Polymer Molecular Weight Distribution Research Articles

Pushing the limits of copper mediated azide–alkyne cycloaddition (CuAAC) to conjugate polymeric chains to cyclic peptides

We have investigated the copper mediated azide–alkyne cycloaddition (CuAAC) of chain-end alkyne-functionalised polymeric chains onto azide-functionalised cyclic peptides. We observe that steric effects limit the efficiency of the conjugation reactions when attempting to ligate four polymeric chains to one cyclic peptide. A maximum of ca. 50% efficiency is obtained, leading to a product containing a mixture of two, three and four-arm conjugates. On the other hand, conjugation of chain-end alkyne-functionalised polymers to a two-arm azido cyclic peptide occurred with 100% efficiency, independently of the polymeric chain length (degree of polymerisation varying from 16 to 108). In this case, optimal conjugation conditions required 1.025 equivalents of polymer, to account for the polymer molecular weight distribution, and two equivalents of CuSO4 relative to azide, in DMF/TFE (1 : 1 v/v) for 15 minutes under microwave irradiation. Independent of the efficiency of the conjugation reaction, all the conjugates were observed to form nanotubes in solution.

Effect of molecular weight distribution on polymer diffusion during film formation of two-component high-/low-molecular weight latex particles

We describe fluorescence resonance energy transfer (FRET) studies of film formation by a new type of two-component latex particles. These particles consist of a miscible blend of two components that have a similar composition but very different molecular weights. In our approach, we used sequential seeded emulsion polymerization to generate (in situ) a fraction of oligomer in poly(butyl acrylate-co-methyl methacrylate) P(BA-MMA) seed particles that contained a relatively high molecular weight (high-M) dye-labeled polymer. In this way we could systematically change the molecular weight distribution of polymer inside the particles. We varied the amount and the molecular weight of the oligomers. For latex films cast from these two-component particles, we studied the diffusion rate of the high molecular weight polymer by FRET. These measurements revealed that oligomers promoted diffusion rate during latex film formation (oligoplasticization). We analyzed our diffusion data in terms of the Fujita–Doolittle free-volume model and showed that higher molecular weight oligomers are less efficient as plasticizers. In separate experiments, oligomers with similar molecular weights as those in the two-component particles were introduced via latex blending. We compared oligoplasticization in latex blends films with that in the two-component particles films. Finally, we investigated the rheological behavior of the two-component polymers with compositions adjusted to have a common Tg (2 °C). The higher the molecular weight of the oligomer, the more that had to be added to achieve Tg = 2 °C. All of the oligomers were much shorter than the entanglement length and act as diluents of the entanglements in the high-M polymer. We found that incorporating larger amounts of oligomers with a higher molecular weight resulted in a more pronounced drop in polymer viscosity, associated with the decrease in the entanglement density.

Experimental and theoretical study of the reaction locus during the dispersion polymerization of methyl methacrylate in a nonpolar hydrocarbon solvent at low temperature

AbstractThe dispersion polymerization of methyl methacrylate (MMA) has been studied in a nonpolar hydrocarbon solvent at low temperature using N,N‐dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiation system. To explain the heterogeneous kinetic characteristics of the polymerization process, the reaction locus has been experimentally and theoretically investigated. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were measured throughout the polymerization. It was found that the significant preferences of LPO and DMA to accumulate in the polymer‐rich phase after the system phase separation are mainly responsible for both the uniformity of particle sizes and the broad polymer MWDs. It was observed that particle agglomeration and breakup mechanisms were enhanced under agitation, thus promoting the formation of broader particle size distributions. The observed kinetics and thermodynamics of the low‐temperature polymerization were also examined through a mathematical model where the distributions of initiators, solvent, and monomer between phases were considered. A good agreement between the experimental and theoretical results was observed and the model was used to estimate the conditions that promote bimodal MWDs. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Effects of contraction ratio on non-linear dynamics of semi-dilute, highly polydisperse PAAm solutions in microfluidics

Highly non-linear flows of semi-dilute ( 3.3 ⩽ c / c ∗ ⩽ 16.6 ) polyacrylamide (PAAm) aqueous solutions through three micro-fabricated 4:1:4, 8:1:8 and 16:1:16 contraction–expansion geometries have been investigated by micro-particle imaging velocimetry (μ-PIV) and pressure drop measurements. A set of quantitative data for PAAm solutions are obtained from: Gel Permeation Chromatography (GPC) analysis; rheometric characterization using Vilastic-3 and piezoelastic axial vibrator (PAV) with frequency up to 6650 Hz for linear viscoelasticity measurements, and using a microfluidic device for the measurement of the nonlinear shear viscosity. With three different flow geometries, and a wide range of Elasticity numbers ( 14.7 ⩽ El ⩽ 476.8 ) and Weissenberg numbers ( 1.4 ⩽ Wi ⩽ 131.7 ) , different nonlinear flow regimes are identified and correlated to vortex growth mechanisms. Results of similar El flows were mapped in a contraction ratio – Wi diagram. We found that under a given flow geometry tuning El can either increase or decrease the stability of the nonlinear flow structures. In addition to Wi and Re, the viscoelastic flow phenomena are dependent on the contraction and aspect ratios of flow geometry, and also sensitive to the molecular weight distribution of polymer. These results are of significance to the further development of microfluidic technologies.

Thermoreversible gelation of helical polypeptide/single-walled carbon nanotubes and their solid-state structures

Single-walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ-benzyl-L-glutamate)s (PBLGs) having well-defined polymer molecular weight (Mn = 7.5–21.1 kg·mol−1) and molecular weight distribution (PDI = 1.05–1.20) by a graft-to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG-functionalized SWCNTs (PBLG-SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (ΔHm) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG-SWCNTs. Small-angle X-ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG-SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG-SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG-SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Effect of monomer feed and production rate on the control of molecular weight distribution of polyethylene in gas phase reactors

The control of the polymer molecular weight distribution via altering the monomer to hydrogen molar ratio in fluidized bed reactors is examined. The molar ratio is altered by manipulating the monomer and hydrogen feed rates using nonlinear model predictive controller. The simulation revealed promising results however a trade-off between utilizing both the monomer and hydrogen flows simultaneously and the hydrogen flow exclusively exists. Utilization of the monomer and hydrogen flows together favors the rapid transition to the required MWD but at the expense of higher purge and inconsistent production rate. Exclusive use of the hydrogen intake leads to steady production rate and less consumption of the purge. However, longer time is needed to achieve the desired MWD. The same phenomena are observed when discrete mechanism for product withdrawal is implemented.

Metallocene‐mediated cationic ring‐opening polymerization of 2‐methyl‐ and 2‐phenyl‐oxazoline

AbstractThe cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline was efficiently used using bis(η5‐cyclopentadienyl)dimethyl zirconium, Cp2ZrMe2, or bis(η5‐tert‐butyl‐cyclopentadienyl)dimethyl hafnium in combination with either tris(pentafluorophenyl)borate or tetrakis(pentafluorophenyl)borate dimethylanilinum salt as initiation systems. The evolution of polymer yield, molecular weight, and molecular weight distribution with time was examined. In addition, the influence of the initiation system and the monomer on the control of the polymerization was studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2011

Development of the Certified Reference Materials for Molecular-Weight Distributions of Synthetic Polymers

合成高分子が有する平均分子量及び分子量分布は，その化学的・物理的性質を特性付ける上で重要な因子となる．本報では，分子量が数千程度までのオリゴマー領域における分子量分布の高精度計測法について研究を行い，その技術を用いてポリスチレン，ポリエチレングリコール，並びにポリエチレングリコールノニルフェニルエーテル標準物質を開発した過程について述べる．これらの標準物質は，含有する重合体の各々の組成が値付けされた非常にユニークな標準物質である．標準物質開発は主に超臨界流体クロマトグラフィー（SFC）によって行われた．SFCを使用して，まず分子量分布の全く存在しない「均一オリゴマー」を分別採取した．均一オリゴマーは，濃度と分子量を厳密に規定することが可能であるため，次にこれを使用してSFCの各種検出器の精密な校正を行った．オリゴマー領域においては検出器感度の分子量依存性が顕著な場合が多く，検出器の校正時に生じる不確かさが分子量分布測定全体へ与える寄与は決して小さくはない．更に，各々の重合体組成が明らかなこれらの標準物質を使って，MALDI-TOFMSの共同測定を行った結果について述べた．

Analysis of solution polybutadiene polymerizations performed with a neodymium catalyst

AbstractThis article is regarding the polymerization of 1,3‐butadiene with a neodymium catalyst activated by diisobutylaluminum‐hydride and diethylaluminum chloride (DEAC). The effects of the polymerization conditions (ratio between DEAC and neodymium molar concentrations, polymerization temperature, catalyst concentration, and butadiene concentration) on the polymer yield and molecular weight distribution (MWD) of polybutadiene (PB) samples were evaluated. It is shown that the DEAC/Nd ratio and the polymerization temperature are the reaction variables that influence the MWD and the catalyst performance most significantly. PBs with broad and sometimes bimodal MWD were produced at the analyzed reaction conditions. For this reason, the MWD of the obtained polymer materials was deconvoluted with the help of the Flory most probable distribution, indicating that three or more catalyst sites are required to explain the final MWD of the polymer samples. Finally, it was observed that the analyzed neodymium catalyst is able to produce branched PBs at mild reaction conditions and that the branching frequency depends on the polymerization conditions, which may be useful for development of operation policies at plant site and production of materials with improved performances. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers

Preparation of highcis‐1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerization

AbstractHighcis‐1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)3), dimethyldichlorosilane (Me2SiCl2), and diisobutylaluminum hydride (Al(i‐Bu)2H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual‐catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of highcis‐1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i‐Bu)2H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i‐Bu)3), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i‐Bu)2H. Finally, CCTP polymerization mechanism is validated by continuously decreasedMw/Mnvalue of polymer when increasing concentration of Al(i‐Bu)2H extra added in the Nd(ver)3/Me2SiCl2/Al(i‐Bu)3catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Evolutionary computing approach for evaluating flory distribution curves in gel permeation chromatography: Study of the poly(1‐octene) system

AbstractWe carried out deconvolution of the molecular weight distribution curves from gel permeation chromatography for polyolefins into individual active sites considering Flory distribution by an evolutionary‐computing‐based real‐coded genetic algorithm, a nonlinear multivariate optimization algorithm. We applied the deconvolution to homopolymers of 1‐octene synthesized using heterogeneous Ziegler–Natta catalysts with different amounts of hydrogen. The molecular weight distribution was deconvoluted in to five Flory distributions, which showed a sensitivity to hydrogen amounts. With no hydrogen presence, the peaks corresponding to high‐molecular‐weight fractions were intense. As the amount of hydrogen was increased, not only did the intensities of the high‐molecular‐weight peaks decrease, but also peaks corresponding to low‐molecular‐weight fractions were observed. The method allowed us to determine the active site distribution of the polymer molecular weight distribution obtained from gel permeation chromatography. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Calculation of molecular weight distributions of polymers synthesized on multisite catalytic systems

Calculation of molecular weight distributions of polymers synthesized on multisite catalytic systems

High Temperature Semibatch Free Radical Copolymerization of Styrene and Butyl Acrylate

AbstractSummary: High temperature semibatch free radical solution copolymerizations of n‐butyl acrylate (BA) and styrene (ST) were carried out over a range of copolymer composition. The significant increase in experimental polymer weight‐average molecular weight with time, as well as the shift in the entire polymer molecular weight distribution, is explained by assuming fast β‐scission of BA midchain radicals with an adjacent styrene unit, followed by subsequent addition of the resultant macromonomer to growing radicals. A mechanistic model including backbiting and β‐scission, macronomer incorporation, long‐chain branching, and propagation and termination penultimate effects was constructed in Predici; the model provides a good representation of the experimental data using rate coefficients taken from literature.

ARGET ATRP of acrylonitrile with ionic liquid as reaction media and 1,1,4,7,7-pentamethyldiethylenetriamine as both ligand and reducing agent in the presence of air

[C12mim][BF4], [C8mim][BF4], and [C4mim][BF4] were first applied as reaction media for atom transfer radical polymerization using activators regenerated by electron transfer (ARGET ATRP) of acrylonitrile (AN) with 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) as both ligand and reducing agent in the presence of air. The rate of polymerization in [C12mim][BF4] was considerably faster than in [C8mim][BF4] and [C4mim][BF4]. ARGET ATRP of AN in [C12mim][BF4] were better controlled than in [C8mim][BF4] and [C4mim][BF4] under the same experimental conditions. With an increase in the content of PMDETA, the polymerization provided an accelerated reaction rate and a broader polymer molecular weight distribution. A slow polymerization rate and a broad polydispersity index were observed using TMEDA instead of PMDETA as both ligand and reducing agent. There was an obvious induction period with CuCl2 instead of CuBr2 as catalyst. Well-defined PAN-b-PMMA with higher molecular weight at 104,560 and relatively broader distribution at 1.35 was successfully prepared with PAN as macroinitiator via ARGET ATRP in [C12mim][BF4] in the presence of air. The resultant fibers were obtained with the fineness at 1.17dtex and the tenacity at 6.03cN · dtex−1. Copyright © 2010 John Wiley & Sons, Ltd.

リビングラジカル重合 ４．立体特異性リビングラジカル重合

Living radical polymerization (LRP) enables the control of molecular weight and molecular weight distribution of polymers synthesized, but it is no effect on stereoregulation (tacticity) of the polymer. With the progress of stereospecific radical polymerizations, several attempts have been made to combine it with LRP to achieve simultaneous control of molecular weight, molecular weight distribution, and tacticity. This forth article describes these stereospecific LRPs. Synthetic routes to stereoblock polymers and stereogradient polymers are also described.

Bimetallic Rare Earth Alkyl Complexes Bearing Bridged Amidinate Ligands: Synthesis and Activity for L‐Lactide Polymerization

AbstractFour novel bridged‐amidines H2L {1,4‐R1[C(=NR2)(NHR2)]2 [R1=C6H4, R2=2,6‐iPr2C6H3 (H2L1); R1=C6H4, R2=2,6‐Me2C6H3 (H2L2); R1=C6H10, R2=2,6‐iPr2C6H3 (H2L3); R1=C6H10, R2=2,6‐Me2C6H3 (H2L4)]} were synthesized in 65%–78% isolated yields by the condensation reaction of dicarboxylic acid with four equimolar amounts of amines in the presence of PPSE at 180°C. Alkane elimination reaction of Ln(CH2SiMe3)3(THF)2 (Ln=Y, Lu) with 0.5 equiv. of amidine in THF at room temperature afforded the corresponding bimetallic rare earth alkyl complexes (THF)(Me3SiCH2)2LnL1Ln(CH2SiMe3)2(THF) [Ln=Y (1), Lu (2)], (THF)(Me3SiCH2)2LnL2Ln‐ (CH2SiMe3)2(THF) [Ln=Y (3), Lu (4)], (THF)(Me3SiCH2)2YL3Y(CH2SiMe3)2(THF) (5), (THF)(Me3SiCH2)2YL4‐ Y(CH2SiMe3)2(THF) (6) in 72% –80% isolated yields. These neutral complexes showed activity towards L‐lactide polymerization in toluene at 70°C to give high molecular weight (M>104) and narrow molecular weight distribution (Mw/Mn≦1.40) polymers

AGET ATRP of acrylonitrile using 1,1,4,7,10,10‐hexamethyltriethylenetetramine as both ligand and reducing agent

AbstractAtom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) initiated by ethyl 2‐bromoisobutyrate was approached for the first time using 1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA) and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as both ligand and reducing agent. AGET ATRP of AN with HMTETA as both ligand and reducing agent was better controlled than with PMDETA as both ligand and reducing agent under the same experimental conditions. With an increase content of HMTETA, the polymerization provided an accelerated reaction rate and a broader polymer molecular weight distribution. The rate of polymerization with DMF as solvent was faster than with acetonitrile, cyclohexanone, toluene, and xylene as solvents. The polymerization apparent activation energy was calculated to be 45.7 kJ mol−1. The end functionality of polyacrylonitrile (PAN) was confirmed by 1H NMR spectroscopy. The living feature of PAN was verified by chain extensions of PAN with methyl methacrylate and AN. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 128–133, 2010

Online Monitoring of Molecular Weight and Other Characteristics during Semibatch Emulsion Polymerization under Monomer Starved and Flooded Conditions

Reaction kinetics in semibatch emulsion polymerization of methyl methacrylate, were monitored by automatic continuous online monitoring of polymerization reactions (ACOMP). Semibatch reagent feed to the reactor at different flow rates allowed the transition between the monomer starved and flooded regimes and the approach to and maintenance of near steady state conditions to be monitored and quantified, and yielded relationships between flow regimes and monomer conversion kinetics, polymer weight-average molecular weight Mw, and intrinsic viscosity (η)w. Polymer molecular weight distributions togetherwithlatexparticlesizeandnumberplayanimportantroleindefiningthemacroscopiccharacteristics and performance of polymeric materials. The change in the monomer feed rates during reaction allowed simultaneous influence on and verification of the evolution of these parameters during synthesis. When flow rate changes to the reactor were made it was verified that the characteristic rate of achieving the new pseudosteady state was close to the first order reaction rate. Multidetector size exclusion chromatography was used to cross-check results and measure full distributions of endproducts. Latex polymer size was measuredwithdynamiclightscattering.AnimportantadvanceforthisfieldisthatpolymerMwisdetermined continuously during the reaction and in an absolute fashion, based on multiangle light scattering detection available.

Theoretical Study on a Multicenter Model Based on Different Metal Oxidation States for the Bis(imino)pyridine Iron Catalysts in Ethylene Polymerization

We have analyzed by DFT methods the reactivity shown by the bis(imino)pyridine catalysts based on the oxidation states, II or III, of the Fe atom. Although it has been proposed that both Fe-based species could be involved in the olefin polymerization process, there is some controversy over which of them is the more active one. Previous theoretical studies based on conceptual DFT descriptors showed that the Fe(III) cationic species was more active than the Fe(II) one. The results obtained in the present work, based on the analysis of energy profiles for the ethylene insertion and β-hydrogen chain transfer steps calculated from DFT, confirm these observations, showing that unlike the Fe(II) species, the Fe(III) oxidation state would be more active in olefin polymerization and would yield polymers with a low molecular weight fraction. This result is in agreement with experimental observations showing the characteristic bimodal polymer molecular weight distribution obtained with these catalysts.

ETHYLENE-1-HEXENE COPOLYMERIZATION WITH A 2,6-DIISOPROPYLPHENOL MODIFIED SUPPORTED ZIEGLER-NATTA CATALYST

研究了新型的改性负载型ZieglerNatta催化剂，以期制备出组成分布较窄的乙烯-α-烯烃共聚物.通过2,6-iPr2C6H3-OH与TiCl4/ID/MgCl2型负载型钛催化剂在室温下的反应可将芳氧基接到催化剂表面，制得一种改性的烯烃聚合催化剂M-cat.改性催化剂对乙烯聚合及乙烯-1-己烯共聚反应的催化活性与未改性催化剂相近，但共单体效应较弱.前者共聚物的1-己烯含量低于未改性催化剂的产物，但组成分布较窄，分子量较高，且共聚物的沸腾正庚烷可溶级分的序列分布较接近无规分布.三异丁基铝为助催化剂所得聚合活性高于甲基铝氧烷活化的体系.改性催化体系的活性中心分布与未改性体系相比有明显的差别.