Elemental analysis, copolymers composition determination

The principle of elemental analysis is to determine the percentage of each type of atom included in a compound. The composition of the copolymer is then... 

The copolymer composition equation relates the r s to either the ratio [Eq. (7.15)] or the mole fraction [Eq. (7.18)] of the monomers in the feedstock and repeat units in the copolymer. To use this equation to evaluate rj and V2, the composition of a copolymer resulting from a feedstock of known composition must be measured. The composition of the feedstock itself must be known also, but we assume this poses no problems. The copolymer specimen must be obtained by proper sampling procedures, and purified of extraneous materials. Remember that monomers, initiators, and possibly solvents are involved in these reactions also, even though we have been focusing attention on the copolymer alone. The proportions of the two kinds of repeat unit in the copolymer is then determined by either chemical or physical methods. Elemental analysis has been the chemical method most widely used, although analysis for functional groups is also employed. 

The copolymers obtained for the P(DMA)-itat-(HPA) (Scheme 9) library revealed relatively low PDI values below 1.3 and increasing Mn,opc values with increasing HPA content, as listed in Tables. It should be noted that a poly(methyl methacrylate) (PMMA) calibration was used for the calculation of the Mn pc values and this causes an overestimation for HPA containing polymers. The copolymer compositions were calculated from the H NMR spectra however, this method was not suitable for reliable conversion determination since the DMA-C//3 groups overlap in the NMR spectra not only with the HPA-O// group but also with broad backbone signals, which obstruct any reliable integration. Therefore, elemental analysis was used as an alternative method for the calculation of the molecular composition of the copolymers. 

Quantitative analysis of copolymers is relatively simple if one of the comonomers contains a readily determinable element or functional group. However, C,H elemental analyses are only of value when the difference between the carbon or hydrogen content of the two comonomers is sufficiently large. If the composition cannot be determined by elemental analysis or chemical means, the problem can be solved usually either by spectroscopic methods, for example, by UV measurements (e.g., styrene copolymers), by IR measurements (e.g., olefin copolymers), and by NMR measurements, or by gas chromatographic methods combined with mass spectroscopy after thermal or chemical decomposition of the samples. 

Average copolymer compositions of SAN samples were determined by elemental analysis, yielding weight percent acrylonitrile in the polymer. Compositions of S/MA and S/MA/MM were determined by sequential hydrolysis and pyridine titration to obtain maleic anhydride content and by infrared analysis for methyl methacrylate content. 

The compositions of copolymers of methacrylates or aldehydes were determined by 1H NMR spectroscopy or elemental analysis. 

Procedures. A standard recipe for the latex preparation is shown below (St + M2) 20 g, (water + buffer) 160 g, and initiator 5 mmole/1. The weight fraction of M2 in monomer charge (f) was varied from 0.01 to 0.50. Polymerizations were carried out at 55°C or 70°C and pH 2.5 or 9.0 under nitrogen. Samples were withdrawn from the reaction mixture at various time intervals and the polymer was precipitated in an excess of acetone. The conversion and polymer composition were determined by gravimetric means and by elemental analysis, respectively. The M2 fraction in instantaneously-formed copolymer ( Fi ) was calculated from eq. 1 ... 

The concentration of the siloxane introduced into the copolymer is most easily determined by proton NMR for soluble systems, as briefly referred to in Sect. 3.1. This was demonstrated by Summers et al. [45] and Arnold and coworkers [46-50], as well as Rogers et al. [52]. Others have routinely conducted these experiments to establish the copolymer composition. Infrared spectroscopy has been particularly useful for demonstrating the transformation of the amic acid, which is often an intermediate for the final imide form. The assignments have been noted in many of the polyimide reviews referred to earlier [1-8]. In addition, it is useful to conduct an elemental analysis for silicon as complementary proof of copolymer composition. Solid-state NMR can be used even for intractable polyimide systems to provide a good estimate of the copolymer composition. 

Copolymer Analysis. Even though the overall copolymer composition can be determined by residual monomer analysis, it still is necessary to have reliable quantitative techniques for copolymer composition measurements on the actual copolymer, mainly because concentration detectors for SEC or HPLC are sensitive to composition and because the conversion histories are not always available. Some of the techniques used to determine copolymer composition are melt viscometry (46), chemical analysis, elemental analysis, infrared spectroscopy (IR), Nuclear Magnetic Resonance (NMR), ultra-violet spectroscopy (UV), etc. Melt viscometry, chemical and elemental analysis are general techniques that can be applied to almost any polymer. The spectroscopic techniques can be applied depending on the ability of the functional groups present to absorb at specific wavelengths. 

Copolymer compositions were determined by a high resolution nuclear magnetic resonance spectrometer (180 HMz). Copolymers of methyl methacrylate and styrene were dissolved in deuterated chloroform for the analysis. Deuterated pyridine was the solvent for the methyl methacrylate - methacrylic acid copolymers. Elemental analysis was also used in copolymer composition analysis to complement the NMR data. 

Synthesis was carried out of the copolymers of 4-vinylpyridine (4VP), styrene (St) and divinylbenzene (DVB) with varied compositions, P(4VP-St-DVB), by suspensionpolymerisationusing 2,2 -azobisisobutyronitrile (AIBN) as an initiator. Preparation of the insoluble (crosslinked) pyridinium-type polymers in benzyl-pyridinium bromide form, which possess various macromolecular chain compositions, was performed by the reaction of eachP(4VP-St-DVB) with benzyl bromide (BzBr), respectively. By using different halohydrocarbon RX in the quatemisation of P(4VP-St-DVB), the insoluble pyridinium-type polymers with various pyridinium group stractures were obtained. FTIR was nsed to identify the stractures of P(4VP-St-DVB) and its quatemised product Q-P(4VP-St-DVB). The 4VP content in each copolymer P(4VP-St-DVB) was measured by non-aqueous titration and the pyridinium group content (Cq) in each Q-P(4 VP-St-DVB) sample was determined by means of the back titration manner in argentometiy and/or the elemental analysis method, respectively. Also, the particle structure... 

Analytical Procedures. The purity of all copolymers, i.e. absence of monomers, was checked by thin layer chromatography (TLC). Composition of the DHA -co-4VP copolymers was determined from elemental analysis data obtained by Micro-Analysis, Inc., Wilmington, Del. Compositions of the DHA-co-NVP copolymers were determined by non-aqueous titration, using 0.1N perchloric acid and gentian violet indicator in glacial acetic acid (11). Isocyanate was determined as reported previously (12). 

Characterization of Block Copolymers. The copolymers were characterized by velocity ultracentrifugation, osmotic pressure, and ordinary element analysis in order to determine the molecular weight monodispersity of the copolymers and the degree of contamination with the corresponding homopolymers, the number average molecular weight (Mn), and the fractional compositions of the block copolymers, respectively. 

Copolymer Characterization. Copolymer compositions were determined by elemental analysis and thermal gravimetric analysis. A Perkin-Elmer TGS-2 ther-mogravimetric analyzer, programmed from ambient to 800 C in N2 and air, was used. Spectroscopic analysis of the copolymers was not as useful as elemental analysis and thermal gravimetric analysis measurements for analyzing these copolymers. Viscometric measurements were made in a solution of water and NaCl with a Contraves low-shear viscometer. 

Elemental analysis (EA) is a convenient method for determination of copolymer and blend composition if one homopolymer contains an element not present in the second one. For example, EA can be properly used to quantify nitrogen in copolymers containing acrylonitrile units and oxygen in polymeric surfactants such as poly(oxy-alkylene). Therefore, for a binary system, every element can be balanced according to the following equation ... 

Analysis of Polymers. The repeat unit structure of a synthetic polymer usually is known from the method of synthesis. Compositions of copolymers often are determined by elemental analysis when one monomer contains an element not present in the other monomer. Soluble polymers are often characterized by their molecular weights and molecular weight distribution, but insolubility prevents such characterization of cross-linked polymers. 

Analysis of plastics is a complex task and involves preliminary tests, determination of nonmetallic and metallic elements, analysis of functional groups and double bonds, molecular weight determinations, chemical compositional analysis, sequence length distribution in copolymers, determination of tacti-city and branching in polymers, and analysis of additives. Because of the great variety in structures in commercially produced plastics, the number of methods that can be applied for their analysis is considerable. 

In order to calculate a copolymerization reactivity ratio, it is first necessary to determine the composition of the copolymer or of the unconverted monomer mixture (or both). Elemental analysis, spectroscopic methods (IR, UV, NMR), refractive index determination, or turbidimetric titration can be suitable for determining the copolymer composition. 

Copolymers are composed of at least two types of monomer unit. Although it can be expected that the composition of copolymers fits well with the composition of the different monomers used during copolymer synthesis, there are different reasons inherent to polymerisation reactions that can explain why the composition of the copolymer can differ from the initial composition of the copolymerisation medium (see Section 3.8). For this reason, the composition of copolymers needs to be determined in the routine characterisation of such a type of polymer. The most widely used methods for this are those based on the elemental analysis or on spectral analysis of the copolymer. 

The composition of the isolated copolymer was determined from (a) the nitrogen elemental analysis, and (b) the sulfur elemental analysis. Both figures were corrected for the small amount (4-12%) of water associated with the polymer. 

The copolymers of acrylamide with sodium-3-acrylamido-3-methylbutanoate (NaAMB), as well as the homopolymer of NaAMB, were prepared in aqueous solution at 30 C using 0.1 mole percent potassium persulfate as the initiator. The feed ratio of AM NaAMB was varied from 95 5 to 25 75, and the total monomer concentration was held constant at 0.456 M. Following reaction, the polymers were purified by precipitation in acetone, dialysis, and lyophilization. Conversions were determined gravimetricallv and compositions were determined using elemental analysis and NMR. ... 

Composition of block copolymers The content of polypeptide (A-component) in each copol3nner, as represented by A mol-%, was determined from elemental analysis. The elemental analyses were carried out in the Organic Microanalyses Center in Kyoto University. As the molecular weight of the middle block is known, the molecular weight of the outer block, polypeptide block, is estimated from the copolymer composition. The molecular weight thus obtained is the number-average molecular weight. 

Copolymer resin (p-CAF) was synthesized by the condensation of p-cresol and adipamide with formaldehyde in the presence of hydrochloric acid as catalyst and using varied molar ratios of reacting monomers. A composition of the copolymers has been determined on the basis of their elemental analysis. The number average molecular weight of resins was determined by conductometric titration in non-aqueous medium. The copolymer resins were characterized by viscometric measurements in dimethylsulphoxide (DMSO), UV-visible absorption spectra in non-aqueous medium, infrared (IR) spectra, and nuclear magnetic resonance (NMR) spectra. The morphology of the copolymers was studied by scanning electron microscopy (SEM). 

Using MAS C NMR, the resonances at 127 and 136 ppm were attributed to the cis and trans double bonds and that at 178 ppm was for the carbonyl groups. The composition of the copolymers was determined by elemental analysis, radioassay of C content in the labeled copolymers and NMR. The copolymers were found to have a composition of 95, 90, and 87 mol% acetylene. The molecular weight of the insoluble copolymers was determined by radioassay of the T content after adjustment for the kinetic isotope effect (KEF). At a reaction temperature of —78 C, copolymers in the form of thin film were obtained with A/n = approximately 4000, whereas at a reaction temperature of 25 C, only powder-like products with A/n = approximately 1000 were obtained. The homopolyacetylene was found to have A/ = 11 000 using... 

Neoh and co-workers [110] investigated the simultaneous chemical copolymerization and oxidation of pyrrole and A-methylpyrrole by bromine and iodine. By varying the monomer feed ratio, they could in effect control the copolymer composition. Based on elemental analysis of the copolymers, they determined that ri = 1.13 and r2 = 0.35 for pyrrole and 1-methylpyrrole, respectively. In the copolymerization induced by bromine, the electrical conductivity, thermal stability and Br content of the doped copolymer decreased with increasing concentration of A/-methylpyrrole in the copolymer. When iodine was included in the charge, the halogen content of the copolymers did not vary substantially, but the electrical conductivity and thermal stability of the doped copolymer also decreased with an increase in the fraction of A/-methylpyrrole in the copolymer. 

Brar and Sunita [58] described a method for the analysis of acrylonitrile-butyl acrylate (A/B) copolymers of different monomer compositions. Copolymer compositions were determined by elemental analyses and comonomers reactivity ratios were determined using a non-linear least squares errors-in-variables model. Terminal and penultimate reactivity ratios were calculated using the observed distribution determined from C( H)-NMR spectra. The triad sequence distribution was used to calculate diad concentrations, conditional probability parameters, number-average sequence lengths and block character of the copolymers. The observed triad sequence concentrations determined from C( H)-NMR spectra agreed well with those calculated from reactivity ratios. 

A three compartment electrolytic cell with two fritted disk separators was used. An auxiliary platinum electrode was placed in each of the two end compartments while an aluminium strip, to which a surface treatment based on chromic acid etching had been applied, was placed in the middle compartment. Ihe monomer solution contained methacrylic acid (0.436 M) and -methylenebisacrylamide (0.145 M) in water. The pH of the above solution was adjusted to desired values by adding either sulfuric acid or aqueous sodium hydroxide. The monomer solution (400 mi) was placed in the middle compartment while two end compartments contained water adjusted to the same pH as the monomer solution. While bubbling nitrogen through the monomers solution, the electrolysis was conducted at 10 vdts for 6 hours such that the cathodic reaction would occur in the center compartment. The polymer coating obtained on the aluminium cathode was washed with fresh water, dried in vacuum oven at room temperature, and weighed. The copolymer was then scraped off from aluminium and its composition determined by elemental analysis. 

The random copolymers were obtained by solution polymerization at 70 X in dioxane or toluene with AIBN as initiator. They were purified by GPC with PVA (Merck) and THF as eluent. The copolymer compositions were determined by UV measurements and elemental analysis. 

Beckett described inductively coupled plasma mass spectrometry (ICP-MS) as an off-line detector for FFF which could be applied to collected fractions [ 149]. This detector is so sensitive that even trace elements can be detected making it very useful for the analysis of environmental samples where the particle size distribution can be determined together with the amount of different ele-ments/pollutants, etc. in the various fractions. In case of copolymers, ICP-MS detection coupled to Th-FFF was suggested to yield the ratio of the different monomers as a function of the molar mass. In several works, the ICP-MS detector was coupled on-line to FFF [150,151]. This on-line coupling proved very useful for detecting changes in the chemical composition of mixtures, in the described case of the clay minerals kaolinite and illite as natural suspended colloidal matter. 

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