ing-opening metathesis polymerization (ROMP) is a polymerization driven by the relief of the ring strain of cyclic olefins to form polymers 1. Monomers such as norbornene derivatives can be polymerized in a living fashion due to the slow rates of irreversible chain-transfer events and termination reactions 2 compared with the relatively fast propagation rates. Typical metathesis initiators for ROMP are based on ruthenium 3 or molybdenum 4,5. The high tolerance of ruthenium complexes towards many polar functional groups, water and oxygen has made them popular choices in organic as well as polymer chemistry 6. The first and third generations of Grubbs' metathesis catalysts (G1 and G3, respectively;
Heterotelechelic polymers were synthesized by a kinetic telechelic ring-opening metathesis polymerization method relying on the regioselective cross-metathesis of the propagating Grubbs' first-generation catalyst with cinnamyl alcohol derivatives. This procedure allowed the synthesis of hetero-bis-end-functional polymers in a one-pot setup. The molecular weight of the polymers could be controlled by varying the ratio between cinnamyl alcohol derivatives and monomer. The end functional groups can be changed using different aromatically substituted cinnamyl alcohol derivatives. Different monomers were investigated and the presence of the functional groups was shown by NMR spectroscopy and MALDI-ToF mass spectrometry. Labeling experiments with dyes were conducted to demonstrate the orthogonal addressability of both chain ends of the heterotelechelic polymers obtained.
A recently developed catalytic living ring opening metathesis polymerisation (ROMP) was investigated using a series of reversible chain transfer agents (CTA) carrying either cyclopentene or cyclohexene rings, differing only in ring strain. All cyclopentene derivatives examined showed significantly faster reaction rates than the corresponding cyclohexene derivatives. This resulted in lower molecular weight dispersities and better control of the molecular weight for the cyclopentene compared to the cyclohexene CTAs. Both Grubbs second and third generation catalysts could be employed in catalytic living ROMP using cyclopentene CTA derivatives. The kinetics of different CTAs were studied, block copolymers were synthesised and residual ruthenium quantified by ICP-OES. All polymers were fully characterised by NMR, GPC and MALDI-ToF mass spectrometry. The new cyclopentene CTAs are readily synthesised in a few straightforward steps and provide faster reaction kinetics than all previously reported reversible CTAs.
Functional enolethers have previously been used to introduce functional end groups at the chain end of ruthenium carbene complex initiated living ring opening metathesis polymers. Here, we investigated whether the weaker p-donating enolesters could equally be used in regio selective reactions with ruthenium carbene complexes and thus as polymer endfunctionalization reagents. Enolesters such as vinyl acetate, butenyl acetate, 3-(4-(tert-butoxy)phenyl)propenyl acetate and 6-(((benzyloxy)carbonyl)amino)hex-1-en-1-yl acetate were used as living ROMP terminating agents. All gave the expected end groups proving that enolesters are synthetically easily accessible targets for living ROMP end-functionalization.
The second-generation Hoveyda–Grubbs (HG2) catalyst, which has a small initiation to propagation rate ratio (ki/kp) in ring-opening metathesis polymerization (ROMP), was successfully used in a recently developed catalytic living ROMP....
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.