Poly(propylene carbonate). 1. More about Poly(propylene carbonate) Formed from the Copolymerization of Propylene Oxide and Carbon Dioxide Employing a Zinc Glutarate Catalyst

Abstract

Propylene oxide, PO, reacts when heated to 60 °C over a zinc glutarate catalyst to form poly(propylene oxide), PPO, which is regioregular, HTHTHT, and favors isotactic triads ii. Under 50 bar of CO2, poly(propylene carbonate), PPC, is formed with less than 5% polyether linkages and with an even smaller component of propylene carbonate, PC. These reactions have been studied as a function of time, and the products have been analyzed by GPC, MALDI−TOF/MS, and 13C {1H} NMR spectroscopy. Polymerization of PO yields PPO with −OH and −H end groups, and in the copolymerization of PO and CO2 the low molecular weight chains are readily identified as an alternating copolymer represented as (PO)n-alt-(CO2)m, where m = n − 1, n − 2, n − 3, n − 4, n − 5, with terminal −OH and −H groups. These results, combined with NMR data, implicate Zn−OH groups as the active initiating species, and furthermore from the molecular weight of the polymer produced at short reaction times, we can infer that some Zn−OH sites are highly active in producing long-chain polymers. The 13C {1H} NMR spectra of PPC formed from rac-PO, 50:50 S-PO + rac-PO, and S-PO reveal the preferential formation of HT junctions in the ring-opening of PO by the alkyl carbonate with a HH:HT:TT ratio of 1:3:1. Certain assignments at the diad, triad, and tetrad levels are offered.