RAFT合成pH和温度响应的双亲水嵌段共聚物

Synthesis of pH- and Temperature-Responsive of the Double Hydrophilic Block Copolymer via RAFT

摘要:

以S-十二烷基-S’-(2-羧基-异丙基）三硫酯（DDATC）为链转移剂，偶氮二异丁氰（AIBN）为引发剂，通过可逆加成-断裂链转移（RAFT）聚合合成了结构明确窄分子量分布（Mw/Mn=1.27）的聚（N-异丙基丙烯酰胺）-b-聚（N,N-二甲胺基甲基丙烯酸乙酯）（PNIPAm-b-PDMAEMA）双亲水两嵌段共聚物。共聚物的结构通过红外光谱（FT-IR）、核磁（1HNMR）和凝胶渗透色谱（GPC）表征。采用透光率法、稳态荧光光谱法、电位滴定和动态光散射（DLS）研究了PNIPAm-b-PDMAEMA在水中温度和pH敏感的胶束化。结果表明：PNIPAm-b-PDMAEMA具有温度响应性，其水溶液的低临界溶液温度（LCST）为32.3 ℃，溶液温度高于LCST时发生温度诱导的胶束化，胶束的流体力学半径（Rh）为50nm左右，Rh随温度升高而稍微增大；PNIPAm-b-PDMAEMA水溶液表现出明显的pH敏感性，25 ℃时两嵌段共聚物pH诱导胶束化的临界pH值为9.8，溶液pH高于临界pH值时发生pH诱导的胶束化，胶束的Rh约为31nm。

Abstract:

A double-hydrophilic diblock copolymer of poly(N-isopropyl acrylamide) -b-poly(N,N-dimethylamino-2-ethyl methacrylate) (PNIPAm-b-PDMAEMA) with well-defined structure and narrow molecular weight distribution (Mw/Mn = 1.27) was synthesized via reversible addition - fragmentation chain transfer (RAFT) polymerization using S-1-dodecyl-S’-(α,α’-dimethyl-α’’-acetic acid) trithiocarbonate (DDATC) and 2,2-azobisisobutyronitrile (AIBN) as chain transfer agent and initiator, respectively. The PNIPAm-b-PDMAEMA was characterized with FT-IR, 1H-NMR and gel permeation chromatography (GPC). The pH and temperature induced micellization of PNIPAm-b-PDMAEMA in the aqueous solution was investigated by transmittance measurement, fluorescence spectroscopy, potentiometric titration and dynamic light scattering (DLS). The copolymer exhibits temperature-responsive micellization in aqueous solution with a lower critical solution temperature (LCST) of 32.3 oC. As raising the temperature over LCST, the PNIPAm block turned to hydrophobic which caused formation of the global micelle composed of PNIPAm core and PDMAEMA shell. The hydrodynamic radius Rh of the micelle measured with DLS about 50 nm and increased with increasing temperautre. The Rh of the micelles increased with increasing temperature. The copolymer exhibits pH-sensitive associate behavior in aqueous solution and the threshold pH value of the pH-induced micellization is about 9.8 at 25 oC. The Rh of the micelle composed of PDMAEMA core and PNIPAm shell is about 31 nm at pH 11.0.