Molecular design of polymer coatings capable of photo‐triggered stress relaxation via dynamic covalent bond exchange

Abstract

Polymer coatings are frequently used to modify surface properties of inorganic substrates. However, the disparity in physical properties between polymer film and substrate often leads to residual stress development, which can be deleterious to the overall performance of coated materials. This work reports the molecular design of polymer films that dissipate stress upon irradiation with ultraviolet (UV) light. These polymers are synthesized by post-polymerization modification of the reactive polymer, poly(2-vinyl-4,4-dimethyl azlactone), to introduce dynamic crosslinks capable of light-initiated addition transfer fragmentation chemistry. Using a custom-built optical cantilever, contrasting film stress responses are observed between films containing dynamic bonds and analogous control films after UV light irradiation, which indicate successful stress relaxation. Further experiments demonstrate the complete relaxation of residual stress in dynamic films after an extended exposure, thereby generating a "stress-free" film. Films fabricated using this approach can be easily tailored to incorporate additional moieties to introduce desired surface properties for future application in a wide array of coatings.

Fully Recyclable Covalent Adaptable Network Composite with Segregated Hexagonal Boron Nitride Structure for Efficient Heat Dissipation

“…19−21 This could be achieved by replacing permanent covalent networks of thermosets with dynamic exchangeable networks. CAN with an exchangeable network can rearrange its topology via either photochemically 22 or thermally activated bond exchange reactions (or BERs) above its topology freezing transition temperature (T v ). 23,24 Above the T v , CANs become malleable and heatprocessable.…”

“…Recently, a new class of polymers called covalent adaptable networks or CANs have attracted much attention as melt-processable analogs of thermosets. − This could be achieved by replacing permanent covalent networks of thermosets with dynamic exchangeable networks. CAN with an exchangeable network can rearrange its topology via either photochemically or thermally activated bond exchange reactions (or BERs) above its topology freezing transition temperature ( T v ). , Above the T v , CANs become malleable and heat-processable. Their rheological properties, including viscosity and relaxation time as a function of temperature, follow the Arrhenius law, as they are kinetically governed by the BER. − Below the T v , CANs with an extremely slow or even dormant BER behave as typical thermosetting polymers.…”

A Versatile Comonomer Additive for Radically Recyclable Vinyl‐derived Polymers

“…Our strategy employs radical ring-opening polymerization (RROP) of CAS monomers to form main chain allyl sulfides (Scheme 2a), [32][33][34][35] and leverages subsequent AFT reactivity of these dynamic motifs to undergo scission and extension (Scheme 2b). [36][37][38][39][40][41] As a difunctional 8-membered CAS, 3,7-bis(methylene)-1,5dithiacyclooctane (BMDTO) was targeted as an ideal comonomer additive because one BMDTO repeat unit generates two main chain allyl sulfide moieties, and 8membered CASs have demonstrated higher RROP reactivity over analogous 7-membered monomers. [42] Prepared by a new cyclization method with improved yield and fewer safety risks than previously reported techniques, [43] BMDTO was copolymerized with S, methyl methacrylate (MMA), butyl methacrylate (BMA), methyl acrylate (MA), 2-vinyl pyridine (2VP), and 2-vinyl-4,4-dimethyl azlactone (VDMA) under free radical conditions.…”

“…In contrast to the comonomer additives previously discussed, our CAS additive achieves radical closed‐loop cyclability via allyl sulfide addition‐fragmentation‐transfer (AFT) (Scheme 1b). Our strategy employs radical ring‐opening polymerization (RROP) of CAS monomers to form main chain allyl sulfides (Scheme 2a), [32–35] and leverages subsequent AFT reactivity of these dynamic motifs to undergo scission and extension (Scheme 2b) [36–41] . As a difunctional 8‐membered CAS, 3,7‐bis(methylene)‐1,5‐dithiacyclooctane (BMDTO) was targeted as an ideal comonomer additive because one BMDTO repeat unit generates two main chain allyl sulfide moieties, and 8‐membered CASs have demonstrated higher RROP reactivity over analogous 7‐membered monomers [42] .…”

Spatiotemporal vitrimerization of a thermosetting polymer using a photo-latent catalyst for transesterification

“…From a practical perspective, on-demand manipulation of bond exchange kinetics and the location of T v of a single vitrimer is highly desirable to meet a wider range of working and processing conditions. In some studies, the photothermal effect of nanosized llers, 19 near-IR light-induced local heating, 20,21 and light-activated bond exchange chemistries [22][23][24] were explored to spatially adjust the network exchange kinetics in vitrimers. However, the bond exchange chemistries in the aforementioned studies could also be thermally activated, implying that a limited temperature range exists for vitrimers to behave as thermosets.…”