Effect of drying catalysts on the properties of thermal copolymers from conjugated linseed oil-styrene-divinylbenzene

Abstract

The effect of addition of a varying concentration of a drying catalyst (cobalt salt as primary drier) and a combination of catalysts such as cobalt, zirconium (secondary drier) and calcium (auxiliary drier) in a fixed concentration (1%) to a 50:20:30 compositions of 87% conjugated linseed oil, styrene (ST), and divinylbenzene (DVB) has been studied by characterizing the resulting polymers from thermal polymerization with various techniques such as soxhlet extraction, 1H NMR (1H nuclear magnetic resonance) spectroscopy, dynamic mechanical analysis (DMA), mechanical and thermogravimetric analysis. The thermal polymerization is performed in the temperature range of 85-160 °C. By soxhlet extraction, it is observed that the polymers contain approximately 64-77% crosslinked materials and the crosslinked insoluble fraction increases with an increase in cobalt catalyst concentration. For fixed concentration (1%) of catalysts, the insoluble fraction from the soxhlet extraction is maximum for the cobalt-zirconium mixture and minimum for the cobalt-calcium mixture. The micro-composition of these polymers obtained from the 1H NMR spectroscopy indicates that the crosslinked materials are composed of both soft oily and hard aromatic phases. The polymers with varying cobalt concentrations up to 0.6 wt% exhibit two separate glass transition temperatures, indicating the presence of two separate phases, one soft rubbery phase with sharp glass transition temperature of -50 °C and a hard brittle plastic phase of broadened glass transition temperature of 70-120 °C. On the other hand, instead of sharp peaks, the polymers with 0.8 and 1.0% cobalt salts exhibit two humps and a distinct peak in between the humps in the tan ? plots, indicating the presence of an additional phase comprised of a copolymer of linseed oil-styrene and DVB. For fixed concentration (1%) of catalysts, the cobalt-calcium combination follows the similar trend in the tan ? as that for the polymers with 0.8-1.0% cobalt whereas other combinations exhibit two phases. These polymers possess crosslink densities of 0.63-0.91 × 104 mol/m3 and compressive strengths of 2.0-26.6 MPa. The catalyzed polymers are thermally stable below 300 °C and exhibit a major thermal degradation with a maximum degradation of 82-88% at a temperature of 500 °C. © 2008 Elsevier B.V.