Enhanced thermal stability of biobased crosslinked poly (isobornylacrylate-co-2-ethylhexylacrylate) copolymers

Polymerization kinetics as well as thermal properties of acrylic copolymers containing Isobornylacrylate- (IBOA) and 2-Ethylhexylacrylate- (2-EHA) units were investigated. Poly(IBOA-co-2-EHA) samples were synthesized via free radical photopolymerization/crosslinking reactions of IBOA and 2-EHA, in the presence of 1,6-hexanedioldiacrylate (HDDA) as crosslinking agent, to obtain chemically crosslinked polymer networks. High conversion rates of the acrylic double bonds of the monomers were obtained from investigation of the polymerization kinetics by infrared spectroscopy. Analysis of the thermal properties using differential scanning calorimetry revealed the appearance of a single glass transition of Poly(IBOA-co-2-EHA) over a large range of temperatures comprised between 208 and 321 K, depending on monomer composition. The evolution of the glass transition temperature was rationalized by applying the Fox, Gordon Taylor, and Brekner-Schneider-Cantow models, revealing presumably the existence of hydrogen bonding interaction involving the carbonyl groups of the acrylates. Several degradation processes were observed by thermogravimetrical analysis, especially that of the isobornylene group at low temperature followed by the degradation of the carbon backbone at higher temperatures. Increasing IBOA content leads to a higher thermal stability of Poly(IBOA-co-2-EHA). Each degradation step could be characterized separately exhibiting activation energies which strongly depend on the degradation time of each step.