Styrene compositional analysis

Detector Technology. For copolymer composition analysis the new diode array UV/vis detectors are extremely attractive the absorption at many wavelengths are instantaneously recorded there is only a single spectrophotometer cell so that transport time delays between detectors and axial mixing in detector cells do not confound comparison of detector response at different wavelengths and for styrene copolymers, extremely low concentrations of polymer can be detected. 

Since the late 1960 s a few papers have demonstrated compositional analysis of various polymer systans by Raman spectroscopy. For example, Boerio and Yuann (U) developed a method of analysis for copolymers of glycidyl methacrylate with methyl methacrylate and styrene. Sloane and Bramston-Cook (5) analyzed the terpolymer system poly(methyl methacrylate-co-butadiene-co-styrene). The composition of copolymers of styrene-ethylene dimethacrylate and styrene-divinylbenzene was determined by Stokr et (6). Finally, Water (7) demonstrated that Raman spectroscopy could determine the amount of residual monomer in poly(methyl methacrylate) to the % level. This was subsequently lowered to less than 0.1% (8). In spite of its many advantages, the potential of Raman spectroscopy for the analysis of polymer systems has never been fully exploited. 

It was shown from the study of styrene and MMA in a KNOa-DMF system using tracer techniques for the composition analysis that the free-radical contribution is apparently confined to the first few percent of polymerization, whereas at later stages the reaction is anionic (34). This is consistent with the inhibitor studies. On the same monomer pair with a variety of solvents with ammonium salts, only with tetrahydrofuran did a possible free-radical reaction accompany the anionic propagation, with the others, DMF and dimethylacetamide, as well as without solvent, an anionic reaction accompanying the free radical one was assumed (35). 

The composition analysis of SBR, i.e., styrene, czs-1,4, trans-1,4 and 1,2 (vinyl) units, has been carried out by 13C-NMR based on signal assignments indicated in Table 11.2. The integrated intensities of regions A to I are used to calculate percent composition by using following equations [17]. 

Gramshaw, J.W., and Vandenburg, H.J., 1995. Compositional analysis of thermoset polyester and migration of ethylbenzene and styrene from thermosct polyester into pork during cooking. Food Add. and Contam. 12, 2, 223-234. 

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. 

The compositional analysis of a copolymer can be achieved by several methods other than NMR spectroscopy, such as elemental analysis, infrared and ultraviolet spectroscopies, and pyrolysis-gas chromatography. However, NMR spectroscopy has several advantages it does not need calibration if the operation conditions are properly set, and it can distinguish impurities easily. Quantitative aspects of compositional analysis by H and 13C NMR have been discussed for styrene-MMA copolymer12 and vinylidene chloride-acrylonitrile copolymer,13 respectively. 

Table 3 shows the results of compositional analysis for radically prepared copolymer of MMA and styrene.14 H and 13C NMR analyses and elemental analysis gave consistent results as seen in the table, indicating good accuracy for all these analyses. 

Table 3. Composition analysis of a copolymer of methyl methacrylate and styrene.

FTIR has also been used for online compositional analysis of polymer blends and copolymers from a plant extruder. Varying concentrations of styrene or acrylic polymer were identified from the resulting FTIR spectra. The online monitoring was accurate when temperature fluctuations were +5°C. The offline measurements were found to be less accurate than the online measurements. 

Improved data analysis has led to the simultaneous determination of the sedimentation coefficient and diffusion coefficient, and a calculation of the molecular weight from the Svedherg equation (142). The Svedherg method is capable of determining molecular weights of up to 40 x 10 (96) on an absolute basis. Sedimentation equihbrium in a density gradient has been used to determine the compositional analysis of copolymers, eg, butadiene-styrene (143). 

Figure 36 Raman bands relevant to composition analysis. A, acrylonitrile B, butadiene S, styrene.

An infrared method has been described [18] for the compositional analysis of styrene-acrylonitrile copolymers. In this method the relative absorbance between a nitrile v(CN) mode at 4.4 pm and a phenyl v(CC) mode at 6. 2 pm is used. 

Figure 3.20. Compositional analysis of rubber products by TGA styrene-butadiene rubber (courtesey of TA Instruments).

Styrene-acrylic copolymers were analyzed via NIR for styrene content using the 2100 nm aromatic C—H combination band [65]. Spectral characteristics of these blends are so distinct that no special sample preparation technique is required. NIR has also been applied for the compositional analysis of styrene-acrylonitrile (SAN), styrene-MMA, styrene/butadiene [15], AS in polyvinylchloride [66], and styrene-acrylic copolymers. 

FIGURE 9.23 2D HPLC-SEC analysis of a four-arm block copolymer consisting of 16 components with four different styrene compositions and four molar masses, respectively (contour map shown peak annotations, see text). (See insert for color representation of the figure.)... 

Kranz and co-workers [126] have shown that acrylonitrile can he determined in styrene - butadiene - acrylonitrile terpolymers via a determination of organic nitrogen by the Kjeldahl procedure. Styrene units can be can be determined by infrared spectroscopy. Butadiene units can be determined by the iodine monochloride procedure. The compositional analysis and details of the microstructure of butadiene - acrylonitrile copolymers can be obtained by Raman spectroscopy [127]. 

The compositional analysis of styrene butadiene copolymers is discussed in Section 2.1.1. 

With regards to the copolymerization, a recent kineuc study by Gruber and KneU (10 has indicated that styrene n-butyl methacrylate obeys the cla ical kinetic theory with regards to composition and sequence length to complete conversion. This theory is applied to high conversion to charau terize copolymer samples for GPC analysis. 

Various techniques have been used for the determination of oligomers, including GC [135], HPLC [136-138], TLC for polystyrene and poly a-methyl-styrene [139] and SEC for polyesters [140,141]. GC and PyGC-MS can also profitably be used for the analysis of the compositions of volatile products formed using different flame retardants (FRs). Takeda [142] reported that volumes and compositions of the volatile products and morphology of the char were affected by FRs, polymers (PC, PPE, PBT) and their reactions from 300... 

Bravo, 1984). Hybrids of these systems, where chromatography and electrophoresis are used in each spatial dimension, were reported nearly 40 years ago (Efron, 1959). Belenkii and coworkers reported on the analysis of block copolymers by TLC (Gankina et al., 1991 Litvinova et al., 1991). Two-block copolymers of styrene and f-butyl methacrylate were separated first with regard to chemical composition by TLC at critical conditions, followed by a SEC-type separation to determine the molar masses of the components. 

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