Polymer backbone, catalytic cleavage

Second, the polymer needs to be broken down into small fragments. Microorganisms excrete extracellular enzymes that cleave the polymeric chains [4]. This enzymatic cleavage reaction, on the one hand, needs functional sites within the polymer backbone where the enzymes can catalyze the cleavage of chemical bonds. On the other hand the polymeric chain needs to be flexible enough that the chain can enter the catalytic site of the enzyme. In most cases, the chemical reaction catalyzed by the exo-enzymes is a hydrolysis process that converts the polymer chain into smaller oligomers and monomers [4]. 

The catalytic activity of all polymers was always higher than that of CD alone and was inversely proportional to the number of CDs on the polymer backbone. The polymer having the lower SD was the best one in terms of catalytic activity. The authors showed that both CD and NH2 groups are important for the esters hydrolysis. CDs concentrate the ester in the polymer enviroiunent, and the NH2 groups are the active functions involved in the cleavage. 

The second type of chemically amplified depolymerization resist mechanism depends upon the incorportation of C-O bonds into the polymer backbone which can be cleaved by either hydrolysis or addolysis. This concept was first advanced by Crivello, who proposed that polymers such as polycarbonates and polyesters could undergo photo-induced add catalyzed hydrolysis reaction in polymeric film (9, 76). Although polymers could be designed to undergo catalytic chain cleavage in the presence of add, such an approach depends upon the inclusion of stoichiometic amounts of water in the polymer film. Uttle further work was reported on this concept until recently, when a new system for dissolution inhibition was described based upon the hydrolysis of polysilyl ethers in a novolac resin (24). 

Much of the work related to the design of chemically amplified resists that depotymerize iqx>n catalytic cleavage of the polymer backbone has been done by Frechet et al. (77-81). In these tystems, the potymer film depolymerizes through... 

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