Multiple Field Spin-Lattice Relaxation Study of Dissolved Poly(4,4'-bicyclo(2.2.1)heptan-2-ylidenebis(phenyl carbonate))

摘要

A dilute-solution spin-lattice relaxation time study was performed on a bisphenol polycarbonate similar to the polycarbonate of bisphenol A except the methyl groups of the bisphenol unit are replaced by a norbornyl ring. Carbon-13 relaxation times are measured at three Larmor frequencies: 22.6, 62.9, and 126 MHz. Motion of the norbornyl group is seen to be isotropic, which implies segmental motion is isotropic since the group is rigidly incorporated into the backbone. Relaxation caused by this segmental motion is interpreted in terms of the Hall-Helfand correlation function. The apparent activation energies for cooperative and individual bond transitions are 24 and 30 kj/mo1, respectively, while the corresponding Arrhenius prefactors are 6 x 10 to the -14th power and 17 x 10 to the 14th power, respectively. The phenyl groups undergo this same segmental motion plus restricted rotation about the C1 C4 axis but not full anisotropic rotation. Since full anistropic rotation is observed in bisphenol A polycarbonate, the larger norborny1 group would appear to sterically hinder phenylene group rotation. In the bulk polymer a low-temperature dynamic mechanical loss peak comparable to that of bisphenol A polycarbonate has been observed for the norbornyl-substituted polymer. This implies phenylene group rotation is not the primary element contributing to dynamic mechanical loss. An alternative motion based on correlated conformational interchange between carbonate groups is an explanation for the low-temperature loss peak, which is in better agreement with the findings of this study.