Analysis of Copolymers

Copolymers are complex macromolecular systems which are formed when two or more monomers of different chemical structures react in a polymerization process. As a result products are obtained which, in addition to the MMD, are characterized by a certain chemical composition. This chemical composition may be expressed by an average number, characterizing the total amount of each monomer in the reaction product. More detailed information, however, is obtained when the chemical heterogeneity (CH) is determined, characterizing the sequence distribution of the different monomer units along the polymer chain. 

In general, when reacting two monomers in a polymerization reaction, different products may be formed, depending on the reactivity ratios of the monomers and the reaction conditions (see Fig. 10). Therefore, in order to describe the reaction products fully it is necessary to analyze the copolymer (MMD, CH) and to determine the amount of homopolymers which may have been formed as unwanted by-products. For a block copolymer it would be of 

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For both copolymers and stereoregular polymers, experimental methods for characterizing the products often involve spectroscopy. We shall see that nuclear magnetic resonance (NMR) spectra are particularly well suited for the study of tacticity. This method is also used for the analysis of copolymers. 

D. Briggs. Org. Mass Spectrom. 22, 91, 1987. Static SIMS analysis of copolymers. 

Applications Applications of SEC-FTIR include quantitative analysis of copolymers [701] product deformulation of hot melt adhesives characterisation of polymer compositional heterogeneity analysis of complex mixtures of urethane oligomers and eventually also the identification and quantitative analysis of polymer additives... 

Spectroscopic analyses are widely used to identify the components of copolymers. Infrared (IR) spectroscopy is often sufficient to identify the comonomers present and their general concentration. Nuclear magnetic resonance (NMR) spectrometry is a much more sensitive tool for analysis of copolymers that can be used to accurately quantify copolymer compositions and provide some information regarding monomer placement. 

Unit distribution in the substituted PMMA (35) was investigated by two independant methods a) Direct analysis of copolymer microstructure by H-NHR at 250 MHz the NMR spectrum (pyridine solution at 80°C) are sufficiently well resolved to allow a quantitative analysis of unit distribution, in terms of A centered triads and isolated B units in ABA triads, b) UV studies of the ionization and of the intramolecular cyclization of the B B and B B dyads in protic basic media (Na0H-H 0 O.IN, NaOMe-MeOH O.IN) in such a medium the partially ionized copolymer chains are the site of a complex series of consecutive intramolecular reactions we have completely elucidated (35). The first step is of interest with respect to B unit distribution ... 

D.J. Vforsfold, NRC, Ont. Problems often arise in carbon-13 NMR work with the integration of the peaks. In the analysis of copolymer systems it would be useful to have very good peak integration. Can you in fact succeed in this ... 

Table I. Results of Gel Permeation Chromatographic Analysis of Copolymers of NIPAAM...

High-resolution nuclear magnetic resonance spectroscopy, especially 13C NMR, is a powerful tool for analysis of copolymer microstructure [Bailey and Henrichs, 1978 Bovey, 1972 Cheng, 1995, 1997a Randall, 1977, 1989 Randall and Ruff, 1988], The predicted sequence length distributions have been verihed in a number of comonomer systems. Copolymer microstructure also gives an alternate method for evaluation of monomer reactivity ratios [Randall, 1977]. The method follows that described in Sec. 8-16 for stereochemical microstructure. For example, for the terminal model, the mathematical equations from Sec. 8-16a-2 apply except that Pmm, Pmr, Pm and Prr are replaced by p, pi2, p2j, and p22. 

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. 

N 074 "Helix-Coil Stability Constants for the Naturally Occurring Amino Acids in Water. XIII. The Presence of By-Products in Amino-Acid Analysis of Copolymers and Their... 

The analysis of copolymer composition indicates that the propagation is entirely radical. These two monomers were carefully dried by trap-to-trap distillation after drying over barium oxide, but no sign of ionic... 

In some instances of electrolytic polymerization studies, it is conceivable that the polymerization may proceed simultaneously by a free-radical, an anionic, or a cationic mechanism in the same reaction mixture. To discriminate among the various propagation mechanisms, the analysis of copolymer compositions is often used. 

Table 5. Analysis of copolymers from MMA-AcN feed in DMF saturated with...

For a statistical analysis of copolymer sequences, different mathematical techniques are used. For mathematically oriented researchers, a copolymer sequence might be considered as a string of symbols whose correlation structure can be characterized completely by all possible monomer-monomer correlation functions. Since the correlations at long distances are typically small, it is important to use the best possible estimates to measure the correlations, otherwise the error due to a finite sample size can be as large as the correlation value itself. 

Styrene enchainment in the syndiospecific polymerisation of styrene with homogeneous catalysts, both containing and not containing a cyclopentadienyl or cyclopentadienyl-like ligand, is through a cis insertion [76,77], This was evidenced by H NMR analysis of copolymers of perdeuterostyrene and... 

Based on monomer charge. b Based on chlorine analysis of copolymer. 

Now we move on to consider the analysis of copolymers. There are usually two things we would like to know. First, the composition of the copolymer and, second, some measure of sequence distributions. Again, in the early years, before the advent of commercial NMR instruments, infrared spectroscopy was the most widely used tool. The problem with the technique is that it requires that the spectrum contain bands that can be unambiguously assigned to specific functional groups, as in the (transmission) spectrum of an acrylonitrile/methyl methacrylate copolymer shown in Figure 7-43 (you can tell this is a really old spectrum, not only because it is plotted in transmission, but also because the frequency scale is in microns). 

Another short essay outline some of the advantages and problems in applying, 3C NMR to the analysis of copolymer sequence distributions. 

Both approaches are accomplished isocratically and therefore the problem of irreproducible gradient production, which is a limitation for the quantitative analysis of copolymers by gradient chromatography, is avoided. 

The thermal stability of the copolymers 6-16 was studied using a TA 2950 TGA instrument in a nitrogen atmosphere. Figure 4 shows the thermogravimetric analysis of copolymer 9. The copolymer exhibits thermal stability to a temperature of over 400 °C before the major weight loss is observed. A smaller weight loss of 2% has been detected at about 345 °C. The amount of organic residue at 800 °C is about 4.4%. 

The considerable importance of copolymers for practical purposes generated a considerable number of studies dedicated to thermal stability and pyrolysis of copolymers (see e.g. [10-15]). The presence of two or more monomeric structures in a macromolecule can influence significantly the thermal behavior and the composition of its pyrolysate. Depending on the ratio of the comonomers, as well as on the structure of the polymer (random, alt, block, graft, etc ), the pyrolysis output can be very different. Based on this, pyrolysis results are frequently used for the analysis of copolymer structures. 

The use of a commercially available software package (QUANT) is described in the analysis of copolymer films by computer assisted infrared spectroscopy. Important features of the software are illustrated by the example of analysis of vinyl acetate/vinyl chloride copolymers. Critical aspects of method development are explained and error sources are examined. Calibration is reported with a correlation coefficient of 0.9998. 

Rapid, accurate analysis of copolymer products is critical to the efficiency and economy of modern industrial copolymer production. Infrared spectroscopy is a well established technique for both qualitative and quantitative analysis of polymeric materials (1, 2). However, the coupling of relatively low-cost data handling hardware and software to a microprocessor-controlled infrared spectrophotometer is a relatively recent development. This coupling considerably enhances the level of performance one can expect from quantitative infrared spectroscopy. The result is that such systems greatly reduce the effort, expense, and time required for a given analysis and simultaneously provide improved accuracy, reliability, and precision. This paper will describe a recently developed, commercially available software system which will be referred to hereafter as QUANT. In the course of application research with the QUANT software a wide variety of copolymer systems... 

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