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The versatile nature of photo-induced thiol-ene chemistry has made it one of the most popular reactions in the design of polymer networks. In the present work, the structure of uniform thiol-ene and complex binary thiol-acrylate networks are studied in detail by photopolymerizing cycloaliphatic and linear alkyl thiols with an allyl monomer and its acrylic counterpart. Along with the crosslink kinetics, the balance between step growth and chain growth mechanism of the two different systems is investigated by FT-IR spectroscopy. Low field NMR experiments are carried out to obtain an insight into the chain dynamics and structure of the photopolymer networks. In addition, tensile properties and glass transition temperature are determined to correlate network properties with mechanical performance.

The present work aims at the preparation of dry adhesives with switchable bonding properties by using the reversible nature of the [4πs+4πs] cycloaddition of anthracenes. Photo-responsive hydrogenated carboxylated nitrile butadiene rubber with photo-responsive pendant anthracene groups is prepared by one-pot synthesis. The formation of 3D networks relies on the photodimerization of the anthracene moieties upon UV exposure (λ > 300 nm). Controlled cleavage of the crosslink sites is achieved by either deep UV exposure (λ = 254 nm) or thermal dissociation at 70 °C. The kinetics of the optical and thermal cleavage routes are compared in thin films using UV-vis spectroscopy and their influence on the reversibility of the network is detailed. Going from thin films to free standing samples the modulation of the network structure and thermo-mechanical properties over repeated crosslinking and cleavage cycles are characterized by low-field NMR spectroscopy and dynamic mechanical analysis. The applicability of the stimuli-responsive networks as adhesives with reversible bonding properties is demonstrated. The results evidence that the reversibility of the crosslinking reaction enables a controlled switching "on" and "off" of adhesion properties. The recovery of the adhesion force amounts to 75 and 80% for photo- and thermal dissociation, respectively. Spatial control of adhesion properties is evidenced by adhesion force mapping experiments of photo-patterned films.

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