Initiators For Ring-opening Metathesis Polymerization Research Articles

Synthesis of end-labeled multivalent ligands for exploring cell-surface-receptor–ligand interactions

Background: Ring-opening metathesis polymerization (ROMP) is a powerful synthetic method for generating unique materials. The functional group tolerance of ruthenium ROMP initiators allows the synthesis of a wide range of biologically active polymers. We generated multivalent ligands that inhibit cell surface L-selectin, a protein that mediates lymphocyte homing and leukocyte recruitment in inflammation. We hypothesized that these ligands function through specific, multivalent binding to L-selectin. To examine this and to develop a general method for synthesizing multivalent materials with end-labels, we investigated functionalized enol ethers as capping agents in ruthenium-initiated ROMP. Results: We synthesized a bifunctional molecule that introduces a unique end group by terminating ruthenium-initiated ROMP reactions. This agent contains an enol ether at one end and a masked carboxylic acid at the other. We conjugated a fluorescein derivative to an end-capped neoglycopolymer that had previously been shown to inhibit L-selectin function. We used fluorescence microscopy to visualize neoglycopolymer binding to cells displaying L-selectin. Our results suggest that the neoglycopolymers bind specifically to cell surface L-selectin through multivalent interactions. Conclusions: Ruthenium-initiated ROMP can be used to generate biologically active, multivalent ligands terminated with a latent functional group. The functionalized polymers can be labeled with a variety of molecular tags, including fluorescent molecules, biotin, lipids or antibodies. The ability to conjugate reporter groups to ROMP polymers using this strategy has broad applications in the material and biological sciences.

A New and Highly Efficient Grubbs Initiator for Ring-Opening Metathesis Polymerization

A New and Highly Efficient Grubbs Initiator for Ring-Opening Metathesis Polymerization

Langmuir−Blodgett Films of Conducting Diblock Copolymers

Novel amphiphilic block copolymers have been synthesized via ring-opening metathesis polymerization (ROMP), where one block is a precursor to a water-soluble polymer and the other block is a precursor to polyacetylene. The water-soluble block is made from a silyl ester protected carboxylic acid functionalized polymer. The silyl ester groups are used to protect the ROMP initiator from the carboxylic acid groups during polymerization and are easily deprotected afterward. The polyacetylene precursor block is made via ROMP using an approach known as the “Durham” route to polyacetylene. These amphiphilic block copolymers are surface active and quite amenable to the Langmuir−Blodgett (LB) technique, whereby films of these materials were fabricated and converted to polyacetylene-containing films by heating. UV−visible spectroscopy showed that the polyacetylene chains are oriented mostly in the plane of the LB film and in the dipping direction of the substrate. Upon doping with iodine, these films were shown to h...

Synthesis of Organic and Water Soluble Poly(1,4-phenylenevinylenes) Containing Carboxyl Groups: Living Ring-Opening Metathesis Polymerization (ROMP) of 2,3-Dicarboxybarrelenes

2,3-Dicarboxybicyclo[2.2.2]octa-2,5,7-triene (barrelene) monomers (4a,b) were synthesized by a novel route and then polymerized by ring-opening metathesis polymerization (ROMP). Complete initiation of the ROMP initiator (5) and living polymerization of monomer 4b were achieved by tuning the activity of 5 with hexafluoro-tert-butanol (HFB) and tetrahydrofuran (THF). The precursor polymers (6a,b) were readily converted to diester-substituted poly(1,4-phenylenevinylenes) (PPVs) (7a,b) by aromatizing the cyclohexadiene rings using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The resulting PPVs were highly luminescent, and polymer 7b, bearing tert-butyl groups on its esters, was soluble in methylene chloride and chloroform. We found that partially oxidizing 6b so that only 80% of the polymer units are aromatized increases both the solubility and photoluminescence quantum yield of 7b. Deprotection of polymer 7b by acid-catalyzed thermolysis of the tert-butyl groups followed by treatment with aqueous base pr...

Initiation of ring-opening metathesis polymerization in protic media. Extension of [Ru(H2O)6]2+ catalyzed polymerizations to less-strained cyclic monomers

Ru II (H 2 O) 6 (tos) 2 (tos= p-toluenesulfonate) is an active catalyst for ring-opening metathesis polymerization (ROMP) of norbornene and 7-oxanorbornene derivatives in protic media. The activity of this catalyst can be extended to less reactive monomers, such as cyclooctene and cyclopentene, by the addition of ethyl diazoacetate to serve as an initiator. Due to the polymer/ring equilibrium for this system, the yield of polymer is low. The GPC trace of the product is distinctly bimodal, consisting of a mixture of cyclic oligomers and higher molecular weight polymer. These results show that the difficulty of polymerizing unstrained cyclic olefins in the original ruthenium systems lies in the initiation step and not in the propagation