Research groups
  • Controlled Radical Polymerisation

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Controlled Radical Polymerisation

The synthesis of materials with controlled compositions, architectures and functionalities has been of great scientific interest in recent years, owing to the development of controlled radical polymerization methods. These methods allow the syntheses of tailored polymers and molecular composites with well-defined structures and functionalities, giving control over the macroscopic properties. The aim of controlled radical polymerization, CRP, is to synthesize polymers with predetermined molar masses and narrow molar mass distributions. The polymers also show a living character - that is, they carry reactive end groups that can continue the polymerisation after a new addition of monomer. The end groups can be further functionalised.1 These features along with the modification of the polymer chain provide for the synthesis of more or less complex polymer architectures.

The CRP methods used in the Laboratory of Polymer Chemistry are RAFT, reversible addition-fragmentation chain transfer and ATRP, atom transfer radical polymerisation. RAFT utilises compounds such as dithioesters as transfer agents for radicals generated initially by decomposition of an initiator2, whereas ATRP is based on a reversible redox process catalysed by a transition metal complex, involving a transfer of a halogen atom.1 The polymerisation methods are based on a dynamic equilibrium between the growing radicals and the dormant species, which keeps the number of free radicals small and thus the amount of growing chains constant. The molar mass should be linearly dependent on the conversion and can be controlled by the reaction stoichiometry.2

In the Laboratory of Polymer Chemistry, CRP methods are used in the synthesis of polymer-grafted particles and gold nanoparticles, various amphiphilic block copolymers that can also have controlled tacticity, fluorinated polymeric surfactants, thermosensitive fibres and fabrics and new cellulose derivatives. An example of the complex polymer architectures is amphiphilic star block copolymers that have been synthesised using multifunctional ATRP initiators based on a macrocyclic compound, resorcinarene (Figure 1).3,4 The synthesis of the amphiphilic stars involves the block copolymerisation of tert-butyl acrylate and methyl methacrylate, or vice versa, followed by the hydrolysis of tert-butyl ester groups to acrylic acid. The resulting amphiphiles exhibit interesting self-assemblies in aqueous solutions.5

figureATRP

Figure 1. Resorcinarene-based ATRP initiators 1 and 2: side (left) and top (right) views of the space-filling models in a boat conformation. Conformations correspond to one of the local minimum energy conformations.3

References

1. Matyjaszewski, K. and Xia, Jianhui Chem. Rev. 2001, 101, 2921-2990

2. a) Moad, G. et al. Polym. Int. 2000, 49, 993-1001
b) Moad, G. et al. Aust. J. Chem. 2005, 58, 379-410

3. Strandman, S., Luostarinen, M.; Niemelä, S.; Rissanen, K.; Tenhu, H. Journal of Polymer Science, Part A: Polym. Chem. 42 (2004) 4189-4201

4. Strandman, S.; Pulkkinen, P.; Tenhu, H. Journal of Polymer Science, Part A: Polym. Chem. 2005, 43, 3349-3358.

5. Strandman, S.; Hietala, S.; Tenhu, H.: Starlike Amphiphilic Block Copolymers. Proceedings of Polymers for Advanced Technologies International Symposium, Budapest, Hungary, 13.-16.9.2005.