Polymers with a thermally triggered phase transition are important in the design of materials for biological applications, where their behavior can be used to trigger release or (dis)assembly events. Despite their advantages, a system with tunable thermal response, end-group reactive sites, low toxicity, and controlled main-chain degradability has not been realized, yet this would be a significant advance. The versatile new poly(oligo(ethylene glycol) vinyl acetate)s are presented with excellent control over their molecular properties obtained through RAFT/MADIX polymerization. Furthermore, we demonstrate structure-controlled thermal transitions, conjugation to human lysozyme through the retained end-group, and moreover show that this class of polymers can uniquely be copolymerized with 2-methylene-1,3-dioxepane (MDO) to generate polymers in which the degradability and cloud point can be independently tuned to create materials that display the same cloud point but degrade differently.
Thiolactones
allow catalyst-free polymer synthesis and modification
under stoichiometric conditions at mild temperatures, without the
need for tedious and costly purification steps. However, there is
a need for simple and general methods for the preparation of functional
thiolactones. We have developed a modular platform for γ-thiolactone
synthesis based on free-radical xanthate addition to alkenes. Because
of the ready availability of a great variety of functional vinyl,
allyl, and maleimido derivatives, numerous substituents (exemplified
here through alkyl, perfluoroalkyl, diethyl phosphonate, and N-substituted
succinimidyl groups) could be efficiently attached to the γ-position
of the thiolactone ring. A second substituent may be added in the
α-position by proper selection of the xanthate leaving group.
In all cases the target thiolactone was obtained in good yield from
the xanthate:alkene monoadduct by consecutive Chugaev elimination
and cyclization. The potential of these new substituted thiolactone
building blocks for polymer chemistry was demonstrated via an amine–thiol–ene
conjugation strategy which resulted in successful end-functionalization
of amino-terminated polymers and a thiol–acrylate step-growth
polymerization to prepare functional poly(ester amide)s. This versatile
method for making functional thiolactones should find broad applications
as a means to prepare new materials with original properties.
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