Poly(acrylonitrile/methyl acrylate) copolymers and clay nanocomposites : structural and property relationships

[摘要] ENGLISH ABSTRACT: The preparation of poly(acrylonitrile/methyl acrylate) [poly(AN-co-MA)] copolymers andpoly(AN-co-MA)/clay nanocomposites, via emulsion polymerization, their characterisation,and the relationships between their molecular structures and physical properties are described.The copolymer composition was varied, and the properties of the products were analysed andcorrelated to copolymer composition.The free volume properties of the copolymer were dependent on the glass transitiontemperature (Tg), which is dependant on the copolymer composition. The copolymercrystallinity decreased with increasing MA content. The decrease in crystallinity and increasein both o-Ps lifetime and o-Ps intensity with decreasing Tg was caused by the enhanced chainmobility brought about by the incorporation of methyl acrylate.The poly(acrylonitrile-co-methyl acrylate)/clay nanocomposites with 60% AN:40%MA (mol:mol) ratio were prepared using montmorillonite clay modified via adsorption, using2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS), via in-situ intercalationpolymerization. The poly(AN-co-MA)/clay nanocomposites with different clay loadingsshowed no difference in morphology. They exhibited improved thermomechanical propertiesand higher thermal stability than the neat copolymers.The melt rheology results of these nanocomposites showed an improved storagemodulus as well as increased shear thinning behaviour with increasing clay content. However,the nanocomposites exhibited long-time relaxation behaviour and their chemical structuresevolved during analysis. This was attributed to cyclisation reactions taking place at thetemperature used during the oscillatory tests.The sorption isotherms of water vapour in these nanocomposites followed a dualmodesorption behaviour (BET type II mode). Hysteresis was observed in sorption/desorptionisotherms of these nanocomposites. The equilibrium water uptake was higher in the nanocomposites compared to the neat copolymers, and it increased with increasing claycontent, especially at high water activities (0.8).Although diffusion and permeability decreased with increasing clay content thesolubility increased due to the hydrophilic nature of the clay. Despite the decrease in diffusionand permeability parameters the free volume hole radius of the nanocomposites remained constant, but a slight decrease in free volume hole number was observed.

[发布机构] Stellenbosch University