Photoinduced thiol-ene crosslinking of globalide/ε-caprolactone copolymers: Curing performance and resulting thermoset properties

The increasing demand for bioderived polymers led us to investigate the potential use of the macrolactone globalide in thermoset synthesis via the photoinduced thiol–ene reaction. A series of six lipase‐catalyzed poly(globalide‐caprolactone) copolyesters bearing internal main‐chain unsaturations ranging from 10 to 50 and 100 mol % were successfully crosslinked in the melt with equal amounts of thiol groups from trimethylolpropane‐trimercapto propionate affording fully transparent amorphous elastomeric materials with different thermal and viscoelastic properties. Three major conclusions can be drawn from this study: (i) high thiol–ene conversions (>80%) were easily attained for all cases, while maintaining the cure behavior, and irrespective of functionality at reasonable reaction rates; (ii) parallel chain‐growth homopropagation of the ene monomer is insignificant when compared with the main thiol–ene coupling route; and (iii) high ene‐density copolymers result in much lower extracted sol fractions and high Tg values as a result of a more dense and homogeneous crosslinked network. The thiol–ene system evaluated in this contribution serve as model example for the sustainable use of naturally occurring 1,2‐disubstituted alkenes in making semisynthetic polymeric materials in high conversions with a range of properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012. A series of poly(globalide‐caprolactone) copolymers were synthesized by enzymatic ring‐opening polymerization from globalide, a naturally occurring macrolactone, using ε‐caprolactone as intercalating monomer to provide linear multifunctional polyesters bearing different degrees in 1,2‐disubstituted unsaturations along the main chain. The random copolymers were successfully photo cross‐linked in the melt with a tri‐functional thiol monomer via the thiol–ene coupling reaction affording thermoset film materials with a range of thermal and viscoelastic properties potentially useful for coating applications. The “green chemistry” concept is exemplified by combination of an environment‐friendly 3‐in‐1 approach that serves as model platform in the formation of semi‐synthetic cross‐linked networks.