Aqueous emulsion copolymerizations of dibenzo[c,e]oxepane‐5‐thione (DOT) were performed with n‐butyl acrylate (BA), styrene (S) and a combination of both. In all cases, stable latexes were obtained in less than two hours under conventional conditions; that is in the presence of sodium dodecyl sulfate (SDS) used as surfactant and potassium persulfate (KPS) as initiator. A limited solubility of DOT in BA was observed compared to S, yielding to a more homogeneous integration of DOT units in the PS latex. In both cases, the copolymer could be easily degraded under basic conditions. Emulsion terpolymerization between DOT, BA and S allowed us to produce stable latexes not only composed of degradable chains but also featuring a broad range of glass transition temperatures.
The synthesis of degradable vinyl polymer nanoparticles/latexes
in aqueous dispersed media is receiving much attention, particularly
for biomedical applications and plastic pollution control, as it can
circumvent the severe limitations associated with the emulsification
of preformed degradable polymers. Polymerization-induced self-assembly
(PISA), which enables the in situ formation of aqueous suspensions
of diblock copolymer nano-objects of high solids content, has become
a very popular polymerization process due to its many advantages in
terms of simplicity, robustness, scalability, and versatility. However,
the preparation of degradable vinyl polymer nanoparticles by direct
aqueous PISA has never been reported. This severely limits the use
of PISA in biomedical and environmental applications. Herein, we report
the first aqueous emulsion PISA able to generate degradable vinyl
polymer nanoparticles. It relies on radical ring-opening polymerization-induced
self-assembly (rROPISA) of traditional vinyl monomers (n-butyl acrylate or styrene) with dibenzo[c,e]oxepane-5-thione (DOT), a thionolactone that features
high stability in protic solvents and favorable reactivity with many
vinyl monomers and is a precursor of labile thioester groups in the
main chain. Stable aqueous suspensions of thioester-containing diblock
copolymer nanoparticles were obtained with both vinyl monomers. Extensive
degradation of the copolymers and the nanoparticles was successfully
demonstrated under aminolytic or basic conditions. Given the success
of the PISA process within the polymer community, this work has the
potential to greatly expand its use in many areas, from nanomedicine
(providing applicability to biocompatible vinyl polymers) to degradable
coatings and sustained materials.
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