RELEASE FILM FOR USE IN MANUFACTURING OF AN ELECTROLYTE MEMBRANE OR A MEMBRANE ELECTRODE ASSEMBLY

Abstract

The present invention relates to a laminate comprising (i) an ion exchange membrane comprising an ion exchange polymer, and (ii) a monolayered release film removably adhered to at least one side of the ion exchange membrane, wherein the monolayered release film comprises at least 95% by weight of syndiotactic polystyrene (sPS). The invention also relates to a method for producing the laminate, use of the monolayered release film in producing an electrolyte membrane or a membrane electrode assembly, and a method for producing an electrolyte membrane or a membrane electrode assembly.

Claims

1. A laminate comprising: an ion exchange membrane comprising an ion exchange polymer; and a monolayered release film removably adhered to at least one side of the ion exchange membrane, wherein the monolayered release film comprises at least 95% by weight of syndiotactic polystyrene (sPS).

2. A laminate comprising: an ion exchange membrane comprising an ion exchange polymer; and a monolayered release film removably adhered to at least one side of the ion exchange membrane, wherein the monolayered release film has a peel force equal to or less than 500 mN/cm using the herein described method for measurement, and a surface energy within the range of from 23 to 50 mJ/m.sup.2 using the herein described method for measurement.

3. A laminate according to claim 1, wherein the monolayered release film comprises a biaxially oriented syndiotactic polystyrene film.

4. A laminate according to claim 1, wherein the monolayered release film comprises syndiotactic polystyrene selected from at least one of: expanded syndiotactic polystyrene; unsubstituted syndiotactic polystyrene.

5. A laminate according to claim 1, wherein the monolayered release film comprises syndiotactic polystyrene having a weight average molecular weight within the range of from 100 000 to 300 000 g/mol.

6. (canceled)

7. A laminate according to claim 1, wherein the monolayered release film has a tensile modulus in at least one of the machine direction and the transverse direction within the range of from 2 000 to 5 000 MPa.

8. (canceled)

9. A laminate according to claim 1, wherein the monolayered release film has a tensile strength in at least one of the machine direction and the transverse direction of at least 50 MPa.

10. (canceled)

11. A laminate according to claim 1, wherein the laminate consists of the ion exchange membrane and the monolayered release film.

12. A laminate according to claim 1, wherein the ion exchange polymer is a fluoropolymer comprising a side chain having a sulfonic acid group.

13. A laminate according to claim 1, wherein the monolayered release film has an average thickness of less than 50 μm, such as within the range of from 25 to 45 μm.

14. A laminate according to claim 1, wherein the ion exchange membrane is an electrode membrane.

15. A laminate according to claim 1, the ion exchange membrane is an electrode assembly in which an electrode membrane is joined to each side of an electrolyte membrane.

16. A laminate according to claim 1, wherein the ion exchange membrane is an electrolyte membrane.

17. A laminate according to claim 16, wherein the ion exchange membrane is a reinforced electrolyte membrane.

18. A method for producing a laminate according to claim 1, comprising a step of applying the ion exchange membrane on the monolayered release film.

19. A method according to claim 18 wherein the step of applying the ion exchange membrane is carried out by a roll-to-roll processing.

20. A method according to claim 18, wherein the step of applying the ion exchange membrane comprises: applying a solution of the ion exchange polymer in a solvent on the monolayered release film thereby providing a wet coating of ion exchange polymer on the monolayered release film; and removing the solvent by drying thereby providing the ion exchange membrane.

21. A method according to claim 18, comprising applying a solution of the ion exchange polymer in a solvent on the monolayered release film thereby providing a wet coating of ion exchange polymer on the monolayered release film; applying a porous reinforcing material, such as expanded polytetrafluorethylene, onto the wet coating of ion exchange polymer; drying to remove solvent; applying additional solution of ion exchange polymer in said solvent onto the porous reinforcing material; and removing the solvent by drying thereby providing the ion exchange membrane.

22. (canceled)

23. (canceled)

24. A method for producing a membrane electrode assembly of a polymer electrolyte fuel cell comprising: providing a laminate according to claim 15; and separating the monolayered release film from the ion exchange membrane.

25. A method for producing an electrolyte membrane comprising: providing a laminate according to claim 16; and separating the monolayered release film from the ion exchange membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG. 1 illustrates an embodiment of a laminate as disclosed herein.

[0051] FIG. 2 shows peel strength (indicative of release characteristics) and surface energy (indicative of adhesion characteristics) for various plastic films, as measured using the herein described methods.

[0052] FIG. 3 illustrates the use of a monolayered release film in the production of a reinforced electrolyte membrane.

DETAILED DESCRIPTION

[0053] In the laminate as disclosed herein, the monolayered release film removably adhered to at least one side of the ion exchange membrane comprises at least 95% by weight of syndiotactic polystyrene (sPS).

[0054] By “removably adhered”, it is meant that in a laminate comprising a monolayered release film that is adhered to an ion exchange membrane, the monolayered release film can be removed from the ion exchange membrane without any damage or irreversible deformation occurring to the ion exchange membrane or the release film.

[0055] FIG. 1 illustrates an embodiment of a laminate 1 comprising an ion exchange membrane 2 and a monolayered release film 3 removably adhered to one side of the ion exchange membrane 2. The ion exchange membrane comprises an ion exchange polymer.

[0056] The monolayered release film of the laminate as disclosed herein comprises at least 95% by weight (based on the total weight of the film) of syndiotactic polystyrene (sPS) and within the range of from 0 to 5% by weight of additives, such as antioxidants, antistatic agents, agents enhancing the handleability of the film, agents modifying adhesiveness, agents improving extrusion properties, and/or agents improving conductivity.

[0057] The monolayered release film preferably consists of a chemically uniform (homogeneous) polymer composition, which means that the release film is uncoated and absent of any chemical surface modification.

[0058] The monolayered release film may have a density gradient and/or a crystallinity gradient along the thickness direction of the film. Such gradients provide a varying density and/or crystallinity of the film.

[0059] In embodiments, the monolayered release film may have an average thickness within the range of from 10 to 100 μm, such as from 10 to 50 μm, for example 12 μm, 25 μm, 35 μm or 50 μm. Preferably, the monolayered release film may have an average thickness of less than 50 μm, such as within the range of from 25 to 45 μm or from 25 to 40 μm.

[0060] In embodiments, the monolayered release film of the herein disclosed laminate may have a peel force equal to or less than 150 mN/cm (using the herein described method for measurement).

[0061] In embodiments, the monolayered release film of the herein disclosed laminate may have a surface energy within the range of from 23 to 50 mJ/m.sup.2 (using the herein described method for measurement), preferably within the range of from 25 to 45 mJ/m.sup.2 or 30 to 40 mJ/m.sup.2 (using the herein described method for measurement)

[0062] In embodiments, the monolayered release film of the herein disclosed laminate may have a tensile modulus in at least one of the machine direction and the transverse direction within the range of from 2 000 to 5 000 MPa (preferably within the range of from 2 500 to 4 000 MPa), a tensile strength in at least one of the machine direction and the transverse direction of at least 50 MPa, a peel force equal to or less than 150 mN/cm (using the herein described method for measurement) and a surface energy within the range of from 23 to 50 mJ/m.sup.2 (using the herein described method for measurement).

[0063] In embodiments, the monolayered release film of the herein disclosed laminate may have a tensile modulus in at least one of the machine direction and the transverse direction within the range of from 2 500 to 4 000 MPa, a tensile strength in at least one of the machine direction and the transverse direction of at least 100 MPa, a peel force equal to or less than 150 mN/cm (using the herein described method for measurement) and a surface energy within the range of from 25 to 45 mJ/m.sup.2 (using the herein described method for measurement).

[0064] In embodiments, the laminate consists of the ion exchange membrane and the monolayered release film. Thus, the laminate according to the invention is preferably a two layer laminate.

[0065] The monolayered release film has a front side (a first planar film surface) and a back side (a second planar film surface) opposite the front side. In the laminate, the front side of the monolayered release film is removably adhered to the ion exchange membrane and the back side of the monolayered release film is preferably non-covered (i.e. non-laminated and non-coated).

[0066] The front side may have a first surface roughness and the back side may have a second surface roughness, where the first and the second surface roughness are different. Preferably, the first surface roughness provides a smooth surface and the second surface roughness provides a rougher surface. A higher surface roughness of the back side of the release film provides less adhesion to the ion exchange membrane and thus a reduced risk for the electrolyte membrane to detach from support film due to adhesion between the back side of the release film and the electrolyte membrane.

[0067] For example, the front side of the monolayered release film may have a first surface roughness (arithmetical average roughness, Ra) of less than 0.10 μm and the back side of the monolayered release film may have a second surface roughness (Ra) of more than 0.05 μm. Particularly, the front side of the monolayered release film may have a first surface roughness (Ra) of less than 0.10 μm and the back side of the monolayered release film may have a second surface roughness (Ra) of equal to or more than 0.10 μm. Arithmetical average roughness, Ra, can be measured by the standard method ISO 4287:1997.

[0068] The monolayered release film may be formed by, for example, melt-extrusion. Some release films according to the present invention are commercially available, for example sPS films sold by the company Kurabo Industries Ltd, Japan, under the trademark Oidys®, such as Oidys® HNL and Oidys® HN.

[0069] The monolayered release film is preferably adjoined to (i.e. in direct contact with) the ion exchange membrane.

[0070] The ion exchange membrane laminated on the release film may be an electrolyte membrane, an electrode membrane or a membrane electrode assembly in which an electrode membrane is joined to each side of an electrolyte membrane.

[0071] In a particular embodiment, the ion exchange membrane is an electrolyte membrane, such as a polymer electrolyte membrane.

[0072] The on exchange membrane laminated on the release film may be a reinforced electrolyte membrane, such as a reinforced electrolyte membrane comprising a porous reinforcing membrane impregnated by an electrolyte. Thus, in a particular embodiment, the ion exchange membrane is a reinforced polymer electrolyte membrane

[0073] The laminate of the present disclosure can be obtained by coating a solution of a solution of an ion exchange polymer in a solvent on the monolayered release film, thereby providing a wet coating of ion exchange polymer on the monolayered release film, and thereafter removing the solvent by drying.

[0074] FIG. 3 illustrates a method for producing a reinforced polymer electrolyte membrane. The method comprises applying a solution of an ion exchange polymer in a solvent on a monolayered release film 4, thereby providing a wet coating 5 of ion exchange polymer on the monolayered release film 4. A reinforcing material 6, such as an ePTFE membrane, is then applied on the wet coating 5 and solvent is subsequently removed by drying. Additional solution of ion exchange polymer in a solvent may be applied in a second coating step. The solvent is removed in second drying step, thereby providing a laminate 7 of reinforced polymer electrolyte membrane (reinforced ion exchange membrane) 8 and monolayered release film 4. The monolayered release film 4 may then be removed and the reinforced polymer electrolyte membrane 8 may be used for producing a membrane electrode assembly.

[0075] The thickness of the ion exchange membrane containing the ion exchange polymer can be adjusted to the expected thickness by adjusting the concentration of the solution of the ion exchange polymer, or repeating coating and drying steps of an ion exchange polymer solution.

[0076] When the ion exchange membrane containing an ion exchange polymer is an electrolyte membrane for a polymer electrolyte fuel cell, an electrolyte solution such as a commercially available Nation® solution can be coated on the monolayered release film, followed by drying. Alternatively, a method of hot-pressing a solid polymer electrolyte membrane made separately to a release film may be used.

[0077] When the ion exchange membrane containing the ion exchange polymer is an electrode membrane for a polymer electrolyte fuel cell, a solution or dispersion containing a component of an electrode membrane (catalyst ink) can be coated on the release film, followed by drying.

[0078] When the ion exchange membrane containing the ion exchange polymer is a membrane electrode assembly for a polymer electrolyte fuel cell; as described above, an anode or cathode electrode membrane is formed on the release film, and then a polymer electrolyte membrane is joined to the electrode membrane by hot press and also the cathode or anode electrode membrane can be combined with the polymer electrolyte membrane. In the case of combining an electrode membrane with a polymer electrolyte membrane, a conventionally known method such as a screen printing method, a spray coating method or a decal method may be employed.

[0079] The ion exchange membrane is preferably a polymer electrolyte membrane for a polymer electrolyte fuel cell. Such an electrolyte membrane is not particularly limited as long as it has high proton (H.sup.+) conductivity and electrical insulating properties and also has air impermeability.

[0080] The polymer electrolyte membrane may have a thickness within the range of from 5 μm and 200 μm. However, since the thickness of the polymer electrolyte membrane exerts a large influence on resistance, the thickness of the polymer electrolyte membrane is generally set within a range from 5 μm to 50 μm, and preferably from 10 μm to 30 μm.

[0081] The laminate comprising an ion exchange membrane and a monolayered release film as disclosed herein may have a thickness within the range of from 15 μm to 2.00 μm, preferably from 15 μm to 100 μm (for example, 17 μm), and more preferably from 20 μm to 50 μm (for example, 22 μm), such as from 30 μm and 50 μm or from 35 μm and 50 μm (for example, 45 μm).

[0082] Suitable ion exchange polymers of the ion exchange membrane include, but are not limited to, fluorine-containing polymers including also sulfonic acid groups, carboxyl groups, phosphoric acid groups or phosphone groups. Typical examples of ion exchange polymers are perfluorinated sulfonic acid resins and perfluorinated carboxylic acid resins.

[0083] The ion exchange polymer of the polymer electrolyte membrane in the present invention is not limited to an entirely fluorine-based polymer compound. It may also be a mixture of a hydrocarbon-based polymer compound and an inorganic polymer compound, or a partially fluorine-based polymer compound containing both a C—H bond and a C—F bond in the polymer chain.

[0084] Specific examples of the hydrocarbon-based polyelectrolyte include polyamide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone or polyether, each having an electrolyte group such as a sulfonic acid group introduced therein, and a derivative thereof; polystyrene having an electrolyte group such as a sulfonic acid group introduced therein; polyamide, polyamideimide, polyimide, polyester, polysulfone, polyetherimide, polyethersulfone or polycarbonate, each having an aromatic ring, and a derivative thereof; polyether ether ketone having an electrolyte group such as a sulfonic acid group introduced therein; and polyetherketone, polyethersulfone, polycarbonate, polyamide, polyamideimide, polyester or polyphenylene sulfide, and a derivative thereof.

[0085] Specific examples of the partially fluorine-based polyelectrolyte include a polystyrene-graft-ethylene tetrafluoroethylene copolymer or a polystyrene-graft-polytetrafluoroethylene, each having an electrolyte group such as a sulfonic acid group introduced therein, and a derivative thereof.

[0086] Specific examples of the entirely fluorine-based polymer electrolyte film include Nation® film (manufactured by DuPont), Aciplex® film (manufactured by Asahi Kasei Corporation) and Flemion® film (manufactured by Asahi Glass Co., Ltd.), each being made of perfluoropolymers having a sulfonic acid group in the side chain.

[0087] The inorganic polymer compound may be a siloxane-based or silane-based organic silicone polymer compound, and in particular an alkylsiloxane-based organic silicone polymer compound, and specific examples thereof include polydimethylsiloxane and γ-glycidoxypropyltrimethoxysilane.

[0088] The ion exchange membrane may comprise one type of ion exchange polymer or two or more ion exchange polymers. In the embodiment of two or more ion exchange polymers, the polymers can be in a mixture or as separate layers.

[0089] Solvents that are suitable for use with the ion exchange polymers include, for example, alcohols, carbonates, THF (tetrahydrofuran), water, and combinations thereof.

[0090] The laminate of the present disclosure can be obtained by [0091] a) applying a solution of an ion exchange polymer in a solvent on the monolayered release film thereby providing a wet coating of ion exchange polymer on the monolayered release film; [0092] b) removing the solvent by drying thereby providing the ion exchange membrane on the monolayered release film.

[0093] The ion exchange membrane may further comprise a reinforcing material, such as a porous material (e.g. ePTFE membrane), fibrous materials or reinforcing particles. In one embodiment, the reinforcing material can be porous membrane. In another embodiment, the reinforcing material may comprise fibres or particles.

[0094] The porous membrane can be defined by a morphological structure comprising a microstructure of elongated nodes interconnected by fibrils which form a structural network of voids or pores. The porous membrane (e.g. expanded polytetrafluoroethylene (ePTFE)) may be substantially impregnated with said ion exchange polymer such that the interior volume of the porous membrane becomes substantially occlusive thereby rendering the membrane essentially air impermeable. The ion exchange polymer may also be present on one or both surfaces of the porous membrane.

[0095] The porous membrane may be an expanded polytetrafluoroethylene having a porous microstructure (e.g. pores having an average size of from about 0.05 to about 0.4 μm). The expanded polytetrafluoroethylene may have a porosity (void fraction) of greater than 35%, such as within the range of from 70 to 95%.

[0096] A solution containing an ion exchange polymer in a solvent may be applied to the reinforcing material by a conventional coating technique including forward roll coating; reverse roll coating, gravure coating, or doctor roll coating, as well as dipping, brushing, painting, and spraying so long as the liquid solution is able to penetrate the interstices and interior volume of the reinforcing material. Excess solution may be removed from the surface of the reinforcing material. The treated reinforcing material is then dried in an oven. Oven temperatures may range from 60° C. to 200° C., but preferably from 160° C. to 180° C. Additional application steps, and subsequent drying, may be repeated until the reinforcing material becomes completely transparent, which corresponds to the ion exchange membrane having a Gurley number of greater than 10,000 seconds. Typically, between 2 to 60 treatments are required, but the actual number of treatments is dependent on the concentration and thickness of the reinforcing material.

[0097] In embodiments; the ion exchange membrane comprises expanded polytetrafluoroethylene impregnated with an ion exchange polymer, such as a perfluoro sulfonic acid resin.

[0098] Alternatively, the laminate of the present disclosure can be obtained by a method as illustrated in FIG. 3 comprising the steps of: [0099] a) applying a solution of an ion exchange polymer in a solvent on the release film thereby providing a wet coating of ion exchange polymer on the release film; [0100] b) applying a porous reinforcing material (e.g. expanded polytetrafluoroethylene) onto the wet coating of ion exchange polymer; [0101] c) drying to remove solvent; [0102] d) applying additional solution of ion exchange polymer in said solvent onto the porous reinforcing material; and thereafter [0103] e) removing the solvent by drying, thereby providing the ion exchange membrane on the monolayered release film.

[0104] The electrode membrane for a polymer electrolyte fuel cell is not particularly limited as long as it contains catalyst particles and an ion exchange polymer. It is possible to use, as the ion exchange polymer, the polymer described for the above electrolyte membrane. The catalyst is usually made of a conductive material containing catalyst particles supported thereon. The catalyst particles may have a catalytic action on an oxidation reaction of hydrogen or a reductive reaction of oxygen, and it is possible to use, in addition to platinum (Pt) and other noble metals, cobalt, iron, chromium, nickel, or alloys thereof. The conductive material is suitably carbon-based particles, for example, carbon black, activated carbon and graphite, and fine powdered particles are used particularly suitably. Typical examples thereof include those obtained by supporting noble metal particles, for example, Pt particles and alloy particles made of Pt and other metals on carbon black particles having a surface area of 20 m.sup.2/g or more. Regarding a catalyst for an anode, since Pt is inferior in resistance to poisoning of carbon monoxide (CO), alloy particles made of Pt and ruthenium (Ru) are preferably used when a fuel containing CO such as methanol is used. The ion exchange polymer in the electrode membrane is a material which serves as a binder that supports a catalyst to form an electrode membrane, and forms a passage through which ions generated by the catalyst migrate. It is possible to use, as an ion exchange polymer, the materials described previously in relation to the solid polymer electrolyte membrane. The electrode membrane is preferably porous so that fuel, such as hydrogen or methanol, can be contacted with the catalyst as much as possible in an anode, whereas, an oxidizing agent gas such as oxygen or air can be contacted with the catalyst as much as possible in a cathode. It is suitable that the amount of the catalyst contained in the electrode membrane is within a range from 0.01 to 4 mg/cm.sup.2 and preferably from 0.1 to 0.6 mg/cm.sup.2.

Example 1

Production of Laminate Made of Ion Exchange Membrane on Monolayered Release Layer

[0105] The ion exchange membranes were fabricated by two times coating processes by bar coater (K202 Control coater, RK Print Coat Instrument Ltd.) and an annealing process in an oven.

[0106] Biaxially oriented expanded PTFE membrane (ePTFE) having an area density of about 3-6 g/m.sup.2 was first impregnated with an ionomer solution, such as Nafion® ionomer solution (commercially available by the company DuPont, USA), provided on a releasable support film of various monolayered polymer films (see Table 1) using Mayer bar #5. The wet ePTFE and polymer film was immediately dried in an oven at 160° C. for 3 minutes (1st pass) to remove the solvents (ethanol and water).

[0107] The membranes were then impregnated again with the ionomer solution using Mayer bar #4 at room temperature and dried in the oven at the same temperature for 3 minutes (2.sup.nd pass).

[0108] The membranes were finally annealed without further coating in the oven at the same temperature for 3 minutes (3.sup.rd pass). The thickness of the final ion exchange membranes was about 10 μm.

Measurement of Peel Strength

[0109] The peel strength was measured by a 90 degree peel test (ASTM D6862 except for modified sample size and peel speed) using a tensile tester (AG-I, Shimadzu Corp.). First, the ion exchange membrane on monolayered release films of various polymer films (see Table 1) was cut into 20 mm width and 150 mm length by a cut stamp. The release film side was stuck on a Bakelite board with a double-stick tape. The board was set on a tensile testing jig with rolls which automatically slides the board during peeling. The jig was attached on the base of the tensile tester. One side of the membrane was clutched by chuck of the tensile tester. The membrane was peeled off of the release film by pulling up the chuck at the speed of 15 mm/min and the peel force was recorded. The peel strength was calculated as the average value of three measurement points from 10 mm to 50 mm distance.

Measurement of Surface Energy

[0110] The surface energy of the various polymer films as release film was determined by a two-component model including measuring contact angles with water and diiodomethane, respectively.

[0111] Each polymer film was provided on a glass plate and put into a contact angle measurement device (DM-501, Kyowa Interface Science Co., Ltd). 2.0 μL of the solvent (water or diiodomethane) was dropped from the needle of the device (tefloncoat22G). The contact angle was detected 1500 ms later from dropping with the θ/2 method (see Yang et al, “A method for correcting the contact angle from the θ/2 method”, Colloids and Surfaces A: Physiochemical and Engineering Aspects, volume 220, issues 1-3, 20 Jun. 2003, pages 199-210, DOI: 10.1016/S0927-7757(03)00064-5). The surface energy of the plastic film was determined using the Kaelble-Uy theory (D. H. Kaelble (1970) Dispersion-Polar Surface Tension Properties of Organic Solids, The Journal of Adhesion, 2:2, 66-81, DOI: 10.1080/0021846708544582).

Results

[0112] Peel strength and surface energy for the various polymer films, as measured using the herein described methods, are shown in Table 1. The peel strength versus surface energy are also shown in FIG. 2 (except for PBT and PP). The film thickness values in Table 1 have either been measured by thickness gauge or it is the thickness provided in product data sheet by the supplier.

TABLE-US-00001 TABLE 1 Thickness of monolayered Peel Surface Tradename release film strength, energy Polymer (supplier) [μm] [mN/cm] [mJ/m.sup.2] PI UPILEX (UBE) 25 72 50 PEN Teonex (JTS) 16 365 44 PET Lumirror (TORAY) 50 450 43 PPS Torelina (TORAY) 50 237 38 COP Zeonor (Zeon) 50 80 38 COC TOPAS (Toyobo) 50 75 34 sPS Oidys HNL (Kurabo) 35 53 32 sPS Oidys HN (Kurabo) 35 67 32 PBT PBT (Goyoshiko) 40 1 402 32 PP CP (Mitsui Chemicals Tohcello) 47 3 000 30 PMP TPX (Mitsubishi chemical) 50 28 24 ETFE Aflex (AGC) 51 28 20 COC (Daicel Value Coating) 50 75 34 (top layer)/ PET(base layer)

[0113] The two sPS films tested (Oidys® HNL and Oidys® HN supplied by Kurabo) were found to have the required release and adhesion characteristics to be advantageous for use as monolayered releasable support film (monolayered release film).

[0114] Also, the sPS films exhibit chemical and heat resistance as required.

[0115] Moreover, the sPS films have the required mechanical strength to be advantageous for use as releasable support film. Table 2 includes data provided by supplier (measured using method JIS K7127).

TABLE-US-00002 TABLE 2 Tensile strength [MPa] Tensile modulus [MPa] Tensile elongation [%] Machine Transverse Machine Transverse Machine Transverse direction direction direction direction direction direction Oidys ® 100 120 3 400 3 700 40 40 HNL Oidys ® 110 110 3 200 3 100 55 65 HN

[0116] The weight average molecular weight of the syndiotactic polystyrene of Oidys® HNL was measured according to the High temperature GPC (Gel permeation chromatography) method using the measurement device HLC-8321GPC/HT (Tosoh corporation). 20 ml o-dichlorobenzene (including 0.025% BHT) was added to 20 mg of sample (sPS film). The sample was shaken and dissolved at 145° C. The dissolution was thereafter thermally filtered by using a sintered filter (1.0 μm pore size) and the filtrate was then analysed. The syndiotactic polystyrene of Oidys® HNL was found to have a weight average molecular weight of about 177 000 g/mol.