Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, United Kingdom.
Langmuir. 2012 Sep 18;28(37):13189-200. doi: 10.1021/la302657x. Epub 2012 Aug 31.
A series of novel polyacid macromonomers based on 2-hydroxypropyl methacrylate (HPMA) were prepared by atom transfer radical polymerization (ATRP) via a two-step route. First, a range of well-defined PHPMA homopolymer precursors were synthesized by ATRP using a tertiary amine-functionalized initiator, 2-(dimethylamino)ethyl-2-bromoisobutyrylamide, and a CuCl/2, 2'-bipyridine (bpy) catalyst in alcoholic media at 50 °C. ATRP polymerizations were relatively slow and poorly controlled in pure isopropanol (IPA), especially when targeting higher degrees of polymerization (DP > 30). Improved control was achieved by addition of water: low polydispersity (M(w)/M(n) < 1.25) PHPMA homopolymers of DP = 30, 40, 50, 60, or 70 were successfully prepared using a 9:1 w/w % IPA/water mixture at 50 °C. These PHPMA homopolymer precursors were then derivatized to produce the corresponding poly(2-(succinyloxy)propyl methacrylate) (PSPMA) macromonomers by quaternizing the tertiary amine end-group with excess 4-vinylbenzyl chloride, followed by esterification of the pendent hydroxyl groups using excess succinic anhydride at 20 °C. These polyacid macromonomers were evaluated as reactive steric stabilizers for polystyrene latex synthesis under either aqueous emulsion polymerization or alcoholic dispersion polymerization conditions. Near-monodisperse polystyrene latexes were obtained via aqueous emulsion polymerization using 10 wt % PSPMA macromonomer (with respect to styrene monomer) with various initiators as evidenced by scanning electron microscopy, disk centrifuge photosedimentometry and light scattering studies. PSPMA macromomer concentrations as low as 1.0 wt % also produced near-monodisperse latexes, suggesting that these PSPMA macromonomers are highly effective stabilizers. Alcoholic dispersion polymerization of styrene conducted in various ethanol/water mixtures with 10 wt % PSPMA(50) macromonomer produced relatively large near-monodisperse latexes. Increasing the water content in such formulations led to smaller latexes, as expected. Control experiments conducted with 10 wt % PSPMA(50) homopolymer produced relatively large polydisperse latexes via emulsion polymerization and only macroscopic precipitates via alcoholic dispersion polymerization. Thus the terminal styrene group on the macromonomer chains is essential for the formation of well-defined latexes. FT-IR spectroscopy indicated that these latexes contained PSPMA macromonomer, whereas (1)H NMR spectroscopy studies of dissolved latexes allowed stabilizer contents to be determined. Aqueous electrophoresis and X-ray photoelectron spectroscopy studies confirmed that the PSPMA macromonomer chains were located at the latex surface, as expected. Finally, these polyacid-stabilized polystyrene latexes exhibited excellent freeze-thaw stability and remained colloidally stable in the presence of electrolyte.
通过两步法，通过原子转移自由基聚合（ATRP）制备了一系列基于 2-羟丙基甲基丙烯酸酯（HPMA）的新型多酸大分子单体。首先，通过 ATRP 使用叔胺官能化引发剂 2-（二甲氨基）乙基-2-溴代异丁酰胺和 CuCl/2,2'-联吡啶（bpy）催化剂在醇介质中于 50°C 合成了一系列具有良好定义的 PHPMA 均聚物前体。在纯异丙醇（IPA）中，ATRP 聚合反应相对较慢且控制不佳，特别是当目标是较高的聚合度（DP>30）时。通过添加水可以实现更好的控制：在 50°C 下，使用 9:1 w/w%IPA/水混合物成功制备了 DP=30、40、50、60 或 70 的低分散度（M(w)/M(n)<1.25）PHPMA 均聚物。然后，通过用过量的 4-乙烯基苄基氯季铵化叔胺端基，然后在 20°C 下用过量的琥珀酸酐酯化悬垂羟基，将这些 PHPMA 均聚物前体制备成相应的聚（2-（琥珀酰氧基）丙基甲基丙烯酸酯）（PSPMA）大分子单体。这些聚酸大分子单体作为反应性空间位阻稳定剂，在水性乳液聚合或醇分散聚合条件下用于合成聚苯乙烯乳胶。通过水性乳液聚合，使用 10wt%（相对于苯乙烯单体）的 PSPMA 大分子单体和各种引发剂，通过扫描电子显微镜、盘离心光沉淀法和光散射研究，得到了近单分散的聚苯乙烯乳胶。即使使用 1.0wt%的 PSPMA 大分子单体，也可以得到近单分散的乳胶，表明这些 PSPMA 大分子单体是非常有效的稳定剂。在各种乙醇/水混合物中，通过醇分散聚合，用 10wt%PSPMA（50）大分子单体进行苯乙烯聚合，得到了相对较大的近单分散乳胶。如预期的那样，增加配方中的含水量会导致乳胶粒径变小。通过 10wt%PSPMA（50）均聚物进行的乳液聚合和醇分散聚合仅产生宏观沉淀物的对照实验表明，大分子单体链末端的苯乙烯基团对于形成具有良好定义的乳胶是必不可少的。傅里叶变换红外光谱表明这些乳胶含有 PSPMA 大分子单体，而溶解乳胶的（1）H NMR 光谱研究允许确定稳定剂含量。水性电泳和 X 射线光电子能谱研究证实，PSPMA 大分子单体链位于乳胶表面，这是意料之中的。最后，这些聚酸稳定的聚苯乙烯乳胶表现出优异的冻融稳定性，并在存在电解质的情况下保持胶体稳定。
