Influence of Initiator and Monomer Structure on the Polymerization of Acetylene Monomers Using Schrock-Type Molybdenum Carbenes

Abstract

The polymerization of acetylene monomers using homogeneous Schrock-type initiators of the general formula Mo(CHR‘)(NAr)(OR)2 with different substitution patterns was investigated. The influence of the ligands at the molybdenum center and of donor functions at the β-position with respect to the monomer's triple bond on the polymerization was studied by means of NMR spectroscopy and size exclusion chromatography. The results clearly indicate that kinetics and mechanism of the metathesis reaction strongly depend on the structures of monomer and initiator. The use of partially fluorinated alkoxy ligands instead of aliphatic alkoxides leads to a change of the regiochemistry of the insertion. Ether functions in the monomer tend to slow the reaction, giving rise to polymers with a narrow molecular weight distribution probably due to coordination of the oxygen atom to the metal center.

Synthesis and characterization of liquid crystalline (norbornene-block-acetylene) block copolymers

“…Materials with polydispersity indices in the order of 2 are obtained. The deviation from a Poisson distribution is probably due to the fact that for the polymerization of acetylenes with these initiator systems the rates of chain propagation and initiation are comparable 36) . Therefore, these polymerizations do not meet the demands of living polymerizations.…”

“…Recently, we could show 36,37) that the polymerization of acetylene monomers is possible with the well-defined Schrock-type molybdenum initiator Mo(CH-t-Bu)(NAr)-(O-t-Bu) 2 1 with NAr = 2,6-diisopropylaniline.…”

Synthesis of novel acetylene monomers with mesogenic moieties and their polymerization using Schrock-type molybdenum carbenes

“…Recently, we showed by NMR experiments that the insertion of the first acetylene monomer into the molybdenum-carbon double bond is relatively slow compared with the insertion of the following monomers into the resulting conjugated system [59]. Therefore, the molecular weight distributions are not as narrow as, for example, for ring-opening metathesis polymerization of liquid crystalline nor-bomenes [60][61][62].…”

Synthesis and characterization of a liquid crystalline polyacetylene with cholesteryl side groups using Schrock-type molybdenum initiators

“…An alternative approach to the synthesis of side chain liquid crystalline polyacetylenes is the polymerization of 1,6-heptadiynes or of bis-(propargyl)a/minoethers which bear one or two mesogenic side groups in the 4-position 1,[36][37][38][39][40] . Recently, we could show 41,42) that the polymerization of acetylene monomers is possible with the well-defined Schrock-type molybdenum initiator Mo(CH-t-Bu)(NAr)-(O-t-Bu) 2 , where NAr = 2,6-diisopropylaniline, t-Bu = tert-butyl. The synthesis of liquid crystalline polyacetylene homopolymers and random copolymers with the methoxybiphenyl group as mesogen has been discussed in a previous contribution 43) .…”