Small-Angle Neutron Scattering Study on Specific Polymerization Loci Induced by Copolymerization of Polymerizable Surfactant and Styrene during Miniemulsion Polymerization

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• 作者：Ryuhei Motokawa ; Tatsuo Taniguchi ; Yusuke Sasaki ; Yuto Enomoto ; Fumiyasu Murakami ; Masakatsu Kasuya ; Michinari Kohri ; Takayuki Nakahira
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：December 11, 2012
• 年：2012
• 卷：45
• 期：23
• 页码：9435-9444
• 全文大小：483K
• 年卷期：v.45,no.23(December 11, 2012)
• ISSN：1520-5835

文摘

We have investigated the origin of a specific polymerization loci that yielded copolymer particles with a bimodal gel permeation chromatographic profile in the early stage of miniemulsion polymerization of styrene (St) with the polymerizable surfactant N-n-dodecyl-N-2-methacryloyloxyethyl-N,N-dimethylammonium bromide (C₁₂DMAEMA). The formation of particles by miniemulsion polymerization using C₁₂DMAEMA was investigated as a function of the polymerization time (t_p) and was compared with that using the nonpolymerizable surfactant cetyltrimethylammonium bromide (CTAB). St was miniemulsified with C₁₂DMAEMA or CTAB and was polymerized with either a water-soluble initiator, 2,2鈥?azobis(2-amidinopropane) dihydrochloride (V50), or an oil-soluble initiator, 2,2鈥?azobis(isobutyronitrile) (AIBN), at 60 掳C in the presence of polystyrene (PSt) as a hydrophobe. Gel permeation chromatography (GPC) and elemental analysis indirectly predicted two different polymerization loci in the St/C₁₂DMAEMA/V50 polymerization system. Time-resolved small-angle neutron scattering (SANS) was used to directly observe and examine the specific polymerization loci in the miniemulsion polymerization solutions. The droplets formed in the St/C₁₂DMAEMA/V50/PSt at the initial stage of the polymerization were not fully stabilized by C₁₂DMAEMA and poly(C₁₂DMAEMA-ran-St) and were found to build up the large aggregates. The spherical droplets were stabilized later in the polymerization (t_p > 20 min) by forming a homogeneous dispersion in the water phase. In contrast, the droplets stabilized by CTAB in St/CTAB/V50/PSt maintained their size and shape throughout the polymerization. As a result, in both polymerization systems of St/C₁₂DMAEMA/V50/PSt and St/CTAB/V50/PSt, the particle size was found to depend strongly on the size of the droplets formed in the early stage of polymerization. Porod analysis of the power law scattering observed by SANS provided direct evidence for the specific polymerization loci, which appeared in the early stage of the polymerization system of St/C₁₂DMAEMA/V50/PSt on the surface of the droplet, and was the origin of the bimodal peaks in the GPC chromatogram.