4-Hydroxy styrene

An attempt to formulate a poly(4-hydroxy styrene)-based resist was less than completely successful because the difference in the rates of dissolution were too small to be used to give high contrast images. Other small molecules were added to the NDS/novolac resist and these were also found to have a profound effect upon the performance of the resist, particularly the development properties. When it was necessary to obtain higher dissolution rates, several triazoles and sulfonamides were found to improve the rate of development in the exposed areas without causing unacceptable thickness losses in the unexposed areas. Dyes incorporated to minimize problems of reflection and scattered light were also found to alter the dissolution behavior of the resist coating. 

The required monomer, 4-t-butoxycarbonyloxystyrene, is widely described in the literature. Because 4-hydroxy styrene is difficult to isolate due to its rapid polymerization, BOC-oxystyrene is generally prepared by treatment of 4-acetoxystyrene with strong base thus giving the corresponding phenoxide, immediately followed by addition of (B0C)20 in THF solution (Ref. 98). 

In the above condensation resist designs, the phenolic resin offers a reaction site as well as base solubility. Self-condensation of polymeric furan derivatives has been utilized as an alternative crosslinking mechanism for aqueous base development (Fig. 126) [375]. The copolymer resist is based on poly[4-hydroxy-styrene-co-4-(3-furyl-3-hydroxypropyl)styrene], which was prepared by radical copolymerization of the acetyl-protected furan monomer with BOCST followed by base hydrolysis. The furan methanol residue, highly reactive toward electrophiles due to a mesomeric electron release from oxygen that facilitates the attack on the ring carbons, readily yields a stable carbocation upon acid treatment. Thus, the pendant furfuryl groups serve as both the latent electrophile and the nucleophile. Model reactions indicated that the furfuryl carbocation reacts more preferentially with the furan nucleus than the phenolic functionality. 

PCL/poly(4-hydroxy styrene) Miscibility concluded from the negative value of Xi2 "0-013, and singleT Lezcano etal., 1996... 

A very prominent example of this type of resist is a copolymer of 4-hydroxy-styrene with tert-butyl ester-protected 4-hydroxystyrene (TBEST) (XXIX) (see scheme 7.33), developed at IBM and sold under the brand name of APEX-E by the Shipley Company. The synthetic route to copolymer (XXIX) can be through direct copolymerization of 4-hydroxystyrene with TBEST or via polymerization of TBEST, followed by partial deprotection to afford a copolymer with repeating units having about 20-30% protecting groups. Partial protection of copolymer... 

Arrighi, V., Cowie, J. M. G., Ferguson, R., McEwen, 1. J., McGonigle, E.-A., Pethrick, R. A., and Princi, E., Physical ageing in poly(4-hydroxy styrene)/poly(vinyl methyl ether) blends, Polym. Int., 55, 749-756 (2006). 

DSC crystallization curves of water sorbed on poly (4-hydroxy styrene). 

PCL/P4HS PCL blends with poly(4-hydroxy styrene) Xiz/k = -0.013 and single Tg indicated miscibility 11... 

Contact allergy to styrene is extremely rare. One patient, sensitive to styrene, cross-reacted on patch testing to 2-, 3- and 4-vinyltoluene (2-, 3- and 4-methylstyrene) and to the metabolites styrene epoxide and 4-vinylphenol (4-hydroxy-styrene). It is assumed that styrene is a prohapten metabolized in the skin by aurylhydrocarbon hydroxylase to styrene epoxide, which acts as a true hapten. Styrene occurs both in nature and as a synthetic product, and vinyltoluenes (methylstyrenes) occur as synthetic products in plastics (Sjoborg et al. 1984). Cases of immediate allergy to styrene have been reported (Bourne and Miller 1963 Conde-Salazar et al. 1989 Moscato et al. 1987 Sjoborg et al. 1984). 

Hydroxycinnamic acids (HCAs), comprising p-coumaric, ferulic, caffeic and sinapic, and their bound forms, are found in citrus fruit parts (d5). During processing and storage of citrus juices, vinyl phenols are produced from the free HCA by acid-catalyzed decarboxylation. The decarboxylation of all HCAs would potentially produce p-vinyl phenol (from p-coumaric acid), p-vinyl guaiacol (ferulic acid), p-vinyl catechol (caffeic acid) and 3,5-dimethyl-4-hydroxystyrene (sinapic acid). P-vinyl phenol and p-vinyl guaiacol have been identified in processed citrus juices, but p-vinyl catechol and 3,5-dimethyl-4-hydroxy styrene have yet to be reported. Vinyl phenols are unpleasant smelling compoimds with very low perception thresholds their presence adversely affects acceptability of citrus juice products. 

Hatakeyama H, Hayashi E, Haraguchi T (1977) Biodegradation of poly(3-methoxy-4-hydroxy styrene). Polym J 18 759-763... 

Poly(4-acetoxystyrene) with = 10000, PDI =1.12 was prepared by bulk RAFT polymerization of 4-acetoxystyrene at 90 °C using AIBN as initiator and a-acetic acid dithiobenzoate as chain transfer agent, and used as a macrotransfer agent in the block copolymerization of St with AIBN initiator after reprecipitation and the removal of residual monomer. The block copolymer, RB-2 was obtained [46]. The block copolymer can be hydrolyzed under mild basic conditions to give poly(4-hydroxy styrene)- )-PSt [46]. 

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