Polymer chain segment orientation during stress relaxation

Abstract

This report presents results on simultaneous measurement of stress and molecular orientation on uniaxially stretched polymer films. Stress is measured using a force transducer and orientation using infrared dichroism. A set of deuterated polystyrene samples were prepared with deuterated blocks at either the center or ends of the polymer chains. Using infrared bands, unique to the deuterated or hydrogenated sample, the relaxation of ends versus middle of the polymer chain can be monitored. The essential feature of the reptation models is that relaxation occurs from the ends of the chains first. Experimental results show: relaxation of the chain ends is more rapid than relaxation of the central portion of the chain, orientation of the chain ends increases linearly with total elongational strain, orientation increases with polymer molecular weight, and the relaxation of overall chain orientation at long times follows stress relaxation, which is in agreement with the classical ''stress-optical law''.