Synthesis and optical properties of thermally and photochemically cross-linkable diacetylene-containing polymers

A series of diacetylene-containing polymers were prepared by oxidative coupling polymerization of 9,9-bis(4-propargyloxyphenyl)fluorene and dipropargyl 4,4'-(hexafluoroisopropylidene)diphthal-imide. The polymers had molecular weights of 42 000-235 300 and polydispersity indices of 1.1-1.8 as determined by gel permeation chromatography using polystyrene standards. All the polymers showed typically amorphous diffraction patterns, good solubility in organic solvents, and good film-forming capability. The polymers were readily cross-linkable upon exposure to UV light at ambient temperature and could also be thermally cured. The diacetylene groups were involved in both thermal and photocuring processes, as determined by C-13 CP/MAS NMR and FTIR means. The in-plane and out-of-plane refractive indices of these polymers varied from 1.5454 to 1.6313 and from 1.5329 to 1.6283 at 1550 nm, respectively, according to the monomer ratios in the feed. The birefringence at 1550 mn was significantly reduced from 1.25% for polymer 3e to 0.3% for polymer 3a by incorporating the fluorenyl and ether linkages into the polymer backbone. All the polymer thin films on substrates could be directly photopatterned by irradiation at 250-450 nm through a photomask.