Modern Theories of Polymer Crystallization

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Abstract
In 1957 three independent papers by Keller [l], Fischer [2], and Till [3] were published which showed that linear polyethylene of high molecular weight formed thin lamellar-like crystals that were quite similar in appearance to those of paraffinic single crystals. These and many subsequent studies have shown that solution-grown polymer crystals are usually about 100 Å thick and that the chains are oriented with their molecular axes perpendicular to the basal plane of the lamellar crystal. Since the crystal is composed of chain molecules whose lengths may exceed by many times the crystal thickness, the conclusion has been drawn that a chain molecule must traverse the lamella several times and in the process must “fold” back on itself. The chain-folding phenomena has now been reported for a wide variety of synthetic organic polymers [4, 5], biopolymers [6–8] including DNA [9], a naturally occurring polysaccharide (amylose) [10], and polymeric selenium [11, 12].