β Scribed by A.J. Staverman
No coin nor oath required. For personal study only.
In polymers, made up of one type of monomer unit, molecular heterogeneity may originate from the molecular weight distribution (MWD) or from differences in branching or stereoregularity. For dilute solutions, information on heterogeneity can be obtained from gel permeation chromatography (GPC), viscosity, sedimentation and diffusion. Each of these methods reflects the distribution of molecular dimensions. For mixtures of linear molecules, this information is sufficient to determine the MWD but, if branched molecules are present, it is insufficient. This is demonstrated by results of measurements on dextrans. In concentrated systems, viscoelastic properties are particularly informative. Some viscoelastic properties are proportional to a high power of the molecular weight M. The equilibrium shear compliance appears to be independent of M but strongly dependent on the MWD. Depending on the molecular model, widely different M-averages are expected to be characteristic for any particular physical property. From an analysis of the transition range between dilute and more concentrated systems, information about dilute systems can be obtained from measurements on concentrated systems and reversely.
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## Abstract A method that combines UV irradiation and pausing was developed to manipulate the regularity and the length scales of the morphology generated by phase separation in __full__βinterpenetrating polymer networks of polystyrene and poly(methyl methacrylate). Upon increasing the pause time o