Bromination of single crystals of trans‐1,4‐polybutadiene. Thermal behavior

It is demonstrated by several methods (DSC, infrared spectroscopy, and small‐angle and wideangle x‐ray diffraction) that bromination of suspensions of single crystals of trans‐1,4‐polybutadiene is selective at the fold surface. As the thickness of the single crystals is increased, a larger number of double bonds per fold are brominated, i.e. a larger number of repeat units become accessible to bromine. This is consistent with an increase in the thickness of disordered surface layers with the crystallization temperature. A reduction of 40–60% in overall apparent enthalpies of transition and of melting and reduced ability of brominated single crystals to refold following annealing are also observed. Crystallization from the melt of trans‐1,4‐PBD with [ CH2CHBrCHBrCH2 ] units along the chain is interpreted by assuming that some of these units are incorporated in the crystal lattice as defects.