Abstract

Achieving well defined control over the monomer sequence in polymers, as e.g. biopolymers do in nature, remains a long standing challenge in polymer chemistry. Sequence control by single unit monomer insertion (SUMI), ‘one at a time’, into dithiobenzoate RAFT agents has been explored. Critical factors for success are a high chain transfer constant for the RAFT agent and addition of the radical (R.) to monomer should be fast relative to further propagation. Macro-RAFT [(CH3)3C(CN)-(M)-SC(=S)-phenyl] synthesis by SUMI of styrene and N-isopropylacrylamide (NIPAm) into 2-cyano-2-propyl dithiobenzoate was successful. However, attempted SUMI of maleic anhydride (MAH) gave low yield consistent with the low reactivity of MAH towards 2-cyano-2-propyl radicals. Insertion of methyl methacrylate (MMA) provided an oligomeric insertion product due to the low transfer constant of the dithiobenzoate in MMA polymerization. Kinetic aspects for the synthesis of macro-RAFT agents by SUMI were investigated with real time 1H-NMR experiments and byproducts were identified. Next, A step towards the controlled synthesis of macro-RAFT [(CH3)3C(CN)-(M1)-(M2)-SC(=S)-phenyl] was taken. The insertion of MAH, styrene and NIPAm into the styrene SUMI product has been investigated. Insertion of MAH into the macro-RAFT was fast, however, reactions with styrene and NIPAm were slow attributed both to the low concentration of monomer used to favor SUMI and the poor leaving group ability of the propagating species compared to the 2-cyano-2-propyl radical. This study demonstrates the potential of RAFT for the synthesis of a new generation of synthetic polymers.

Highlights

  • Controlled compositions, well-defined architectures and narrow molecular weight distributions are basic requirements for functional polymers utilized in biomedical, biotechnology and nanotechnology

  • Well-defined architectures and narrow molecular weight distributions are basic requirements for functional polymers utilized in biomedical, biotechnology and nanotechnology. These requirements can be achieved by applying techniques for reversibledeactivation radical polymerization (RDRP) [1], such as reversible addition fragmentation chain transfer (RAFT) [2,3,4]

  • The initial RAFT agent utilized in the present work is 2-cyanopropan-2-yl dithiobenzoate (1), azobis(isobutyronitrile) (AIBN) was used as an initiator to ensure there would be no initiator derived insertion products

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Summary

Introduction

Well-defined architectures and narrow molecular weight distributions are basic requirements for functional polymers utilized in biomedical, biotechnology and nanotechnology. These requirements can be achieved by applying techniques for reversibledeactivation radical polymerization (RDRP) [1], such as reversible addition fragmentation chain transfer (RAFT) [2,3,4]. Shadi et al explored the scope and limitations for performing successive SUMI for styrene or NIPAm into a trithiocarbonate RAFT agent [8]. Vandenbergh and coworkers [11] synthesized sequence controlled acrylate oligomers via four consecutive RAFT single monomer additions whereby they made use of automated recycling GPC to provide purification after each SUMI step, which poses the biggest problem when several monomer units are consecutively added. Insertion of styrene NIPAm and MAH into the so-formed styrene single unit insertion product were examined

Results and Discussion
Experimental Section
Conclusions

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