Ge Junhao, Trujillo-Lemon Marianela, Stansbury Jeffrey W
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado.
Macromolecules. 2006 Dec 26;39(26):8968-8976. doi: 10.1021/ma061284w.
Efficient photopolymerization of a potentially expandable monomer is of practical importance for a variety of polymeric applications demanding dimensional stability, particularly if the polymerization process is well controlled based on a detailed investigation of the reaction. In the current study, photoinitiated polymerization kinetics of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane (MPN) either with cationic initiation alone or with combined cationic/free radical initiation was examined using real-time FT-IR. A proposed mechanism based on the simplified propagation steps of the cationic double ring-opening polymerization of MPN was confirmed by both computer modeling and NMR spectroscopic analysis of resulting polymers as well as the experimentally observed apparent activation energy. According to this mechanism, alpha-position attack is the predominant mode for the second ring opening during cationic polymerization of MPN. Further, cationic photopolymerization was performed along with a free radical co-initiator or with exposure to moisture to get an improved understanding of the complex cationic double ring-opening polymerization. As a result, free radical-promoted cationic polymerization helps increase the polymerization rate of MPN while even a trace amount of moisture was found to significantly impact both the reaction kinetics and the polymerization course.
对于各种要求尺寸稳定性的聚合物应用而言，潜在可膨胀单体的高效光聚合具有实际重要性，特别是如果基于对反应的详细研究，聚合过程得到良好控制的话。在当前研究中，使用实时傅里叶变换红外光谱（FT-IR）研究了2-亚甲基-7-苯基-1,4,6,9-四氧杂螺[4.4]壬烷（MPN）仅通过阳离子引发或阳离子/自由基联合引发的光引发聚合动力学。通过计算机建模以及对所得聚合物的核磁共振（NMR）光谱分析和实验观察到的表观活化能，证实了基于MPN阳离子双开环聚合简化传播步骤的提出机制。根据该机制，α-位进攻是MPN阳离子聚合过程中第二个环开环的主要模式。此外，进行阳离子光聚合时同时加入自由基共引发剂或暴露于湿气中，以更好地理解复杂的阳离子双开环聚合。结果，自由基促进的阳离子聚合有助于提高MPN的聚合速率，同时发现即使痕量的湿气也会对反应动力学和聚合过程产生显著影响。
