Theoretical investigation of the chain length effects on the NMR chemical shifts of oligomers

Chain length effects on the ¹H and ¹³C NMR chemical shifts have been theoretically investigated for increasingly large oligomers of isotactic and syndiotactic polypropylene and poly(vinyl chloride). Chains ranging from the dimer to the octamer and decamer have been considered for polypropylene and poly(vinyl chloride), respectively. Helical structures displaying successive TG backbone conformations represent the isotactic chains, whereas syndiotactic chains are considered to be all-trans. The calculations are carried out by employing density functional theory (DFT) with the B3LYP exchange-correlation functional and the 6-311+G(2d,p) basis set.