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.

The synthesis of propargyl-functional poly(carbonate)s with different content of glycidyl propargyl ether (GPE) units is achieved via the copolymerization of propargyl glycidyl ether and carbon dioxide. A new type of functional poly(carbonate) synthesized directly from CO(2) and the glycidyl ether is obtained. The resulting polymers show moderate polydispersities in the range of 1.6-2.5 and molecular weights in the range of 7000-10 500 g mol(-1). The synthesized copolymers with varying number of alkyne functionalities and benzyl azide are used for the copper-catalyzed Huisgen-1,3-dipolar addition. Moreover, the presence of vicinal alkyne groups opens a general pathway to produce functional aliphatic poly(carbonate)s from a single polymer scaffold.

Multi-arm star copolymers based on a hyperbranched poly(propylene oxide) polyether-polyol (hbPPO) as a core and poly(propylene carbonate) (PPC) arms are synthesized in two steps from propylene oxide (PO), a small amount of glycidol and CO2 . The PPC arms are prepared via carbon dioxide (CO2 )/PO copolymerization, using hbPPO as a multifunctional macroinitiator and the (R,R)-(salcy)CoOBzF5 catalyst. Star copolymers with 14 and 28 PPC arms, respectively, and controlled molecular weights in the range of 2700-8800 g mol(-1) are prepared (Mw /Mn = 1.23-1.61). Thermal analysis reveals lowered glass transition temperatures in the range of -8 to 10 °C for the PPC star polymers compared with linear PPC, which is due to the influence of the flexible polyether core. Successful conversion of the terminal hydroxyl groups with phenylisocyanate demonstrates the potential of the polycarbonate polyols for polyurethane synthesis.