In-Situ Bulk Polymerization of Dilute Particle/MMA Dispersions

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• 作者：Mustafa M. Demir ; Patrice Castignolles ; Ü ; mit Akbey ; Gerhard Wegner
• 刊名：Macromolecules
• 出版年：2007
• 出版时间：June 12, 2007
• 年：2007
• 卷：40
• 期：12
• 页码：4190 - 4198
• 全文大小：461K
• 年卷期：v.40,no.12(June 12, 2007)
• ISSN：1520-5835

文摘

Composites of poly(methyl methacrylate) and various nanoscale inorganic particles (zinc oxide,titanium dioxide, zirconium dioxide, silicon dioxide, and aluminum nitride) were prepared by in-situ bulkpolymerization using 2,2'-azobis(isobutyronitrile) as initiator. The particles of ZnO, TiO₂, and ZrO₂ were surface-modified by alkylphosphonic acids to render them dispersible in the monomer. The effect of these nanoparticleson the free radical polymerization was investigated. Regardless of chemical nature and size, the particles suppressthe autoacceleration which would otherwise occur in the bulk free-radical polymerization of methyl methacrylate(MMA). A degenerative chain transfer is proposed to take place between surface-adsorbed water on the particlesand propagating chain radicals. This reaction competes with normal termination. Formation of vinylidene chainsends originating from disproportionation is suppressed. In consequence, thermal stability of PMMA produced inthe presence of particles is improved. Aggregation of individual particles upon polymerization has been observedand presumably is due to interparticle depletion attraction, even though the particles are individually dispersed inthe monomer. Formation of particle clusters is suppressed when a difunctional monomer (e.g., ethylene glycoldimethacrylate) is used as comonomer. The cross-linked medium slows down the diffusion of the particles andtherefore interferes with particle aggregation via a depletion mechanism.