P-Hydroxystyrene

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... 

Preparation of 4-(l-phenvlethvloxvl-stvrene. This benzylic ether of p-hydroxystyrene was prepared by a Wittig reaction on the precursor aldehyde as described above. The final product was obtained in 73% yield after purification by preparative HPLC using 5% ethyl acetate in hexane as eluent. The product had analytical characteristics in agreement with the proposed structure. 

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. 

C and H NMR spectra of the polymer isolated after irradiation show the formation of essentially pure p-hydroxystyrene polymer but provide no... 

Preparation of p-Formyloxystyrene An aliquot of 4.30 g of formic acid was combined with 9.54 g acetic anhydride (29). After cooling the mixture to room temperature 5.20 g of p-hydroxystyrene and 0.15 g pyridine were added. The mixture was stirred in the dark for 3 days. A TLC obtained of the crude reaction mixture using an 8 2 hexane/ethyl acetate mixture indicated the reaction had gone to completion. Removal of the acids and anhydrides at low temperature under vacuum left a yellow residue which upon fractional distillation gave 6.39 g (66.5%) of -formyloxystyrene (b. p. 83 °C at 3 mm Hg). 

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...

Yates and coworkers have examined the mechanism for photohydration of o-OH-8. The addition of strong acid causes an increase in the rate of quenching of the photochemically excited state of o-OH-8, and in the rate of hydration of o-OH-8 to form l-(o-hydroxyphenyl)ethanol. This provides evidence that quenching by acid is due to protonation of the singlet excited state o-OH-8 to form the quinone methide 9, which then undergoes rapid addition of water.22 Fig. 1 shows that the quantum yields for the photochemical hydration of p-hydroxystyrene (closed circles) and o-hydroxystyrene (open circles) are similar for reactions in acidic solution, but the quantum yield for hydration of o-hydroxystyrene levels off to a pH-independent value at around pH 3, where the yield for hydration of p-hydroxystyrene continues to decrease.25 The quantum yield for the photochemical reaction of o-hydroxystyrene remains pH-independent until pH pAa of 10 for the phenol oxygen, and the photochemical efficiency of the reaction then decreases, as the concentration of the phenol decreases at pH > pAa = 10.25 These data provide strong evidence that the o-hydroxyl substituent of substrate participates directly in the protonation of the alkene double bond of o-OH-8 (kiso, Scheme 7), in a process that has been named excited state intramolecular proton transfer (ESIPT).26... 

Fig. 1 The pH profile for absolute quantum yields (Oabs) for the photohydration reaction of o-hydroxystyrene (open circles) and p-hydroxystyrene (closed circles). Reprinted with permission of the American Chemical Society from Ref.25...

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]. 

It should be pointed out that the same type of graft copolymers has been obtained by Asami130) in a quite different manner involving deactivation of living poly-THF on a backbone chain of polystyrene with some randomly distributed p-hydroxystyrene units which have been metalated beforehand. 

Preparation of Poly(2-Ethyl-2-Adamantyl Methacrylate-co-p-Hydroxystyrene)... 

The entire Step 1 product was mixed with 4-dimethylaminopyridine and 239 g of methanol and then refluxed 20 hours. After cooling the mixture was neutralized with glacial acetic acid (0.133 mol) and precipitated in water. The precipitate was dissolved in acetone and then re-precipitated in water, the process being repeated three times. The precipitate was dried, and 102.8 g of polymer product were isolated, consisting of 70% p-hydroxystyrene and 30% 2-ethyl-2-adamantyl methacrylate with a of 8200 daltons and polydispersity of 1.68. 

Some of block copolymers with styrene derivatives are also amphiphilic, such as methyl vinyl ether-p-alkoxystyrene [88] and alkyl vinyl ether-p-hydroxystyrene (from p-r-butoxystyrene) [89] (Fig. 6). 

---