Influence of para-substitution on the polymerisation kinetics of 2-phenyl-2-oxazolines†

A series of cationic ring opening polymerisations (CROP) were conducted on a library of electronically diverse para-substituted 2-phenyl-2-oxazolines. Polymerisations were conducted under microwave irradiation and monitored by ¹H NMR spectroscopy to elucidate kinetic parameters for both homo- and co-polymerisations. The inclusion of electron donating substituents in the para-position led to decreases in the rates of homopolymerisation compared to an unsubstituted 2-phenyl-2-oxazoline. Conversely, in copolymerisations, monomers containing electron donating substituents were incorporated at a higher rate than 2-phenyl-2-oxazoline, with the inverse effect observed with monomers displaying electron withdrawing substituents. The reactivity ratios of four representative monomer combinations were then determined using ¹H NMR spectroscopy and are consistent with a proposed model where copolymerisation kinetics are dictated largely by the relative nucleophilicity of the monomer.