Fourier-transform infra-red dichroism study of molecular orientation in synthetic high cis-1,4-polyisoprene and in natural rubber

Abstract

Infra-red dichroism was used to investigate the molecular orientation of uniaxially stretched networks of natural rubber (pale crepe) and of a synthetic polyisoprene with 92% cis-1,4 content. Separate orientation functions were derived for the crystalline and amorphous phases of the natural rubber. The extension ratio dependence of the orientation of the transition moments of the considered vibrational modes relative to the polymer chains highlighted the occurrence of conformational changes. The results are in agreement with conformational energy calculations performed by Abe and Flory.