Chemistry Department, Mount Holyoke College, South Hadley, Massachusetts 01075, United States.
Langmuir. 2011 May 3;27(9):5403-9. doi: 10.1021/la2002892. Epub 2011 Apr 6.
Surface grafting of cyclic olefins with low strain energies, including cyclopentene (CP), 1,4-cyclohexadiene (CHD), cycloheptene (CHP), cis-cyclooctene (CO), cis,cis-1,5-cyclooctadiene (COD), 1,3,5,7-cyclooctatetraene (COT), cyclododecene (CD), and trans,trans,cis-1,5,9-cyclododecatriene (CDT), was explored using ring-opening metathesis polymerization in the vapor phase. These monomers do not polymerize when SiROMP is carried out in solution because of pronounced chain transfer on surfaces where chains are in close proximity to one another. In the vapor phase, however, chain transfer is suppressed at the solid-vapor interfaces, which permits the polymerization of most of these monomers. A minimal required strain energy of 2.2 kcal/mol was determined in this study, which is significantly lower than the estimated 13.3 kcal/mol for SiROMP carried out in solution, indicating that the enhancement in monomer polymerizability is significant using the vapor-phase approach. A series of polyalkenamers with a controlled fraction of unsaturation from 8 to 50% along the polymer backbone were grafted to solid substrates. It was observed that the logarithm of the largest grafted layer thickness obtained before the removal of chain-transfer products, which correlates with the extent of polymerization, scales with the monomer strain energy. This confirms that the release of ring strain is the thermodynamic driving force for SiROMP. It was also found that although chain transfer is suppressed in the vapor phase it is important in monomer/polymer systems where the fraction of unsaturated bonds is high. In these cases, the grafted polymer thickness is dominated by chain transfer rather than the monomer strain energy. A quantitative relationship is established for estimating the graft thickness of a particular monomer using its strain energy and fraction of unsaturated bonds in the monomer.
用开环易位聚合在气相中探索具有低应变能的环状烯烃的表面接枝，包括环戊烯（CP）、1,4-环己二烯（CHD）、环庚烯（CHP）、顺式-环辛烯（CO）、顺式,顺式-1,5-环辛二烯（COD）、1,3,5,7-环辛四烯（COT）、环十二烯（CD）和反式,反式,顺式-1,5,9-环十二碳三烯（CDT）。由于在彼此靠近的表面上链转移明显，当在溶液中进行 SiROMP 时，这些单体不会聚合。然而，在气相中，在固-气界面处抑制了链转移，这使得大多数这些单体能够聚合。在这项研究中确定了最小需要的应变能为 2.2 kcal/mol，这明显低于在溶液中进行 SiROMP 时估计的 13.3 kcal/mol，表明使用气相方法显著提高了单体的聚合能力。在固体基底上接枝了一系列具有可控的不饱和分数（从 8%到 50%）的聚烯丙基聚合物。观察到在去除链转移产物之前获得的最大接枝层厚度的对数，这与聚合度相关，与单体应变能成比例。这证实了释放环应变是 SiROMP 的热力学驱动力。还发现，尽管在气相中抑制了链转移，但在不饱和键分数高的单体/聚合物体系中，它仍然很重要。在这些情况下，接枝聚合物的厚度主要由链转移而不是单体应变能决定。建立了一个定量关系，用于使用单体的应变能和不饱和键分数估计特定单体的接枝厚度。
