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Photo-Cross-Linkable Coumarin-Based Poly(ε-caprolactone) for Light-Controlled Design and Reconfiguration of Shape-Memory Polymer Networks
journal contribution
posted on 2018-12-28, 12:19 authored by Thomas Defize, Jean-Michel Thomassin, Heidi Ottevaere, Cédric Malherbe, Gauthier Eppe, Rachid Jellali, Michaël Alexandre, Christine Jérôme, Raphaël RivaPhotochemically cross-linked shape-memory
polymer (SMP) materials have been achieved by functionalizing chain-ends
of star-shaped poly(ε-caprolactone) (PCL) with 7-hydroxypropoxy-4-methylcoumarin
followed by photodimerization of these end-groups. The kinetics of
the network formation in function of the photosensitizer concentration
has been studied by swelling experiments and rheology. Thanks to the
design of a dedicated homemade mold, highly reproducible irradiation
conditions have been achieved allowing to study the network formation
and properties, especially the shape-memory properties, in relation
to the coumarin dimerization degree as determined by Raman spectroscopy.
In optimized conditions, PCL-based SMP materials exhibiting high fixity
and recovery have been achieved in remarkably short irradiation time,
typically 5 min. In addition, the precise control of the network cross-link
density with the irradiation time, so as the high stability of the
formed networks toward temperature variations was also demonstrated
allowing the fine-tuning of the network properties by the irradiation
process. Finally, the reversible character of the coumarin dimerization
under light irradiation of appropriate wavelength has been quantified
by Raman spectroscopy. The dimer photocleavage allows the photoreconfiguration
of the networks offering the ability to modify the “permanent”
shape of the SMP material, while preserving the excellent shape-memory
properties.