Regioregular and regioirregular oligoether carbonates:: A 13C{1H} NMR investigation

Oligoether carbonates R(PO)(n)OCO2(PO)(n)R, where R = Me, Et, or H, PO = propylene oxide ring-opened unit, and n = 1, 2, 3, 4, similar to10, and similar to30, have been prepared and characterized by ESI/MS or MALDI/MS and C-13{H-1} NMR spectroscopy in addition to H-1 NMR, DEPT, COSY, and HMQC. The propylene oxide (PO) units have been derived from S-PO and rac-PO. The compounds have been examined as potential models for polyether carbonate units in poly(propylene carbonate). For HH junctions, assignments of isotactic (i) and syndiotactic (s) diads and iii, iis/sii, sis, isi, ssi/iss, and sss tetrads are unequivocal. Assignments at the hexad level are limited. For higher oligoether carbonates, i.e., n similar to 10 or similar to30, only the i and s diad sensitivity is possible at 150 MHz C-13{H-1} NMR. Calculations on the compounds MeOCH2CHMeOCO2CHMeCH2OMe (RR (i) and SR (s)) and MeOCO2CH2CHMeOCO2CHMeCH2OCO2Me were carried out employing density functional theory (DFT) at the B3LYP/6-31G(d) level for geometry optimization and the B3LYP/6-311+G(2d,p) level for NMR calculations. These results are compared with the experimental work and structures of dimethyl carbonate.