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Chapter 2: Structure of solid polymers > 2.8 Chain-extended polymers

2.8 Chain-extended polymers

As discussed in Section 2.7.2 above, in chain-folded linear-chain polymers with spherulitic morphology, where lamellae could have a high concentration of chain folds with adjacent reentry, annealing of the polymer close to the melting temperature and under pressure promotes monotonic thickening of lamellae. As discussed there, this occurs through stochastic drift of dispirations along molecules that progressively squeeze out chain folds until lamellae are effectively made up solely of parallel chain molecules (Anderson 1964; Wunderlich and Melillo 1966, 1968; Geil et al. 1964). A dramatic example of a chain-extended lamella in PE is shown in Fig. 2.24, where in the thickest portion of the central lamella the thickness has reached roughly 2.5 μm. The figure shows several kinks in the lamella, having arisen most likely in response to interlamellar compressive stresses due to development of material misfit. Such chain-extended polymers tend to be generally quite brittle, no doubt due to their large interfaces across parallel molecules interacting only through weak van der Waals interactions.


  

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