Polymer photoenolization

Laser flash photolysis of o-tolyl vinyl ketone-methyl vinyl ketone copolymers [e,g., (17)] has produced some interesting observations. The triplet state of the aromatic carbonyl decays to give 1,4-biradicals that are capable of transferring an electron to an acceptor such as paraquat. In the absence of an acceptor the macroradicals decay to yield photoenols, which then tautomerize to regenerate the original polymer (Scheme 30). 

Spatially resolved functionalization via photoenol chemistry cannot only be applied on planar surfaces as described above, but also on cellulose and HA for the spatially controlled conjugation of S5mthetic polymers and peptides [BAL 77, DIS 09, SWA 70, TIS 13]. The general strategy is depicted in Figure 9.8. 

Figure 9.8. Modification ofhyaluronan or cellulose via photoenol chemistry. When the FMP moiety is tethered to a surface, spatially controlled surface modification can be achieved with either a peptide sequence or a polymer strand. Right ToF-SIMS images of GIGKFLHS-grafted HA with mapping of corresponding to the peptide sequence (top) and...

Poly(o-tolyl vinyl ketone) (5.20) is much more photochemically stable than poly(phenyl vinyl ketone) (5.15). The o-methylbenzoyl group stabilizes the polymer, which would otherwise undergo the Norrish Type II reaction. The effect is due to the photoenolization of this chromophore, a process which competes favourably with the photofragmentation [197, 198] ... 

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