Organic media gelators

The properties of polymethylsiloxanes are also greatly determined by the conditions of the reaction and the type of the solvent used. Thus, the hydrolytic condensation of methyltrichlorosilane (the main raw stock in the production of polymethylsiloxanes) with iced water or water vapour in a medium of nonpolar solvents forms a nonmeltable and nonsoluble amorphous substance. If the condensation is carried out by pouring methyltrichlorosilane into the emulsion of water and butyl alcohol gradually (to avoid gelation), at intensive agitation and reduced temperature (about 0 °C), it forms a viscous substance, which is soluble in organic solvents and briefly heated to 150 °C loses its meltability and solubility. 

There are two families of monolithic gels obtained from organic solutions. The first is basically identical to those obtained in aqueous medium. Similarities come from the mineral compound, which undergoes gelation the solvent and additives are organic compounds. The second refers to gels prepared from alkoxides in organic solvent. This kind of gel is the most popular and has been extensively reported in the literature. 

We have recently adopted a novel chitosan-based ionic gelation process for the preparation of PMAA-based microparticles. " Methacrylic acid was polymerized in the presence of chitosan in aqueous medium, and particles were obtained spontaneously during the polymerization without the addition of any organic solvents and steric stabilizers. PMAA-CS particles displayed good protein encapsulation efficiency and demonstrated pH responsive release behavior at stimulated gastric and intestinal pH. Application of these microparticles toward oral protein delivery was evaluated using insulin and bovine serum albumin (BSA) as model proteins. 

The octadecylamide of N-benzyloxycarbonyl-L-isoleucine 79 and N-benzyloxycarbonyl-L-Val-L-Val alkylamide 80, as well as some other N-Z-dipeptide alkylamides [60], exhibited excellent gelation properties toward many organic solvents of low, medium, and high polarity at mgc values in the range of 5-40 g L The compound was used for the preparation of organogel electrolytes and porous titania with fibrous structure by sol-gel transcription of gel fibers using polymerization of titanium tetraisopropoxide [61,62]. 

Fluorescence polarization of several organic dopants in a polymerizing Si02 sol-gel system was recently described by Winter et al. (80). Their main conclusion has been that the mobility of small and medium sized probe molecules is hardly affected by the gelation and that there is no rigidity at the microscopic level however, this conclusion seems to be in variance with other previously cited studies, including McKiernan s (79). 

---