C-13 CP-MAS NMR-STUDY ON CONTENT AND MOBILITY OF DOUBLE-BONDS IN POLY(TRIMETHYLOLPROPANE TRIMETHACRYLATE)

The content and mobility of unreacted methacrylic units in the polymer obtained from trimethylolpropane trimethacrylate, polyTRIM, has been investigated using solid-state NMR techniques. Porous particles of polyTRIM were prepared by suspension polymerization with toluene and isooctane as porogenic agents. The content of remaining double bonds was determined by cross-polarization magic angle spinning (CP-MAS)13C NMR. In unreacted units, the carbonyl resonance is shifted ca. 10 ppm upfield compared to the reacted units, due to conjugation with the carbon-carbon double bond. A detailed analysis of the cross-polarization behavior showed that quantitative results can be obtained. The amount of unreacted units, typically 0-15%, was found to depend on the polymerization parameters. Conditions favoring mobility, i.e., higher temperatures or increased solvent quality, resulted in lower content of residual double bonds. Bromine addition can also be used to determine the unreacted units, although the obtained values are somewhat higher than the NMR data. The reactivity toward bromine further indicates that the mobility is reasonably high. This has also been confirmed by measurements of the rotating-frame relaxation time constant, T1ρ(13C). Most likely, T1ρ is dominated by spin-lattice processes; i.e., it can be interpreted in terms of molecular dynamics. The values obtained for C=O and >C*=CH2 in unreacted units are about twice that of C=O in reacted units, indicating increased mobility. The reactivity of the remaining double bonds in a radical polymerization with a chiral monomer was also demonstrated. © 1990, American Chemical Society. All rights reserved.