PULSED NMR OF CIS-POLYISOPRENE .1.

Proton spin-spin (T2), and spin-lattice (T1) relaxation time measurements are reported for six monodisperse cis-polyisoprenes ( M ̄n from 2000 to 200 000) over the temperature range from -50° to 170°C. At low temperatures (-30° to 10°C) T1 and T2 are determined by the short range segmental motions but above 10°C T2 is sensitive to the long range motions. When M ̄n {equal to or succeeds} 30 000 T2 becomes influenced by the presence of entanglements which produce a transient network structure and this confers on the spin-spin relaxation a pseudo-solid-like response. Similar behaviour is observed in crosslinked networks produced by irradiation. The results are discussed in terms of the types of motion occurring in amorphous polymers above Tg and the analogy with dynamic mechanical measurements is discussed. © 1979.