Disassembly of Elastomers: Poly(olefin sulfone)−Silicones with Switchable Mechanical Properties

Synthesis and characterization of novel poly(sulfone siloxane)s with good solubility and recyclability based on siloxane units

A controllable circulation between poly(sulfone siloxane)s (PSS) and sulfone-containing cyclosiloxane monomers (SCS) was acheived in the presence of KHSO4.

Stimuli-responsive temporary adhesives: enabling debonding on demand through strategic molecular design

Stimuli-responsive temporary adhesives constitute a rapidly developing class of materials defined by the modulation of adhesion upon exposure to an external stimulus or stimuli. Engineering these materials to shift between two characteristic properties, strong adhesion and facile debonding, can be achieved through design strategies that target molecular functionalities. This perspective reviews the recent design and development of these materials, with a focus on the different stimuli that may initiate debonding. These stimuli include UV light, thermal energy, chemical triggers, and other potential triggers, such as mechanical force, sublimation, electromagnetism. The conclusion discusses the fundamental value of systematic investigations of the structure-property relationships within these materials and opportunities for unlocking novel functionalities in future versions of adhesives.

Poly(carboxypyrrole)s That Depolymerize from Head to Tail in the Solid State in Response to Specific Applied Signals

This Article describes the design, synthesis, and analysis of a new class of polymer that is capable of depolymerizing continuously, completely, and cleanly from head to tail when a detection unit on the head of the polymer is exposed to a specific applied signal. The backbone of this polymer consists of 1,3-disubstituted pyrroles and carboxy linkages similar to polyurethanes. Diverse side chains or reactive end-groups can be introduced readily, which provides modular design of polymer structure. The designed depolymerization mechanism proceeds through spontaneous release of carbon dioxide and azafulvene in response to a single triggering reaction with the detection unit. These poly(carboxypyrrole)s depolymerize readily in nonpolar environments, and even in the bulk as solid-state plastics.

Recyclable sulfone-containing polymersviaring-opening polymerization of macroheterocyclic siloxane monomers: synthesis, properties and recyclability

The first recyclable sulfone-containing polysiloxanes were synthesizedviaan anionic ring-opening polymerization of macroheterocyclic siloxane monomers.

Low-Ceiling-Temperature Polymer Microcapsules with Hydrophobic Payloads via Rapid Emulsion-Solvent Evaporation

We report a microencapsulation procedure based on rapid solvent evaporation to prepare microcapsules with hydrophobic core materials and low-ceiling-temperature polymer shell wall of cyclic poly(phthalaldehyde) (cPPA). We use and compare microfluidic and bulk emulsions. In both methods, rapid solvent evaporation following emulsification resulted in kinetically trapped core-shell microcapsules, whereas slow evaporation resulted in acorn morphology. Through the systematic variation of encapsulation parameters, we found that polymer-to-core weight ratios higher than 1 and polymer concentrations higher than 4.5 wt % in the oil phase were required to obtain a core-shell structure. This microencapsulation procedure enabled the fabrication of microcapsules with high core loading, controlled size, morphology, and stability. This procedure is versatile, allowing for the encapsulation of other hydrophobic core materials, i.e., mineral oil and organotin catalyst, or using an alternative low-ceiling-temperature polymer shell wall, poly(vinyl tert-butyl carbonate sulfone).

Base-Triggered Degradation of Poly(vinyl ester sulfone)s with Tunable Sensitivity

A series of poly(vinyl ester sulfone)s are synthesized and are found to rapidly degrade in the presence of base. Solution phase NMR indicates that the sensitivity of these polymers to base depends on the identity of the ester functional group of the polymers. From most to least sensitive these are poly(vinyl chloroacetate sulfone) > poly(vinyl acetate sulfone) > poly(vinyl benzoate sulfone) > poly(vinyl pivalate sulfone). Significantly, these polymers were more reactive to base than the aliphatic poly(1-hexene sulfone). Additionally, degradation of these polymers in bulk occurs rapidly with exposure to aqueous solutions of base. The polymers are stable in water and possess good barrier properties; films of 30 μm thickness allow on average <1% crossover of dye over 7 days. Based on the data collected, poly(vinyl ester sulfone) polymers are promising for use in microcapsules, in particular, for applications where sustained or staged release would benefit from a series of different microcapsule compositions.

Depolymerizable Poly(O-vinyl carbamate-alt-sulfones) as Customizable Macromolecular Scaffolds for Mucosal Drug Delivery

Interest in stimulus responsive materials and polymers has grown over the years, having shown great promise in a diverse set of applications. For drug delivery, stimulus-responsive polymers have been shown to encapsulate therapeutic cargo such as small molecule drugs or proteins, deliver them to specific locations in the body, and release them so that they can induce a therapeutic effect in the patient. Most hydrolytically degradable polymers are synthesized via nucleophilic, anionic, or cationic polymerization, which generally requires protection of nucleophilic or protic side chains prior to polymerization. Here, we report the synthesis of novel, alternating copolymers of sulfur dioxide and O-vinyl carbamate monomers that boast excellent functional group tolerance and pH-dependent instability. Alternating copolymers were synthesized containing pendant functionalities such as alcohol, carboxylic acid, ester, and azide without deprotection or post-polymerization modification. The copolymers were then formulated via nanoprecipitation into polymer nanoparticles capable of encapsulating small molecule dyes. The polymer nanoparticles were found to degrade rapidly at pH > 6 and were stable even in highly acidic conditions. Based on this observation, a proof-of-concept study for mucosal delivery was performed in polymer nanoparticles entrapped in a mucus model. At pH 8 the diffusion of encapsulated dye was found to be similar to free dye, while at pH 5 the diffusion coefficient was an order of magnitude lower. Cell viability was retained at 200 µg/mL particles after 24 h incubation. These polymers thus show promise as highly customizable scaffolds for mucosal drug delivery.

Heat and solvent responsive polytriazole: shape recovery properties in different solvents

Shape memory polytriazole actuatable by both heat and solvents is presented. Hydrogen bonding solvents exhibit strong influence on shape recovery.

Alternating Sulfone Copolymers Depolymerize in Response to Both Chemical and Mechanical Stimuli

This work describes the depolymerization of poly(vinyl acetate-alt-sulfur dioxide) (PVAS) as initiated by chemical and mechanical stimuli. In recent years, macromolecules that are able to depolymerize in response to specific stimuli have been highly sought because of their ability to amplify signal for sensing and drug delivery. Examples include self-immolative polymers from alkoxyphenol derivatives and polyaldehydes. We show here that alternating copolymers of sulfur dioxide and vinyl acetate are able to undergo similar depolymerization into their monomer components in response to various chemical and mechanical stimuli. Certain vinyl monomers such as vinyl acetate are able to polymerize with sulfur dioxide in a perfectly alternating manner, and the resulting copolymer possesses a low ceiling temperature. We show that this polymer is able to break down into its monomer components when subjected to UV/acetone, various Reactive Oxygen Species (ROS), and ultrasonication. In the case of UV, the acetone reacted via a Norrish reaction to produce free radicals that caused clean monomer production. For ROS, the polymer showed reactivity to both oxidizing and radical-containing ROS. Through kinetic studies, these polymers were shown to proceed via a two-part, first-order kinetic model with a fast initiation phase and a slow depolymerization phase. Finally, the polymers were subjected to probe ultrasonication, and depolymerization occurred as well. Most tellingly, the polymer again showed a fast initiation step and continued to depolymerize even after ultrasonication stopped. This class of polymers shows potential for drug delivery in response to both endogenous chemical and externally-applied mechanical cues.

Tunable Thermal Degradation of Poly(vinyl butyl carbonate sulfone)s via Side-Chain Branching

Polymeric materials that depolymerize into volatiles on command may function as vanishing substrates or packaging for transient electronics. Poly(vinyl tert-butyl carbonate sulfone) is known to afford low-boiling byproducts upon heat-activated degradation; however, the polymer is rather unstable, even to the degree of being difficult to process and handle. Understanding the origin of this instability is important for the development of robust materials capable of programmed self-destruction. In this work, we show that poly(vinyl tert-butyl carbonate sulfone)s thermally decompose via carbonate elimination as the rate-determining step, indicating that its thermal instability stems from the lability of the tert-butyl carbonate group. We further examined the effect of isomeric butyl carbonate side chains on the thermal degradation of poly(vinyl butyl carbonate sulfone)s and found that the degradation onsets range from 91 to 213 °C, yielding as little as 2.77 ± 0.53 wt % residue. Results from our findings will aid in the development of vanishing polymers with tunable thermal degradation.