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摘要
The synthesis of epoxidized star-shaped polymers by incorporation of living anionic polymerization with polyhedral oligomericsilsesquioxane (POSS) is seldom reported. In this study, the living (polyisopryl) lithium (PI-Li) is first synthesized in cyclohexane via high-vacuum living anionic polymerization using sec-butyllithium as the initiator and isoprene as the monomer. Subsequently, PI-Li is used to react with octavinyl polyhedral oligomericsilsesquioxane (OVPOSS) in cyclohexane to prepare an eight-arm star-shaped polyisoprene (8PI-POSS) in one pot. Purified 8PI-POSS is obtained after fractionation precipitation using cyclohexane/ ethanol as solvent/nonsolvent, and characterized by nuclear magnetic resonance (H-1-and C-13-NMR), gel permeation chromatography (GPC), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy and Fourier transform infrared spectroscopy (FTIR), respectively. Star-shaped polyisoprenes with different arm lengths are synthesized by changing the feed ratio of the monomer to the initiator. The compositions of the polymers are determined by comparison of integrals of characteristic signals from H-1-NMR spectra. GPC tests demonstrate that the eluent curves of the crude star-shaped polyisoprenes show an apparent shift to higher molecular weight compared with that of the base PI. The purified star-shaped polyisoprene (8PI-POSS) by fractionation precipitation possesses symmetric peaks with relatively narrow polydispersity. MALDI-TOF MS analysis indicates that the observed molecular weight of base PI is in good agreement with the calculated value. In addition, there are two minor peaks with an interval of 16 Da in the MALDI-TOF MS spectrum, which may be attributed to the possible oxidation reaction during storage or MALDI-TOF MS test. Unfortunately, the MALDI-TOF MS spectra of 8PI-POSS are not obtained probably due to their high molecular weights. Finally, the epoxidized star-shaped polyisoprene (8EPI-POSS) is obtained by oxidation of 8PI-POSS catalyzed by HCOOH/ H2O2. The 8EPI-POSS polymer is also characterized by H-1-and C-13-NMR, GPC and FTIR analyses, respectively. The characteristic signals found in H-1-and C-13-NMR spectra, as well as in FTIR spectra confirm the formation of epoxy group in the 8EPI-POSS. By changing the temperature and time of oxidation reaction, the star-shaped 8EPI-POSS with different percentages of epoxidation (PE) are prepared. It is also found that the GPC eluent curve of 8EPI-POSS change a little after the oxidation reaction. TGA tests show that the thermal decomposition temperature of 8PI-POSS and 8EPI-POSS are higher than that of the base PI. Moreover, it is also found that about 3% residue is left at about 800 degrees C, which maybe because of the incorporation of POSS segment in the star-shaped polymers. The epoxidized star-shaped polyisoprenes reported here may serve as an important intermediate in the preparation of highly branched polymers and as the novel tougheners for epoxy resins.
- 出版日期2018-3
- 单位苏州大学
