1. Field of the Invention
The invention relates to a polymer alloy comprising a brittle polymer and either a ductile polymer, a rubbery polymer, or a ductile polymer and a rubbery polymer. More particularly, the invention pertains to a polymer alloy comprising at least a brittle polymer component having a weight average molecular weight greater than 180,000 and a plasticizer in an amount greater than 0.4 weight percent. The polymer alloy gives improved toughness with excellent transparency and/or improved low haze with improved toughness and stiffness.
2. Background Art
It is known in the art that some physical properties of styrenic or acrylic type polymers may be improved by alloying them with one or more additional polymers. In some cases, the resulting mixture can have improved mechanical properties, such as improved impact strength or toughness. However, as impact strength or toughness is improved, the stiffness of the alloy usually is decreased.
Chemical Abstracts 109:171278v [Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1988, 29(2), 180-1] discloses that physical blends of block SBR (styrene content: 75.2 weight percent) and a copolymer of methyl methacrylate and styrene are mechanical properties of the blend are partially compatible. The morphological and mechanical properties of the blend are strongly dependent on the molding/mixing process used to produce the blend. The SBR could only be toughened when the ideal morphology of the blend was obtained.
Chemical Abstracts 106:85901z [JP 61/200,151] discloses thermoplastic compositions comprising from 5 to 95 weight percent of a block copolymer and from 95 to 5 weight percent of a thermoplastic polymer (e.g. ABS). The block copolymer is derived from coupling an aromatic vinyl polymer block with an aromatic vinyl monomer-conjugated diene copolymer block. The subject thermoplastic compositions apparently have improved impact strength.
Chemical Abstracts 112:8285y [JP 61/291,610] discloses the use of xe2x80x9cimpact modifiersxe2x80x9d for thermoplastic polymers. The modifiers are basically similar to the block copolymer disclosed by Chemical Abstracts 106:85901z.
Chemical Abstracts 99:196070j [JP 58/122,954] discloses improvement of anisotropy of a styrene hydrocarbon-conjugated diene block copolymer by blending it with a styrene-methacrylic ester copolymer. Such a blend, when extruded to form a molded plate, apparently possesses superior physical properties.
Chemical Abstracts 111:8522c [JP 01/45614] discloses high-impact styrene polymer compositions comprising a major amount of a styrene (50 to 90 weight percent)-conjugated diene (50 to 10 weight percent) block copolymer and a minor amount of a styrene-based polymer (e.g. styrene-methyl methacrylate copolymer).
U.S. Pat. No. 5,290,862, assigned to the same assignee as that of the present invention, discloses a polymer alloy comprising (i) from 30 to 82 weight percent of a brittle polymer; (ii) from 3 to 50 weight percent of a rubbery polymer; and (iii) from 15 to 67 weight percent of a ductile polymer which is compatible with the rubbery polymer. The polymer alloy possesses a combination of improved properties, including improved impact strength. Typically these alloys have a Notched IZOD impact strength of greater than 0.5 foot pound/inch, preferably greater than 1.0 foot pound/inch, and may have a haze of less than 10, most preferably less than 5. The brittle polymer generally may have a molecular weight of about 220,000.
Even though the polymer alloy of the above U.S. Pat. No. 5,290,862 is adequate for certain end use applications, such as patio tumblers, requiring extremely low haze and good impact resistance, some critical applications may require a polymer alloy material with improved low haze with improved toughness and stiffness and/or improved toughness with excellent transparency.
The invention has met the above need. The invention provides an improved tough and transparent polymer alloy comprising:
from 90 to 20 weight percent of a brittle polymer;
from 0 to 60 weight percent of a rubbery polymer; and
from 0 to 80 weight percent of a ductile polymer whereby the ductile polymer and the rubbery polymer are compatible; and
greater than 0.4 weight percent of a plasticizer.
The brittle polymer has a weight average molecular weight greater than 180,000. In a first embodiment, the weight average molecular weight is greater than 220,000, preferably ranging between 270,000 and 300,000, and most preferably is 280,000. In a second embodiment of the invention, the weight average molecular weight ranges between about 190,000 and 300,000; and preferably ranges between 195,000 and 270,000. Both the first and the second embodiments comprise the brittle polymer and the plasticizer and either the rubbery polymer or the ductile polymer or both.
The polymer alloy of the first embodiment is comprised of from about 80 to 20 weight percent, preferably from about 70 to about 40 weight percent, and most preferably, about 50 to about 55 weight percent of the brittle polymer; from 0 to about 3 weight percent, and more preferably, 0 weight percent of the rubbery polymer; from about 20 to 80 weight percent, preferably from about 30 to 60 weight percent, and most preferably about 50 to about 45 weight percent of the ductile polymer; and from about 0.5 to about 3.0 weight percent, preferably from about 1 to about 2 weight percent, and most preferably about 1.5 weight percent of plasticizer.
The polymer alloy of the second embodiment is comprised of from about 80 to 20 weight percent, preferably from about 70 to 50 weight percent, and most preferably, from about 65 to about 55 weight percent of the brittle polymer; from about 5 to about 60 weight percent, preferably from about 5 to about 20 weight percent, and most preferably from about 8 to about 12 weight percent of the rubbery polymer; from about 0 to about 60 weight percent, more preferably from about 20 to about 40 weight percent; and most preferably from about 25 to about 35 weight percent of the ductile polymer; and greater than 0.4 weight percent, more preferably from about 0.5 to about 3.0 weight percent, and most preferably from about 0.7 to about 1.5 weight percent of the plasticizer.
The brittle polymer preferably is a copolymer of a styrene and methyl methacrylate and preferably, the plasticizer is mineral oil. The plasticizer can be part of any one of the polymers comprising the polymer alloy or it can be blended along with the polymers to form the polymer alloy of the invention. Preferably, the plasticizer is part of the brittle polymer and resides in the brittle polymer prior to the brittle polymer being blended with the other polymer components of the polymer alloy of the invention.
The ductile polymer preferably is a styrene butadiene block copolymer and may be present in the polymer alloy in an amount ranging from about 30 to about 60 weight percent. Preferably, the butadiene is present in this styrene butadiene block copolymer in an amount ranging between 20 to 35 weight percent, preferably from about 24 to about 26 weight percent, and more preferably, about 25 weight percent.
The rubbery polymer preferably is a styrene butadiene block copolymer having 55 to 70 weight percent butadiene.
The polymer alloys of the invention have improved low haze with improved toughness and stiffness and/or improved toughness with excellent transparency. For the first embodiment, when the indices of refraction of the different phases of the polymer alloy formed by the polymers and the plasticizer are matched within a + or xe2x88x920.005, the haze will be less than 5%; when matched within a + or xe2x88x920.002 the haze will be less than 3%, and more preferably the haze will be less than 1.5%. For the second embodiment, when the indices of refraction of the different phases of the polymer alloy formed by the polymers and the plasticizer are matched within a + or xe2x88x920.005, the haze will be less than 10%; when matched within a + or xe2x88x920.002 the haze will be between 1% and 4%.
The polymer alloy of the invention has a Notched IZOD impact strength ranging between about 1.0 to about 6.0, and preferably, ranging between about 2.0 and 4.5 foot pound per inch measured according to ASTM D-256.
These and other objects of the invention will be better appreciated and understood by those skilled in the art from the following description and appended claims.
The polymer alloy of the present invention is an improvement of the polymer alloy described and claimed in the aforesaid U.S. Pat. No. 5,290,862, the teachings of which are incorporated herein by reference.
As used in this specification, the term xe2x80x9cbrittlexe2x80x9d means a polymer having an elongation at break up to 15%, preferably less than 10%, as measured by ASTM D-638. The term xe2x80x9cductilexe2x80x9d means a polymer having an elongation at break greater than 15%, as measured by ASTM D-638. The term xe2x80x9crubberyxe2x80x9d means a natural or synthetic polymer, which at room temperature can be stretched to at least twice its original length, and upon immediate release of the stress, will return to its approximate original length. The term xe2x80x9ccompatiblexe2x80x9d means two or more polymers that have good interfacial adhesion (for example, the blended polymers exhibit physical properties approximating those expected from the rule of mixtures). The term xe2x80x9cmisciblexe2x80x9d means two or more polymers which, when blended form a single phase that remains clear, even if the refractive indices of the polymers do not match.
The polymer alloy of the invention is comprised generally of a brittle polymer with a weight average molecular weight greater than 180,000; a rubbery polymer; and/or a ductile polymer; and a plasticizer in an amount greater than 0.4 weight % based on the total weight of the polymer alloy and preferably residing in the brittle polymer.
The brittle polymer used in the improved polymer alloy of the invention may be selected from the group of polymers consisting of polymers comprising:
(i) from 80 to 45 weight percent of one or more C8-12 vinyl aromatic monomers which are unsubstituted or substituted by a C1-4 alkyl radical;
(ii) from 20 to 55, weight percent of one or more C1-6 alkyl esters of C3-6 ethylenically unsaturated carboxylic acids; and
(iii) from 0 to 5 weight percent of one or more C3-6 ethylenically unsaturated carboxylic acids or anhydrides.
The C8-12 vinyl aromatic monomer suitable for use in the brittle polymer component is not particularly restricted and may be unsubstituted or substituted by a C1-4 alkyl radical. Preferably, the C8-12 vinyl aromatic monomer is selected from the group comprising styrene, xcex1-methyl styrene, p-methyl styrene and t-butyl styrene. The preferred C8-12 vinyl aromatic monomer is styrene.
The choice of C1-6 alkyl ester of a C3-6 ethyenically unsaturated carboxylic acid for use in producing the brittle polymer is not particularly restricted. Non-limiting suitable examples of alkyl esters include acrylic ester, methyl methacrylate, methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate and butyl methacrylate. The preferred alkyl ester is methyl methacrylate.
A brittle polymer suitable for use in the polymer alloy of the invention is a copolymer of styrene and methyl methacrylate (SMMA). Preferably, such a copolymer comprises from about 80 to about 45 weight percent, preferably from about 80 to about 65 weight percent, styrene, and from about 20 to about 55 weight percent, preferably from about 20 to about 35 weight percent, methyl methacrylate (MMA). Such a copolymer is commercially available from NOVA Chemicals Inc. under the trademark NAS 90.
The production of a brittle polymer suitable for use in the polymer alloy of the present invention is within the purview of a person skilled in the art. Such polymers may be produced by suspension, solution, emulsion, or bulk polymerization. This brittle polymer may be made in a reactor in which the plasticizer, especially if mineral oil, can also be added.
The brittle polymer suitable for use in the polymer alloy of the present invention has a weight average molecular weight greater than 180,000. In a first embodiment, the weight average molecular weight of the brittle polymer is greater than 220,000, preferably between about 270,000 to about 300,000, and most preferably about 280,000. In the second embodiment, the weight average molecular weight of the brittle polymer is greater than 180,000, preferably between about 190,000 and 300,000, and most preferably between about 195,000 and 270,000. In some end-use applications, the weight average molecular weight may be as high as 400,000.
The method for producing a polymer alloy with molecular weights of this magnitude are well known to those skilled in the art. For example, a desired molecular weight can be obtained by varying the conditions of the reactor in which the brittle polymer is polymerized, i.e. temperature, amount and type of initiator, and the type of polymerization process.
The inventors have found that by increasing the weight average molecular weight of the brittle polymer, and by adding a plasticizer, such as mineral oil, to the polymer alloy of the invention, very little or no rubbery polymer or ductile polymer may be needed in the polymer alloy in order to provide a tough, transparent high impact alloy with an acceptable Notched IZOD value and with very little haze. More specifically, the inventors have found that the combination of increasing the weight average molecular weight of the brittle polymer and adding the plasticizer to the polymer alloy increases 1) the efficiency of the rubbery and/or ductile components and 2) the toughness of the polymer alloy when compared to only increasing the molecular weight of the brittle polymer. This improved efficiency of the rubbery and ductile polymers allows lower amounts of these components to be used in the polymer alloy of the invention or allows one of these components to be eliminated from the polymer alloy of the invention. Thus, the negative effects which are usually associated with high amounts of these two components, which relate to xe2x80x9chazexe2x80x9d and/or xe2x80x9cstiffnessxe2x80x9d of the polymer alloy are lessened or decreased.
In a broad aspect of the invention, the brittle polymer is used in the polymer alloy in an amount from 90 to 20 weight percent, based on the total weight of the polymer alloy. In the first embodiment, this amount will range from about 80 to 20 weight percent, more preferably from about 70 to 40 weight percent, and most preferably, from about 50 to about 55 weight percent, based on the total weight of the polymer alloy, and the weight average molecular weight is greater than 220,000, more preferably between 270,000 and 300,000, and most preferably, is about 280,000.
In the second embodiment, the amount of brittle polymer ranges between about 80 to 20 weight percent, more preferably, 70 to 50 weight percent, and most preferably, from about 65 to about 55 weight percent, based on the total weight of the polymer alloy, and the weight average molecular weight is greater than 180,000, more preferably is between about 190,000 and 300,000, and most preferably, ranges between about 195,000 and 270,000.
Preferably, the ductile polymer of the polymer alloy ranges between about 0 to about 80 weight percent. This ductile polymer preferably is derived from 65 to 80 weight percent of one or more C8-12 vinyl aromatic monomers; and 35 to 20 weight percent of one or more C4-6 conjugated diolefins.
A ductile polymer suitable for use in the polymer alloy of the present invention is a tapered, linear or radial di-block (vinyl aromatic monomer-conjugated diene) or tri-block (vinyl aromatic monomer-conjugated diene-vinyl aromatic monomer) copolymer. The production of such copolymers is known to those skilled in the art. Such polymers can be produced by living solution polymerization (e.g. using a lithium catalyst). Examples of suitable ductile polymers for use in the present invention are available from Chevron-Phillips, Kraton, and AtoFina.
In the first embodiment, the ductile polymer of the polymer alloy ranges from between 20 to 80 weight percent, preferably from between 30 to 60 weight percent, and most preferably, is about 45 to 50 weight percent. In the second embodiment, the ductile polymer of the polymer alloy ranges between 0 to 60 weight percent, preferably between 20 to 40 weight percent, and most preferably ranges between 25 to 35 weight percent.
The rubbery polymer of the polymer alloy broadly ranges between about 0 to about 60 weight percent based on the total weight of the polymer alloy. This rubbery polymer preferably is derived from 30 to 45 weight percent of one or more C8-12 vinyl aromatic monomers and from 70 to 55 weight percent of one or more C4-6 conjugated diolefins.
A rubbery polymer suitable for use in the present polymer alloy may be a linear, tapered, or radial di-block (aromatic vinyl monomer-conjugated diene) or a tri-block copolymer (vinyl aromatic monomer-conjugated diene-vinyl aromatic monomer). As is known in the art, a tapered di-block copolymer is a copolymer comprising a block which becomes progressively rich in one of the constituent monomers in a segment (typically, the end) of the block.
The process by which such a tapered copolymer is obtained is similar to the process by which block copolymers are obtained except that there is an incremental adjustment in the monomer feed (e.g. richer or poorer in vinyl aromatic/conjugate diolefin) to produce a block polymer which is xe2x80x9ctaperedxe2x80x9d. Examples of suitable rubbery polymers for use in the present polymer alloys are commercially available from Ato-Fina, Dexco Polymers, and Firestone Synthetic Rubber and Latex Company.
In the first embodiment, the amount of rubbery polymer more preferably, ranges from about 0 to about 3 weight percent, most preferably, 0 weight percent, based on the total weight of the polymer alloy. In the second embodiment, the amount of rubbery polymer ranges from about 5 to about 60 weight percent, more preferably, from about 5 to about 20 weight percent, and most preferably, from about 8 to 12 weight percent, based on the total weight of the polymer alloy.
Suitable C8-12 vinyl aromatic monomers for use in the ductile polymer and the rubbery polymer of the present invention are not particularly restricted and may be unsubstituted or substituted by a C1-4 alkyl radical. Preferably, the C8-12 vinyl aromatic monomer is selected from the group comprising styrene, xcex1-methyl styrene, p-methyl styrene and t-butyl styrene. A preferred C8-12 vinyl aromatic monomer is styrene. Generally, the ductile polymer will contain a larger amount of vinyl aromatic monomer, typically in the range from 65 to 80 weight percent; and the rubbery polymer will contain lower amounts of vinyl aromatic monomer, typically in the range 30 to 45 weight percent.
The C4-6 conjugated diolefin suitable for use in the ductile polymer and the rubbery polymer of the polymer alloy of the present invention is not particularly restricted and may be unsubstituted or substituted by a chlorine atom. Preferably, the C4-6 conjugated diolefin is selected from the group comprising 1,3-butadiene and isoprene. The preferred diolefin, particularly for the ductile polymer is butadiene. Thus, the preferred ductile polymer is a styrene butadiene block copolymer. The preferred diolefin particularly for the rubbery polymer is butadiene, and thus the preferred rubbery polymer is a styrene butadiene block copolymer. Generally, the amount of the C4-6 conjugated diolefin in the rubbery polymer will range from about 55 to about 70 weight percent based on the total weight of the rubbery polymer. The amount of the C4-6 conjugated diolefin in the ductile polymer will range from about 20 to about 35 weight percent, based on the total weight of the ductile polymer.
If a rubbery polymer and the ductile polymer are both used in the polymer alloy of the present invention, then the rubbery and ductile polymers should at least be compatible. Preferably, the polymers will be miscible, as defined herein.
The plasticizer is used in the polymer alloy of the invention in an amount greater than 0.4 weight percent based on the total weight of the polymer alloy. More specifically, the amount of plasticizer used in the polymer alloy of the first embodiment will range from about 0.5 to about 3.0 weight percent, more preferably between about 1.0 to about 2.0 weight percent, and most preferably, about 1.5 weight percent. The amount of plasticizer used in the polymer alloy of the second embodiment will be greater than 0.4, preferably from about 0.5 to about 3.0 weight percent, most preferably between about 0.7 to about 1.5 weight percent.
The plasticizer is not particularly limited and a suitable plasticizer may be selected from conventional plasticiziers used for thermoplastic acrylic resins as taught in U.S. Pat. No. 6,280,835. For example, plasticizers having good compatibility with the brittle polymer, the rubbery polymer, and the ductile polymer of the invention can be used. Examples of such plasticizers include alkyl benyzl phthalates, such as octyl benzyl phthalate and myristyl benzyl phthalate; dialkyl phthalates, such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; esters of phosphoric acid, such as tricresyl phosphate and trioctyl phosphate; esters of fatty acids, such as dibutyl sebacate and acetyl tributyl citrate; polyesters, such as polyesters derived from adipic acid, polyesters derived from sebacic acid, and polyesters derived from phthalic acid; derivatives of glycols, such as diethylene glycol dibenzoate, dipropylene glycol dibenzoate, and triethylene glycol di(2-ethylhexoate; derivatives of glycerol, such as glycerol triacetate and glycerol tributyrate; and epoxy derivatives, such as epoxidized soy bean oil.
The plasticizer may be selected from the group consisting of mineral oil, vegetable oil, animal oil, synthetic oil, silicone oil, and fluorinated oil. Preferably, the plasticizer used in the invention is mineral oil.
The plasticizer can be part of any one of the polymers comprising the polymer alloy or it can be blended along with the polymers to form the polymer alloy of the invention. That is, the plasticizer can be added to any of the polymers during its production or it can be compounded into any of the polymers in a separate step or it can be compounded along with the polymers during the production of the polymer alloy of the invention or it can be added using a combination of these methods. Preferably, the plasticizer is blended with the brittle polymer, more preferably the plasticizer is added during the production of the brittle polymer, and preferably, the plasticizer resides in the brittle polymer when the brittle polymer is added to or compounded with the rubbery polymer and/or the ductile polymer to form the polymer alloy.
The rubbery and ductile phases are at least compatible. That is, these components of the polymer alloy of the invention will have good interfacial adhesion. Under stress they will not delaminate. Preferably, the rubbery and ductile components are miscible. That is, when blended they will form a clear component, whether or not their refractive indices are matched or close.
The components of the polymer alloy, i.e. the brittle polymer, the rubbery polymer, the ductile polymer and the plasticizer, constitute different phases within the polymer alloy. Preferably, only two different phases will be formed. The amounts of these components in each phase will preferably be optimized so that the refractive indices of the different phases match each other. The refractive index of the polymer alloy of the invention will depend on the reflective indices of the individual polymers and on the ratio of the individual polymers in the polymer alloy. Likewise, the refractive index of each phase will depend on the refractive indices of the individual polymers and on the ratio of the individual polymers within each phase.
The plasticizer, particularly if the plasticizer is mineral oil can easily migrate phase to phase depending on the amount and nature of the individual polymers. This migration will affect the apparent refractive index of each phase. This migration of the plasticizer has to be taken into account in order to get the refractive indices of the phases each composed of several components, to match. By measuring the haze of various formulations, the nature of the migration can be understood and used to develop the clearest formulations, i.e. formulations that create the best clarity and lowest haze.
As taught herein above, the brittle polymer, the ductile polymer, and the rubbery polymer are preferably copolymers, i.e. consisting of more than one monomer. The refractive index of a copolymer depends on the ratio of the individual monomers in the copolymer. In this instance, adjustments can be made to the refractive index of either phase by changing the copolymer ratio during polymerization, if feasible, or by blending like copolymers of different ratios, if they are miscible. In this way, clear blends with a balance of toughness, stiffness and impact resistance can be obtained.
For the first embodiment of the invention, when the refractive indices of the different phases of the polymer alloy match within + or xe2x88x920.005, the material will be transparent with a haze less than 5%. When the refractive indices of the different phases of the polymer alloy match within + or xe2x88x920.002, the material will have excellent clarity and a very low haze less than 3%, preferably less than 1.5%.
For the second embodiment, when the refractive indices of the different phases of the polymer alloy match within + or xe2x88x920.005, the material will be transparent with a haze less than 10%. When the refractive indices of the different phases match within + or xe2x88x920.002, the material will have a very low haze preferably between 1% and 4%.
The polymer alloy of the invention has a Notched IZOD impact strength ranging between about 1.0 to about 6.0, and preferably, ranging between about 2.0 and 4.5 foot pound per inch measured according to ASTM D-256.
The above is not intended to place any limitation on the order of mixing the polymers. It is not necessary to have a specific sequenced addition of polymers to the mixer.
In preparing the polymer alloy of the present invention, solution blending of the components is generally not useful, as it is difficult to find a common solvent for each polymer in the blend. As stated herein above, preferably, the plasticizer is blended with the brittle polymer prior to the brittle polymer being blended with the other polymers and the plasticizer resides in the brittle polymer when the brittle polymer is blended or mixed with the other polymers of the polymer alloy. Typically, adequate mixing of the several polymers of the polymer alloy of the invention can be achieved by mechanical mixing in a suitable intensive mixer, preferably a single screw or twin screw extruder. If a single screw extruder is used, it should preferably be equipped with a modified mixing section to ensure adequate mixing of the components. Examples of common modified mixing sections are the Maddock mixing head and various designs from the Spirex Company such as the xe2x80x9cZ-mixerxe2x80x9d.
Operation of an extruder to achieve this end is within the purview of a person skilled in the art. For example, for an inch and a half extruder having an L to D ratio of about 24:1, the extruder is operated at from 30 to 150, preferably from 50 to 135, most preferably from 75 to 100, RPM. During such operation, the barrel temperature of the extruder is in the range of from 190 to 240xc2x0 C., preferably from 200 to 220xc2x0 C.
Both the ductile polymer and the rubbery polymer may be individually fed to the extruder. Alternatively they may be mixed together and then fed to the extruder, or mixed together and then extruded, and then chopped into pellets. The resulting pellets may then be extruded with the brittle polymer that contains the mineral oil. However, the components of the polymer alloy of the present invention may also be dry-blended in, for example, a tumbler blender and then extruded. In an alternative procedure, the polymers may be fed directly to an extruder using loss-in-weight feeders for accurate composition control. As is common for twin screw extrusion, some of the polymers and/or the plasticizer may be accurately metered into the extruder downstream of the main feed zone.
In a broad aspect of the invention, the brittle polymer will range from about 20 to 90 weight percent with a weight average molecular weight greater than 180,000 and comprising from 80 to 45 weight percent of one or more C8-12 vinyl aromatic monomers (preferably, styrene) and from 20 to 55 weight percent of one or more C1-6 alkyl esters of C3-6 ethylenically unsaturated carboxylic acids (preferably, methyl methylacrylate (MMA)) and from 0 to 5 weight % of one or more C3-6 ethylenically unsaturated carboxylic acids or anhydrides; the rubbery polymer will range from about 0 to 60 weight percent; the ductile polymer will range from about 0 to about 80 weight percent; and the plasticizer will be greater than 0.4 weight percent, based on the total weight of the polymer alloy.
The invention will be illustrated with reference to the following Examples, which should not be construed so as to limit the scope of the present invention.