Molecular Weight Distribution of Polystyrene and of Butadiene-Styrene Copolymers Prepared in Emulsion Systems

1970 ◽  
Vol 43 (6) ◽  
pp. 1424-1438
Author(s):  
C. A. Uraneck ◽  
J. E. Burleigh

Abstract Polystyrene and butadiene—styrene copolymers (SBR) were parepared in emulsion systems with a homologous series of commercial mercaptan modifiers. The molecular weight distribution (MWD) of the sets of polymers changed in a consistant manner when the regulating index of the mercaptan was relatively low. However the shape of the MWD curves appeared distorted in comparison to theoretical curves when the modifier depleted rapidly and when divinyl-benzene was present in the system. The divergence from the theoretical curve is attributed to a higher degree of branching in the high molecular weight fractions. Differences in MWD of SBR made with n- and tert-dodecyl mercaptans was marked. Notable differences were also found for SBR 1500 samples from the industry at random, but only slight differences were seen in a set of SBR 1503 samples. This study shows how the MWD of polymers prepared in emulsions can be varied simply by use of modifiers with different regulating indexes.

1970 ◽  
Vol 43 (6) ◽  
pp. 1439-1450 ◽  
Author(s):  
W. V. Smith ◽  
S. Thiruvengada

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.


1967 ◽  
Vol 40 (2) ◽  
pp. 590-601 ◽  
Author(s):  
F. C. Weissert ◽  
B. L. Johnson

Abstract More than a million miles of tire testing is generally required to prove the utility of a new elastomer. For example, such a program has recently demonstrated that an alkyllithium solution polymerized butadiene styrene copolymer (Duradene rubber) has improved abrasion resistance over that of emulsion SBR1. It is, thus, extremely important to find meaningful relationships between the structure of an elastomer and its commercial importance to further guide the polymer chemist toward the development of new general purpose or specific application elastomers from laboratory sample through to final tire evaluation. Butadiene homopolymers and butadiene styrene copolymers prepared by alkyllithium catalysis in hydrocarbon solution offer unique opportunities to relate basic polymer structure parameters to tire compound performance. Their mixed micro-structure (cis-1, 4, trans-1, 4, and vinyl) preclude crystalline transitions which would otherwise complicate the interpretation of structural behavior. Furthermore, this polymerization system permits the production of controlled and specific variations in molecular weight distribution and degree of branching. n-Butyllithium catalyzed 1, 4-polybutadiene with its mixed microstructure and high cis-1, 4-polybutadiene have both shown outstanding abrasion resistance, especially under conditions of severe tire service. There is as yet no generally clear molecular interpretation for the outstanding abrasion resistance of the 1, 4-polybutadienes. For reasons of both improved processing and increased wet traction, these 1, 4-polybutadienes are seldom used alone but are blended with either natural rubber or SBR plus large amounts of extending oils. As a start, using as few fundamental concepts as possible, attempts were made to relate the industrial processing, heat build up, traction, and abrasion resistance characteristics of amorphous elastomers to two features measurable in terms of molecular parameters. The macrostructure (molecular weight distribution and branching) of the polymer is especially related to processing behavior. The glass temperature, Tg, of a polymer characterizes both the temperature and rate of deformation conditions in which the polymer exhibits rubbery behavior. Hence, the polymer Tg is directly related to both heat build-up and failure characteristics of an elastomer. Thus we shall be mostly discussing polymer structure in just two terms (i) macrostructure and (ii) Tg.


2019 ◽  
Vol 78 ◽  
pp. 02004
Author(s):  
Tingting Li ◽  
Yan Yang ◽  
Linjun Chen ◽  
Wanling Yang

The physicochemical properties of Phellinus baumii polysaccharides extracted from the fruiting bodies by different grinding methods were studied in this paper. Compared with ordinary grinding methods, superfine grinding technology exerts significantly higher yields of crude polysaccharides, polysaccharide contents and β-Glucan contents of six samples. HPSEC-MALLS- RI analysis shows the molecular weight distribution of P.baummii crude polysaccharides, which indicates superfine grinding technique generates higher molecular weight fractions and larger polydispersities. The 6 kinds of crude polysaccharides have obvious effects on NO generation of RAW264.7 cells, which indicated that crude polysaccharides from P.baumii may have some immune-enhancing effects. Meanwhile, CW30 and FP30 show the best immune enhancing effects. However, CW50 and CW70 exert weaker immune-enhancing effects compared with FP50 and FP70.


1961 ◽  
Vol 39 (10) ◽  
pp. 1888-1891 ◽  
Author(s):  
W. R. Blackmore ◽  
W. Alexander

An apparatus is described for fractionating large quantities (400 g) of polythene into five roughly equal fractions using a fractional precipitation technique. Application of this method of fractionation to a linear polythene has shown that the width of the molecular-weight distribution of the successive fractions decreases as the fractionation proceeds. Consequently, the initial high-molecular-weight fractions require refractionation to produce equally narrow distributions in them as are found in later fractions. Good agreement is obtained with the experimentally determined values of the number-average and weight-average molecular weight for the parent polymer when the measured values of Mn and Mw for each fraction are used to calculate the values for the parent. The differential molecular-weight distribution function of the parent polymer was calculated on a Bendix G-15 computer from the data for the fractions by using the weight, number-average and weight-average molecular weight, measured for each fraction in conjunction with an assumed log-normal or negative binomial molecular-weight distribution function in each fraction.


1993 ◽  
Vol 71 (6) ◽  
pp. 779-789 ◽  
Author(s):  
Ronald W. Thring ◽  
Esteban Chornet ◽  
Ralph P. Overend

Thermal organosolv glycol lignins and their fractions have been characterized by means of elemental composition, molecular weight distribution, and 1H and 13C NMR spectroscopy. Fractionation of each lignin by sequential solvent extraction produced fractions of increasing molecular weight and polydispersity. Structures in the highest molecular weight fractions were found to be linked by a high proportion of β-O-4 type bonds, whilst the lowest molecular weight fractions consisted of a high content of saturated aliphatic side-chain structures. A noticeable difference in the content of carbohydrate contaminants in both starting lignins indicated the formation of relatively stable lignin–carbohydrate complexes, especially in the lignin recovered from pretreated wood. In addition, depolymerization of the lignins and their fractions to monomeric compounds was explored using alkaline hydrolytic and nitrobenzene oxidative routes. The highest molecular weight fractions from each lignin were identified as the best candidates for production of useful monomeric phenolic compounds.


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