Toward stable unimolecular micelles by means of “Living” free radical polymerization (LFRP) techniques

Abstract

The synthesis of linear, star-shaped and cylindrical styrene and 4-vinylpyridine (4-VP) block copolymers as stable unimolecular micelles was studied. Different initiators like 4-tert-butylphenyl(2-chloropropionate) producinglinear block copolymers, theoctafunctional initiator 5,11,17,23,29,35,41,47-octa-tert-butyl-(49–56)-octakis-(2-chloropropionyloxy)calix[8]arene 3, forming star-like polymers, as well as poly(styrene-co-4-chloromethylstyrene) 4 as initiator for a “grafting-from” polymerization yielding cylindrical structures were employed. The polymerizations of styrene initiated by these initiators were carried out in the presence of different CuCl/ligand catalyst systems and were well-controlled for all initiators studied. Furthermore, the block copolymerization of 4-VP initiated by a linear PS end-capped with chlorine was successful as indicated by the pseudo-first order kinetics. When multifunctionalmacroinitiators were used for the polymerization of 4-VP gel-formation occurs regardless to theconditions. This is most likely due to the fact that the applied ligand Me₆TREN results in a copper complex to active for the ATRP of 4-VP. On the other hand, a weaker ligand result in poor control over reaction, since only a strong ligand is capable of suppressing the complexation reaction of CuCl with 4-VP or P4VP.

Acknowledgements: Funding for this work was provided by the “Fond der Chemischen Industrie”. MCL acknowledges financial support due to a Georg-Christoph Lichtenberg grant from the Ministry of Science and Culture of Lower Saxony.