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On the Limits of Benzophenone as Cross-Linker for Surface-Attached Polymer Hydrogels

Freiburg Center für Interactive Materials and Bioinspired Technologies (FIT) and Department of Microsystems Engineering (IMTEK), Albert-Ludwigs-Universität, Georges-Köhler-Allee 105, 79110 Freiburg, Germany
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Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Polymers 2017, 9(12), 686; https://doi.org/10.3390/polym9120686
Received: 17 November 2017 / Revised: 29 November 2017 / Accepted: 4 December 2017 / Published: 7 December 2017
(This article belongs to the Special Issue Microgels and Hydrogels at Interfaces)
The synthesis of different photo-reactive poly(alkenyl norbornenes) and poly(oxonorbornenes) containing benzophenone (BP) via ring-opening metatheses polymerization (ROMP) is described. These polymers are UV irradiated to form well-defined surface-attached polymer networks and hydrogels. The relative propensity of the polymers to cross-link is evaluated by studying their gel content and its dependency on BP content, irradiation wavelength (254 or 365 nm) and energy dose applied (up to 11 J·cm2). Analysis of the UV spectra of the polymer networks demonstrates that the poly(oxonorbornenes) show the expected BP-induced crosslinking behavior at 365 nm, although high irradiation energy doses and BP content are needed. However, these polymers undergo chain scission at 254 nm. The poly(alkenyl norbornenes), on the other hand, do not cross-link at 365 nm, whereas moderate to good cross-linking is observed at 254 nm. UV spectra demonstrate that the cross-linking at 254 nm is due to BP cross-linking combined with a [2 + 2] cylcoaddition of the alkenyl double bonds. This indicates limitations of benzophenone as a universally applicable cross-linking for polymer networks and hydrogels. View Full-Text
Keywords: benzophenone cross-linking; coatings; hydrogels; photo-reactive polymers; ring-opening metathesis polymerization (ROMP); surface-attached polymer networks benzophenone cross-linking; coatings; hydrogels; photo-reactive polymers; ring-opening metathesis polymerization (ROMP); surface-attached polymer networks
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MDPI and ACS Style

Riga, E.K.; Saar, J.S.; Erath, R.; Hechenbichler, M.; Lienkamp, K. On the Limits of Benzophenone as Cross-Linker for Surface-Attached Polymer Hydrogels. Polymers 2017, 9, 686.

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