Combination of living anionic polymerization and ATRP via "click" chemistry as a versatile route to multiple responsive triblock terpolymers and corresponding hydrogels

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Reinicke, Stefan ; Schmalz, Holger:
Combination of living anionic polymerization and ATRP via "click" chemistry as a versatile route to multiple responsive triblock terpolymers and corresponding hydrogels.
In: Colloid and Polymer Science. Bd. 289 (2011) Heft 5-6 . - S. 497-512.
ISSN 1435-1536
DOI: https://doi.org/10.1007/s00396-010-2359-7

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Abstract

A combination of anionic polymerization, atom transfer radical polymerization (ATRP) and "click" chemistry was used to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N-3) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N-3 diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (''click'' chemistry). For the ``click'' step, P2VP-b-PEO-N-3 diblock copolymers with either an azidoacetyl or a 2-azidoisobutyryl group were tested. In the latter case, however, a side reaction involving the cleavage of the formed ``click'' product via nucleophilic substitution occurred, preventing a permanent attachment of PDMAEMA or POEGMA to the P2VP-b-PEO-N-3 diblock copolymer. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO(2)MA-co-MEO(8.5)MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. A concentrated solution of P2VP(56)-b-PEO370-b-P(MEO(2)MA)(89)-co-(MEO(8.5)MA)(7)] showed a gel-sol-gel transition at pH 7 upon temperature increase, whereas in the case of P2VP(56)-b-PEO370-b-PDMAEMA(70), a gel-sol or a weak gel-strong gel transition was observed, depending on the applied pH. Finally, the addition of trivalent hexacyanocobaltate(III) ions to the P2VP(56)-b-PEO370-b-PDMAEMA(70) solution induced an upper critical solution temperature for the PDMAEMA block, which led to gel formation. This allows for the construction of light-sensitive hydrogels, utilizing the photo-aquation of hexacyanocobaltate(III) ions.