Retrieving the starting monomer from polymers synthesized by reversible deactivation radical polymerization has recently emerged as an efficient way to increase the recyclability of such materials and potentially enable their...

The impact of conditions was investigated on a model photoinduced electron/energy transfer reversible addition−fragmentation chain transfer (PET-RAFT) polymerization. Within the cylindrical geometries studied, with relatively small changes in path length, the impact of reaction vessel dimensions and dilution was relatively small on the polymerization kinetics and control of the polymerization. This suggests that PET-RAFT can be relatively insensitive to small changes in reactor geometry and reaction volume when cylindrical systems are used. The intensity of the photoreactor was a key factor in determining reaction rate, with an approximate 1/2 order scaling of the apparent rate with intensity. Reactant concentration ratios were also important, with an approximate 1/2 order of the apparent rate with the photocatalyst loading and an approximate −1/2 order scaling apparent polymerization rate coefficient with the RAFT agent concentration. However, there is a limit to rate increases with higher Ir catalyst loadings due to the optical density.

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Surprisingly, a few seconds–minutes of compression at room temperature can increase the rate of dynamic bond exchange as measured by better self-healing, even for thermoresponsive dynamic bonds which do not exchange under ambient conditions.

Dynamic materials (DMs) or dynamers have potential applications across a broad range of material science challenges. These applications include sustainable materials as a part of the circular plastics economy, advanced materials with tailored high stress properties and biomedical agents. DMs are comprised of polymers that crosslinked through reversible covalent and noncovalent linking groups. This group provides reversible bonds, which impart properties such as (re)healing, adaptability, toughness into a material. The nature of the linker dictates the dynamer's stability and dynamic properties, although for many applications one linker alone cannot give materials with complex multiresponsive functions. The combination of multiple dynamic linkers can introduce complementary functionalities into a single material. This combination of linkers enhances the collective material properties by matching their strengths and offsetting the weaknesses, or by selecting linkers for specific functions, such as one linker for rapid exchange and the other to respond to external stimuli. This contribution highlights the possibilities and unique features of materials containing multiple dynamic linkers, reviewing both fundamental discoveries of materials possessing multiple dynamic bonds and applications facilitated by the presence of multiple linking group chemistry.

Phenyl vinyl ketone (PVK) is known for its responsiveness to light, with initiation promoted under visible light and degradation of poly­(PVK) promoted under UV radiation. Thus, expensive radical sources such as photocatalysts and initiators can be substituted by PVK to promote intrinsic photoinitiation giving well-defined polymers. Homo polymers and block copolymers are readily synthesized by reversible deactivation radical polymerization techniques; this study is the first approach of formation of block polymers through the intrinsically generated radicals of PVK monomers, where the monomer serves as both the chain forming unit and the radical source. In this work, the photoinitiation of PVK was used to generate poly­(PVK) homopolymers, which were chain extended with butyl acrylate (BA) and PVK to synthesize poly­(PVK-BA-PVK) block polymers. The structural differences of PVK and BA caused microphase separation of the block segments to form thermoplastic elastomers (TPEs) with interesting thermomechanical properties. Due to the differences in glass transition temperature, the poly­(PVK) blocks formed the hard segments of the TPE, with the poly­(BA) segments forming the soft elastic domains. The TPE materials could achieve a maximum of 1000 kPa stress and 400% strain at break. Irradiation of the TPE materials with 310 nm UV light promoted the degradation of poly­(PVK) segments, with associated changes such as a decrease in mechanical strength and elasticity. Molecular dynamics simulations confirmed the trends observed in TPE mechanical properties with the changes in the polymer composition. Further, the simulations provided atomistic insights into the underlined degradation mechanism of PVK in block polymers and its effect on TPE mechanical properties.

Reversible addition-fragmentation chain transfer (RAFT) photopolymerization of phenylvinylketone (PVK) is investigated. The polymerization is investigated both in the presence of two photocatalysts (iridium tris(phenylpyridine (Ir(ppy) 3 ) and zinc tetraphenylporphyrin (ZnTPP)). The polymerization was efficient in the absence of photocatalyst, and accelerated by Ir(ppy) 3 , whereas ZnTPP was found to lead to retardation of polymerization. In all cases, well-controlled polymers were synthesized with linear growth in M n with conversion and narrow molecular weight distributions. The observed photopolymerization kinetics were consistent with a Norrish Type 1 reaction of PVK to give two radicals. The polymerization kinetics were investigated as a function of wavelength, with the reaction rate being fastest with blue irradiation (440 nm), which is surprisingly far from the absorption maximum of PVK and Ir(ppy) 3 . Photodegradation of PVK was observed under UV irradiation, but the polymers were stable against visible light. block copolymers, [45] and PET-RAFT vinyl ketone work using Eosin Y as the photoredox catalyst. [46,47] The previous work from our group prompted further study, as only polymerization under catalyst free conditions and under two wavelengths of light were studied. As photodegradable polymers are an important class of polymers and photoRAFT methods are useful in a wide range of applications, a systematic study of photo-RAFT and PET-RAFT polymerization of PVK was undertaken. 2 3 4 5 6 7 8

Photoinduced-RAFT polymerization is a technique of increasing interest due to the combination of control over polymerization that RAFT processes afford with the mild reaction conditions and spatial and temporal control...