Thermal-history dependence of polymerization-induced phase separation
Thermal-history dependence of polymerization-induced phase separation
复制标题
聚合诱导相分离的热历史依赖性
DOI：
10.1021/ma981744o
复制
发表时间：
1999
期刊：
影响因子：
5.5
通讯作者：
T. Sakaguchi
中科院分区：
文献类型：
--
作者：
M. Okada;T. Sakaguchi
聚合诱导相分离的动力学由相分离速率与反应速率之间的比率决定。1，2聚合诱导相分离的特征之一是粘度随着聚合反应的进行而急剧变化。在链聚合的情况下，相分离速率和反应速率表现出不同的依赖于粘度，和由链聚合引起的相分离的动力学可以定性地解释由这两个速率的比值的变化所引起的粘度急剧增加。由于粘度是温度的函数，因此比率的变化也取决于温度。事实上，在2-氯苯乙烯/聚苯乙烯混合物中，根据温度观察到非常不同的域结构。因此，可以预期，相分离过程中的温度变化对随后的相分离行为具有明显的影响。换句话说，根据先前的热历史，在相同的最终温度下将产生不同的畴结构。这个简短的交流的目的是以明确的方式表明，由自由基聚合引起的相分离的动力学强烈依赖于热历史。3.采用相分离过程中的逐步温度变化作为热历史的最简单形式。为了研究热历史的影响，我们改变了在第一相分离温度下的持续时间，并观察了逐步温度变化后的相分离行为。使用2-氯苯乙烯、聚苯乙烯和邻苯二甲酸二丁酯的混合物作为样品。聚苯乙烯的重均分子量和多分散指数分别为Mw）5 × 10 4和Mw/Mn）1.06。加入邻苯二甲酸二丁酯以降低高单体转化率下的粘度。混合物的组成固定为45/45/10重量。不使用引发剂，通过升高温度引发2-氯苯乙烯的自由基聚合。在自由基聚合中，产物的平均分子量和分子量分布随反应时间（转化率）保持不变，而产物的浓度增加。电子显微镜和时间分辨光散射技术被用来跟踪相分离域结构的发展，和尺寸排阻色谱法被用来确定2-氯苯乙烯的转化率。样品和仪器与以前的工作中使用的相同，样品制备和仪器的细节在参考文献1中给出。第一和第二相分离温度分别设定为130和160 ℃。因此，本工作中采用的整个热历史如下：温度从室温跳到130 ℃（第一次跳）并在该值下保持t1的持续时间，然后温度进一步跳到160 ℃（第二次跳）并固定。图1显示了在单步跳跃（t1）0）到160 ℃后聚合诱导相分离的畴结构的发展。这些扫描电子显微照片中较暗的部分对应于富含聚苯乙烯（PS）的相。富含聚合产物即聚（2-氯苯乙烯）（P2ClS）的相形成液滴。在我们的整个调查期间，只观察到液滴型域结构。（由于玻璃化转变温度低，无法用电子显微镜观察到的非常早期的形态结构不在本讨论范围内。）发展…
The dynamics of polymerization-induced phase separation is dominated by the ratio between phase separation rate and reaction rate. 1, 2 One of the characteristics of polymerization-induced phase separation is a drastic change of viscosity with progress of polymerization reaction. In the case of chain polymerization, the phase separation rate and reaction rate exhibit a different dependence on the viscosity, and the dynamics of phase separation induced by chain polymerization can be explained qualitatively by the change of the ratio of these two rates caused by this drastic increase of viscosity. Since viscosity is a function of temperature, the change of the ratio also depends on temperature. In fact, in a 2-chlorostyrene/polystyrene mixture quite different domain structures were observed depending on temperature. 1 Hence, it is expected that a temperature change over the course of phase separation has an appreciable influence on the subsequent phase separation behavior. In other words, different domain structures will be produced at the same final temperature depending on the previous thermal history. The purpose of this short communication is to show in a definite fashion that the dynamics of phase separation induced by radical polymerization strongly depends on thermal history. 3 A stepwise temperature change over the course of phase separation was adopted as a simplest form of thermal history. To examine the effects of thermal history, we varied the duration at the first phase-separation temperature and observed phase separation behavior after the stepwise temperature change. A mixture of 2-chlorostyrene, polystyrene, and dibutyl phthalate was used as a sample. The weight-average molecular weight and polydispersity index of polystyrene were Mw) 5× 104 and Mw/Mn) 1.06, respectively. Dibutyl phthalate was added to reduce the viscosity at high monomer conversions. The composition of the mixture was fixed at 45/45/10 by weight. No initiator was used, and radical polymerization of 2-chlorostyrene was initiated by raising the temperature. In radical polymerization the average molecular weight and molecular weight distribution of the product remain unchanged with reaction time (conversion), while the concentration of the product is increasing. Electron microscopy and time-resolved light scattering techniques were used to follow the development of phaseseparation domain structures, and size exclusion chromatography was used to determine the conversion of 2-chlorostyrene. The sample and instruments were the same as those used in a previous work, and details of the sample preparation and instrumentation were given in ref 1.The first and second phase-separation temperatures were set to be 130 and 160 C, respectively. Thus, the entire thermal history employed in this work was as follows: the temperature was jumped from room temperature to 130 C (the first jump) and kept at this value for the duration of t1, and then the temperature was further jumped to 160 C (the second jump) and fixed. Figure 1 shows the development of domain structures of polymerization-induced phase separation after a single-step jump (t1) 0) to 160 C. Darker parts in these scanning electron micrographs correspond to the polystyrene (PS)-rich phase. The phase rich in the polymerization product, namely poly (2-chlorostyrene)(P2ClS), formed droplets. Over the entire period of our investigation, only droplet-type domain structure was observed.(Morphological structure in a very early period, which could not be observed with the electron microscope because of low glass transition temperature, was left out of the present discussion.) Development of …