The synthesis of polystyrene suspensions in the presence of a mixture of water-soluble and waterinsoluble

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1 Plasticheskie Massy, No , 2015, pp The synthesis of polystyrene suspensions in the presence of a mixture of water-soluble and waterinsoluble surfactants D.B. Adikanova, 1 G.Zh. Eligbaeva, 1 I.A. Gritskova, 2 E.V. Milushkova, 2 N.I. Prokopov, 2 and S.M. Levachev 3 1 K.I. Satpaev Kazakh National Technical University, Almaty, Kazakhstan 2 M.V. Lomonosov Moscow State University of Fine Chemical Technologies, Moscow, Russia 3 M.V. Lomonosov Moscow State University, Moscow, Russia Selected from International Polymer Science and Technology, 43, No. 7, 2015, reference PM 15/11-12/17; transl. serial no Translated by P. Curtis Summary Polystyrene suspensions with an average particle diameter of µm and a narrow particle size distribution were synthesised in the presence of a mixture of surfactants sodium alkyl sulphonate (E- 30), oxyethylated sulphated alkylphenol (AP-9), and organosilicon surfactant α,ω-bis[10-carboxydecyl] polydimethylsiloxane (CS). It was shown that the absence of a highly disperse particle fraction in the suspension is observed only when the polymerisation of styrene is carried out with an ionogenic surfactant content close to the critical micelle concentration (CMC). The problem of synthesising polystyrene suspensions with a narrow particle size distribution that are stable during polymerisation is extremely urgent, as the area of their practical application is extremely broad. They are used as calibration standards in electron and optical microscopy and light scattering, for determining the pore size of filters and biological membranes, as medal colloids, for investigating the kinetics and mechanism of film formation of latexes, and also as polymer supports of biological ligands in immunochemical investigations [1 3]. For these purposes, polymer suspensions with wide-ranging diameters are required. Polymer suspensions with a narrow particle size distribution are produced under conditions ensuring the formation of particles by the same mechanism from microdrops of monomer. Such conditions are satisfied when polymerisation is carried out in the presence of water-insoluble surface-active substances (SASs) capable of forming a direct oil in water emulsion [4]. Surfactants of this type include diparatolylcarbalkoxyphenylcarbinol, oligoglycol maleinate benzoates, and monoalkyl phthalates [4], and also organosilicon surfactants [5 8]. In their presence, polymer suspensions of a wide range of diameters ( µm) were synthesised, and have already been used as supports of bioligands in immunochemical reactions [9]. Polymer suspensions with a smaller particle diameter could not be obtained, which was attributed to the influence of water-insoluble surfactants on the dispersion of the monomer. This work is devoted to synthesising highly disperse polymer dispersions with particle diameters of µm and a narrow size distribution in the presence of a mixture of organosilicon, α,ω-bis[10-carboxydecyl] polydimethylsiloxane (CS), and the ionogenic surfactants sodium alkyl sulphonate (E-30) and oxyethylated sulphated alkylphenol (AP-9). EXPERIMENTAL Technical-grade styrene was purified to remove the stabiliser with a 5% aqueous solution of caustic soda, 2016 Smithers Information Ltd. T/17

2 dried over calcined potassium chloride, and distilled twice in vacuum. Use was made of a fraction boiling 20 at t = 41 C (10 mmhg), d 4 = g/cm 3 20, n d = Potassium persulphate (K 2 S 2 O 8 ) was used without additional purification with a content of the main substance of 99.9%. a,w-bis[10-carboxydecyl]polydimethylsiloxane (CS) was synthesised at the State Scientific Research Institute of Chemical Technology of Heteroorganic Compounds (GNIIKhTEOS), MW = 2728 g/mol, viscosity h 25 = 132 cst, %COOH pract = 3.60 wt%. Sodium alkyl sulphonate (E-30) (C 15 H 31 SO 3 Na), a product of Sigma-Aldrich Chemie GmbH, was used without additional purification. Oxyethylated sulphated alkylphenol (AP-9) (R C 6 H 4 O(C 2 H 4 O) 10 SO 3 NH 4, where R is C 9 H 19 ) was produced by PO Orgsteklo in accordance with TU The interphase tension at the phase boundary was measured by stalagmometry [10]. The kinetics of polymerisation was studied by dilatometry [1]. The particle size of the polymer suspensions was determined by photon correlation spectroscopy on a Zetasizer Nano ZS particle analyser of the UK company Malvern, and by electron microscopy on an S-570 instrument of the Japanese company Hitachi [11]. The ξ-potential of the particles was determined by electrophoretic light scattering on the Zetasizer Nano ZS instrument (Malvern) [11]. The molecular weight of the polymers was calculated by means of the Mark Kuhn Houwink equation: in Figure 1, the polydimethylsiloxane (CS) lowers the interphase tension at the boundary between the styrene solution of the surfactant and water to 23 mn/m, and E-30 lowers s 1,2 at the boundary between the aqueous solution of E-30 and styrene to 4 mn/m. The interphase tension at the boundary between the styrene solution of CS and the aqueous solution of E-30 is lowered to a s 1,2 value of 8 mn/m. The colloid chemical properties of the interphase adsorption layers of the surfactants are presented in Table 1. The results of calculating the colloid chemical parameters of the surfactants in individual and mixed adsorption layers, given in Table 1, showed that the mixed interphase layer has a combination of the parameters of the individual surfactants. Above all, this applies to the magnitudes of the maximum adsorption (G max ) and the thickness of the adsorption layer (δ). For E-30, G max is equal to mol/m 2, and for a mixture of the surfactants it is lowered to a value of mol/m 2. Here, the thickness of the layer increases accordingly from 1.4 to 4.7 nm. This dependence of the parameters of the adsorption layers of the surfactants demonstrates a change in their structure, which will undoubtedly affect the stabilisation of the polymer monomer particles (PMPs). It may be thought that, when a mixture of surfactants is used, the reaction system will retain its stability even where [h] is the intrinsic viscosity, which was determined by the procedure described in Prokopov et al. [11], and K and α are constants for the polymer solvent system at a certain temperature. RESULTS AND DISCUSSION Investigations began with a study of the isotherms of interphase tension. As can be seen from the data given Figure 1. Interphase tension isotherms of individual surfactants CS (1) and E-30 (2) and of a mixture of E-30 and CS (3) with a fixed CS concentration in the mixed system of 1 wt% in terms of styrene. T = 298 K Table 1. The colloid chemical properties of interphase adsorption layers of the surfactants Phase boundary s 1,2, mn/m G max 10 6, mol/m 2 G, mn m 2 /mol S 0, δ 10 9, Å 2 m Styrene solution of CS/water Styrene/aqueous solution of E Styrene solution of CS/aqueous solution of E T/18 International Polymer Science and Technology, Vol. 43, No. 10, 2016

3 with low concentrations of the ionogenic surfactant. This will make it possible to reduce the probability of PMPs forming from surfactant micelles, and microdrops of the monomer will become the main source of PMPs. Taking into account the structure of the ionogenic and organosilicon surfactants and their colloid chemical properties, it can be assumed that, in the E-30 mixture, the ionogenic surfactant, capable of creating a charge on the surface of the microdrops of monomer and PMPs, will ensure the formation of an electrostatic barrier in the adsorption layers of the PMPs, while the organosilicon surfactant, soluble in the monomer phase, will form a strong adsorption layer through the formation of a structural mechanical barrier, thus ensuring stability of the polymer suspension. This determined the conditions for conducting the polymerisation of styrene in the presence of a mixture of surfactants. The E-30 concentration was varied from values close to the critical micelle concentration (CMC) to those normally used in the process of emulsion polymerisation, and the amount of organosilicon surfactant was varied from concentrations corresponding to the formation of a saturated adsorption layer to concentations ensuring ~50% saturation of the adsorption layer. Thus, the E-30 concentration amounted to 0.05, 0.5, 2.0, and 4.0 wt% in terms of aqueous phase, and the CS concentration amounted to 01, 0.2, and 3.0 wt% in terms of styrene. The monomer/water volume ratio was varied from 1:4 to 1:1 respectively. The initiator was potassium persulphate taken in a concentration of 1 wt% in terms of the monomer. The polymerisation temperature was 80 C. Let us examine the influence of the monomer/aqueous phase volume ratio on the polymerisation rate, the particle diameter, and the stability of the reaction system. The conversion time kinetic curves obtained with a styrene/water volume ratio of 1:4 are given in Figure 2. It can be seen that polymerisation proceeds without an induction period to total monomer conversion. With increase in the E-30 concentration from 0.05 to 4.0 wt% in terms of aqueous phase with a constant concentration of CS of 3.0 wt% in terms of styrene, the polymerisation rate increases from 0.75 to 1.3%/min respectively, while the particle diameter decreases from 0.08 µm (with an E-30 concentration of 0.05% in terms of styrene) to 0.05 µm (with an E-30 concentration of 4.0 wt% in terms of styrene). The stability of the reaction system was retained until total conversion of the monomer, while the polymer suspensions were characterised by a narrow particle size distribution, and the ξ-potential of the particles remained low and equal to 12.5 mv (Figure 3). Electron micrographs of particles and histograms of their distribution with respect to the ξ-potential are given Figure 2. The dependence of polymer yield on time during the polymerisation of styrene. T = 80 C, monomer/ water volume ratio 1:4, initiator (potassium persulphate) concentration 1 wt% in terms of styrene, CS concentration 3.0 wt% in terms of styrene, E-30 concentration (in terms of aqueous phase): wt%; wt%; wt%; wt% (b) (a) Figure 3. (a) Micrographs of particles of polystyrene suspensions obtained during the polymerisation of styrene with a monomer/water volume ratio of 1:4 respectively, a temperature of 80 C, an initiator concentration of 1 wt% in terms of styrene, a CS concentration of 3.0 wt% in terms of styrene, and an E-30 concentration in terms of aqueous phase of (1) 0.05 wt% and (2) 4.0 wt%. (b) Histogram of the ξ-potential distribution between polymer particles 2016 Smithers Information Ltd. T/19

4 in Figure 3, and the characteristics of the polystyrene suspensions are set out in Table 2. Reduction in the CS concentration to 0.2 and 0.1 wt% in terms of styrene led to a reduction in the polymerisation rate and to a reduction in the stability of the system with an E-30 concentration of 0.1 wt% in terms of aqueous phase, and the coagulum content amounted to ~15%. Increase in the E-30 concentration, whatever the CS concentration, led to broadening of the particle size distribution and to the appearance of a highly disperse particle fraction, especially pronounced at an E-30 concentration of 4 wt% in terms of water. The appearance of a highly disperse particle fraction is confirmed by an increase in the molecular weight of the polymer at an E-30 concentration of 4 wt% in terms of aqueous phase, whatever the CS concentration. The conversion time kinetic curves obtained with a monomer/aqueous phase volume ratio of 1:2, respectively, are presented in Figure 4. In this case, too, polymerisation proceeds without an induction period at a constant rate to a high monomer Figure 4. The time dependence of the polymer yield during the polymerisation of styrene. T = 80 C, monomer/ water volume ratio 1:2 respectively, initiator (potassium persulphate) concentration 1 wt% in terms of styrene, CS concentration 3.0 wt% in terms of styrene, E-30 concentration (in terms of aqueous phase): wt%; wt%; wt%; wt% Table 2. Characteristics of polystyrene suspensions obtained with different monomer/aqueous phase volume ratios and stabilised with E-30 and CS of different concentration. Polymerisation temperature 80 C, potassium persulphate concentration 1.0 wt% in terms of styrene Monomer/ water volume CS concentration, wt% in terms of monomer E-30 concentration, wt% in terms of aqueous phase Polymerisation rate, %/min Average particle diameter, µm Viscosity-average molecular weight of polymer Coagulum content, % ratio M η : ~ ~ ~ ~ : ~ ~ T/20 International Polymer Science and Technology, Vol. 43, No. 10, 2016

5 conversion. With reduction in the E-30 concentration to 0.05 wt% at a CS concentration of 3 wt% in terms of the monomer, the polymerisation rate decreases, the particle diameter increases a little, the stability of the reaction system falls, and a coagulum appears. With E-30 concentrations above 1.0 wt% in terms of water and with CS concentrations of 0.1 and 0.2 wt% in terms of styrene, the polymer suspensions are stable during polymerisation, the particle size distribution is broad, and the suspensions contain a highly disperse particle fraction (Figure 5). With a monomer/aqueous phase volume ratio of 1:1, an E-30 concentration of 1 wt% in terms of water, and a CS concentration of 3 wt% in terms of the monomer, the particle size distribution was always broad, as the stablity of the reaction system was low, and a coagulum was always formed. During the polymerisation of styrene in the presence of a mixture of the organosilicon surfactant CS and the oxyethylated sulphated alkylphenol AP-9, in a concentration of less than 1 wt% in terms of styrene, polymers with a narrow particle size distribution that were stable during polymerisation were obtained. The polymerisation of styrene was conducted with monomer/aqueous phase volume ratios of 1:2 and 1:4, respectively, and a CS concentration of 1 and 3 wt% in terms of the monomer. The characteristics of the synthesised polystyrene suspensions are given in Table 3. A narrow particle size distribution was observed only with a CS concentration of 3 wt% in terms of the monomer and an AP-9 concentration of 0.5 and 1 wt% in terms of the monomer, with a monomer/water volume ratio of 1:2 respectively. Increase in the AP-9 concentration above 1 wt% in terms of styrene led to broadening of the particle size distribution through the appearance of a highly disperse particle fraction. Micrographs of polymer microspheres obtained with a CS concentration of 3 wt% in terms of styrene and with AP-9 concentrations of 0.5 and 1 wt% in terms of the monomer are given in Figure 6. Figure 5. Histogram of particle distribution of polystyrene suspensions produced during the polymerisation of styrene with a monomer/water volume ratio of 1:2 respectively, a temperature of 80 C, an initiator concentration of 1 wt% in terms of styrene, a CS concentration of 3.0 wt% in terms of styrene, and an E-30 concentration of 0.2 wt% in terms of aqueous phase Figure 6. Micrographs and histograms of particle size distribution of polystyrene suspensions produced during the polymerisation of styrene with a monomer/aqueous phase volume ratio of 1:2, a temperature of 80 C, an initiator concentration of 1 wt% in terms of the monomer, a CS concentration of 3 wt% in terms of the monomer, and an AP-9 concentration in terms of the monomer of (1) 0.5 wt% and (2) 1.0 wt% Table 3. The characteristics of polystyrene suspensions produced in the presence of mixtures of CS and AP-9 Surfactant content in initial emulsion, wt% in terms of styrene CS AP-9 Monomer/water volume ratio Polymerisation rate, min Molecular weight 10 5 Average particle diameter d, mm Polydispersity coefficient M w /M n Coagulum content, % : : : : Smithers Information Ltd. T/21

6 CONCLUSIONS Thus, the investigations conducted showed that stable polystyrene dispersions with a narrow particle size distribution and a particle diameter of µm can be obtained only when ionogenic surfactant concentrations close to values of the critical micelle concentration (CMC) are used in a mixture with the nonionic oil-soluble organosilicon surfactant α,ω-bis[10-carboxydecyl] polydimethylsiloxane. REFERENCES 1. Gritskova I.A., Emulsion polymerisation of water-insoluble monomers. Author s abstract of Doct. Chem. Sci. dissertation, MITKhT, Moscow, 24 pp. (1978). 2. Men shikova A.Yu., Monodisperse polymer particles with a controllable surface structure. Author s abstract of Doct. Chem. Sci. dissertation. SPbGTI, St Petersburg, 43 pp. (2008). 3. Eliseeva V.I. and Aslamazova T.R., Emulsion polymerisation in the absence of an emulsifer and latexes based on it. Uspekhi Khim., 60(2): (1991). 4. Krasheninnikova I.G., Polymer suspensions of medical and biological designation with a narrow particle size distribution. Author s abstract of Doct. Tech. Sci dissertation, MITKhT, Moscow, 38 pp. (2007). 5. Gritskova I.A. et al., The heterophase polymerisation of styrene in the presence of organosilicon compounds of different nature. Vys. Soed., A49(3):1 8 (2007). 6. Chirikova O.V., The synthesis of functional polymer suspensions in the presence of organosilicon compounds. Author s abstract of Cand. Chem. Sci. dissertation, MITKhT, Moscow, 24 pp. (1994). 7. Shragin D.I. et al., Novel approach to synthesis of monodisperse polymeric microspheres: heterophase polymerization of styrene and methyl methacrylate in presence of waterinsoluble functional PDMSs. Silicon, 7: (2015). 8. Zlydneva L.A., Heterophase polymerisation of vinyl monomers in the presence of organosilicon surfactants of different nature. Author s abstract of Cand. Chem. Sci. dissertation, MITKhT, Moscow, 25 pp. (2013). 9. Volkova E.V., The creation of diagnostic test systems using polymer microspheres. Author s abstract of Cand. Chem. Sci. dissertation, MITKhT, Moscow, 26 pp. (2014). 10. Kulichikhin V.G. (ed.), Laboratory Manual on Colloid Chemistry. Moscow, p. 288 (2012). 11. Prokopov N.I. et al., Laboratory Manual on Methods for Investigating Polymers. MITKhT, Moscow, 150 pp. (2013). T/22 International Polymer Science and Technology, Vol. 43, No. 10, 2016