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 opening metathesis polymerization (ROMP)

Abstract

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 opening metathesis polymerization (ROMP) using a well-defined catalyst, {Cl 2Ru(CHPh)[P(C 6H 11) 3] 2}. The diblock copolymers were characterized by means of gel permeation chromatography (GPC), 1H nuclear magnetic resonance (NMR), UV–visible, fluorescence, dynamic light scattering (DLS), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The molecular weight distributions of the diblock copolymers are narrow ( Mw / Mn =1.10–1.47). Diblock copolymers showed four distinct UV absorptions characteristic of the carbazole group at 255, 295, 319 and 332 nm. Diblock copolymers exhibited a strong carbazole fluorescence, with monomer emission occurring in the near-UV at approximately 377 nm and extending into the blue-violet region (470 nm). In tetrahydrofuran and methylene chloride solution, the emission around 470 nm was not observed. Diblock copolymers showed two T g values owing to poly(CbzNB) and polybutadiene segments. However, after hydrogenation, they showed only one T g for poly(CbzNB) segment and one T m for polyethylene segment. The diblock copolymer [poly(CbzNB- b-PB)-1] with longer CbzNB chain exhibited better thermal stability than copolymer with shorter CbzNB chain [poly(CbzNB- b-PB)-2]. Two kinds of hydrogenated diblock copolymers, hydrogenated poly(CbzNB- b-PB)-1 and hydrogenated poly(CbzNB- b-PB)-2, have poorer solubility, but better thermal stability than unhydrogenated diblock copolymers, owing to the polyethylene segments. Furthermore, the larger hydrodynamic diameter of 324.2 nm was obtained after hydrogenation, indicating that the mobility of the main chain was increased.