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

Kunze, Lena, Tseng, Shih-Yu, Schweins, Ralf, Sottmann, Thomas, Frey, Holger
Langmuir 2019 v.35 no.15 pp. 5221-5231
carbon, carbon dioxide, composite polymers, copolymerization, emulsions, epoxides, gel chromatography, micelles, molecular weight, neutron diffraction, nuclear magnetic resonance spectroscopy, oils, polyethylene glycol, solubilization, surface tension, surfactants, temperature, thermal properties
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 = Mw/Mₙ) from 1.07 to 1.18. Furthermore, the thermal properties, i.e., Tg, Tₘ, and Td, 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.