4(%3)3 - Ecole nationale supérieure de chimie de Montpellier

A different kind of sulfur chemistry has also been investigated in the form of trithiocarbonates,which are capable to undergo reshuffling reactions when irradiated with UV light (Figure – 1.28a). Achemical simulation based proof of concept study 156 was reported on this in 2010 followed by practicalexamples in the following years 157,158 . In the most recent example based on this approach, self healingpolymer gels were prepared from reversible addition fragmentation transfer (RAFT) copolymerization ofn-butyl acrylate and a trithiocarbonate cross-linker to obtain Poly(n-butylacrylate) (PBA), a polymer witha low T g value ( 50 o C) having high chain mobility at room temperature (Figure – 1.28b).Healing was reported in terms of joining of pieces of monolithic polymer gel (in acetonitrile) whenirradiated with UV light under nitrogen atmosphere with 10 g wt pressure with time duration varyingbetween 4hrs – 12 hrs. The tensile modulus obtained for the healed monolith was 65±11 kPa while thatfor pristine monolith was 69±6 kPa indicating an almost complete recovery of mechanical strength.1.4.2.3 Miscellaneous ChemistriesIn addition to above discussed classical dynamic covalent chemistries, some novel chemistrieshave also been demonstrated of their potential for the synthesis of self-healing materials.Figure – 1.29: Mechanoresponsive chemistry based Self-healing, a) Dog bone shaped specimens of poly(methacrylate) (PMA) which changes from being colorless (spiropyran) to colored (merocyanine), b) Sample of PMAstretched until broken with corresponding change in color, the yellow colored controlled sample does not containthe mechanoresponsive moieties, c) Optical photos of PMMA beads containing mechanophore moieties undercompression, d) Threshold stress and yield stress remain coincident for PMMA beads as a function of strain rate 159 .34