More insight into tandem ROMP and ADMET polymerization for yielding reactive long-chain highly branched polymers and their transformation to functional polymer nanoparticles

Tandem chain transfer ring-opening metathesis polymerization (ROMP-CT) and acyclic diene metathesis (ADMET) polymerization were carried out in a controlled one-pot procedure, and behaved noticeable differences in polymerization of monomers by different ruthenium catalysts, whereas there indeed had been two distinctly polymerization stages. In the first one, ROMP-CT of functional monomers was conducted in the presence of a symmetrical multi-olefin as chain transfer agent within various reaction time scales, yielding linear telechelic polymers. Next, ADMET polymerization of telechelic polymers was performed and generated a series of reactive long-chain highly branched polymers (LCHBPs) with acrylate and/or azobenzene groups having molecular weights of 8.5-47.9 kDa under varied conditions. LCHBPs were fully characterized by several techniques, and interestingly, UV-vis analysis displayed the specific peak at 278 nm, which offered a new evidence for the existence of internal acrylate structure on the LCHBP backbone, and supported the highly branched architecture of polymers. LCHBP containing a number of pendent acrylate groups was readily converted, by thiol-Michael addition click reaction, to novel thiol-functionalized intro-molecular crosslinked unimolecular polymer nanoparticles with diameter of 40-60 nm, which provided a facile method for post-functionalization of branched polymers. (C) 2011 Elsevier Ltd. All rights reserved.