The distinguishing feature of commercial polymers is that they have molecular weights far in excess of the entanglement molecular weight of about 10,000 gmole. The number average molecular weight of the polymer can be calculated by measuring the ratio of nmr absorptions of chain segments in a polymeric structure to those of nonpolymeric segments nearend groups. Despite a wealth of literature on the molecular weight effects on the mechanical properties of glassy polymers 1012, there is surprisingly little information addressing the role of molecular weight on the viscoelastic response of glassy polymers. For molecular weight determination, it is necessary to dissolve the polymer in an appropriate solvent and begin with a dilute solution. The molecular weight of a polymer introduction a po. Determine the viscosity average molecular weight of a polymer. The method is based on the measurement of the instantaneous values of zeroshearrate viscosity of the degrading polymer melt, and a formula is derived which enables the calculation of the initial value ofm w i. A single polymer molecule may consist of hundreds to a million monomers and may have a linear, branched, or network structure. We have investigated the ability of the fiser to make extensional viscosity measurements in such materials using a concentrated solution 5 wt% of high molecular weight polystyrene in a mixture of tricresyl phosphate and dioctyl phthalate tcpdop. Thus, samples of ps and all other polymers are polydispersed have a mixture of mws. The average molecular weight or molar mass of a polymer depends on the molecular weight distribution, which, in turn, depends on the type of monomer and the polymerization process conditions.
One is the gpc method 9,10,11, which usually conducted for cellulose derivatives. Intrinsic viscosity determination is used in the field of polymer chemistry, a chemistry subdiscipline which deals with the synthesis of polymers as well as the analysis of a polymer s structure and properties. An empirical blending law on complex viscosities is first developed. Sep 11, 2014 determination of molecular weight of polymers by ostwald viscometry slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Staudinger that first proposed that polymers are connected with covalent bonds. An astm designation number identifies a unique version of an astm standard.
Cambridge polymer group molecular weight determination. Ch2 ch ch2 ch ch2 ch ch2 ch staudinger got the nobel prize in chemistry in 1953. Introduction to physical chemistry laboratory chem 3851. Viscosity average molecular weight defines as \ref9, where m i is molecular weight and n i is number of molecules, a is a constant which depend on the polymer solvent in the viscosity experiments. From the value of intrinsic viscosity, the viscosity average molecular weight of the polymer can be calculated by using the equation. This equation was then used to predict the viscosity for molecular weights and concentrations used in this study. Arun experiment 5 lab report chem 3851 ecu studocu. Ppt polymers molecular weight powerpoint presentation.
Determination of the molecular weight distribution of linear. Determination of the molecular weight of a polymer from intrinsic viscosity measurements fig. Fifty milligrams of the gum was dissolved in 100 ml of water to get concentration of 0. Nmr method for the determination of the molecular weight of soybean oilbased polymers kenneth m. But since a solution is the basis for analysis using gpc, the technique is limited to thermoplastic, uncrosslinked polymers.
High resolution nmr technique was used for all measurements. As the molecular weight increases, the compound is more greaselike, and, if the mw is greater than about 6000, peg is a white solid. Solomon2 1 centre of research excellence in corrosion, research institute, king fahd university. Validation of gel permeation chromatographic method for determination of mn, mw, mv, mp, mz, mwd and intrinsic viscosity of polystyrene and other thf soluble polymers. Viscometry molecular weight is very important factor for the characterization of polymers. This method can be applied to narrow as well as broad. Astmd4001 standard test method for determination of weight. The intrinsic viscosity for the uncleaved polymer was calculated to be. Ep49879b1 system and method for determining molecular.
The use of solution viscosity data where ethylene polymers are known or suspected to contain colorants, carbon black, low molecular weight hydrocarbons, fillers, or other additives needs to be considered. Extraction, characterization, and molecular weight. Determination of viscosity average molecular weight of. Determination of molecular weight distributions for polymers.
Light scattering, for example, only yields the weight average molecular mass. Molecular weight determination chemistry libretexts. The appearance and everincreasing role of synthetic polymers in daily life has led to a greater scope of analytical methods for polymer characterization. In this work the intrinsic viscosity is determined by different methods being huggins taken as standard. A graph is drawn by plotting reduced viscosity against concentration and inherent viscosity against concentration. Determination of the molecular weight of a polymer. Rheological method for determining molecular weight and. The effect of polymer molecular weight on the microencapsulation variables was studied and published by jalil and nixon. When the complete mmd is available from gpc, any average molecular mass can be computed simply and easily.
Academy of sciences received 23 june 1964 the viscosity of polymers in the viscousflow state is dependent on molecular. Determination of molecular weight and molecularweight. Intrinsic viscosity has been measured as a parameter of the molecular weight of ha, and the relation between intrinsic viscosity and molecular weight is defined by the markhouwink equation. A new method for the direct molecular mass determination from sedimentation velocity experiments is presented. Measuring molecular weight of polymer from kinematic viscosity. For example, the zero shear viscosity is well known to depend on the weight average molecular weight to the 3. Viscositymolecular weight relation in bulk polymers i h. Determination of the molecular weight of a polymer from lec. The average molecular weight can be expressed as a number, weight, or viscosity average molecular weight. Chem355 experiment 6 viscosity of high polymer solutions.
It is applicable to all nonionic homopolymers linear or branched that dissolve completely without reaction or degradation to form stable solutions. Polymer molecular weight an overview sciencedirect topics. Molecular weight determination of polyethylene terephthalate. From this equation the molecular weight of a polymer can be determined from data on the intrinsic viscosity and vice versa. Initial attempts to determine the molecular weight of polymers were performed with natural polymers. Standard practice for dilute solution viscosity of polymers.
A theory of a twopoint rheometrical method of determination of the weight average molecular weightm w of polyamide6 is presented. A convenient lowresolutionnmr method for the determination. It is usually determined using size exclusion chromatography, but this is sometimes difficult and timeconsuming. Polymer molecular weight is defined as a distribution rather than a specific number because polymerization occurs in such a way to produce different chain lengths.
Standard test method for determination of properties of. There are a variety of analytical techniques used to characterize molecular weight in polymers, each providing useful information about the influence of molecular weight on the measured properties. Application of molecular rotors to the determination of. Basically a measure of molecular size and not molecular weight, the dilute solution viscosity can be correlated appropriately with molecular weight or chain length only if there is a unique relationship between the mass and the size of the dissolved polymer molecules. A novel approach for the determination of the viscosity.
These methods were used to characaterise the polymers for numberaverage m. The properties of polymers such as mechanical strength and melt viscosity can be. Molecular weight determination of polymers by viscometry. Xu, in functional nanofibers and their applications, 2012. A polymers molecular weight is the sum of the atomic weights of individual atoms that comprise a molecule. This variation of a was different from that observed bycornet and was discussed in terms of the excluded volume effect in polymer coils. Lecture i structure and molecular weight chapters 1 and 3. This can be easily understood by considering the strong dependence of the linear viscoelastic material functions on molecular weight and molecular weight distribution.
The method presented in this paper allows to calculate the molecular weight distribution mwd of linear homopolymer melts from the complex shear modulus data measured in a wide frequency domain. Viscosity is an internal property of a fluid that offers resistance to flow. Mw, number average molecular weight mn and the viscosity average. With linear macromolecules, viscosity number measurements can provide a method for the rapid determination of molecular weight when the relationship between viscosity and molecular weight has been established. High molecular weight polymers greatly increase the viscosity of liquids in which they are dissolved. It is confirmed that viscosity depends uniquely upon the weight average molecular weight and no other moment. Following methods are used to determine molecular mass, i diffusion method for gases. Osmotic method of determining the numberaverage molecular. For mixtures of polyelectrolytes, it has been reported that the determination of broad molecular weight distributions is challenging due to interference among molecules from different molecular weight populations. Dp mwpolymer mwmer dp 200,000 gmol 104 gmol 1923 or n 1923 3 polymers molecular weight. An empirical method for absolute molecular weight determination of polymers from viscosity measurements is described. Standard test method for determination of weightaverage. Determination of the weightaverage molecular weight of.
For solvents, a value of is indicative of a theta solvent. If we combine the carreauyasuda flow curve empiricism11,12 along with the parameter characterization of rohlfing and janzen, we can obtain a modified carreauyasuda equation. Typically a gaussian curve results, sometimes distorted by a small tail to the low molecular weight side, the vertical axis indicating the quantity, by weight, of the various molecular weight. The accurate determination of molecular weight is one of the key issues for the development of cellulosebased materials in laboratory research, as well as industry.
The increase in viscosity is caused by strong internal friction between the randomly coiled and swollen macromolecules and the surrounding solvent molecules. The ostwald method is a simple method for the measurement of viscosity, in which. Relationship between polymer concentration and molecular. Here we show that rheology can be used to provide the same information, and compare the algorithms developed by mead and. This equation describes the dependence of the intrinsic viscosity of a polymer on its relative molecular weight. It has been found that a low molecular weight solution. Intrinsic viscosity determination of high molecular weight. Thus hr2i 0m is a constant for a particular polymer that is independent of molecular weight. Determination of the molecular weight of polymers from.
Determination of molecular weight of polymers by visometry. Viscosity theory 81 but, both hr2i 0 and m are proportional to the number of bonds or n. Solomon2 1 centre of research excellence in corrosion, research institute, king fahd university of petroleum and minerals, dhahran 31261, saudi arabia 2 corrosion protection and materials research laboratory, department of chemistry, faculty of science, university of. The dependence of viscosity on molecular weight, temperature. Molecular weight of polymer by viscosity method youtube. Determination of molecular weights in polyelectrolyte. Weight average molecular weight m w and number average molecular weight m n are two ways we can characterize the polymer molecular weight. A system and method for analyzing data from a gel permeation chromatography gpc or size exclusion chromatography sec system for determining a polymeric samples molecular weight distribution mwd and intrinsic viscosity law ivl. The different methods are compared and evaluated with their respective percentage relative errors. Molecular weight polymers an overview sciencedirect. A monomer is a low molecular weight compound from which the polymer is obtained through the polymerization reaction. In linear polymers the individual polymer chains rarely have exactly the same degree of polymerization and molar mass, and there is always a distribution around an average value. Estimation of molecular weight of a given polymer by.
A webaccessible exercise is presented in which upperdivision undergraduate students can explore the method of determining polymer molecular weight from osmotic pressure measurements. The curve has a slope as high as about 5 at the highest. Although by viscosity measurements alone it is only possible to observe the changes in molecular weight, the absolute value of molecular weight can be determined if suitable calibration of intrinsic viscosity. Determination of the molecular weight of a polymer from. The values of the markhouwink parameters, and, depend on the particular polymer solvent system. From what i know, you can use intrinsic viscosity to measure the molecular weight of polymer via markhouwinks eq. Temperature and molecular weight dependence of the melt. Standard test method for dilute solution viscosity of.
Measuring molecular weight, size and branching of polymers. Precise determination of protein molecular weight using the. The molar mass distribution or molecular weight distribution describes the relationship between the number of moles of each polymer species n i and the molar mass m i of that species. Jan 26, 2018 viscosity method is one of the simplest method to determine the molecular weight. Pdf molecular weight determination of polyethylene. Polymer molecular weight reflects the number of entanglements of polymer chains in solution, thus solution viscosity. The ratio of rates of diffusion of two gases is inversely proportional to the square root of their molecular masses. Effects of molecular weight and solution concentration on. This is the case for linear, but not for most branched, polymers. Many methods are available for measuring viscosity of polymer. Back to characterization lab to polymer physics to polymer analysis. Doll national center for agricultural utilization research, agricultural research service, peoria, il b y studying a series of soybean oilbased polymers, using lowresolution nuclear magnetic resonance nmr spectroscopy, an easy method to estimate. The measurement and analysis of molecular weight and molecular weight distribution remain matters of fundamental importance for the characterization and physical properties of polymers. West nonnewtonian flow in polymers appears to occur only at molecular weights above me, the critical molecular weight above which chain entanglement is believed to occur.
Vinogradov institute of petrochemical synthesis, u. By means of intrinsic viscosity is determined the molecular weight with a value of 3846000gmol. The exponent,a, was different for different molecular weight range and amounted to 0. Determination of the molecular weight of a polymer from intrinsic viscosity measurements. Introduction gel permeation chromatography gpc method is a widely used and accepted method for. Rheological method for determining molecular weight and molecular weight distribution huiru zhang research center for composite materials, school of materials science and engineering, shanghai university, people s republic of china 1. Determination of molecular weight of polymers by ostwald viscometry slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. To validate a method to characterize the molecular weight distribution of thf soluble polymers. If you continue browsing the site, you agree to the use of cookies on this website. How does the molecular weight of a high polymer differ from that of a low molecular weight substance.
L is the steadyshear nonnewtonian viscosity, co is the shear rate, m w is the weightaverage molecular weight, and c 1c 5 are. Many methods are available for measuring viscosity of polymer solution. The measured viscosity data from the literature has been fitted to equation 6. Determination of viscosity average molecular weight of polymer. Molecular weight determination methods can be classed as absolute, equivalent, or relative. Viscositymolecular weight relation in bulk polymersi. When a is equal 1, m v is equal to the weight average molecular weight, if it isnt equal 1 it is between weight average molecular weight and. Gel permeation chromatography gpc is the most routinely used method. Intrinsic viscosity can be obtained by extrapolating the graph to zero concentration.
The numberaverage molecular weight of polymers 725 conclusions 1 in osmotic determinations of the numberaverage molecular weight of polymers changes in the concentration of the solutions during the measurements must be taken into account. Viscosity measurements were carried out with ostwald viscometer tubes after 24 hours of hydration of the gum. Validation of gel permeation chromatographic method for. Polymer science fundamentals of polymer science molecular weights of polymers. There are several methods for determining the molecular weight of a polymer. You will use dsv to measure the viscosity of the name brand of peg. Active standard astm d3835 developed by subcommittee. Osmotic pressure and polymer molecular weight determination. Polymers have a large molecular weight that depends on the number of. The different techniques are used for the determination of molecular weight of polymers such as gpc, light scattering, endgroup analysis, mass spectrometry, ebulliometry and cryometry etc. Extensional rheometry of polymeric fluids and the uniaxial. The intrinsic viscosity is used to classify polymers and helps to identify the applications that specific polymers can be used for. The use of the term molecular weight is somewhat misleading, because it implies that a sample of a polymer has a uniform formula weight i.
Polymer functionality is defined by its molecular weight mw, molecular size and structure, mw distribution and the degree of cross linking or chain branching. There are three methods for determination of molecular weight of cellulose. The molecular weight of a polymeric or biological material usually has a direct effect on its mechanical properties, thermal behavior, and viscosity characteristics. Staudinger investigated cellulose and rubber by viscometry 5. It is based on a nonlinear least squares fitting procedure of the concentration profiles and simultaneous estimation of the sedimentation and diffusion coefficients using approximate solutions of the lamm equation. Viscosity analysis of polymers university of cincinnati. By using polyllactic acid and phenobarbitone, they demonstrated that the molecular weight differences of polyl. Absolute methods allow the molecular weight to be calculated directly from the measured quantities. Molecular weight determination by intrinsic viscosity method. Application of molecular rotors to the determination of the molecular weight dependence of viscosity in polymer melts.
Molecular mass determination by sedimentation velocity. Quantifying relationships among the molecular weight. Chem355 experiment 6 viscosity of high polymer solutions a polymer is a large molecule macromolecule composed of many simple units that are called repeating units. Methods of determination of molecular mass, chemistry study. Polymers are extensively used throughout industry, whether as naturally occurring materials like starch and cellulose, or synthetic commodities like nylon, polystyrene and polyethylene. In this method, the viscosities of pure solvent and dilute polymer solutions are. Data from two or more detectors 18 is used with a leastsquares minimization fit. Providing absolute determination of molecular weight, timeintensive calibration becomes obsolete.
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