Synthesis and characterization of hydrogenated poly(norbornene endo-dicarboximide)s prepared by ring opening metathesis polymerization

Poly(norbornene imide)s prepared by ring opening metathesis polymerization (ROMP) have been generally synthesized from 5-norbornene-exo,exo-2,3-dicarboximides (exo-NDIs), since 5-norbornene-endo,endo-2,3-dicarboximides (endo-NDIs) exhibit considerably lower reactivity toward conventional ROMP catalysts as compared with exo-NDIs. Therefore, there has been limited information on poly(endo-NDI)s, although the endo-stereoisomer monomers are the principal products in Diels–Alder reaction between cyclopentadiene and maleimides. Here we synthesized various poly(endo-NDI)s using available Grubbs catalysts, and subsequently hydrogenated their backbone double bonds to obtain high molecular weight samples with Mn > 150,000. The thermal, thermo-mechanical, mechanical, and optical properties of poly(endo-NDI)s before and after hydrogenation were then investigated, together with the structural properties by wide-angle X-ray scattering and refractive index, in comparison with those of the corresponding poly(exo-NDI)s. Surprisingly, poly(endo-NDI)s exhibit significantly higher glass transition temperatures (by ca. 34 °C) and refractive index values than the exo-counterparts, probably due to increased intermolecular packing. Other properties such as thermal stability, tensile modulus, coefficient of thermal expansion, optical transparency, water absorption, and water transmission rate are quite comparable. Overall, convenient monomer preparation coupled with attractive physical properties makes poly(endo-NDI)s very interesting for practical applications such as optical films and flexible substrates for optoelectronics.