POLYMERIZATION OF VINYL BROMIDE IN SOLUTION
POLYMERIZATION OF VINYL BROMIDE IN SOLUTION
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DOI：
10.1002/pol.1959.1203813316
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发表时间：
1959-01-01
影响因子：
3.4
通讯作者：
KATCHALSKY, A
中科院分区：
文献类型：
--
作者：
BLAUER, G;SHENBLAT, M;KATCHALSKY, A
以偶氮二异丁腈为热引发剂，研究了溴乙烯在1，2-二溴乙烷溶液中的聚合反应。在高真空中通过粘度计和重量测量跟踪聚合速率。在所采用的条件下，聚合没有显示出速率的加速。直到约12小时的反应，聚合物中溴没有显著损失。35°C时。在1- 5 M单体浓度范围内，初始速率与单体浓度的2次方有关。在35°C下的速率。也依赖于在0.01-0.1M范围内的引发剂浓度的接近1.0的幂。在类似的实验条件下，苯乙烯产生的指数为0.5的引发剂。通过光散射和粘度测定在上述条件和浓度范围内制备的初始聚合物的平均分子量。分子量约为100，000，并且不显著依赖于引发剂浓度。当单体浓度增加三倍时，特性粘度仅增加50%，并且当反应温度降低至20°C时显示出甚至更小的变化。这表明，聚合体系，虽然在表观均匀的溶液中，是接近相分离，超过聚合度的临界范围的高度卷曲的大分子自由基是无法终止的双分子碰撞，而在更高的程度，甚至内的传播埋自由基停止。这一机制得到了先前发现的温度依赖性可逆缔合现象的支持。其他解释的基础上链转移反应涉及不活泼的自由基进行了讨论。
The polymerization of vinyl bromide in 1,2‐dibromoethane solution has been investigated using 2,2′‐azobisisobutyronitrile as thermal initiator. Rates of polymerization were followed in high vacuum by dilatometric and gravimetric measurements. Under the conditions employed, the polymerization showed no acceleration of rate. Up to about 12 hours reaction there was no significant loss of bromine from the polymer. At 35°C. and in the monomer concentration range 1–5M, the initial rate was dependent on a power close to 2 of the monomer concentration. The rate at 35°C. was also dependent on a power close to 1.0 of the initiator concentration in the range 0.01–0.1M. Styrene yielded an exponent 0.5 for the initiator at analogous experimental conditions. The average molecular weight of the initial polymers prepared under the conditions and in the concentration ranges indicated above were determined by light scattering and viscometry. The molecular weights were of the order of 100,000 and did not depend significantly on the initiator concentration. The intrinsic viscosities increased by only 50% when the monomer concentration was increased threefold and showed even less variation when the reaction temperature was lowered to 20°C. It is suggested that the polymerization system, though in apparent homogeneous solution, is close to phaseseparation, and beyond a critical range of degree of polymerization the highly coiled macromolecular radicals are unable to terminate by bimolecular collision, while at still higher degrees, even propagation inside the buried radicals ceases. This mechanism is supported by temperature dependent reversible association phenomena found previously. Alternative explanations based on chain transfer reactions involving unreactive radicals are discussed.