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This copolymer was dissolved uniformly in the solvents such as acetone, THF, DMF and HFC-225. 

Synthesis of cyclopentene Having -C(CF 3 ) $_{2}$OH Group 

A 500 ml four-necked glass flask equipped with a blowing tube was charged with 100 g of cyclopentadiene, followed by stirring in nitrogen gas atmosphere while cooling in dry ice/ acetone bath. HCl gas was slowly introduced at a solution temperature of not more than 0° C. through a gas feeding tube and sometimes the flask was separated to measure the weight thereof. HCl gas was introduced up to 90% of theoretical amount to synthesize 3-chlorocyclopentene which was not isolated and used for the following reaction. 

Magnesium was put in an amount of 24 g into a I-liter four-necked glass flask equipped with a blowing tube, dry ice condenser and dropping funnel and was dried by heating in vacuo. Thereto was added 200 ml ofTHF, followed by cool- ing in ice bath. A solution obtained by mixing 31 g of previ› ously prepared 3-chlorocyclopentene to 150 ml of THF was slowly added dropwise through the dropping funnel in a state of the solution temperature being 10° to 15° C. After comple› tion of the addition, hexafluoroacetone was introduced slowly through the gas feeding tube so that the solution temperature did not exceed 20° C. Hexafluoroacetone was introduced until generation of heat was not recognized. After completion of the introduction ofhexafluoroacetone, stirring was further continued at room temperature for three hours. The reaction mixture was put in 500 ml of 1 N hydrochloric acid, followed by separating an organic layer, washing with water, drying and distilling after concentration. As a result, 56.0 g of fluo› rine-containing alcohol represented by the formula: 

<img src='content_image/939006.jpg'>

having a boiling point of from 62° to 64° C./45 mmHg was obtained. The monomer obtained above was determined by $^{19}$F-NMR, $^{1}$H-NMR, $^{13}$C-NMR and IR analyses. 

Synthesis of Copolymer Comprising tetrafluoroethylene and cyclopentene Having -C(CF$_{3}$ ) $_{2}$OH Group) 

A 100 ml autoclave was charged with 5.5 g of the cyclo› pentene having----C(CF $_{3}$ ) $_{2}$OH group obtained in Example 12, 40 ml ofHCFC-141b and0.7 g ofbis(4-tert-butylcyclohexyl) 65 peroxydicarbonate (TCP), and the inside of a system was sufficiently replaced with nitrogen gas while cooling with dry 

## Example 12 

## Example 13 

ice/methanol solution. Then 10.0 g of tetrafluoroethylene (TFE) was introduced through a valve, followed by shaking for reaction at 40° C. for 18 hours. With the advance of the reaction, a gauge pressure was decreased from 0.88 MPaG (9.0 kgf/cm $^{2}$G) before the reaction to 0.85 MPaG (8.7 kgf/ cm $^{2}$G). 

After releasing the un-reacted monomer, the polymeriza› tion solution was removed, followed by re-precipitation with hexane to separate a copolymer. Until a constant weight was reached, vacuum drying was continued and 1.2 g of a copoly› mer having a structure represented by the following formula was obtained. 

<img src='content_image/939001.jpg'>

As aresultof1H-NMRand $^{19}$F-NMRanalyses, the copoly› mer was one comprising TFE/cyclopentene having ----C(CF $_{3}$ ) $_{2}$OH group in a percent by mole ratio of 50/50. 

Measurement of Transparency at a Wavelength of 157 nm 

(1) Preparation of Coating Composition 

The fluorine-containing polymers prepared in Examples 1 to 3, 6 to 10 and 13 were dissolved in butyl acetate so that the concentration thereofbecame 3%, respectively. Thus coating compositions were prepared. 

(2) Coating 

(i) Coating on a Substrate (MgF$_{2}$ ) for Measuring Transpar› ency 

Each coating composition was applied on a MgF $_{2 }$substrate at room temperature with a spin coater under the condition of 1,000 rpm. After the coating, the coating composition was baked at 100° C. for 15 minutes to form transparent coating films. 

(ii) Measurement of Coating Thickness 

Coating films were formed by applying the respective coat› ing compositions under the same conditions as above except that a silicon wafer was used instead of the MgF $_{2 }$ substrate. 

The coating thickness was measured with a AFM device (SPI3800 available from SEIKO DENSHI KABUSHIKI KAISHA). The results are shown in Table 1. 

(3) Measurement of Transparency in Vacuum Ultraviolet Region 

(i) Measuring Device 

Setani-Namioka type spectrometer (BL-7B available from HIGH ENERGY KENKYU KIKO) 

Slit: 7 /8-7 /8 

Detector: PMT 

Grating (GII: Blaze wavelength 160 nm, 1,200 gratings/ mm) 

For an optical system, refer to Rev. Sic. Instrum., 60(7), 1917 (1989) by H. Namba, et al. 

(ii) Measurement of Transmitting Spectrum 

A transmitting spectrum at a wavelength of 200 to 100 nm in a coating film formed by applying each coating composi- 

## Example 14 

