Song Han Byul, Baranek Austin, Bowman Christopher N
Department of Chemical and Biological Engineering, University of Colorado Boulder, 596 UCB, Boulder, CO 80309-0596, USA.
Department of Chemical and Biological Engineering, University of Colorado Boulder, 596 UCB, Boulder, CO 80309-0596, USA; Materials Science and Engineering Program, University of Colorado Boulder, 596 UCB, Boulder, CO 80309-0596, USA.
Polym Chem. 2016 Jan 21;7(3):603-612. doi: 10.1039/c5py01655j. Epub 2015 Nov 18.
Photoinitiation of polymerizations based on the copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction enables spatio-temporal control and the formation of mechanically robust, highly glassy photopolymers. Here, we investigated several critical factors influencing photo-CuAAC polymerization kinetics systematic variation of reaction conditions such as the physicochemical nature of the monomers; the copper salt and photoinitiator types and concentrations; light intensity; exposure time and solvent content. Real time Fourier transform infrared spectroscopy (FTIR) was used to monitor the polymerization kinetics . Six different di-functional azide monomers and four different tri-functional alkyne monomers containing either aliphatic, aromatic, ether and/or carbamate substituents were synthesized and polymerized. Replacing carbamate structures with ether moieties in the monomers enabled an increase in conversion from 65% to 90% under similar irradiation conditions. The carbamate results in stiffer monomers and higher viscosity mixtures indicating that chain mobility and diffusion are key factors that determine the CuAAC network formation kinetics. Photoinitiation rates were manipulated by altering various aspects of the photo-reduction step; ultimately, a loading above 3 mol% per functional group for both the copper catalyst and the photoinitiator showed little or no rate dependence on concentration while a loading below 3 mol% exhibited 1 order rate dependence. Furthermore, a photoinitiating system consisting of camphorquinone resulted in 60% conversion in the dark after only 1 minute of 75 mW cm light exposure at 400-500 nm, highlighting a unique characteristic of the CuAAC photopolymerization enabled by the combination of the copper(i)'s catalytic lifetime and the nature of the step-growth polymerization.
基于铜（I）催化的叠氮化物-炔烃环加成（CuAAC）反应的聚合光引发能够实现时空控制，并形成机械性能稳健、高度玻璃态的光聚合物。在此，我们研究了影响光引发CuAAC聚合动力学的几个关键因素，系统地改变了反应条件，如单体的物理化学性质、铜盐和光引发剂的类型及浓度、光强度、曝光时间和溶剂含量。使用实时傅里叶变换红外光谱（FTIR）监测聚合动力学。合成并聚合了六种不同的双官能叠氮单体和四种不同的三官能炔单体，这些单体含有脂肪族、芳香族、醚和/或氨基甲酸酯取代基。在相似的辐照条件下，将单体中的氨基甲酸酯结构替换为醚部分可使转化率从65%提高到90%。氨基甲酸酯导致单体更硬且混合物粘度更高，这表明链迁移率和扩散是决定CuAAC网络形成动力学的关键因素。通过改变光还原步骤的各个方面来控制光引发速率；最终，对于铜催化剂和光引发剂，每个官能团负载量高于3 mol%时，速率对浓度几乎没有依赖性，而负载量低于3 mol%时表现出一级速率依赖性。此外，由樟脑醌组成的光引发体系在400 - 500 nm波长下75 mW/cm²光照仅1分钟后，在黑暗中就能实现60%的转化率，突出了铜（I）的催化寿命与逐步增长聚合性质相结合所实现的CuAAC光聚合的独特特性。
