The determination of Monomers

HPLC using the reverse phase mode, has been used [12,13] to determine acrylamide 

---

W 1. Wiesser, M. Temperaturverlauf bei der thermischen Hartung von un-gesattigten Polyestem mit Styrol. Diplomarbeit, TH Stuttgart (1963/64). W 2. Wiley, R. H., and E. E. Sale Tracer techniques for the determination of monomer reactivity ratios. II. Monomer reactivity ratios in copolymerisations with divinyl monomers. J. Polymer Sci. 42, 491 (1960). 

Size-exclusion chromatography (SEC) has been used by several workers to separate monomer, dimer, and trimer. Bartosiewics (65) reported the determination of monomer and dimer acids with cross-linked polystyrene beads but did not attempt quantitative analysis. 

Silver porphyrins are interesting because of the existence of disilver(I), paramagnetic silver(II), and diamagnetic silver(III) complexes which has been known for a long time [7, 8]. The latter are favorably prepared by electrochemical [299] or peroxodisulfate [300-302] oxidation of silver(II) porphyrins. The Ag(III) porphyrins were used for and 2H resonance experiments [299] on one hand and for the determination of monomer-dimer equilibria [301] or self-exchange rate constants [301] at water-soluble silver porphyrins. 

Most kinetic studies on copolymerizations using coordination catalysts have been restricted to the determination of monomer reactivity ratios. There are problems both experimentally and in interpretation since the major simplification assumed to hold for most free radical initiated systems, namely that monomer incorporation is determined only by the monomer concentrations and the four rate coefficients, cannot be taken for granted. Further, catalyst activity and selectivity are influenced by the conditions of catalyst preparation including the manner and order of... 

Numerous methods for the determination of monomer purity, including procedures for the determination of saponification equivalent and bromine number, specific gravity, refractive index, and color, are available from manufacturers (68—70). Concentrations of minor components are determined by iodimetry or colorimetry for HQ or MEHQ, by the Karl-Fisher method for water, and by turbidity measurements for trace amounts of polymer. 

Previous work of one of the authors dealt with mid IR monitoring of IB polymerization using fiber-optic equipment. Fourier transform near infrared spectroscopy can be accomplished without expensive hardware. It therefore seemed to be a desirable goal to combine the advantage of fiber optics with low-cost fibers available for measurements in the NIR range. The NIR spectrum of IB obtained after solvent subtraction (Figure 2) reveals at least three signals, which should be suitable for the determination of monomer conversion. 

Other gas chromatographic methods available for the determination of monomers are reviewed in Table 4.6. 

We limit our discussion to the application of these equations in NMR and UV-vis dilution experiments for the determination of monomer-dimer equilibria. 

The reduction wave of alkylmethacrylates, observed in the presence of tetraalkylammonium salts at —1-9 V, can be used for the determination of monomers in the presence of polymers. 

Van Doremaele and co-workers [22] applied H-NMR spectroscopy to the determination of monomer ratios in styrene methyl acrylate copolymers 400-MHz H-NMR spectra were obtained in CDCI3 solutions at 25 °C. Expansions of the methoxy region display additional fine splitting due to combined configurational (i.e., tacticity) and compositional sequence effects. Mean copolymer composition (mole fraction styrene, Fj) can be readily obtained by using absorbances, which represent the total peak areas of the aromatic and methoxy proton resonances, respectively. The initial feed (q = [S]/[M]), the average copolymer composition, and the conversion are summarised in Table 4.6, [S] = concentrated styrene in feed, [M] = concentration of methyl acrylate in feed. 

Van Doremaele and co-workers [89] applied H-NMR spectroscopy to the determination of monomer ratios in styrene methyl acrylate copolymers. Figure 4.10 depicts, as a typical example, the 400 MHz H-NMR spectrum of a low-conversion solution styrene - methyl acrylate copolymer dissolved in CDCI3 at 25 °C, whereas in... 

A method involving head space analysis gas chromatography has been described for the determination of monomers and volatiles in PVC. ... 

Gas chromatography is used extensively for the determination of residual monomers and other volatiles in copolymers. In diis technique the polymer is dissolved in a suitable, non-interfering solvent, and the solution to which a suitable internal standard is added, injected directly into the gas chromatograph. Head space analysis techniques, discussed later in section 2.3.2 (method 57) have also been applied to the determination of monomers in copolymers. 

Functional group analysis and the determination of monomer unit concentrations can be used to determine the monomer composition and hence the empirical formula of a copolymer or terpolymer. Thus, if a styrene-butadiene copolymer contains 6% (6/56 moles) bound butadiene and 94% (94/104 moles) bound styrene, then the empirical formula is ... 

This pyrolysis - gas chromatography procedure enables the determination of monomer units such as butadiene, isoprene and propylene to be determined in natural and synthetic rubbers in amounts down to 0.5%. 

In addition to polymer structural details such techniques are proving very useful in polymer decomposition studies, also in the determination of monomers, oligomers and additives. 

The kinetic studies, which were based exclusively on the determination of monomer consumption, allowed only an apparent rate constant to be determined (Equation 1.39). 

---