聚乙二醇在异丁酸+水临界点附近的构象变化。

Conformational change of poly(ethylene glycol) near the critical point of isobutyric acid + water.

作者信息

Castellanos Patricia, Norman Alexander I, Greer Sandra C

机构信息

Department of Chemical and Biomolecular Engineering, The University of Maryland College Park, College Park, Maryland 20742, USA.

出版信息

J Phys Chem B. 2006 Nov 9;110(44):22172-7. doi: 10.1021/jp056154o.

DOI:10.1021/jp056154o

PMID:17078654

Abstract

In solutions of isobutyric acid + water, poly(ethylene glycol) (PEG) can assume a helical conformation. [Alessi, M. L.; Norman, A. I.; Knowlton, S. E.; Ho, D. L.; Greer, S. C. Macromolecules 2005, 35, 9333-9340.] Here we report new measurements of the kinematic viscosity, nu, as a function of temperature for a solution of isobutyric acid + water at the critical composition, to which PEG (number average molecular weight = 1.01 x10(3) g/mol) was added at a concentration of 6.01 mg/mL. The data show that nu decreases near the critical point, with a maximum in nu at about 0.05 degrees C above the critical temperature, Tc. We interpret this change in nu in terms of a change in conformation of the polymer from helix to coil. This interpretation is supported by polarimetry measurements on the same mixture doped with (S)-(+)-1,2-propanediol, which indicates the loss of helicity near Tc and also a second helix-to-coil transition at about 60 degrees C.

摘要

在异丁酸 + 水的溶液中，聚乙二醇（PEG）可呈现螺旋构象。[阿莱西，M. L.；诺曼，A. I.；诺尔顿，S. E.；何，D. L.；格里尔，S. C.《大分子》2005年，35卷，9333 - 9340页。] 在此我们报告了对处于临界组成的异丁酸 + 水溶液的运动粘度ν随温度变化的新测量结果，该溶液中添加了浓度为6.01 mg/mL的PEG（数均分子量 = 1.01×10³ g/mol）。数据表明，ν在临界点附近降低，在高于临界温度Tc约0.05℃时ν出现最大值。我们将ν的这种变化解释为聚合物构象从螺旋变为卷曲的变化。对掺杂了（S） - （ + ） - 1,2 - 丙二醇的同一混合物进行的旋光测量支持了这一解释，该测量表明在Tc附近螺旋性丧失，并且在约60℃时还发生了第二次螺旋 - 卷曲转变。