Coupling agent modification varieties

The surface modification of an inorganic support with organophosphorus coupling agents (OPCA) is an extremely versatile route to hybrid materials. This route has been applied to a variety of supports, including metal oxides, metals, aluminosilicates, silica, metal hydroxides, and carbonates. 

A recent publication described preparation of dendrimers from functional aliphatic polyesters that are based on 2,2-bis(hydroxymethyl)propionic acid [249]. A, Al -dicyclohexylcarbodiimide was used as the coupling agent in a double-stage convergent approach that reduced the number of synthetic and Uquid chromatographic steps required in the preparations and purifications. The hydroxyl functional dendrimers were then subjected to a variety of surface modifications by reactions with different acid chlorides [249]. 

Natural fibers are hydrophilic and do not tend to be easily wetted or bond well with many matrix materials, particularly the commodity thermoplastics. Coupling agents, such as maleated polyolefins, silanes, and isocyanates, are often necessary for adequate performance. A wide variety of coupling agents, fiber surface modifications, and treatments has been investigated for use in natural fiber plastic composites and are reviewed elsewhere [22]. 

While several companies produce organo-titanates for a variety of uses, one group of workers (Monte and Sugerman) have specialised in producing compounds for filler modification, which they refer to as coupling agents. As well as producing an enormous... 

Zeta potential is the potential difference between the dispersion medium (eg, polymer) and the layer of fluid attached to the dispersed particle (eg, soUd filler). This value is used to quantity the electrokinetic potential in a colloidal system and is used to evaluate the stabihty of colloidal dispersions. The modification of HA powder with methoxysilane coupling agents (possessing a variety of functionalities) was shown to significantly increase the zeta potential (Dupraz et al., 1996). 

Ceramic powders were obtained from a wide variety of sources and included alumina, hydroxyapatite, and lithium aluminum silicate. This latter sample was also used after surface modification with a silane coupling agent. Ceramic powders were also obtained by chloroform extraction of two proprietary tooth restorative composite materials viz. Estilux (Kulzer and Fotofil (Johnson and Johnson). Particle sizes and shapes were noted. 

The bispecific antibody approach is very flexible since antibodies or ligands to virtually any membrane site can be easily coupled with the effector-bearing antibody to form a variety of highly specific delivery agents. Variations in potency are precluded since no modification of the effector molecule is needed for attachment to the carrier. 

Among substituents, electron-withdrawing o-Cl and o-Br substituents appear to induce better enantioselectivities. Besides, they represent a convenient handle for further synthetic modification, e.g. through coupling reactions [25]. Chiral benz-hydryl fragment can be found in a variety of pharmaceutically relevant molecules. Synthetic application of the reduction of prochiral diaryl ketones was illustrated by enantioselective synthesis of antihistamine agents (I )-orphenadrine (37) and (5)-neobenodine (38) [26]. The former was synthesized in two easy steps from alcohol 35, whereas synthesis of 38 from 36 also included debromination step. 

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