Radical living graft polymerization on the surface of polymeric materials
Radical living graft polymerization on the surface of polymeric materials
复制标题
DOI：
10.1021/ma9515543
复制
发表时间：
1996-04-22
期刊：
影响因子：
5.5
通讯作者：
Ranby, B
中科院分区：
文献类型：
--
作者：
Yang, WT;Ranby, B
定义明确的聚合物和共聚物（如嵌段、接枝）通常在没有转移和终止反应的活性聚合物体系中制备。对于自由基聚合，实现“活性过程”的主要困难是通过自由基偶联或双链化的双分子终止反应。由于终止是二级反应，而增长是增长链自由基的一级反应，因此终止的比例随着自由基浓度的增加而增加。然而，低浓度的生长自由基有利于形成高分子量聚合物，而不控制分子量和多分散性。“自由基活性聚合”发展的最新突破是发明了通过与稳定的自由基或清除剂偶联来可逆地使增长的自由基失活。1 r3 25年前，Braun等人研究了芳族频哪醇作为引发剂的反应性。4十年后，他们报道了使用1，1，2，2-四苯基-1，2-二苯氧基乙烷作为引发剂合成具有两个苯氧基二苯基甲基端基的甲基丙烯酸甲酯（MMA）的低聚物。他们指出，这些遥爪化合物是乙烯基单体进一步自由基聚合的有效引发剂。5受这些初步结果的启发，结合本实验室已开展了10多年的光接枝聚合实践，我们设计了本工作。目的是将“自由基活性聚合”植入到表面接枝聚合中。实验程序包括两个部分：第一部分是通过已知的光接枝方法在聚合物膜表面上合成与所报道的结构相似的端基（4和5），第二部分是通过光活化和热活化聚合来鉴定这些端基的反应性。结果表明，用这种方法可以得到一种新的大分子结构--表面接枝嵌段共聚物。作为一个实验过程，这里提出的表面接枝系统具有以下优点。(1)与溶液和本体聚合体系相比，由于链键合的固体表面的限制、低自由基浓度和低流动性，植根于聚合物表面的生长自由基不容易被双分子反应终止。因此，表面接枝聚合有望有利于“活性聚合”与过程控制。(2)活性或受控聚合体系的特征通常在于单体转化率与所形成的聚合物的分子量之间的线性关系，以及当涉及与增长速率相比快速引发过程时聚合物的多分散性。在表面接枝聚合中，活性端基化学键合在聚合物表面上，我们可以通过测量基材的重量增加来跟踪聚合过程。
Well-defined polymers and copolymers (eg, block, graft) are usually prepared in a living polymeric system in which transfer and termination reactions are absent. For radical polymerization, the main difficulty to realize a “living process” is the bimolecular termination reaction by radical coupling or disproportionation. Because termination is a second-order reaction and propagation is first order of growing chain radicals, the proportion of termination increases with the concentration of free radicals. However, low concentration of growing radicals favors formation of high molecular mass polymers with no control of molecular weight and polydispersity. A recent breakthrough in the development of “radical living polymerization” is the invention of the reversible deactivation of growing radicals by coupling with a stable free radical or scavenger. 1r3 Twenty-five years ago, Braun et al. studied the reactivity of aromatic pinacols as initiator. 4 Ten years later, they reported the synthesis of oligomers of methyl methacrylate (MMA) with two phenoxydiphenylmethyl end groups using 1, 1, 2, 2-tetraphenyl-1, 2-diphenoxyethane as initiator. They pointed out that these telechelic compounds are effective initiators of further free radical polymerization of vinyl monomers. 5 Enlightened by these precursory results and combined with the practice of photografting polymerizations which have been initiated and carried out for more than 10 years in our laboratory, 6r8 we designed the present work. The intention is to implant “radical living polymerization” onto the surface-grafting polymerization. The experimental program contains two parts: The first is to synthesize end groups which are structurally similar to the ones reported (4 and 5) on the surface of polymer film by the known photografting method, and the second is to identify the reactivity of these end groups by photo-and thermoactivating polymerizations. As a result, a new macromolecular architecture, surfacegrafted block copolymer, can be obtained by this method. As an experimental process, the surface-grafting system presented here has the following advantages.(1) In comparison with solution and bulk polymerization systems, the growing radicals rooted on the polymer surface are not easily terminated by bimolecular reactions due to the limitation of a solid surface to which the chains are bonded, the low free radical concentration, and the low mobility. Therefore, the surfacegrafting polymerization is expected to favor “living polymerization” with process control.(2) A living or controlled polymerization system, in general, is characterized by the linear relationship of the conversion of monomer and the molecular mass of polymer formed and also the polydispersity of the polymer when a fast initiation process comparatively with the propagation rate is concerned. In the surface-grafting polymerization, with the living end groups bound chemically on the surface of polymer, we can follow the polymerization process by measuring the increase in weight of the substrate.