Inverse Vulcanization of Norbornenylsilanes: Soluble Polymers with Controllable Molecular Properties via Siloxane Bonds

The inverse vulcanization produces high sulfur content polymers from alkenes and elemental sulfur. Control over properties such as the molar mass or the solubility of polymers is not well established, and existing strategies lack predictability or require large variations of the composition. Systematic design principles are sought to allow for a targeted design of materials. Herein, we report on the inverse vulcanization of norbornenylsilanes (NBS), with a different number of hydrolysable groups at the silicon atom. Inverse vulcanization of mixtures of NBS followed by polycondensation yielded soluble high sulfur content copolymers (50 wt % S) with controllable weight average molar mass (M$_{W}$), polydispersity (Đ), glass transition temperature (TG), or zero-shear viscosity (η$_{0}$). Polycondensation was conducted in the melt with HCl as a catalyst, abolishing the need for a solvent. Purification by precipitation afforded polymers with a greatly reduced amount of low molar mass species

Inherently UV Photodegradable Poly(methacrylate) Gels

Organogels (hydrophobic polymer gels) are soft materials based on polymeric networks swollen in organic solvents. They are hydrophobic and possess a high content of solvent and low surface adhesion, rendering them interesting in applications such as encapsulants, drug delivery, actuators, slippery surfaces (self-cleaning, anti-waxing, anti-bacterial), or for oil-water separation. To design functional organogels, strategies to control their shape and surface structure are required. Herein, the inherent UV photodegradability of poly(methacrylate) organogels is reported. No additional photosensitizers are required to efficiently degrade organogels (d ≈ 1 mm) on the minute scale. A low UV absorbance and a high swelling ability of the solvent infusing the organogel are found to be beneficial for fast photodegradation, which is expected to be transferrable to other gel photochemistry. Organogel arrays, films, and structured organogel surfaces are prepared, and their extraction ability and slippery properties are examined. Films of inherently photodegradable organogels on copper circuit boards serve as the first ever positive gel photoresist. Spatially photodegraded organogel films protect or reveal copper surfaces against an etchant (FeCl3 aq.)

Hydrogels with Preprogrammable Lifetime via UV-Induced Polymerization and Degradation

Hydrogels are 3D networks infused with water. When formed via radical polymerization, inherently stable hydrogels are created due to stable covalent carbon–carbon bonds. As such, they remain static soft scaffolds, unlike the dynamic tissue they are often compared to. Herein, a hydrogel capable of autonomously converting from a liquid hydrogel precursor solution into a solid hydrogel for a defined period of time, followed by a further transformation back into a liquid polymer solution, is designed. These antagonistic processes are initiated by the same UV light, which is used as stimulus for both a photopolymerization and a photodegradation simultaneously. It is demonstrated how the lifetime of the hydrogel state can be controlled and visualized on the minute scale. Both the photopolymerization and the photodegradation reactions are studied with various methods such as NMR, IR, and confocal microscopy. The different stages of the transformation, e.g., the hydrogel precursor (liquid), hydrogel (solid), and degraded hydrogel (liquid) are investigated with rheometry, viscosimetry, dynamic light scattering, and gel permeation chromatography. Small changes in the molecular composition of the precursor solution result in macroscopically measurable differences. Such time‐dependent twofold photoreactive systems can be of interest for designing dynamic materials, such as glues and photoresists or for biomedical applications

Hydrogels with Preprogrammable Lifetime via UV‐Induced Polymerization and Degradation

Hydrogels are 3D networks infused with water. When formed via radical polymerization, inherently stable hydrogels are created due to stable covalent carbon–carbon bonds. As such, they remain static soft scaffolds, unlike the dynamic tissue they are often compared to. Herein, a hydrogel capable of autonomously converting from a liquid hydrogel precursor solution into a solid hydrogel for a defined period of time, followed by a further transformation back into a liquid polymer solution, is designed. These antagonistic processes are initiated by the same UV light, which is used as stimulus for both a photopolymerization and a photodegradation simultaneously. It is demonstrated how the lifetime of the hydrogel state can be controlled and visualized on the minute scale. Both the photopolymerization and the photodegradation reactions are studied with various methods such as NMR, IR, and confocal microscopy. The different stages of the transformation, e.g., the hydrogel precursor (liquid), hydrogel (solid), and degraded hydrogel (liquid) are investigated with rheometry, viscosimetry, dynamic light scattering, and gel permeation chromatography. Small changes in the molecular composition of the precursor solution result in macroscopically measurable differences. Such time‐dependent twofold photoreactive systems can be of interest for designing dynamic materials, such as glues and photoresists or for biomedical applications