Stimuli-responsive polymers processed into microfibers bear the potential to be fabricated as systems detecting stress-induced failures. Microfiber processing of spiropyran (SP)-functionalized polymer poly­(methyl acrylate) (PMA), in pristine form and as a blend with poly­(methyl methacrylate) (PMMA), was studied. Material inhomogeneities such as bead formation and fiber–fiber fusion affected the durability of the microfibers which were aimed to be applied as self-reporting materials. The present study investigates the effect of polymer blending to improve the structural stability, i.e., the shape of the fibers compared to the nonblended PMA fibers (NBF). Blended microfibers (BF) with <4 wt % PMMA could overcome the structural malfunctions observed in NBF. Rheological analyses confirmed that there were no drastic alterations in the mechanical properties due to blending with a low amount of PMMA. We report the mechanoactivation in the structurally stable and durable BF processed via centrifugal force spinning (CFS). These fibers detected high strain deformations and retained the mechanochromic response after unloading. The color change in the BF confirms strain-induced isomerization of SP which will further assist in the visual inspection of damage before failure. The microfibers also showed reversible photochromism upon irradiation with ultraviolet (UV) light (360–370 nm) and green light (520–530 nm). The outstanding benefit of processing microfibers from polymer blends is the ease of obtaining structurally stable, self-reporting material with longer durability.

Poly(N-isopropylacrylamide) PNIPAAm hydrogels were modified with a new azobenzene-containing co-monomer. In this work, light responsiveness as an additional functionality, is conceptualized to induce two phase transitions in the same material, which can be controlled by light. For a hydrogel with merely 2.5 mol% of this co-monomer, the lower critical solution transition temperature (LCST) was lowered by 12 °C (to 20 °C) compared to PNIPAAm (LCST at 32 °C), as analyzed by differential scanning calorimetry (DSC). The untreated unimodal endotherm split into a bimodal peak upon irradiation with UV-light, giving a second onset due to the switched (Z) isomer-rich regions, LCST*H2.5%-(Z) = 26 °C. On irradiation with 450 nm, leading to the reverse (Z) to (E) isomerization, the endotherm was also reversible. Thus, a photo-switchable hydrogel whose LCST and structure are tunable with the hydrophobicity-hydrophilicity of the (E) and (Z) isomeric state of azobenzene was obtained. The influence of the increase in the mol% of azoacrylate on the LCST was evaluated via DSC, in combination with NMR studies, UV-vis spectroscopy and control experiments with linear polymers. The large light-driven modulation of the LCST adds bistability in thermoresponsive hydrogels, which may open diverse applications in the field of soft robotics actuators.

Diazocine-functionalized initiators for atom transfer radical polymerization (ATRP) were synthesized and tested for their efficiency in controlled radical polymerizations of methyl acrylate and methacrylate under reaction conditions for activators regenerated by electron transfer (ARGET). The α-bromoisobutyl condensates of anilide and benzyloxycarbonate required high amounts of reducing agents and catalysts for the initiation. On the other hand, violet light irradiation during ATRP caused severe retardation or termination during initiation of the anilide compound, in contrast to the previously reported photoinduced initiation under otherwise very similar conditions. The final linear elastomers obtained from optimized polymerization kinetics responded to light irradiation of 405 and 525 nm wavelengths by Z/E photoisomerization of diazocine in both solution and in the solid state. The E → Z thermal relaxation rate was highly influenced by electronic effects on the diazocine ring, the solvent, and the polymer matrix in the solid state. Our polymers find potential use as photonic materials in ultraviolet light sensors and optical waveguides.