Unexpected proton spin-lattice relaxation in the solutions of polyolefin and tetrachloroethane.
'Unexpected' proton spin-lattice relaxation (T(1)) times are reported for the solutions of poly(ethylene-co-1-octene) and tetrachloroethane-d(2). For the residual protons of the deuterated solvent and the methyl and vinyl protons at the polymer chain ends, their T(1) relaxation times vary significantly with both the polymer concentration and molecular weight over a wide range. The T(1)s also decrease with increasing temperature at relative high temperatures. Such behaviors are in contrast to most reported polymer solutions in which the T(1) 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 T(1)s, but cannot account for the unexpected T(1) dependences. Spin rotation is proposed to provide a reasonable explanation.
Analytical Sciences, The Dow Chemical Company, Midland, MI 48674, USA. YHe@dow.com
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