Aliphatic polycarbonates synthesized from carbon dioxide (CO 2 ) and epoxides are resource-saving, highly biocompatible and biodegradable polymers. Since the discovery of the copolymerization of epoxides and CO 2 in 1969 by Inoue et al., this has become an important and useful technology for the large-scale utilization of CO 2 in chemical synthesis, employing mainly propylene oxide, and cyclohexene oxide (CHO). Only in recent years, functionalized polycarbonates have become an emerging topic with a broad scope of potential applications. This review summarizes synthetic routes and properties of numerous functionalized polycarbonates synthesized from CO 2 and functional epoxide monomers. Implications for new materials and possible applications, for instance for pharmaceutical purposes and membranes are reviewed. Besides polycarbonates based on oxirane and CHO derivatives, particular emphasis is placed on the manifold synthetic approaches and postpolymerization modifications of glycidyl ether based polycarbonates. Not only functionalized linear polycarbonates are presented but also a variety of novel polycarbonate architectures, e.g., star and hyperbranched polymers.

Well-defined poly((furfuryl glycidyl ether)-co-(glycidyl methyl ether) carbonate) (P((FGE-co-GME)C)) copolymers with varying furfuryl glycidyl ether (FGE) content in the range of 26% to 100% are prepared directly from CO2 and the respective epoxides in a solvent-free synthesis. All materials are characterized by size-exclusion chromatography (SEC), (1)H NMR spectroscopy, and differential scanning calorimetry (DSC). The furfuryl-functional samples exhibit monomodal molecular weight distributions with Mw/Mn in the range of 1.16 to 1.43 and molecular weights (Mn) between 2300 and 4300 g mol(-1). Thermal properties reflect the amorphous structure of the polymers. Both post-functionalization and cross-linking are performed via Diels-Alder chemistry using maleimide derivatives, leading to reversible network formation. This transformation is shown to be thermally reversible at 110 °C.

Hyperbranched, multifunctional polycarbonate polyols based on CO2, cyclohexene oxide (CHO), and the “inimer” (initiator–monomer) (4-hydroxymethyl)­cyclohexene oxide (HCHO) were prepared in one-pot syntheses. The related linear poly­(hydroxymethyl cyclohexene carbonate) structures based on protected HCHO and postpolymerization deprotection were also synthesized as model compounds. The content of hydroxyl functionalities was adjustable for both linear and hyperbranched terpolymer systems. All CO2/epoxide polymerizations were catalyzed by the (R,R)-(salcy)-Co­(III)­Cl complex. The polycarbonates obtained were comprehensively investigated using various 1D and 2D NMR techniques, SEC, FT-IR, UV–vis spectroscopy, and contact angle measurements. Rigid polyols with molecular weights between 3600 and 9200 g mol–1 and moderate dispersity between 1.18 and 1.64 (M w/M n) were obtained. In addition, the materials were examined with respect to their thermal properties, intrinsic viscosity, and their three-dimensional structure. Glass transition temperatures in the range of 113–141 °C (linear) and 72–105 °C (hyperbranched) were observed. The intrinsic viscosity of the hyperbranched systems is in the range of 5.69–11.51 cm3 g–1 and mirrors their compact structure. The hyperbranched polyols were also studied regarding their successful reaction with phenyl isocyanate to convert the free hydroxyl groups into urethanes.

Multiarm star copolymers, consisting of hyperbranched poly­(ethylene oxide) (hbPEO) or poly­(butylene oxide) (hbPBO) polyether copolymers with glycerol branching points as a core, and linear aliphatic polycarbonate arms generated from carbon dioxide (CO2) and epoxide monomers, were synthesized via a “core-first” approach in two steps. First, hyperbranched polyether polyols were prepared by anionic copolymerization of ethylene oxide or 1,2-butylene oxide with 8–35% glycidol with molecular weights between 800 and 389,000 g·mol–1. Second, multiple arms were grown via immortal copolymerization of CO2 with propylene oxide or 1,2-butylene oxide using the polyether polyols as macroinitiators and (R,R)-(salcy)-CoCl as a catalyst in a solvent-free procedure. Molecular weights up to 812,000 g·mol–1 were obtained for the resulting multiarm polycarbonates, determined by online viscometry with universal calibration and 1H NMR. Comparing the synthesis of different multiarm star polycarbonates, a combination of a highly reactive macroinitiator with a less reactive epoxide monomer was found to be most suitable to obtain well-defined structures containing up to 88 mol% polycarbonate. The multiarm star copolymers were investigated with respect to their thermal properties, intrinsic viscosity, and potential application as polyols for polyurethane synthesis. Glass transition temperatures in the range from −41 to +25 °C were observed. The intrinsic viscosity could be adjusted between 5.4 and 17.3 cm3·g–1 by varying the ratio of polyether units and polycarbonate units.

Partially degradable, nonionic AB and ABA type di-and triblock copolymers based on poly(propylene carbonate) and poly(ethylene glycol) blocks were synthesized via immortal copolymerization of carbon dioxide and propylene oxide, using mPEG or PEG as a macroinitiator, and (R,R)-(salcy)-CoOBzF 5 as a catalyst in a solvent-free one-pot procedure. The amphiphilic surfactants were prepared with molecular weights (M n ) between 2800 and 10,000 g·mol −1 with narrow molecular weight distributions (1.03-1.09). The copolymers were characterized using 1 H-, 13 C-and DOSY-NMR spectroscopy and size exclusion chromatography (SEC). Surface-active properties were determined by surface tension measurements (critical micelle concentration, CMC; CMC range: 1-14 mg·mL −1 ). Degradation of the acid-labile polycarbonate blocks was investigated in aqueous solution using online 1 H-NMR spectroscopy and SEC. The amphiphilic polymers were used as surfactants in a direct miniemulsion polymerization for poly(styrene) (PS) nanoparticles with mean diameter of 270 to 940 nm. The usage of an acid-triggered precipitation of the emulsion simplified the separation of the particles from the surfactant and purification of the nanoparticles.