Well-Defined Alternating Copolymers of Benzaldehydes with Vinyl Ethers: Precision Synthesis by Cationic Copolymerization and Quantitative Degradation to Cinnamaldehydes
Well-Defined Alternating Copolymers of Benzaldehydes with Vinyl Ethers: Precision Synthesis by Cationic Copolymerization and Quantitative Degradation to Cinnamaldehydes
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DOI：
10.1021/ma902840d
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发表时间：
2010-04-13
期刊：
影响因子：
5.5
通讯作者：
Aoshima, Sadahito
中科院分区：
文献类型：
--
作者：
Ishido, Yasushi;Aburaki, Ryosuke;Aoshima, Sadahito
介绍。芳香族醛难以阳离子聚合，目前只有少数与苯乙烯或异戊二烯的分离共聚研究，而与乙烯醚等反应性更强的单体的共聚研究较少。最近，我们已经证明了各种路易斯酸与路易斯碱结合可以有效地诱导各种单体的活性阳离子聚合，其中一些单体在不同类型的引发体系下不能以活性方式聚合。5r7在引发体系方面的进展甚至允许苯甲醛（BzA）与异丁基乙烯醚（IBVE）的可控共聚。在低温条件下，在添加碱的情况下，用GaCl3得到了8个分子量为25r30% BzA单元的窄分子量分布共聚物。共聚反应的一个特点是在反应中不产生BzAr - BzA键。因此，繁殖有三个基本反应：BzA生长端的交叉反应和IBVE活性中心的同增殖和交叉反应。自扩散反应和交叉反应的相对反应活性决定了两种单体在聚合物链上的顺序分布。如果一种比BzA活性更高的BzA衍生物（BzA）与IBVE结合，或者一种比IBVE活性更低的VE与BzA共聚[例如，对甲氧基BzA （pMeOBzA）与IBVE， BzA与2-氯乙基VE (CEVE)]，则会进行甚至交替共聚。bza与VE的交替共聚物是一种有吸引力的可降解聚合物，因为易于降解的缩醛键有规律地位于主链上。此外，骨架中玻璃化BzA单元的高含量有望产生具有更高玻璃化转变温度（Tg）和刚度的材料。因此，在本研究中，在添加碱的情况下，使用GaCl3研究了各种bza与VEs的阳离子共聚。结果表明，以乙磺酸(EtSO3H)/GaCl3为引发体系，以1,4 -二氧六环为催化剂，pMeOBzA与IBVE和BzA与CEVE阳离子共聚，可得到低分散性的交替共聚物。共聚物的酸水解产生几乎所有的单一低分子量化合物。结果和讨论。用EtSO3H/GaCl3引发体系共聚BzAs与VEs。BzA与VEs的阳离子共聚是用EtSO3H/GaCl3引发体系（引发剂/催化剂）在r78℃的甲苯中添加1,4 -二恶烷作为刘易斯碱进行的。在这些条件下，BzA与IBVE的可控共聚进行（表1，入口1）。如引言所述，在适当的单体组合下，可以得到结构交替的共聚物。因此，作为共聚的单体组合，我们选择了pMeOBzA与IBVE和BzA与CEVE。
Introduction. Aromatic aldehydes are difficult to polymerize cationically, 1r3 and there have only been a few isolated copolymerization studies with styrene or isoprene, 2, 4 not with more reactive monomers, such as vinyl ethers (VEs). 2 Recently, we have demonstrated that various Lewis acids in conjunction with Lewis bases were effective for inducing living cationic polymerizations of various monomers, some of which could not be polymerized in a living fashion with different types of initiating systems. 5r7 This progress in initiating systems even permitted controlled copolymerization of benzaldehyde (BzA) with isobutyl vinyl ether (IBVE). 8 Copolymers of 25r30% BzA units with narrow molecular weight distributions (MWDs) were obtained using GaCl3 in the presence of an added base at low temperature. One feature of the copolymerization was that no BzAr BzA linkages were produced in the reaction. Consequently, there are three elemental reactions for propagation: the crossover reaction from the BzA growing end and the homopropagation and crossover from the IBVE active center. The relative reactivity of the self-propagation and crossover reactions determines the sequence distribution of the two monomers in the polymer chain. If a more reactive BzA derivative (BzAs) than BzA is combined with IBVE, or a less reactive VE than IBVE is copolymerized with BzA [eg, p-methoxyBzA (pMeOBzA) with IBVE, BzA with 2-chloroethyl VE (CEVE)], then even alternating copolymerization would proceed. An alternating copolymer of a BzAs with a VE is attractive as a degradable polymer because easily degradable acetal linkages are regularly located in the main chain. 9 In addition, the high content of glassy BzA units in the backbone is expected to yield materials with higher glass transition temperature (Tg) and rigidity. In the present study, therefore, cationic copolymerization of various BzAs with VEs was examined using GaCl3 in the presence of an added base. As a result, we found that alternating copolymers with low polydispersity could be obtained from cationic copolymerization of pMeOBzA with IBVE and BzA with CEVE using an ethanesulfonic acid (EtSO3H)/GaCl3 initiating system with 1, 4-dioxane. Acid hydrolysis of the copolymers yielded nearly all single lowmolecular-weight compounds.Results and Discussion. Copolymerization of BzAs with VEs Using EtSO3H/GaCl3 Initiating System. Cationic copolymerization of BzAs with VEs was conducted with the EtSO3H/GaCl3 initiating system (an initiator/a catalyst) in the presence of 1, 4-dioxane as an added Lewis base in toluene at r78 C. Under these conditions, controlled copolymerization of BzA with IBVE proceeded (Table1, entry 1). 8 Copolymers with alternating structures are expected under appropriate monomer combinations, as mentioned in the Introduction. Therefore, as monomer combinations in the copolymerization, pMeOBzA with IBVE and BzA with CEVE were selected.