Monomer synthesis polymerization behaviors

Heller and colleagues at Advanced Polymer Systems (Redwood City, CA) continue to develop additional polyorthoesters with a variety of physical properties and potential applications. ° Generally speaking, polyorthoesters do possess the potential to exhibit surface-eroding behavior. However, several issues that may limit the commercial application of this class of polymers are still present. One issue is that synthesis of these polymers involves complicated monomers and polymerization chemistry. The second issue is, to date, the toxicology and biocompatibility of these polymers and their degradation products have not yet been fully characterized. Finally, the requirement for pH-regulating additives such as acids and bases... 

Zhang et al. reported the synthesis of ohgofethylene glycol)-based dendronized polymers (G1-G3) (5 Figure 37.3) [3, 15]. When the polymerization behavior of the G1 and G2 monomers was studied imder a conventional free-radical technique, both the tetrahydropyran (THP)-protected G1 and G2 monomers, as well as the... 

The enzymatic reaction kinetics on the HRP-catalyzed oxidation of p-cresol in aqueous 1,4-dioxane or methanol showed that the cataljdic turnover niunber and Michaelis constant were larger than those in water (235). Numerical and Monte Carlo simulations of the peroxidase-catalyzed polymerization of phenols were demonstrated (236). The simulations predicted the monomer reactivity and polymer molecular weight, leading to synthesis of polymers with specific molecular weight and index. In an aqueous 1,4-dioxane, the formation of monomer aggregate was observed (237), which might elucidate the specific polymerization behaviors in such a medium. 

NEW VINYL ORGANOMETALLIC MONOMERS SYNTHESIS AND POLYMERIZATION BEHAVIOR... 

For several years our research group has been studying the synthesis, polymerization and copolymerization of monomers containing 5-fluorouracil (5-FU) and/or 6-methylthiopurine (6-MTP). - We have observed that the polymeric systems hydrolyzed in an aqueous medium to release the anticancer drug in a zero-order kinetic pattern. " Other studies, by Kaetsu, et al., on the release of 5-f luorouracil have not shown a similar zero-order behavior, but instead have shown a release pattern in which the 5-FU concentration was proportional to the square root of time."- These studies used highly crosslinked and fairly hydrophilic polymeric materials in which the 5-FU was monolithically dispersed. Our copolymer systems also contain the 5-FU dispersed in a monolithic manner, but, in these cases, the 5-FU is covalently attached to the polymer backbone. In the present study, we have compared the release rates of some monolithic 5-FU dispersions in poly(caprolactone) with the profiles obtained with our 5-FU containing copolymers. These monolithic dispersions in the poly-... 

Cationic polymerization was considered for many years to be the less appropriate polymerization method for the synthesis of polymers with controlled molecular weights and narrow molecular weight distributions. This behavior was attributed to the inherent instability of the carbocations, which are susceptible to chain transfer, isomerization, and termination reactions [48— 52], The most frequent procedure is the elimination of the cation s /1-proton, which is acidic due to the vicinal positive charge. However, during the last twenty years novel initiation systems have been developed to promote the living cationic polymerization of a wide variety of monomers. 

Characteristic initiation behavior of rare earth metals was also found in the polymerization of polar and nonpolar monomers. In spite of the accelarated development of living isotactic [15] and syndiotactic [16] polymerizations of methyl methacrylate (MMA), the lowest polydispersity indices obtained remain in the region of Mw/Mn = 1.08 for an Mn of only 21 200. Thus, the synthesis of high molecular weight polymers (Mn > 100 x 103) with Mw/Mn < 1.05 is still an important target in both polar and nonpolar polymer chemistry. Undoubtedly, the availability of compositionally pure materials is a must for the accurate physical and chemical characterization of polymeric materials. 

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