COMPOSITIONAL HETEROGENEITY OF BUTADIENE–ACRYLONITRILE COPOLYMERS PREPARED IN EMULSION AT 5°C

1951 ◽  
Vol 29 (3) ◽  
pp. 253-269 ◽  
Author(s):  
W. H. Embree ◽  
J. M. Mitchell ◽  
H. Leverne Williams
Keyword(s):  
Molecular Weight ◽  
Weight Distribution ◽  
Viscosity Data ◽  
Reactivity Ratios ◽  
Compositional Heterogeneity ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Conventional Solution ◽  
Acrylonitrile Copolymers ◽  
Butadiene Styrene

The copolymerization of butadiene and acrylonitrile is very similar to the copolymerization of butadiene and styrene. Polymers predominantly butadiene may be studied by conventional solution techniques but the study of polymers rich in acrylonitrile requires improved solvents for these materials. Polymerization rates are greatest for monomer ratios approximating equal proportions. The mercaptan modifier disappears much more slowly than in the butadiene–styrene system, the regulating index approximating unity. The number average molecular weights calculated from the mercaptan disappearance curves indicate uniform polymer molecular weights to relatively high conversions after which there is a decrease. The viscosity data indicate a rise in viscosity with conversion, which effect is overcome for charges rich in acrylonitrile by the lessening of branching, the more rapid disappearance of mercaptan at high conversion, and the tendency of polymers containing over 50% acrylonitrile to show very low dilute solution viscosities in the solvents tested. Viscosity molecular weights have been calculated and estimates of the molecular weight distribution made. These distributions appear to be quite narrow and the usual broadening at higher conversions is prevented by the increased modifier consumption and increased vinyl content of the polymer prepared with 50 parts acrylonitrile in the charge. The bound acrylonitrile has been determined at various conversions and the reactivity ratios have been found to be r1 = 0.28 and r2 = 0.02 for emulsions and r1 = 0.18 and r2 = 0.03 for oil phase portion only. Q is 0.74 and e is 1.47 as calculated by the Alfrey–Price equations.

The Structure of Neoprene. I. The Molecular-Weight Distribution of Neoprene Type GN

1949 ◽  
Vol 22 (3) ◽  
pp. 680-689
Author(s):  
W. E. Mochel ◽  
J. B. Nichols ◽  
C. J. Mighton
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Osmotic Pressure ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Distribution Curve ◽  
Pressure Measurements ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Good Agreement

Abstract Polychloroprene rubber (Neoprene Type GN) was fractionated by partial precipitation from dilute solution in benzene and the fractions were examined both osmotically and viscometrically in benzene solutions. The molecular-weight distribution curve for Neoprene Type GN based on osmotic pressure measurements shows a pronounced maximum at 100,000, but has a long extension to molecular weights of over one million, indicating the presence of branched or cross-linked material which is still soluble. The uniformity is somewhat less than that of sol natural rubber, while in shape the Neoprene distribution curve resembles more closely that of peptized natural rubber than fresh sol rubber. Observed variations in the slopes of the π/c vs. c and the ηsp/c vs. c curves also indicate the presence in solution of complex, branched and (or) cross-linked molecules. Calibration of the intrinsic viscosity-molecular weight relationship by osmotic pressure measurements gave good agreement with the equation: [η]=KMa, where K=1.46×10−4 and a=0.73.

THE COMPOSITIONAL HETEROGENEITY OF BUTADIENE-STYRENE COPOLYMERS SYNTHESIZED AT −18°C. IN EMULSION

1951 ◽  
Vol 29 (3) ◽  
pp. 270-283 ◽  
Author(s):  
R. J. Orr ◽  
H. Leverne Williams
Keyword(s):  
Transfer Reaction ◽  
Chain Transfer ◽  
Polymerization Temperature ◽  
Viscosity Data ◽  
Compositional Heterogeneity ◽  
Molecular Weights ◽  
Styrene Copolymers ◽  
Chain Transfer Reaction ◽  
Molecular Weight Heterogeneity ◽  
Butadiene Styrene

A study has been made of butadiene-styrene copolymers formed at −18°C. From analyses for bound styrene in the product for various conversions and initial butadiene-styrene ratios the reactivity ratios were calculated to be r1 = 1.37 and r2 = 0.38 compared with 1.8 and 0.6 at 45°C. Q and e for butadiene were 1.38 and 0.008 relative to styrene at 1 and −0.8. Increment bound styrene curves calculated for each stage of the reaction indicated that the polymers were remarkably homogeneous at low conversions. The chain transfer reaction using mixed tertiary mercaptans as the modifier was studied. Regulating indices were found to have decreased with polymerization temperature. Number average [Formula: see text] and viscosity average [Formula: see text] molecular weights were calculated from mercaptan disappearance and vistex intrinsic viscosity data respectively. The molecular weight heterogeneity increased with increasing conversion and initial mercaptan content. The increment number average molecular weights were found to diminish with conversions, whereas the increment viscosity average increased at higher conversions as conversion increased.

scholarly journals Matrix-graph model of the polymer materials destruction process

2018 ◽  
Vol 80 (3) ◽  
pp. 50-55
Author(s):  
A. A. Khvostov ◽  
S. G. Tikhomirov ◽  
I. A. Khaustov ◽  
A. A. Zhuravlev ◽  
A. V. Karmanov
Keyword(s):  
Mathematical Model ◽  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Graph Model ◽  
Polymer Materials ◽  
Simulation Environment ◽  
Destruction Process ◽  
Molecular Weights ◽  
The Mathematical Model

The paper deals with the problem of mathematical modeling of the process of thermochemical destruction using the theory of graphs. To synthesize a mathematical model, the Markov chain is used. For the formalization of the model a matrix-graph method of coding is used. It is proposed to consider the process of destruction as a random process, under which the state of the system changes, characterized by the proportion of macromolecules in each fraction of the molecular mass distribution. The intensities of transitions from state to state characterize the corresponding rates of destruction processes for each fraction of the molecular weight distribution (MWD). The processes of crosslinking and polymerization in this work have been neglected, and it is accepted that there is a probability of transition from any state with a lower order index (corresponding to fractions with higher molecular weights) to any state with a higher index (corresponding fractions with lower molecular weights). A computational formula is presented for estimating the number of arcs and model parameters from a given number of fractions of the molecular weight distribution of the polymer. An example of coding in a matrix form of a graph model of the process of degradation of polybutadiene in solution for the case of six fractions of the molecular weight distribution is shown. As the simulation environment, the interactive graphical simulation environment of MathWorks Simulink is used. To evaluate the parameters of the mathematical model, experimental studies of the degradation of polybutadiene in solution were carried out. The chromatography of the polybutadiene solution was used as the initial data for the estimation of the MWD polymer. The considered matrix-graph representation of the structure of the mathematical model of the polymer destruction process makes it possible to simplify the compilation of the model and its software implementation in the case of a large number of vertices of the graph describing the process of destruction

scholarly journals Water vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

2021 ◽  
Author(s):  
Maciej Łojkowski ◽  
Adrian Chlanda ◽  
Emilia Choińska ◽  
Wojciech Swieszkowski
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Self Assembly ◽  
Secondary Phase ◽  
Honeycomb Structure ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Secondary Phase Separation

<p>The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.</p>

EFFECTS OF FRESH PLASMA OR WHOLE BLOOD TRANSFUSIONS ON PATIENTS WITH VARIOUS TYPES OF MUCOPOLYSACCHARIDOSIS

PEDIATRICS ◽  
1972 ◽  
Vol 50 (5) ◽  
pp. 688-692
Author(s):  
Anatole S. Dekaban ◽  
Kenton R. Holden ◽  
George Constantopoulos
Keyword(s):  
Molecular Weight ◽  
Weight Distribution ◽  
Whole Blood ◽  
Blood Transfusions ◽  
Molecular Weights ◽  
The Third ◽  
Clinical Observations ◽  
Before And After ◽  
Fresh Plasma

Repeated fresh plasma or whole blood transfusions were given to five patients with either Hurler, Hunter, or Sanfilippo types of mucopolysaccharidosis. Clinical observations and total 24-hour urinary AMPS and their composition and molecular weight distribution were determined before, during, and after transfusions. The two patients who received plasma transfusions showed no noticeable change in the amount of AMPS excreted; of the three patients who received whole blood transfusions, two had slightly less excretion of AMPS while the third showed no difference. The AMPS in the CSF were measured in one patient before and after blood transfusions and found to be unchanged; likewise, the determination of molecular weights in the isolated AMPS was virtually identical. In the patients studied, the transfusions caused no demonstrable difference in the patients' clinical condition.

THE VISCOSITY – MOLECULAR WEIGHT RELATION FOR POLY-levo-2,3-BUTANEDIYL o-PHTHALATE

1948 ◽  
Vol 26b (12) ◽  
pp. 783-797
Author(s):  
R. W. Watson ◽  
N. H. Grace
Keyword(s):  
Molecular Weight ◽  
High Purity ◽  
Molecular Orientation ◽  
Degree Of Polymerization ◽  
Solution Viscosity ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Complex Relation ◽  
End Group ◽  
Long Chain

The inherent viscosities of dilute solutions of acidic polyesters of high purity have been compared with number average molecular weights accurately determined by end-group titration. For unfractionated resins with a degree of polymerization from 2 to 11 [Formula: see text] the viscosity – molecular weight relation is linear in chloroform at 25 °C. Where [Formula: see text], K = 1.923 × 10−5 and β = 0.0176. For fractionated polyesters from DP 5 to 8, K = 1.959 × 10−6 and β = 0.0161. For unfractionated resins with a DP > 11, molecular weights increase more rapidly than inherent viscosities. Above [Formula: see text] for fractionated resins linearity is resumed, and the slope increases. Several attempts have been made to explain this complex relation. Apparently the short chains remain linear, and the formation of anisotropic fibers at a DP close to 100 establishes a degree of molecular orientation in the long-chain superpolyesters. Isomerization of levo-diol to the diastereoisomer during polycondensation is without effect on the dilute solution viscosity of the resulting resin. Preferential degradation of the longer chains is assumed to be partially responsible for the decreasing slope from DP 11 to 65. As yet it has not been possible to assess the roles played by changes in size distribution, and variation in solvation with increasing chain length, but the data point to a curved viscosity – molecular weight relation in chloroform at 25 °C.

Equilibrium Molecular Weight Distribution of Cyclic and Linear Methylsiloxanes

1967 ◽  
Vol 40 (4) ◽  
pp. 1084-1093 ◽  
Author(s):  
Jack B. Carmichael ◽  
James Heffel
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Equilibrium Constants ◽  
Molecular Size ◽  
Size Distributions ◽  
Flory Theory ◽  
Molecular Weights ◽  
Cyclic Molecules

Abstract Data are reported for the equilibrium molecular size distributions of cyclic and linear methylsiloxanes in five polymers with number average molecular weights ranging from 459 to 1348. The distributions of linear species agree with the earlier work of Scott and agree reasonably well with the Flory theory of random reorganization. The amounts of cyclic molecules are sharply dependent on molecular weight. However, the equilibrium constants for cyclic formation for cyclic species with four to eight units are shown to be virtually identical with the equilibrium constants for cyclic formation in high molecular weight polymers reported in a previous publication. For octamethylcyclotetrasiloxane, Kav in moles of siloxane units per liter was found to be 0.72 in this study. For high polymers, Kav was previously reported to be 0.74.

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