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Polymer libraries offer straightforward opportunities for the investigation of structure property relationships and for a more thorough understanding of certain research problems. Furthermore, if combined with high-throughput methods for their preparation as well as screening, they offer the additional advantage of time savings and/or the reduction of experimental efforts. Thus, the herein discussed methods of polymer library preparation and selected literature examples of polymer libraries describe efficient and state-of-the-art methods to tackle difficult research challenges in polymer and materials science.
Two synthetic approaches to functionalize plant oil derived platform chemicals were investigated. For this purpose, methyl 10-undecenoate, which can be obtained by pyrolysis of castor oil, was used in olefin cross-metathesis under neat conditions forming an unsaturated a,?-acetoxy ester. A catalyst screening with 11 different ruthenium-based metathesis catalysts was performed, revealing that well-suited catalysts allow for full conversion and very good cross-metathesis selectivity at a loading of only 0.5?mol%. An alternative possibility to the aforementioned synthetic method is a palladium-catalyzed reaction of methyl 10-undecenoate with acetic acid in the presence of dimethyl sulfoxide. Here, the formation of linear and branched unsaturated acetoxy esters as well as a ketone was observed. The conversion as well as the selectivity of this procedure was studied under different reaction conditions and compared to the cross-metathesis results. Based on the successful functionalization of methyl 10-undecenoate, methyl oleate was investigated in this palladium-catalyzed C?H activation reaction. Due to the lower reactivity of the internal double bond the desired acetoxy ester was only obtained in moderate conversion in this case. In summary, this study clearly shows that palladium-catalyzed functionalization of unsaturated fatty compounds via C?H activation is an attractive alternative to the well-established olefin cross-metathesis procedure.
Thiol-ene additions of methyl 10-undecenoate, a castor oil derived renewable platform chemical, were studied with the goal of preparing a set of renewable monomers. Good to excellent yields were obtained for these solvent and initiator free thiol-ene additions. The resulting monomers were then polymerized using TBD as a catalyst, to linear as well as hyperbranched polyesters that also contain thio-ether linkages. All thus prepared polymers were fully characterized (NMR, GPC, DSC, and TGA) and the results of these investigations will be discussed within this contribution. The thermal analysis of these polymers revealed melting points in the range from 50 to 71 degrees C. Moreover, no significant weight loss was observed below 300 degrees C.
The relevance of biological Si cycling for dissolved silica (DSi) export from terrestrial biogeosystems is still in debate. Even in systems showing a high content of weatherable minerals, like Cambisols on volcanic tuff, biogenic Si (BSi) might contribute > 50% to DSi (Gerard et al., 2008). However, the number of biogeosystem studies is rather limited for generalized conclusions. To cover one end of controlling factors on DSi, i.e., weatherable minerals content, we studied a forested site with absolute quartz dominance (> 95 %). Here we hypothesise minimal effects of chemical weathering of silicates on DSi. During a four year observation period (05/2007-04/2011), we quantified (i) internal and external Si fluxes of a temperate-humid biogeosystem (beech, 120 yr) by BIOME-BGC (version ZALF), (ii) related Si budgets, and (iii) Si pools in soil and beech, chemically as well as by SEM-EDX. For the first time two compartments of biogenic Si in soils were analysed, i.e., phytogenic and zoogenic Si pool (testate amoebae). We quantified an average Si plant uptake of 35 kg Si ha(-1) yr(-1) - most of which is recycled to the soil by litterfall - and calculated an annual biosilicification from idiosomic testate amoebae of 17 kg Si ha(-1). The comparatively high DSi concentrations (6 mg L-1) and DSi exports (12 kg Si ha(-1) yr(-1)) could not be explained by chemical weathering of feldspars or quartz dissolution. Instead, dissolution of a relictic, phytogenic Si pool seems to be the main process for the DSi observed. We identified canopy closure accompanied by a disappearance of grasses as well as the selective extraction of pine trees 30 yr ago as the most probable control for the phenomena observed. From our results we concluded the biogeosystem to be in a transient state in terms of Si cycling.
Acyclic diene metathesis a versatile tool for the construction of defined polymer architectures
(2011)
Two decades have passed since the metathesis polymerisation of alpha,omega-dienes was successfully demonstrated by the group of Wagener and the term acyclic diene metathesis (ADMET) polymerisation was coined. Since then, the advances of metathesis chemistry have allowed to expand the scope of this versatile polymerisation reaction that nowadays finds applications in different fields, such as polymer, material, or medicinal chemistry. This critical review provides an insight into the historical aspects of ADMET and a detailed overview of the work done to date applying this versatile polymerisation reaction (221 references).
Due to depleting fossil resources, the ever increasing emission of greenhouse gases and toxic waste, as well as the inefficient utilization of our available resources, we have to implement the principles of green chemistry whenever and wherever possible. Plant oils are already the most important renewable resource for the chemical industry. Due to their inherent double-bond functionality, they offer the possibility of being transformed via several very efficient catalytic processes. Especially, new developments in olefin metathesis allow the chemist to directly polymerize or introduce a variety of functional groups to these renewable resources in an efficient manner. Therefore, olefin metathesis with plant-oil-derived fatty acids and their derivatives can contribute to a sustainable development of our future, since this approach has great potential for the substitution of currently used petrochemicals and a variety of value-added chemical intermediates, especially for the polymer industry, can be derived from these resources in a straightforward fashion. This contribution will address and discuss the most recent developments in this field of research.