Controlled/living radical polymerization of tert-butyl acrylate mediated by chiral nitroxides.: A stereochemical study

The two diastereomeric alkoxyamines of tBP-DEPN, where tBP is 1-(tert-butoxycarbonyl)ethyl and DEPN is N-(2-methylpropyl)-N-(1-diethylphosphophono-2,2-dimethylpropyl)aminoxyl, have marked differences in their thermodynamic stability (ratio of diastereomers is 5:1 at 100 degreesC in o-dichlorobenzene). They were used as initiators for the controlled/living radical polymerization of tertbutyl acrylate to test the premise that such moderators could potentially affect the tacticity of the resulting poly(tert-butyl acrylate). 2D NMR was used,to analyze the end group configuration for the samples with shorter chain lengths (DPn = 15-20). Although the diastereomeric excess in the Polymer alkoxyamine end group is even higher than for the model compound (ratio of diastereomers is 7:1), the distribution of terminal triads in poly(tert-butyl acrylate) does not differ from those in the entire chain and is identical to that of the polymers prepared by ATRP. Thus, the tacticities of the poly(tert-butyl acrylate)s prepared by DEPN-mediated polymerization, atom transfer radical polymerization (ATRP), and conventional free radical polymerization were the same.