Linking groups ester

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Polyesters are defined as polymers containing at least one ester linking group per repeating unit. They can be obtained by a wide range of reactions, the most important being polyesterifications between dibasic acids and diols or their derivatives (Scheme 2.1). 

On the other hand, ligand 3b may be modified at the carboxylate donor instead of the OH-linker. This prevents the carboxylate donor from acting as linking group. Although the most obvious protecting group is the methyl ester 52 (Scheme 27), direct esterification of... 

Additional BHT-derived 5-LO inhibitors bear heteroatom-linked 4-substituents. Searle s SC-45662 (50) was selective (25 1) for 5-LO over CO in cRBL (3.7 /iM) and in A23187-stimulated RBL-1 cells (7.1 yuM) [146]. Besides NSAID-like activity in RAA (down to 10 mg/kg p.o.), SC-45662 also inhibited GPB (ED30 16.7 mg/kg p.o.), and LTB4 release from ulcerative colitis rectal mucosal biopsy samples was decreased [147]. Several patents have described similar compounds where the alkyl substituent on sulphur is varied quite widely [148 151]. Oxidation of the distal sulphur was consistent with activity, while replacement of this sulphur with oxygen gave reduced potency. Simple alkyl groups, alkylene-linked esters and amides, and disulphide-linked alkanoic esters were also active in cRBL with similar potency free carboxylic acids were somewhat less potent. Oxidation of the sulphur attached to the phenolic ring destroyed the activity. 

Scheme 7 Application of the Glycolate Ester Linking Group 311...

Polymer IX illustrates that it is possible to include a limited proportion, for example 20 moles %, of amide linking groups into this type of copolymer without destroying the thermotropic property. In this case the melting point of the copolymer containing 60 moles % of 2,6-oxynaphthoyl units and 20 moles % each of p-oxybenzoyl and p-iminobenzoyl units is only 277 °C 43>, similar to that just noted for the copolymer with ester instead of amide groups. 

Polymer-linked tartrate esters have been prepared and used for asymmetric epoxidation in efforts to simplify reaction workup procedures and to allow recycling of the chiral tartrate [21]. The tartrates were linked through an ester bond to either a hydroxymethyl or a hydroxyethyl group on the polymer backbone to form 4 and 5, respectively. 

Bayle presented liquid crystal 34 (Scheme 19) bearing four aromatic units linked by ester and azo functional groups [56]. Two butyloxy groups are attached at the ends of the molecule and the crown ether is bound at the side of the molecule. The nematic phase exhibited by 34 is quite broad (AT = 96 K). Upon complexation with LiBF4, the nematic range diminishes with increasing amounts of added salt and disappears completely at 0.5 equiv. of added LiBF4 which is most likely due to the formation of a 2 1 crown lithium complex. From 0.2 equiv. of salt, a smectic... 

A more systematic approach has been taken by the Fyles group. In an effort to understand the important structure-activity relationships underpinning simple ion transport, alkyl chains of variable lengths, polyethers and amino acids have been linked by esters to produce an extensive library, examples of which are to be seen in Fig. 5.17 [60], The transport rates and selectivities of these compounds gave valuable information on the essential and desirable characteristics of these, the simplest, transmembrane ion channels. 

The linking groups of the ALS molecules, cholesteryl 4-(2-anthryloxy)buta-noate (CAB) and cholesteryl anthraquinone-2-carboxyIate (CAQ), allow them to adopt an overall rodlike shape. (See Structure 4.) CAB forms gels with hydrocarbons, alcohols, aldehydes, esters, amines, etc. (Table l) [76[, and both CAB and CAQ gel more complex fluids, like silicone oils [77[. Many CAB gels are luminescent and some are metastable, exhibiting a gel-to-liquid/solid phase separation after various periods of time. 

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