Arraez Francisco J, Steenberge Paul H M Van, D'hooge Dagmar R
Laboratory for Chemical Technology, Department of Materials, Textiles and Chemical Engineering, Ghent University, Technologiepark 125, Zwijnaarde, 9052 Ghent, Belgium.
Centre for Textile Science and Engineering, Department of Materials, Textiles and Chemical Engineering, Ghent University, Technologiepark 70A, Zwijnaarde, 9052 Ghent, Belgium.
Polymers (Basel). 2020 Jun 23;12(6):1409. doi: 10.3390/polym12061409.
One of the challenges for brush synthesis for advanced bioinspired applications using surface-initiated reversible deactivation radical polymerization (SI-RDRP) is the understanding of the relevance of confinement on the reaction probabilities and specifically the role of termination reactions. The present work puts forward a new matrix-based kinetic Monte Carlo platform with an implicit reaction scheme capable of evaluating the growth pattern of individual free and tethered chains in three-dimensional format during SI-RDRP. For illustration purposes, emphasis is on normal SI-atom transfer radical polymerization, introducing concepts such as the apparent livingness and the molecular height distribution (MHD). The former is determined based on the combination of the disturbing impact of termination (related to conventional livingness) and shielding of deactivated species (additional correction due to hindrance), and the latter allows structure-property relationships to be identified, starting at the molecular level in view of future brush characterization. It is shown that under well-defined SI-RDRP conditions the contribution of (shorter) hindered dormant chains is relevant and more pronounced for higher average initiator coverages, despite the fraction of dead chains being less. A dominance of surface-solution termination is also put forward, considering two extreme diffusion modes, i.e., translational and segmental. With the translational mode termination is largely suppressed and the living limit is mimicked, whereas with the segmental mode termination occurs more and the termination front moves upward alongside the polymer layer growth. In any case, bimodalities are established for the tethered chains both on the level of the chain length distribution and the MHD.
利用表面引发的可逆失活自由基聚合（SI-RDRP）进行先进生物启发应用的刷状聚合物合成面临的挑战之一，是理解受限环境对反应概率的影响，特别是终止反应的作用。本工作提出了一种基于矩阵的新型动力学蒙特卡罗平台，其具有隐式反应方案，能够在SI-RDRP过程中以三维形式评估单个自由链和接枝链的生长模式。为便于说明，重点在于常规的SI-原子转移自由基聚合，引入了表观活性和分子高度分布（MHD）等概念。前者基于终止反应的干扰影响（与传统活性相关）和失活物种的屏蔽作用（由于位阻产生的额外校正）的综合来确定，后者则有助于从分子水平出发，鉴于未来刷状聚合物的表征，识别结构-性能关系。结果表明，在明确的SI-RDRP条件下，尽管死链比例较小，但（较短的）受阻休眠链的贡献仍然显著，且对于较高的平均引发剂覆盖率更为明显。还提出了表面-溶液终止的主导作用，考虑了两种极端的扩散模式，即平移扩散和链段扩散。在平移扩散模式下，终止反应在很大程度上受到抑制，模拟了活性极限，而在链段扩散模式下，终止反应发生得更多，终止前沿随着聚合物层的生长向上移动。无论哪种情况，接枝链在链长分布和MHD水平上都呈现出双峰性。
