wt % MA, M-w similar to 4 x 10(4) g mol(-1)), and poly(styrene-co-acrylon itrile), [(CN)-C-13]SAN (27 wt % ACN, M-w = 1.3 x 10(5) g mol(-1)), it is demonstrated that SMA and SAN are miscible on the molecular level. However, a specific orientation of the nitrile moieties in SAN with r espect to the carbonyl groups in SMA is unlikely. This suggests that t he miscibility of SAN and SMA copolymers is associated mainly with a d ecrease of intramolecular repulsion upon mixing, as opposed to a speci fic exothermic binary interaction. In addition, spin-diffusion experim ents show that upon selective cross-linking of the SMA phase semi-inte rpenetrating networks are formed. Increasing the degree of cross-linki ng results in increasing degrees of phase separation.