MOSIEWICKI mirna Alejandra
congresos y reuniones científicas
Smart copolymers from vegetable oils and styrene obtained by cationic polymerization
Congreso; 11th ICFPAM, Pretoria, SOUTH AFRICA; 2011
In this work, the preparation and characterization of smart copolymers based on highly unsaturated vegetable oils is reported. The carbon-carbon double bonds in oils are reactive in cationic polymerization reactions, which allows using them without chemical modification [1-3]. Different compositions of copolymers obtained by cationic polymerization with varying tung oil/styrene weight ratios lead to materials with a wide range of final properties. For some of the compositions the obtained materials present shape memory behavior. In those cases, the polymers are able of “remembering” their original shape after having been deformed above a switch temperature that in these thermoset copolymers is the glass transition temperature. By further application of an external stimulus, which in this study is temperature, the original shape is recovered [4]. The mechanical properties, dynamic-mechanical properties, damping and shape memory behavior were analyzed. The glass transition temperatures are close to room temperature for all the copolymers, and generally decrease with the content of tung oil. Similar trend is observed in the elastic modulus. The glass transition temperatures, as well as the mechanical properties at room temperature are related to the crosslinking and mobility degree in the network. The shape memory behavior was investigated by subjecting the films to cyclic thermal and tensile loads. These hard elastomers exhibit shape memory behavior with high recovery and fixity ratios for copolymers with at least 40 wt.% of styrene in a low temperature range. The copolymer with 30 wt.% tung oil reachs elongation of 100% and almost complete fixing of the transition shape (fixity ratio=100). Additionally, high damping factors (between 0.4 and 1.38) for the tung oil homopolymer and the copolymer with 70 wt.% styrene, respectively, were measured in a temperature range between 28.9 and 43.3°C. This material property also opens possibilities for important practical applications requiring material reponse close to room temperature.