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Polymer Chain Ends (polymer + chain_end)
Selected AbstractsBorane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010Wentian Lin Abstract This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl-B-9-borabicyclononane (Me-B-9-BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]-catalyzed ethylene (Cp2ZrCl2 and rac -Me2Si(2-Me-4-Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found,in most cases,able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)-terminated PE and s -PS polymers after an oxidative workup process, suggesting the formation of the B-polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac -Me2Si(2-Me-4-Ph)2ZrCl2. Both TEB and Me-B-9-BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO-catalyzed ethylene polymerization; nevertheless, Me-B-9-BBN failed in vain with rac -Me2Si(2-Me-4-Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH-bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane-terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534,3541, 2010 [source] Synthesis of ethylene/propylene elastomers containing a terminal reactive group: The combination of metallocene catalysis and control chain transfer reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2005U. Kandil Abstract This article discusses a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as ,-CH3 and OH. The chemistry involves metallocene-mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent,a mixture of hydrogen and styrene derivatives carrying a CH3 (p -MS) or a silane-protected OH (St-OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St-f) at the polymer chain end, in other words, altering the St-f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C5Me4)SiMe2N(t -Bu)]TiCl2 and rac-Et(Ind)2ZrCl2, under certain H2 pressures, were found to be suitable catalyst systems to perform the combined task. A broad range of St-f terminated EP copolymers (EP- t -p-MS and EP- t -St-OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St-f]/[monomer]. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1858,1872, 2005 [source] Synthesis and properties of carbazole-layered polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2009Yasuhiro Morisaki Abstract New aromatic ring-layered polymers consisting of carbazole as a layered aromatic group and xanthene as a scaffold were designed and synthesized via the Sonogashira,Hagihara coupling reaction. Their optical and electrochemical behaviors were investigated in detail; the results showed that these polymers could be used as hole-transporting materials. Polymers with nitrobenzene moieties at the polymer chain ends quenched the emission from the layered carbazoles to the nitrobenzene termini; thus, the polymers acted as the molecular wire that transferred photoexcited energy and/or electrons to the polymer termini. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4279,4288, 2009 [source] Acyclic diene metathesis polymerization of 2,5-dialkyl-1,4-divinylbenzene with molybdenum or ruthenium catalysts: Factors affecting the precise synthesis of defect-free, high-molecular-weight trans -poly(p -phenylene vinylene)sJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2005Kotohiro Nomura Abstract Factors affecting the syntheses of high-molecular-weight poly(2,5-dialkyl-1,4-phenylene vinylene) by the acyclic diene metathesis polymerization of 2,5-dialkyl-1,4-divinylbenzenes [alkyl = n -octyl (2) and 2-ethylhexyl (3)] with a molybdenum or ruthenium catalyst were explored. The polymerizations of 2 by Mo(N -2,6-Me2C6H3) (CHMe2 Ph)[OCMe(CF3)2]2 at 25 °C was completed with both a high initial monomer concentration and reduced pressure, affording poly(p -phenylene vinylene)s with low polydispersity index values (number-average molecular weight = 3.3,3.65 × 103 by gel permeation chromatography vs polystyrene standards, weight-average molecular weight/number-average molecular weight = 1.1,1.2), but the polymerization of 3 was not completed under the same conditions. The synthesis of structurally regular (all- trans), defect-free, high-molecular-weight 2-ethylhexyl substituted poly(p -phenylene vinylene)s [poly3; degree of monomer repeating unit (DPn) = ca. 16,70 by 1H NMR] with unimodal molecular weight distributions (number-average molecular weight = 8.30,36.3 × 103 by gel permeation chromatography, weight-average molecular weight/number-average molecular weight = 1.6,2.1) and with defined polymer chain ends (as a vinyl group, CHCH2) was achieved when Ru(CHPh)(Cl)2(IMesH2)(PCy3) or Ru(CH-2-OiPr-C6H4)(Cl)2(IMesH2) [IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene] was employed as a catalyst at 50 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6166,6177, 2005 [source] Synthesis of thermally crosslinkable fluorine-containing poly(arylene ether ketone)s,II.POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2004Propargyl ether terminated poly(arylene ether ketone)s Abstract Novel thermally crosslinkable fluorine-containing poly(arylene ether ketone)s comprised of 2,3,5, 6-tetrafluoro-1,4-phenylene moiety were synthesized by the termination of polymer chain ends with propargyl ether groups in order to improve solvent resistance. Crosslinking reaction occurred over 250°C through the formation of both chromen ring and polyene structure. This structure change brought about not only the outstanding solvent resistance but also the increase in glass transition temperature (Tg). The cured films also exhibited excellent thermal stability, transparency and hydrophobicity derived from fluorine atoms. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||