Thermolysis, acid-catalyzed

The formation of phenolic polymers by Claisen Rearrangement of poly(4-allyloxystyrenes) under acid catalyzed thermolysis conditions has previously been reported in connection with the development high resolution photoresists (14,15). This work was primarily focused on the production of soluble phenolic polymers that could be imaged on the basis of differential dissolution. In this regard, allyloxysty-rene polymers bearing alkyl substituents at the a-position to the ether oxygen atom... 

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

Thermolytic Cleavage of Allvlic and Benzvlic Ethers and Polvethers. The thermal lability of the types of ethers which are of interest in the context of this study was discovered during a thorough study of the application of certain benzylic carbonates as labile protecting groups for alcohols and phenols [IS]. It was observed that, under acid catalysis, the bis-methylcarbonate derivative of l-(4-hydroxyphenyl)ethanol (4, in Equation 1) was transformed into the benzylic ether (5) which then underwent clean acid-catalyzed thermolysis to the corresponding styrene (6) in very high yield [14]. 

Figure 8. Acid catalyzed thermolysis of the t-BOC protected copolymer is responsible for the change in solubility. The quantum efficiency for generation of the phenolic is the product of the efficiency of photoacid generation and the catalytic chain length. Exposure generates a local concentration of acid. Subsequent heating to a temperature below that at which uncatalyzed thermolysis occurs allows local acidolysis of the t-BOC protecting group.

These systems are based on acid-catalyzed thermolysis of side-chain protecting groups. Examples of polymers that function in this fashion are listed in Chart 3.1. 

The tertiary butyl ester and carbonate groups are particularly useful in this application because they are sensitive to A l-I hydrolysis that does not require a stoichiometric amount of water. These materials undergo acid-catalyzed thermolysis. Consequently, a resist system can be formulated by casting these polymers from solutions that also contain a substance that... 

Another example is thermally depolymerizable polycarbonates that are sensitized with onium salt cationic photoinitiators (139). As discussed previously (Section 3.2.3), one of the positive-negative resists based on polystyrene with pendant tertiary butyl carbonate protecting groups undergoes acid-catalyzed thermolysis to generate poly( p-vinylphenol), carbon dioxide, and isobutene. Therefore, if the tertiary butyl carbonate moiety is incorporated in the polymer backbone as a repeating unit, such polymers will... 

Compound (79) was easily de-t-butylated by Lewis acid-catalyzed thermolysis to yield (80) and an isomeric betaine (81) (Equation (5)) <93JOC6620>. 

Scheme 6.13 Chemical amplification mechanism involving acid-catalyzed cross-linking of a benzyl carbocation (from benzyl acetate) and a substituted phenol. Note that in step 1, photolysis of the acid generator produces a latent image of acid, while in step 2, acid-catalyzed thermolysis of the acetate produces a carbocation ion. Step 3 shows the carbocation reacting with an appropriately substituted aromatic compound in an electrophilic substitution reaction that produces a covalent linkage and regenerates the acid. There is no net consumption of acid.

The cycloaliphatic backbone of these polymers contributes to dry etch resistance and thermal stabihty and serves to tether the pendant functionalities required for imaging. The materials incorporate a pendant acid-cleavable group such as a ferf-butyl ester that undergoes acid-catalyzed thermolysis accompanied by a... 

These materials all undergo acid catalyzed thermolysis and thus, a resist may be formulated by combining such polymers with an onium salt cationic photoinitiator that is known to generate strong acid upon exposure. 

The oldest method for the preparation of acrolein, the acid-catalyzed thermolysis of glycerol (dehydration) at about 190 °C, is still used today to obtain acrolein on a laboratory scale [3] ... 

The concept of photogenerating a latent image that could be dry developed in a dry bake process has been described for certain copolycarbonates." In this process a polymer such as (8), containing a photoacid catalyst such as an iodonium" or sulfonium" salt, is exposed to UV irradiation to photogenerate acid. Upon heating, an acid-catalyzed thermolysis occurs in the exposed areas to degrade the initial polymer back to volatile monomeric fragments. This reaction is shown in equation (6) for (8). 

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