Base-catalyzed polymerization kinetics

PHOST is often prepared by polymerization of 4-acetoxystyrene followed by base-catalyzed hydrolysis (Fig. 29). The acetoxystyrene monomer s stabihty and polymerization kinetics allow production of PHOST of higher quaUty than is easily obtained by direct radical polymerization of HOST. The PHOST homopolymer product is then partially or fully derivatized with an acid-cleavable functionaUty to produce the final resist component. 

The kinetics are much simpler in homogeneous metallocene-based catalyst systems, especially in base-free cationic catalyzed polymerization systems, than those in heterogeneous systems. The polymerizations with homogeneous metallocene catalysts are no doubt the best systems for kinetic study of Ziegler-Natta polymerization. The a-olefin polymerization with these catalysts also offers a good opportunity to study the durability and deactivation of the catalysts, since the polymerization systems remain homogeneous over a considerable long reaction period [50]. 

A similar case was later found in the base-catalyzed ringopening polymerization of cyclic siloxanes. In this case, on the basis of kinetic measurements, it was shown (7, that the active species is the free silanolate anion (-Si-0 ) and no true... 

Poly(hydroxystyrene) (PHOST) is often prepared by polymerization of 4-acetoxystyrene, followed by base-catalyzed hydrolysis (Fig. 9a). The ace-toxystyrene monomer s stability and polymerization kinetics allow production of PHOST of higher quality than is easily obtained via direct radical polymerization of HOST. The PHOST homopolymer formed thereby is then partially or fiilly derivatized with an acid-cleavable functionality to produce the final resist component. In some instances the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (23,45), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, for example, the copolymerization of acetoxystyrene with tert-butyl acrylate, followed by selective removal of the acetoxy group (46) (Fig. 9b). 

The polymerization character and the kinetics of the base-catalyzed alcohol-glycidyl ether reaction are consistent with the following mechanism First, some concentration of alkoxide ion is generated from the catalyst and either the epoxide or the alcohol. This anion then reacts with epoxide to form a new alkoxide ion, which can continue to add epoxide ... 

Balfe and Martinez [108] investigated the acid- and base-catalyzed hydrolysis of TMOS, and the dimer (15) and linear trimer (16) (H2O/ OCH3 = 0.5-1.0). They observed cyclic tetramer in the condensation products of the monomer and dimer but not in the products of trimer polymerization. From this they concluded that hydrolytic decomposition of the trimer is kinetically unimportant under their reaction conditions. Similarly they observed a resonance attributable to cyclic trimer in the condensation products of the monomer or trimer but not in the products... 

It is well known that the base hydrolysis of polyacrylamide is catalyzed by OH ions (first order reaction) and obeys autoretarded kinetics due to the electrostatic repulsion between the anionic reagent and the polymeric substrate(3-5). In the range of slightly acid pH (3 < pH < 5), Smets and Hesbain(6) have demonstrated a... 

Although some depolymerases act processively in cleaving their polymeric substrates, others act by what can be described as multiple attack which results in nonselective scission or random scission. The analysis of cleavage products during the course of enzyme-catalyzed depolymerization can provide important clues about the nature of the reaction. With random scission, the rate of bond scission must be proportional to the total number of unbroken bonds present in the solution. Thomas measured the rate of base addition in a pH-Stat (a device with an automated feedback servomotor that expels ti-trant from a syringe to maintain pH) to follow the kinetics of DNA bond scission by DNase. The number of bonds cleaved was linear with time, and this was indicative of random scission. In other cases, one may apply the template challenge method to assess the processivity of nucleic acid polymerases. See Processivity... 

We note that there are NMR-based kinetic studies on zirconocene-catalyzed pro-pene polymerization [32], Rh-catalyzed asymmetric hydrogenation of olefins [33], titanocene-catalyzed hydroboration of alkenes and alkynes [34], Pd-catalyzed olefin polymerizations [35], ethylene and CO copolymerization [36] and phosphine dissociation from a Ru-carbene metathesis catalyst [37], just to mention a few. 

The different catalytic responses of peroxidase in dioxane and methanol versus acetone are intriguing. It is clear that the effects of water-miscible solvents on enzymatic catalysis are not equivalent and for the first time quantitative kinetic data have been obtained which highlight this. However, the cause of this effect remains unresolved. We are continuing and expanding this kinetic study to include other solvents, both water-miscible and immiscible, and other phenols. This future study will enable rational and quantitative approaches for peroxidase-catalyzed phenolic polymerizations to be based on optimal solvent and phenol choices. From a more fundamental standpoint, this work has shown that enzymes may be more active in organic media than in water as long as optimal conditions are employed. There is no reason to believe peroxidase is unique in this respect. 

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