Chain folding in poly-trans-1,4-butadiene crystals grown from various solvents

Crystals of poly-trans-1,4-butadiene of uniform size have been grown from three solvents (n-heptane, methyl isobutyl ketone, and toluene) by using a minimum dissolution temeprature technique. The percentage of double bonds available for reaction in the crystals was determined by epoxidation in suspension; crystal thicknesses were measured by electron microscopy. These values were used to calculate the number of monomer units per fold. The number of available double bonds was found to increase with decreasing molecular weight, evidence for the presence of non-reentrant chains (cilia) at the crystal surfaces. The nature of the chain fold in poly-trans-1,4-butadiene crystals is discussed.