Macromolecular Rapid Communications, Vol.32, No.18, 1447-1453, 2011
Synthesis of Cyclopentadienyl Capped Polyethylene and Subsequent Block Copolymer Formation Via Hetero Diels-Alder (HDA) Chemistry
In the current contribution it is demonstrated - for the first time - that poly(ethylene) ((M)over bar n = 1400 as well as 2800 g . mol(-1), PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels-Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) ((M)over bar n = 4600 g . mol(-1), PDI = 1.10) and poly(styrene) ((M)over bar n = 6300 g . mol(-1), PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin-2-yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high-temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non-poly(ethylene) containing segment via filtration of the poly(ethylene)-containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead - depending on the block copolymer type - to the occurrence of retro Diels-Alder processes. The present study thus demonstrates that RAFT-HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.
Keywords:cyclopentadienyl capped polymers;hetero Diels-Alder cycloaddition;poly(ethylene);reversible addition fragmentation chain