Proton spin lattice relaxation and mechanical loss in a series of acrylic polymers

Abstract

Measurements are reported of the proton spin lattice relaxation time, T 1 (effective frequency 35 Mc/s), and for the dynamic mechanical loss (at about 200 c/s) for a series of acrylic polymers with a variety of α main chain and of side chain substituents. The highest temperature T 1 minimum can always be associated with the main (softening) mechanical loss peak. Lower temperature T 1 minima can usually be associated with the presence of particular groups, e.g. if a methyl side group is present there is a T 1 minimum (for our frequency) at about 260°K. An α-methyl group gives a T 1 minimum below 90°K. In neither case is there an associated mechanical loss. Bulkier groups, e.g. ethyl give T 1 minima at a slightly higher temperature together with a mechanical loss process. A phenyl side group gives no obvious effect whereas a flexible cyclohexyl group gives interesting effects in both T 1 and tan δ.