INVESTIGATION OF HIGH-TEMPERATURE RADIATION EFFECTS ON POLY(METHYL METHACRYLATE) OF SPECIFIC TACTICITY

The high-temperature radiation properties of isotactic and syndiotacti c poly(methyl methacrylate) (PMMA) have been investigated by NMR spect roscopy. The tacticity changes for the isotactic PMMA during gamma-irr adiation have been simulated by a model which allows for recombination of a scissioned bond and for the recombined bond to be in either the meso or racemic configuration with probability P-t. The calculated val ues of P-t were found to be consistent with the tacticity parameter P- m values for the free-radical polymerization of a methyl methacrylate monomer. The G-value of the temporary chain scission and then recombin ation, G(TCS), for the isotactic PMMA sample which was gamma-irradiate d at 80 degrees C was found to be 18.6, which is much higher than the G-value of the permanent main-chain scission, G(S). A mechanism to exp lain the observed tacticity changes have been proposed.