Fabrication of composite polymer particles by stabilizer-free seeded polymerizationby Hossein Adelnia, Jaber Nasrollah Gavgani, Mohammad Soheilmoghaddam

Colloid Polym Sci

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SHORT COMMUNICATION

Fabrication of composite polymer particles by stabilizer-free seeded polymerization

Hossein Adelnia1 & Jaber Nasrollah Gavgani1,2 & Mohammad Soheilmoghaddam3

Received: 14 April 2015 /Revised: 26 May 2015 /Accepted: 19 June 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract This paper reports the fabrication of polymer composite particles through stabilizer-free seeded polymerization.

Various monomers were polymerized in the presence of submicron sodium styrene sulfunate-functionalized polystyrene seed particles without using swelling agent, emulsifier, or stabilizer. It was found that stable monodisperse composite particles are obtained even without using any ionic comonomer provided that the used monomer is nonpolar enough to facilitate swelling of the seeds. Utilizing the proposed method, copolymerization of styrene/divinyl benzene was successfully performed, resulting in highly crosslinked composite particles. Interestingly, Janus amphiphilic particles were achieved after the extraction of polystyrene by toluene from the particles. Overall, it is demonstrated that the proposed approach can be adopted as a facile and green process for the fabrication of various composite Janus particles.

Keywords Seeded polymerization . Stabilizer-free .

Composite polymer particles . Janus amphiphilic particles .

Anionic particles

Introduction

In recent years, a great deal of attention has been devoted to the synthesis and characterization of composite polymeric particles possessing monodisperse size distribution which is considered as a crucial factor in wide ranges of applications from drug delivery to heat storage [1, 2]. The deep interest in these particles arises particularly from the capability of benefiting simultaneously from certain properties of the different components. In general, such particles are synthesized through some techniques such as seeded emulsion [3, 4] and seeded dispersion polymerization [5] in which the seed particles serve not only as one component of the composite material but also as micro-reactors and/or nuclei for reaction of other components. Up until now, using these methods, various nonspherical shapes have been produced [6–9].

Despite their advantages and usefulness, conventional seeded emulsion and dispersion polymerizations suffer from a major drawback, and that is the presence of high quantities of emulsifier or stabilizer which can adversely affect mechanical, optical, and other pivotal features of the resulting latexes [10]. Their removal by suitable methods not only is timeconsuming and expensive but also is associated with other difficulties such as destabilization of dispersion, the formation of anomalous morphology, and so forth [11]. Therefore, the importance of the fabrication of as-prepared stabilizer-free latexes is highlighted.

The preparation of clean single-component particles by soap-free emulsion [12, 13] and stabilizer-free dispersion polymerizations (SFDP) [14, 15] have widely been developed.

Generally, ionic comonomers, in the range of 1–5 wt% with respect to the total amount of monomer, are employed to endow the final particles with high colloidal stability and surface functional groups [16, 17]. It has been demonstrated that the synthesized latexes having comonomers with high acidic/

Electronic supplementary material The online version of this article (doi:10.1007/s00396-015-3675-8) contains supplementary material, which is available to authorized users. * Mohammad Soheilmoghaddam mohammad.soheilmoghaddam@uqconnect.edu.au 1 Department of Polymer Engineering and Color Technology,

Amirkabir University of Technology, P.O. Box 15875-4413,

Tehran, Iran 2 Department of Chemical Engineering, Amirkabir University of

Technology, P.O. Box 15875-4413, Tehran, Iran 3 Tissue Engineering and Microfluidics Laboratory, Australian

Institute for Bioengineering and Nanotechnology, University of

Queensland, St. Lucia, QLD 4067, Australia

Colloid Polym Sci

DOI 10.1007/s00396-015-3675-8 basic strength are highly stable and have high surface charge density. Though a great attention has been focused on clean single-component particles, to our knowledge, there is no study on the synthesis of composite particles without using any kind of stabilizer or emulsifier by seeded polymerization methods. To follow this objective, here, we investigate the preparation of such particles via stabilizer-free seeded polymerization (SFSP). Various monomers were polymerized in the presence of both anionic and cationic polystyrene seeds prepared in our previous work [18], and the whys and wherefores of the stability of the composite particles are discussed in this report.

Experimental

Materials

Styrene (Sty), methyl methacrylate (MMA), butyl methacrylate (BuMA), 2-ethylhexyl methacrylate (EHMA), divinylbenzene (DVB), sodium styrene sulfonate (NaSS), vinyl benzyl trimethyl ammonium chloride (VBTMAC), 2acrylamido-2-methylpropane sulfonic acid (AMPS), and sodium styrene sulfonate (NaSS) were purchased from SigmaAldrich Co. and used without further purification. 2,2Azobis(isobutyronitrile) (AIBN) and benzoyl peroxide (BPO) along with other reagents including solvents were also supplied by Merck Co.

Typical stabilizer-free dispersion polymerization

The stabilizer-free dispersion polymerization (SFDP) of Sty was carried out as follows; first, 18.24 g ethanol was added to 12.16 g water as polymerization medium. Then, the monomer phase, 1.6 g in total (including 1.52 g Sty, 0.016 g BPO, and 2.5 mol % ionic comonomer with respect to total) was added to the medium. The mixture was purged with nitrogen, capped, sealed, and finally placed in a constant-temperature water bath at 70 °C and stirred 24 h at 60 rpm. NaSS, AMPS, and VBTMAC were used as ionic comonomers. The detailed procedure, results, and discussion of the polymerization have been provided in our previous work [18].

Typical stabilizer-free seeded polymerization

Stabilizer-free seeded polymerization (SFSP) of various monomers was performed in sealed glass bottles under the condition listed in Table 1. The reactions were carried out in a constant-temperature water bath at 70 °C at 60 rpm for 24 h under nitrogen atmosphere. Prior to the polymerization, the mixture was gently agitated for 2 h at 40 °C to swell the seeds as much as possible. It should be mentioned that monomer/seed ratio was set in all the batch polymerizations equal to 1:1 (w/w).