Analysis of the Formation Mechanism for Thermoresponsive-Type Coacervate with Functional Copolymers Consisting of N-Isopropylacrylamide and 2-Hydroxyisopropylacrylamide

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• 作者：Tomohiro Maeda ; Miki Takenouchi ; Kazuya Yamamoto ; and Takao Aoyagi
• 刊名：Biomacromolecules
• 出版年：2006
• 出版时间：July 2006
• 年：2006
• 卷：7
• 期：7
• 页码：2230 - 2236
• 全文大小：458K
• 年卷期：v.7,no.7(July 2006)
• ISSN：1526-4602

文摘

We now report the formation mechanism of the thermoresponsive-type coacervate with the novel functionaltemperature-sensitive polymer, poly(N-isopropylacrylamide-co-2-hydroxyisopropylacrylamide) (poly(NIPAAm-co-HIPAAm)), synthesized in our laboratory. The effects of introducing the hydrophilic comonomer (HIPAAm)into the copolymer chains and adding salts on the behaviors of the coacervate droplets induced in the poly(NIPAAm-co-HIPAAm) aqueous solutions were investigated. Not only the particle sizes of the coacervate dropletsbut also the cloud points of the copolymer solutions could be modulated by the HIPAAm content incorporatedin the copolymers. Moreover, the particle sizes of the coacervate droplets were also changed by adding salts.Namely, the particle sizes increased with the decreasing HIPAAm composition and increasing NaCl concentration.In addition, the ¹H NMR and differential scanning calorimetric measurements suggested that as the HIPAAmcontent decreased or NaCl concentration increased, dehydration of the copolymers induced in the phase transitionand/or separation became much easier. Therefore, on the basis of the findings obtained from these measurements,we determined that the particle sizes of the coacervate droplets induced in the temperature-sensitive polymersincreased as the number of the water molecules, which are dissociated from the polymeric chains during thephase transition and/or separation, increased. Besides, to examine the separation of the model solutes, the aqueoustwo-phase separation with the coacervate droplets of poly(NIPAAm-co-HIPAAm) was carried out. The partitionsof Methyl Orange as a model solute under both acidic (pH 2) and basic (pH 12) conditions were performed. Theamount of Methyl Orange partitioned into the coacervate droplets at pH 12 is much greater than that at pH 2,which indicated that the coacervate droplets could recognize a slight difference in the polarity or structure betweenthe model solutes.