¹³C NMR study of the tacticity of poly(propylene oxide)s prepared by polymerization with α,β,γ,δ‐tetraphenylporphyrin/AlEt₂Cl as initiator system: An example of first‐order markovian statistics in ring‐opening polymerization

Abstract

Abstract Racemic and enantiomerically enriched poly(propylene oxide)s were prepared using α, β, γ, δ‐tetraphenylporphyrin/AlEt 2 Cl as initiator system. Triad tacticity of the polymers was analyzed by 13 C NMR spectroscopy (62,89 MHz). A predominance of isotactic triads was observed in the case of the racemic polymer, corresponding to a non‐random distribution of configurational units in the polymer chain. A model correlating tacticity with enantiomeric excess of starting monomer in the case of a first‐order Markovian distribution was established. Good agreement between experimental results and calculated triad contents (according to the model previously described) was observed for enantiomerically enriched polymers. This indicates a steric control by the last unit of the growing chain end. The influence of the size of the substituent was examined for the case of poly(1,2‐epoxybutane). The origin of the chain‐end effect is discussed.