The photodecomposition of the Ar‐laser sensitive photo‐initiator bis(pentafluorophenyl)titanocene 1 was investigated. Two intermediate species were postulated: a pentafluorophenylcyclopentenyl radical 16 which acts as quencher and a ketene acetal radical of the structure CH2‐CH=C(OCH3)OTiRx 17 which could initiate the polymerization.

An overview is given on auto‐photosensitive polyimides as introduced for the first time in 1985. It is shown how development proceeded and how the chemical basis of auto‐photosensitive polyimides was extended beyond BTDA. Novel “photosensitizer tetracarboxylic dianhydrides” like 2,3,6,7‐thioxanthonetetracarboxylic dianhydride (TXDA) were synthesized and copolymerized into preimidized nonphotoactive polyimides containing tetracarboxylic acids like 6FDA or ODPA. Novel photosensitive polyimides were obtained that carry all essential features of BTDA based systems plus higher photospeed. They provide the ability to better tailor material properties to specific applications.

Crystalline 1,4-diethynylnaphthalene (1) is photochemically polymerized in the solid state by a radical mechanism. Only the chain initiation step is induced by light, whereas chain propagation also occurs in the dark. The polymerization is controlled by diffusion processes within partially melted domains of the crystal, ultimately leading to a completely disordered system. The reaction rate, however, also depends on the packing of the monomer in the crystal lattice and-in the beginning of the reaction-the polymer chains have a preferential orientation with regard to the crystal axes of the monomer. Radical polymerization in solution indicates that -due to the lack of effective chain termination steps-1 can be polymerized rather effectively as compared to other acetylenes. The photochemically induced polymerization is approximately of second order with regard to monomer concentration.

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