CA2045093C - A process for making low optical density polymers and copolymers for photoresists and optical applications - Google Patents

Abstract

The present invention pertains to a process for the preparation of polymers comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both. The polymers have low optical density (absorbance) over a wavelength range from about 240 to about 260 nm, as well as low optical density over the near UV and visible spectrum (310 to 800 nm). Such polymers arc produced by polymerizing 4-acetoxystyrene and/or substituted 4-aeetoxystyrene monomers, with or without other comonomers, and subsequently performing transesterification. In the most preferred embodiment of the present invention, the polymers are produced using at least one alcohol as a reaction medium, a chain transfer agent and a transesterification reactant, providing an unusually economic process. These polymers are particularly useful as photoresist components for use in combination with deep UV, X-ray, and E-Beam imaging systems.

To obtain polymers having low optical density over the 240 to 260 nm radiation wavelength range, it is necessary to use an initiator which does not comprise a substantially absorbant structure over the 240 to 260 nm range or to use an initiator concentration of less than about 3 mole % of the monomer(s), to obtain a polymerization conversion of the initial polymerization monomers of at least about 90% by weight, or to remove residual monomer(s) from the reaction medium prior to transesterification, and to obtain a transesterification conversion of the polymerized monomers of at least 85% by weight. It is also necessary to avoid the use of transesterification catalysts which can cause the formation of chemical structures which can absorb over the 240 to 260 nm radiation wavelength range.

Description

1 A PROCESS FOR MAKING LOW OPTICAL. DENSITY POLYMERS AND

1. Field of the Invention The present invention pertains to a process for making and to 6 compounds comprising homopolymers, copolymers, and terpolymers (hereinafter 7 referred to as "polymers") of 4-hydroxystyrene and/or substituted 4-8 hydroxystyrene. The polymers have low optical density (absorbance) over a 9 wavelength range from about 240 to 260 nm, as well as low optical density over the visible and near UY spectrum (310 to 800 nm). Such polymers can be 11 produced using a single compound which serves as a reaction medium for the 12 polymerization, as a chain transfer agent and as a transesterification reactant, 13 providing an unusually economical process. The polymers of the present 14 invention are particularly useful (directly or in modified form) as photoresist materials for deep UV, X-ray, and E-Beam imaging systems.
16 2 Description of the Background Art 17 There are numerous applications within the semiconductor industry 18 which require photoresists materials having low absorbance in the deep U.V.
(240 1 to 260 nm) wavelength region. The novolakTMphotoresist polymers which have 2 been used for optical lithography are limited to wavelengths longer than 300 nm 3 because of the high absorbance of the novolak material at shorter wavelengths. It 4 has mcently been learned that polymers and copolymers of 4-hydroxystyrene and substituted 4-hydroxystyrenes are particularly useful over a wavelength range 6 from about 240 to 260 nm. The molar absorbtivity (e) of such polymers and 7 copolymers over this wavelength range is as low as about 50 1 cm' mole '.
8 There is a need for an economic method or process for producing 9 polymers and copolymers of 4-hydroxystyrene and substituted 4-hydroxystyrene.
U.S. Patent No. 4,822,862, issued April 18, 1989, to R. W. Rupp et al., 11 describes the homopolymerization and copolymerization of 4-acetoxystyrene 12 monomer (4-ASM) in an aqueous emulsion and, without isolation, the hydrolysis 13 of the polymers and copolymers of 4-ASM to homopolymers and copolymers of 14 4-hydroxystyrene using a base.
U.S. Patent No. 4,912,173, issued March 27, 1990, to D. L. Keene et 16 al., discloses a process for hydrolyzing homopolymers of 4-ASM to 17 hvmopolymers of 4-hydroxystyrene. The hydrolysis is carried out in an aqueous 18 suspension in the presence of a nitrogen-comprising base.
19 European Patent No. 343,986, issued November 29, 1989, to R. Vicari et al., describes the preparation of polymers of 4-ASM or polymers of 4-21 hydroxystyrene by suspension polymerization. The suspension polymerization 22 comprises forming an aqueous suspension of 4-ASM in the presence of ,. .
~c~J~~~Y
1 polyacrylic acid and at least 2 free radical catalysts, one of which has a half life 2 of 1 hour below 100°C and the other which has a half life of 1 hour above 100°C.
3 The suspension is heated to 70-95°C to achieve about 50 wt%n 4 polymerization, and then polymerization is completed by heating above 95°C. To form the polymer of 4-hydroxystyrene (4-HSM), the reaction temperature is then 6 reduced to between 30-95°C and the suspension is reacted with ammonium hydroxide in an amount of at least 2 moles of ammonia for each equivalent of 4-S ASM.
9 The poly(4-hydroxystyrene) produced by the above-described method, typically has an absorbance at 24S nm which ranges from about 3U0 to 350 11 liters/czri' mole' (molar absorbdvity, ~).
12 U.S. Patent No. 4,S9g,916, issued 1~ebruary 6, 1990, to 13. Cupta et al.
13 describes a pxocess for the conversion of poly(4-aeetoxystyrene) (4-PAS) to 14 poly(4-hydroxystyrene) (4-PHS). The process comprises: a) forming an alcoholic iS slurry of (4-PAS); b) adding an acid to the slurry; and c) maintaining slurry 16 temperature at 20-55°C until the polymer dissolves in the alcohol, indicating 17 complete acetoxy to phenolic group conversion.
18 Processes wherein the 4-ASM is polymerized into a homopolymer or a 19 copolymer with another copolymerisable monomer, and especially wherein the comonomer is styrene, are claimed. The 4-PHS or copolymers of 4-HSM is 21 expected to have a molar absorptivity, ~, ranging from about 300 to 1,QQU
22 depending on the 4-PAS used as the pa~ecursor for the reaction described.

1 U.S. Patent No. 4,689,379, issued August 25, 1987, to J. D. Elmore et 2 al., discloses the hydrolysis of polymers of 4-ASM by methanolsis with 3 quaternary ammonium hydroxides to 4-PHS.
4 European Patent Publication No. EP 0 260 104, published March 16, 1988, discloses a prxess for preparing polymers comprising 4-PHS by initially 6 reacting 4-ASM and methanol, with subsequent reaction of 4-ASM, methanol, 7 4-HSM, polymers of 4-ASM, and polymers of 4-HSM, in the presence of an 8 ammonium base using a free radical initiator. The initiator is selected from a 9 group of initiators including benzoyl peroxide, lauroyl peroxide, acetyl peroxide, cumene hydroperoxide, paramethane hydroperoxide, etc.
11 G. Pawlowski et al. disclosed the polymerization of 3-methyl-4-12 acetoxystyrene using 2,2'-azobis(2-methylpropanenitrile) in tetrahydrofuran 13 (THF~ to produce poly(3-methyl-4-acetoxystyrene) at the March 1990 SPIE
14 meeting held at San Jose, California.
The poly(3-methyl-4-acetoxystyrene) polymerized by G. Pawlowski et 16 al. in THF was isolated (precipitated) and dried prior to subsequent use.
This 17 dried poly(3-methyl-4-acetoxystyrene) can then be slurried in methanol and 18 processed as described above by B. Gupta et al. to provide homopolymers and 19 copolymers of poly(3-methyl-4-hydroxystyrene).
However, preparation of 4-HSM polymers using a combination of the 21 above techniques would be very expensive. The THF solvent used by Powlowski 22 et al. in polymerizing the 4-PAS is toxic. In addition, the precipitation and 23 drying of the 4-PAS adds additional cost in the form of unit operations and waste disposal. In addition, the method of Gupta et al. disclosed in U.S. Patent No. 4,898,916 is difficult to accomplish on a large scale due to problems encountered in a making of a slurry of the 4-PAS in alcohol. The 4-PAS tends to "clump"
or remain in agglomerated form in the alcohol, due to insolubility.
SUMMARY OF THE TNVENTION
According to one aspect of the present invention, there is provided a process for preparation of_ polymers having low optical density at. 240-260 nm, comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both, said process comprising the steps of: a) reacting a mixture comprising 4-acetoxystyrene monomer or substituted 4-acetoxystyrene monomer or both and an initiator, wherein said initiator and its decomposition products alone or as polymer capping groups do not substantially absorb radiation over wavelengths .ranging from about 240 to abaut 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer, in a reaction medium comprising at least one organic solvent, to produce a polymer comprising poly(4-acetoxystyrene) or substituted poly(4-acetoxystyrene) or both, whereby, either as a result of monomer conversion, or due to removal ~f residual monomer, 10 wt % or less residual monomer, based on the weight of polymer produced, is present in the reaction mixture used during a subsequent transesterification reaction step; and b) subsequently transesterifying said poly(4-acetoxystyrene) to poly(4-hydroxystyrene) or transesterifying said substituted poly(4-acetoxystyrene) to substituted poly (4-hydroxystyrene) or t:r_ar3sesterifying both, in a transesterification reaction medium comprising at least one equivalent of alcohol per equivalent: of non-transesterified poly(4-acetoxystyrene) or substituted poly(4-acetoxystyrene), using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification, wherein at least 85% by weight conversion of s;~id poly(4-acetoxystyrene) to said poly(4-hydroxystyrene) or conversion of said substituted poly(4-acetoxystyrene) to said substituted poly(4-hydroxystyrene) or at least 85% by weight transesterification of both is obtained.
According to another aspect of t-he present invention, there is provided a process for preparation of polymers having low optical density at 240-260 nm, comprising poly(4-hydroxystyrene) or substituted poly(4-hydroxystyrene) or both, said process comprising the steps of: a) reacting a mixture comprising 4-acetoxystyrene monomer or substituted 4-acetoxystyrerze monomer or both and a comonomer having at least one vinyl group present, wherein said comonomer does not substantially <absorb radiation over wavelengths ranging from about 240 to about 260 nm; and an initiator, wherein said in:i.tiator and :its decomposition products alone or as capping groups do not. substantially absorb radiation over wavelengths rang~Lng from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer;
in a reaction medium comprising at lea:~t one organic solvent, to produce a copolymer of poly(4-acetoxystyrene) or said substituted poly(4-acetoxystyrene) with said comonomer, whereby, either as a result of monomer conversion or due to removal of residual monomer, 10 wt % or less residual monomer, based on the weight of polymer. produced, is present in the reaction mixture during a subsequent, transesterification reaction step; and b) subsequently transesterifying ;paid poly (4-acetoxyst:yrene) t.o poly (4-hydroxystyrene) or transesterifying said substituted poly(4-5a hydroxystyrene) to substi.t.uted poly(4-hydroxystyrene) or transesterifying both to a conversion of at least 85% by weight, in a transesterification react~.ion medium comprising at least one equivalent. of: alcohol per equivalent of non-transesterified copolymer, using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification.
According to still another aspect of the present invention, there is provided a process for preparation of low optical density copolymers of poly(4-hydroxystyrene) with substituted poly(4-hydroxystyrene), said process comprising the steps of: a.) reacting a mixture comprising 4-acetoxystyrene monomer, substituted 4-acetoxystyrene monomer and an initiator, wherein said initiator and its decomposition products alone or as polymer capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer, in a reaction medium comprising at least one alcohol to produce a copolymer of poly(4-<~cetoxystyrene) with substituted poly (4-acetoxystyrene), wherein at least 90% by weight conversion of said 4-acetoxystyrene monomer and said substituted 4-acetoxystyrene monomer combined is obtained; and b) subsequently transesterifying said poly(4-acetoxystyrene) and said substituted poly(4-acetoxystyrene) to poly(4-hydroxystyrene) and substituted poly(4-hydroxystyrene), in substantially said reaction medium of step a), using approximately 5-2000 ppm of: an acid catalyst to achieve said transesterif.ica.tion, wlzere~in at least 85% by weight conversion of the combination of said poly(4-acetoxystyrene) to said poly(4-hydroxystyrene) and said substituted poly(4-acetoxystyrene) to said substituted poly(4-hydroxystyrene) is obtained.
5b 77484,2 According to yet: another aspect of the present invention, there is provided a polymer comprising 4-hydroxystyrene having a molar absorbt:i.vity of about 211 or less, at a wavelength of about 250 nm, and a weight average molecular weight MW less than about 22,000 as measured by gel permeation chromatography using polystyrene standards, wherein said polymer contains less than about 2.5% by weight of residual 4-hydroxystyrene monomer or derivative residues thereof.
l0 In accordance with the present invention, it has been discovered that despite the partial insolubility of poly(4-acetoxystyrene) (4-PAS) in alcohols, it is possible to polymerize horriopolymers, copolymers, and terpolymers (hereinafter referred to as "polymers") comprising poly(4-acetoxystyrene) a.nd/or substituted poly (4--acetoxystyrene) (S-4-PAS) in an alcohol reaction medium, and to subsequently transesterify the polymer comprising 4-PAS and/or S-4-PAS, preferably in the same alcohol reaction medium, to produce a polymer comprising poly(4-hydroxystyrene) (4-PHS) and/or substituted poly(4-hydrox.ystyrene) (S-4-PHS). The initial polymerization of 4-acetoxystyrene monomer (4-ASM) and/or substituted 4-acetoxystyrene monomer (S-4-ASM) to produce a polymer comprising 4-PAS and/or S-4-PAS is carried out in a manner which permits formation of a transesterification reaction mixture comprising no more than LO% by weight of residual monomers) (based on the polymer produced). This 10% by weight residual monomer can be achieved by obtaining 90% conversion of the combination of all monomers initially present during the polymerization reaction, or by removing such monomers from the reaction mixtu:rE=_ al::ter the:
polymerization .is completed but prior i~o t:he transesterification reaction. The 5c ' ~ ' ~ ~~~~ a~~
1 initial concentration of monomer in the rnonomer/reaction medium mixture is 2 preferably greater than 40% by weight. The transesterification of 4-PAS
and/or 3 S-4-PAS is carried out so that at least 8~% of the 4-PAS and/or S-4-PAS is 4 converted to 4-PHS and/or S-4-PHS.
As described above, it would be possible to produce polymers 5 comprising the 4-PAS and/or S-.4-PAS by polymerizing the starting monomers to 7 less than 90% conversion, so long as residual monomer is removed from the 8 polymerization reaction mixture prior to the transesterification reaction.
It has 9 been discovered that, in the production of hornopolymers and copolymers of 4-PAS and/or S-4-PAS, as the polymerization of monomers progresses and the 11 polymer formed therefrom increases in molecular weight, the polymer becomes 12 insoluble fn an alcohol polymerization medium. It is then possible to discontinue 13 agitation of the reaction mixture, permitting the swollen polymer to separate, to 14 decant the alcohol reaction medium containing the residual monomer, to replace 1S the decanted alcohol with fresh, clean alcohol, and to proceed with the 16 uansesterification. This removal of the 4-PAS and/or S-4-PAS alcohol 1T polymerization medium (and replacement with fresh clean alcohol) accomplishes 18 the removal of excess initiator, initiator fragments, unreacted monomer and 19 aligomers, all of which can be sources for harmful, optical-density-increasing contamination of the 4-PHS and/or S-4-PHS product.
21 The above description is in terms of the use of an alcohol solvent as the 22 polymerization reaction medium, since this is the most preferred embodiment of 23 the present invention. However, other solvents can be used In the method of the arc-oo 11 ~rY
1 present invention, so long as there is sufficient alcohol present du~~~~'~
2 transesteriftcation step for transesteriftcation to take place.
3 Preferred "other solvents" are polar solvents which do not contain 4 acetate groups. In a less preferred embodiment of the present invention, these polar solvents can be used as the sole solvent during polymerisation of the 6 polymer comprising 4-acetoxystyrene and/or substituted 4-acetoxystyrene;

7 however, an alcohol must then be added prior to the transesterification to a & polymer comprising 4-hydroxystyrene and/or substituted 4-hydroxystyrene. In a 9 more preferred embodiment of the present invention, the polar solvent would be used as a co-solvent with an alcohol throughout the process of the present 11 invention. Examples of suitable polar solvents include tetrahydrofuran, I2 methylethyl ketone, acetone, and I,4-dioxane.
13 Nonpolar solvents can be used as co-solvents in combination with an 14 alcohol, provided the concentration of the nonpolar solvent is sufficiently Iow.
Typically, the nonpolar solvent is present at a concentration of Less than 25%
by 16 weight. Examples of suitable nonpolar solvents include heptane, hexane, and I7 cyclohexane.
1 g C)ther comonomers can be copolymerized in combination with the 4-19 AS1VI and/or S-4-ASM so long as the other comonomers do not absorb at radiation wavelengths ranging from about 240 to ,about 260 nm.
21 "Substituted", as referred to above is intended to mean that the ring 22 structure of the molecule has subsdtuent groups thereon, wherein the substituent ' .
1 groups are methyl or ethyl. Preferred substituent groups are meehyl and the 2 preferred substituted positions are the 3, 5, or 3 and S positions.
3 It is possible to obtain polymers comprising 4-PI-iS and/or S-4-PHS
4 having a molar absorbtivity, ~, ranging from about 40 to about 250 (at a wavelength of 248 nm) using the method described above. To obtain a polymer 5 comprising 4-PHS and/or a S-4-PHS having this molar absorbtivity at 248 nm, it 7 is necessary to:

8 I) a. Use a polymerization initiator which does riot comprise an absorbent 9 skmcture; absorbent structures such as aromatic rings increase molar . absarbtivity, ~,a, tygically by a factor of 2 when the weight average l I molecular weight of the polymer comprising 4-PHS or S-4-PHS ranges 12 from about 5,000 to about 25,0Q0 (as determined by gel permeation 13 chromatography (GPC vs. polystyrene standards), ar 14 b. Use a polymerization initiator which does comprise an absorbent structure IS but limit the initiator concentration to less than about 3 mole % of the 16 monomer used to produce tire polymer.
17 2) Ubtain a polymerization conversion of the monomers) of at least 90% by I8 weight; or remove residual monomers) from the reaction medium so that I9 residual monomer in the subsequent transesterification reaction mixture comprises no more than 10% by weight of the polymer comprising 4-PAS
21 and/or S-4-PAS polymer;
22 3) Obtain a transesterification conversion of at least 85% by weight;

4) Use acid catalysts in the al.coholysis transesterification of the polymer comprising 4-PAS or S-4-PAS to the polymer comprising 4-PHS or' S-~~-PHS, respectively; use of basic catalysts can cause the formation of quinones and other chemical structi_z:res which absorb over the 240-260 nm wavelength range, and can also absorb over the near UV and visible wavelengths from about 310-800 nm.
4-PHS prepared using basic catalysts is typically opaque and brown in color.
It is also advisable to avoid monomer storage inhibitors which substantially absorb over the deep UV
wavelengths.
The composition of the polymers made by the process described above has empirically been determined to meet specific requirements which result:: iii thE: desired low optical density (absorbtivity of 250 or less) over the 240 to 260 nm wavelength. In particular, the polymer comprising 4-PHS (and/or S-4-PHS) contains less than about 2.5% by weight of residual 4-hydroxystyrene monomer (or derivative residues thereof). When the polymer contains as much as 2.5~ (or less than about 2.5%) by weight of such residual 4-hydroxystyrene monomer, then the amount of poly(4-acetoxystyrene) which remains in the polymer (due to less than 100°s transesterificat:ion) must be less than about 2.5%
by weight of the polymer. When the pcalymer contains less than 2.5% by weight of the residual 4-hydroxystyrene monomer (or derivative residues thereof), the amount of poly(4-acetoxystyrene) which remains in the polymer can be larger.
For example, when residual 4-hydroxyst~rrene monomer is less than about 0.7°s by weight of the flTC-~ I 1 YY
' , ' 1 polymer, the poly(4-acetoxystyrene) content must be less than about 13% by 2 weight of the polymer.
3 1~or purposes of clear expression of the concept of the present invention, 4 the language is simplified in portions of the following text by describing the invention in terms of the preparation of polymers comprising poly(4-6 hydroxystyrene). However, it is intended that polymers comprising substituted 7 poly(4-hydroxystyrene) be included as well. When it is necessary to ma3ce a 8 distinction, or when the language does not become too cumbersome, substituted 9 d-acetoxystyrene monomers are discussed specifically.
I0 The "single pot", simplified process of the present invention, can be 11 used for the preparation of polymers comprising of poly(4-hydroxystyrene) and 12 comprises the following steps:
13 a) reacting a mixture comprising 4-acetoxystyrene (monomer) and an initiator, 14 which itself, its decomposition products, and capped stxuctures which it produces, do not substantially absorb over the wavelengths ranging between 16 about 240-260 nm; or, using no more than about 3 mole % of an absorbing 17 initiator per mole of monomer, in an organic solvent reaction medium, to 18 produce a polymer comprising 4-acetoxystyrene; wherein, either as a result of 19 monomer conversion or due to removal of residual monomer after polymerization, residual monomer in the subsequent transesterification 21 reaction medium comprises no more than 10% by weight of the polymer .
22 comprising 4-acetoxystyrene which is produced; and .. ' 1 b) subsequently transesterifying the polymer comprising 4-acetoxystyrene to a 2 polymer comprising 4-hydroxystyrene in a transesterifieation reaction medium 3 comprising at least one equivalent of alcohol par equivalent of non-4 transesterified poly(4-acetoxystyrene), using an acid catalyst, wherein at least 85~o conversion of the poly(4-acetoxystyrene) to poly(4-hydroxystyrene) is 6 achieved.
? In the most preferred embodiment of the above-described invention, at 8 least the majority of the organic solvent reaction medium of step a) is a C,-C~
9 (straight or branched) alcohol. In addition, the step b) transesterification reaction medium is essentially the same reaction medium as that used in step a) or is a 11 funcrional equivalent thereof.
12 V6~hen monomers) other than 4-ASIvI andlor S-4-ASM ans used in 13 combination with these monomers in the above-described process, the other 14 monomer must have at least one vinyl group present and must not substantially I5 absorb radiation over wavelengths ranging from about 240 to about 260 nm.
16 'The simplified process of the present invention can be used for the 17 preparation of copolymers of 4-hydroxystyrene with substituted 4-hydroxystyrene, 18 wherein the preferred substituted 4-hydroxystyrene monomer is selected from the 19 group consisting of 4-hydroxystyrene substituted in the 3, S, or 3 and 5 positions with methyl or ethyl substituenes. The process steps for producing a copolymer 21 of 4-PI-IS with S-4-PI-iS comprise:
22 a) reacting a mixture comprising 4-acetoxystyrene monomer, substituted 4-23 acetoxystyrene monomer and an initiator, wherein said initiator end its ATe-oo 11 ~
-- ~~~~()9~
1 decomposition products alone, and capped structures which ii produces, do 2 not substantially absorb radiation over wavelengths ranging from about 240 to 3 about 260 nm; or, using no more than about 3 mole % of an absorbing 4 initiator per mole of monomer, in an organic solvent reaction medium to produce a copolymer of poly(4-acetoxystyrene) with substituted poly(4-6 acetoxystyrene), in a manner such that residual monomers present in the 7 reaction mediurrt during subsequent trnnsest~et~iCcation reaction steps) 8 comprises no more than 10% by weight of the copolymer formed during the 9 reaction; and b) subsequently transesterifying the copolymer of poly(4-acetoxystyrene) and 11 substituted poly(4-hydroxystyrene) to copolymers of poly(4-hydroxystyrene) 12 and substituted poly(4-hydroxystyrene), in a transesterification reaction 13 medium comprising at least one equivalent of alcohol per equivalent of non-14 transesteri~ted copolymer, using an acid catalyst to achieve transesteriFcation of at least 85%a of the poly(4-acetoxystyrene) and paly(d-hydroxystyrene).
16 In the most preferred embodiment of the above-described invention, at 1'~ least the majority of the organic solvent reaction medium of step a) is a C,-CS
1 g (straight or branched) alcohol. In addition, the step b) transesterig'tcation reaction 19 medium is essentially the same reaction medium as that used in step a) or is a functional equivalent thereof.
21 The following description applies to the embodiments of the invention 22 for which the process steps are disclosed above.

-- ~t~~~~~~~
1 The initiator used in step a) must not comprise a structure which 2 decomposes to an initiating free radical which alone or as a polymer capping 3 group substantially absorbs in the 240-260 nm wavelength range, when the 4 quantity of such initiator is more than about 3 mole % of the monomer. Such absorbing free radical initiators, which should be avoided at concentrations above 6 that described above, include those having aromatic components, for example 7 benzoyl peroxide, t-butylperoxybenzoate, and diet-butyl di-peroxyphthalate.
8 Exr~tmples of useful initiators which do not substantially absorb over the 9 nm wavelength'range include, but are not limited to, 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis{2-methylpropanenitrile, 2,2'-azobis(2-I1 methylbutaneniirile, 1,I'-azobis(cyclohexanecarbonitrile), t-butyl peroxypivalate, 12 t-amyl peroxypivalate, t-butyl peroxy-2-ethylhexanoate, diisononanoyl peroxide, 13 decanoyl peroxide, succinic acid peroxide, di(n-propyl) peroxydicnrbonate, di(sec-14 bueyl) peroxydicarbonate, di(2-ethyl-hexyl) peroxydicarbonate, t-butylperoxy-neodecanoate, 2,5-dimethyl-2,S-di(2 ethylhexanoylperoxy)hexane, t-amylperoxy_ 16 neodecanoate, t-butylperoxy-neodeconate, and combinations thereof. The most 17 preferred initiators include 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2,4-18 dimethylpentanenitrile, and t-butylperoxipivalate.
19 The useful initiator for step a) of the present invention should have a half life ranging from about O.S to about 10 hours at the temperature at which the 21 reaction is carried out. Typically the reaction temperatut~ is the reflux 22 temperature of the alcohol reaction medium. However, it is not necessary that the 23 reaction temperature be the alcohol reaction medium reflux temperature.
Reaction ATC-~11YY
1 vessel pressure can be used to adjust the reaction temperature. A preferred 2 initiator half life ranges from about 0.75 to about 5 hours at the reaction 3 temperature, with a most preferred initiator having a half life ranging from about 4 1 to about 2 hours.
An alcohol used in step a) as the reaction medium can be any of the 6 known alcohols which dissolve the monomer(s), preferably C, to Cs alcohols in 7 view of reaction rate considerations of step b), with C, to ~ and n-alcohols being 8 more preferred. The most preferred alcohols are methanol and ethanol, which 9 function well in the step b) iransesterification reaction, Methanol reacts faster i0 than ethanol in the transesterification reaction. Mixtures of alcohols with other 11 alcohols or with other organic solvents can be used as the step a) arid step b) 12 reaction medium. Methanol or ethanol can be added to or used as the reaction 13 medium in step b) to achieve transesterification.
14 It is an added benefit when the solvent used in step a} can function as a chain transfer agent, whereby the molecular weight of the polymer can be 16 controlled. The alcohols described above and in particular solvents such as THF
17 appear to function well as chain transfer agents.
18 To achieve at least 90% conversion of the monomers) in the 19 polymerization reacrion of step a) periodic or continuous addition of initiator during the reaction is required. Failure to convert the 4-ASM to 4-PAS (or 5-4-21 ASM to S-4-PAS) permits the formation of 4-hydroxystyrene (4-HSM) during 22 step b). The 4-FiSM or S-4-HSM can form quinones which highly absorb in the 23 240-260 nm wavelength: range. When a monomers) conversion of at least 90%

ATC-UU l l'YY
~~~ ~~~~
1 is not achieved, excess monomer must be removed prior to the transesterification 2 step. Such excess monomer can be removed using a decantation step or other 3 means so that residual monomer present is no more than 10% by weight of the 4 polymer produced. , The transesterification step b) is most preferably carried out in the b alcohol reaction medium of step a). However, at least one transesterefying 7 alcohol must be present in step b) or substituted for the reaction medium of step 8 a) after decantation. The preferred transesterifying alcohols include methanol and 9 ethanol when this reaction is carried out at the re;flux temperature of the reaction medium organic solvent at atmospltcric pressure (or at tito retlux tetntperuture 11 above atmospheric pressure). Other alcohols up to about C4 alcohols ran be used 12 to provide an acceptable transesterification reaction rate, at temperatures above 13 their atmospheric pressure reflex temperature.
14 It is important that the transesteriflcation of 4-PAS to 4-PHS (also 5-4-PAS to S-4-PHS, etc.) in step b) be at least 85% by weight, preferably 9S% by 16 weight, and most preferably 98% by weight, since residual PAS absorbs in the 17 240-260 nm wavelength range.
18 Typically steps a) and b) of the present invention will be followed by a 19 step c) in which the polymer comprising 4-PHS ~ndlor S-4-PHS which is produced in step b) is precipitated from the organic solvent reaction medium 21 using water. Other non-solvents for the polymer such as hexane can be used in 22 place of water for the precipitation. It is icnportant that the precipitation be 23 accomplished by adding the polymer/reaction medium mixture to water (or other IS

' ~ ~:~~45~1~3 1 non-solvent) which is in motion. Typically, at room temperature, the weight 2 amaunt of water should be in excess of the weighe amount of polymer/reaction 3 medium mixture by at least a factor of eight. .A,ddidon of water to the 4 polymer/reaction medium mixture causes formation of an agglomeration of polymer containing residual alcohol and alcohol acetate rather than the formation 6 of discreet particles.
7 The amount of polymer which comprises 4-Pd-1S and/or S-4-PHS in the 8 final, ~ansesterifacation reaction mixture typically ranges between about 10 wt%
9 to abort 30 wt%. The preferred weight % polymer range is between about 15%
and about 25%, since the particle size of the precipitated homopolymer or 11 copolymer is typically larger than about 25 microns when a concentration of I2 polymer of less than about 30% by weight is present in the final reaction mixture.
13 Residual acid catalyst from step b) can be removed by: 1) adding a 14 base to the reaction medium at the completion of the transesterification step b); 2) processing the polymer/reaction medium after completion of step b) through an 16 ion exchange resin, wherein the ion exchange resin contains a chemically bound 17 base; 3) adding a base to the water used in the precipitation step c); 4) water I8 washing the precipated polymer from step c) using a neutral pH water, or;
5) 19 water washing the precipitated polymer from step c) using a base-containing 2U water, preferably having a pH ranging from about 7.5 to about 1U.
21 The method or process of the present invention is particularly 22 economical when an alcohol functions as the reaction medium in steps a) and b), 23 since the alcohol can function as the chain transfer agent during polymerization of ATC-oo 11 ~r ~~~~~3~~
1 the d-ASbI and as the transesterification reactant used to form 4-F'HS. The initial 2 alcohol acetate formed during the transesteriftcation reaction also aids in the 3 dissolution of the 4-PAS, which helps to speed up the transesieriftcation reaction.

g The process of the present invention is shown in the rection sequence 6 swctttres depicted below for the production of homopolymers of PHS produced 7 in an alcohol reaction medium:
cx~~~x2 ( r:x-~tg 1 " ( cx-cx=y "
~ZC'e~h~1 PeC~a a A1C~3301 a.~.os.m-o~ys.~-~.' ~lc~~a~~
Tll~.'t~8t~s' ~ x~8~
g ~ ~t~p al ~ step b>
~~~-~$ ~-c-Cx3 ' ox II
o 9-~15~4 4-~1~' ' 4-Px:3 g Homopolytraers of S-d-PHS, wherein the substituent groups are methyl lIl or ethyl, or cogoiymers of 4-PHS and S-4-PHS can be produced in the same 11 manner.
1z '!~'Iten other monomers are used in combination with 4-ASM 0s S-4-13 ASM to produce copolymers or terpoiymers of 4-PHS or S-4-PHS, such 14 monomers are added to step a). Such monomers include compounds having at IS least one vinyl group present, which compounds do not substantially absorb in the 16 2~-260 nm wavelength range. Examples of monomers which do not 17 substantially absorb int:lude, but are not limited to:

CA 02045093 2002-07-29 A~'-0()lln' r iH3 CH==CH CHZ=C

Methylacrylate and Methylmethacrylate (~) (MMhr) 2 When copolymers of 4-PHS with S-4-PHS are prepared by the method 3 of the present invention, the preferred substatuent groups on the S-4-PHS
4 molecule are methyl and ethyl. The preferred substituent positions on the 4-hydroxystyrene molecule are the 3, 5, or 3 and 5 positions.
1 The most preferred method of the present invention, wherein 2 homopolymers of 4-PHS and S-4-PHS were produced, is described in 3 EXAMPLES 1 to S7 which follow. EXAMPLES 58-60 pertain to the method of 4 the invention wherein the reaction medium comprises a mixture of organic 5 solvents. ° The method of the present invention wherein a copolymer of 4-PHS
6 and methyl mechacrylate was produced is described in EXAMPLE 61.
7 EXAMPLE 62 is a comparative example in view of published related art.
8 EXAMPLES 1 to b2 were carried out as batch reactions in reactor 9 vesscis ranging fmm about 500 ml to 2,000 ml in volume. Each reaction vessel was a 4-neck flask outfitted with a chilled water reflux condenser, nitrogen purge 11 line (used to exclude oxygen from the reaction vessel), overhead stirrer/mixer, 12 and a temperature indicator (thermocouple).
13 A premix of an alcohol, an alternative organic solvent, or an alcohol/
14 co-organic solvent reaction medium, the 4-ASM, or S-4-ASM, or 4-ASM and methyl methacrylate and the initiator was prepared in a beaker and the premix -_ 1 was placed in the reaction vessel. The initial concentration of 4-ASM (or other 2 monomer(s)) in the reaction medium-monomer mixture typically ranged from 3 about 10% by weight to about SO% by weight. Preferably the relative amount of 4 4-ASM (or other monomer(s)) to reaction medium was greater than 30% by S weight and most preferably greater than 40% by weight. Conversion of 4-ASM
6 to 4-PAS appears to be reduced when the relative amount of 4-ASM to reaction 7 medium is reduced.
8 The mixer was started (typically mixing speed was about IO(? to 400 9 rpm). The premix was then nitrogen purged at aoom temperature for a time perm of about 5 to 10 minutes, 11 After the 5 to 10 minute time period, the temperature of the premix was 12 increased to the reflex temperature of the reaction medium using an electrically I3 heated jacket on the exterior of the flask reaction vessel.
14 The 4-ASM (or other monomer(s)) was permitted to polymerise for a time period equal to about one half Life of the initiator at the reflex temperature 1~ (at atmospheric pressure). The "half life" as used herein is the time required for 17 one half by weight of the initiator to thermally decompose to produce free I8 radicals (typically two free radicals per initiator molecule).
19 At the time about one half by weight of the initiator had decomposed, additional initiator (dissolved in a solvent such as the same alcohol as that 21 typically used as at least a portion of the reaction medium), was added to the 22 reaction vessel. The amount of additional initiator added ranged from about 10%
23 to about 90% of the amount of initiator in the premix.

A TC-OO l 1 YY

--- ~~~~~~3 1 The above procedure for adding initiator to progressing polymerization 2 was repeated as necessary to achieve at least 90% conversion of 4-ASM to 4-3 P.AS. Typically 4 to 8 additions of initiator were made during the 4 polymerization. One skilled in the art can use a continuous addition of initiator during polymerization to accomplish the at least 90%
conversion described above.

6 Applicants carried out a batch polymerization wherein there was no 7 initiator in the premix, but initiator was added continuously to the prernix during 8 the polymerization. The initiator was dissolved in the alcohol used for the 9 reaction medium. The amount of initiator added was Eased on the amount of initiator required for previous polymerizations but was reduced by about 30% in 11 view of anticipated,continuous free radical availability.
See Example 2~ of 12 TABLE 1.

13 The time period for the polymerization of 4-ASM to 4-PAS was that 14 sufficient to achieve at least 90% by weight conversion of the 4-ASM to 4-PAS.
Conversion was typically determined by capillary gaslliquid chromatography of 16 the reaction mixture, Typically reaction tunes ranged from about 4 hours to 17 about 9 hours.
18 The weight average molecular weight of 4-PAS produced by the above-19 described method ranged from about 6,500 to about 27,000.
The transesterification reaction was typically carried out in the Z1 polymerization reaction medium. However, whereas the polymerization of ~-22 ASM to 4-PAS can be carried out in a non-alcohol-comprising reaction medium, 23 the transesterification reaction requires the presence of an alcohol. The amount of ATC-!~11 YY
1 alcohol which must be present at any time during the transesterification reaction 2 is at least about one equivalent based on the amount of unreacted (non-3 transesterifted) 4-acetoxystyrene. Typically, at least about ten equivalents of 4 alcohol based on unreacted d-acetoxystyrene are used, since the transesteriftcation rate is improved by an increase in the number of equivalents of alcohol.
6 An example wherein the polymerization reaction medium (alcohol) was 7 decanted and replaced with clean alcohol prior to the transesterification is marked 8 with a # in the tables containing the Examples. The replacement alcohol in this 9 example was the same alcohol as that used doting the polymerization.
lteflux temperature of the reaction medium was typically maintained 11 during the transesterification reaction (at atmospheric pressure).
12 Trattsesterification was carried out using an acid catalyst, to cause the alcohol 13 present in the reaction medium to react with the 4-PAS, converting the ~-PAS to 14 4-PHS. The acid catalyst concentration typically ranged from about 100 to about 400 ppm based on the total weight of the reaction mixture. However, acid 16 catalyst concentrations ranging from about 5 ppm to about 10,000 ppm can be 17 used, with catalyst concentration preferably ranging from about 50 ppm to about 18 2,000 ppm, and most pti=ferably from about 100 ppm to about 500 ppm. The 19 acid was eypically dissolved in the same alcohol as that used for at least a portion of the reaction medium, to pr~uce an alcohol solution containing alt acid catalyst 2I concentration ranging from aboue O.S% by weight to 2.0% by weight acid based 22 on the total acid catalyst solueion. The acid catalyst solution was added to the 1 reaction vessel in a single addition. However, acid catalyst can be added during 2 the reaction, if desired.
3 Acids which were used as acid catalyst included hydrochloric acid, 4 phosphoric acid, nitric acid, sulfuric acid, methane suifonic acid, and toluene sulfonic acid. The particular acid used is not critical to the invention.
Preferred 6 acids were those which did not substantially react with the 4-PAS or the 4-PHS
7 formed from the 4-PAS. In the present embodiments, non-reacting acids included g hydrochloric acid and phosphoric acid. Hydrochloric acid was used in 9 EXAMPLES I-60 shown in TABLES 1 and 2, and in EXAMPLE 61.
1~ To drive the reaction eoward complete conversion of 4-PAS to 4-PHS, it I1 was necessary to maintain an excess of the alcohol present in the reaction 12 medium, or to remove alcohol acetate from the reaction medium as it is formed.
I3 Typically, an excess of alcohol was used, wherein the molar equivalents of IA alcohol to initial 4-ASM ranged from about 5 to about IS. In addition, alcohol acetate was periodically or continuously removed after the concentration of I6 alcohol acetate was such that the solubility of the 4-PAS resulted in a translucent 17 polymer/reaction medium mixture. The alcohol acetate was removed as an 18 aaeottrope with alcohol and other reactian medium co-solvents (if present), and 19 typically the combined amount by weight of the alcohol (or alcohol/co-organic solvent)/alcohol acetate removed was replaced with an equivalent amount by 2I weight of the alcohol.
22 The transesterificadon reaction was carried out at the reflux temperature 23 of the reaction mixture at atmospheric pressure (about 66°C for a methanol 1 reaction medium or about 78°C for an ethanol reaction medium). The time period 2 for reaction was that sufficient to provide at least 85% conversion of 4-PAS
to 4-3 PHS. Conversion was measured by Fousier-Transform Infrared Spectroscopy 4 (FTTR), quantitating the acetate carbonyl peak at about 1700 cm', on precipitated, washed and dried polymer. Reaction tame periods ranged from about 2 hours to 6 about 1G hours depending on the alcohol used for transesteriftcation 7 (predominantly methanol). The required reaction time period can be decreased by 8 increasing the reaction temperature, by increasing the acid catalyst concentration 9 and or by more rapid removal of alcohol acetate as it is formed.

~.~ "_~~°g~ ~ zZZZ~x~~~r~~~~ps-~~;=ga~~e$_ 3~~~~e~e.~~ o00 ocio~Booooooo0ooco ~~~~~tt<tattt <t r~~0.~cG'~'~~ZZZZ~z~~~zZ~osovv~~aaoooo~,~°,~vf~a~
3 ~' H A V A A A Y V V V V V A 'r V
H
~~<~i~~~~~~~~~~~~~~~~~~~g~~~~~~~~~
w~~o rov,..:~~~'~~.~..°~~~~~ ~a : i3oee~i'..:oo ~'v ei ~ ~ 3 D

s "' ~~:x~~~~~~~~~~~a~~os~m~~

m m N
t V

. ~. t H

~ p y . y ~ . y n H ;
1 ~
~
.
~
' C, e z p ~~ ~ ~~, ~ .1 ofe ~a , ].
w B
~ Z
D
W HOt~ ~.~ Va~ Ven1 V1 VD
0 !~a ~ Wf~ i~
.
~~~~o~oO~~a~~~.~.~~~~~

s ~ a~
~~i J
O

~~ '~1 h h "T '% R
OOOOO~~O., ~1 ~ fir l'~ 0~ ,., ~! ~ l~1 c~
'' n.. _R
..Moo~ddd »~~:oWn.s.o.y~r~osen a ~v~ Y~ ya Ry$
T~ C v~ .r ~ N Vl f v1 h .O N N H N N N N N f ~ ~ ~ ~ ~ V (d Ti f ,8 ~
yp '~ zzzzz zzz z z z z ~ '~
~mmmmm~~'~'~'~~~mm~ m~ m m :~'aaa'ta~'a~~3Jaa~~aaaa~aa~~t~a ~~
~.~ N M f v1 ~0 1~ CD fA ~ .~" "N~ ,~" . .~. . a .H.. ~ ~ N ~ ~ ~ ~ ~ ~ ~ g A~-(X111 YY
'-000 0 00000000 zozzz~ o ~R~~y~~~o~ooor°i,.N.aoaWO.'~~~oRwA~aa,.'~,ooc~oan=
3~y.p'~"'v vvv" vvvv-' vvn vvv vvvvvvv _< ~~~~~<~~~~~~~~~~g~~~~~s~~~~~s~~
°~'' .a..°..°'°z ..ooao ;
wn"~,e~ogpoo0oo~.°.e'ne~-.a' v~3" "' ...
r ~v~nBn~RSi~f',p'.R:o'~~n n~i~ ~o ~ii:,:~"d~8'r~n~i roI'in' '~
.-..o ...ro..~..... .~. ..a...,..,..~.vro~..~
S

s '~
<

i s QV
O
O
av f' !
oyn ~0 a H
P
e~
Y, M
a ro <
P, ~n en O
f~

<
<

~~~~~0~~a~a~n~~~P~.~.~~:~~~.~.P~~~zz~:
a .~~8 ~~< ~~~nh~~~ H~~~~~n~n~nnnH~n o~l~n~

~

0 00 0 0. 00a O
O

~g ~! ~1 Q~d~GG1ti00(~C~~11~IO, ~t~O,O~G~CO,O~~dG00(~O, RaKi r h ~ I~n~, P r n h r P n n r ~
fH~. H i~ ~ h Q
O CI Cj O O i~ C3 A 0 0 Y.1 OO O
0 1~ C~ C

~ , ~~"h n1 ~v'1h '~vlvlM v1 'i1'~hh~'~wl~C$~
vj~ ro O QO QmMawON M

'.OO~aOCJOOrt~ OOOT~

'~~y y.ia~.0ia~~vR,~cH6.rTrvc~e~e~e~w~i~.'~lr~c~a~e~e~e~~e~vvve~e~e~ '~A~.
~

F.

~~w~~neMWn~~,~~~vvv~v~i~v~~n~~n~h~~~

ATC-~1 lYY
1 ~To further illustrate the method of the present invention in a m~~ er~~'~
2 which assists one skilled in the art in reproducing the E3CAMPLES contained in 3 TABLES 1 and 2, EXAMPLES 24 and 28 are described below in more specific 4 detaal.
Examale 24 6 To a 500 ml glass round-bottom flask reactor fatted with a chilled water 7 reflex condenser, a thermowell with thermocouple, a nitrogen puxge fitting, an 8 overhead stirrer, and an external heating mantle, a reaction mixture of 80 grams 9 of 4-acetoxystyrene (4-ASM), 120 grams of methanol and 2.0 grams of 2,2'-azobis(2,4-dimethylpentanenitrile) initiator was added. The reaction mixture was 11 stirred for 5 minutes under nitrogen purge to remove oxygen gas pavsent in the 12 reactor. The reaction mixture was then raised to about 66°C, the reflex 13 temperaeure of traethanol. After ona hour of polymerization, 0.4 grfams of 2,2'-14 azobis(2,4-dimethylpentanenitrile) dissolved in about 10 grams of methanol was added. At each hour, for the next 7 hours, 0.4 grams of 2,2'-azobis(2,4-16 dimethylpentanenitrile) in 10 grams of methanol was added. After each addition, 17 a sample of dae polymer mixture was withdrawn from the reactor. Analysis of 18 the fmai polymer mixture sample by capillary gas chromatography showed 94.8%
19 by weight conversion of the 4-acetoxystyrene to paly(4-acetoxystyrene). The transesterification reaction was begun without cooling the reaction ravxture;
0.2 21 grams of 37% hydrochloric acid in water was combined with about 10 grams of 22 methanol and the combination was added to the inaction mixture. The reaction 23 mixture was permitted to react until the color of the mixture turned from white to .. ~ r ~~~~t)~~3 1 clear, at which time 150 grams methyl acetate/methanol was removed as a 2 distillate and 150 grams of fresh methanol was added. The transesterification was 3 allowed to proceed for about 4.5 hours, at which time the clear reaction mixture 4 was cooled, precipitated in deionized water, the precipitant was isolated by filtration, the acid was washed from the precipitant (essentially poly(4-6 hydroxystyrene) with deionized water, and the poly(4-hydraxystyrene) was dried 7 in a vacuum oven at about 70°C until less than 2 wt~'~ water remained in the 8 poly(4-hydroxystyrene). An F~TIR analysis of the poly(4-hydroxystyrene) showed 9 Less than 0.5 wt%n 4-acetoxystyrene grougs remained in the poly(4-hydroxystyrene) as determined by quantitating the absorbance of the carbonyl 11 peak at about 1760 ctrl', the acetoxy carbonyl absorbance. A UV-VIS scan I2 showed a molar absorbtivity of 144 1 ctrl t mole' at 248 nm. The product was 13 visually very whiee.
14 Examyle 2,8 To a 2000 ml glass round-bottom flask reactor fitted with a chilled 16 water reflux condenser, a thermowell with thermocouple, a nitrogen purge f;tting, 17 an overhead stirrer, and an external heating mantel, a reaction mixture of 18 grams of 3-methyl-4-acetoxystyrene (3-M-4-ASll~i), 800 grams of absolute 19 ethanol, and 8.0 grams of 2,2'-azobis(2-methylpropanenitrile) initiator was added.
The reaction mixture was stirred for five minutes under nitrogen pwge to remove 21 oxygen gas present in the reactor. The reaction mixture was then raised to about 22 78°C, the reflex temperature of ethanol. After two hours of polymerization, 2.0 23 grams of 2,2'-azabis(2-methylpropanenitrile) dissolved in about 20 grams of :. ° ~ ~ ~~3~~IC~~~
1 ethanol was added to the reaction mixture. Every two hours, for the next four 2 hours, 2.0 grams of 2,2'-azobis(2-methylpropanenitrile) in about 20 grams of 3 ethanol was added. Analysis of the final polymer mixture sample, two hours 4 after the last initiator addition, by capillary gas chromatography showed 97.6% by weight conversion of the 3-methyl-4-acetoxystyrene, to poly(3-methyl-4-6 acetoxystyrene).
? The transesterification reaction was begun without cooling the reaction 8 mixture; 1.0 gram of 37% hydrochloric acid in water was combined with about 9 20 grams of ethanol and the combination was added to the reaction mixture.
The reaction mixture was permitted to react until the color of the mixture tamed from 11 white to clear, at which time about 250 grams of ethyl acetate%thanol was I2 removed as a distillate and about 250 grams of fresh ethanol was added. The 13 transesterification was allowed to proceed for 7 hours at which time the clear 14 reaction mixttu~ was cooled, precipitated in deioniaed water, the precipitant was isolated by filtration, the acid was washed from the precipitant (essentially poiy(3-16 methyl-4-hydroxystyrene) with deionized water, and the poly(3-methyl-4-17 hydroxystyrene) was dried in a vacuum oven at about 70°C until less than 2 wt%
I8 water remained in the poly(3-methyl-~4-hydsoxystyrene). An 1~'ITR analysis of the 19 poly(3-methyl-Q-hydroxystyrene) showed less than 2.0 wt% (3-meehyi-4-acetoxystyrene) groups remaining in the poly(3-methyl-4-hydroxystyrene) as 21 determined by quantitating the absorbance at about 1760 cni', the acetoxy 22 carbonyl absorbance. A UV-YIS scan showed a molar absorbtivity of 163 1 ctai' 23 mole ~ at 248 nm. The product was visually white.

1 The method of the present invention wherein copolymers comprising 2 PHS were produced is described in EXAMPLE 61 which follows.
3 EXAMPLE 61 was carried out using the same reaction conditions and 4 using the same reactants as those described for production of homopotymers of 4-Pl-15 except that the comonomer was added to the premix comprising ASM. A
6 specifically detailed description of EXAMPLE 6I follows. .
7 Example 61 8 A copolymer of 4-acetoxystyrene and methyl methacrylate was prepared 9 and transesterifted to a poly(4-hydroxystyrene-methyl methacrylate) copolymer using the following method.
11 To a S00 ml glass round-bottom flask reactor fitted with a chilled water 12 reflux condenser, a thermowell with thermocouple, a nitrogen purge fitting, an 13 overhead stirrer, and an external heating mantel, a reaction mixture of 62.5 grams 14 of 4-acetoxystyrene (4-ASM), 62.5 grams of methylmethacrylate, 125 grams of methanol, and 1.5 grams of 2,2'-azobis(2,4-dimethylpentanenitrile) initiator was 16 added.. The reaction mixtut~ was stirred for five minutes under nitrogen purge to 17 remove oxygen gas present in the reactor. The reaction mixture was then raised 18 to about 64°C, the reflex temperature of the mixture. After one hour of 19 polymerization, 0.3 grams of 2,2°-azobis(2,4-dimethylpentanenitrile) dissolved in about 10 grams of methanol was added eo the reaction mixture. Two hours after 21 the start of the polymerization, 0.5 grams of 2,2°-azobis(2,4- ' 22 dimetttylpentanenitrile) in about 10 grams of methanol was added to the reaction 23 mixture. Three hears after the start of the polymerization, 0.65 grams of 2,2'-t I

~t~T~~~
1 aaobis(2,4-dimethylpentanenitrile) was added to the reaction nuxture. Pour hours 2 after the start of the polymerisation, 0.8 grams of 2,2'-azobis(2,4-3 dimethylgentanenitrile) was added to the reaction mixture. Analysis of the final 4 polymer mixture sample, two hours after the last initiator addition, by capillary gas chromatography showed 98.3% by weight conversion of the 4-acetoxystyrene 6 and methylmethacrylate to poly(4-acetoxystyrene-co-methylmethacrylate). The ? transesterification reaction was begun without cooling the reaction mixture;
0.3 8 grams of 3?% hydrochloric acid in water was combined with about 10 grams of 9 methanol and the combination was added to the reaction mixture. The reaction mixture was permitted to react until the color of the mixture turned from white to I 1 clear, at which time about 150 grams of methyl acetate/methanol was removed as I2 a distillate and about 150 grams of fresh methanol was added. The 13 transesterification was allowed eo proceed for 4 hours at which dme the clear I4 reaction mixture was cooled, precipitated in deionized water, the precipitant was isolated by filtration, the acid was washed from the precipitant (essentially poly(4-I6 hydroxystyrene-co-methylmethacrylate) with deionized water, and the poly(4-1? hydroxystyrene-co-methylmethacrylate) (4-PHS/MI~IA). The 4-PHS/MMA was 18 dried in a vacuum oven at about ?0°C until less tiaan 2 wt% water remained in 19 the 4-PHS/1VIMA. An analysis of flee 4-PHS/Ivl~A showed less than 2.0 wt% (4-acetoxystyrene) groups remaining in the 4-PHSIIVI~IA. The weight 21 average molecular weight of the 4-PHS/IvIP~IA was about 22,000 by GPC. A UV-22 V1S scan showed a malar absorbdvity of 48 1 cari' mole' at 248 rm. The 23 product was visually white.

7?484-1 Example 62 - Comparative Example 2 The purpose of this Example is to demonstrate that the simultaneous 3 polymerization and hydrolysis method of producing poly(4-hydroxystyrene) 4' described by Elmore, European Patent Publication No. EP 0 260 104, even if carried out using an acid catalyzed methanolysis as disclosed by Gupta, U.S.
6 Patent No. 4,898,916, provides a reaction product which does not have the low 7 optical density (absorbance over a 240-260 nm wavelength) characteristics of the 8 product produced by the method of the present invention.
9 A 500 ml glass round-bottom flask reactor fitted with a chilled water reflux condenser, a thermowell with thermocouple, a nitrogen purge fitting, an 11 overhead stirrer, and an external heating mantle, was charged with 100 gm of 12 methanol (MeOH) and 2.7 gm of 379'o HCl (0.5°70 by weight HCl based on the 13 MeOH and the 4-ASM to be added subsequently). Separately 100 gm of 4-14 acetoxystyrene (4-ASM), 2,2'-azobis(2-methylpropanenitrile) were mixed and kept cold in an ice bath. The methanol/HCl mixture was stirred for about 5 16 minutes under a nitrogen purge to remove gases other than nitrogen from the 17 reactor. The temperature of the methanol/HCl mixture was then raised to about 18 66°C, the reflux temperature of methanol at atmospheric pressure.
The 4-19 ASMlnitiator mixture was periodically added to the flask reactor over a 3 hour period 110 gm of methylacetate/methanol was removed during the reaction.
21 Upon the initial addition of 4-ASM/initator solution, the temperature of the 22 reactants in the flask reactor dropped to 61.4°C, indicating the production of i~ ~~ ~~~a~
1 methyl acetate. As methyl acetate was removed, and fresh methanol added, the 2 temperature climbed to 64.5°C toward the end of the reaction.
3 Analysis of the final polymer mixture sample by capillary gas 4 chomatography showed a 99% by weight conversion of the 4-acetoxystyrene.
After completion of the simultaneous polymerization-hydrolysis 6 reaction, the reaction mixture was cooled, and precipitated in deionized water, the 7 precipitate was isolated by filtration, residual acid was washed from the 8 precipitant using deionized water, and the reaction product was dried in a vacuum 9 oven at about 70°C until less than 2 weight % vvater remained in the reaction product.
11 An FI'Ilt analysis of the precipitant portion of the reaction product 12 showed the precipitant to comprise PHS, wherein less than about 1.7 wt% 4-13 acetoxystyrene groups remained in the PHS. 'fhe weight average molecular 14 weight (lMiw) of this PHS portion of the reaction product was about 2,000.
This reaction method does not permit the isolation of PHS. This reaction method also 16 did not permit control of the Mw of the reaction product. The lVdw of the PHS
17 could not be controlled, in part because hydroxystyrene monomer (HSM) was 18 formed and polymerized not only via free radical means, but possibly by cationic 19 means.
The molar absorbtivity, ~, of the PHS portion of the reaction product at 21 UV~,~ measured 868 (far greater than the 250 or less desired for the product 22 produced by the method of the present invention). This high E is apparently due 1 to the formation of quinones or other highly absorbing species due to the 2 simultaneous polymerization and hydrolysis reaction technique.
3 Pertaining to the method of the present invention, the homopolymers 4 and copolymers comprising 4-PHS (and S-4-PHS) were isolated from the final, transesterification reaction medium by precipitation. The preferred precipitation 6 medium is water although organic solvents, such as heptane, hexane, and 7 cyclohexane, in which the PHS homopolymers and copolymers thereof are 8 sufficiently insoluble can be used.
9 When water was used as the precipitation medium, the polymer/reaction medium mixture was added to water which water was in motion. Typically, ut 11 room temperature, the weight amount of water was in excess of the weight 12 amount of polymer/reaction medium mixture by at Ieast a factor of eight.
The 13 preferred alcohol reaction medium is methanol for a water precipitation, since the 14 PHS polymer or copolymer thereof precipitates at a particle size larger than about 5U microns. Use of higher molecular weight alcohol reaction mediums appears to 16 cause the precipitated particle size of the PHS homopolymer (or copolymer 17 thereofy to be smaller than.about 50 microns. Larger particle size is easier to 18 filter.
19 Although the present invention is described in terms of polymers of 4-hydroxyseyrene and/or substituted 4-hydroxystyrene, further functionalization of 21 these polymers which provides enhanced performance in particular optical 22 applications is considered to fall within the scope of the present invention. For 23 example, when these polymers are to be used as polymeric components in 77484-~2 photoresists, it is known to be desirable to replace the hydroxy group at the 4 position of the compound structure with a t-butoxycarbonyl group, or at least a portion of said hydroxy groups in a sample. The presence of this t-butoxycarbonyl group on the polymer improves the sensitivity of polymer to imaging radiation striking the photoresist.
It is also known to replace the hydroxy group with a t-butoxy group, also for use irx photoresist applications. The present invention provides polymeric compounds (and a method for their preparation) which meet the optical (radiation absorption) requirements necessary to function as a deep UV, X-ray, or E-Beam photoresist material. Further functionalization of this basic polymeric material, which does not detrimentally affect the overall performance of the polymer in the intended application, is irutended to fall within the scope of the present invention.
While specific reaction conditions, reactants, and equipment are described above to enable ome skilled in the art to practice the invention, one sk:i.lled in the art will be able to make modifications and adjozstments which are obvious extensions of the present inventions. Such obvious extensions of or equivalents to the present invention are intended to be within the scope of the present invention, as demonstrated by the claims which follow.

Claims (55)

1. A process for preparation of polymers having low optical density at 240-260 nm, comprising poly(4-hydroxystyrene) or methyl or ethyl substituted poly(4-hydroxystyrene) or both, said process comprising the steps of:
a) reacting a mixture comprising 4-acetoxystyrene monomer or methyl or ethyl substituted 4-acetoxystyrene monomer or both and an initiator, wherein said initiator and its decomposition products alone or as polymer capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer, in a reaction medium comprising at least one organic solvent, to produce a polymer comprising poly(4-acetoxystyrene) or methyl or ethyl substituted poly(4-acetoxystyrene) or both, whereby, either as a result of monomer conversion, or due to removal of residual monomer, wt % or less residual monomer, based on the weight of polymer produced, is present. in the reaction mixture used during a subsequent transesterification reaction step; and b) subsequently transesterifying said poly(4-acetoxystyrene) to poly(4-hydroxystyrene) or transesterifying said methyl or ethyl substituted poly(4-acetoxystyrene) to methyl or ethyl substituted poly(4-hydroxystyrene) or transesterifying both, in a transesterification reaction medium comprising at least one equivalent of alcohol per equivalent of non-transesterified poly(4-acetoxystyrene) or methyl or ethyl substituted poly(4-acetoxystyrene), using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification, wherein at least 85% by weight conversion of said poly(4-acetoxystyrene) to said poly(4-hydroxystyrene) or conversion of said methyl or ethyl substituted poly(4-acetoxystyrene) to said methyl or ethyl substituted poly(4-hydroxystyrene) or at least 85% by weight transesterification of both is obtained.

2. The process of claim 1, wherein a C1-C5 alcohol comprises at least the majority of said reaction medium of step a).

3. The process of claim 2, wherein said transesterification reaction medium of step b) is essentially the same reaction medium as that used in step a) or is a functional equivalent thereof.

4. The process of claim 1, claim 2, or claim 3, including an additional step:
c) isolation of said polymer comprising poly(4-hydroxystyrene), or said polymer comprising methyl or ethyl substituted poly(4-hydroxystyrene), or a polymer comprising both from said transesterification reaction medium.

5. The process of claim 1, claim 2, or claim 3, wherein said reacting mixture comprises methyl or ethyl substituted 4-acetoxystyrene monomer, and wherein the substitution is on the ring structure of said 4-acetoxystyrene at the 3, or 5, or 3 and 5 positions.

6. The process of claim 1, claim 2, or claim 3, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide, decanoyl peroxide, succinic acid peroxide, di(n-propyl) peroxydicarbonate, di(secbutyl) peroxydicarbonate, di(2-ethyl-hexyl) peroxydicarbonate, t-butylperoxyneodecanoate 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, t-amylperoxy-neodecanoate, t-butylperoxy-neodecanoate, and combinations thereof.

7. The process of claim 1, 2 or 3, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxypivalate, t-amyl peroxypivalate, and combinations thereof.

8. The process of claim 1, claim 2, or claim 3, wherein said initiator is selected from the group consisting of benzoyl peroxide, t-butylperoxybenzoate, and di-t-butyl diperoxyphthalate, and wherein the mole % of said initiator is less than about 3 mole % of said monomer.

9. The process of claim 2 or claim 3, wherein said alcohol reaction medium is selected from alcohols having 1 to 2 carbon atoms and combinations thereof.

10. The process of claim 1, claim 2, or claim 3, wherein said acid catalyst will not substantially react with said poly(4-acetoxystyrene), said methyl or ethyl substituted poly(4-acetoxystyrene) or with said poly(4-hydroxystyrene) or said substituted poly(4-hydroxystyrene) formed therefrom.

11. The process of claim 10, wherein said acid catalyst is selected from the group consisting of hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid, methane sulfonic acid, and toluene sulfonic acid.

12. The process of claim 1, claim 2, or claim 3, wherein said initiator is added periodically or continuously during step a), whereby at least 90% by weight conversion of said 4-acetoxystyrene monomer or said substituted 4-acetoxystyrene monomer is achieved.

13. The process of claim 1, claim 2, or claim 3, wherein said initiator exhibits a half life ranging from about 0.5 hours to about 10 hours at the temperature at which said reaction is carried out.

14. The process of claim 12, wherein said initiator exhibits a half life ranging from about 0.5 hours to about hours at the temperature at which said reaction is carried out.

15. The process of claim 2 or claim 3, wherein said alcohol reaction medium is selected from alcohols having from 3 to 5 carbon atoms and wherein an additional alcohol is added during step b) and wherein said additional alcohol is selected from alcohols having 1 to 2 carbon atoms or combination thereof.

16. The process of claim 4, wherein said step c) isolation is accomplished by precipitation of said poly(4-hydroxystyrene) or said methyl or ethyl substituted poly(4-hydroxystyrene) from said reaction medium.

17. The process of claim 16, wherein said precipitation is accomplished by adding the reaction mixture of step b) to water which is in motion.

18. The process of claim 17, wherein the precipitate of said poly(4-hydroxystyrene) or said methyl or ethyl substituted poly(4-hydroxystyrene) is treated to remove residual acid.

19. The process of claim 1, claim 2, or claim 3, wherein the amount of said poly(4-hydroxystyrene) or said methyl or ethyl substituted poly(4-hydroxystyrene) or both in said reaction mixture ranges from about 10% to about 30%
by weight.

20. A process for preparation of polymers having low optical density at 240-260 nm, comprising poly(4-hydroxystyrene) or methyl or ethyl substituted poly(4-hydroxystyrene) or both, said process comprising the steps of a) reacting a mixture comprising 4-acetoxystyrene monomer or methyl or ethyl substituted 4-acetoxystyrene monomer or both and a comonomer having at least one vinyl group present, wherein said comonomer does not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm; and an initiator, wherein said initiator and its decomposition products alone or as capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer; in a reaction medium comprising at least one organic solvent, to produce a copolymer of poly(4-acetoxystyrene) or said methyl or ethyl substituted poly(4-acetoxystyrene) with said comonomer, whereby, either as a result of monomer conversion or due to removal of residual monomer, 10 wt % or less residual monomer, based on the weight of polymer produced, is present in the reaction mixture during a subsequent, transesterification reaction step; and b) subsequently transesterifying said poly(4-acetoxystyrene) to poly(4-hydroxystyrene) or transesterifying said methyl or ethyl substituted poly(4-hydroxystyrene) to methyl or ethyl substituted poly(4-hydroxystyrene) or transesterifying both to a conversion of at least 85% by weight, in a transesterification reaction medium comprising at least one equivalent of alcohol per equivalent of non-transesterified copolymer, using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification.

21. The process of claim 20, including an additional step:
c) isolation of said polymer comprising poly(4-hydroxystyrene) or said methyl or ethyl substituted poly(4-hydroxystyrene) or both from said reaction medium.

22. The process of claim 20 or claim 21, wherein said reacting mixture comprises methyl or ethyl substituted 4-acetoxystyrene monomer, and wherein the substitution is on the ring structure of said 4-acetoxystyrene at the 3, 5, or 3 and 5 positions.

23. The process of claim 20 or claim 21, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide, decanoyl peroxide, succinic acid peroxide, di(n-propyl) peroxydicarbonate, di(secbutyl) peroxydicarbonate, di(2-ethyl-hexyl) peroxydicarbonate, t-butylperoxyneodecanoate 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, t-amylperoxy-neodecanoate, t-butylperoxy-neodecanoate, and combinations thereof.

24. The process of claim 20 or 21, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxypivalate, t-amyl peroxypivalate, and combinations thereof.

25. The process of claim 20 or claim 21, wherein said initiator is selected from the group comprising benzoylperoxide, t-butylperoxybenzoate, and di-t-butyl diperoxyphthalate, and wherein the mole % of said initiator is less than about 3 mole % of said monomer.

26. The process of claim 20 or claim 21, wherein said reaction medium of step a) is an alcohol reaction medium selected from alcohols having 1 to 5 carbon atoms and combinations thereof.

27. The process of claim 26, wherein said transesterification reaction medium of step b) is essentially the same reaction medium as that used in step a) or is a functional equivalent thereof.

28. The process of claim 27, wherein said alcohol reaction medium is selected from methanol and ethanol and combinations thereof.

29. The process of claim 20 or claim 21, wherein said acid catalyst will not substantially react with said poly(4-acetoxystyrene) or said methyl or ethyl substituted poly(4-acetoxystyrene), the polymer of said comonomer, said poly(4-hydroxystyrene) or said methyl or ethyl substituted poly(4-hydroxystyrene) or any transesterified form of said comonomer.

30. The process of claim 20 or claim 21, wherein said initiator is added periodically or continuously during step a), whereby at least 90% by weight conversion is obtained for the combination of said 4-acetoxystyrene monomer or said methyl or ethyl substituted 4-acetoxystyrene monomer and said comonomer.

31. The process of claim 26, wherein said alcohol reaction medium is selected from alcohols having from 3 to 5 carbon atoms, wherein an additional alcohol is added during step b) and wherein said additional alcohol is selected from alcohols having 1 to 2 carbon atoms or combinations thereof.

32. The process of claim 21, wherein said step c) isolation is accomplished by precipitation of said polymer comprising poly(4-hydroxystyrene) or methyl or ethyl substituted poly(4-hydroxystyrene) or both from said reaction medium.

33. The process of claim 32, wherein the precipitate of said polymer is treated to remove residual acid.

34. The process of claim 1, claim 2, or claim 3, wherein said 4-acetoxystyrene monomer or said methyl or ethyl substituted 4-acetoxystyrene monomer or both of step a) contains no inhibitor which substantially absorbs radiation over wavelengths ranging from about 240 to about 260 nm.

35. The process of claim 20 or claim 21, wherein said 4-acetoxystyrene monomer or said methyl or ethyl substituted 4-acetoxystyrene monomer or both and said comonomer of step a) contain no inhibitor which substantially absorbs radiation over wavelengths ranging from about 240 to about 260 nm.

36. A process for preparation of low optical density copolymers of poly(4-hydroxystyrene) with methyl or ethyl substituted poly(4-hydroxystyrene), said process comprising the steps of:

a) reacting a mixture comprising 4-acetoxystyrene monomer, methyl or ethyl substituted 4-acetoxystyrene monomer and an initiator, wherein said initiator and its decomposition products alone or as polymer capping groups do not substantially absorb radiation over wavelengths ranging from about 240 to about 260 nm, or wherein said initiator is present at a concentration of less than about 3 mole % of said monomer, in a reaction medium comprising at least one alcohol to produce a copolymer of poly(4-acetoxystyrene) with methyl or ethyl substituted poly(4-acetoxystyrene), wherein at least 90% by weight conversion of said 4-acetoxystyrene monomer and said methyl or ethyl substituted 4-acetoxystyrene monomer combined is obtained; and b) subsequently transesterifying said poly(4-acetoxystyrene) and said methyl or ethyl substituted poly(4-acetoxystyrene) to poly(4-hydroxystyrene) and methyl or ethyl substituted poly(4-hydroxystyrene), in substantially said reaction medium of step a), using approximately 5-2000 ppm of an acid catalyst to achieve said transesterification, wherein at least 85% by weight conversion of the combination of said poly(4-acetoxystyrene) to said poly(4-hydroxystyrene) and said methyl or ethyl substituted poly(4-acetoxystyrene) to said methyl or ethyl substituted poly(4-hydroxystyrene) is obtained.

37. The process of claim 36, including an additional step:

c) isolation of said copolymer from said reaction medium.

38. The process of claim 36 or claim 37, wherein said methyl or ethyl substituted 4-acetoxystyrene monomer is substituted on the ring structure at the 3, or 5, or 3 and 5 positions.

39. The process of claim 36 or claim 37, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide, decanoyl peroxide, succinic acid peroxide, di(n-propyl) peroxydicarbonate, di(sec-butyl) peroxydicarbonate, di(2-ethyl-hexyl) peroxydicarbonate, t-butylperoxyneodecanoate 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, t-amylperoxy-neodecanoate, t-butylperoxy-neodecanoate, and combinations thereof.

40. The process of claim 36 or 37, wherein said initiator is selected from the group consisting of 2,2'-azobis(2,4-dimethylpentanenitrile), 2,2'-azobis(2-methylpropanenitrile), 2,2'-azobis(2-methylbutanenitrile), 1,1'-azobis(cyclohexanecarbonitrile), t-butyl peroxypivalate, t-amyl peroxypivalate, and combinations thereof.

41. The process of claim 36 or claim 37, wherein said initiator is selected from the group consisting of benzoylperoxide, t-butyl-peroxybenzoate, and di-t-butyl diperoxyphthalate, and wherein the mole % of said initiator is less than about 3 mole % of said monomer.

42. The process of claim 36 or claim 37, wherein said alcohol reaction medium is selected from alcohols having 1 to 5 carbon atoms and combinations thereof.

43. The process of claim 36 or claim 37, wherein said initiator is added periodically or continuously during step a) whereby at least 90 by weight conversion is obtained of said 4-acetoxystyrene monomer and said methyl or ethyl substituted 4-acetoxystyrene monomer combined.

44. The process of claim 37, wherein said step c) isolation is accomplished by the precipitation of said copolymer from said reaction medium.

45. The process of claim 44, wherein the precipitate of said copolymer is treated to remove residual acid.

46. The process of claim 36, wherein said 4-acetoxystyrene monomer and said methyl or ethyl substituted 4-acetoxystyrene monomer of step a) contain no inhibitor which substantially absorbs radiation over wavelengths ranging from about 240 to 260 nm.

47. The process of claim 1, claim 20, or claim 36, wherein said step a) conversion of monomer to polymer is less than 90% by weight, but wherein said reaction medium of step a) is substantially decanted from said polymer and replaced with fresh, clean alcohol reaction medium prior to said step b) transesterification.

48. The process of claim 47, wherein C1-C5 alcohol comprises at least the majority of said reaction on medium of step a) and wherein said replacement alcohol reaction medium is essentially the alcohol reaction medium as that used in step a) or a functional equivalent thereof.

49. The process of claim 47, wherein said fresh, clean alcohol reaction medium is a substantially different kind of alcohol reaction medium from that used in step a).

50. The process of claim 47, wherein said replacement alcohol reaction medium comprises at least one alcohol selected from alcohols having from 1 to 5 carbon atoms.

51. A polymer comprising 4-hydroxystyrene having a molar absorbtivity of about 211 or less, at a wavelength of about 250 nm, and a weight average molecular weight M w less than about 22,000 as measured by gel permeation chromatography using polystyrene standards, wherein said polymer contains less than about 2.5% by weight of residual 4-hydroxystyrene monomer or derivative residues thereof.

52. The polymer of claim 51, wherein said polymer comprises less than about 2.5% by weight of poly(4-acetoxystyrene).

53. A polymer comprising 4-hydroxystyrene having a molar absorbtivity of about 211 or less, at a wavelength of about 250 nm, and a weight average molecular weight M w less than about 22,000 as measured by gel permeation chromatograhy using polystyrene standards, wherein said polymer contains less than about 0.7% by weight of 4-hydroxystyrene monomer or derivative residues thereof, and comprises less than about 13% by weight poly(4-acetoxystyrene).

54. The polymer of any one of claims 51 to 53, wherein said polymer has been further functionalized by replacing at least a portion of the hydroxy functional groups with t-butylcarbonyloxy functional groups.

55. The polymer of any one of claims 51 to 53, wherein said polymer has been further functionalized by replacing at least a portion of the hydroxy functional groups with t-butoxy functional groups.