Stereospecific polymerization of 2‐vinylpyridine
Stereospecific polymerization of 2‐vinylpyridine
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DOI：
10.1002/pol.1961.1205115608
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发表时间：
1961-06
影响因子：
3.4
通讯作者：
G. Natta;G. Mazzanti;P. Longi;G. Dall'asta;F. Bernardini
中科院分区：
文献类型：
--
作者：
G. Natta;G. Mazzanti;P. Longi;G. Dall'asta;F. Bernardini
一些正电性很强的金属（如锂、钠、铍、镁和铝）的金属有机化合物或金属酰胺化合物会引起2-乙烯基吡啶的聚合。而铍和铝的化合物提供轻微结晶的2-乙烯基吡啶聚合物，通过使用镁衍生物，可以获得通过X射线高度结晶的聚合物。报道了在酰胺或镁的金属有机化合物存在下聚合的系统研究结果。特别地，已经检查了单体/催化剂摩尔比、温度、聚合时间和与镁结合的取代基的性质对聚合过程和对所得聚合物的性质的影响。通过红外光谱法的检查使我们能够得出结论，至少一部分大分子含有作为端基的有机基团，这些有机基团最初与用作催化剂的化合物中的金属结合。该方法的立体定向性必须归因于催化剂与进入生长链的单体分子配位的可能性。事实上，向体系中加入有机刘易斯碱会导致立体特异性的降低或消失。所得结果使我们能够得出结论，2-乙烯基吡啶的立体定向聚合通过阴离子配位机制发生。4-乙烯基吡啶，在催化剂的存在下，这是立体特异性的聚合2-乙烯基吡啶，得到无定形非结晶聚合物。我们将其归因于这样的事实，即在4-乙烯基吡啶的情况下，氮原子离乙烯基双键太远而不能与催化剂形成加成络合物，该加成络合物能够在聚合的非常时刻为所有单体分子提供相同的取向。
Some metalloorganic or metal amide compounds of very electropositive metals, such as lithium, sodium, beryllium, magnesium, and aluminum, cause the polymerization of 2‐vinylpyridine. Whereas the compounds of beryllium and of aluminum furnish slightly crystalline 2‐vinylpyridine polymers, by using magnesium derivatives it is possible to obtain polymers which are highly crystalline by x‐rays. The results obtained from the systematic study of the polymerization in the presence of amides or of metalloorganic compounds of magnesium are reported. In particular, it has been examined the influence of the monomer/catalyst molar ratio, of the temperature, of the polymerization time, and of the nature of the substituents bound to magnesium, on the course of the polymerization and on the properties of the obtained polymers. Examination by IR spectrography allowed us to conclude that at least a part of the macromolecules contain, as endgroup, the organic groups which were initially bound to the metal in the compounds used as catalyst. The stereospecificity of the process must be ascribed to the possibility of coordination of the catalyst to the monomer molecules entering the growing chain. In fact, the addition of organic Lewis bases to the system, causes the reduction or the disappearence of stereospecificity. The obtained results allowed us to conclude that the stereospecific polymerization of 2‐vinylpyridine takes place by an anionic coordinated mechanism. 4‐Vinylpyridine, in the presence of catalysts which are stereospecific for the polymerization of 2‐vinylpyridine, gives amorphous noncrystallizable polymers. That was ascribed by us to the fact that the nitrogen atom, in the case of 4‐vinylpyridine is too far from the vinyl double bond to form, with the catalyst, an addition complex able to give the same orientation to all the monomer molecules, at the very moment of the polymerization.