Abstract
The effect of pressure on crystallization from the melt and annealing of nylon-6 fractions has been investigated. Pressures exceeding 5 kbar and temperatures 40°C below the final melting temperature of the fractions under pressure, were sufficient to produce the extended-chain crystals by an isothermal crystallization from the melt as well as by annealing of the chain-folded material. Crystalline structure and the thermal characteristics of the extended-chain crystals formed from the fractionated nylo̧n-6, were identical to those of unfractionated polymer. G.p.c. analysis of the extended-chain material formed from the fractions of narrow molecular weight distribution showed that this material most probably had a wide molecular weight distribution, similar to that of unfractionated nylon-6. Based on a change in the molecular weight distribution and decrease in the molecular weight, concurrent with the extended-chain crystallization it is suggested that on the thermal treatment of polyamides under pressure a transamidation reaction occurs between the CONH groups of the broken folds of adjacent lamellae, which may lead to the chain extension.
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