Identification of the monomeric composition of poly(styrene)acrylates

The work is devoted to qualitative analysis of poly(styrene)acrylates, the definition of the content of styrene in them. The methods of IR, NMR spectroscopy and gas chromatography-mass spectrometry were used for analysis. It was shown that the integrated use of modern spectral methods allows unambiguous to lead identification of the components in the copolymer and to use of spectral data for quantitative determinations.


Introduction
The modern polymer science of materials is one of the actively developing branches of organic synthesis. The getting of new materials on the basis of new synthesized polymers and copolymers with desired valuable properties is one of the most interesting and promising tasks in the chemical industry.
At present the modern manufacturers of polymeric materials in order to save money and time try to use the already known polymer compositions and to establish their own production to meet the needs of consumers. In this regard there are tasks often related to identification, determination of the composition of branded polymer materials. Currently there is the significant number of different chemical and physico-chemical methods of analysis of polymers, but the specifics of this matter is that they are time-consuming and often have difficulty in solving even routine tasks.
For example, there is the well-known method for quantitative analysis of monomer composition of poly(styrene) acrylates which is based on the saponification of the ester groups of the acrylate units of the copolymer in the presence of alkali [1,2]. However, some researchers have noted that the saponification is subjected to only a part of the ester groups [3] and in addition in this method there are restrictions from the point of view of solubility of the analyzed polymers, the formation of precipitations in the process of titration and, as a consequence, the low reliability of the results.
In this regard in our work we have focused on the use of spectral methods of analysis. We have examined three samples of polymers, it was known previously that they are derived from poly(styrene) acrylates (SOLO 1, 2, 3). The tasks on confirmation of the nature of the polymer and its identification were proposed by analysis of the IR spectra of the samples by help the database of the spectra of polymers and organic intermediates using the software OPUS (firm Bruker) and OMNIC (firm ThermoFisher). More accurate qualitative analysis was to be conducted using the mass-spectrometric investigation of products of thermal destruction of polymers SOLO 1-3 with identification of components on the basis of the data library of mass spectra NIST (The NIST Mass Spectral Search Program for the NIST/EPA/NIH Mass Spectral Library Version 2.0). Also it was necessary to determine the styrene content, which was supposed to research according to 1 H-NMR and IR spectra of solutions of samples.

Discussion of results
To solve the set tasks we used methods of NMR, IR spectroscopy and gas chromatography-mass spectrometry. For substances was recorded 1 H NMR spectra (NMR spectrometer Bruker AVANCE II 400 MHz, solvent (CD 3 ) 2 СО), infrared spectra (IR Fourier spectrometer Bruker Alpha prefix FTIR, ZnSe) and carried out the mass spectrometric analysis of the products of thermal destruction of samples (gas chromatograph GC-2010 Plus, the console thermal degradation of Optic, "Shimadzu Corporation", Japan).
Analysis of the absorption bands in the IR spectra of samples SOLO 1-3 and comparison of spectra of polymers and organic intermediates with the database of spectral data with using of the software OPUS (Bruker) and OMNIC (firm ThermoFisher) showed that the polymers SOLO 2 and SOLO 3 are copolymers of styrene and esters of methacrylic acidmethyl, butyl, octyl. It was discovered the coincidence of the spectra of polystyrenemethylmethacrylate, -butylmethacrylate, -octylmethacrylate ( Fig. 1-4). While SOLO 1 does not contain styrene units in its composition -there are no absorption bands characteristic of stretching vibrations of aromatic C-H bonds in the IRspectrum (Fig. 5, 6).
Data of 1 H-NMR spectra also confirmed that the sample SOLO 1 is copolymer of methacrylic acid esters which does not contain styrene (there are no signals of aromatic protons in the region of 6-8 m. d.) and samples of SOLO 2 and SOLO 3 contain styrene fragments and the relative content of styrene in SOLO 2 is much less than in SOLO 3 ( Fig. 7-9 6. Comparison of the IR spectrum of the sample SOLO 1with data base ThermoFisher tion (EI), which in turn allowed the use of a database of mass spectra for identification of molecules of monomers. Thus, it was found that the sample SOLO 1 is copolymer of the two acrylates: methyland n-butylmethacrylate (Fig. 10); samples SOLO 2 and SOLO 3 are ternary copolymers of styrene with various acrylates (Fig. 12, 14). The registered spectra of all monomers showed high percentage of similarity to spectra contained in the database (Fig. 11, 13, 15), which suggests the reliability of the qualitative analysis of the products of thermal destruction of samples SOLO 1-3. Thus, the general formula of copolymers can be represented as follows: Fig. 9. The 1H-NMR spectrum of the sample SOLO 3 Since it has been found that the polymers SOLO 2 and SOLO 3 are ternary copolymers and the signals of protons in 1H-NMR spectra of the aliphatic part is much overlap, then to calculate the content of styrene in the 1H-NMR spectra failed.
Previously the method for quantitative determination of styrene in the IR spectra of solutions of styrene-containing of polymers was described [3]. The analysis is based on the integration of characteristic absorption bands in the region 694 cm -1 and the final calculation of the mass fraction of styrene in the sample. Sorry, we were not able to reproduce the conditions of the methodology due to the lack of liquid cell of the required thickness and insufficient solubility in solvents used in the procedure (tetrahydrofuran and acetone). Therefore, to determine the percentage content of styrene in the analyzed solutions the solutions of polystyrene in toluene with predetermined concentration were prepared and the diagram of dependence of the integrated intensity of bands in the range from 679 cm -1 to 708 cm -1 from the mass fraction of the polymer was build. Fig. 11. The comparison of registered and "library" of mass spectra of methylmethacrylate

Experimental part (description of the quantitative analysis by IR spectroscopy)
To construct the calibration curve (Fig. 16)  Shinko Denshi, Japan 2010) were previously prepared, respectively, their concentrations were 0,01225 g/ml, 0,0342 g/ ml, 0,0461 g/ml. The solutions of analyzed samples SOLO 2 (0,0681 g, concentration 0,03405 g/ml) and SOLO 3 (0,0842 g, concentration 0,0421 g/ml) were prepared similarly. For all solutions IR spectra were recorded in the range of 500-1000 cm -1 and by integrating the absorption bands in the range of 679 cm -1 to 708 cm -1 the areas under the curve were determined: S 1 = 5,490, S 2 = 5,708, S 3 = 5,842. For the investigated solutions values of the resulting areas were S SOLO 2 = 5,458, S SOLO 3 = 5,613. Then the mass fraction of styrene in the copolymer is as follows: where %S is the mass fraction of styrene, % S comp is concentration of SOLO 2 and SOLO 3, g/ml; c s is the concentration of styrene, g/ml;