Title

A novel 4-dimensional modeling strategy for optimization of NMP mini- and microemulsion

Conference Dates

May 10-15, 2015

Abstract

A 4-dimensional modeling strategy is presented to optimize mini- and microemulsion nitroxide mediated polymerization (NMP), considering styrene and n-butyl acrylate as monomers and N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl (SG1) and 2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO) as mediating agents. Despite the well-known potential of NMP in dispersed nanoparticles, [1-3] the identification of optimal process polymerization conditions is still a very demanding task, since many competitive phenomena play an important role. For instance, homogenous kinetic studies have revealed that diffusional limitations and side reactions such as thermal initiation and backbiting can influence the NMP characteristics [5]. Moreover, it has been indicated that the exit/entry of small species (e.g. nitroxide molecules X) from/into the nanoparticles cannot be ignored. In this contribution, the relevance of these competitive phenomena is studied into detail, using an advanced kinetic model which allows the calculation of all important polymerization characteristics, including the conversion profile, the evolution of the control over chain length and livingness, and for the first time the short chain branch (SCB) content [6]. In particular, nitroxide partitioning coefficients (Γ values: [X]org:[X]aq) have been measured to ensure an accurate optimization of the selected NMP processes. As shown in Figure 1, the sensitivity of the simulation results is largely depending on the Γ value, specifically at lower particle diameters, highlighting the relevance of these experimental efforts. It is also demonstrated that NMP mini- and microemulsion cannot be described as “zero-one” systems, since termination reactions cannot be ignored despite the low extensive termination rates. The latter observation implies thus the necessity of tracking polymer nanoparticles possessing more than one nitroxide and one macroradical. It is further shown that for the studied acrylate cases SCB formation cannot be neglected despite the limited amount of SCB branches per chain. The results showcase the potential of model-based optimization of heterogeneous controlled radical polymerization.

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