DOI: 10.1002/adsc.200800788 Poly(trimethylene carbonate) from Biometals-Based Initiators/ Catalysts: Highly Efficient Immortal Ring-Opening Polymerization Processes Marion Helou, a Olivier Miserque, b Jean-Michel Brusson, b Jean-FranÅois Carpentier, a, * and Sophie M. Guillaume a, * a Laboratoire Catalyse et OrganomØtalliques, CNRS – UniversitØ de Rennes 1 – Sciences Chimiques de Rennes (UMR 6226), Campus de Beaulieu, 35042 Rennes Cedex, France Fax: (+ 33)-2-2323-6939; phone: (+ 33)-2-2323-5880; e-mail: sophie.guillaume@univ-rennes1.fr or jean-francois.carpentier@univ-rennes1.fr b Total Petrochemicals Research, Zone Industrielle C, 7181 Feluy, Belgium Received: December 18, 2008; Revised: April 15, 2009; Published online: June 3, 2009 Abstract: The ring-opening polymerization (ROP) of trimethylene carbonate (TMC) was evaluated in bulk at 60–110 8C using various catalyst systems based on bio-friendly metals, including the metal bis(trimethylsilylamides) Mg[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] 2 , Ca[N- ACHTUNGTRENNUNG(SiMe 3 ) 2 ] 2 ACHTUNGTRENNUNG(THF) 2 , Y[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] 3 , (BDI)Fe[N- ACHTUNGTRENNUNG(SiMe 3 ) 2 ] [BDI = CH(CMeNC 6 H 3 -2,6-i-Pr 2 ) 2 ], Fe[N- ACHTUNGTRENNUNG(SiMe 3 ) 2 ] 2 , Fe[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] 3 , Zn[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] 2 , (BDI)Zn[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] and ZnEt 2 , associated with an alcohol such as isopropyl or benzyl alcohol. The actual metal alkoxide initiating species has been formed in situ prior to the addition of TMC. Intro- duction of the alcohol component in excess leads to the “immortal” ring-opening polymerization (ROP) of TMC. According to such an “immortal” ROP pro- cess of TMC, whichever the metal species, as many as 200 polycarbonate chains could be successfully grown from a unique metal center in a well con- trolled ROP process. The best performances were obtained using the discrete (BDI)Zn[NACHTUNGTRENNUNG(SiMe 3 ) 2 ] pre- cursor. Under optimized conditions, as many as 50,000 equivalents of TMC could be fully converted from as little as 20 ppm of this metallic precursor, al- lowing the preparation of a polytrimethylene carbon- ate (PTMC) with a molar mass as high as 185,200 g mol 1 with a relatively narrow molar mass distribution (M w /M n = 1.68). A double monomer feed experiment carried out with the (BDI)Zn[N- ACHTUNGTRENNUNG(SiMe 3 ) 2 ]/BnOH initiating system proved the “living” character of the polymerization. Characteri- zation of the PTMCs by NMR and size exclusion chromatography (SEC) showed well-defined a-hy- droxy-w-alkoxycarbonate telechelic polymers, high- lighting the controlled character of this “living and immortal” ROP process. Using the (BDI)Zn[N- ACHTUNGTRENNUNG(SiMe 3 ) 2 ] precursor, varying the alcohol (ROH) to 2- butanol, 3-buten-2-ol or 4-(trifluoromethyl)benzyl al- cohol, revealed the versatility of this approach, al- lowing the preparation of accordingly end-function- alized HO-PTMC-OR polymers. The very low initial loading of metal catalyst considerably limits the po- tential toxicity and thus allows such polycarbonates to be used in the biomedical field. Keywords: biometals; catalysis; living and immortal ring-opening polymerization; polycarbonates; trans- fer agents; trimethylene carbonate Introduction Biomass-derived polymers have nowadays become, from a mere curiosity a decade ago, a crucial necessi- ty. Facing the general problems of oil prices and over- all depleting fossil feedstocks, of global warming and of resulting environmental concerns, developing bio- compatible polymers from monomers issued from re- newable natural resources within green and sustaina- ble chemistry has emerged as a research priority. [1] Polymers derived from plant-based raw materials are of increasing interest as alternatives/substitutes to more traditional commodity thermoplastics such as polystyrene, polypropylene or polyethylene, as well as for their applications in the biomedical field including tissue and bone engineering and controlled drug de- livery systems. [2] Within these challenging contexts, we have focused our attention on establishing highly effective catalytic systems for the ring-opening polymerization (ROP) of cyclic carbonates derived from biomass, to access polycarbonates containing as little as possible of toxic 1312  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Synth. Catal. 2009, 351, 1312 – 1324 FULL PAPERS