Dendrimers as Scaffolds for Reversible Addition Fragmentation Chain Transfer (RAFT) Agents: a Route to Star-Shaped Block Copolymers

Xiaojuan Hao; Eva Malmström; Thomas P. Davis; Martina H. Stenzel; Christopher Barner-Kowollik

doi:10.1071/CH05036

RESEARCH ARTICLE

Previous Next Contents Vol 58(6)

Dendrimers as Scaffolds for Reversible Addition Fragmentation Chain Transfer (RAFT) Agents: a Route to Star-Shaped Block Copolymers

Xiaojuan Hao ^A , Eva Malmström ^B , Thomas P. Davis ^A , Martina H. Stenzel ^A and Christopher Barner-Kowollik ^A ^C

+ Author Affiliations

- Author Affiliations

^A Centre for Advanced Macromolecular Design, School of Chemical Engineering and Industrial Chemistry, University of New South Wales, Sydney NSW 2052, Australia.

^B Royal Institute of Technology, Fibre and Polymer Technology, 100 44 Stockholm, Sweden.

^C Corresponding author. Email: camd@unsw.edu.au

Australian Journal of Chemistry 58(6) 483-491 https://doi.org/10.1071/CH05036
Submitted: 29 January 2005 Accepted: 1 March 2005 Published: 14 June 2005

Abstract

Star-shaped block copolymers of styrene and n-butyl acrylate having three, six, and twelve pendent arms were successfully synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Dendritic cores (based on 1,1,1-trimethylolpropane) of generation 0, 1, and 2 have been functionalized with 3-benzylsulfanylthiocarbonylsulfanylpropionic ester groups and have subsequently been employed to mediate the polymerization of styrene and n-butyl acrylate to generate macro-star-RAFT agents as starting materials for chain extension. The chain extension of the macro-star-RAFT agents with either styrene or n-butyl acrylate by bulk free radical polymerization at 60°C gives narrowly distributed polymer (final polydispersities close to 1.2) increasing linearly in molecular weight with increasing monomer-to-polymer conversion. However, with an increasing number of arms (i.e., when going from three- to twelve-armed star polymers), the chain extension becomes significantly less efficient. The molecular weight of the generated block copolymers was assessed using ¹H NMR spectroscopy as well as size exclusion chromatography calibrated with linear polystyrene standards. The hydrodynamic radius, R_h, of the star block copolymers as well as the precursor star polymers was determined in tetrahydrofuran by dynamic light scattering (90°) at 25°C. Interestingly, the observed R_h–M_n relationships indicate a stronger dependence of R_h on M_n for poly(butyl acrylate) stars than for the corresponding styrene polymers. R_h increases significantly when the macro-star-RAFT agent is chain extended with either styrene or n-butyl acrylate.

Acknowledgments

C.B.-K. and M.S. acknowledge financial support from the Australian Research Council (ARC) in the form of a Discovery grant. C.B.-K., X.H., and E.M. acknowledge additional funding from the Faculty of Engineering (University of New South Wales). Financial support from BHP Pty Ltd is also acknowledged. T.P.D. acknowledges the receipt of an Australian Professorial Fellowship (ARC). The authors thank Professor Axel Müller, Professor Walther Burchard, and Dr Wolfgang Radke for the stimulating discussions about the interpretation of the unusual R_g–M_n relationships. The authors thank Dr Leonie Barner and Istvan Jacenyik for their excellent management of CAMD.

References

Dendrimers as Scaffolds for Reversible Addition Fragmentation Chain Transfer (RAFT) Agents: a Route to Star-Shaped Block Copolymers

Abstract

Acknowledgments

Subscriber Login