One-pot orthogonal thiol-ene click polymerization and ring-opening grafting reaction of CO2-based disubstituted δ-valerolactone

Being a disubstituted delta-valerolactone synthesized by the telomerization of carbon dioxide with 1,3-butadiene, 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVL) contains a six-membered ring and two unsaturated groups. This report describes the synthesis of an amphiphilic graft copolymer by the combination of thiol-ene click polymerization and ring-opening grafting reaction of EVL, ethyldithiol (EDT), and methoxy polyethylene glycol (mPEG-OH). The alternating copolymer of P(EVL-alt-EDT) with 17.9 wt% CO2 content and weight-average molecular weight (M-w) of 7 kg/mol was prepared by means of the free radical thiol-ene click polymerization of EVL with EDT initiated by 2,2-dimethoxy-1,2-diphenylethanone under UV irradiation. The following alcoholysis of the lactone ring of P(EVL-alt-EDT) backbone by mPEG-OH is catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene, producing the amphiphilic graft copolymer P(EVL-alt-EDT)-g-PEG(750) with M-w of 12 kg/mol. The polymers are characterized by nuclear magnetic resonance, Fourier transform infrared, matrix-assisted laser desorption ionization-time of flight mass spectra, size exclusion chromatography and differential scanning calorimetry. The one-pot orthogonal strategy is a new utilization of EVL in synthetic polymers and it is significant to the carbon dioxide transformation.