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A morphological, mechanical and thermodynamic investigation of the isotactic polyvinylmethylether/polystyrene polymer blend
Abstract
A novel technique for the production of toughened polymers using LCST behavior as a mechanism for the production of rubbery domains is discussed. The polymer blend of isotactic polyvinylmethylether (PVME) with polystyrene (PS) is used. Synthesis, fractionation and characterization of isotactic PVME is reviewed. Thermodynamic effects of tacticity on miscibility are extensively investigated using light and neutron scattering. A simple critical point analysis is presented which indicates an entropic nature to the tacticity effect in this blend. Flory-Huggins-Staverman (F-H-S) theory is next applied to the tacticity effect. This more elaborate analysis also indicates an entropic nature to the tacticity effect. Accounting for polydispersity results in a predicted fractionation in the phase separated blends which is supported by mechanical data. F-H-S theory was used to generate a functional form for the interaction parameter in terms of the temperature and composition dependence of miscibility. From these functions a dramatic shift in the kinetics of phase separation with tacticity is predicted. Experimental data affirms this prediction. A novel, modified Cahn-Hillard analysis is presented for analysis of intermediate stages. Neutron scattering data yields the composition and temperature dependence of the statistical segment length, b, of tactic PVME. A functional form for b is derived which predicts the equilibrium melting point and melting point depression behavior for the blends. A relationship between b and thermodynamic miscibility from a geometric perspective is discussed. The tacticity effect can be described in terms of an interaction parameter whose change with tacticity in terms of entropy is functionally related to the volume of an interacting group and in terms of enthalpy is functionally related to the surface area of an interacting group. Two related studies are presented. The first pertains to a shift in glass transition of thin PS films with thickness as investigated using ellipsometry. The second study used neutron reflection data to disprove the supporting argument for a minus two thirds dependence of surface tension with molecular weight. An alternative theory for the molecular weight dependence of surface tension is presented.
Subject Area
Polymer chemistry|Materials science|Plastics
Recommended Citation
Beaucage, Gregory, "A morphological, mechanical and thermodynamic investigation of the isotactic polyvinylmethylether/polystyrene polymer blend" (1991). Doctoral Dissertations Available from Proquest. AAI9132817.
https://scholarworks.umass.edu/dissertations/AAI9132817