Solution-to-gel transition

J. Yang, L. Jia, Q. Hao, Y. Li, Q. Li, Q. Fang, et al. New biodegradable amphiphihc block copolymers of e-caprolactone and 6-valerolactone catalyzed by novel alumimun metal complexes II. Micellization and solution to gel transition, Macromolecular Bioscience, 5, 896-903, 2005. 

The solids content at the solution boundary must be high in order to cause a rapid transition from solution to gel. 

When a tetraethoxysilane-water-hydrochloric add-alcohol solution of appropriate composition is held at near room temperature, hydrolysis and polycondensation occur and the solution viscosity increases. Fibers can be drawn at a viscosity about 10 Pa s, which occurs during the course of sol to gel transition. It should be pointed out that for an alkoxide solution to be spinnable (Sakka,... 

Jeong et al. studied the gelation behavior of poly(ethylene glycol)-h-poly(L-alanine) (PEG-h-L-PA) block copolymers in water [117, 118]. They suggested that the P-sheet structure of l-PA plays a critical role in developing a fibrous nanostructure as well as in the sol-to-gel transition of the copolymer solutions (Fig. 14). The conformation of l-PA in water is random coil at low concentrations. As the concentration increases, block copolymers start to aggregate and the conformation... 

Aqueous solutions of Poloxamer or Pluronic undergo sol-to-gel transition as the temperature increases (Fig. 13.4). However, the implanted gel of Poloxamer is quickly eroded and does not persist for more than a few days at most. To improve the system, end-group modified Poloxamers, and multiblock copolymers consisting of Poloxamer and biodegradable polymers have been developed. In addition, random multibloek eopolymers consisting of PEG, PPG, and a biodegradable polymer were reported. 

Aqueous solutions of chitosan-g-PEG and hyamlonic acid-g-Poloxamer undergoing thermal gelation were reported. Aqueous solutions of hydroxy-propyl methylcellulose or methyl cellulose also show thermal gelation. The hydrophobic interactions were suggested as the sol-to-gel transition mechanism. Aqueous solutions of the inclusion complexes between methylated a-... 

During the formation of noncovalent cryogels from the polymeric precursors exhibiting an upper-critical-solution-temperature (UCST) behavior, cooling down the reaction solution also facilitates the sol-to-gel transition. 

FIGURE 2.3.4 Chemical structures of linear-type biodegraciable block polymers exhibiting temperature-responsive sol-to-gel transition in aqueous solutions, (a) PLGA-b-PEG-b-PLGA triblock copolymer, (b) PEG/PLLA multiblock copolymer,... 

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