SYNTHESIS OF GLYCOPOLYMERS OF CONTROLLED MOLECULAR-WEIGHT BY RING-OPENING METATHESIS POLYMERIZATION USING WELL-DEFINED FUNCTIONAL-GROUP TOLERANT RUTHENIUM CARBENE CATALYSTS

A series of sugar-substituted norbornenes were synthesized in order to determine whether monodisperse glycopolymers might be prepared by ring-opening metathesis polymerization (ROMP) using the ruthenium carbene initiators (R(3)P)(2)Cl2Ru=CHCH=CPh(2) (R = phenyl (Ph), 1; R = cyclohexyl (Cy), 2). The polymerization of 2-((+/-)-exo-5-norbornene-2-carboxamido)-2-deoxy-D-glucopyranose (3) and the protected sugar derivatives based on this monomer, 2-((+/-)-exo-5-norbornene-2-carboxamido)-2-deoxy-1,3,4,6-tetra-O-acetyl-D-glucopyranose (4), 2-((+/-)-exo-5-norbornene-2-carboxamido)-2-deoxy-1,3,4,6-tetra-O-benzyl-D-glucopyranose (5), 2-((+/-)-exo-5-norbornene-2-carboxamido)-2-deoxy-1,3,4,6-tetra-O-triethylsilyl-D-glucopyranose (6), and 2-((+/-)-exo-5-norbornene-2-carboxamido)-2-deoxy-6-O-trityl-D-glucopyranose (7), were investigated. The Cy(3)PRu catalyst, 2, initiated the polymerization of monomers 3-7; only the acetate monomer, 4, could be polymerized by the less active Ph(3)PRu catalyst 1. Benzene is a more effective polymerization solvent than methylene chloride for the ether-protected sugar derivatives 5-7, whereas methylene chloride is a better solvent for the acetate monomer, 4, which is prone to gelation. The reaction rates are highly dependent upon the sugar protecting group and range from <5 min for the acetate protected sugar, 4, to 2-3 days for the triethylsilyl ether derivative, 6. Narrow-dispersity materials were obtained using 2 when reactions were run at elevated temperature (50 degrees C). For example, the polydispersity indices of poly[5] and poly[6] prepared in benzene solution at 50 degrees C were 1.17 and 1.10, respectively. More polydisperse products resulted from reactions at 25 degrees C. Deprotonation of poly[4], poly[5], and poly[6] was also investigated. The silyl ether polymer, poly[6], was readily deprotected using tetrabutylammonium fluoride (TBAF) in THF. Incomplete reaction and complex products were observed in preliminary attempts to remove the acetate and benzyl ether groups. Due to poor solubility, the unprotected sugar monomer, 3, could not be polymerized by 2 in homogeneous solution. However, water-insoluble 3 was quantitatively polymerized in an aqueous emulsion system containing dodecyltrimethylammonium bromide (DTAB) and a small amount of CH2Cl2 to dissolve the catalyst, 2.