Preparation of Polystyrene‐Poly(N‐isopropylacrylamide) (PS‐PNIPA) Core‐Shell Particles by Photoemulsion Polymerization

Summary: Monodisperse thermosensitive PS‐NIPA core‐shell particles composed of a PS core and a cross‐linked PNIPA shell can be successfully synthesized by a novel method: photoemulsion polymerization. Cryo‐TEM images indicate clearly the core‐shell morphology of the PS‐NIPA particles: A homogeneous regular PNIPA shell has been affixed on the spherical PS core. DLS measurements indicate that the obtained PS‐NIPA latex particles are thermosensitive. The shell of PNIPA networks with different cross‐linking densities can shrink and re‐swell with temperature and the volume transition temperature is around 32 °C in all cases.

Cryo‐TEM image of PS‐NIPA core‐shell particles.     

PNIPA类纳米水凝胶在药物缓控释研究中的应用

简要介绍了聚N-异丙基丙烯酰胺(Poly N-isopropylacrylamide, PNIPA)类纳米水凝胶的性质及智能响应机理,并重点综述了近年来此类纳米水凝胶在药物缓控释研究中的应用:作为脂溶性小分子药物的载体,达到增溶及缓控释药物的效果,并增强药物的稳定性及生物活性;作为水溶性小分子药物的载体,达到缓释该类药物的效果;作为生物大分子药物(蛋白,多糖)的载体,克服直接用药时的弊端;此外,还可作为基因工程载体.     

Positron annihilation lifetime study of continuous volume phase transition of poly(N-isopropylacrylamide) gel induced in methanol–water mixed solvent

The macroscopic volume shrinkage and swelling of poly(N-isopropylacryl-amide) (PNIPA) gel induced by the compositional change in the methanol–water mixed solvent is correlated to the change in the nanoscopic free volume size and numerical concentration formed in the PNIPA gels. The free volume size and numerical concentration are estimated from the longest component appearing in the positron annihilation lifetime curves. The apparent free volume fraction calculated by the free volume size and numerical concentration, and dispersion of the free volume deduced by the size distribution are utilized to analyze the origin and location of the free volumes. The free volume parameters obtained by analysis of the positron annihilation data show various nanoscopic phases occuring within the PNIPA gels during the volume change, implying the variation of the strength of the interactions among the solvent molecules and the polymer chains of the PNIPA. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1141–1151, 1998     

Thermo-responsive polymer coated fiber-in-tube capillary microextraction and its application to on-line determination of Co, Ni and Cd by inductively coupled plasma mass spectrometry (ICP-MS)

The poly(N-isopropylacrylamide) (PNIPA) gel is a widely studied thermo-responsive material that exhibits discontinuous change in volume when the external temperature is increased. In this paper, PNIPA gel was prepared and applied as a novel polymer coating for fiber-in-tube capillary microextraction of trace Co, Ni and Cd followed by on-line ICP-MS detection. The PNIPA coating was synthesized by using ethylene triethoxysilane (ETEOS) as the cross-linking agent under acidic conditions. This siloxane incorporated PNIPA gel achieves a dramatically rapid response rate when the external temperature is changed. The micro-structure of PNIPA coating was examined by scanning electron micrograph (SEM). Various experimental parameters including pH, temperature, sample flow rate and volume, elution solution and interfering ions affecting the extraction of the target analytes have been carefully investigated and optimized. Under the optimized conditions, the limits of detection were 0.45, 4.6 and 6.9 ng L⁻¹ for Co, Ni and Cd, respectively. With a sampling frequency of 13 h⁻¹, the relative standard deviations (RSDs) for Co, Ni and Cd were 4.8, 5.1 and 6.4% (C = 1 μg L⁻¹, n = 7), respectively. The proposed method had been successfully applied to the determination of Co, Ni and Cd in human urine. To validate the proposed method, certified reference materials of NIES No. 10-b rice flour and GBW07601 (GSH-1) human hair were analyzed and the determined values were in a good agreement with the certified values. The PNIPA coated fiber-in-tube capillary can be reused for more than 150 times without decreasing the extraction efficiency.     

分子量分布对线性PNIPA/D20溶液相变和扩散性质的影响

利用¹H NMR谱和NMR自扩散方法研究了2种不同分子量分布的聚（N-异丙基丙烯酰胺）（PNIPA）的相变行为和扩散性质,发现分子量分布对PNIPA水溶液的相变行为和扩散性质都有明显影响. 在PNIPA水溶液的相变温度-浓度曲线中,宽分子量分布PNIPA的曲线下降比较平缓,而低分子量分布PNIPA的曲线先是快速降低,然后趋于缓和. 在扩散实验中,宽分子量分布PNIPA的自扩散衰减曲线呈现一定的曲率,而且温度越低,浓度越高,曲率越大;而窄分子量分布PNIPA的自扩散衰减曲线几乎是直线,受温度和浓度的影响很小. 通过基于经典的Kohlrausch Williams-Watts延展指数关系式来拟合宽分子量分布PNIPA自扩散系数和常规方程拟合窄分子量分布PNIPA自扩散系数的2种方法对比,可以得到基于Kohlrausch-Williams-Watts的延展指数拟合,有效改善分子量分布造成的影响.