The Thiol-Isocyanate Click Reaction: Facile and Quantitative Access to ω-End-Functional Poly(N,N-diethylacrylamide) Synthesized by RAFT Radical Polymerization
The Thiol-Isocyanate Click Reaction: Facile and Quantitative Access to ω-End-Functional Poly(N,N-diethylacrylamide) Synthesized by RAFT Radical Polymerization
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DOI：
10.1021/ma9010878
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发表时间：
2009-09-08
期刊：
影响因子：
5.5
通讯作者：
Lowe, Andrew B.
中科院分区：
文献类型：
--
作者：
Li, Haibo;Yu, Bing;Lowe, Andrew B.
通过可逆加成-断裂链转移（RAFT）自由基聚合使N，N-二乙基丙烯酰胺（DEAm）均聚，得到计算聚合度为30（PDEAm 30）的均聚物，如通过H-1 NMR光谱端基分析测定的，和多分散指数1.10。二硫酯端基的氨解，然后用三（羧乙基）膦盐酸盐处理，得到相应的大分子仲硫醇（PDEAm 30-SH）。由NEt 3催化的PDEAm 30-SH与一系列市售异氰酸酯的反应以基本上定量的产率得到相应的硫代氨基甲酸酯末端官能聚合物，如通过H-NMR光谱和UV-可见分光光度法的组合所测定的。这些反应显示为快速的，如在NEt 3存在下PDEAm 30-SH与异氰酸己酯之间的反应的实时动力学所证明的。此外，这些容易的反应显示出对基本聚合物结构没有任何明显的有害作用/副反应，如通过尺寸排阻色谱证明的，所有改性的聚合物保持其窄的分子量分布。通过比浊法评价所得共改性PDEAm均聚物的低临界溶解温度（LCST）。对于可溶于水性介质的那些样品，测得的LCST比PDEAm 30-SH测定的LCST（34 ° C）低3至11 ° C。这种差异归因于新引入的端基的疏水性，该效应在前体均聚物的分子量相对较低的情况下是显著的。在两种情况下，特别是由与9-异氰酸根合-9H-芴和4-（2-异氰酸根合乙基）联苯反应获得的末端改性的PDEAm均聚物，所得材料即使在接近0 ℃的温度下也不溶于水。
N,N-Diethylacrylamide (DEAm) was homopolymerized by reversible addition-fragmentation chain transfer (RAFT) radical polymerization yielding a homopolymer with a calculated degree of polymerization of 30 (PDEAm30), as determined by H-1 NMR spectroscopic end-group analysis, and a polydispersity index 1.10. Aminolysis of the dithioester end groups followed by treatment with tris(carboxyethyl)phosphine hydrochloride yielded the corresponding macromolecular secondary thiol (PDEAm30-SH). Reaction of PDEAm30-SH with a range of commercially available isocyanates, catalyzed by NEt3, gave the corresponding thiocarbamate end-functional polymers in essentially quantitative yield as determined by a combination of H-1 NMR spectroscopy and UV-vis spectrophotometry. These reactions were shown to be rapid as evidenced by the real-time kinetics for the reaction between PDEAm30-SH and hexyl isocyanate in the presence of NEt3. Additionally, these facile reactions were shown to proceed without any apparent detrimental effect/side reactions to the basic polymer structure as evidenced by size exclusion chromatography with all modified polymers retaining their narrow molecular weight distributions. The lower critical solution temperatures (LCSTs) of the resulting co-modified PDEAm homopolymers were evaluated by turbidimetry. For those samples that were soluble in aqueous media the measured LCSTs were between 3 and 11 degrees C lower than that determined for PDEAm30-SH (34 degrees C). Such differences were attributed to the hydrophobic nature of the newly introduced end groups-the effect being pronounced given the relatively low molecular weight of the precursor homopolymer. In two instances, and specifically the end-modified PDEAm homopolymers obtained from reaction with 9-isocyanato-9H-fluorene and 4-(2-isocyanatoethyl)biphenyl, the resulting materials were not soluble in water even at temperatures approaching 0 degrees C.