Weight/number-average Molecular Weight (weight + molecular_weight)

Distribution by Scientific Domains

Kinds of Weight/number-average Molecular Weight

  • molecular weight molecular weight
  • weight-average molecular weight molecular weight

  • Selected Abstracts

    Synthesis of a linear polyethylene macromonomer and preparation of polystyrene- graft -polyethylene copolymers via grafting-through atom transfer radical polymerization,

    Hiromu Kaneyoshi
    Abstract A vinyl-terminated linear polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight = 1.7, functionality = 92%) prepared by ethylene coordination polymerization was transformed into a monohydroxy-terminated linear polyethylene by hydroalumination of the vinyl group with diisobutylaluminum hydride and subsequent oxidation and hydrolysis. This monohydroxy-terminated linear polyethylene was quantitatively converted into a linear polyethylene macromonomer with a terminal ,-methacrylate group through esterification followed by dehydrobromination. A grafting-through atom transfer radical polymerization of the ,-methacrylate-terminated polyethylene and styrene was performed to yield a well-defined polystyrene- graft -polyethylene copolymer. The number-average molecular weight of the graft copolymers, measured by gel permeation chromatography, was lower than the predetermined number-average molecular weight, presumably because of the intramolecular aggregation of polyethylene side chains. The ,-methacrylate-terminated polyethylene content and number-average molecular weight of polystyrene- graft -polyethylene were determined by 1H-NMR. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 3,13, 2007 [source]

    Cationic copolymerization of ,-caprolactone and L,L -lactide by an activated monomer mechanism

    gorzata Ba
    Abstract The cationic homopolymerization and copolymerization of L,L -lactide and ,-caprolactone in the presence of alcohol have been studied. The rate of homopolymerization of ,-caprolactone is slightly higher than that of L,L -lactide. In the copolymerization, the reverse order of reactivities has been observed, and L,L -lactide is preferentially incorporated into the copolymer. Both the homopolymerization and copolymerization proceed by an activated monomer mechanism, and the molecular weights and dispersities are controlled {number-average degree of polymerization,=,([M]0 , [M]t)/[I]0, where [M]0 is the initial monomer concentration, [M]t is the monomer concentration at time t, and [I]0 is the initial initiator concentration; weight-average molecular weight/number-average molecular weight ,1.1,1.3}. An analysis of 13C NMR spectra of the copolymers indicates that transesterification is slow in comparison with propagation, and the microstructure of the copolymers is governed by the relative reactivity of the comonomers. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7071,7081, 2006 [source]

    Synthesis of amphiphilic copolymer brushes: Poly(ethylene oxide)-graft-polystyrene

    Zhongyu Li
    Abstract A well-defined amphiphilic copolymer brush with poly(ethylene oxide) as the main chain and polystyrene as the side chain was successfully prepared by a combination of anionic polymerization and atom transfer radical polymerization (ATRP). The glycidol was first protected by ethyl vinyl ether to form 2,3-epoxypropyl-1-ethoxyethyl ether and then copolymerized with ethylene oxide by the initiation of a mixture of diphenylmethylpotassium and triethylene glycol to give the well-defined polymer poly(ethylene oxide- co -2,3-epoxypropyl-1-ethoxyethyl ether); the latter was hydrolyzed under acidic conditions, and then the recovered copolymer of ethylene oxide and glycidol {poly(ethylene oxide- co -glycidol) [poly(EO- co -Gly)]} with multiple pending hydroxymethyl groups was esterified with 2-bromoisobutyryl bromide to produce the macro-ATRP initiator [poly(EO- co -Gly)(ATRP). The latter was used to initiate the polymerization of styrene to form the amphiphilic copolymer brushes. The object products and intermediates were characterized with 1H NMR, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, Fourier transform infrared, and size exclusion chromatography in detail. In all cases, the molecular weight distribution of the copolymer brushes was rather narrow (weight-average molecular weight/number-average molecular weight < 1.2), and the linear dependence of ln[M0]/[M] (where [M0] is the initial monomer concentration and [M] is the monomer concentration at a certain time) on time demonstrated that the styrene polymerization was well controlled. This method has universal significance for the preparation of copolymer brushes with hydrophilic poly(ethylene oxide) as the main chain. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4361,4371, 2006 [source]

    Interfacial living radical copolymerization of oil- and water-soluble comonomers to form composite polymer capsules

    Mir Mukkaram Ali
    Abstract The suspension copolymerization of methyl methacrylate with hydroxy-functional poly(ethylene glycol) monomethacrylate (PEGMA) by atom transfer radical polymerization (ATRP) yielded soluble, controlled-molecular-weight amphiphilic copolymers (weight-average molecular weight/number-average molecular weight <1.3). Despite extensive partitioning of PEGMA into the water phase, copolymers containing up to 24 mol % PEGMA were formed in the oil phase, from comonomer feeds containing 30 mol % PEGMA. Conversions by suspension polymerization were comparable to those obtained by solution polymerization, at over 70%. Suspension copolymers with high PEGMA contents contained high-molecular-weight polymer formed by uncontrolled polymerization, unless poly(vinyl pyrrolidone) was added to displace the growing polymer from the interface. The addition of diethylene glycol dimethacrylate gave capsules at 17 mol % PEGMA with ATRP, whereas conventional free-radical polymerization required 24 mol % PEGMA to form capsules. The lower PEGMA level required for capsule formation with ATRP was attributed to the lower rates of propagation and crosslinking and to improved incorporation of PEGMA into the final gels. Suspension ATRP with 24 mol % PEGMA in the feed gave two-layer capsule walls consisting of an inner layer visible by transmission electron microscopy and an outer layer visible by both transmission electron microscopy and environmental scanning electron microscopy, which indicated a compositional gradient across the capsule wall. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 156,171, 2006 [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)s

    Kotohiro 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, crystallization, and morphology of star-shaped poly(,-caprolactone)

    Jing-Liang Wang
    Abstract Six-arm star-shaped poly(,-caprolactone) (sPCL) was successfully synthesized via the ring-opening polymerization of ,-caprolactone with a commercial dipentaerythritol as the initiator and stannous octoate (SnOct2) as the catalyst in bulk at 120 C. The effects of the molar ratios of both the monomer to the initiator and the monomer to the catalyst on the molecular weight of the polymer were investigated in detail. The molecular weight of the polymer linearly increased with the molar ratio of the monomer to the initiator, and the molecular weight distribution was very low (weight-average molecular weight/number-average molecular weight = 1.05,1.24). However, the molar ratio of the monomer to the catalyst had no apparent influence on the molecular weight of the polymer. Differential scanning calorimetry analysis indicated that the maximal melting point, cold crystallization temperature, and degree of crystallinity of the sPCL polymers increased with increasing molecular weight, and crystallinities of different sizes and imperfect crystallization possibly did not exist in the sPCL polymers. Furthermore, polarized optical microscopy analysis indicated that the crystallization rate of the polymers was in the order of linear poly(,-caprolactone) (LPCL) > sPCL5 > sPCL1 (sPCL5 had a higher molecular weight than both sPCL1 and LPCL, which had similar molecular weights). Both LPCL and sPCL5 exhibited a good spherulitic morphology with apparent Maltese cross patterns, whereas sPCL1 showed a poor spherulitic morphology. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5449,5457, 2005 [source]

    Synthesis of well-defined three-armed polystyrene having thiourethane,isocyanurate as the core structure derived from trifunctional five-membered cyclic dithiocarbonate

    Akane Suzuki
    Abstract The synthesis of a three-armed polymer with an isocyanurate,thiourethane core structure is described. Monofunctional reversible addition,fragmentation chain transfer (RAFT) agent 2 and trifunctional RAFT agent 5 were prepared from mercapto-thiourethane and tris(mercapto-thiourethane), which were obtained from the aminolysis of mono- and trifunctional five-membered cyclic dithiocarbonates, respectively. The radical polymerization of styrene in the presence of 2,2,-azobis(isobutyronitrile) and RAFT agent 2 in bulk at 60 C proceeded in a controlled fashion to afford the corresponding polystyrene with desired molecular weights (number-average molecular weight = 3000,10,100) and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.13). On the basis of the successful results with the monofunctional RAFT agents, three-armed polystyrene with thiourethane,isocyanurate as the core structure could be obtained with trifunctional RAFT agent 5 in a similar manner. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5498,5505, 2005 [source]

    Fast living cationic polymerization accelerated by SnCl4.


    A conventional catalyst, SnCl4, for cationic polymerization, combined with EtAlCl2 and an ester as an added base, has been used to realize the fast living cationic polymerization of not only alkyl vinyl ethers but also those containing hetero atoms in the pendant. Two important features of this system are the clearly defined roles of two Lewis acids: EtAlCl2 generates initiating species quantitatively from 1-(isobutoxy)ethyl acetate [CH3CH(OiBu)OCOCH3], and SnCl4 accelerates the polymerization, which proceeds with livingness (weight-average molecular weight/number-average molecular weight = 1.02,1.08) at a rate 103,105 greater than that with only EtAlCl2 (or Et1.5AlCl1.5). SnCl4 alone induces rapid and living-like polymerization but produces byproducts under similar reaction conditions. [source]

    Synthesis of homopolymers and multiblock copolymers by the living ring-opening metathesis polymerization of norbornenes containing acetyl-protected carbohydrates with well-defined ruthenium and molybdenum initiators

    Yoshitaka Miyamoto
    Abstract The ring-opening metathesis polymerization (ROMP) of norbornenes containing acetyl-protected glucose [2,3,4,6-tetra- O -acetyl-glucos-1- O -yl 5-norbornene-2-carboxylate (1)] and maltose [2,3,6,2,,3,,4,,6,-hepta- O -acetyl-maltos-1- O -yl 5-norbornene-2-carboxylate (2)] was explored in the presence of Mo(N -2,6- iPr2C6H3)(CHCMe2Ph)(OtBu)2 (A), Ru(CHPh)(Cl)2(PCy3)2 (B; Cy = cyclohexyl), and Ru(CHPh)(Cl)2(IMesH2)(PCy3) (C; IMesH2 = 1,3-dimesityl-4,5-dihydromidazol-2-ylidene). The polymerizations promoted by B and A proceeded in a living fashion with exclusive initiation efficiency, and the resultant polymers possessed number-average molecular weights that were very close to those calculated on the basis of the monomer/initiator molar ratios and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.18) in all cases. The observed catalytic activity of B was strongly dependent on both the initial monomer concentration and the solvent employed, whereas the polymerization initiated with A was completed efficiently even at low initial monomer concentrations. The polymerization with C also took place efficiently, and even the polymerization with 1000 equiv of 1 was completed within 2 h. First-order relationships between the propagation rates and the monomer concentrations were observed for all the polymerization runs, and the estimated rate constants at 25 C increased in the following order: A > C > B. On the basis of these results, we concluded that ROMP with A was more suitable than ROMP with B or C for the efficient and precise preparation of polymers containing carbohydrates. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4248,4265, 2004 [source]

    Synthesis of well-defined poly(N -isopropylacrylamide) by the anionic polymerization of N -methoxymethyl- N -isopropylacrylamide

    Takashi Ishizone
    The anionic polymerization of N -methoxymethyl- N -isopropylacrylamide (1) was carried out with diphenylmethylpotassium in the presence of Et2Zn in tetrahydrofuran at ,78 C for 20 h. Poly(1)s, having predicted molecular weights and narrow molecular weight distributions (weight-average molecular weight/number-average molecular weight < 1.1), were obtained in quantitative yields. The methoxymethyl protecting group of the resultant poly(1)s was completely removed, and this yielded poly(N -isopropylacrylamide) possessing well-defined chain structures because of treatment with aqueous hydrochloric acid in 1,4-dioxane at room temperature for 20 h. [source]

    Rare-earth-metal-initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomers

    Hajime Yasuda
    Abstract The organo-rare-earth-metal-initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C5Me5)2LnR (where R is H or Me and Ln is Sm, Yb, Y, or La) as an initiator. These polymerizations provided highly syndiotactic (>96%) poly(methyl methacrylate) (PMMA) with a high number-average molecular weight (Mn > 1000 103) and a very narrow molecular weight distribution [weight-average molecular weight/number-average molecular weight (Mw/Mn) < 1.04] quantitatively in a short period. Bridged rare-earth-metallocene derivatives were used to perform the block copolymerization of ethylene or 1-hexene with MMA, methyl acrylate, cyclic carbonate, or ,-caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight (Mn > 500 103, Mw/Mn < 1.1) PMMA was first obtained in 1998 with [(Me3Si)3C]2Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties. 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 1955,1959, 2001 [source]