Relaxation, styrene-methacrylic acid

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

Relaxation in Styrene-Methacrylic Acid, Sodium Salt Ionomers... 

While ionomers of many types have been made and characterized [1,2,3], there is little work on the overall relaxation mechanisms. For polymers with low ionic concentrations, there is general agreement on the fundamental relaxation step. The stress relaxes by detachment of an ion pair from one cluster and reattachment to another. For the styrene/methacrylic acid Na salt (ST/-MAA-Na) system, there is a secondary plateau in the relaxation modulus which depends on the ionic content and can be described as a rubbery modulus [4], While a rubbery modulus with stress relaxation due to ionic interchange has been invoked earlier, it does not adequately describe the relaxation curves. A different approach is taken here. 

This chapter discusses the dynamic mechanical properties of polystyrene, styrene copolymers, rubber-modified polystyrene and rubber-modified styrene copolymers. In polystyrene, the experimental relaxation spectrum and its probable molecular origins are reviewed further the effects on the relaxations caused by polymer structure (e.g. tacticity, molecular weight, substituents and crosslinking) and additives (e.g. plasticizers, antioxidants, UV stabilizers, flame retardants and colorants) are assessed. The main relaxation behaviour of styrene copolymers is presented and some of the effects of random copolymerization on secondary mechanical relaxation processes are illustrated on styrene-co-acrylonitrile and styrene-co-methacrylic acid. Finally, in rubber-modified polystyrene and styrene copolymers, it is shown how dynamic mechanical spectroscopy can help in the characterization of rubber phase morphology through the analysis of its main relaxation loss peak. 

Some of the effects of random copolymerization on secondary mechanical relaxation processes will be illustrated here on styrene-co-acrylonitrile (SAN) and on styrene-co-methacrylic acid (SMAA). 

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