In Situ Photocrosslinking of Cinnamate Functionalized Poly(methyl Methacrylate-co-2-hydroxy Ethyl Acrylate) Fibers during Electrospinning

3.1 Chapter Summary A novel methodology for in situ crosslinking of polymeric fibers during electrospinning is described. The electrospinning apparatus was modified to facilitate UV irradiation of the electrospun fibers while in flight to the collector target. Three copolymers with different mol% of the photoreactive cinnamate functional group (4, 9 and 13 mol% respectively) were synthesized and utilized for this study. Fibers of cinnamate functionalized poly(methyl methacrylate-co-2-hydroxy ethyl acrylate) were crosslinked in situ by UV irradiation during electrospinning. Subsequent FTIR measurements on irradiated and non-irradiated electrospun fibers indicated both [2π+2π] cycloaddition of the vinylene C=C and trans-cis photoisomerization of the cinnamate group. Furthermore, the irradiated copolymers were observed to form insoluble gels which indicated that the photodimerization was the primary photoprocess during UV irradiation leading to the formation of a crosslinked network. As expected, it was found that the gel fraction increased with increasing mol% of the cinnamate species. 3.2 Introduction Polymers that are sensitive to ultraviolet (UV) irradiation have been widely utilized as photoresists. For instance, in the manufacture of printed circuit boards, negative photoresists are coated on a conducting substrate. A patterned mask placed over the coated substrate then imprints a conducting circuit when the substrate is washed with a solvent to remove the non-irradiated photoresist. Conventional negative-working photoresists based on poly(vinyl cinnamate) (PVCi) and its derivatives have played a leading role in the scientific development of photopolymers since their invention more than four decades ago. The photofunctionality of PVCi arises from photodimerization that leads to insolubilization due to the formation of crosslinks. In the late 1970s, it was reported that the photoinduced chemical transformation of PVCi and its derivatives