PIEZOELECTRIC OR PYROELECTRIC VINYLIDENE CYNAMIDE COPOLYMER MATERIAL

Abstract: A vinylidene cyanide copolymer obtained by copoly­ merizing vinylidene cyanide represented by formula (I) and a vinyl compound represented by formula (II) CH₂ = - Z (II) wherein Z represents a hydrogen atom or a saturated hydrocarbon group having from 1 to 6 carbon atoms; when Z is a hydrogen atom, R represents C n H 2n+1 COO-, wherein n represents 0 or an integer of from 4 to 9; and when Z is a saturated hydrocarbon group, R represents CH₃COO- ­ or a group having a benzene ring. The copolymer has excellent transparency and provides an electret exhibiting excellent pyroelectricity or piezoelectricity upon polar­ ization.

Description: This invention relates to a piezoelectric or pyroelectric vinylidene cyanide copolymer material prepared by molding a vinylidene cyanide copolymer and a vinyl compound, the material in transparent molded articles having high dielectric constants. Many copolymers comprising vinylidene cyanide and various vinyl compounds are known as described, e.g. in H. Gilbert et al., J. Am. Chem. Soc., Vol. 78, 1669 (1956), but there is no report of the particular copolymer used according to the present invention. US-A-2615866, 2615867 and 2615868 and 2615875 disclose copolymers of vinylidene cyanide with various vinyl compounds including vinyl esters, especially of aliphatic monocarboxylic acids, e.g. made by using a polymerisation catalyst (US-2615866); the products may be made into filaments or films. The present invention provides a piezoelectric or pyroelectric material prepared by molding a vinylidene cyanide copolymer prepared by copolymerizing vinylidene cyanide of formula (I) and a vinyl compound represented by formula (II) wherein Z is hydrogen or a saturated hydrocarbon group having from 1 to 6 carbon atoms; with the provisos that when Z is hydrogen, R is C n H 2n+1 COO-, wherein n represents 0 or an integer of from 4 to 9, and when Z is a saturated hydrocarbon group, R is CH₃COO-, or a group having a benzene ring, and then polarizing said molded vinylidene cyanide polymer. The copolymer used in the present invention has excellent transparency and provides an electret exhibiting excellent piezoelectricity and pyroelectricity upon polarization. The vinylidene cyanide copolymer used in the present invention is a random copolymer or alternating copolymer obtained by copolymerizing a vinylidene cyanide monomer represented by formula (I) above and a vinyl compound monomer represented by formula (II). The random copolymer comprises a repeating unit (B) derived from the vinyl compound and a repeating unit (A) derived from vinylidene cyanide at a (B)/(A) molar ratio of from 0.8 to 20, and preferably from 0.9 to 15. Both the random and alternating copolymers used in the present invention are low crystalline resins having a glass transition point of from 100 to 250°C, and preferably from 140 to 200°C, and a molecular weight of from 200,000 to 1,500,000, and preferably from 500,000 to 1,000,000. In formula (II), when Z is a hydrogen atom, R represents a carboxyl group having a hydrogen atom (n=0) or a straight or branched chain saturated hydrocarbon group having from 4 to 9 carbon atoms (n=4 to 9), i.e., a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group or a nonyl group. Preferred examples of those having a branched hydrocarbon group are groups having a secondary hydrocarbon group or a tertiary hydrocarbon group, e.g., (CH₃)₃CCOO- and (C₂H₅)₃CCOO-. When Z is a saturated hydrocarbon group having from 1 to 6 carbon atoms, R represents CH₃COO- or a group having a benzene ring. Preferred examples of the group having a benzene ring include a phenyl group and a naphthyl group. The saturated hydrocarbon group as represented by Z may be either a straight chain group or a branched chain group having a secondary or tertiary carbon atom. Examples of the hydrocarbon groups are a methyl group and an ethyl group. The copolymer according to the present invention can be prepared by, for example, polymerizing vinylidene cyanide and the vinyl compound of formula (II) in the presence of a radical initiator with or without a solvent. The copolymerization may also be carried out by slurry polymerization or in an ampule. In the copolymerization, the vinyl compound is usually used in an amount of from 0.8 to 20 mols per mol of vinylidene cyanide, and preferably from 1 to 8 mols when obtaining an alternating copolymer and from 8 to 20 mols when obtaining a random copolymer. The solvent, if used, includes an aprotic solvent, such as benzene, toluene or xylene, an aliphatic hydrocarbon, such as pentane, hexane or heptane, and mixtures thereof. The polymerization temperature ranges from 0 to 150°C, and preferably from 50 to 80°C, in the case of slurry polymerization. The polymerization temperature when effected in an ampoule is not particularly restricted and usually ranges from 0 to 100°C. Any known radical initiator can be used as a polymerization catalyst. Specific examples of useful radical initiators include oxygen; dialkyl peroxides or the derivatives thereof, e.g., di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide; diacyl peroxides, e.g., diacetyl peroxide, dioctanyl peroxide; peroxydicarbonates, e.g., diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate; peroxy esters, e.g., t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-butyl peroxylaurate; ketone peroxides, e.g., methyl ethyl ketone peroxide, cyclohexanone peroxide; peroxy ketals, e.g., 2,2-bis-t-butyl peroxyoctane, 1,1-bis(t-butyl peroxy)cyclohexane; hydroperoxides, e.g., t-butyl hydroperoxide, cumene hydroperoxide; and azo compounds, e.g. 2,2′-azobisisobutyronitrile. After completion of polymerization, an aprotic solvent is poured into the reaction mixture, followed by filtration. The polymer thus collected is then washed and dried to obtain the desired product. The copolymer used in the present invention contains a cyano group and an ester group having large polarity. It can be molded by commonly employed molding methods, such as cast molding, press molding, and injection molding. The resulting molded articles have high dielectric constants and are useful as an insulating layer for condensers, electroluminescence elements, etc. Again, molded articles having been subjected to polarization are applicable as high performance materials, such as piezoelectric or pyroelectric materials. Further, since the molded articles obtained from the copolymer used in the present invention have excellent transparency, they are also suitable for use as optical materials, such as optical fibers and lenses, as well as optical elements taking advantage of their high dielectric constant. The present invention will now be illustrated in greater detail with reference to the following Examples; in the accompanying Figures 1, 2 and 3 referred to therein, ν CO =1740 cm⁻¹ and ν CN =2250 cm⁻¹. EXAMPLE 1 In a 300 ml-volume four-necked flask equipped with a stirrer, a Dimroth condenser and a thermometer were charged 10 g (0.13 mol) of vinylidene cyanide synthesized in a usual manner, 45 g (0.63 mol) of vinyl formate (produced by K & K), 25 ml of toluene, 25 ml of heptane, and several grains (several tens milligrams) of diisopropyl peroxydicarbonate, and the mixture was heated at 50°C for 3 hours under stirring in an argon gas stream. The precipitated polymer was collected by filtration, washed successively with toluene and ethanol, and dried at 80°C under reduced pressure overnight to obtain 10.1 g (53%) of a polymer product. The resulting product was confirmed to be a 1:1 alternating copolymer by ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. The IR spectrum is shown in Fig. 1. Main physical properties of the copolymer (powder) were as shown below. Glass transition point (Tg): 152°C Intrinsic viscosity [η]: 0.5 Vinylidene cyanide (VDCN) content: 53 mol% (calculated from the elementary analysis results) The powder was dissolved in dimethylacetamide (DMA), and the solution was cast to form a film. The dielectric constant of the resulting film was measured at room temperature (25°C), and the results obtained are shown in Table 1 below. Frequency (KHz) Dielectric Constant 0.1 5.06 1 4.82 100 4.32 EXAMPLE 2 In the same flask as used in Example 1 were charged 6 g (0.08 mol) of vinylidene cyanide synthesized in a usual manner, 50 g (0.4 mol) of vinyl pivalate (produced by Wako Pure Chemical Industries Ltd.), 12 ml of heptane, and 6 mg of lauroyl peroxide, and the mixture was heated at 70°C for 4 hours under stirring in an argon gas stream. The precipitated polymer was collected by filtration, washed successively with toluene and ethanol, and dried at 80°C under reduced pressure overnight to obtain 7.4 g (47%) of a polymer product, which was confirmed to be a 1:1 alternating copolymer by ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. Main physical properties of the copolymer (powder) were as follows. Tg: 171°C [η]: 2.2 VDCN Content: 55 mol% The dielectric constant (25°C) of a cast film prepared from the copolymer in the same manner as in Example 1 is shown in Table 2. Frequency (KHz) Dielectric Constant 0.1 3.84 1 3.74 100 3.47 Further, the cast film was subjected to polarization and determined for piezoelectric constant (d₃₁). The results obtained are shown in Table 3 below. Polarization Temperature (°C) Field Strength (KV/cm) Polarization Time (hr) d₃₁ (C.G.S.e.s.u.) 160 450 2 10.2 x 10⁻⁸ 160 600 2 12.5 x 10⁻⁸ 160 750 2 14.8 x 10⁻⁸ EXAMPLE 3 In the same flask as used in Example 1 were charged 10 g (0.13 mol) of vinylidene cyanide synthesized in a usual manner, 68 g (0.64 mol) of isopropenyl acetate (produced by Wako Pure Chemical Industries Ltd.), 20 ml of toluene, and several grains (several tens milligrams) of diisopropyl peroxydicarbonate, and the mixture was heated at 70°C for 1 hour while stirring in an argon gas stream. The resulting viscous reaction mixture was poured into toluene, and the precipitated polymer was collected by filtration, washed successively with toluene and ethanol, and dried at 80°C under reduced pressure overnight to obtain 12 g (53%) of a polymer product. The product was confirmed to be a 1:1 alternating copolymer by ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. The IR spectrum is shown in Fig. 2. The main physical properties of the copolymer (powder) were as follows. Tg: 112°C [η]: 0.5 VDCN Content: 50 mol% The dielectric constant (25°C) of a cast film obtained from the copolymer in the same manner as in Example 1 is shown in Table 4. Frequency (KHz) Dielectric Constant 0.1 4.12 1 3.85 100 3.45 EXAMPLE 4 In the same flask as used in Example 1 were charged 20 g (0.26 mol) of vinylidene cyanide synthesized in a usual manner, 30 g (0.26 mol) of α-methylstyrene (produced by Wako Pure Chemical Industries Ltd.), 50 ml of toluene, and 20 mg of lauroyl peroxide, and the mixture was stirred at room temperature in an argon gas stream. At the time when heat generation subsided, the mixture was heated at 70°C for 1.5 hours with stirring. The precipitated polymer was collected by filtration, dissolved in acetone, and reprecipitated in toluene. The precipitate was washed with ethanol and dried at 80°C under reduced pressure overnight to obtain 7.1 g (14%) of a polymer product. The product was confirmed to be a 1:1 alternating copolymer from the results of ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. The main physical properties of the product (powder) were as follows. Tg: 151°C [η]: 0.4 VDCN Content: 52.6 mol% The dielectric constant (25°C) of a cast film obtained from the copolymer in the same manner as in Example 1 is shown in Table 5 below. Frequency (KHz) Dielectric Constant 0.1 3.96 1 3.84 100 3.55 EXAMPLE 5 In the same flask as used in Example 1 were charged 5 g (0.06 mol) of vinylidene cyanide synthesized in a usual manner, 40 g (0.35 mol) of vinyl butyrate (produced by Tokyo Kasei K.K.), and 5 mg of lauroyl peroxide, and the mixture was heated at 70°C for 2 hours while stirring in an argon gas stream. The precipitated polymer was collected by filtration, washed successively with toluene and ethanol, and dried at 80°C under reduced pressure overnight to obtain 10.5 g (85%) of a polymer product. The product was confirmed to be a 1:1 alternating copolymer by ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. The IR spectrum is shown in Fig. 3. The main physical properties of the copolymer (powder) were as follows. Tg: 192°C [η]: 6.3 VDCN Content: 50 mol% The dielectric constant (25°C) of a cast film obtained from the copolymer in the same manner as in Example 1 was as shown in Table 6 below. Frequency (KHz) Dielectric Constant 0.1 3.95 1 3.83 100 3.62 Further, the dielectric constant of the cast film was measured at a frequency fixed to 100 Hz at various temperatures. The results obtained are shown in Table 7. Measurement Temperature (°C) Dielectric Constant 160 7.86 172 14.77 176 32.27 180 99.71 184 82.11 The cast film was uniaxially stretched about 3 times in a silicone oil bath maintained at 190°C and then subjected to polarization. The resulting stretched film was determined for piezoelectric constants d₃₁ and K t . The results obtained are shown in Table 8. Polarization Temperature (°C) Field Strength (KV/cm) Polarization Time (hr) d₃₁ (C.G.S.e.s.u.) K t (%) 180 450 1 11.2 x 10⁻⁸ 8.6 180 600 1 13.4 x 10⁻⁸ 10.9 180 750 1 16.9 x 10⁻⁸ 12.4 EXAMPLE 6 In the same flask as used in Example 1 were charged 5 g (0.06 mol) of vinylidene cyanide synthesized in a usual manner, 50 g (0.35 mol) of vinyl hexanoate (produced by Tokyo Kasei K.K.), and 5 mg of lauroyl peroxide, and the mixture was heated at 70°C for 3 hours with stirring in an argon gas stream. The precipitated polymer was collected by filtration, washed successively with toluene and ethanol, and dried at 80°C under reduced pressure overnight to obtain 9.6 g (68%) of a polymer product. The product was confirmed to be a 1:1 alternating copolymer by ¹H-NMR analysis, ¹³C-NMR analysis, IR spectroscopic analysis, and elementary analysis. The main physical properties of the copolymer (powder) were as follows. Tg: 214°C [η]: 2.5 VDCN Content: 51 mol% The dielectric constant (25°C) of a cast film obtained from the copolymer in the same manner as in Example 1 was as shown in Table 9 below. Frequency (KHz) Dielectric Constant 0.1 3.85 1 3.73 100 3.66 Further, the dielectric constant of the cast film was measured at a frequency fixed to 100 Hz at various temperatures. The results obtained are shown in Table 10. Measurement Temperature (°C) Dielectric Constant 188 5.63 192 12.51 196 28.65 200 95.38 204 78.25 Furthermore, the piezoelectric constants d₃₁ and K t were measured in the same manner as in Example 5. The results obtained are shown in Table 11. Polarization Temperature (°C) Field Strength (KV/cm) Polarization Time (hr) d₃₁ (C.G.S.e.s.u.) K t (%) 200 450 1 10.9 X 10⁻⁸ 8.1 200 600 1 13.5 X 10⁻⁸ 9.9 200 750 1 16.5 x 10⁻⁸ 11.8

Claims: A piezoelectric or pyroelectric material prepared by molding a vinylidene cyanide copolymer prepared by copolymerizing vinylidene cyanide of formula (I) and a vinyl compound represented by formula (II) wherein Z is hydrogen or a saturated hydrocarbon group having from 1 to 6 carbon atoms; with the provisos that when Z is hydrogen, R is C n H 2n+1 COO-, wherein n represents 0 or an integer of from 4 to 9, and when Z is a saturated hydrocarbon group, R is CH₃COO-, or a group having a benzene ring, and then polarizing said molded vinylidene cyanide polymer. A piezoelectric or pyroelectric material as claimed in Claim 1, wherein Z is a hydrogen atom, n is an integer of from 4 to 9, and R contains a secondary or tertiary carbon atom. A piezeoelectric or pyroelectric material as claimed in Claim 1, wherein Z is a saturated hydrocarbon group having from 1 to 4 carbon atoms. A piezoelectric or pyroelectric material as claimed in Claim 1, wherein Z is a saturated hydrocarbon group and R is a phenyl group or a naphthyl group. A piezoelectric or pyroelectric material as claimed in any preceding claim, wherein said copolymer is a 1:1 alternating copolymer. A piezoelectric or pyroelectric material as claimed in any one of Claims 1 to 4, wherein said copolymer is a random copolymer. A piezoelectric or pyroelectric material as claimed in Claim 6, wherein said copolymer comprises a repeating unit derived from the vinyl compound (B) and a repeating unit derived from the vinylidene cyanide (A) at a (B)/(A) molar ratio of from 0.8 to 20. A piezoelectric or pyroelectric material as claimed in Claim 7, wherein said molar ratio is from 0.9 to 15. A molded material as claimed in any preceding claim.

Inventors: KISHIMOTO, MANABU MITSUBISHI, NAKAJIMA, KENJI MITSUBISHI, SEO, IWAI MITSUBISHI
Applicants: MITSUBISHI PETROCHEMICAL CO., LTD.
Application year: 1987
Main classification: C08F222
IPC codes: H01L37, H01L41, H01G7, C08F222