Dissociation and thermal characteristics of poly(acrylic acid) modified pluronic block copolymers in aqueous solution

被引:12
作者
Tian, Y. [1 ,2 ]
Hatton, T. Alan [1 ,4 ]
Tam, Kam C. [3 ]
机构
[1] Singapore MIT Alliance, Singapore, Singapore
[2] Nanyang Technol Univ, Sch Mech & Aerosp Engn, Singapore 639798, Singapore
[3] Univ Waterloo, Waterloo Inst Nanotechnol, Dept Chem Engn, Waterloo, ON N2L 3G1, Canada
[4] MIT, Dept Chem Engn, Cambridge, MA 02139 USA
基金
加拿大自然科学与工程研究理事会;
关键词
Pluronics; Polyacrylic acid; Self-assembly; OXIDE) TRIBLOCK COPOLYMERS; POTENTIOMETRIC TITRATION; POLYELECTROLYTE SOLUTIONS; COUNTERION CONDENSATION; COMPLEX-FORMATION; PHASE-BEHAVIOR; LIMITING LAWS; MICELLIZATION; POLYMER; PH;
D O I
10.1016/j.polymer.2014.05.048
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
The effect of salt on the dissociation behavior of a Pluronic-polyacrylic acid penta-block copolymer (P85PAA65) was examined. The average Gibbs energy corresponding to the energy for extracting a proton from P85PAA65 copolymer chains decreased with increasing NaCl concentration, suggesting that the addition of salt favors the dissociation process. A fluorescence study showed a two-step dissociation in which the formation of polymer complexes composed of a hydrophobic core surrounded by a hydrophilic shell was observed at pH 3.7, where the hydrodynamic radius (R-h) of the micellar structure increased from 145.6 to 302 nm due to coulombic repulsion of slightly charged PAA segments. As a consequence, the pyrene's first and the third vibronic peaks (I-1/I-3) ratio increased from 1.408 to 1.580, indicating a less hydrophobic or loose-coiled conformation compared to at a higher pH. At a pH of 7.22, the dissociation of the P85PAA65 copolymer was complete, yielding a dissociated polymer chain with apparent hydrodynamic radius (R-h(aPP)) of about 3.2 nm. A reduction of the critical micelle temperature (CMT) attributed to the hydrogen bonding between Pluronic and PAA segments was observed. (C) 2014 Elsevier Ltd. All rights reserved.
引用
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页码:3886 / 3893
页数:8
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