WO2005012401A1

WO2005012401A1 - Films based on syndiotactic polystyrene with new kinds of preferential orientation of the crystalline phase

Info

Publication number: WO2005012401A1
Application number: PCT/EP2004/051554
Authority: WO
Inventors: Gaetano Guerra; Vincenzo Venditto; Giuseppe Mensitieri; Paola Rizzo
Original assignee: Universita' Degli Studi Di Salerno
Priority date: 2003-07-21
Filing date: 2004-07-20
Publication date: 2005-02-10
Also published as: ITSA20030014A1; ITSA20030014A0

Abstract

The present invention relates to semicrystalline films based on syndiotactic polystyrene which are characterized by two new kinds of preferential orientation of the crystalline phase with respect to the film plane and to processes for their preparation.

Description

FILMS BASED ON SYNDIOTACTIC POLYSTYRENE WITH NEW KINDS OF PREFERENTIAL ORIENTATION OF THE CRYSTALLINE PHASE DESCRIPTION The present invention relates to semicrystalline films based on syndiotactic polystyrene which are characterized by two new kinds of preferential orientation of the crystalline phase with respect to the film plane and to processes for their preparation. State of art The invention is located in the scientific-technical fields of the industrial chemistry and engineering and more particularly in the field of functional polymeric materials . Molecular orientation is a phenomenon of great technical importance for all materials. The effects of orientation on properties, although formally similar to those on other materials, are more relevant for polymeric materials. For instance, for polymers, the extent to which it is possible to increase stiffness, and more particularly, strength, and the ease with which this can be done, find no parallel with other materials. Orientation is particularly relevant for functional polymeric materials, like for instance polymers presenting particular electric or optical properties. Of course, when the functionality is based on the crystalline phase, the functional properties mainly depend on the control of the orientation of the crystalline phase. The orientation of the crystalline phases assumes additional relevance for polymers, such as syndiotactic polystyrene, which can host in suitable crystalline phases some active guest molecules, whose properties can be modified by the orientation itself. In general, traditional drawing techniques when applied to semicrystalline polymers lead to crystalline phase orientations presenting parallel to the film plane the chain axes (axial orientation) or crystalline planes including the chain axes (uniplanar orientation) . For instance, as described in the Italian patent application No. SA2000A000023 (filed on 29/12/00) (Eur.Pat. Appl . 01830779.3) by casting procedures from solutions of syndiotactic polystyrene in chloroform or benzene a crystalline phase orientations, which presents the chain axes (corresponding to the crystallographic c axis) parallel to the film plane, and more precisely the orientation of the (010) crystalline plane parallel to the film plane, can easily be achieved. The same kind of orientation, with also higher degrees of orientation, can be achieved by biaxial drawing processes in the solid state of initially unoriented films, which in turn can be obtained by a melt processing technique, such as for instance extrusion. For the case of syndiotactic polystyrene, the crystalline phase orientation for which the chain axes are perpendicular to the film plane, has been till now achieved only for solution grown polymeric lamellar single crystals (with a typical thickness of tenths of nanometers) as well as for single crystal mats, as for instance described in a scientific paper (Y. K. Wang, J. D. Savage, D.Yang, S.L.Hsu Macromolecules 1992, 25, 3659) . Such perpendicular orientation, on the contrary, is not available for semicrystalline polymeric films of high thickness (larger than 1 μm) , as required by most industrial applications . There was therefore in the art a need to provide semicrystalline syndiotactic polystyrene films having a thickness suitable for industrial applications and presenting an orientation of the chain axes of the crystalline phase perpendicular to the film plane, which would be able to generate anisotropy for physical properties of the films as well as of the guest molecules . The present invention refers to semicrystalline films based on syndiotactic polystyrene presenting an orientation of the chain axes of the crystalline phase perpendicular to the film plane, which show anisotropic physical properties and are able to make anisotropic physical-chemical properties of their guest molecules. Therefore are an object of the present invention semicrystalline films of syndiotactic styrene homopolymer (syndiotactic polystyrene) or syndiotactic styrene copolymers with CH₂=CH-R olefins, wherein R is an alkyl- aryl or a substituted aryl radical containing 6-20 carbon atoms, having thickness in the range O.iμm and 200μm, preferably in the range 0.5μm and 50μm, for which the orientation of the chain axes of the crystalline phase is preferentially perpendicular to the film plane and the degree of perpendicular orientation, which can be evaluated by a Herman orientation factor, is in the range 0.2-1, preferably in the range 0.5-1. By syndiotactic polystyrene (sPS) is meant the polymer where the fraction of syndiotactic (also indicated by r) dyads is larger than 0.9. This polymer may be obtained, for instance, according to the method described in European patent application n.0271875

Himont Italy. According to the invention may also be used syndiotactic copolymers of styrene with CH₂=CH-R olefins, where R is an alkyl-aryl or a substituted aryl radical with 6-20 carbon atoms. In said copolymers the syndiotactic fraction is likewise larger than 0.9 and the copolymers are crystallizable. The present invention also refers to semicrystalline films based on syndiotactic polystyrene presenting an orientation of the crystalline ( 210) plane preferentially parallel to the film plane, which present anisotropic physical properties and are able to make anisotropic the physical-chemical properties of their guest molecules. An additional object of the present invention are therefore semicrystalline films of syndiotactic styrene homopolymer (syndiotactic polystyrene) or syndiotactic styrene copolymers with CH₂=CH-R olefins, where R is an alkyl-aryl or a substituted aryl radical with 6-20 carbon atoms, including a clathrate or a nanoporous phase, wherein the orientation of the crystalline ( 210) plane is preferentially parallel to the film plane and present a degree of orientation, which can be evaluated by a Herman orientation factor, in the range 0.2-1, preferably in the range 0.5-1. The present description contains two drawings showing : Fig.lA, IB, IC and ID four X-ray diffraction patterns of films according to the invention, as reported in the examples 1 and 2 _? Fig.2 A, B e C the Fourier Transform Infrared absorbances of films according to the invention reported in the example 1. In the present invention are therefore described semicrystalline films based on syndiotactic polystyrene, having also high thickness (in the range 0. lμm and 200μm, preferably in the range 0.5μm and 50μm) , characterized by two new kinds of preferential orientation of the crystalline phase with respect to the film plane: the orientation of the chain axes preferentially perpendicular to the film plane or the orientation of the crystalline ( 210) planes preferentially parallel to the film plane. Films produced according to the present invention, and hence for both orientations, show a degree of orientation, which can be evaluated by a Herman orientation factor being in the range 0.2-1, preferably in the range 0.5-1. These kinds of orientation are particularly relevant for films presenting crystalline clathrate phases of syndiotactic polystyrene, which are characterized by unit cells in which polymer helices can host low molecular mass molecules ("guest"), generally isolated, with a guest content in the range 1-50% by weight, and more commonly in the range 5-30% by weight. In fact, in such case, the molecular orientation not only affects the physical properties of the host polymer but also the properties of the guest molecules. Such effect is particularly relevant for active guests, like for instance molecules showing fluorescent, photochromic, photoreactive, non-linear optical properties and with rotatory optical power (chiral) , for which these properties are made anisotropic by the new kinds of orientation of the crystalline phase of said oriented films . Both new kinds of orientations can be easily detected by X-ray diffraction patterns, as collected by an automatic powder diffractometer . In particular, films with perpendicular orientation of the chain axes present a very strong reflection with Miller indexes (002) , characterized by a Bragg distance d = 3.87A, which for the case of CuK radiation is located at 2θαικα ~23 (Figure 1A) . This reflection is instead very weak, so that it is not easily detectable, in analogous X-ray diffraction patterns of films containing clathrate crystalline phases with preferential parallel orientation of the (010) crystalline planes with respect to the film plane or unoriented (Figures IB and IC, respectively) . Films with the orientation of the ( 210) crystalline planes preferentially parallel to the film plane present a very strong reflection with ( 210) Miller indexes, characterized by a Bragg distance d = 8.75A, which for the case of CuKα radiation is located at 2θcυκα ~ 10° (Figure ID) . For the two new kinds of orientation of the crystalline phase, the degree of orientation can be evaluated using Hermans 'orientation functions. In particular, for the perpendicular orientation of the chain axes, the orientation factor of the crystallographic axis c, with respect to the normal to the film plane, can be evaluated as: f_c =(3cos²y-l)/2 (1) where cos²7 is the average cosine squared value of the angle γ between the normal to the film surface and the chain axes of the different crystallites. For the ( 210) crystalline planes preferentially parallel to the film plane, the orientation factor of this crystallographic plane with respect to the film plane, can be evaluated as:

/. =(3cos^: 210 β-\)l2 (2)

where cos β is the average cosine squared value of the angle β between the normal to the film surface and the normal to the ( 210) crystalline plane of the different crystallites. In these assumptions, f_c or f ₂1₀ are equal to 1 if, for all crystallites which are present in the film, the chain axes are perpendicular to the film plane and the ( 210) crystallographic planes are parallel to the film plane, respectively. The orientation factors f_c or f ₂₁₀ are equal to 0 if the chain axes and the ( 210) crystallographic planes are completely unoriented, respectively. The quantities cos² γ and cos²/? can be easily experimentally evaluated, by using the following

wherein I (χoo₂) and I (χ ₂₁₀) are the intensity distributions of the (002) and ( 210) reflections on the

Debye rings as collected by sending the X-ray beam parallel to the film surface, and χ₀₀₂ and χ ₂ι_o are the azimuthal angles . The semicrystalline films object of the present invention are characterized by degrees of orientation which can be evaluated by Herman orientation factors in the range 0.2-1, preferably in the range 0.5-1. A further object of the present invention is a process for the production of syndiotactic polystyrene films with orientation of the chain axes of crystalline clathrate phases preferentially perpendicular to the film plane (that is to say the value of the Hermann's function is between 0,2 and 1, preferably between 0,5 -1) by solution crystallizations techniques, like for instance casting, spray-coating or spin-coating, which utilize solvents whose molecules are suitable guests of clathrate phases of syndiotactic polystyrene. For the described procedure, the molecular volume of the solvent has to be lower than 400 A³ and higher than 13θA³, preferably lower than 260 A³ and higher than 145A³. The molecular volume can be simply evaluated from the molar volume of the liquid at room temperature just divided by the Avogadro's Number. Preferred solvents for these casting, spray- coating or spin-coating procedures are trichloroethylene, tetrachloroethylene, ortho-dichlorobenzene, trichlorobenzene and their mixtures . The polymer concentration in the solution can be in the range 0.1-20 % by weight and preferably in the range 0.5-5%by weight.

^'The solutions can be prepared by the normal procedures to dissolve semicrystalline polymeric materials. The temperature of the process can be included in the range between -50°C and the boiling temperature of the solvent and preferably in the range between 0°C and 70°C. A further method to obtain syndiotactic polystyrene films with orientation of the chain axes of crystalline clathrate phases preferentially perpendicular to the film plane, which is a further object of the present invention, comprises the exposition of films based on syndiotactic polystyrene, presenting a degree of crystallinity lower than 5% (but able to crystallize at least up to a degree of crystallinity of 10%) , to solvents, the molecules of which are suitable guests of clathrate structures of syndiotactic polystyrene . Films of syndiotactic polystyrene with the orientation of the ( 210) crystalline plane preferentially parallel to the film plane can be obtained by treatments with ortho-xylene, 1, -dimethyl-naphthalene or their admixtures of films based on syndiotactic polystyrene, presenting a degree of crystallinity lower than 5% but able to crystallize at least up to a degree of crystallinity of 10%. A suitable film treatment corresponds to its immersion in liquid ortho-xylene at a temperature included in the range between -50°C and the boiling temperature of the solvent and preferably in the range between 0°C and 70°C. An additional suitable film treatment comprises the film exposition to vapors of ortho-xylene at a temperature included in the range between 0°C and the boiling temperature of the solvent, and preferably in the range between 20°C and 100°C. As indicated above, another suitable solvent to be used with the same procedure, is 1, 4 -dimethyl-naphtalene . Also mixtures of the two solvents may be used. The two new kinds of orientation of clathrate crystalline phases of syndiotactic polystyrene can also be maintained after known procedures leading to transitions between clathrate crystalline phases. As a consequence, it is possible to obtain films with the two new kinds of orientation for all clathrate phases of syndiotactic polystyrene. This corresponds to the achievement of two new kinds of orientation for all molecules of each guest, and hence leads to a higher control of electrical and optical properties of the guest molecules. The semicrystalline syndiotactic polystyrene films, with the two new kinds of orientation of clathrate crystalline phases show a content of guest molecules in the range 1-50% by weight and preferably in the range 5- 30% by weight. Films based on syndiotactic polystyrene presenting one of the crystalline phases which do not include guest molecules (the so called α, β, γ and δ phases) with one of the new kinds of orientation can be obtained by suitable procedures starting from the corresponding oriented clathrate crystalline phases. For instance, according the teaching of IT 1271842, films in the nanoporous δ form can be obtained by treatments with suitable solvents, or in gas steams, of films presenting clathrate crystalline phases and suitable solvents are, for instance, acetone and methyl- ethyl-ketone . Moreover, as described by the Italian Patent ITSA980008, particularly efficient are processes of extraction with carbon dioxide, liquid or in supercritical conditions . The two new kinds of orientation obtained for semicrystalline films presenting a crystallline clathrate phase of syndiotactic polystyrene can be also maintained after procedures leading to transitions between clathrate crystalline phases. In particular, it is possible to directly treat the film presenting the oriented clathrate phase with the new guest, both liquid or vapor.

An alternative procedure comprises the preliminary achievement of a film presenting the nanoporous δ phase with perpendicular orientation of the chain axes or with parallel orientation of the ( 210) crystalline plane preferentially parallel to the film plane and subsequently the treatment of such film by the desired guest . As a consequence it is possible to obtain both kinds of orientations for all clathrate forms of syndiotactic polystyrene. This technical achievement is useful since the molecular orientation can modify not only the properties of the host polymer but mainly the properties of the guest molecules. For instance, for the case of clathrates with aromatic hydrocarbons like, benzene, toluene, o-dichlorobenzene or naphthalene, the perpendicular orientation of the chain axes assures a preferential orientation of the planar guest molecules nearly parallel to the film plane, while parallel orientation of the ( 210) crystalline plane with respect to the film plane, assures a preferential orientation of the planar guest molecules nearly perpendicular to the film plane. This effect is particularly relevant for active guest molecules which can give to the film specific electrical or optical properties, like for instance molecules being fluorescent, photochromic, photoreactive, presenting non-linear optical properties or rotatory optical power (chiral) . Suitable molecules as guest of clathrate structures of syndiotactic polystirene are, for instance, halogenated compounds (chloroform, methylene chloride, carbon tetrachloride, dichloroethane, trichloroethylene, tetrachloroethane, dibromoethane, methyl iodide) , aromatic compounds (benzene, toluene, stirene) cyclic compounds (cycloesane, tetraidrofurane) as well as compounds containing sulfur, such as carbon sulfide. A further object of the present invention are devices which exploit the property to render anisotropic the properties of the guest molecules, said devices incorporating films of syndiotactic polystirene with the orientations produced according to the present invention. The following examples are supplied in order to illustrate the invention without limiting the scope thereof. EXAMPLE 1 Syndiotactic polystyrene homopolymer, supplied by

Dow Chemical under the trademark Questra 101, was dissolved into trichloroethylene (0.5% b.w. solution).

The solution was used in a casting procedure at room temperature and after the solvent evaporation a film having a thickness close to 40 μm was obtained. The thus obtained film presents a clathrate cystalline phase including trichloroethylene in amount close to 10% b.w. The thus obtained film presents a preferential orientation of the chain axes of the crystalline phase perpendicular to the film plane, as pointed out by the X- ray diffraction pattern obtained by a automatic powder diffractometer and shown in Figure 1A. In fact, in this diffraction pattern, the reflection with (002) Miller indexes located at 2θ_cuα -23° is definitely the most intense. This perpendicular orientation has been evaluated by an Herman orientation factor of 0.75. As a consequence of annealing processes at 170°C and 220 °C, it is possible to obtain films with α and γ crystalline phases, still presenting a preferential orientation of the chain axes of the crystalline phase perpendicular to the film plane, which have been evaluated by Herman orientation factors of 0.60 and 0.54, respectively. As for the film presenting the clathrate crystalline phase including as guest trichloroethylene, characterized by a perpendicular Herman's orientation factor of 0.75, the Fourier transform infrared absorbance spectrum (indicated by thick continue lines) is shown in Figure 2. In the same figure, for comparison, it is also shown the absorbance spectrum (indicated by thin continue lines) of the 50 μm film presenting the clathrate crystalline phase including trichloroethylene with orientation of its (010) crystalline planes preferentially parallel to the film plane, whose X-ray diffraction pattern is shown in Figure IB. The comparison between the spectra shows intensity variations of infrared peaks of vibrational modes both of the host polymer (Figure 2A) and of the trichloroethylene guest molecule (Figure 2B,C) . In fact, as for the polymer host, the film with perpendicular orientation of the chain axes, shows a higher intensity of the peaks at 1068 and 1169cm-l and a lower intensity of the peaks at 1278 e 1354 cm-1 (Figure 2A) . As for the trichloroethylene guest, the film with perpendicular orientation of the chain axes shows a higher intensity of the peaks 1250 and 1235 cm^"1 (Figura 2B) and a lower intensity of the peak at 455 cm^"1 (Figure 2C) . EXAMPLE 2 Syndiotactic polystyrene homopolymer in form of pellets, supplied by "Dow Chemical" under the trademark Questra 101, has been used. By melt extrusion, substantially amorphous films with a thickness of 180μm have been obtained. This film is immersed in liquid ortho-xylene at room temperature for 48 hours. After this treatment the film presents the crystalline clathrate phase including ortho-xylene, in a amount close to 15% by weight. This film presents the orientation of the ( 210) crystalline plane preferentially parallel to the film plane, which can be evaluated by a Herman orientation factor of 0.5. The presence of crystalline form with orientation of the ( 210) crystalline plane preferentially parallel to the film plane is pointed out by the X-ray diffraction pattern, obtained by an automatic powder diffractometer, which is shown in Figure ID and presents a high intensity of the ( 210) reflection at 2θ ~ 10.1° (for CuKα radiation) . EXAMPLE 3 Syndiotactic polystyrene homopolymer in form of pellets, supplied by "Dow Chemical" under the trademark Questra 101, has been used. By melt extrusion, substantially amorphous films with a thickness of lOOμm have been obtained. This film is exposed to chloroform vapors for 48 hours. After this treatment the film presents the crystalline clathrate phase including chloroform, in a amount close to 15% by weight. This film presents the orientation of the chain axes preferentially perpendicular to the film plane, which can be evaluated by a Herman orientation factor of 0.5. Trirefrangence measurements, obtained by using an Abbe refractometer "Atago 3T" with a rotatable film analyzer mounted on the eyepiece, indicate that the refractive index perpendicular to the film (nj_ =1.586) is definitely lower than that one parallel to the film (n|| =1.596) . EXAMPLE 4 Syndiotactic polystyrene homopolymer in form of pellets, supplied by "Dow Chemical" under the trademark Questra 101, has been used. By melt extrusion, substantially amorphous films with a thicknes of 80μm have been obtained. This film is immersed in tetraydrofurane for 4 hours. Subsequently the film is treated by supercritical C0₂ at a temperature of 40°C and at a pressure of 200 atm for 3 hours. The residual amount of tetraydrofurane in the film, as measured by thermogravimetry in the temperature range 40-200°C, is lower than 1% by weight. This film presents the nanoporous δ phase with orientation of the chain axes preferentially perpendicular to the film plane, which can be evaluated by a Herman orientation factor di 0.5.

Claims

CLAIMS 1. Semicrystalline films of syndiotactic styrene homopolymer or syndiotactic styrene copolymers with CH₂=CH-R olefins, where R is an alkyl-aryl or a substituted-aryl radical with 6-20 carbon atoms, having thickness in the range 0. lμm and 200μm, preferably in the range 0.5μm and 50μm, wherein the orientation of the chain axes of the crystalline phase is preferentially perpendicular to the film plane and the degree of perpendicular orientation, which can be evaluated by a Herman orientation factor, is in the range 0.2-1, preferably in the range 0.5-1. 2. Semicrystalline films of syndiotactic styrene homopolymer or syndiotactic styrene copolymers with CH₂=CH-R olefins, where R is an alkyl-aryl or a substituted-aryl radical with 6-20 carbon atoms, presenting a clathrate or a nanoporous phase for which the orientation of the crystalline ( 210) planes is preferentially parallel to the film plane and the degree of orientation, which can be evaluated by a Herman orientation factor, is in the range 0.2-1, preferably in the range 0.5-1. 3. Oriented semicrystalline films, as claimed in claims 1 and 2, showing one of the clathrate crystalline phases of syndiotactic polystyrene and including an amount of guest molecules in the range 1-50% by weight, preferably in the range 5-30% by weight. 4. Oriented semicrystalline films, as claimed in claims 1 to 3, where the guest molecules are chosen among the classes of fluorescent, photochromic, photoreactive molecules, of molecules presenting non-linear optical properties or rotatory optical power, wherein said properties are made anisotropic by the new kinds of orientation of the polymeric crystalline phase. 5. A process for the production of semicrystalline films as claimed in claim 1, wherein a polymer solution with concentration in the range 0.1-20 % by weight preferably in the range 0.5-5%by weight, in a solvent with molecular volume lower than 400 A³ and greater than 13θA³, preferably lower than 260 A³ and greater than 145A³, is cast or spray-coated or spin-coated at temperatures between -50°C and the boiling temperature of said solvent preferably between 0°C and 70°C. 6. The process according to claim 5, wherein said solvent is chosen from the class formed by trichloroethylene, tetrachloroethylene, ortho- dichlorobenzene, trichlorobenzene and their mixtures. 7. A process for the production of the semicrystalline films as claimed in claim 1, wherein a film based on syndiotactic polystyrene able to crystallize but with a degree of crystallinity lower than 5%, is exposed to solvents whose molecules are suitable as guest of clathrate structures of syndiotactic polystyrene. 8. A process for the production of semicrystalline films as claimed in claim 2, comprising treatments with ortho-xylene, 1, 4-dimethyl-naphthalene or their mixtures of films based on syndiotactic polystyrene, able to crystallize but with a degree of crystallinity lower than o^ . 9. Semicrystalline films, as claimed in claims 1 and 2, showing the nanoporous crystalline δ phase. 10. A process for the production of films based on syndiotactic polystyrene showing the nanoporous crystalline δ phase, as claimed in claim 9, which comprise a polymer processing from solution, as claimed in claims 6-8, to obtain a film which presents a clathrate crystalline phase, followed by a process of extraction of the guest molecules. 11. Devices which exploit the property to render anisotropic the properties of said guest molecules, containing films as claimed in claims 3 or 4.