Synthesis of ABA Type Block Copolymers of Poly(Ethylene Glycol) and Poly(Dodecyl Vinyl Ether) and Its Using as Surfactant in Emulsion Polymerization ()
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Table 1. Formulation used in polymerizations.
Received November 23, 2013; revised December 26, 2013; accepted January 5, 2014
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Figure 1.FT-IR spectrum of the polymeric surfactant.
bonyl group and alkyl chains of dodecyl group, respec- tively.
Also, the C-O stretching vibration occurs at 1054 cm−1 belongs to etheric group. 1H-NMR spectrum of the po- lymer was given in Figure 2. Aliphatic protons of alkyl chains of dodecyl groups were observed as a multiplet at 1.20 - 1.80 ppm and etheric protons of PEG were ob- served at 3.0 - 4.0 ppm.
The number average molecular weight and polydisper- sity of the polymeric surfactant were detected as 1152 g/mol and 1.10 respectively (Figure 3). The narrow mo- lecular weight clearly show that the polymerization quan- titatively proceeds in a controlled fashion to afford a po- lymer with well-defined chain structure under the condi- tion employed.
3.1. Viscosity
Dispersion with a large number of small particles exhi- bits a higher viscosity than one with a small number of large particles [21]. Polymeric surfactant accelerated the reaction, because of increasing with the length of the hydrophobic part of the surfactant. Increasing sur- factant concentration in the polymer recipe slightly increased the latex viscosities, but it does not affect very seriously on the viscosities of VAc and St latexes
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Figure 2.1H-NMR spectrum of the polymeric surfactant.
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Figure 3.GPC traces of the polymeric surfactant.
(Table 2).
The main advantages of block copolymer synthesis in emulsion, over conventional bulk or solution poly- merizations, are that such polymerizations do not re- quire drastic experimental conditions such as anionic or cationic “living polymerizations”. Moreover, free rad- ical emulsion polymerizations are environmentally friendly methods for the production of polymers due to the absence of volatile organic compounds. These po- lymerizations often reach very high conversions; the heat produced by exothermic reactions is dissipated by the water and high-molecular weight polymers can be obtained in a low viscosity media. The final product can thus be directly used in its latex form, in coating applications for instance [18].
3.2. Surface Tension
The surface tension measurements were performed on a Sigma 701 model tensiometer (KSV instruments, Hel- sinki, Finland) equipped with a Pt du Nouy ring at 24˚C, and results were given in Table 2. Surface tension of homopolymer latexes increased with surfactant concen- tration. This can be explained by taking into account that the surface area stabilized by the surfactant increases with an increase of the concentration of the surfactant
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Table 2. Colloidal characteristics of latexes.
resulting in smaller particles due to mass balance consid- erations. The increasing hydrophobic character into po- lymer causes to increasing emulsifier adsorption onto polymer particles. Thus the increasing of free emulsifier concentration in latex by blocking of emulsifier adsorp- tion and the decreasing of polarity differences between interfaces cause to increase the surface tension, especial- ly for VAc latexes.
Surface tension can be used as a measure for the cov- erage of particles. As can be derived from the surface tension values, the particle surfaces of the latexes are incompletely covered with surfactant molecules because the surface tensions of the latexes lie well above the val- ues of the saturated surfactant solution. The smaller the particles are, the higher the surface tension is and, there- fore, the coverage of the particles with surfactant in- creases with decreasing particle size [22].
3.3. Particle Size
The particle size of the final latexes was determined by Zetasizer, and can be seen in Table 2. It was found that the particle size mainly depends on the amount of sur- factant in both latex series. The presence of the long hy- drophobic chain of the Pluronic surfactants had a screen- ing effect on the Coulombic forces which prevents the surfactant adsorption. Consequently, the higher the chain lengths of the hydrophobic part of the surfactant, the higher the surfactant adsorption on the polymer [23]. The polymeric surfactant causes to decrease the number of particles in the volume unit, thus viscosity of latexes in- creased, and particle size decreased.
An increase of the surfactant quantity from 0.103 to 0.360 (wt) results in a decrease of the particle size and an increase viscosity. The viscosity of the dispersions measured increases drastically (Table 2). This can be explained by taking into account that the surface area stabilized by the surfactant increases with an increase of the concentration of the surfactant resulting in smaller particles due to mass balance considerations. A disper- sion with a large number of small particles exhibits a higher viscosity than one with a small number of large particles [21].
4. Conclusion
In this study, commercially available PEG-400 was mod- ified to prepare macroinitiator which was then used in the cationic polymerization of dodecyl vinyl ether. The new surfactant was used in emulsion polymerization of vinyl acetate and styrene. It was determined that when the concentration of the polymeric surfactant was increased, the resulting latex viscosity slightly increases, particle size decreases regularly, and the viscosity molecular weight of final latex increases. The surface tension and particle size of polymer latex follow different trends with the increasing of the surfactant concentration. Meanwhile, they were changed very seriously. It was found that the surfactant concentration was sensitive to such parameters as viscosity, molecular weight, surface tension, and par- ticle size.
Acknowledgements
This work were supported by the Turkish Scientific and Technological Research Council (TUBITAK) (Project Number: 108T722) and Scientific Research Projects Coordination Center of Yildiz Technical University (Project Number: 2012-01-02-KAP04).
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