Unexpected proton spin-lattice relaxation in the solutions of polyolefin and tetrachloroethane.

‘Unexpected’ proton spin-lattice relaxation (T1) times are reported for the solutions of poly(ethylene-co-1-octene) and tetrachloroethane-d2. For the residual protons of the deuterated solvent and the methyl and vinyl protons at the polymer chain ends, their T1 relaxation times vary significantly with both the polymer concentration and molecular weight over a wide range. The T1s also decrease with increasing temperature at relative high temperatures. Such behaviors are in contrast to most reported polymer solutions in which the T1 has nearly no concentration or molecular weight dependence in the dilute and semi-dilute regime, and normal dependence on temperature. Further investigation revealed that the paramagnetic oxygen effect did shorten the measured proton T1s, but cannot account for the unexpected T1 dependences. Spin rotation is proposed to provide a reasonable explanation. Copyright © 2010 John Wiley & Sons, Ltd.