Synthesis of poly(p-hydroxy-α-methylstyrene) by cationic polymerization and chemical modification

Abstract

High molecular weight, soluble poly(p-hydroxy-a-methylstyrene) has been synthesized for the first time by cationic polymerization of p-[(fert-butoxycarbonyl)oxy]-«-methylstyrene with boron trifluoride etherate as an initiator in liquid sulfur dioxide followed by thermolytic deprotection. Cationic polymerization of p-acetoxy-a-methylstyrene in dichloromethane followed by hydrazinolysis afforded the title compound, but the polymerization was accompanied by partial cleavage of the protecting group. Conventional cationic polymerization of p-[ (tert-butoxycarbonyl) oxy] --methylstyrene in dichloromethane resulted in formation of low molecular weight polymer accompanied by partial cleavage of the protecting group. Ether monomers, such as p-methoxy-and p-(ethoxymethoxy)-a-methylstyrenes, readily underwent cationic polymerization, while the p-(2-methoxyethoxy)methyl derivative suffered from partial deprotection and cross-linking. Removal of the ether protecting group was, in all cases, accompanied by chain degradation and/or cross-linking. Chemical modification of poly(a-methylstyrene) and poly(p-bromo-«-methylstyrene) by lithiation followed by hydroxylation produced cross-linked materials.

Chemical amplification based on acid-catalyzed depolymerization.

“…pPBOCMS can be obtained by cationic polymerization in liquid S02 with the acid-labile tBOC group intact (Scheme VII) [26]. In contrast to the thermolysis, however, acid-catalyzed deprotection of pPBOCMS in solution is accompanied by backbone scission (depolymerization) [26]. We have continued to study the acid-catalyzed depolymerization behavior of poly(a-methylstyrene) derivatives [18], which was also reported by Houlihan et al recently [27].…”

“…Scheme PACOST pPHOMS can be readily prepared by heating poly(p-t-butoxycarbonyloxy-a-methylstyrene) (pPBOCMS) to "200°C (Scheme VII) [26]. pPBOCMS can be obtained by cationic polymerization in liquid S02 with the acid-labile tBOC group intact (Scheme VII) [26].…”

“…pPBOCMS can be obtained by cationic polymerization in liquid S02 with the acid-labile tBOC group intact (Scheme VII) [26]. In contrast to the thermolysis, however, acid-catalyzed deprotection of pPBOCMS in solution is accompanied by backbone scission (depolymerization) [26].…”

Evolution and Progress of Deep UV Resist Materials.

“…In Fig. 9 are presented tBOC-protected polymers evaluated as deep UV resist materials [44,[46][47][48][49][50][51].…”

Positive-Working DUV Resist Based on Terpene Derivatives as Cross-linker.

“…After the concept of chemically amplified resist was proposed [1][2], positive working resist using protecting group such as t-butoxycarbonyl, tetrahydropyranyl or alkoxyethyl is main current in microlithography [3][4]. Yamaoka and co-workers have been studying cross-linking type positive working resist using vinyl ether cross-linker [5][6][7][8][9][10][11].…”