Enhanced thermal stability of biobased crosslinked poly (isobornylacrylate-co-2-ethylhexylacrylate) copolymers
Résumé
Polymerization kinetics as well as thermal properties of acrylic copolymers containing Isobornylacrylate- (IBOA) and2-Ethylhexylacrylate- (2-EHA) units were investigated. Poly(IBOA-co-2-EHA) samples were synthesized via free radicalphotopolymerization/crosslinking reactions of IBOA and 2-EHA, in the presence of 1,6-hexanedioldiacrylate (HDDA) ascrosslinking agent, to obtain chemically crosslinked polymer networks. High conversion rates of the acrylic double bondsof the monomers were obtained from investigation of the polymerization kinetics by infrared spectroscopy. Analysis of thethermal properties using differential scanning calorimetry revealed the appearance of a single glass transition of Poly(IBOAco-2-EHA) over a large range of temperatures comprised between 208 and 321 K, depending on monomer composition. Theevolution 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 theacrylates. Several degradation processes were observed by thermogravimetrical analysis, especially that of the isobornylenegroup at low temperature followed by the degradation of the carbon backbone at higher temperatures. Increasing IBOA contentleads to a higher thermal stability of Poly(IBOA-co-2-EHA). Each degradation step could be characterized separatelyexhibiting activation energies which strongly depend on the degradation time of each step.