THE FRACTIONAL PRECIPITATION OF GR-S: THE EFFECT OF CONCENTRATION OF THE SOLUTION ON THE EFFICIENCY OF FRACTIONATION

1953 ◽  
Vol 31 (9) ◽  
pp. 868-880
Author(s):  
L. H. Cragg ◽  
D. F. Switzer
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Intrinsic Viscosity ◽  
Average Molecular Weight ◽  
Conclusive Evidence ◽  
Careful Study ◽  
Dilute Solution ◽  
Fractional Precipitation

A careful study was made of the fractionation of GR-S (commercial poly(butadiene-co-styrene)) by stepwise precipitation, from solution in benzene, with the precipitant 50:50 (by volume) methanol-benzene. To determine the reproducibility of fractionation, particularly in the high-molecular-weight region, three runs were made with 2% solutions; and to determine the effect of concentration on efficiency, comparable fractionations were performed from solutions of three different concentrations—1, 2, and [Formula: see text] respectively. In each of the fractions the value of intrinsic viscosity, the viscosity slope constant β, and the viscosity-average molecular weight were determined. These provide conclusive evidence that in such a primary fractionation a much cleaner separation is accomplished from a dilute solution (1% or less).

Some Osmotic Measurements of the Molecular Weight of a High Molecular-Weight Fraction of Rubber Hydrocarbon

1955 ◽  
Vol 28 (2) ◽  
pp. 504-507
Author(s):  
G. W. Drake
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Average Molecular Weight ◽  
Weight Fraction ◽  
Considerable Proportion ◽  
Prolonged Storage ◽  
High Molecular Weight Fraction ◽  
The United Kingdom ◽  
Molecular Weight Fractions ◽  
Temperate Climates

Abstract Fractionation of the rubber hydrocarbon in temperate climates has usually resulted in high molecular-weight fractions, with a molecular weight of the order of one million. Bloomfield has shown that fresh latex contains a considerable proportion of hydrocarbon having an intrinsic viscosity (η) of 10 or over and, therefore, a molecular weight of well over 106. The fractionation technique used by Bloomfield in Malaya has now been applied by the writer to smoked sheet and to F rubber, working in the United Kingdom. No very high molecular-weight fractions were found in the smoked sheet, but the F rubber yielded a fraction of (η)=7.3 and a number average molecular weight 6×106, determined osmometrically. The average molecular weight of natural rubber when freshly prepared is probably well over a million, and includes a substantial portion having a molecular weight of several millions. By the time smoked sheet has reached temperate climates, the high molecular-weight portion has probably been converted to gel. F rubber, presumably because of its different method of preparation, retains the major part of its high molecular-weight material during prolonged storage.

Preparation and characterization of high molecular weight poly(trimethylene terephthalate) by solid-state polymerization

e-Polymers ◽  
2011 ◽  
Vol 11 (1) ◽  
Author(s):  
Kim Seok Hoon ◽  
Kim Joon Ho
Keyword(s):  
Molecular Weight ◽  
Reaction Time ◽  
Solid State ◽  
High Molecular Weight ◽  
Melting Temperature ◽  
Average Molecular Weight ◽  
Pellet Size ◽  
Solid State Polymerization ◽  
Trimethylene Terephthalate ◽  
High Molecular Weight Poly

AbstractSolid-state polymerization has been widely used to prepare high molecular weight poly(ethylene terephthalate). Solid-state polymerization is generally carried out by heating solid, melt-phase-polymerized polymer below its melting temperature but above its glass transition temperature. Solid-state polymerization of poly(trimethylene terephthalate)(PTT) is not an independent process but rather an additional process with respect to melt polymerization that is used when PTT of a higher molecular weight is required. Two kinds of commercial PTT chips were polymerized in the solid state to prepare high molecular weight PTT, which were characterized by end group contents, molecular weight, thermal analysis and X-ray diffraction. In the solid-state polymerization of PTT, the overall reaction rate was governed by the reaction temperature, reaction time and pellet size. The content of carboxyl end groups was decreased during the solid-state polymerization with increasing reaction time and temperature. The melting temperature and crystallinity of solid-state-polymerized PTT were higher at longer times and higher temperatures of polymerization. The activation energy for the solid-state polymerization of PTT was in the range of 24~25 kcal/mol for each chip. Through the solid-state polymerization of commercial PTT chips, we could get high molecular weight polymers up to an intrinsic viscosity value of 1.63 dl/g, which is equivalent to about a 117,000 weight-average molecular weight.

Cryoscopy in molten pyridinium chloride

1967 ◽  
Vol 20 (12) ◽  
pp. 2583 ◽  
Author(s):  
H Bloom ◽  
VC Reinsborough
Keyword(s):  
Solid Solution ◽  
Molecular Weight ◽  
High Molecular Weight ◽  
Heat Of Fusion ◽  
Dilute Solution ◽  
Pyridinium Chloride ◽  
Cryoscopic Constant

The molal cryoscopic constant in molten pyridinium chloride (m.p. 146.0�) has been found to be 17.4� (subject to confirmation by calorimetry) and the cryoscopic heat of fusion, 2310�40 cal mole-1. In pyridinium chloride as a solvent, iodides appear to dissociate completely while bromides do not yield the expected depression possibly because of solid solution. Tetraalkylammonium and alkyl-pyridinium halides of high molecular weight are ideally dissociated in extremely dilute solution but with increasing concentration apparently form micelles.

Molecular Weights and Intrinsic Viscosities of Polyisobutylenes

1943 ◽  
Vol 16 (3) ◽  
pp. 493-508
Author(s):  
Paul J. Flory
Keyword(s):  
Molecular Weight ◽  
Intrinsic Viscosity ◽  
Average Molecular Weight ◽  
Chain Structure ◽  
Molecular Weight Range ◽  
Molecular Weights ◽  
Satisfactory Precision ◽  
Heterogeneous Polymers ◽  
Definition Of

Abstract Experimental methods for fractionating polyisobutylene and for determining osmotic pressures have been described. The ratio π/c of osmotic pressure to concentration has been found in the case of cyclohexane solutions of polyisobutylene to vary nonlinearly with concentration, contrary to recent theories advanced by Huggins and the writer. The slope of this relationship appears to be independent of molecular weight. Reliable methods for extrapolating π/c to c=0 have been established, enabling the determination of absolute molecular weights with satisfactory precision up to values of about 1,000,000. Molecular weights of polyisobutylenes calculated from Staudinger's equation are too low; the discrepancy is more than ten-fold at high molecular weights. On the basis of data for carefully fractionated samples covering a two-hundred-fold molecular weight range, the intrinsic viscosity is found to be proportional to the 0.64 power of the molecular weight. This decided deviation from Staudinger's “law”cannot in this instance be attributed to nonlinear chain structure, as Staudinger has sought to do in other cases. This dependence of molecular weight on intrinsic viscosity leads to the definition of a “viscosity average”molecular weight which is obtained when the relationship is applied to heterogeneous polymers. The viscosity average is less than the weight average molecular weight, which would be obtained if Staudinger's equation were applicable, and greater than the number average obtained by osmotic or cryoscopic methods.

scholarly journals The presence of a high-molecular-weight (guanine-plus-cytosine)-rich segment at the 3' end of rabbit 28S ribosomal ribonucleic acid.

1975 ◽  
Vol 147 (3) ◽  
pp. 625-628 ◽  
Author(s):  
A A Hadjiolov ◽  
R A Cox ◽  
P Huvos
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Ribonucleic Acid ◽  
Average Molecular Weight ◽  
28S Rrna ◽  
Number Average Molecular Weight ◽  
Ribonuclease T1 ◽  
Naphthoic Acid ◽  
Rrna Molecule ◽  
Ribosomal Ribonucleic Acid

The 3′ hydroxyl end of 28S L-rRNA (major RNA species of the larger subribosomal particle) was labelled by coupling its 2-hydroxy-3-naphthoic acid hydrazine with diazotized [3H]aniline. The RNA was hydrolysed partially with ribonuclease T1 and fractionated on Sephadex G-200. The results show that a highly structured segment with 78% G+C content and a number-average molecular weight of at least 1.0×10(5)-1.8×10(5) is located at the 3′ hydroxyl end of the 28S rRNA molecule.

Isoprene and Rubber. XIX. The Molecular Size of Rubber and Balata

1930 ◽  
Vol 3 (3) ◽  
pp. 519-521 ◽  
Author(s):  
H. Staudinger ◽  
H. F. Bondy
Keyword(s):  
Molecular Weight ◽  
Organic Solvent ◽  
Average Molecular Weight ◽  
Molecular Size ◽  
Dilute Solution ◽  
Decomposition Products ◽  
Viscosity Measurements ◽  
Gutta Percha ◽  
Preceding Work

Abstract It was shown in the preceding work that a very dilute solution of balata in an organic solvent contains macromolecules in solution and not micelles. The same is true of rubber. On the basis of these findings it is possible to calculate the molecular weight of rubber and balata from viscosity measurements by means of the formula developed in a previous work: M=η8p/c. Km. The supposition is made that the molecules of rubber and balata have the form of threads and double threads, respectively. Also it is necessary to determine the constant KKm, and this may be calculated in the case of low molecular products, where the average molecular weight can be determined as well as the viscosity of the solutions. Such semi-colloidal decomposition products were obtained by heating rubber or gutta-percha in either tetralin or xylene. As shown by the following table the four samples thus obtained gave the constant: 0.3×10−3,5

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