Synthesis and Characterization of New Diblock Copolymers Using Ring-Opening Metathesis Polymerization (ROMP)

摘要

Ring-opening metathesis polymerization (ROMP) has been performed with {RuCl_2(CHPh)[P(C_6H_(11))_3]_2} catalyst to make low polydispersity block copolymers of 5-(N-carbazolyl methyl)bicyclo[2.2.1]hept-2-ene (CbzNB) and 5-(phthalimide methyl)bicyclo[2.2.1]hept-2-ene (NBMPI). The novel diblock copolymers were characterized by means of gel permeation chromatography (GPC), ~1H NMR, fluorescence, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The molecular weight distributions of the diblock copolymers are narrow (Mw~(-)/Mn~(-)-1.5). Unhydrogenated diblock copolymers exhibited a strong carbazole fluorescence, with monomer emission occurring in the near-UV at approximately 380 nm and extending into the blue-violet region. The similar result was also observed on hydrogenated diblock copolymers. All diblock copolymers exhibited good solubility in a variety of solvents such as methylene chloride, chloroform, tetrahydrofuran and 1, 2-dichlorobenzene; however, there is no remarkable difference for the solubility between unhydrogenated and hydrogenated diblock copolymers. Two T_g values were observed for CbzNB segment and NBMPI segment before and after hydrogenation. Unhydrogenated diblock copolymers exhibited good thermo-oxidative stability, losing 10% mass in the range of 400 to 416°C in nitrogen. However, hydrogenated diblock copolymers showed better thermal stability than unhydrogenated diblock copolymers, and the 10% mass loss temperatures were recorded in the range of 415 to 428°C in nitrogen. Further, two kinds of diblock copolymers derived from CbzNB or NBMPI and 1, 5-cyclooctadiene (COD) have been successfully synthesized by ROMP. Agreement for carbazole moiety content in copolymers was obtained by the measurements of ~1H-NMR and GPC results. The molecular weight distributions of various diblock copolymers are narrow (Mw~(-)/Mn~(-) <1.5). The UV-visible absorption spectra and fluorescence emission spectra showed the characteristics of carbazole group in diblock copolymer. Increasing the length of the CbzNB-segment and lowering the length of the ethylene segment, the solubility has been improved. Two T_g values were observed for diblock copolymers before hydrogenation. However, one T_g value and one T_m value were observed for diblock copolymers after hydrogenation due to the CbzNB or NBMPI segments and ethylene segments, respectively. The diblock copolymer with longer CbzNB or NBMPI segment having higher molecular weight [poly(CbzNB-b-PB)-l or poly(NBMPI-b-PB)-l] exhibited better thermal stability than copolymer with shorter CbzNB or NBMPI segment having lower molecular weight [poly(CbzNB-b-PB)-2 or poly(NBMPI-b-PB)-2]. By increasing the length of CbzNB or NBMPI segment and lowering the length of poly(ethylene) segment, the solubility has been improved.