Nonionic Aliphatic Polycarbonate Diblock Copolymers Based on CO₂, 1,2-Butylene Oxide, and mPEG: Synthesis,...

Carbon dioxide (CO₂) is a renewable carbon source that is easily available in high purity and is utilized as a co-monomer in the direct ring-opening polymerization of epoxides to obtain aliphatic polycarbonates. In this work, degradable aliphatic polycarbonate diblock copolymers (mPEG- b-PBC) are synthesized via catalytic copolymerization of CO₂ and 1,2-butylene oxide, starting from monomethoxy poly(ethylene glycol) (mPEG) as a chain transfer reagent. The polymerization proceeds at low temperatures and high CO₂ pressure, utilizing the established binary catalytic system ( R, R)-Co(salen)Cl/[PPN]Cl. Amphiphilic nonionic diblock copolymers with varying PBC block lengths and hydrophilic-lipophilic balance values between 9 and 16 are synthesized. The polymers are characterized via NMR and Fourier transform infrared spectroscopies as well as size exclusion chromatography, exhibiting molecular weights ranging from 2400 to 4100 g mol^-1 with narrow dispersities ( Đ = M_w/ M_n) from 1.07 to 1.18. Furthermore, the thermal properties, i.e., T_g, T_m, and T_d, are determined. Surface tension measurements prove that the amphiphilic polymers form micelles above the critical micelle concentration, whereas small-angle neutron scattering shows that they are of nearly spherical shape. Adding small amounts of the synthesized mPEG- b-PBC polymers to different microemulsion systems, we found that the polymers were able to strongly increase the efficiency of medium-chain surfactants to solubilize polar oils.