Z-RAFT star polymerizations of acrylates: Star coupling via intermolecular chain transfer to polymer
Z-RAFT star polymerizations of acrylates: Star coupling via intermolecular chain transfer to polymer
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DOI：
10.1021/ma0627626
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发表时间：
2007-04-17
期刊：
影响因子：
5.5
通讯作者：
Vana, Philipp
中科院分区：
文献类型：
--
作者：
Boschmann, Daniel;Vana, Philipp
通过可逆加成-断裂链转移（RAFT）聚合，在60℃下制备了丙烯酸甲酯（MA）、丙烯酸丁酯（BA）和丙烯酸十二酯（DA）的六臂星形聚合物。采用六功能的三硫代碳化物作为中介化合物，其中活性的RAFT-agent部分通过稳定的z基团与中心核心分子相互连接。通过Z-RAFT聚丙烯酸酯的星形聚合得到了定义明确的星形聚合物，其可预测的数-平均分子量大于1 × 10(6) g.mol（-1）。在中间单体转化前，分子量分布窄且呈单峰分布。在单体转化率较高的情况下，从MA / BA聚合到DA聚合时，意想不到的高分子量组分的出现程度越来越大。这种高分子量材料被分配到一个包含两个活核的星形-星形偶，其形成不符合基本的Z-RAFT星形聚合机制，而很可能是由分子间链转移到聚合物反应引起的。星-星对的数量作为长链分支程度的指示，被量化为单体转化的函数，随后通过动力学模拟进行建模。通过这种方法，估计在60℃时分子间转移到聚合物的速率系数为k(tr)(P,inter) = 0.33 l mol（-1）。s(-1), k(tr)(P,inter) = 7.1 l mol（-1）。s（-1）在DA聚合中。研究发现，在单体转化率较高的情况下，活性过程是非常有效的，这表明，在实际RAFT过程发生的星型聚合物核心附近的空间位阻并没有显著阻碍丙烯酸酯的Z-RAFT星型聚合。
Six-arm star polymers of methyl acrylate (MA), butyl acrylate (BA), and dodecyl acrylate (DA) were generated in bulk at 60 degrees C via reversible addition-fragmentation chain transfer (RAFT) polymerization. A hexafunctional trithiocarbonate was employed as mediating compound, in which the active RAFT-agent moieties are interlinked to the central core molecule via the stabilizing Z-group. Well-defined star polymers with predictable number-average molecular weights of more than 1 x 10(6) g.mol(-1) were obtained by this Z-RAFT star polymerization of acrylates. Narrow and monomodal molecular weight distributions were found up to intermediate monomer conversions. At higher monomer conversions, an unexpected high molecular weight component occurred with increasing extent when going from MA over BA to DA polymerization. This high molecular weight material was assigned to a star-star couple containing two living cores, which formation is not in accordance to the basic Z-RAFT star polymerization mechanism, but most likely arises from an intermolecular chain transfer to polymer reaction. The amount of star-star couples, which is an indication for the extent of long-chain branching, was quantified as a function of the monomer conversion and subsequently modeled via kinetic simulations. By this approach, the rate coefficient of intermolecular transfer to polymer at 60 degrees C was estimated to be k(tr)(P,inter) = 0.33 L.mol(-1).s(-1) in BA polymerization and k(tr)(P,inter) = 7.1 L.mol(-1).s(-1) in DA polymerization. The living process was found to be very effective up to high monomer conversions, indicating that steric congestion next to the star polymer core, where the actual RAFT process takes place, is not significantly hampering the Z-RAFT star polymerization of acrylates.