Poly p-hydroxystyrene

The mechanism of photodegradation of poly(p-hydroxystyrene) (5.89) can be presented by the following reactions [2236, 2240]  

Polyenes and quinoide (3.90) and/or (3.91) structures are probably responsible for the yellow colouring of a polymer sample. 

It has also been suggested that the triplet state of a hydroxyphenylene group can directly react with oxygen, giving a phenoxy radical (3.92) [1546]  

Phenoxy radicals (3.92) can isomerize to more stable cyclohexadienoyl radicals (3.93) and (3.94) [1768]  

All radicals formed can terminate each other, resulting in gel formation. 

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Synthesis of the Polymers Containing Reactive Ether Pendant Groups, We have previously described the synthesis of high purity poly(p-hydroxystyrene) free from deleterious oxidized species by polymerization of 4-t-butyloxycarbonyloxy-styrene followed by the removal of... 

Figure 50, Schematic function of the t-Bocstyrene resist, S is a sensitizer such as diphenyliodonium hexafluoroarsenate which undergoes radiolysis to produce a strong acid (A), The acid attaches the side chain of the poly-(t-Bocstyrene) where it catalyzes acidolysis of the carbonate to liberate CO2 and isobutylene and free the phenolic hydroxyl group to produce poly (p-hydroxystyrene) in the exposed areas of the resist film. The acid A is a catalyst and can cleave many carbonate groups.

This reaction sequence is satisfactory although the overall yield is approximately 50%. A different route for the preparation of poly(p-acetoxystyrene) involves the direct acetylation of poly (p-hydroxystyrene) with acetic anhydride. The main problem with this approach is the lack of commercial availability of high purity poly(p-hydroxystyrene). 

Similarly, poly (p-formyloxy styrene) (IV) can be prepared by formylation of poly(p-hydroxystyrene) using formic acid-acetic anhydride mixture as a formylating agent (Scheme 4). The formylation reaction is best... 

The sharp increase in adsorbance which is observed near 256 and 340 nm is characteristic of the o-rearranged product. Similar results are also obtained when the irradiation experiments are carried out under nitrogen atmosphere, indicating that the photo-oxidation reported by Hiraoka and Pacansky (23) for poly(p-hydroxystyrene) is not a factor in this instance. 

Although the acetate ester of poly (p-hydroxystyrene) is more readily prepared than the corresponding formate (IV), the occurrence of a photostabilizing rearrangement during photolysis of III makes it ultimately ill-suited for use as an imaging system. A survey of the literature on the photo-... 

Fries rearrangement of aromatic formate esters suggests that phenols are the major products (.24) obtained in the reaction. As poly(p-hydroxystyrene) is remarkably clear in the deep UV, it is likely that poly(p-formyloxystyrene) will not suffer from the same problem of photostabilization upon exposure as was the case with poly (p-acetoxystyrene). This expectation was confirmed by our study of the photo-Fries reaction of p-cresyl formate no ortho rearranged product was isolated after reaction while p-cresol and a small amount of starting material were obtained. 

Table II. Second-Harmonic Coefficients ( 33) and Temporal Decay Parameters for Corona-Poled, NPP-Functionalized Poly(p-hydroxystyrene) Films as a Function of Thermal Cross-Linking a...

A binary monolayer of another kind was examined by means of the mechanical relaxation technique in conjunction with SLS by Rivillon et al. [110]. The system was PVAc and poly(p-hydroxystyrene) (P4HS). They have studied over a broad range of frequency (0.1 mHz-200 kHz) and finer composition resolution. Their conclusion is somewhat the same as our example of the PVP-PVAc system, but they can advance further details of the composition-dependent relaxation modes, after having established that the P4HS mono-layer is in a poor solvent condition with the same set of two techniques [111]. 

DUV exposure of poly( p-substituted styrenes), such as poly( p-chloro-styrene), poly( p-chloromethylstyrene), and poly( p-hydroxystyrene) [poly(p-vinylphenol)] (structure 3.11), in air leads to photocross-linking and photooxidation. Consequently, DUV hardening is applicable to resists based on these polymers as well as novolac-based resists (168, 169). 

The surface photo absorption for contrast enhancement (SPACE) process has been recently reported for use with a negative-working electron-beam resist (42). By addition of a controlled UV-flood exposure step, enhancements in both contrast and sensitivity of MRS RD2000N resist, a negative working resist composed of poly(p-hydroxystyrene) and 3,3 diazido-diphenylsulfone, have been obtained. However, its application is iimited to negative working resists. 

We wish to report first dry developable photoresists with poly(olefin sulfones) with photosensitizers like pyridine N-oxide, and then we present our study on composite resists made of poly(olefin sulfones) with novolac resins or with poly(p-hydroxystyrenes). 

Figure 3. UV absorption spectra of PMPS in brominated poly(p-hydroxystyrene).

Asami has reported grafting of living polyTHF on polymer with pendant alkali phenolates 157). Poly(p-hydroxystyrene-co-styrene) gave 100% grafting efficiency at 0 °C with Na countercations extraction with isopropanol gave 30 %-78 % copolymer the rest being insoluble gel. 

Faced with the shortcomings of the polyphthaldehyde resist (presented helow in chemical amplification resists based on depolymerization), the search for chemically amplified DUV resists resulted in a quick switch to more stable materials based on poly(p-hydroxystyrene), a phenolic polymer that Willson et al. were studying as a potential replacement for novolac. They observed that poly(p-tert-butoxycarbonyloxystyrene) (PBOCST), which is poly(vinyl phenol) protected with tert-butoxycarbonyl groups (t-BOC), is far more stable than the unprotected p-hydroxystyrene and could be purified and polymerized under controlled conditions. The resulting protected polymer could be easily deprotected thermally by heating it to 200°C or to a much lower temperature (100°C) by treatment with acid generated from the exposure of onium salts, just as in the poly(phthaldehyde)... 

Hanrahan and K.S. Hollis, Comparison of the dissolution behavior of poly(p hydroxystyrene) with novolac, Proc. SPIE 771, 128 (1987). 

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