GB1584009A

GB1584009A - Radiation-sensitive copolymer

Info

Publication number: GB1584009A
Application number: GB3242977A
Authority: GB
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1976-08-02
Filing date: 1977-08-02
Publication date: 1981-02-04
Also published as: JPS5317688A; FR2360611A1; FR2360611B1; CA1099849A; DE2733912C2; JPS613804B2; DE2733912A1

Abstract

A photocrosslinkable polymer and imaging element containing said polymer are described wherein acid resistance is achieved by vinyl ester recurring units. A process for etching an element so prepared features exposure, development, and etching in an acid bath.

Description

(54) RADIATION-SENSITIVE COPOLYMER (71) We, EASTMAN KODAK COMPANY, a Company organized under the Laws of the State of New Jersey, United States of America of 343 State Street, Rochester, New York 14650, United States of America do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a photoresist copolymer.

Photoresists are commonly used to protect metal or other surfaces from etchants in photomechanical and photofabrication processes. A photoresist may be prepared by coating a surface with a solution containing a radiation-sensitive polymer, drying the coating, exposing the layer thereby obtained imagewise to actinic radiation (normally ultraviolet radiation or visible light) to form therein an imagewise distribution of altered solubility, and then treating the layer with a solvent which dissolves only the more soluble portions thereof, the residual lesssoluble portions constituting the resist.

According to the present invention there is provided a radiation-sensitive filmforming copolymer which comprises from 30 to 97 mole per cent of recurring units of the formula:

wherein R2 is hydrogen, an alkyl group having up to 5 carbon at(5ms, a halogen atom, or a nitro group, R2 when a nitro group being in the ortho or meta position; and from 3 to 70 mole per cent of recurring units of the formula:

wherein n is 0 or I and R' is hydrogen or an alkyl or alkoxyl group having up to 5 .carbon atoms.

Photoresist polymers have been provided in the past by esterifying poly(vinyl alcohol) with at least a cinnamoyl acid chloride. The present invention is based on the discovery that a sensitive copolymer having enhanced acid resistance, particularly useful in photoresist applications, is achieved by a co-esterifying at least a portion of poly(vinyl alcohol) with a naphthoyl chloride or a 3-(naphthyl) acryloyl chloride, as well as with a cinnamoyl chloride, to provide a copolymer containing as dependent moieties both a cinnamate cross-linking moiety, and a naphthoate or 3-(naphthyl)acrylate moiety. If the naphthoate recurring unit exceeds 70 mole per cent of the copolymer, the crosslinkability of the cinnamate becomes significantly impaired.

A copolymer of the invention can contain other vinyl ester repeating units, such as the unit

the mole percentage of such a benzoate recurring unit being no more than l0V.

Such additional repeating units can be produced by adding the proper molar quantity of benzoyl chloride to poly(vinyl alcohol), according to procedures hereinafter discussed.

It is common for poly(vinyl alcohol) to be acetylated to a certain degree, and a copolymer of the invention may comprise up to 25 mole per cent of acetate groups without its photo-resist properties being adversely affected. For example, as noted in Example 2, the "Vinol 523" (Trade Mark) poly(vinyl alcohol) has a theoretical acetate content of 10 to 15 /". Small amounts of free hydroxyl groups may also be present.

A copolymer of the invention will provide, upon imagewise exposure to ultraviolet radiation and development, a pattern of crosslinked copolymer which will resist hot concentrated nitric acid long enough to provide a "deep etch" i.e. an etch sufficient to remove at least 370 microns of the support. Removal of as much as 1000 microns is common. The time required for a deep etch depends upon the material to be etched.

A copolymer of the invention can be prepared by the addition simultaneously, or sequentially in either order, of a naphthoyl halide or 3-(naphthyl)acryloyl halide and a cinnamoyl halide to a suspension of poly(vinyl alcohol) (hereinafter, PVA) in a tertiary amine solvent such as pyridine, to esterify the alcohol groups. The mole ratio of added reactants is adjusted to achieve the desired mole percentage of the copolymer recurring units. It is not essential to add all of a given halide at once.

Thus it is possible to add, in sequence, a portion of the first acid halide, all of the second, and then the remainder of the first. Except as just noted with regard to the sequence of addition, the conditions of the reactions, such as temperatures and times, are those of the art, for instance as disclosed in U.S. Patent No. 3,560,465.

A copolymer of the invention may be used as a photoresist polymer or as a coating for a lithographic plate. In the latter case, the coating will preferably include a sensitizer and a pigment or a print-out dye precursor. Where used in a lithographic coating, the copolymer can further include a print-out dye former and an accelerator.

Suitable sensitizers for the copolymer include anthrones, such as 1 - carbethoxy - 2 - keto - 3 - methyl - 3 - azabenzanthrone, benzanthrone and those anthrones described in U.S. Patent No. 2,670,285; nitro sensitizers such as those described in U.S. Patent No. 2,610,120; triphenylmethanes such as those described in U.S. Patent No. 2,690,966; quinones such as those described in U.S. Patent No.

2,670,286; cyanine dye sensitizers; naphthone sensitizers such as 6 - methoxybeta 2 - furyl - 2 - acrylonaphthone; pyrylium or thiapyrylium salts, such as 2,6 bis(p - ethoxyphenyl) - 4 - (p - n - amyloxyphenyl) - thiapyrylium perchlorate and 1,3,5-triphenylpyrylium fluoroborate; furanone; anthraquinones such as 2 chloroanthraquinone; thiazoles such as 2 - benzoylcarbethoxymethylene - 1 methyl - betanaphthothiazole and methyl 2-(N-methylbenzothiazolylidene) dithioacetate; methyl 3-methyl-2-benzothiazolidene dithioacetate; thiazolines such as 3 - ethyl - 2 - benzoylmethylenenaphthol[l,2 - d] - thiazoline, benzothiazoline, 2 - [bis(2 - furoyl)methylene] - 1 - methyl naphtho[l,2-d]thiazoline and (2 benzoylmethylene) - 1 - methylbeta - naphthothiazoline; 1,2 - dihydro - 1 - ethyl - 2 - phenacylidenenaphthol[l,2 - dl - thiazole; naphthothiazoline; quinolizones; Michler's ketone; and Michler's thioketone as well as other sensitizers, such as those described in French Patent Nos. 1,238,262; 1,089,290 and 1,086,257 and U.S. Patent Nos. 2,670,285 and 2,732,301; and nitro aromatics such as nitroacenaphthalene.

The crosslinkable copolymers of this invention, such as those incorporating one or more of the cinnamate repeating units, are directly responsive to actinic radiation. The sensitizers noted above enhance this responsiveness and in some instances appear to extend the wavelength range of radiation to which the copolymer is responsive.

The crosslinkable copolymers of this invention need not be directly crosslinked in response to exposure to actinic radiation. Certain radiation-responsive sensitizers such as ketone-type and azide-type sensitizers can act as crosslinking agents. Typical aryl ketone sensitizers of this class include such compounds as benz(a)- anthracene- 7,12- dione and 4,4'- bis - (dimethylamino)benzophenone. Other advantageous ketone-type sensitizers are, for example, 4,4'tetraethyldiaminodiphenyl ketone, dibenzalacetone and 4,4'-bis(dimethylamino)benzophenone imide, as well as sensitizers of the type described in U.S. Patent No.

2,670,287.

Another class of sensitizers for the photocrosslinkable polymers of the invention are 3-substituted coumarins which have an absorption maximum between about 250 to about 550 nm. Such coumarins are described in United Kingdom Patent Application 4241/77 (Serial No. 1,578,662) and preferably have the formula:

wherein Q is -CN or -Z-R10 in which Z is a linking group selected from carbonyl, sulphonyl, sulphinyl or arylenedicarbonyl. R10 is alkyl including cycloalkyl and substituted alkyl, having 1---10 carbon atoms, aryl, substituted aryl, amino, substituted amino, alkoxy, aryloxy or a heterocyclic group having about 5 to 15 nuclear carbon and hetero atoms such as pyridyl and pyridinium, nicotinyl, nicotinium, furyl, 2-benzofuranyl, 2-thiazolyl or 2-thienyl; or 3-coumarinyl and wherein R5, R6, R7 and RB each independently is hydrogen, alkoxy having 1-6 carbon atoms, dialkylamino with each alkyl of the dialkylamino group having 19 carbon atoms, halogen, nitro, or a 5- or 6-membered heterocyclic group such as pyrrolidino, morpholino, piperidino or pyridinium; and R9 is hydrogen, alkyl having 14 carbon atoms or aryl of 6-12 carbon atoms; it being noted that two or three of R5-R8 and the nuclear carbon atoms to which they are attached can together form a fused ring or fused ring system, each ring being a 5- or 6-membered ring.

The sensitizer can be present in the coating composition in any concentration, it being generally preferred to use a concentration of from 0.01 to 20 per cent by weight of the crosslinkable polymer.

Pigments may be mixed with the copolymer so that developed image areas are visually distinct from the nonimage areas. Suitable pigments include the Victoria Blue (Color Index Pigment Blue I), Palomar Blue (Color Index Pigment Blue 15), Monastral Blue BF (Color Index Pigment Blue 15 (74160)), and Watchung Red B (Color Index Pigment Red 48).

Sensitive copolymers and compositions of the invention can be coated on a variety of supports according to the intended photographic use. Suitable support materials include fibre based materials such as paper, polyethylene-coated paper, polypropylene-coated paper, parchment and cloth; sheets and foils of such metals as aluminium, copper, magnesium and zinc; glass and glass coated with such metals as chromium, chromium alloys, steel, silver, gold, and platinum; synthetic resin and polymeric materials such as poly(alkyl acrylates), e.g., poly(methyl methacrylate), polyester film base-e.g., poly(ethylene terephthalate), poly(vinyl acetals), polyamides-e.g., nylon and cellulose ester film base-e.g., cellulose nitrate, cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate.

Of these, particularly useful support materials for photoresist etching are magnesium and copper. Supports which are useful in forming printing plates, particularly lithographic printing plates, include those of zinc, anodized aluminium, grained aluminium, copper and specially prepared metal and paper supports; superficially hydrolyzed cellulose ester films; and polymeric supports such as of polyolefins, polyesters and polyamides.

For lithographic uses, the supports can be preliminarily coated-i.e.; before receipt of the radiation-sensitive coating-with known subbing layers such as those containing copolymers of vinylidene chloride and acrylic monomers-e.g., acrylonitrile and methyl acrylate and unsaturated dicarboxylic acids such as itaconic acid; carboxymethyl cellulose; gelatin; polyacrylamide; and similar polymeric materials. The support can also carry a filter or antihalation layer of a dyed polymer.

A coating composition of the invention may contain a variety of addenda such as agents to modify the flexibility, surface characteristics, and adhesion of the coating to the support, antioxidants, preservatives, and phenolic resins, such as thermoplastic "Novolac" resins or solvent-soluble resole resins which improve the resistance of the coating to etchants.

A coating composition containing a light-sensitive polymer of this invention can be prepared by dispersing or dissolving the polymer in a solvent or solvent mixture, suitable solvents including ketones such as 2-butanone, 4-methyl-2pentanone, cyclohexanone, 4-butyrolactone, 2,4-pentandione and 2,5-hexandione; esters such as 2-ethoxyethyl acetate, 2-methoxyethyl acetate and n-butyl acetate; chlorinated solvents such as chloroform, dichloroethane, trichloroethane and tetrachloroethane; dimethylformamide and dimethylsulphoxide; and mixtures of these solvents. Usually the light-sensitive copolymer is present in the coating composition at a concentration in the range I to 30 per cent by weight (based on the weight of solids). Preferably the copolymer concentration is from 5 to 20 per cent by weight of the composition.

A layer containing a copolymer of the invention and any mixed therewith can be formed on a support in any desired manner, for instance by conventional coating techniques or by lamination of a preformed layer. Conventional coating techniques, include application with, a spray, brush, roller or immersion coater, following the composition over the surface, and dipping the substrate into the composition. Sensitive materials thus formed are dried at room temperature, under vacuum or at elevated temperature.

Typical coating thicknesses are 0.05 to 10.0 microns. For use as a photoresist, the coating is preferably from I to 5 microns thick, whereas thicknesses of from 0.1 to 2.5 microns are preferred for lithographic plate coatings.

Photomechanical images can be prepared with photosensitive materials of the invention by imagewise exposing the material to a radiation source to harden or insolubilize the polymer in exposed areas. Suitable radiation sources include carbon arc lamps, mercury vapour lamps, fluorescent lamps, tungsten lamps and photoflood lamps.

The exposed material is developed with a solvent for the unexposed, uncrosslinked polymer which is a non-solvent for the exposed hardened polymer.

Such a solvent can be selected from the solvents listed above as suitable coating solvents and other known solvents.

When the developed material is to be etched in an acid etching bath, it is customary to employ a 1 to 5 minute treatment in an acid such as 20% nitric acid at a temperature of from 38 to 660C depending on the depth of etching required. This produces excellent relief images significantly free from acid attack in the portions protected by the copolymer.

The invention is illustrated by the following Examples.

Example I Preparation of Poly[vinyl Cinnamate-co-vinyl a-naphthoate] (50:50 mole %) A suspension of 13.7 g "Elvanol 71-30-M" (Trade Mark) PVA [a medium molecular weight poly(vinyl alcohol) from 100% hydrolyzed poly(vinyl acetate), manufactured by DuPont] was stirred in 300 ml of pyridine at 600C for 16 hours to swell the polymer. The suspension was cooled to 500C and 28.5 g of a-naphthoyl chloride was added. After stirring for 6 hours at 500 C, 25 g of cinnamoyl chloride was added. Warming was continued for another 16 hours after which the solution was cooled. The reaction mixture was poured into water to precipitate the resultant fibrous polymer which was washed thoroughly with water and dried to give 41.8 g of copolymer. The product was readily soluble in solvents such as cyclohexanone and 1,2-dichloroethane.

Example 2 Preparation of Poly[vinyl Cinnamate-co-vinyl A-naphthoate] (80:20 mole %) "Elvanol 71-30-M" (Trade Mark) PVA (4.4 g) was suspended in 150 ml of pyridine at 600C for 16 hours. The suspension was cooled to 500C and 3.8 g of A- naphthoyl chloride was added. Stirring at 500C continued for 6 hours after which 12.4 g of cinnamoyl chloride was added. The reaction mixture was warmed at 500C for 16 hours, then cooled and filtered. The copolymer was precipitated from solution by pouring into water. It was thoroughly washed with water. After drying, 13.4 g of polymer was obtained.

Example 3 Preparation of Poly[vinyl Cinnamate-co-vinyl a-naphthoate Co-vinyl Acetate (44:44:12 mole %) "Vinol 523" (Trade Mark) PVA (4.9 g), a medium molecular weight poly(vinyl alcohol) from 88% hydrolyzed poly(vinyl acetate), manufactured by Air Products Co., was suspended in 150 ml of pyridine at 600C for 16 hours. The suspension was cooled to 500C and 8.4 g of a-naphthoyl chloride was added. After additional warming for 6 hours, 7.3 g of cinnamoyl chloride was added and the reaction mixture was warmed for 16 hours. The cool solution was filtered and precipitated into water. The resulting fibrous product was dried, giving 9.8 g of product.

Example 4 Preparation of Poly[vinyl Cinnamate-co-vinyl 3-(a-naphthyl) Acrylate] (50:50 mole %) "Elvanol 71-30-M" (Trade Mark) PVA (4.4 gm) was suspended in 150 ml of pyridine at 600C for 16 hours. The suspension was cooled to 500C and 8.4 g of cinnamoyl chloride was added. The reaction mixture was stirred at 500C for 6 hours after which 10.9 g of 3-(a-naphthyl)acryloyl chloride was added. The reaction mixture was then stirred at 500C for 12 hours followed by 4 hours at 750C. The amber, viscous solution was cooled and filtered. The resulting solution was then poured into vigorously stirred water to precipitate the resulting copolymer which was collected and blended with water in a high speed Waring blender. The copolymer, consisting of small granules, was dried at 500C for 4 days in an air oven to a final weight of 14.2 g.

Example 5 Preparation of Poly[vinyl Cinnamate-co-vinyl a-naphthoate] (95:5 mole %) A copolymer was prepared as in Example 1 except that 1.0 g naphthoyl chloride and 15.9 g cinnamoyl chloride were added to 4.4 g of "Elvanol 71-30-M" in 150 ml of pyridine. A slightly off-white granular polymer was obtained in a dry yield of 13.1 g.

Example 6 Preparation of Poly[vinyl Cinnamate-co-vinyl 3-(4-methoxy l-naphthyl)acrylate] (50:50 mole %) A copolymer was prepared as in Example 1 except that 6.25 g 3-(4-methoxy-lnaphthyl) acryloyl chloride and 4.15 g cinnamoyl chloride were added to 2.2 g "Elvanol 71-30-M" in 70 ml of pyridine. The yellowish polymer was isolated in a yield of 8.2 g.

The following nonexhaustive examples are further illustrative of the invention: Example 7 A coating composition was prepared as follows: 10.0 g the copolymer of Example 1 5.0 g 4-butyrolactone 35.0 g 2-ethoxyethyl acetate 100.0 mg hydroquinone (as a thermal stabilizer) 200.0 mg 2-[bis(2-furoyl)methylene]- 1 - methylnaphtho[ 1 2-dithiazoline The photoresist coating composition was stirred for 24 hours and filtered through a filter disk having a pore size of 2--4 microns. To 30 g of the filtered composition was added 2.0 g of the following pigment formulation: Monastral Blue BF 15.68% "FC-98" (a C8F,7 fluorocarbon sulphate anionic surfactant, believed to be a potassium salt, manufactured by 3M Corp.) 0.32% 2-Ethoxyethyl acetate 84.0% This coating composition was roller coated on Dowetch Deadline PRC (Trade Mark) magnesium plate via a Gyrex Micro-9 (Trade Mark) roller coater using a roller with a pressure setting of 2.5 pounds. Passing the plate twice through the rollers with a 30-second dwell yielded a resist coating of 3.25 microns thickness when dried. The plates were prebaked for 10 minutes at 80OC and exposed to a 200 watt mercury-vapor lamp in an "Exposure I" (Trade Mark) light unit manufactured by Colight, Inc., Minneapolis Minnesota for one minute through a Kodak T-14 (Trade Mark) stepwedge. The exposed portion yielded an insoluble resist (under the first to the 9th step (1.2 density)) after 30 second spray development in hot trichloroethylene. The magnesium plate bearing a resist image was then etched with 20% nitric acid in a "Dynamil" (Trade Mark) spray etcher for 2 minutes at 49"C. The nitric acid etchant was prepared as follows: Etchant Formula 6000 ml Distilled Water 400 ml Hunt Auto-Express Etching Additive (Trade Mark) Manufactured by Hunt Chemical Corp.

1600 ml Concentrated nitric acid The nitric acid consumed during etching was replaced by the addition of 6 ml of concentrated nitric acid for each gram of magnesium reacted.

The resist coating yielded excellent protection for the magnesium. No sign of resist chipping, blistering or pinholing was observed after etching to a depth of 625 microns.

Example 8 A coating composition was prepared as follows: 2.0 g Copolymer of Example 2 3.6 g 4-Butyrolactone 11.0 g 2-Ethoxyethyl acetate 20.0 mg Hydroquinone 40.0 mg 2-(Benzoylmethylene)- 1 -methyl-naphtho [1,2-d]-thiazoline The above materials were mixed 24 hours and filtered through a disk filter having a pore size of 24 microns.

The filtered composition was whirl-coated at 115 rpm yielding 3.75 micron thick coatings on 'PRC' magnesium after drying. The plates were exposed for 2 minutes to crosslink steps 1-8 under a 14 step-wedge and processed as in Example 7, yielding excellent etched images.

Example 9 A resist composition was prepared as follows: 2.0 g Copolymer of Example 4 4.0 g 4-butyrolactone 12.0 g 2-ethoxyethyl acetate 20.0 mg hydroquinone 40.0 mg 3,3'-carbonylbis (7-diethylaminocoumarin) A plate was prepared as in Example 7, was exposed for 30 seconds to crosslink the 1st to the 8th step under a 14 step wedge, and was processed as in Example 7.

Although the quality of the coating was initially less than that of Example 7, the resist image withstood the nitric acid etchant equally as well as the resist of Example 7.

Example 10 A coating composition of the copolymer of Example 5 and a plate were prepared in the manner of Example 7. The resulting plate was exposed, developed to render steps 1-9 insoluble under a 'Kodak' T-14 stepwedge, and etched also as in Example 7. The etched image was judged good to excellent compared to a poly(vinyl cinnamate) control which was judged poor to fair with extensive chipping.

Example 11 A coating composition of the copolymer of Example 6 and a plate were prepared in the manner of Example 9 except using 3,3'-carbonylbis(5,7-dipropoxy coumarin) as the sensitizer. The resulting plate was exposed, and developed as in Example 7 of theappiication to render the 1st to the 7th steps insoluble under a 'Kodak' T-14 stepwedge, and etched also as in Example 7. The etched image was judged excellent with no chipping or blistering.

The following examples, submitted by way of comparison, indicate the superiority of the acid resistance of the copolymers of the invention.

Comparative Example No. 1 A coating was prepared as in Example 7, except that an equivalent amount of a homopolymer of poly(vinyl cinnamate), was used instead of the copolymer. After exposure, development, and etching as in Example 7, the "protected" areas were found to be chipped, blistered and pinholed.

Comparative Example No. 2 A coating was prepared as in Example 7, except that an equivalent amount of a copolymer comprising 50 mole percent benzoate in place of the 50 mole per cent anaphthoate was used, to show the importance of the presence of the a-naphthoate groups. The photoresist containing the benzoate was evaluated as described for Example 7, and it was found that the exposed "protective" coating was removed during the acid etch, permitting etching of the exposed areas. Thus, the benzoate containing copolymer did not give the excellent acid resistance available with the copolymer containing naphthoate groups.

WHAT WE CLAIM IS: 1. A radiation-sensitive film-forming copolymer which comprises from 30 to 97 mole per cent of recurring units of the formula:

wherein R2 is hydrogen, an alkyl group having up to 5 carbon atoms, a halogen atom, or a nitro group, R2 when a nitro group being in the ortho or meta position; and from 3 to 70 mole per cent of recurring units of the formula:

wherein n is 0 or I and R' is hydrogen or an alkyl or alkoxyl group having up to 5 carbon atoms.

2. A copolymer according to claim 1 which comprises up to 10 mole per cent of recurring units of the formula:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 10 A coating composition of the copolymer of Example 5 and a plate were prepared in the manner of Example 7. The resulting plate was exposed, developed to render steps 1-9 insoluble under a 'Kodak' T-14 stepwedge, and etched also as in Example 7. The etched image was judged good to excellent compared to a poly(vinyl cinnamate) control which was judged poor to fair with extensive chipping. Example 11 A coating composition of the copolymer of Example 6 and a plate were prepared in the manner of Example 9 except using 3,3'-carbonylbis(5,7-dipropoxy coumarin) as the sensitizer. The resulting plate was exposed, and developed as in Example 7 of theappiication to render the 1st to the 7th steps insoluble under a 'Kodak' T-14 stepwedge, and etched also as in Example 7. The etched image was judged excellent with no chipping or blistering. The following examples, submitted by way of comparison, indicate the superiority of the acid resistance of the copolymers of the invention. Comparative Example No. 1 A coating was prepared as in Example 7, except that an equivalent amount of a homopolymer of poly(vinyl cinnamate), was used instead of the copolymer. After exposure, development, and etching as in Example 7, the "protected" areas were found to be chipped, blistered and pinholed. Comparative Example No. 2 A coating was prepared as in Example 7, except that an equivalent amount of a copolymer comprising 50 mole percent benzoate in place of the 50 mole per cent anaphthoate was used, to show the importance of the presence of the a-naphthoate groups. The photoresist containing the benzoate was evaluated as described for Example 7, and it was found that the exposed "protective" coating was removed during the acid etch, permitting etching of the exposed areas. Thus, the benzoate containing copolymer did not give the excellent acid resistance available with the copolymer containing naphthoate groups. WHAT WE CLAIM IS:

1. A radiation-sensitive film-forming copolymer which comprises from 30 to 97 mole per cent of recurring units of the formula:

3. A copolymer according to claim I or 2 which comprises up to 25 mole per cent of recurring units of the formula:

4. A copolymer according to claim I substantially as described in any of Examples I to 6 herein.

5. A radiation-sensitive composition which comprises a copolymer according to any of the preceding claims and a sensitizer therefor.

6. A composition according to claim 5 wherein the sensitizer is a thiazoline.

7. A composition according to claim 5 substantially as described in any of Examples 7 to 9 and 11.

8. A radiation-sensitive sheet material which comprises a support bearing a layer of a copolymer according to any of claims 1 to 4.

9. A radiation-sensitive sheet material which comprises a support bearing a layer of a composition according to any of claims 5 to 7.

10. A method of making a resist which comprises exposing imagewise to actinic radiation a sheet material according to claim 8 or 9 and removing the relatively more soluble portions of the copolymer-containing layer with a developing solvent.

11. A method of etching a pattern in a metal support which comprises coating the support with a layer of a copolymer according to any of claims 1 to 4 or of a composition according to any of claims 5 to 7, exposing the layer with actinic radiation to a negative of the patterns, removing the relatively more soluble portions of the layer with a developing solvent to form a resist and then treating the resist-bearing surface of the support with an etchant.

12. A method of making a copolymer according to any of claims I to 3 which comprises reacting polyvinyl alcohol with cinnamoyl chloride and with a naphthoyl chloride or a 3-naphthyl acryloyl chloride.

13. A method according to claim 12 substantially as described in any of Examples 1 to 6 herein.