Synthesis and characterization of new diblock copolymers of 5-(N-carbazolyl methyl)bicyclo[2.2.1]hept-2-ene and 1,5-cyclooctadiene using ring openingmetathesis polymerization (ROMP)

The novel diblock copolymer of 5-(N-carbazolyl methyl)bicyclo[2.2.1]hept-2- ene (CbzNB) with 1,5-cyclooctadiene (COD) has been synthesized by ring open ing metathesis polymerization (ROMP) using a well-defined catalyst, {Cl2Ru( CHPh)[P(C6H11)(3)](2)}. The diblock copolymers were characterized by means of gel permeation chromatography (GPC),H-1 nuclear magnetic resonance (NMR) , UV-visible, fluorescence, dynamic light scattering (DLS), differential sc anning calorimeter (DSC) and thermogravimetric analysis (TGA). The molecula r weight distributions of the diblock copolymers are narrow (<(Mw)over bar> /<(Mn)over bar> = 1.10-1.47). Diblock copolymers showed four distinct UV ab sorptions characteristic of the carbazole group at 255, 295, 319 and 332 nm . Diblock copolymers exhibited a strong carbazole fluorescence, with monome r emission occurring in the near-UV at approximately 377 nm and extending i nto the blue-violet region (470 nn). In tetrahydrofuran and methylene chlor ide solution, the emission around 470 nm was not observed. Diblock copolyme rs showed two T-g values owing to poly(CbzNB) and polybutadiene segments. H owever, after hydrogenation, they showed only one T-g for poly(CbzNB) segme nt and one T-m for polyethylene segment. The diblock copolymer [poly(CbzNB- b-PB)-1] with longer CbzNB chain exhibited better thermal stability than co polymer with shorter CbzNB chain [poly(CbzNB-b-PB)-2]. Two kinds of hydroge nated diblock copolymers, hydrogenated poly(CbzNB-b-PB)-1 and hydrogenated poly(CbzNB-b-PB)-2, have poorer solubility, but better thermal stability th an unhydrogenated diblock copolymers, owing to the polyethylene segments. F urthermore, the larger hydrodynamic diameter of 324.2 nm was obtained after hydrogenation, indicating that the mobility of the main chain was increase d. (C) 2000 Elsevier Science B.V. All rights reserved.