Determination of residual levels of unsaturation in partially hydrogenated poly(2,3-diphenyl-1,3-butadiene) using thermogravimetry

The thermal degradation characteristics of head-to-head poly(styrene) (HHPS) should provide insight with respect to the impact of head-to-head placement on the thermal stability of the traditional atactic head-to-tail polymer (HTPS). The synthesis of head-to-head poly(styrene) must be accomplished indirectly. The HHPS is most satisfactorily obtained by dissolving metal reduction of poly(2,3-diphenyl-1,3-butadiene) (PDBD) generated by radical polymerization of the corresponding diene monomer. Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of PDBD is prominent at 374 °C and that for HHPS is similarly facile at 406 °C, it seemed feasible that TGA of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent of hydrogenation. This has been demonstrated for various levels of unsaturation remaining—from approximately 90 to less than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected by the asymmetry of the decomposition peak for the polymer.