pubs.acs.org/Macromolecules Published on Web 06/15/2010 r 2010 American Chemical Society Macromolecules 2010, 43, 5611–5617 5611 DOI: 10.1021/ma100779q Synthesis of Well-Defined ω-Oxanorbornenyl Poly(ethylene oxide) Macromonomers via Click Chemistry and Their Ring-Opening Metathesis Polymerization D. Le, † V. Montembault, † J.-C. Soutif, † M. Rutnakornpituk, ‡ and Laurent Fontaine* ,† † LCOM-Chimie des Polym eres, UCO2M, UMR CNRS 6011, Universit e du Maine, Avenue O. Messiaen, 72085 Le Mans Cedex 09, France, and ‡ Department of Chemistry, Faculty of Science, Naresuan University, Muang, Phitsanuloke, 65 000, Thailand Received April 9, 2010; Revised Manuscript Received June 3, 2010 ABSTRACT: ω-Oxanorbornenyl poly(ethylene oxide) monomethyl ether macromonomers were synthe- sized with molecular weights ranging from 500 g/mol to 5000 g/mol through the Huisgen 1,3-dipolar cycloaddition between acetylene-functionalized oxanorbornene and ω-azido poly(ethylene oxide) mono- methyl ether. Thermal analysis showed that the ω-exo-norbornenyl end-group of the macromonomers is converted into a maleimide group through a retro-Diels-Alder process at 130 °C. Ring-opening metathesis polymerization (ROMP) of these macromonomers was investigated using Grubbs’ catalyst in dichloro- methane at room temperature. Poly(oxanorbornene)-g-poly(ethylene oxide)s were obtained with polydis- persities between 1.04 and 1.17 and molecular weights between 9900 and 57 800 g/mol leading to comb or brush copolymers according to the lengths of backbone and graft chains. Introduction Macromonomers are unique precursors for the preparation of well-defined graft copolymers using the so-called “grafting through” strategy which allows the control of grafts, backbone length, and grafting density. 1-3 The combination of ring-opening metathesis polymerization (ROMP) and various ionic and radical processes has been used for the preparation of graft copolymers starting from inimers (initiator-monomers) bearing “ROMP-able” entities such as norbornene, 4-26 oxanorbornene, 27-29 cyclobutene, 30-34 and cyclooctadiene moieties. 35 Poly(ethylene oxide) (PEO), also referred as poly(ethylene glycol) for structures bearing hydroxyl end-groups, is one of the most important and most widely used polymer in pharma- ceutical and biomedical applications. Despite considerable work devoted to PEO in the literature, very little has been reported on PEO macromonomers which undergo ROMP. 20-24,35-37 The synthesis of such “ROMP-able” PEO macromonomers was pio- neered by H eroguez et al., who polymerized ethylene oxide anionically from a norbornene functionalized initiator. 36,37 Huisgen 1,3-dipolar cycloaddition reaction between azides and terminal alkynes, one of the different “click” reactions described by Sharpless and co-workers, 38 has attracted widespread atten- tion in polymer science. 25,26,39-50 “Click” chemistry provides an ideal platform for the synthesis of various well-defined macro- monomers starting from commercially available polymers such as PEO. However, while 1,3-dipolar “click” reactions have been widely used for the functionalization of ROMP polymers, only a few examples of such a combination have been reported so far in the literature for the preparation of graft copolymers. 25,26 Herein, we report the synthesis of new ω-oxanorbornenyl-PEO macromonomers using Huisgen 1,3-dipolar cycloaddition (click chemistry) and their ROMP using third generation Grubbs’ catalyst ([1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidene] dichloro(phenylmethylene)bis(3-bromopyridine) ruthenium). 51 The oxanorbornene-based group was chosen as the “ROMP-able” entity for two reasons. First, pure exo-oxanorbornene diastereo- isomers are easily prepared starting from exo-7-oxabicyclo- [2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, available in high yield through Diels-Alder cycloaddition. 52 Indeed, it is well-known that exo-diastereoisomers are much more reactive in ROMP than their endo- counterparts. 53-59 Second, as pointed out by Czelusniak et al., 28 it is expected that the oxygen in the oxanorbornene group makes the backbone more hydrophilic 60 and hence increases the probability of biocompatibility of the resulting graft copolymers. The simple and flexible method reported in this work, precluding the need for anionic polymerization of ethylene oxide, yields polymers of unique structures, which are potential candidates for biomedical applications. Experimental Section Materials. Dichloromethane (DCM, 99%þ) and triethyl- amine (99%) were distilled over CaH 2 and were stored at -4 °C after purification. Prior to use, PEO monomethyl ether (PEO- OH) 500 ( M n,NMR =530 g/mol), 2000 ( M n,NMR =2010 g/mol) and 5000 ( M n,NMR =4590 g/mol) were heated at 120 °C for 3 h under nitrogen atmosphere to remove excess water. Grubbs’ catalyst [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidene] dichloro(phenylmethylene)bis(3-bromopyridine) ruthenium(II) C 38 H 40 Br 2 Cl 2 N 4 Ru (G3) 51 and exo-7-oxabicyclo[2.2.1]hept- 5-ene-2,3-dicarboxylic anhydride 22,52 (1) were prepared accord- ing to literature procedures. All other chemicals were purchased from commercial sources and used without further purification. Azido-terminated PEO monomethyl ethers (PEO-N 3 ) were synthesized according to literature procedures. 61,62 General Characterization. NMR spectra were recorded on a Bruker Avance 400 spectrometer for 1 H NMR (200 MHz) and 13 C NMR (50 MHz). Chemical shifts are reported in ppm relative to the deuterated solvent resonances. Molecular weights and molecular weight distributions were measured using size exclusion chromatography (SEC) on a system equipped with a *Corresponding author. Telephone: þ33 (0)2 43 83 33 30. Fax: þ33 (0)2 43 83 37 54. E-mail: laurent.fontaine@univ-lemans.fr..