Degradable Polystyrene via the Cleavable Comonomer Approach

Abstract

Polystyrene (PS) is a major commodity polymer widely used in various applications ranging from packaging to insulation thanks to its low cost, high stiffness, and transparency as well as its relatively high softening temperature. Similarly to all polymers prepared by radical polymerization, PS is constituted of a C–C backbone and thus is not degradable. To confer degradability to such materials, the copolymerization of vinyl monomers with a cyclic monomer that could undergo radical ring-opening is an efficient method to introduce purposely cleavable bonds into the polymer backbone. Dibenzo­[c,e]-oxepane-5-thione (DOT) is a cyclic thionolactone monomer known for its efficient copolymerization with acrylate derivatives but so far could not be incorporated into PS backbones. From a theoretical study combining density functional theory (DFT) and kinetic models using the PREDICI software, we showed that the modification of experimental conditions could overcome these limitations and that high molar mass degradable polystyrene (M w close to 150 000 g·mol–1) could be prepared via statistical insertion of thioester groups into the polymer backbone. This copolymerization process is compatible with conventional free radical polymerization and reversible deactivation radical polymerization (RDRP) techniques such as nitroxide mediated polymerization (NMP). Thanks to favorable reactivity ratios allowing only a few mol % of thioester units to be randomly incorporated, there was no major modification of the thermal and mechanical properties of the PS. The degradation of such PS could be performed in tetrahydrofuran (THF) at room temperature (RT) in 1 h using 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD) as a base, leading to oligomers with M n close to 2000 g·mol–1. We successfully demonstrate further applicability of these copolymerization systems for the phototriggered decomposition of PS in solution as well as the synthesis of cross-linked PS networks degradable into soluble side products.

Degradable Vinyl Copolymer Nanoparticles/Latexes by Aqueous Nitroxide-Mediated Polymerization-Induced Self-Assembly

“…While it has been shown that DOT does not easily copolymerize with S in anisole at 80 °C, ,, its free-radical aqueous emulsion copolymerization at the same temperature showed a more homogeneous distribution of DOT units in the PS backbone due to a compartmentalization effect and/or the absence of solvent . Our results also confirm the strong effect of increasing temperature, which tends to drastically promote DOT incorporation, as recently shown during its free-radical copolymerization with S in anisole at 150 °C . In addition, the expected difference in water solubility between DOT and S may also result in a higher concentration of DOT in the growing particles and, thus, a faster consumption.…”

“…Like A1 , the faster incorporation of DOT during the copolymerization led to a decrease in F DOT with S conversion from 5.3 to 1.3 mol % (Figure a). While it has been shown that DOT does not easily copolymerize with S in anisole at 80 °C, ,, its free-radical aqueous emulsion copolymerization at the same temperature showed a more homogeneous distribution of DOT units in the PS backbone due to a compartmentalization effect and/or the absence of solvent . Our results also confirm the strong effect of increasing temperature, which tends to drastically promote DOT incorporation, as recently shown during its free-radical copolymerization with S in anisole at 150 °C .…”

“…More recently, they have also been shown to degrade under physiological conditions in the presence of cysteine or glutathione at concentrations mimicking extra- and intracellular conditions, respectively. Herein, we used isopropylamine to perform aminolysis, TBD was used as a strong base …”

“…Their polymerization is based on a thiocarbonyl addition–ring-opening (TARO) mechanism, which relies on a radical addition onto the CS function followed by fragmentation via β-scission. In particular, copolymerization of dibenzo­[ c , e ]­oxepane-5-thione (DOT) with traditional vinyl monomers has recently been first reported by Roth − and Gutekunst and followed by others. − Interestingly, DOT exhibits several key benefits compared to CKAs, such as high stability in protic solvents, easy synthesis, and quantitative ring-opening during polymerization. The use of DOT also results in much higher reactivity ratios when copolymerized with acrylates.…”

Degradable Linear and Bottlebrush Thioester-Functional Copolymers through Atom-Transfer Radical Ring-Opening Copolymerization of a Thionolactone

“…Despite the ability to make degradable copolymers with narrow size distributions, the seemingly unpreventable loss of typically 50% of the DOT feed and the inability to form polymers from formulations containing more than 15 mol % of DOT meant that it was not possible to make copolymers containing more than ∼7 mol % DOT through the above methods. Although copolymers with lower DOT content have been shown to be useful (e.g.,, fully degradable networks), ,, we sought to increase the DOT content of ATRP-made copolymers. In a typical copolymerization, approximately 25 μmol of DOT were converted to lactone.…”