Abstract
Carbon-13 spin-lattice relaxation times, T1's, were measured for cis-1,4, trans-1,4 and cis-trans isomerized polyisoprenes in chloroform-d1 at 25 MHz and mainly at 27°C. Cis-polyisoprene generally showed longer T1 than the trans-polymer except for methyl carbon, showing the greater segmental mobility of cis-polymer chain. The T1 of methyl carbon was longer for the trans-polymer than for the cis-polymer. This indicates the greater freedom of the internal rotation of methyl group in trans-polyisoprene. The segmental motion was found not to be isotropic, especially for cis-polyisoprene. The T1's of the main chain carbons in cis-trans isomerized polyisoprenes increased with increasing content of the cis-unit.
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