Andreas Mühlebach

Synthesis and reactivity of novel ruthenium carbene catalysts. X-ray structures of [RuCl2(CHSC6H5)(PiPr3)2] and [RuCl2(CHCH2CH2-C,N-2-C5H4N)(PiPr3)]

Abstract Two novel classes of very air-stable ruthenium carbene complexes have been developed. The arylthio substituted ruthenium carbenes containing two bulky phosphines are deep purple solids, whereas the 2-pyridylethanyl substituted ruthenium carbene complexes contain only one bulky phosphine and are light-brown colored. One member of each class has been characterized with X-ray crystallography. The metathesis activity of these complexes has been investigated in the polymerization of dicyclopentadiene. Several excellent catalysts were identified. Desired geltimes and initiation temperatures could be easily tuned by changing the substitution pattern on the pendant ligand in the 2-pyridylethanyl substituted ruthenium carbenes.

Design of new pigment dispersants by controlled radical polymerization

Abstract Polymeric pigment dispersants are essential for the formulation of high solids and waterborne coatings. New technologies for controlled polymerization play an important role for the development of improved pigment dispersants. In the last years, big progress has been made especially on nitroxide-mediated controlled free radical polymerization, as well as on atom transfer radical polymerization (ATRP). Both techniques overcome limitations of classical polymerization methods and provide an efficient route to functional copolymers with exact control of molecular weight distribution and molecular architecture. New developed nitroxide polymerization regulators as well as ATRP were used for the synthesis of acrylic block copolymers, which are a promising class of dispersants, especially for difficult to disperse organic pigaments. On the example of selected pigments, it was investigated how structural parameters like chemical composition, block length and molecular weight influence the dispersant performance. Special attention will be given to the rheological behavior of pigment concentrates.

Thermal stability and degradation of hydrocarbon metathesis polymers

Abstract The thermal stability of poly(dicyclopentadiene), made with RuCl 2 ( p -cymene)(PCy 3 ) as initiator, was investigated by ageing 2 and 5 mm plates up to 1 year at 180°C in air, or 360 h in a weather-o-meter. The surface roughness and microhardness of unstabilized and stabilized (0.1% Irganox® 1520, 0.5% Tinuvin® 171) probes were determined. Stabilization leads to an overall softer material but with a harder surface oxide layer with finer cracks, limiting the oxygen diffusion rate into the material and therefore protecting the underlaying material from fast oxidation. This is further supported by chemiluminescence (CL) measurements of 50 and 150 μ m films of poly(DCPD) under strong oxidative conditions (150°C in pure O 2 ). It was found that even the unstabilized material is extremely resistant to oxidation, far superior to saturated poly( α -olefins) like poly(propylene). Pyrolysis of poly(DCPD) and poly(cyclooctene) (Vestenamer®) at 670°C under an inert atmosphere gave mixtures of cyclic and open-chain unsaturated hydrocarbons. Surprisingly, the pyrolysis of poly(norbornene) (Norsorex®) gives squalene in >90% yield.

Thermal- and photoinduced ring-opening metathesis polymerization (ROMP)/(PROMP): an efficient tool in polymer chemistry

Abstract Properties and applications of newly developed homogeneous ring-opening metathesis polymerization catalysts as well as photoinduced ring-opening metathesis polymerization catalysts are discussed. It is shown that simple alkyl complexes, e.g. [W(NPh)(CH 2 SiMe 3 ) 3 Cl] as well as [Ru(arene) 2 ] 2+ or [Ru(NC–R) 6 ] 2+ complexes act as one-component Photo-ROMP initiators. Catalysts with good thermal latency are described for both classes. High quantum yields are observed for the photochemically induced solvation of Ru(II) complexes. Polymer structure and kinetic aspects of the reaction are consistent with [Ru(solvent) 6 ] 2+ acting as the catalytically active species. The mechanism of aqueous ROMP with Ru(II) salts is discussed, which differs considerably from the classical ROMP reaction with Schrock-type catalysts in the sense that it is a chain reaction and not a living polymerization. Homo- and copolymers using exo-oxa-norbornene-carboximide ester derivatives were prepared with the ROMP technology and used, inter alia, to formulate very sensitive positive tone high-resolution microresists.

Ruthenium Catalysts for Ring-Opening Metathesis Polymerization (ROMP) and Related Chemistry

Ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM) and ring-opening cross metathesis (RO/CM) are interesting methods to synthesize polymers with attractive mechanical and electrical properties, and specialty chemicals. Ruthenium and osmium based catalysts are water stable and possess a remarkable tolerance towards most functional groups. Whereas the first generation of well defined ruthenium based ROMP catalysts, cationic complexes like Ru(H2O)6tos2 (tos=toluene-4-sulfonate) and Ru(arene)2tos2 (activated by UV-irradiation) showed much lower reactivities as compared to “activated” early transition metal catalysts, Ru-phosphine complexes like RuCl2(p-MeC6H4CHMe2)(PCy3) (1, Cy=cyclohexyl) developed by Ciba SC and later Ru-phoshine-carbenes, developed by Grubbs et al. and Ciba SC are able to polymerize a large range of cycloolefins including DCPD (in technical quality and in mixtures with additives and fillers) very efficiently. The new classes of ruthenium carbene complexes are accessible by a novel synthesis which avoids the use of hydrogen gas and is therefore easy to scale up. Catalyst reactivities in ROMP of different monomers (characterized in terms of their turn-over frequencies (TOF) and compared with other catalysts for olefin polymerization), in RCM and RO/CM are very much dependent on the ligand sphere and the type of monomer used. Polymerizations were conducted in bulk, solution and dispersion with a large range of non-functionalized and functionalized 2-norbornene derivatives to obtain linear and crosslinked homo- and copolymers (block and random) which may find useful applications in the near future.