Number average molecular weight


This quantity is called the weight average molecular weight, reflecting the chemist s customary carelessness about distinguishing between mass and weight, and is given the symbol M. By contrast, the mean, where number fractions are used, is called the number average molecular weight and is given the symbol M .  [c.37]

This result shows that the square root of the amount by which the ratio M /M exceeds unity equals the standard deviation of the distribution relative to the number average molecular weight. Thus if a distribution is characterized by M = 10,000 and a = 3000, then M /M = 1.09. Alternatively, if M / n then the standard deviation is 71% of the value of M. This shows that reporting the mean and standard deviation of a distribution or the values of and Mw/Mn gives equivalent information about the distribution. We shall see in a moment that the second alternative is more easily accomplished for samples of polymers. First, however, consider the following example in which we apply some of the equations of this section to some numerical data.  [c.39]

Table 1.5 lists the different molecular weight averages most commonly encountered in polymer chemistry. Table 1.5 also includes the definition of these averages for easy reference, some experimental methods that produce them, and cross-references to sections of this volume where the specific techniques are discussed. Note that end group analysis produces a number average molecular weight, since it is a technique based on counting. This is especially evident when we compare end group analysis with the procedure for evaluating M in Example 1.5. In the latter, is given by dividing the total mass of the sample by the total number of moles of polymer it contains. This is exactly what is done in end group analysis.  [c.41]

In the next section we shall describe the use of Eq. (8.83) to determine the number average molecular weight of a polymer, and in subsequent sections we shall examine models which offer interpretations of the second virial coefficient.  [c.546]

The algebra and arithmetic of this section have led us to the correct conclusions, but the underlying physical reality may be obscured by all these manipulations. The situation is simply this In the complete absence of indifferent electrolyte, the polymer ion and its counterions are restricted to the same phase. The polymer is held back by the membrane, the counterions are held back by electroneutrality. The polymer side of the membrane, therefore, contains z + 1 mol of solute particles for every molar mass of polymer introduced. Since osmotic pressure gives a number average molecular weight, Eq. (8.127) is the logical result. With a sufficiently large excess of indifferent electrolyte, the small ions effectively swamp out the charge contributed by the polymer, and the latter behaves as if it were uncharged.  [c.575]

In the propagation reaction, the monomer molecule reacts with an existing free-radical polymer chain end to make the chain one repeat unit longer. The polymer chains have two active ends, and they grow from both ends at the same time. Under normal coating conditions, the consumption of monomer by propagation must be much higher than its consumption by initiation to obtain high molecular weight polymer. In fact, the number-average molecular weight is determined by the proportion of monomer consumed by the two reactions, and is diminished by increases in deposition temperature or monomer partial pressure.  [c.433]

The number-average molecular weight of most commercially available acetal resins is between 20,000 and 90,000. Weight-average molecular weight may be estimated from solution viscosities.  [c.57]

Fiber dyeabiUty is critically dependent on molecular weight distribution of the polymer because most acryhc fibers derive their dyeabiUty from sulfonate and sulfate initiator fragments at the polymer chain ends. Thus the dye site content of the fiber is inversely related to the number average molecular weight of the polymer and very sensitive to the fraction of low molecular weight polymer. A critical balance must be maintained between the molecular weight distribution required for good rheological properties and the distribution required for good fiber dyeabiUty. Where such a balance caimot be achieved it is usual practice to incorporate one of the sulfonated monomers as a means of estabUshing the required fiber dyeabiUty. Du Font s Odon 42, for example, is beheved to contain a small amount of sodium styrene sulfonate as a supplemental dye receptor. The very dense fiber stmcture, produced by Du Font s dry spinning process, results in very low dye diffusion rates. The addition of a sulfonated monomer, therefore, compensates by increasing the total dye site content of the fiber.  [c.276]

The extrusion of olefin fibers is largely controlled by the polymer. Polyolefin melts are strongly viscoelastic, and melt extmsion of polyolefin fibers differs from that of polyesters and polyamides. Polyolefins are manufactured in a broad range of molecular weights and ratios of weight-average to number-average molecular weight (M /MJ. Unlike the condensation polymers, which typically have molecular weights of 10,000—15,000 and MJM of approximately 2, polyolefins have weight-average molecular weights ranging from 50,000 to 1,000,000 and, as polymerized, MJM ranges from 4 to 15. Further control of molecular weight and distribution is obtained by chemical or thermal degradation. The full range of molecular weights used in olefin fiber manufacture is above 20,000, and MJM varies from 2 to 15. As molecular weight increases and molecular weight distribution broadens, the polymer melt becomes more pseudoplastic as indicated in Table 4 and shown in Figure 7 (30). In the sizing of extmsion equipment for olefin fiber production, the wide range of shear viscosities and thinning effects must be considered because these affect both power requirements and mixing efficiencies.  [c.316]

In general, esterification is conducted in one or two vessels forming low molecular weight oligomers with a degree of polymerization of about 1 to 7. The oligomer is pumped to one or two prepolymerization vessels where higher temperatures and lower pressures help remove water and 2G the degree of polymerization increases to 15 to 20 repeat units. The temperatures are further increased and pressures decreased in the final one or two vessels to form polymer ready to spin into fiber. For most products, the final degree of polymerization is about 70 to 100 repeat units. Number average molecular weight is about 22,000 weight average molecular weight is about 44,000. Typical process conditions are shown in Figure 2.  [c.328]

Gel permeation chromatography can be used to determine the molecular weight and molecular weight distribution of polyester polymers. Polymer molecular weight can also be evaluated using wet chemistry techniques. Polyester polymers are dissolved in strong solvents such as phenol, o-chlorophenol, dichloroacetic acid, tetrachloroethane—phenol mixtures, and hexafluoro-2-propanol (17,47,49). Relative viscosities, comparing the solution viscosity of polymer solutions at standard concentrations vs the solvent viscosity, are commonly used for quaUty assurance and control. Intrinsic viscosity, Tj, is measured from solution and several studies have correlated the number average molecular weight to intrinsic viscosity by a variety of mathematical equations (19,47,49,50).  [c.332]

The physical properties of PCTFE are primarily determined by a comhination of molecular weight and percent crystallinity. Because of the lack of suitable solvents, a correlation between the number average molecular weight and zero-strength time (ZST typical values of 200 to 400 s) has been developed (3,4). The high molecular weight thermoplastic has a melt temperature (T ) of 211—216°C, a glass-transition temperature (7p of 71—99°C (5), and is thermally stable up to 250°C. The useful operational temperature range is considered to be from —240 to 200°C although an iacrease ia service temperature can be achieved through selected fiber filling of the polymer (fiber glass, from 1 to 20% weight of the fiber).  [c.393]

Typical hydrocarbon resins range in appearance from hard, britde soHds to viscous Hquids. They may come in flakes, pellets, dmms, or in molten form. Depending on appHcation requirements, many resins are available as solutions in organic solvents or oils. Anionic, cationic, or nonionic emulsion forms are also manufactured. Hydrocarbon resins typically have a number average molecular weight (M ) of less than 2000. The colors of these resins range from water-white to dark brown. Water-white resins usually are produced from the Lewis acid polymerization of pure olefinic monomers or by the hydrogenation of catalyticaHy or thermally produced precursors. Colors are determined on the Gardner and Saybolt scales.  [c.350]

Table 7 shows M and M (number-average molecular weight) values of kraft lignins and lignosulfates deterrnined by light scattering and vapor pressure osmometry, respectively. Kraft lignins invariably have lower molecular weights than lignosulfonates, indicative of a more extensive degradation of the lignin during the kraft pulping process.  [c.142]

T is the glass-transition temperature at infinite molecular weight and is the number average molecular weight. The value of k for poly(methyl methacrylate) is about 2 x 10 the value for acrylate polymers is approximately the same (9). A detailed discussion on the effect of molecular weight on the properties of a polymer may be found in Reference 17.  [c.261]

Molecular weights of polymers are determined by the weight—average molecular weight, and the number—average molecular weight, M. The  [c.368]

The dynamic shear behavior of the polymer melt can be used to determine the ratio of weight average, to number average, molecular weight (33).  [c.408]

In addition, dsc has been found suitable for the determination of second-order transitions (T = glass transition) and, in some cases, P-transitions. Procedures for the determination of T are discussed in the Hterature (105,106), which includes data on the dependence of T on number-average molecular weight (M for polymers. This shows a significant effect until a critical is reached with Htfle or no effect beyond. A technique employing dsc to measure specific heat of rapidly quenched polyethylene samples, which are subsequently annealed at low temperatures, shows the formation of secondary crystals that melt near the annealing temperature with small endotherms. The endotherms increase and melting points rise as time increases leading to the potential use of this technique for studying the thermal history of samples (107). Additional work on the correlation of enthalpy changes with the aging of samples has been completed on PBT (108). For amorphous polymers, changes in T can be used to determine aging that has occurred below and near T. Accuracy is improved by matching the heating rates of dsc to cooling rates on specimen preparation (105,106). The T response to aging relates to the continued relaxation of frozen molecular stmcture that continues over time below T and results in changes in free volume (118). Reduction in free volume due to aging can be correlated to reduced impact strength and improved creep response at low strain rates for polymers.  [c.150]

The number-average molecular weight is adjusted in the 12,000—15,000 range for apparel fibers, >20, 000 for high strength yams for tires and industrial end uses.  [c.250]

The addition of small, but specific, amounts of a monofunctional acid to the polymerization is often used to control molecular weights and catalyze reactions. The polymerization is controlled to produce a number-average molecular weight of 18,000—30,000, depending on the end use.  [c.251]

General Procedure of Base Catalysis. This yields a 3000 number-average molecular weight triol. In order to make this polyol in a reasonable amount of time, high temperature and consequendy high pressure are requited therefore a stainless steel autoclave reactor is employed instead of a glass apparatus. The reactor is nominally 3.78 L (1 gal) in size, and has the following features an oxide addition tube which extends to the bottom of the vessel and is pointed toward a high speed stirrer a means of adding the oxide at a constant rate such as a pump or a dow controller an inlet for vacuum or inert gas a means to monitor the temperature and pressure (the oxide feed rate should also be monitored to give reproducible results) a charge port to add starter and catalyst a water and steam inlet and oudet for cooling and heat a high speed stirrer a water jacket to help control the temperature and a discharge port.  [c.350]

Na" > > Cs". The amount of unsaturation also iacreases with number-average molecular weight (M ) suggesting that the rate of polymerisation  [c.352]

Termination. THF can be polymerised in the virtual absence of termination and transfer reactions. Under these conditions a living polymerisation results and the number-average molecular weight of the polymer produced can be calculated from the number of active sites introduced and the amount of polymer produced at equiUbrium. For many initiators, the number of active sites corresponds directiy to the number of moles of initiator used. In other cases, a number of methods are available that allows analytical determination of the number of active sites (6). In order to eliminate all termination and transfer reactions, it is necessary to carry out the polymerisation while carefully avoiding any adventitious impurities such as air or water. This is generally most easily accompHshed by working under high vacuum. In living polymerisations, the head group of the polymer is generally determined by the initiator, whereas the end group is a function of the method of termination chosen. Any strong nucleophile can be used for chain termination. For example, water leads to hydroxyl end groups ammonia gives amine end groups. Some counterions, such as the haUdes, are strong enough nucleophiles to prevent polymerisation. They can be used to terminate a polymerisation by addition at the desired time. Some counterions, such as BF or SbClg, are weak nucleophiles and their use results in slow chain termination during the course of the polymerisation, especially if used at room temperature or above. In the case of SbClg, the SbCl that forms upon termination can itself initiate a new active center. The net result is one of chain transfer. Termination by some nucleophiles allows the determination of the number of active sites that were present at the time of termination. Thus, the use of sodium phenoxide is followed by a uv analysis of phenoxide end groups (69), and triphenylphosphine permits analysis with P-nmr (31,66). Mercaptans or sulfides are also effective terminating agents. If a polymerizable cycHc sulfide is employed, a block polymer of PTHF and the cycHc sulfide results (168). No further polymerization of the THF occurs. The cycHc ether polymerization is effectively terrninated because sulfur is a much stronger nucleophile than oxygen.  [c.363]

Analytical and Test Methods. General analytical procedures are appHcable in most cases, although a number of specific test methods have been developed for the analysis of polyether glycols. One of the most important tests is the deterrnination of the hydroxyl number, ie, the number of milligrams of KOH (formula weight = 56.1) equivalent to the hydroxyl content of 1 g of the polymer diol sample (264). Because all the PTME chains are strictly difunctional, the number-average molecular weight is calculated from the hydroxyl number according to the following relation  [c.366]

Except when non drying alkyds are used strictly as plasticizers for other thermoplastic polymers, alkyd resins do not remain thermoplastic in their ultimate appHcations. The film integrity is largely derived after the resin molecules have been cross-Hnked, either through the unsaturation functionaHties on their fatty acid side chains, or through the reactions of their residual hydroxyl or carboxyl functionaHties with such cross-linking agents as amino resins or polyisocyanate materials. In a sense, alkyds are usually made and appHed as "B-stage" resins. Therefore, it is not necessary to build the molecules of alkyd resins to huge molecular weights, as one would for thermoplastic polymers. In fact, too high a molecular weight leads to poor solubiHty and high solution viscosity, and is undesirable for practical appHcations. Most pubHshed data show that the number average molecular weight of alkyds is less than 10,000. Nevertheless, within practical limits, it is stiU preferable to have a linear backbone stmcture and high molecular weight to give the best film-forming and film properties. Alkyd formulations with an equimolar ratio of dibasic acids and polyols tend to have the best chance of achieving a linear molecular stmcture and high molecular weight.  [c.36]

For higher molecular weight polydimethyl siloxanes (Af > 2500), the number-average molecular weight is related to the bulk viscosity by the foUowiag formula, where the viscosity units are mm /s(=cSt).  [c.51]

The number-average molecular weight of dimethylsiloxane can also be determined from the intrinsic viscosity [Tj, dL/g] (extrapolated to zero viscosity) ia toluene or methyl ethyl ketone according to the foUowiag equatioa (339,340)  [c.51]

Determination of Physical Properties. Common properties of siUcone polymers, such as refractive index, density, and viscosity, are measured using conventional techniques (488). Molecular weights can be determined by standard methods, provided suitable reference standards are available. Empirical viscosity/molecular weight correlations are also useful as a simple means of obtaining approximate molecular weights (489). End group analysis by suitable spectroscopic or chemical methods can give rehable number-average molecular weight data. Long-chain branching in siUcone polymers can be ascertained chemically, by determining the ratio of branch sites to end groups using degradation methods (444,445), or instmmentaHy, by measuring molecular size—viscosity relationships, for example, using a gpc instmment coupled to a differential viscometry or light-scattering detector (490,491). The level of cross-linking in siUcone polymers, quantified in terms of the average molecular weight of strands between cross-links, is often measured by solvent swelling or modulus measurements, which are related to the combined effects of physical and chemical cross-links (492,493). Chemical cross-links can be quantified by nmr techniques or be degradative analysis to determine actual concentrations of T and Q cross-link sites.  [c.60]

Ever since the demonstration that the initiation system of hydrogen iodide and molecular iodine (HI/I2) induces living polymerization of VE monomers (34), numerous studies have been performed to extend the scope of this type of VE polymerization, living polymerization is characterized by an increasing number-average molecular weight as the monomer is consumed. The rate of increase is inversely proportional to the initial concentration of hydrogen iodide, not iodine, and the molecular weight distribution (MWD) of the polymer is very narrow throughout the course of the polymerization M /< 1.1). Thus, this type of polymerization can be stopped and started by consumption or addition of fresh monomer. It is similar to ethylene oxide/propylene oxide (EO/PO) anionic polymerization in this regard, but the initiation system is longer Hved (see PoLYETPiERs).  [c.516]

Polyethylene Waxes. Low molecular weight (less than ca 10,000 Mn) polyethylenes [9002-88 ] having waxlike properties are made either by high pressure polymerisation or low pressure (Zeigler-type catalysts) polymerisation. AH the products have the same basic stmcture, but the processes yield products with distinctly different properties. Some polyethylenes have fairly low densities, owing to branching that occurs during the polymerisation. Molecular weight distributions, expressed as the weight average molecular weight divided by the number average molecular weight, or polydispersity, also varies widely among the different processes, as does the range of molecular weights available. Annual production in the United States is estimated at 100,000-140,000 t.  [c.317]

There has been significant progress in the development of polyesters for high soHds coatings. In contrast to acryHc resins, the preparation of low molecular-weight and hence high soHds polyesters, where substantiaUy aU of the molecules have a minimum of two hydroxyl groups is straightforward. The lower limit of the average molecular weight that is usehil in baking systems is controUed by the volatiHty of the lowest molecular weight fractions. Eor conventionaUy prepared polyesters, the optimum number-average molecular weight for baking enamels has been reported to be 800—1000 (29). Eurther improvements are achieved by synthetic techniques that give narrower molecular-weight distributions (30,31). Very narrow molecular-weight, linear.  [c.336]

Hydroxy-functional thermosetting acryhcs are widely used in baking enamels for automobile and apphance top coats, exterior can coatings, and coil coating. Research efforts have been directed at increasing the sohds content of such coatings while maintaining the exceUent properties. In contrast to polyesters, where virtually ah. molecules have at least two hydroxyl groups, synthesis of very low molecular-weight acryhc resins having an average functionahty of two to three and containing few molecules that are nonfunctional or only monofunctional is difficult. Eree-radical polymerization, the usual method for synthesizing thermosetting acryhcs, results in a random distribution of the 2-hydroxyethyl methacrylate (2-methyl-2-propenoic acid 2-hydroxyethyl ester) [868-77-9] C H qO, comonomer in the oligomer chains and hence significant fractions of nonfunctional and monofunctional molecules unless the number average molecular weight is on the order of 3500 or higher and the average functional monomers per molecule is on the order of three or higher (43).  [c.338]

Molecular Weight Determination and Solution Behavior. Molecular weight determinations using dilute solution viscosity measurements have been reported for ECH (23,24). Intrinsic viscosity is related to molecular weight by the Mark-Houwink equation [rj] = K, where K and a are measured experimentally. The molecular weight is a viscosity average molecular weight, but with the use of the required correction factors, the equation may be used to obtain the number average molecular weight, AfZ, and the weight average molecular weight MI (25). Constants have been  [c.555]

The statistical nature of the reaction leads to a distribution of polymer molecular weights. Figures quoted for molecular weights are thus averages of which different types exist. The number average molecular weight takes into account the numbers of molecules of each size when assessing the average whereas the weight average molecular weight takes into account the fraction of each size by weight. Thus the presence of 1% by weight of monomer would have little effect on the weight average but since it had a  [c.32]

While breadth, skewness and modality of a distribution are all of some interest the most important parameter is the average molecular weight. This however can be defined in a number of different ways. Conceptually the simplest is the number average molecular weight, invariably given the symbol This is essentially the same as the arithmetic mean molecular weight where the sum of the weights of all the molecules are divided by the number of molecules. This is the same as saying that is the sum of the product of the number fraction of each molecular weight ( ,) times the molecular weight (M,) i.e  [c.41]

In contrast to low-molecular-weight compounds and polymers with specific roles in biochemical processes, most polymers consist of similar molecules with different molecular weights. The mean value and the distribution of the molecular weight depend on the preparation conditions and decisively influence the material properties. Both quantities can be obtained from different teclmiques such as light scattering, viscosity measurements or gel penneation cliromatography. However, each teclmique provides a different average molecular weight [2]. The most important ones are the number average molecular weight  [c.2513]

The preceding discussion and example are based on the premise that classified molecular weight data are available. While this is sometimes the case, the average molecular weight of a polydisperse system is usually the information available to characterize the sample. The significant thing about this, however, is the fact that different experimental techniques yield different averages. We shall see in Chap. 8, for example, that osmostic pressure experiments can be interpreted to give the number average molecular weight in Chap. 10 we shall see that light scattering produces a weight average. Hence these different experimental methods applied to the same sample will provide and M, thus yielding some statistical information about the molecular weight distribution.  [c.41]

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice.  [c.505]

Polytetrafluoroethylene does not dissolve in any common solvent therefore, its molecular weight caimot be measured by the usual methods. A number-average molecular weight has been estimated by determining the concentration of end groups derived from the initiator. Earlier estimates, based on an iron bisulfite system containing radioactive sulfur, ranged from 142 x 10 to 534 x 10 for low molecular weight polymer. The same technique apphed to polymers of industrial interest gave molecular weights of 389 x 10 to 8900 x 10 (60,61). In the absence of a normal molecular weight determination method, an estimated relative molecular weight is used for all practical purposes. It is obtained by measuring the specific gravity following a standardized fabricating and sintering procedure (ASTM D1457-83). Because the rate of crystallization decreases with increasing molecular weight, samples prepared from the high molecular weight polymer and cooled from the melt at a constant slow rate have lower standard specific gravities than those prepared from low molecular weight polymer cooled at the same rate (62). The correlation between number-average molecular weight (M ) based on end group estimations, and standard specific gravity (SSG) is given by  [c.350]

The xyloglucan found in tamarind seeds has a greater molecular weight than that found in the cell walls but it does not contain L-fucose, acetyl, or pymvyl substituents. The latter probably plays a unique role in the development and growth of plants (112,115). Xyloglucan is polydisperse, the number-average molecular weight of the polymer from the cambium tissues of poplar and linden is 62,000 Daltons, and the distribution shows a pronounced left-hand skewness (108). A similar distribution was found for tamarind amyloid although the molecular weight was much greater (1.4 X 10 Daltons) (116).  [c.32]

Gumyl Potassium. Cumyl potassium [3003-91-6] (pif > 43 based on toluene) (6) is another useful initiator for anionic polymeri2ation of a variety of monomers, including styrenes, dienes, methacrylates, and epoxides. This carbanion is readily prepared from cumyl methyl ether as shown in equation 17 (93). It is necessary to remove the potassium methoxide salt which precipitates from the solution cooling to low temperature prior to filtration is recommended. The concentration of active initiating species can be determined by titration with standardi2ed acid or by using this initiator with a known amount of styrene monomer and measuring the number average molecular weight of the polymer assuming that one initiator moiety produces one polystyrene macromolecule. This initiator is generally used at low temperatures in a polar solvent such as THF, which limits the microstmcture of polydienes to low 1,4-contents.  [c.240]

The number-average molecular weight for typical bottie resin is between 24,000 and 31,000 daltons /mol. As has been stated, one of the most objectionable by-products of PET polymerization is acetaldehyde which affects the taste of cola drinks at concentrations as low as 60 ppb. The specification for acetaldehyde in the final product must not exceed 3 pg of acetaldehyde per Hter of headspace. The bulk of the acetaldehyde produced in the polymerization process is removed during the final SSP stage. Because blow mol ding is carried out well below 200°C, only minute amounts of aldehyde are formed at the last stage. Originally, bottie preforms weighed 60—70 g but this has been reduced to about 50 g. The lighter weight bottles have thinner walls so that during biaxial drawing excessive stress crystallization (opacity) again becomes a problem. As a result some manufacturers (115,116) have introduced copolymers of PET containing minor amounts (2—5 mol %) of such comonomers as isophthaUc acid or cyclohexanedimethanol to reduce the polymer melting point by about 4—12°C with a correspondingly lower tendency to crystallize. This solves unwanted opacity problems. Another problem which may arise is bottie peadescence due to microvoids in the bottle wall. These result from mechanical degradation due to excessive deformation rates during blow mol ding. Polyesters hydrolyze very rapidly at 280°C in the melt and rigorous polymer drying to a chip moisture content below 50 ppm moisture is necessary before any melt processing, such as the injection mol ding of bottle preforms. Some customers requite colored bottles for thein specific products, eg, certain popular noncola sodas are packed in pale green bottles. Melt-dyed polymers using U.S. PDA approved dyes are used to mold the preforms for colored bottles.  [c.296]

Molecular Weight. Unsaturated polyester resins are relatively low in molecular weight, and are formulated to achieve low working viscosities when dissolved in styrene. The normally falls between 1800—2500, although dicyclopentadiene and orthophthaUc resins can be usehil below this range. The molecular weight follows a Gaussian distribution curve (Fig. 3), the shape of which influences final solution viscosities. In phthaUc resins, the presence of a low molecular weight fraction is usually observed, whereas in high maleic resins, a high molecular weight shoulder is observed. This indicates significant glycol addition across the double bond to form a trifunctional reactant. Polymers having different chain lengths and compositions exist as a compatible mixture, the ratio of weight-average molecular weight M and number-average molecular weight (M ) is defined as the polydispersity, D. For (9-phthahc and isophthaUc resins, D is just over two, but higher molecular weight resins and resins containing high maleic levels are more polydisperse and the distribution curve becomes flatter as the resin viscosity increases.  [c.315]

Polymetallocarbosilanes. PolymetaHocarbosilanes having a number-average molecular weight of 700—100,000 can be prepared by reaction of polycarbosilane, /2 2 fx where R is H, or lower alkyl, with a tetraalkyl titanate, to give a mono-, di-, tri-, or tetrafunctional polymer  [c.152]

PVC molecular weights are usually determined in the United States using inherent viscosity or relative viscosity measured according to ASTM D1243 0.2 g/100 mL of cyclohexanone at 30°C. In Europe, iC values are used, measured at 0.5% in cyclohexanone. The relationship among inherent viscosity, iCvalue, number-average molecular weight (Af ), and weight-average molecular weight (Af for commercial grades of PVC is shown in Table 4.  [c.501]

An antioxidant such as phenyl-(3-naphth larnine, was then added to the latex (1.25 parts) prior to coagulation by salt—acid mixtures and drying of the mbber cmmb, which was compressed into 34-kg bales. The SBR produced by this recipe had a Mooney viscosity of about 50 and a number-average molecular weight M of 100,000—200,000.  [c.468]


See pages that mention the term Number average molecular weight : [c.68]    [c.543]    [c.163]    [c.316]    [c.336]   
Plastics materials (1999) -- [ c.32 , c.174 , c.206 , c.215 , c.236 , c.702 ]

Chemistry of Petrochemical Processes (2000) -- [ c.319 ]