Dual‐Responsive Polydimethylsiloxane Networks

Abstract

Exploiting the salient features of o‐nitrobenzyl chemistry, this work aims at the preparation of polydimethylsiloxane networks that undergo well‐defined bond cleavage in response to either UV light or different pH values as external trigger. Polydimethylsiloxane (PDMS) oligomers with terminal anhydride groups are thermally crosslinked in the presence of a bi‐functional epoxy monomer containing a photolabile o‐nitrobenzyl ester (o‐NBE) group. The susceptibility of the ester groups toward hydrolytic cleavage reactions is used for a pH‐triggered network degradation. Sol–gel analysis confirms that the degradation time can be easily controlled by the base concentration over different time scales varying between hours and weeks. Along with classical ester hydrolysis, photoinduced degradation of the elastomeric networks is carried out by photoisomerization and cleavage of the o‐NBE links upon exposure with UV light. Positive‐tone patterns with a structure size of 100 μm are obtained by photolithographic techniques confirming the spatial control of solubility properties. However, by increasing the exposure dose, recrosslinking of the networks is observed due to side reactions of the primary photocleavage products. As the reformed crosslinks are less sensitive to ester hydrolysis, the side reactions are employed to inscribe negative‐tone microstructures in the PDMS network. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2319–2329

Photopatternable Epoxy-Based Thermosets

“…This correlates well with the UV-induced changes in surface hardness and T g , which are less pronounced in flexible networks. Similar behavior was also observed in recent studies on photocleavable thiol-ene, thiol-yne, and polydimethyl siloxane networks, which have a T g below room temperature and are highly susceptible to re-crosslinking due to secondary photoreactions [36,37,38,39].…”

Stimuli-responsive thiol-epoxy networks with photo-switchable bulk and surface properties

“…In previous work, we demonstrated the fabrication of positive tone photoresists by controlled degradation of thermally and photochemically cured epoxy based networks containing o-NBE functionalities upon UV exposure. [23][24][25] In terms of the cationic ring opening, it should be noted, that epoxy monomers bearing o-NBE groups show a low reactivity and thus, an additional post-curing step at elevated temperature is required for efficient chain propagation and full conversion of the monomers. 25,26 In the current work, we extended the concept of photocleavable networks to thiol-epoxy click systems.…”

Recent Trends in Applying Ortho-Nitrobenzyl Esters for the Design of Photo-Responsive Polymer Networks

“…The first study on PDMS polymer networks with o-NBE junctions was conducted by Giebler and co-workers [134] in 2018. In this work, polydimethylsiloxane (PDMS) oligomers with terminal anhydride groups were thermally crosslinked with epoxy-NBE.…”

“…( d ) Schematic representation of the formation of a negative-tone resist. ( e and f ) Confocal micrographs of negative-tone relief structures (50 and 100 μm lines and spaces) inscribed into polymer network by photolithography after the development in 1 M aqueous NaOH (Reprinted with permission from reference [ 134 ]).…”