ABSTRACT:Multifunctional crosslinkers having two, three, four and six functionalities were synthesized using a convergent method and were applied to a photocrosslinking system having thermally degradable properties. The multifunctional crosslinkers contained epoxy units and tertiary ester linkages. When the blended films of epoxides/poly-(p-vinylphenol) with a photoacid generator were irradiated and followed by baking at relatively lower temperatures (<100 C), the films became insoluble in solvents. Heating conditions strongly affected the insoluble fraction of the blends. Insoluble fraction of the blended films increased with the number of the epoxy unit of a molecule. The crosslinked films became soluble after prolonged bake at relatively higher treatments (>120 C). The reaction pathway of the blended system was studied by in situ FT-IR measurements. [doi:10.1295/polymj.PJ2006007] KEY WORDS Photocrosslinking / Decrosslinking / Thermal Degradation / Multifunctional / Epoxide / Photoacid Generator / Reworkable resins which are easily removable after use are getting more important in terms of environmental aspects. In this point of view, some thermosets which are thermally or chemically degradable under a given condition have been extensively studied. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] We have previously reported the photocurable epoxy resins which can be re-dissolved in solvents by thermal treatments.12-18 The resins consist of epoxy moieties and tertiary ester linkages. Epoxy moieties acted as photocrosslinkable units by photo-induced acid catalyzed polymerization. Tertiary ester linkages were thermally cleavable units by heating to produce carboxylic acids and alkenes. The network was destroyed by the scission of tertiary ester linkages. In practical point of view, reactivity, sensitivity, thermal or chemical stability, and re-dissolution property of the polymers must be improved. Multifunctional epoxides are expected to show higher reactivity and sensitivity compared to mono-and difunctional epoxides. We have reported that trifunctional epoxide/poly(p-vinylphenol) (PVP) blended system works as a reworkable resin and the sensitivity of the system is higher than the difunctional epoxide/PVP blended system. 18In this paper, we report the synthesis of novel multifunctional epoxides having tertiary ester linkages. The multifunctional epoxides were synthesized by a convergent technique, where two or three molecules having both epoxy unit and tertiary ester unit in a molecule were linked together via another molecule. The multifunctional epoxides were used as crosslinkers of the system that has photocrosslinking and de-crosslinking properties. The system is a blend of PVP, the crosslinker, and a photoacid generator. The concept of the present system is shown in Figure 1. On irradiation, network formation occurs by the photoinducedacid catalyzed reaction of the epoxy moieties of the crosslinker and PVP. Thermal treatment of the crosslinked polymers induces the cleavage of the tertiary est...

A novel thermally degradable photocrosslinking system was investigated. Difunctional and trifunctional epoxides with tertiary ester linkages were synthesized. When blended films of epoxides and poly(vinyl phenol) or epoxides and poly(methacrylic acid‐co‐ethyl methacrylate) with a photoacid generator were irradiated and then baked at relatively low temperatures (<100 °C), the films became insoluble in solvents. The heating conditions strongly affected the insoluble fractions of the blends. The insoluble fractions of the blended films containing the trifunctional epoxide were higher than the fractions of the films containing the difunctional epoxide. The crosslinked films became soluble after baking at relatively high temperatures (>120 °C). The reaction pathway of the blended system was studied with in situ Fourier transform infrared measurements. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3685–3696, 2004

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