Poly(propylene carbonate). 1. More about poly(propylene carbonate) formed from the copolymerization of propylene oxide and carbon dioxide employing a zinc glutarate catalyst

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 C-13 {H-1} 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)., 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 C-13 {H-1} 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.