Characterization of poly(1,4-phenyleneterephthalamide) in concentrated sulphuric acid. 2: Determination of molecular weight distributions

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By combining static and dynamic properties (Mw, A2, kd Rg and Rh) of poly(1,4-phenyleneterephthalamide), PPTA (commercially known as Kevlar), with a detailed analysis of measured time correlation functions at different scattering angles in dilute solution, we have been able to estimate the molecular weight dependence of the radius of gyration, Rg(M), the persistence length ϱ (), and the molecular weight distribution (Mz:Mw:Mn ≈ 6.2:1.8:1) using an unfractionated PPTA sample (Mw = 4.3 × 104 g/mole). Laplace inversion of the time correlation function was accomplished independently by means of two different algorithms: the singular value decomposition technique with discrete multi-exponentials to approximate the normalized characteristic linewidth distribution function G(г) and the method of regularization whereby a linearized smoothing operator was used. The non-intrusive laser light scattering technique permits us to characterize, for the first time, the molecular weight distribution of PPTA which has been difficult to perform by means of other more established methods, such as size exclusion chromatography, because of the corrosive nature of solvents used in preparing PPTA solutions.


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