Belsey Kate E, Topping Claire, Farrand Louise D, Holder Simon J
Functional Materials Group, School of Physical Sciences, University of Kent , Canterbury, Kent CT2 7NH, United Kingdom.
Merck Chemicals Limited , Chilworth Technical Centre, University Parkway, Southampton SO16 7QD, United Kingdom.
Langmuir. 2016 Mar 22;32(11):2556-66. doi: 10.1021/acs.langmuir.6b00063. Epub 2016 Mar 9.
Polymeric particle dispersions have numerous potential applications; currently one of the most relevant is their use as inks in electrophoretic displays. These colloidal particles are synthesized from the appropriate monomer using nonaqueous dispersion (NAD) polymerization in a nonpolar solvent, which requires a stabilizer to control particle size and morphology. We have previously reported the facile synthesis of poly(methyl methacrylate)-block-poly(octadecyl acrylate) (PMMA-b-PODA) by atom transfer radical polymerization (ATRP), and its use in the NAD polymerization of MMA in hexane/dodecane solvent mixtures. Here we report the synthesis of monodisperse PMMA particles in dodecane following a standard "industrial" procedure using these PMMA-b-PODA stabilizers. However, it was observed that the particle suspensions solidified when they were left at temperatures below ∼18 °C yet redispersed upon being heated. Differential scanning calorimetry, dynamic light scattering, and rheological studies demonstrated that this thermoresponsive behavior was due to a liquid-gel transition occurring at 17.5 °C as a consequence of the upper critical solution temperature of PODA in dodecane being traversed. Consequently, new copolymers were synthesized by ATRP with an ethylhexyl acrylate (EHA) co-monomer incorporated into the lyophilic (dodecane compatible) block. Dispersions stabilized by these PMMA-b-P(ODA-co-EHA) polymers with high EHA contents exhibited lower gelation temperatures because of the greater solvent compatibility with dodecane. The use of a PMMA65-b-(ODA10-co-EHA45) copolymer stabilizer (with the highest EHA content) gave PMMA dispersions that showed no gelation down to 4 °C and monodisperse cross-linked PMMA particles containing organic dyes (cyan, magenta, red, and black) giving colored particles across the size range of approximately 100-1300 nm.
聚合物颗粒分散体有许多潜在应用；目前最相关的应用之一是它们在电泳显示器中用作墨水。这些胶体颗粒是在非极性溶剂中通过非水相分散（NAD）聚合由合适的单体合成的，这需要一种稳定剂来控制颗粒大小和形态。我们之前报道了通过原子转移自由基聚合（ATRP）简便合成聚（甲基丙烯酸甲酯）-嵌段-聚（丙烯酸十八酯）（PMMA-b-PODA），以及它在己烷/十二烷溶剂混合物中用于甲基丙烯酸甲酯的NAD聚合。在此我们报道使用这些PMMA-b-PODA稳定剂按照标准“工业”程序在十二烷中合成单分散PMMA颗粒。然而，观察到颗粒悬浮液在温度低于约18°C时会固化，但加热后会重新分散。差示扫描量热法、动态光散射和流变学研究表明，这种热响应行为是由于PODA在十二烷中的上临界溶液温度被跨越，导致在17.5°C发生液-凝胶转变。因此，通过ATRP合成了新的共聚物，其中丙烯酸2-乙基己酯（EHA）共聚单体被引入亲液（与十二烷相容）嵌段。由这些具有高EHA含量的PMMA-b-P(ODA-co-EHA)聚合物稳定的分散体表现出较低的凝胶化温度，因为与十二烷的溶剂相容性更好。使用PMMA65-b-(ODA10-co-EHA45)共聚物稳定剂（EHA含量最高）得到的PMMA分散体在4°C以下不发生凝胶化，并且含有有机染料（青色、品红色、红色和黑色）的单分散交联PMMA颗粒在大约100 - 1300 nm的尺寸范围内呈现出彩色颗粒。
