Association and physical gelation of ABA triblock copolymer in selective solvent
Association and physical gelation of ABA triblock copolymer in selective solvent
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DOI：
10.1016/s0032-3861(03)00534-2
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发表时间：
2003-08-01
期刊：
影响因子：
4.6
通讯作者：
Nose, T
中科院分区：
文献类型：
--
作者：
Inomata, K;Nakanishi, D;Nose, T
本文系统地研究了阿坝三嵌段共聚物在硼选择性溶剂中从稀溶液到中等浓度溶液的缔合行为和物理成胶机理。静态和动态光散射和核磁共振测量聚（甲基丙烯酸甲酯）-嵌段-聚（丙烯酸叔丁酯）-嵌段-聚（甲基丙烯酸甲酯）（PMMAPtBuA-PMMA）在1-丁醇（PtBuA选择性溶剂）的稀溶液表明，PMMA-PtBuA-PMMA链分子溶解高于50 degreesC。随着温度的降低，三嵌段共聚物形成由PMMA缔合核和PtBuA壳组成的缔合胶束。对中等浓度（3.9- 12.0wt%）溶液的线性动态粘弹性测量表明，该体系在60 ℃时为粘性溶胶状态。剪切储能模量（G '）随温度的降低而急剧增加，在25 ℃时，G'呈现橡胶态平台，频率依赖性较弱，表明形成了弹性物理凝胶。胶束形成温度与0增加时的温度之间的一致性表明物理凝胶化是由于PMMA链和连接PMMA核的桥连PtBuA链缔合而形成网络的结果。动态模量的主曲线是通过沿着频率轴的时温叠加得到的。就在溶胶-凝胶转变浓度（C-凝胶）以上，主曲线表明存在不被纳入宏观网络中的聚集体。随着聚合物浓度的增加，主曲线变得揭示麦克斯韦型粘弹性与狭窄的松弛时间分布，这表明瞬态网络的形成，容易产生和破坏的交联。平台模量的浓度依赖性强于理论预期，这意味着宏观瞬态网络随着聚合物浓度的增加而增长，这是通过增加弹性有效桥接PtBuA链的分数来实现的，该分数高于Cgel（C）2003 Elsevier Ltd.。
Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMAPtBuA-PMMA) in 1-butanol (PtBuA selective solvent) indicated that PMMA-PtBuA-PMMA chains are molecularly dissolved above 50 degreesC. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and PtBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9-12.0 wt%) revealed that the system was viscous sol state at 60 degreesC. Drastic increase of shear storage modulus (G') occurred with decreasing temperature, and at 25 degreesC, G' showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in 0 indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging PtBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by timetemperature superposition along the frequency axis. Just above sol-gel transition concentration (C-gel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging PtBuA chain above Cgel (C) 2003 Elsevier Ltd. All rights reserved.