Molecular uniform macromolecules of polyamide 6

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Abstract
The molecular weight distribution (MWD) of an autoclave‐polymerized polyamide 6 (PA 6) was determined by solution fractionation to be a mixed distribution, consisting of three regions. The top corresponds to a small fraction of low molecular weight (∠ 1%) and the tail, to a small, weakly crosslinked component of high molecular weight (∠ 1%). Cutting the wings of the distribution by fractionation yields linear PA 6 fractions with an extreme narrow partial distribution accounting for more than 98% by wt. The linear molecular weight averages areMn, lin= 24,800 andMω, lin= 24,810. The nonuniformity isU= 0.3 × 10−3(compared toUPoisson= 4.6 × 10−3). The fractionation efficiency amounts to ϕ = 99%.A distribution function for the molecular uniform PA 6 is given. Kinetic considerations are discussed. As is shown, the molecular uniformity is then appreciably larger than that of, for example, aPoissondistribution (more than a power of ten), if the rate of the initiation reaction (ki) is appreciably larger than that of the propagation of the chain (kω):r = kω/ki≪ 1.The extreme narrow linear PA 6 distribution found by solution fractionation is confirmed by fast turbidimetric titration according to dynamic volume pulse technique. Furthermore, the results are supported by the recovery and the evaluated mean properties, such as intrinsic viscosity, melting points and endgroup molecular weight (MW).

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