Block Copolymer Nanoparticles of Controlled Sizes via Ring-Opening Metathesis Polymerization ALVARO CARRILLO, RAVI S. KANE The Howard P. Isermann Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 Received 18 December 2003; accepted 20 February 2004 DOI: 10.1002/pola.20130 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: This article describes the formation and characterization of self-assembled nanoparticles of controlled sizes based on amphiphilic block copolymers synthesized by ring-opening metathesis polymerization. We synthesized a novel hydrophobic deriva- tive of norbornene; this monomer could be polymerized using Grubbs’ catalyst [Cl 2 Ru(CHPh)(PCy 3 ) 2 ] forming polymers of controlled molecular weight. We synthe- sized amphiphilic block copolymers of controlled composition and showed that they assemble into nanoparticles of controlled size. The nanoparticles were characterized using dynamic light scattering and transmission electron microscopy. Tuning the composition of the block copolymer enables the tuning of the diameters of the nano- particles in the 30- to 80-nm range. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3352–3359, 2004 Keywords: block copolymers; living polymerization; nanoparticles; ring-opening metathesis polymerization (ROMP); self-assembly; multivalency INTRODUCTION Nanostructures with controlled size, shape, and chemical functionality are required for numerous applications in nanotechnology. 1–4 Nanoparticles obtained through the micellization of amphiphilic block copolymers have aroused considerable in- terest because of their increased stability and lower critical micellar concentrations as com- pared with low-molecular-weight surfactant mi- celles. 5,6 Block copolymer micelles have been formed from a wide variety of polymers, 6 –11 and recent developments include the formation of zwitterionic micelles, 12 micelles with environ- mentally or chemically responsive blocks, 10,13–15 shell crosslinked 16,17 and core crosslinked 18 nano- particles, nanocages, 19 –21 and shell-functional- ized nanoparticles. 22 These nanoparticles have applications in biosensors, 23 drug delivery, 3,24 –26 controlled release of hydrophobic drugs, 8,27–29 and gene therapy. 22,30 In addition to the applications mentioned above, we believe that block copolymer nanopar- ticles of controlled sizes will serve as novel scaf- folds for the multivalent display of ligands. Bio- functionalized nanoparticles of controlled size and shape may be used as multivalent antago- nists. 31–35 They may also be used to control the size and shape of receptor clusters on cells, thereby serving as cellular effectors—molecules that promote or activate biological processes and cellular responses. 36 Block copolymer nanoparticles have been formed by the assembly of polymers synthesized by a variety of procedures, such as anionic poly- merization, 37–39 group transfer polymerization, 10 atom transfer radical polymerization, 19,40 ring- opening polymerization, 7,19 and melt polyconden- Correspondence to: R. S. Kane (E-mail: kaner@rpi.edu) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 42, 3352–3359 (2004) © 2004 Wiley Periodicals, Inc. 3352