Free Radical Polymerization Initiated By Cyclic Aromatic Semipinacol Initiator

In this paper, the reversible breaking and coupling mechanism ofsemipinacol radicals to initiate living radical polymerization was explored.Anthracene diols initiator was applied to a variety of the polymerizationsystem based on this mechanism. The main contents were listed as followed:1. MAH/IP-XTOH microspheres containing initiator fragments on itssurface was prepared by the addition reaction between semipinacol radicalsgenerated from the homolytic cleavage of9,9’-bixanthydrol (BXAN) initiatorand double bond on the surface of the cross-linked microspheres ofpolymaleic anhydride/isoprene. Analysis of IR and UV spectroscopyconfirmed the presence of the initiator fragments on the surface ofcross-linked microspheres. Using the MAH/IP cross-linked microspherecontaining BXAN fragment as a macroinitiator, the solution polymerization ofdifferent monomer (MMA, St, BA) was carried out, and core-shellmicrosphere was obtained. The relationship between the conversion, reactiontime, particle size was explored. In the polymerization process, the monomerconversion and the core-shell microsphere size both increased with reaction time, the volume of the core-shell microspheres increased linearly with theconversion. SEM measurements indicated that the core-shell microsphereshad good uniformity, monodisperse and coefficient of variation.2. PB-XTOH polymer containing initiator fragments in its side chain wasprepared by the double bond addition reaction between semipinacol radicalsgenerated from the homolytic cleavage of9,9’-bixanthydrol initiator andpolybutadiene rubber. Using the PB-XTOH polymer containing BXANfragment as a macroinitiator, the solution polymerization of MMA was carriedout, and a PB-g-PMMA copolymer was obtained.3.9,9’-biisopropylthioxanthene-9,9’-diol(BITX) was synthesized byreductive coupling of two isopropyl thioxanthone(ITX) molecules.Semipinacol radicals generated from the homolytic cleavage of BITX initiatorin the heating and lighting conditions initiated polymerization of monomer.Radical polymerization characteristics of the different polymerization systemwhich contains MMA bulk polymerization with natural light, MMA bulkpolymerization with visible light, MMA bulk polymerization with heat andMMA solution polymerization with heat has been studied. The mainpolymerization characteristics of the different polymerization system werelisted as followed: The monomer conversion increased with reaction time, themolecular weight increased linearly with the conversion from10000to60000,the molecular weight distribution was in the range1.3to3.4. The high molecular weight of PMMA was synthesized by isopropyl thioxanthone(ITX) in the visible light or heat. ITX initiated bulkpolymerization of MMA with visible light at14℃, the molecular weight ofPMMA was about2.8million. ITX initiated bulk polymerization of MMAwith avoid light at80℃. The molecular weight is reduced with the increase ofthe concentration of ITX, the molecular weight decline to7.5million in theITX concentration of4%from16million in the ITX concentration of0.2%.