Copolymerization of δ-lactone derived from CO2 and butadiene with ε-caprolactone towards functional copolymers

Poly( ε -caprolactone) (PCL) possesses considerable biocompatibility, biodegradability, and favorable mechanical properties, yet the lack of functional groups on the PCL backbone or side chain limits its applications. α -Ethylidene- δ -vinyl- δ -valerolactone (EVL), an intermediate derived from carbon dioxide (CO 2 ) and 1,3-butadiene, possesses abundant carbon-carbon double bonds that provide sites for modification. In this contribution, the living and controlled copolymerization of CL with EVL is achieved at 0 °C with TBD as catalyst, resulting in linear P(EVL- co -CL) with number average molecular weights ( M n ) up to 22.7 kg/mol. Using methoxy poly(ethylene glycol) (mPEG) as macroinitiator, PEG- b -P(EVL- r -CL) with modifiable double bonds are synthesized and functionalized via thiol-ene “click” reactions. The resulting block copolymers are capable of forming micelles in aqueous solution and the introduction of thioether and carboxyl groups enables the formation of stimuli-responsive micelles, whereas the introduction of amino groups leads to micelles that are degradable under alkaline conditions. This method offers a straightforward approach to synthesize amphiphilic block terpolymers from CO 2 , 1,3-butadiene, CL and PEG.