Variable temperature, high resolution solid state carbon-13 NMR study of 1,4-trans-polybutadiene.

High resolution carbon-13 NMR spectra recorded for solution crystallized 1,4-trans-polybutadiene (TPBD) over the temperature range 23 - 83C have revealed significant differences in the conformations and motions of TPBD chains in the well-known low and high temperature crystalline phases, Forms 1 and II. In high temperature, Form II crystals the chemical shifts observed for the olefinic and methylene carbons are similar to those of the amorphous carbons, ie.1.2 and 1.8 ppm upfield from the resonances observed for the low temperature, Form I crystalline carbons. The solid state transformation of Form I crystals to Form II crystals in a ten fold reduction in the spin-lattice relaxation time, T sub (1), observed for both types of carbons in the crystalline TPBD chains. The non-spinning spectrum of Form II indicates the presence of anisotropic chain motion. These observations lead us to tentatively conclude that the TPBD chains in the high temperature, Form II crystals are conformationally disordered and motionally labile compared to the rigid, low temperature, Form I crystalline chains.