NMR investigations of molecular motion in synthetic polyisoprenes at liquid helium temperatures

Abstract

AbstractThe behaviour of the molecular motion in synthetic cis‐ and trans‐1,4‐polyisoprenes was studied by nuclear magnetic resonance. The line‐widths (ΔHpp), second (M2) and fourth moments (M4) of the absorption curves were measured at 77, 4.2, and 1.3 K. The obtained values of ΔHpp and M2 for cis‐polyisoprene indicate that the molecular motions are apparently not completely quenched at 77 K since there is a further increase in the values of M2 and ΔHpp when decreasing the temperature from 77 to 4.2 K. It was found also that the value of M2 at 4.2 and 1.3 K (≅ 20 G2) was larger than the previously computed one for a rigid lattice (18.5 G2). The temperature dependence of M2 and ΔHpp for trans‐polyisoprene is different from that for cis‐polyisoprene. The values of M2 are constant in the range from 77 to 1.3 K (≅ 19.5 G2), which suggests that the molecular motion is presumably stopped in this polymer already at 77 K.