In the 21st century, the central focus of research both in academia and industries is directed towards the design of environmentally-benign materials produced from reagents that have minimal deleterious effects on our environment. The synthesis of biodegradable polypropylene carbonate (PPC) by the copolymerization of naturally abundant, bio-renewable, inexpensive carbon dioxide (CO2) and cheaply available propylene oxide (PO) obtained from petroleum feedstock propylene is one such example.1 The release of ring-strain of the three-membered heterocycle upon ring-opening during copolymerization serves as the driving force for the reaction. Despite the favourable driving force, the major challenge in the production of PPC is the formation of thermodynamically stable five-membered cyclic propylene carbonate (PC) and homopolymerization of the epoxide to give polypropylene oxide (PPO).2 In 1969 Inoue et al. for the first time reported heterogeneous catalyst (ZnEt2−H2O) for the copolymerization of PO and CO2. There was no significant formation of the cyclic product, but the yield was low.3 In 2002, Coates and coworkers reported highly active unsymmetrical β-diiminate zinc complexes that gave regio irregular PPC in good yield with > 99 % carbonate linkage and narrow PDI value.4 Chakraborty et al. in 2015 reported that Zr(IV) complexes with diamine bis(phenolate ) ligand in the presence of cocatalyst TBAB copolymerize CO2 and PO with moderate PPC selectivity (PPC/PC) =(81/19).5 Recently in 2020, Darensbourg et al. for the first time reported highly regio regular polypropylene carbonate obtained from PO and 13CO2 with no cyclic carbonate formation.6 Thus, the study mainly focuses on diverse parameters including temperature, the pressure of CO2, nature and amount of cocatalyst, steric and electronic environment of catalyst that play a crucial role in determining selectivity for PPC vs PC formation. In addition, regiochemistry and stereochemistry of the PPC that govern the physiochemical properties of the polymer will also be discussed.
OCO2+OOOThermodynamic productOOOnKinetic productPPCPC PPC vs. PC1. Temperature2. Pressure of CO23. Nature of cocatalyst and loading4. Steric and electronic environment of catalystEnergy difference low for POReaction coordinateEnergy
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(1) Darensbourg, D. J. Chem. Rev. 2007, 107, 2388−2410. (2) Huang, J.; Worch, J. C.; Dove, A. P.; Coulembier, O. ChemSusChem 2020, 13, 469−487. (3) Inoue, S.; Koinuma, H.; Tsuruta, T. J. Polymer Sci. B 1969, 7, 287−292. (4) Allen, S. D.; Moore, D. R.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 14284−14285. (5) Mandal, M.; Chakraborty, D.; Ramkumar, V. RSC Adv. 2015, 5, 28536−28553. (6) Bhat, G. A.; Darensbourg, M. Y.; Darensbourg, D. J. Polym. J. 2020, 1−4.