Structure of Polybutadienes

1967 ◽  
Vol 40 (5) ◽  
pp. 1529-1543 ◽  
Author(s):  
W. S. Bahary ◽  
D. I. Sapper
Keyword(s):  
Light Scattering ◽  
Molecular Size ◽  
Structural Features ◽  
Melting Point Depression ◽  
Linear Polymers ◽  
Long Chain Branching ◽  
Molecular Weights ◽  
Catalyst Systems ◽  
Molecular Size Distribution

Abstract Polybutadienes made with six different catalyst systems were examined: (1) butyllithium, (2) “nickel-based”, (3) alfin, (4) “titanium-based”, (5) “cobalt-based”, and (6) free radical emulsion. The microstructure and macrostructure of the polybutadienes have been determined and are compared to the results published in the literature. These polybutadienes may be considered to be random terpolymers of cis, trans, and vinyl addition of butadiene. The glass transition temperature is specified by the vinyl content. The crystalline melting points of the high trans and also the high cis polybutadienes obey to a high measure Flory's equation for melting point depression of a random terpolymer. The molecular weights of the polybutadienes have been determined by light scattering and osmometry and the degree of long chain branching has been determined by the branching index, 〈g′〉. The macro-structural features of the linear polymers are confirmed by fractionation. However, the polydispersities calculated from fractionation data do not agree with those determined from light scattering and osmometry for the branched samples. The discrepancy is attributed to the method of characterization of the fractions. A distinction is made between molecular weight distribution and molecular size distribution.

Synthesis and characterization of macrocyclic poly(.-methylstyrene)

e-Polymers ◽  
2001 ◽  
Vol 1 (1) ◽  
Author(s):  
Dahai Dong ◽  
Thieo E. Hogen-Esch
Keyword(s):  
Size Exclusion ◽  
Careful Study ◽  
Coupling Reactions ◽  
Linear Polymers ◽  
High Dilution ◽  
Fractional Precipitation ◽  
Molecular Weights ◽  
Vinyl Polymers ◽  
High Concentrations

AbstractThe synthesis is described of macrocyclic poly(α-methylstyrene) (PAMS) by the lithium naphthalide initiated polymerization of AMS followed by high dilution end to end coupling with 1,4-bis(bromomethyl)benzene (DBX). The cyclization is carried out by simultaneous addition of tetrahydrofuran solutions of the PAMS dianion and DBX at about -100ºC. A sample of the matching linear PAMS is obtained by protonation of the PAMS dianion. The purified cycles are obtained by fractional precipitation that is monitored by size exclusion chromatograhy. A careful study of the coupling reactions carried out at high concentrations indicates that coupling is efficient and this is borne out by the ratios (<G>) of apparent molecular weights (MW’s) of cycles and matching linear polymers. The <G> values of the cycles tend to vary with MW in the same manner as was demonstrated for polystyrene and other vinyl polymers and increase from around 0.74 at MW of about 30000 to values of around 0.82 at MW of about 2500. A higher apparent <G> value was observed for a very low MW PAMS but this sample could not be purified and analyzed adequately. As was also observed for other macrocyclic vinylpolymers, the glass transition temperatures of the cycles are MW independent above MW of about 5000 but decrease sharply at lower MW’s.

Characterization of Landfill Leachates by Molecular Size Distribution, Biodegradability, and Inert Chemical Oxygen Demand

2009 ◽  
Vol 81 (5) ◽  
pp. 499-505 ◽  
Author(s):  
Míriam C. S. Amaral ◽  
Cynthia F. A. Ferreira ◽  
Liséte Celina Lange ◽  
Sérgio F. Aquino
Keyword(s):  
Chemical Oxygen Demand ◽  
Size Distribution ◽  
Oxygen Demand ◽  
Molecular Size ◽  
Landfill Leachates ◽  
Molecular Size Distribution

scholarly journals Molecular Growth Pathways in Silica Sol-Gel Polymerization

1988 ◽  
Vol 121 ◽  
Author(s):  
W. G. Klemperer ◽  
S. D. Ramamurthi
Keyword(s):  
Sol Gel ◽  
Molecular Size ◽  
Weight Fraction ◽  
Degree Of Polymerization ◽  
Partial Hydrolysis ◽  
Linear Polymers ◽  
Mole Percent ◽  
Molecular Weights ◽  
Low Degree ◽  
Acidic Conditions

ABSTRACTCapillary gas chromatography has been used to monitor the stoichi-ometries, structures, and abundances of low molecular weight polysilicate esters formed by partial hydrolysis of methanolic tetramethylorthosili-cate and redistribution of methanolie hexamethyoxydisiloxane under acidic (HC1) and basic (KOH) conditions. The polysilicate molecular size distributions, expressed in terms of mole percent of total silicon present as a function of degree of polymerization, show maxima near the number average degree of polymerization under acidic conditions. Under basic conditions, the distribution has its maximum at the monomer percent and extends to very high molecular weights, yielding a distribution far broader than the one observed under acidic conditions. These features are in agreement with covalent network theories of silica gelation, as opposed to particle aggregation theories. Weight fraction distributions of the type observed under acidic conditions are characteristic of linear polymers with a low degree of crosslinking and weight fraction distributions of the type observed under basic conditions are characteristic of branched polymers with high degree of crosslinking. The low degree of crosslinking obtained under acidic conditions is observed to arise from steric crowding that discourages branching in polysilicate structures.

Multiple scattering and the scattering of light by large or small molecules in solution

1965 ◽  
Vol 258 (1090) ◽  
pp. 387-420 ◽  
Keyword(s):  
Light Scattering ◽  
Small Molecules ◽  
Multiple Scattering ◽  
Additional Term ◽  
Molecular Size ◽  
Internal Field ◽  
Single Scattering ◽  
Particle Correlation ◽  
Molecular Weights ◽  
Two Component

The scattering equations for two-component fluids are formulated so that individual scattering processes take place in vacuo. A gauge transformation is made which transforms these processes to ones taking place in a medium of refractive index m. Certain previously controversial factors apparently associated with the internal field are thereby isolated and shown to be multiple scattering terms. The formulae for the scattered intensity and turbidity of a two-component fluid of small molecules are calculated by an entirely molecular argument; they agree with the forms usually quoted as Einstein’s formulae except that the additional term reported previously is confirmed. It is conjected that a very precise identity exists between the phenomenological and molecular treatments of scattering when multiple scattering is properly included. It is shown that the concept of an excess molecular polarizability in a two-component system of small molecules is valid only up to an approximation of single scattering: but the concept of excess scattering remains valid in the multiple scattering theory of such systems. It is also shown that without additional assumptions both these concepts cease to be valid even in the single scattering approximation when the solute molecules are large. These assumptions amount to a ‘uniform distribution’ (in a sense here specified) of the solvent round the solute in regions of radius of the order of iA: they can be interpreted as hydration (or solvation) conditions. From a crude model of a macromolecular solution it is suggested that the Debye corrections which derive from a finite molecular size to estimates of molecular weights determined by light scattering, could be in error by as much as 100% (~ 5% of molecular weights) or perhaps even more: estimates of molecular size by dissymmetry can also be in similar error. For a given solute, both these and the molecular weight corrections should vary from solvent to solvent. As this has not been reported experimentally, solutions of large molecules may satisfy the hydration conditions which are indeed shown to be both necessary and sufficient for the formal reduction of the scattering equations to Debye’s form. It may therefore, be possible to use light scattering to investigate the state of hydration of such molecules in a solvent and to investigate the three two-particle correlation functions of such systems.

Plasmin Digestion of factor VIII: Characterization of the Breakdown Products with Respect to Antigenicity and von Willebrand Activity

1978 ◽  
Vol 40 (02) ◽  
pp. 302-315 ◽  
Author(s):  
J A Guisasola ◽  
C G Cockburn ◽  
R M Hardisty
Keyword(s):  
Factor Viii ◽  
Biological Activities ◽  
Molecular Size ◽  
Progressive Increase ◽  
Gel Chromatography ◽  
Molecular Weights ◽  
Von Willebrand ◽  
Ristocetin Cofactor

SummaryHighly purified factor VIII was incubated for up to 24 hours in the presence of plasmin, and the biological activities and peptide structure of the digestion products determined at intervals. Procoagulant activity (VIIIC) was rapidly lost, but 17-32% of the initial ristocetin cofactor (VIIIR: WF) activity remained after 24 hours. Immunoelectrophoresis showed a progressive increase in rocket height and a concomitant increase in electrophoretic mobility of the factor-VIII-related antigen (VIIIR: AG). Crossed immunoelectrophoresis of the 24- hour digest showed three distinct precipitin arcs, of which the major one, with intermediate anodal mobility, gave reactions of non-identity with the other two. On sepharose gel chromatography the 24-hour digest gave three peaks: peak II contained about 80% of the residual VIIIR: WF and resolved on SDS-polyacrylamide gels into a series of peptides with apparent molecular weights between 125,000 and 185,000; these were reduced by mercaptoethanol to fragments of 15,000-80,000 daltons, a 65,000 dalton fragment being particularly strongly PAS positive. We conclude that large molecular size is not a prerequisite for VIIIR :WF activity, and that the presence of factor-VIII breakdown products may be a cause of misleading results in the determination of VIIIR:AG by immunoelectrophoresis.

Fractionation and characterization of lignin-carbohydrate complexes (LCCs) from eucalyptus fibers

Holzforschung ◽  
2011 ◽  
Vol 65 (1) ◽  
pp. 43-50 ◽  
Author(s):  
Jiebing Li ◽  
Raquel Martin-Sampedro ◽  
Cristiane Pedrazzi ◽  
Göran Gellerstedt
Keyword(s):  
Milling Time ◽  
Molecular Size ◽  
Solvent System ◽  
Tetrabutylammonium Hydroxide ◽  
Flax Fibers ◽  
Tetrabutylammonium Fluoride ◽  
Solvent Systems ◽  
Time Required ◽  
Molecular Size Distribution

Abstract The effect of milling time on the structure of lignin was investigated by analyzing the quantity and molecular size distribution of thioacidolysis products obtained from wood and pulp of eucalypt (Eucalyptus globulus). After milling, the ability of three solvent systems was determined to completely dissolve the wood or pulp meal. It was found that a mixture of DMSO and 50% aqueous tetrabutylammonium hydroxide was superior to either dimethylacetamide-LiCl or DMSO-tetrabutylammonium fluoride as solvent. By applying the minimum milling time required for complete dissolution, structurally unaltered wood or pulp could be further separated into lignin-carbohydrate fractions. These were analyzed by thioacidolysis. From eucalypt pulp, two different lignin-carbohydrate fractions were obtained, one glucan- and one xylan-enriched fraction, with the latter having more syringyl units in its lignin moieties. The developed solvent system seems to be universal because spruce and flax fibers and pulps could also be dissolved in it after milling.

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