Effect of Ca2+ Ion and Temperature on Association of Thermally Sensitive PAA-b-PNIPAM Diblock Chains in Aqueous Solutions

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• 作者：Xiaobing Liu ; Shikai Luo ; Jing Ye ; Chi Wu
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：June 12, 2012
• 年：2012
• 卷：45
• 期：11
• 页码：4830-4838
• 全文大小：507K
• 年卷期：v.45,no.11(June 12, 2012)
• ISSN：1520-5835

文摘

Poly(tert-butyl acrylate)-b-poly(N-isopropylacrylamide) (PtBA-b-PNIPAM) was first synthesized by sequential reversible addition鈥揻ragmentation chain transfer polymerization of tert-butyl acrylate and N-isopropylacrylamide. Its hydrolysis led to amphiphilic poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PAA-b-PNIPAM) that can form micelles in aqueous solutions at temperatures higher than 37 掳C because PNIPAM is a thermally sensitive polymer. In the presence of Ca²⁺, the complexation between one Ca²⁺ and two COO^{鈥?/sup> groups on different PAA blocks can induce the chain association. Using a combination of static and dynamic laser light scattering, we studied the effect of Ca2+ and temperature as well as the sequence of adding Ca2+ ions and heating the solution on such association. We found that (1) the association is controllable and reversible, (2) a distinct hysteresis is observed between the heating and cooling processes, (3) the time evolution of the average aggregation number (N_agg) and the average hydrodynamic radius (R_h) of the aggregates can be expressed by a single-exponential equation, (4) the aggregates have a fractal dimension of 1.5鈥?.9, suggesting a diffusion-limited process, and (5) adding Ca2+ before heating results in the aggregates with a more open and looser structure. The current study provides a model system to investigate a more complicate problem, namely, the effect of metal ions on the stability of protein chains.}