Molecular weights between

Riazi s method applies to fractions whose specific gravities are less than 0.97 and whose boiling points are less than 840 K. The Lee and Kesler method is applicable for fractions having molecular weights between 60 and 650. 

A second family is based on isobutene polymers (PIB) having molecular weights from 600 to 2000 that are equally important raw materials for detergent additives. So as to render them reactive with the hydrophilic part, they can be chlorinated or condensed with the maleic anhydride. A third way is based on the utilization of polypropylphenols of molecular weights between 600 and 3000. 

These products have molecular weights between 2000 and 10,000, well below those of additives improving the viscosity index (100,000). They are added in very small concentrations (0.01 to 0.3 weight percent) and at these concentrations they can lower the pour point 30°C. 

Oxidation first produces soluble oxygenated compounds of molecular weights between 500 and 3000 that increase the viscosity of oil then they polymerize, precipitate, and form deposits. Oxidation also causes formation of low molecular weight organic acids which are very corrosive to metals. 

Method 2. The procedure described under Benzenesulphonyl Chloride, Method 2 (Section IV,206) may be used with suitable adjustment for the difierence in molecular weights between sodium p-toluenesulphonate (Section IV,30) and sodium benzenesulphonate. When the reaction product is poured on to ice, the p-toluenesulphonyl chloride separates as a sohd. This is filtered with suction it may be recrystaUised from hght petroleum (b.p. 40-60°) and then melts at 69°. 

As a polymer prototype consider an n-alkane molecule consisting of n methylenes and 2 methyl groups. How serious an error is made in M for different n s if the difference in molecular weight between methyl and methylene groups is ignored ... 

A cross-linked polymer has a density of 0.94 g cm" at 25°C and a molecular weight between crosslinks of 28,000. The conformation of one bond in the middle of the molecule changes from trans to gauche, and the molecule opens up by 120°. In w-butane, the trans to gauche transformation requires about 3.3 kJ mol". Estimate a value for AH of stretching based on this model, and use the law of cosines to estimate the magnitude of the opening up that results. 

Model Networks. Constmction of model networks allows development of quantitative stmcture property relationships and provide the abiUty to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionahty, and controlled molecular weight distribution of cross-linked chains. Sihcones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, ffl-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

Fig. 8. Lateral tip amplitude response vs. temperature curves for PS films 200-300 nm thick of molecular weights between 3 and 6500 kg/mol. Reprinted with permission from ref. [73].

For thermosets with molecular weight between crosslinks M, the crosslink density Px, is described by Px N /Mx- As Px increases, the nets become tighter and stiffer, and thus require more stress to break via... 

The properties of styrenic block copolymers are dependent on many factors besides the polymerization process. The styrene end block is typically atactic. Atactic polystyrene has a molecular weight between entanglements (Me) of about 18,000 g/mol. The typical end block molecular weight of styrenic block copolymers is less than Mg. Thus the softening point of these polymers is less than that of pure polystyrene. In fact many of the raw materials in hot melts are in the oligomeric region, where properties still depend on molecular weight (see Fig. 1). 

To determine the crosslinking density from the equilibrium elastic modulus, Eq. (3.5) or some of its modifications are used. For example, this analysis has been performed for the PA Am-based hydrogels, both neutral [18] and polyelectrolyte [19,22,42,120,121]. For gels obtained by free-radical copolymerization, the network densities determined experimentally have been correlated with values calculated from the initial concentration of crosslinker. Figure 1 shows that the experimental molecular weight between crosslinks considerably exceeds the expected value in a wide range of monomer and crosslinker concentrations. These results as well as other data [19, 22, 42] point to various imperfections of the PAAm network structure. 

Analysis of data pertaining to the modulus of PEO gels obtained by the polyaddition reaction [90] shows that even in this simplified case the network structure substantially deviates from the ideal one. For all samples studied, the molecular weight between crosslinks (M p) exceeds the molecular weight of the precursor (MJ. With decreasing precursor concentration the M xp/Mn ratio increases. Thus, at Mn = 5650 a decrease in precursor concentration from 50 to 20% increases the ratio from 2.3 to 12 most probably due to intramolecular cycle formation. 

The presence of long chain branches in low density polyethylene (LDPE) accounts for the difference in properties e.g. higher melt strength, greater toughness for the same average molecular weight) between LDPE and linear low density polyethylene (LLDPE, made by coordination polymerization). 

Recently, Tong et al. [195] have shown that in methyl methacrylate-b-alkyl acrylate-b-methyl methacrylate (MAM) and SIS-type triblock copolymers, the ultimate tensile strength is inversely proportional to the molecular weight between the chain entanglements in the middle soft block at comparable proportion of the outer block. 

Swelling data and stress-strain results in SBS have shown that Me is approximately the molecular weight between entanglements. Choudhury and Bhowmick [201] have shown in the case of different NR-based TPEs the following relation ... 

Tong J.D. and Jerome R., Dependence of the ultimate tensile strength of thermoplastic elastomers of the triblock type on the molecular weight between chain entanglements of the central block. Macromolecules, 33, 1479, 2000. 

FIGURE 24.6 Specific volume as a function of temperature at the indicated pressures for 1,2-PB network (molecular weight between cross-hnks 8 kg/mol) [81]. The solid squares denote the glass transition defined from the intersection of the glassy and liquid data. 

Iron dextran injection contains a complex of iron hydroxide with dextrans of average molecular weight between 5000 and 7000, and is used for the treatment of iron-defieiency anaemia in situations where oral therapy is ineffeetive or impractical. The sodium salt of sulphurie aeid esters of dextran, i.e. dextran sodium sulphate, has anti-eoagulant properties eomparable with heparin and is formulated as an injection for intravenous use. 

The nonionic monomer can be acrylamide, N,N-dimethylacrylamide, N-vinyl-2-pyrrolidone, N-vinyl acetamide, or dimethylamino ethyl methacrylate. Ionic monomers are AMPS, sodium vinyl sulfonate, and vinylbenzene sulfonate. The terpolymer should have a molecular weight between 200,000 to 1,000,000 Dalton. 

---