scholarly journals Syntheses, Structures and Properties of Polycarbosilanes Formed Directly by Polymerization of Alkenylsilanes

1992 ◽  
Vol 271 ◽  
Author(s):  
John Masnovi ◽  
Xin Y. Bu ◽  
Kassahun Beyene ◽  
Paula Heimann ◽  
Terrence Kacik ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Structures And Properties ◽  
Weight Distributions

ABSTRACTVinylsilane polymerizes to form predominantly a carbosilane polymer using dimethyltitanocene catalyst. This is in contrast to alkylsilanes, which afford polysilanes under the same conditions. The mechanism of polymerization of alkenylsilanes has been shown to be fundamentally different from that for the polymerization of alkylsilanes. The silyl substituent apparently activates a double bond to participate in a number of polymerization processes in this system, particularly hydrosilation. Isotopie labeling indicates the involvement of silametallocyclic intermediates, accompanied by extensive nuclear rearrangement. Polymers and copolymers derived from alkenylsilanes have relatively high char yields even for conditions which afford low molecular weight distributions. Formation of crystalline β-SiC is optimum for a copolymer of an alkylsilane and an alkenylsilane having a silane/carbosilane backbone ratio of 85/15 and a C/Si ratio of 1.3/1.

Tertiary amine catalyzed photo-induced controlled radical polymerization of methacrylates

2015 ◽  
Vol 6 (30) ◽  
pp. 5362-5368 ◽  
Author(s):  
Qiang Fu ◽  
Thomas G. McKenzie ◽  
Shereen Tan ◽  
Eunhyung Nam ◽  
Greg G. Qiao
Keyword(s):  
Molecular Weight ◽  
Radical Polymerization ◽  
Uv Irradiation ◽  
Tertiary Amine ◽  
Controlled Radical Polymerization ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
End Group

A novel tertiary amine catalyst and trithiocarbonate synergistic photo-induced controlled radical polymerization of methacrylates has been realized under mild UV irradiation, yielding polymethacrylates with low molecular weight distributions and excellent end-group fidelity.

Characterization of Elution Chromatography Fractions from CIS-Polybutadiene by GPC

1970 ◽  
Vol 43 (6) ◽  
pp. 1439-1450 ◽  
Author(s):  
W. V. Smith ◽  
S. Thiruvengada
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Log Normal ◽  
Analytical Fractionation ◽  
Molecular Weight Fractions ◽  
Elution Chromatography

Abstract A preparative fractionation of about 23 g of a commercial cis-polybutadiene rubber is described. The method employed was a solvent elution chromatographic method with very little temperature gradient. The molecular weight distributions of the fractions obtained were determined by an analytical fractionation of 20 mg of polymer. The method was similar to the preparative fractionation and involved solvent elution chromatography. The fractions obtained were assayed for quantity, molecular weight, and molecular weight distribution by GPC. The low molecular weight fractions of the preparative fractionation had molecular weight distributions which could be closely approximated by two log normal distributions, the low molecular weight component having the narrower width. The ratio of weight to number average molecular weight was found to be about 1.1 for these samples. The higher molecular weight fractions could also be approximated by two log normal distributions; however, in these fractions the low molecular weight component had a very broad distribution but constituted only a small portion of the sample. The widths of the GPC curves of the fractions correlate satisfactorily with the molecular weight distributions found by the analytical refractionations. The GPC width is a sensitive criterion of the width of the molecular weight distribution even when only two columns are used. It is felt that the analytical fractionation procedure presented gives more detailed information on the molecular weight distribution than is easily obtainable from an ordinary GPC curve.

Molecular Weight Determinations Of Low Molecular Weight (LMW) Heparins By Ultracentrifugation And High Pressure Liquid Chromatography

1981 ◽  
Author(s):  
Grant Barlow ◽  
N Sugisaka ◽  
F J Petracek
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Liquid Chromatography ◽  
High Pressure Liquid Chromatography ◽  
Low Molecular Weight ◽  
Analytical Ultracentrifuge ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Heparin Fractions

Molecular weights were independently determined on nitrous acid depolymerized LMW heparin fractions ranging from 2-15 daltons using the analytical ultracentrifuge and high pressure liquid chromatography (HPLC).Sedimentation-diffusion equilibria were obtained in the analytical ultracentrifuge using speeds ranging from 20,000 to 56,000 rpm. Near theta conditions were obtained using 0.5M NaCl as the solvent. Calculations of molecular weight distributions and, from those figures, weight average molecular weights were made using the method described by Scholte (N.Y. Acad Sci. 164, 156, 1969). The results show that weight average values as low as 2,000 daltons can be determined.Sedimentation-diffusion equilibria were obtained in the analytical ultracentrifuge using speeds ranging from 20,000 to 56,000 rpm. Near theta conditions were obtained using 0.5M NaCl as the solvent. Calculations of molecular weight distributions and, from those figures, weight average molecular weights were made using the method described by Scholte (N.Y. Acad Sci. 164, 156, 1969). The results show that weight average values as low as 2,000 daltons can be determined.The HPLC results were obtained using previously described methods (Fed Proc. 36, 89, 1977) and a new highly efficient gel column (TSK gels). Fractionated dextrans were used as reference standards.

Etude de quelques polymères obtenus lors de la déshydratation en système statique d'alcools allyliques disubstitués

1973 ◽  
Vol 51 (2) ◽  
pp. 288-291 ◽  
Author(s):  
Claude Roux ◽  
Hubert Daoust
Keyword(s):  
Molecular Weight ◽  
Allyl Alcohol ◽  
Thermal Dehydration ◽  
Low Molecular Weight ◽  
Static System ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Allyl Alcohols ◽  
Specific Volumes

Diolefins, produced by thermal dehydration of disubstituted allyl alcohols in a static system, polymerize as they are formed giving low molecular weight polymers. The microstructure of the product is similar to that of thermal polymers of 1,3-dienes. Number- and weight-average molecular weights, partial specific volumes, and molecular weight distributions have been studied for the polymers obtained from 3-methyl-2-butene-1-ol and 3,3-dimethyl-allyl alcohol.

Polymerization of Nitrophenyl and 3-Diethylaminophenyl Prop-2-yn-1-yl Ethers with PdCl2. Polymers and Copolymers Characterization

1998 ◽  
Vol 63 (11) ◽  
pp. 1803-1814 ◽  
Author(s):  
Hynek Balcar ◽  
Petr Holler ◽  
Jan Sedláček ◽  
Vratislav Blechta
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Size Exclusion Chromatography ◽  
Main Chain ◽  
Size Exclusion ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Exclusion Chromatography

2-, 3- and 4-Nitrophenyl prop-2-yn-1-yl ethers were polymerized with PdCl2 in N,N-dimethylformamide (DMF) giving brown polymers soluble in DMF, dimethyl sulfoxide and N-methylpyrrolidone. Broad (mostly bimodal) molecular weight distributions were observed by size-exclusion chromatography (SEC) with maxima at molecular weight of about 4 . 103 and 1 . 105. With the same catalyst, 3-diethylaminophenyl prop-2-yn-1-yl ether gave predominantly low molecular weight homopolymer (Mn = 4 200) soluble in DMF, N-methylpyrrolidone, CHCl3 and tetrahydrofuran-soluble copolymers with 4-nitrophenyl prop-2-yn-1-yl ether (Mn about 3 000). IR, NMR and UV-VIS spectra of prepared polymers and copolymers proved the structure to consist of the polyene-type main chain with phenoxymethyl pendant groups bearing nitro or diethylamino substituents.

Comparison of treatment efficiency and molecular weight distribution of membrane concentrate from textile wastewater

2016 ◽  
Vol 18 (2) ◽  
pp. 348-359
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Textile Wastewater ◽  
Anaerobic Treatment ◽  
Low Molecular Weight ◽  
Treatment Efficiency ◽  
Molecular Weight Distributions ◽  
Weight Distributions

<div> <p>This study investigated the treatability and changes in molecular weight distributions (MWD) of membrane concentrate. Nanofiltration (NF) concentrate from textile wastewater was subjected sole anaerobic treatment (R1) and pre-ozonation (R2) plus anaerobic treatment. BOD<sub>5</sub>, COD and TOC, color, sulphate and specific ultraviolet absorbtion at 254 nm (SUVA<sub>254</sub>) were analysed. Pre-ozonation improved the biodegradability of the membrane concentrate. The low molecular weight (LMW) organics was an important reason for the overall biodegradability enhancement of the membrane concentrate. Color was caused mainly by matters with higher than MWD of 10 kDa and 80% of HMW organics were removed during anaerobic treatment. Nearly half of sulfate was lower than 0.5 kDa which indicates that sulfate hardly treated by NF membranes. SUVA<sub>254</sub> values after anaerobic treatment were generally higher than 2 l mg<sup>-1</sup>m<sup>-1</sup> which indicates that membrane concentrate was in hydrophobic characteristics.&nbsp;</p> </div> <p>&nbsp;</p>

scholarly journals Evaluation of the Degree of Polymerization of the Proanthocyanidins in Cranberry by Molecular Sieving and Characterization of the Low Molecular Weight Fractions by UHPLC-Orbitrap Mass Spectrometry

Molecules ◽  
2019 ◽  
Vol 24 (8) ◽  
pp. 1504 ◽  
Author(s):  
Claudio Gardana ◽  
Paolo Simonetti
Keyword(s):  
Molecular Weight ◽  
Molecular Sieves ◽  
Degree Of Polymerization ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Orbitrap Mass Spectrometry ◽  
Weight Distributions ◽  
Molecular Weight Fractions ◽  
Molecular Sieving

4-dimethylammino-cinnamaldehyde (DMAC) assays quantify total proanthocyanidins (PACs) but do not provide qualitative PAC molecular weight distribution information and cannot discriminate between A- and B-type PACs. We developed an efficient method for assessing PAC molecular weight distributions. The PACs from three commercial cranberry extracts (A1–A3) were fractionated by molecular sieves with cut-offs of 3, 10, 30, 50, and 100 kDa, and each fraction was analyzed by DMAC assays. A1, A2, and A3 contained 27%, 33%, and 15% PACs, respectively. Approximately 28 PACs, 20 flavonols, and 15 phenolic acids were identified by UHPLC-DAD-Orbitrap MS in A1 and A3, while A2 contained only flavan-3-ols. Epicatechin was the main monomer in A1 and A3, and catechin was the main in A2. Procyanidin A2 was the main dimer in A1 and A3, representing more than 85% of the total dimers, while it constituted approximately only 24% of A2. A1 and A3 contained quercetin, isorhamnetin, myricetin, and their glycosides, which were totally absent in A2. In A1 and A3 the PACs were mainly distributed in the fractions 30–3 and <3 kDa, while in A2 more than 70% were present in the fraction less than 3 kDa. Overall, obtained data strongly suggests that A2 is not cranberry-derived, or is adulterated with another source of PACs.

Removal of Dissolved Hydrophobic and Hydrophilic Organic Substances during Coagulation/Flocculation of Surface Waters

1993 ◽  
Vol 27 (11) ◽  
pp. 143-152 ◽  
Author(s):  
J. P. Croué ◽  
E. Lefebvre ◽  
B. Martin ◽  
B. Legube
Keyword(s):  
Molecular Weight ◽  
Surface Waters ◽  
Apparent Molecular Weight ◽  
Weight Fraction ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Hydrophobic Substances ◽  
Moderate Change ◽  
Final Effluent

Dissolved organic carbon (DOC) from raw and coagulated surface waters was fractionated at acidic pH using two superposed XAD 8 and XAD 4 resin columns, into three fractions : hydrophobic substances (i.e. humic substances) adsorbed on XAD 8, hydrophilic acids adsorbed on XAD 4 and “non-acid” hydrophilics which represent the organics contained in the final effluent. DOC of untreated waters was evenly split between the hydrophobic and hydrophilic fractions. The “non-acid” hydrophilics were generally as or slightly more abundant than the corresponding hydrophilic acids. For three of the six waters studied, DOC distribution was not modified after coagulation/clarification treatment. These waters also exhibited a low reduction in THMFP and TOXFP per unit of DOC after treatment. One water showed moderate change and two a significant change in DOC distribution. With the latter, a large decrease of their THMFP/DOC and/or TOXFP/DOC ratios was observed. As expected, the apparent molecular weight distributions(1000 daltons nominal membrane cutoff) have been shifted toward the low molecular weight fraction. Aluminum coagulation experiments were carried out on isolated humic, fulvic and hydrophilic acids. Humic acids were identified as the most reactive fraction, with a dramatical reduction of their THMFP/DOC and TOXFP/DOC ratios after coagulation. Fulvic and hydrophilic acids were found to react to the same extent with the coagulant, and showed comparable THMFP and TOXFP perunit of DOC before and/or after coagulation.

scholarly journals Chemoselective Lewis pair polymerization of renewable multivinyl-functionalized γ-butyrolactones

2017 ◽  
Vol 375 (2101) ◽  
pp. 20170003 ◽  
Author(s):  
Ravikumar R. Gowda ◽  
Eugene Y.-X. Chen
Keyword(s):  
Molecular Weight ◽  
Double Bond ◽  
High Molecular Weight ◽  
Organic Solvents ◽  
Lewis Acid ◽  
Room Temperature ◽  
Lewis Base ◽  
Functionalized Polymers ◽  
Molecular Weight Distributions ◽  
Weight Distributions

Multivinyl-functionalized γ-butyrolactones, γ-vinyl-γ-methyl-α-methylene-γ-butyrolactone ( γ VMMBL) and γ-allyl-γ-methyl-α-methylene-γ-butyrolactone ( γ AMMBL), have been synthesized from biorenewable ethyl levulinate and effectively polymerized by Lewis pairs consisting of an organic N -heterocyclic carbene Lewis base and a strong organo-Lewis acid E(C 6 F 5 ) 3 (E = Al, B). This Lewis pair polymerization is quantitatively chemoselective, proceeds exclusively via polyaddition across the conjugated α-methylene double bond without participation of the γ-vinyl or γ-allyl double bond, and produces high-molecular-weight functionalized polymers with unimodal molecular-weight distributions. The Al-based Lewis pair produces a polymer with approximately 5.5 times higher molecular weight than that produced by the B-based Lewis pair. The resulting vinyl-functionalized polymers are soluble in common organic solvents and stable at room temperature, and can be thermally cured into crosslinked materials. This article is part of the themed issue ‘Frustrated Lewis pair chemistry’.

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