Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

Abstract

AbstractThe bromine chain‐end functionality of polystyrene (PSt) prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was analyzed using 500 MHz 1H nuclear magnetic resonance (NMR). Bulk polymerization of styrene (St) was carried out with 50 ppm of copper in the presence of tris[2‐(dimethylamino)ethyl]amine (Me6TREN) ligand and tin(II) 2‐ethylhexanoate [Sn(EH)2] reducing agent at 90 °C. Due to the use of a low concentration of an active Cu/ligand catalyst complex, it was possible to significantly decrease the occurrence of catalyst‐based side reactions (β‐H elimination). As a result, compared to PSt prepared via normal ATRP, PSt with improved chain‐end functionality was obtained. For example, at 92% monomer conversion in normal ATRP only 48% of chains retained chain‐end functionality, whereas 87% of the chains in an ARGET ATRP still contained halogen functionality. PSt with controlled molecular weight ($\overline M _{{\rm n,NMR}}$ = 11 600 g · mol−1, $\overline M _{{\rm n,theor}.}$ = 9 600 g · mol−1) and narrow molecular weight distribution ($\overline M _{\rm w} /\overline M _{\rm n}$ = 1.14) was prepared under these conditions. In addition, as a result of decreased frequency of side reactions in ARGET ATRP, PSt with relatively high molecular weight was successfully prepared ($\overline M _{{\rm n,GPC}}$ = 185 000 g · mol−1, $\overline M _{\rm w} /\overline M _{\rm n}$ = 1.35).magnified image