colloidal molecules. [10] As the polystyrene particle core can be easily removed by solvents or elevated temperatures, hollow metal oxide particles can be synthesized from polystyrene colloidal templates. [11,12] Finally, polystyrene colloidal particles have been extensively used in self-assembly processes to create ordered structures with high precision in two [13] and three dimensions. [14] Similar to the single particle level, such structures can serve as sacrificial templates to create arrays of surface nanostructures, [15] or nanoporous materials. [16] For all these applications of PS particles, control of particle size, polydispersity, and surface chemistry are of key importance. Hence, the development and understanding of reaction conditions leading to tailored and predictable size and surface functionality are crucial. Especially for small colloidal particle sizes with diameters below 100 nm, emulsion polymerization reactions often lead to high polydispersities, which can result from the short growth phase with decreasing monomer concentration and an incomplete separation of nucleation and growth. [17] Here, we focus on positively charged PS particles, which are commonly synthesized by emulsion polymerization with cationic initiators [11,18] or cationic comonomers. [19] Typically, such comonomers introduce charges via quaternary ammonium groups that can be used in styrene emulsion poly merizations with, [20] or without [17] additional surfactants. We use surfactant-free copolymerization of styrene and the quaternary ammonium salt (vinylbenzyl)trimethyl-ammonium chloride (VBTMAC) with 2,2-azobis (2-methylpropionamidine) dihydrochloride (AAPH) as initiator and investigate the role of the VBTMAC concentration on the resulting particle properties. We show that we can precisely control the particle size by the variation of VBTMAC concentration at three different styrene to water volume fractions. To clearly demonstrate the effect of VBTMAC on the particle size for each styrene volume fractions used control samples were synthesized without comonomer following a recipe similar to Nandiyanto et al. [11] We investigate the mechanistic origins of this control and the role of the monomer and comonomer in nucleation events and particle growths. We propose an PS particles growth mechanism which can be understood as an extension of the mechanism suggested by Liu et al. for a wide range of styrene to VBTMAC monomer ratios. [17] Importantly, our method enables the fabrication of highly Colloidal SynthesisThe formation of positively charged polystyrene latex particles via the surfactant-free emulsion polymerization of styrene with cationic initiator is investigated. Using the comonomer (vinylbenzyl)trimethyl-ammonium chloride (VBTMAC) it is shown that the particle size can be tuned rather precisely between above 350 nm and below 70 nm. The simple functional dependence of the particle size on the inverse cube root of the comonomer concentration leads to propose, with reasonable assumptions, that VBTMAC comonomer addition...

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