Strain-induced crystallization and reversible phenomena in transpolyisoprene. II. X-Ray studies

The results of wide- and small-angle X-ray studies on bulk oriented transpolyisoprenes are presented here. Variables investigated include thermal history, degree and temperature of elongation, cross-linking, and annealing temperature. At room temperature, discrete X-ray peaks occur at small angles. Upon heating the oriented specimens, the small-angle X-ray long period, as determined by Bragg's law, continuously increases from about 150 Å at 26°C to about 250 Å at ∼70°C; and it decreases continuously upon cooling and reaches a value of about 170 Å at 26°C. The small-angle X-ray peak intensity also exhibits significant thermal reversibility in the same temperature range. These results in conjunction with electron microscopy data (Part I) are discussed in light of current concepts concerning long period reversibility in bulk polymers. It is concluded that the present results again indicate recrystallization by refolding as the most plausible mechanism for the various reversible phenomena observed in this research.