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Chain-transfer Reaction (chain-transfer + reaction)
Selected AbstractsAlternating copolymerization of carbon dioxide and epoxide catalyzed by an aluminum Schiff base,ammonium salt systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2005Hiroshi Sugimoto Abstract The alternating copolymerization of carbon dioxide (CO2) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO2 and CHO with the (Salophen)AlMe (1a),tetraethylammonium acetate (Et4NOAc) system. When a mixture of the 1a,Et4NOAc system and CHO was pressurized by CO2 (50 atm) at 80 °C in CH2Cl2, the copolymerization of CO2 and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO2 and CHO with an almost perfect alternating structure. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis indicated that an unfavorable reaction between Et4NOAc and CH2Cl2 and a possible chain-transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172,4186, 2005 [source] Effect of hydrogen-bonding interaction on radical polymerization of di- n -butyl itaconateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2003Tomohiro Hirano Radical polymerizations of di- n -butyl itaconate (DBI) were examined in the presence of amide compounds that could form a complex with DBI monomer via a hydrogen-bonding interaction. The use of amide compounds as solvents succeeded to suppress the intramolecular chain-transfer reaction significantly, whereas catalytic amounts of amide compounds were of little effect. It was also assumed that a hydrogen-bonding interaction plays an important role not only for suppression of the intramolecular chain-transfer reaction but for stereospecificity of polymerization. These results suggested that even a weak hydrogen-bonding interaction could be used for control of a radical polymerization reaction. [source] Cyclopolymerization and Copolymerization of Functionalized 1,6-Heptadienes Catalyzed by Pd Complexes: Mechanism and Application to Physical-Gel FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010Sehoon Park Dr. Abstract Cationic Pd complexes, prepared from [PdCl(ArNC12H6NAr)(Me)] and Na[B{3,5(CF3)2C6H3}4] (NaBARF), catalyze the cyclopolymerization of 4,4-disubstituted 1,6-heptadienes. The polymers produced contain a trans -fused five-membered ring in each repeating unit. NMR spectroscopy and FAB mass spectrometry of the polymers formed indicated that the initiation end of the chain contains either the cyclopentyl group derived from the preformed Pd,monomer complex or a hydrogen atom left on the Pd center by the chain-transfer reaction. The stable cyclopentylpalladium species are involved in both initiation and propagation steps and undergo isomerization into (cyclopentylmethyl)palladium species followed by the insertion of a CHCH2 bond of a new monomer molecule into the PdCH2 bond. Copolymerization of 1,6-heptadiene derivatives with ethylene, catalyzed by the Pd complexes, yields polymers that contain trans five-membered rings and branched oligoethylene units. Copolymerization of isopropylidene diallylmalonate with 1-hexene affords a polymer with 26,% diene incorporation. The copolymerization consumes 1-hexene more readily than isopropylidene diallylmalonate, although gel permeation chromatography and NMR spectroscopy of the polymers produced show the formation of copolymers rather than of a mixture of homopolymers. Polymerization of 1-hexene initiated with a Pd,barbiturate complex and terminated with 5-allyl-5-hexylpyrimidine-2,4,6(1H,3H,5H)-trione/Et3SiH leads to polyhexene with barbiturate moieties at both terminal ends. Addition of 5-hexyl-2,4,6-triaminopyrimidine to a toluene solution of the telechelic poly(1-hexene) converts the solution into gel. [source] Actuation in Crosslinked Polymers via Photoinduced Stress Relaxation,ADVANCED MATERIALS, Issue 16 2006F. Scott Photoinduced polymer actuation by relieving stress unevenly through the thickness of a chemically crosslinked, rubbery polymer upon light exposure is demonstrated (see figure). The sensitivity of this method to light is greater than previously developed photoinduced actuation techniques, as the recurring chain-transfer reactions amplify the effects of each absorbed photon and subsequently generated radical on the stress-relief and actuation processes. [source] | ||||||||||