Photocleavable Regenerative Network Materials with Exceptional and Repeatable Viscoelastic Manipulability

Abstract

The development of solventless system for modulating properties of network materials is imperative for the next generation sustainable technology. Utilization of photostimulation is important owing to its spatial and temporal locality, yet designing photoresponsive network materials exhibiting repeatable and dramatic change in their properties remains a challenge. Here, the authors report a photocleavable regenerative network (PRN) linked with photoresponsive hexaarylbiimidazoles (HABIs) synthesized from narrow dispersity star-shaped poly(dimethylsiloxane)s (PDMSs) having 2,4,5-triphenylimidazole end groups. The use of urea anion as a catalyst for ring opening polymerization (ROP) of cyclic siloxane initiated from silanols enables control of molecular weight and dispersity. The rheological measurements for the synthesized PRNs exhibit drastic changes in storage and loss moduli (G′ and G″) upon photoirradiation in the solid state (G′ > G″). This photocontrolled change in viscoelasticity with retaining solidity enables application of PRNs as a remotely-controlled photo-melt adhesive and photo-scissible string. The developed PRNs will enable a wide variety of applications such as industrially important next-generation sustainable adhesive, sealant, and reversibly-deformable 3D printing materials with their spatially and temporally local manipulability, solventless handleability, and excellent reversibility.

Ring-Opening Polymerization (ROP) and Catalytic Rearrangement as a Way to Obtain Siloxane Mono- and Telechelics, as Well as Well-Organized Branching Centers: History and Prospects

“…Urea anion catalysts are particularly useful for producing lower molecular weight polysiloxane stars. Moreover, the combination of silanols and urea anion catalysts overcomes the solubility problem arising from the polarity mismatch between the initiators, D3 and PDMS [67]. However, this process remains rather complicated.…”

Star polymer networks: a toolbox for cross-linked polymers with controlled structure

“…There are several more reversible end-linking methods that are less popular but of great interest (Fig. 16): [2 + 2] or [4 + 4] cycloaddition, 6,[253][254][255][256][257][258][259] hydrogen bonding, 260 reverisble Alderene reaction, 261 reversible radical coupling, [262][263][264] peptide coiled coil formation, 265 and DNA hybridization. 266,267 Some π-electron systems undergo cycloaddition (Fig.…”

“…Despite its popularity in chemistry, the use of hydrogen bonds for SPN end-linking is somewhat rare. Tan and coworkers adopted a Watson-Crick base pair, adenine and thymine, as a reversible linkage between star polymers 260 260 (c) reversible Alder-ene reaction, 261 (d) reversible radical coupling, [262][263][264] (e) peptide coiled coil formation, 265 and (f ) DNA hybridization. 266,267…”

“…This type of reversible chemistry is often termed the dynamic covalent chemistry. Honda and coworkers used hexaarylbiimidazole (HABI), which was formed by homocoupling of 2,4,5-triphenylimidazolyl radicals (TPIR), as a reversible end-link to create SPNs whose flowability could be reversibly controlled by UV irradiation 262,263 (Fig. 16d, upper).…”

“…For example, ring-opening polymerization of hexamethylcyclotrisiloxane (D 3 ) initiates from water or alcohol in the presence of a suitable catalyst. 263,286,287 Various end groups can be introduced by capping the silanol end group with chlorosilane derivatives. Despite the practical importance, the use of polysiloxanes as the SPN component is extremely rare.…”