(130c) Improvement of Molecular Weight Distribution in Synthesis of Liquid Polymers for Reactive Resins by Micro Flow-through Polymerization

Polymeric materials made of mixed monomer composition are of particular interest for reactive resins. The products should possess molecular weights in the range of about 1.5 kDa and a low dispersity. Products with a mean molecular weight Mn of about 2000 Da and a dispersion (Mw/Mn) of about 2.3 are typically obtained in 4-component batch synthesis of mixed oligomers from methylacrylate (57 mol%), ethylhexylacrylate (12 mol%), 2- hydroxyethylmethacrylat (30 mol%) and acrylic acid (1%) in methylethylketone (MEK). We investigated the influence of the conversion of the batch polymerization into a polymerization process under micro continuous flow conditions. Therefore, the monomer mixture with the initiator were dissolved in MEK and applied by a syringe pump. The reaction mixture was conducted through a PTFE tube (1 mm inner diameter,length up to 40 m). The polymerization was carried out in a thermostating bath (70oC). The flow rate was varied between 2.5 and 10 mL/h. The mean residence time at elevated temperature was kept at about 2 h. The obtained products (after removal of residual monomers) show a significant reduction of dispersity (Mw/Mn = 1.83 ..1.88). In addition, the experiments show a slow tendency of reduction of molecular weight with increasing flow rate (fig. 1). In order to come to a lower molecular weight without loss of homogeneity, the residence time was shortened down to 15 minutes and the temperature was strongly increased up to 120oC. This conditions demand for a pressure-controlled flow-through process, because boiling points of components are exceeded. A 0.5 mm PTFE capillary inside a PEEK tube was applied instead of the larger PTFE tube. The reaction mixture was applied as a multiphase flow (plug-like transport) using perfluorinated hydrocarbons as immiscible carrier liquid. In result, a further reduction of dispersity and a strong reduction of molecular weight was achieved at high yield (fig. 2). The comparison with a batch process at same temperature and same pressure made the advantages of the micro flow through process clear: The dispersity was lowered from 2.28 down to 1.69 and the molecular weight Mw reduced from 4763 down to 1993. The experiments show the high potential of micro reaction technology for the preparation of polymer materials with particular specifications. Fig. 1 Flow rate effect on molecular weight in micro flow-through polymerization (normal pressure) Fig. 2 Comparison of polymerization products from different processes: batch polymerization (enhanced pressure), micro flow polymerization (normal pressure) and segmented flow polymerization (enhanced pressure)