OF VINYLIDENE CHLORIDE TERPOLYMERS

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates to vinylidene chloride (VDC) polymers. In one aspect, the invention relates to a batch suspension process for making VDC terpolymers while in another aspect, the invention relates to the VDC terpolymers made by the process.

2. Description of the Related Art

[0002] Current copolymers of vinylidene chloride and vinyl chloride are desirable for manufacture of mono-layer films. These copolymers, however, have a relatively high melting point, e.g., 165°C, making them relatively difficult to extrude. Increasing the comonomer, i.e., vinyl chloride, content decreases the melting point of the copolymer, but this has several undesirable side effects, e.g., it reduces the crystallinity and barrier properties of the copolymer.

[0003] Alternatively, methyl acrylate can be substituted for vinyl chloride. Besides having excellent barrier properties, copolymers of vinylidene chloride and methyl acrylate also have a relatively low melting point, e.g., 150°C. Unfortunately, however, these copolymers also exhibit certain undesirable properties, e.g., a slow crystallization rate which can result in a failure to crystallize in a standard double bubble blown film process.

[0004] In general, the deficiencies of these vinylidene chloride copolymers can be avoided only by taking extra-ordinary measures during the polymerization process by which they are made, such as preferentially adding or removing significant amounts of comonomer or stopping the polymerization reaction at a relatively low conversion. In a continuous process, e.g., a continuous emulsion polymerization process, controlling these amounts is accomplished by controlling the rate of addition of the monomers into the process. In a batch process in which all of the monomers are added at the same time, however, this method of control is not available.

[0005] Another alternative solution to this problem of lowering the melting point of a vinylidene chloride polymer without significantly adversely affecting its barrier and crystallinity properties is to make a terpolymer of vinylidene chloride and two other mono- ethylenically unsaturated comonomers, e.g., vinyl chloride and methyl acrylate. In this manner the desired combination of barrier, crystallinity and crystallinity rate may be obtained by varying the relative amounts of the three monomers incorporated into the terpolymer.

SUMMARY OF THE INVENTION

[0006] In one embodiment the invention is a batch suspension polymerization process for the manufacture of a vinylidene chloride (VDC) terpolymer consisting of mer units derived from VDC as a first monomer, a second monomer and a third monomer, and the VDC terpolymer characterized by having

more mer units derived from the VDC monomer than from the second monomer, and more mer units derived from the second monomer than from the third monomer, and

a melting point lower than the melting point of a VDC copolymer consisting of mer units derived from the VDC monomer and the second monomer, the VDC copolymer (i) made from a monomer mixture comprising the same amount of VDC monomer as the monomer mixture from which the VDC terpolymer is made, and (ii) made under essentially the same batch suspension polymerization conditions as the VDC terpolymer,

the process comprising the step of contacting under batch suspension polymerization conditions VDC monomer, the second monomer and the third monomer, both the second and third monomers mono-ethylenically unsaturated and each monomer having a reactivity ratio of which the reactivity ratio of the VDC monomer (ri ₂ ) is greater than the reactivity ratio of the second monomer (r ₂ i) and the reactivity ratio of the third monomer (r ₃ i) is equal to or greater than the reactivity ratio of the VDC monomer ( ₃ ). In these ratios, 1 is the first (VDC) monomer, 2 is the second monomer and 3 is the third monomer.

[0007] In one embodiment the invention is a VDC terpolymer made by the batch suspension polymerization process described above, particularly a VDC terpolymer comprising mer units derived from vinylidene chloride, vinyl chloride and one of methyl acrylate, methyl methacrylate and acrylonitrile. In one embodiment the invention is a film or film layer comprising the VDC terpolymer. In one embodiment the invention is an article, e.g., packaging for food, medicine, etc., comprising the film or film layer comprising the VDC terpolymer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Definitions

[0008] The numerical ranges in this disclosure are approximate, and thus may include values outside of the range unless otherwise indicated. Numerical ranges include all values from and including the lower and the upper values, in increments of one unit, provided that there is a separation of at least two units between any lower value and any higher value. As an example, if a compositional, physical or other property, such as, for example, molecular weight, etc., is from 100 to 1 ,000, then all individual values, such as 100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated. For ranges containing values which are less than one or containing fractional numbers greater than one (e.g., 1.1 , 1.5, etc.), one unit is considered to be 0.0001 , 0.001 , 0.01 or 0.1 , as appropriate. For ranges containing single digit numbers less than ten (e.g., 1 to 5), one unit is typically considered to be 0.1. These are only examples of what is specifically intended, and all possible combinations of numerical values between the lowest value and the highest value enumerated, are to be considered to be expressly stated in this disclosure. Numerical ranges are provided within this disclosure for, among other things, relative amounts of mer units in the VDC terpolymer.

[0009] The term "comprising" is synonymous with "including," "containing," "having" or "characterized by," is inclusive or open-ended, and does not exclude additional, unrecited elements, material, or steps. The term "consisting essentially of indicates that in addition to specified elements, materials, or steps; elements, unrecited materials or steps may be present in amounts that do not unacceptably materially affect at least one basic and novel characteristic of the subject matter. The term "consisting of indicates that only stated elements, materials or steps are present.

[0010] "Composition", "formulation" and like terms means a mixture or blend of two or more components. In the context of a mix or blend of materials from which barrier packing, e.g., film, is made, the composition includes the blend of the invention and any other additives, fillers and the like.

[0011] "Film" refers to a sheet, non-woven or woven web or the like or combinations thereof, having length and breadth dimensions and having two major surfaces with a thickness therebetween. A film can be a monolayer film (having only one layer) or a multilayer film (having two or more layers). A film, in most instances, has a thickness of up to about 20 mils (5x1ο ^-4 m).

[0012] "Layer", "film layer" and like terms mean a member or component forming all or a fraction of the thickness of a structure in which the component is preferably substantially coextensive with the structure and has a substantially uniform composition.

[0013] "Barrier" means that property of a film (monolayer or multilayer) measured as permeability of the film to one or more gasses or vapors, e.g., oxygen, water vapor, an odor, etc. A "barrier resin" or "barrier polymer" means a polymer or polymer composition suitable for use in forming a barrier.

[0014] "Polymer" means the polymerization product of one or more monomers and is inclusive of homopolymers as well as interpolymers, copolymers, terpolymers, tetrapolymers, and the like and blends and modifications of any of the foregoing, including block, graft, addition or condensation forms of polymers.

[0015] "Mer", "mer unit" and like terms means that portion of a polymer derived from a single reactant molecule; for example, a mer unit from ethylene has the general formula -CH ₂ CH ₂ -.

[0016] "Copolymer" refers to a polymer that includes mer units derived from two monomers and is inclusive of random, block, segmented, graft, and the like copolymers.

[0017] "Terpolymer" refers to a polymer that includes mer units derived from three monomers and is inclusive of random, block, segmented, graft, and the like terpolymers.

[0018] "Reactivity ratio" and like terms mean the ratio of the rate constant for reactive propagating species adding its own type of monomer to the rate constant for addition of another monomer. Reactivity ratios are determined based on experimental determination of copolymer composition formed from several different comonomer feed compositions. Lists of reactivity ratios are extensively compiled in the literature, for example, Bandrup & Immergut, Polymer Handbook, 3 ^rd addition, Wiley Interscience (1989).

[0019] "Melting point" and like terms mean the peak temperature of the melting endotherm as measured by differential scanning calorimetry (DSC). Completion of melting is the temperature at which the melting peak essentially returns to baseline as measured by DSC. These properties are measured by a differential scanning calorimeter by scanning from ambient temperature to 200°C at a scan rate of 10°C/min. [0020] "Batch suspension polymerization conditions" and like terms mean the conditions under which vinylidene chloride, vinyl chloride and a mono-ethylenically unsaturated third monomer will react to form a terpolymer comprising mer units derived from each monomer. The conditions include, but are not limited to, temperature; pressure; residence time; solvents, catalysts and other reagents; mixing and the like.

[0021] "Molecular weight" is the weight average molecular weight (Mw) in Daltons. It is measured by size exclusion chromatography using polystyrene calibration. Sample preparation includes dissolving a polyvinylidene chloride resin sample in tetrahydrofuran (THF) at 50°C. The polymers are then analyzed for determination of molecular weight by gel permeation chromatography (GPC) using the Polymer Laboratories Software on a Hewlett Packard 1 100 chromatograph equipped with two columns in series. These columns contain 5 μηι styrene/divinylbenzene copolymer beads commercially available from Polymer Laboratories under the trade designation PLGel 5μ MIXED-C. The solvent is nitrogen purged HPLC Grade THF. The flow rate is 1.0 milliliter/minute and the injection size is 50 microliters. The molecular weight determination is deduced by using ten narrow molecular weight distribution polystyrene standards (commercially available from Polymer Labs under the trade designation Narrow PS set (about 3,000,000 to 2000 Mp)) in conjunction with their elution volumes.

Vinylidene Chloride (VDC) Terpolymer

[0022] Vinylidene chloride terpolymers made by the process of this invention typically comprise mer units derived from vinylidene chloride in an amount of at least 60, more typically at least 70, even more typically at least 80, and still more typically at least 85, weight percent (wt%).

[0023] The vinylidene chloride terpolymers made by the process of the present invention further comprise mer units derived from second and third monomers which are mono- ethylenically unsaturated compounds each having a reactivity ratio. The reactivity ratio of the second monomer is smaller than the reactivity ratio of VDC, and the reactivity ratio of the third monomer is equal to or greater than the reactivity ratio of VDC. Typically, ri ₂ /r ₂ i is greater than 1, more typically greater than 10. Typically, ri ₂ /r ₂ i is less than 1 ,000, more typically less than 100 and even more typically less than 20. Typically, rj ₃ /r ₃ i is equal to or less than 1 and greater than 0.01 , more typically greater than 0.04. The mer units derived from the second monomer, are typically present in an amount of not greater than 40, more typically not greater than 30 and even more typically not greater than 20, and still more typically not greater than 15 wt% of the terpolymer. The mer units derived second monomer are typically present in an amount greater than 5, more typically greater than 10, wt%. Representative second monomers include, but are not limited to, vinyl chloride and vinyl acetate.

[0024] The mer units derived from the third monomer are typically present in an amount of not greater than 5, more typically not greater than 3 and even more typically not greater than 2, wt% of the terpolymer. The mer units derived the third monomer are typically present in an amount greater than 0, more typically greater than 0.1 and even more typically greater than 0.5, wt%. Representative third monomers include, but are not limited to, alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid, itaconic acid, acrylonitrile, and methacrylonitrile. The alkyl acrylates and alkyl methacrylates typically have from 1 to 4 carbon atoms per alkyl group. The alkyl acrylates and alkyl methacrylates are preferably selected from the group consisting of the methyl acrylates, ethyl acrylates, and methyl methacrylates.

[0025] The weight average molecular weight (Mw) of the VDC terpolymers made by the process of this invention are typically of 50,000 to 250,000 Daltons, more typically of 70,000 to 130,000 as measured by size exclusion chromatography using polystyrene calibration. Batch Suspension Polymerization

[0026] Batch suspension polymerization is well known in the art. See, for example, Wessling et al., Vinylidene Chloride Monomer and Polymers, Kirk Othmer; Encyclopedia of Chemical Technology, 4 ^th ed. Vol. 24. John Wiley, 1997 (pg 908-910). In one embodiment, the monomers and other reagents are loaded into a reactor, and the reactor closed and brought to polymerization conditions, e.g., 60°C at vapor pressure for 30-60 hours. The progress of the polymerization is monitored in any convenient manner, e.g., time, heat release, rate or pressure drop, etc., and when the desired conversion of the monomers to the terpolymer is reached, the polymerization is stopped in any convenient manner, e.g., adding a free radical scavenger, venting excess monomer, cooling, etc., and the product recovered. Recovery of the product typically includes the steps of stripping of residual monomer, de-watering and drying. Reactivity Ratio

[0027] In the preparation of a VDC copolymer consisting of mer units derived from VDC and vinyl chloride (VC), the VDC monomer incorporates much more quickly into the growing copolymer chain than does the VC monomer or, in other words, the VDC monomer has a greater reactivity ratio, e.g., ri ₂ =4.1 and r ₂ ]=0.23. In a continuous process, this can be controlled by regulating the amount of both VDC and VC monomer fed to the reactor over the course of the process. In a batch process in which both of the monomers are fed to the reactor at the start of the process, this mode of regulation is not available and reaction kinetics determine the comonomer content of the copolymer.

[0028] The melting point of a VDC copolymer consisting of mer units derived from VDC and VC monomers is a function, in large part, of the VDC mer unit content of the copolymer. The more VDC mer unit content in the copolymer, the higher the melting point of the copolymer (all else being equal). However, due to the nature of the batch process, the incorporation of the VDC monomer into the copolymer is uneven over the course of the polymerization. Since the VDC monomer is the dominant monomer in the reaction mass and since it has a higher reactivity ratio than the VC monomer, copolymer molecules formed early in the process contain considerably more VDC mer units (and thus considerably less VC mer units) than the copolymer molecules formed late in the process (which may contain twice or more VC mer units and, thus, a proportionate amount less of VDC units). This results in a finished product, i.e., the bulk copolymer, comprising copolymer molecules with a wide range of VDC and VC mer content and this, in turn, results in a higher melting point for the bulk copolymer than if the VDC copolymer molecules made early in the process had the same or nearly the same VDC mer unit content as did the VDC copolymer molecules made later in the process.

[0029] By selecting a third monomer with a reactivity ratio as great as, preferably greater, than that of VDC monomer for incorporation into the growing polymer chain, the VDC monomer now has a lesser opportunity to incorporate into the growing polymer (now a terpolymer) chain early in the polymerization. This not only results in a finished bulk terpolymer product with a lower melting point than that of a VDC copolymer with essentially the same content of VDC mer units in the finished bulk copolymer, but it does so surprisingly without a significant adverse effect on one or more of the barrier, crystallinity and crystallization rate properties of the bulk copolymer. These results are obtained using only a small amount, e.g., less than 5, typically less than 3 and even more typically less than 2, wt% of the third monomer.

Terpolymer

[0030] In one embodiment the invention is the terpolymer made by the inventive process. The terpolymer has desirable barrier properties and as such, can be fabricated into useful packaging articles, e.g., film. In one embodiment, the terpolymer of this invention is formulated into a composition comprising (1) VDC terpolymer, and (2) one or more additives and/or fillers and/or other polymers. Additive type and amount depends on several factors. One factor is the intended use of the finished article. Another factor is the tolerance of the terpolymer for the additive, i.e., how much additive can be added to the terpolymer before adversely affecting the physical properties of the terpolymer to an unacceptable level. Other factors are known to those skilled in the art of polymer formulation and compounding.

[0031] Representative additives that can be used with the terpolymers of this invention include, but are not limited to, antioxidants, heat stabilizers (e.g., epoxidized soybean or linseed oil), plasticizers (e.g., acetyl tributyl citrate, dibutyl sebacate), light stabilizers, pigments, processing aids, lubricants, acid scavengers, waxes, fillers and the like. Such additives are used in known amounts and in known ways. Typically, additives are used in amounts of less than 10, more typically less than 5 and even more typically less than 3, wt% based upon the weight of the composition.

[0032] The terpolymer-containing compositions of this invention can optionally contain one or more other polymers known to those with skill in the art. Polymer type and amount will depend upon several factors. One such factor is the intended use of the composition. Another factor is compatibility of the polymers, that is, whether the polymers can form a sufficiently homogeneous mixture that does not separate undesirably for the intended purpose. Other factors are apparent to those skilled in the art.

[0033] The terpolymer-containing compositions of the present invention can be used to form a variety of cast, blown, extruded, molded, injection molded, or calendered articles. Films made from the compositions of this invention are useful as packaging and wrapping films and may be monolayer or multilayer films. The films of the present invention can be used alone or laminated to another film or a packaging film component thus forming a package, which contains a product. The films of the present invention are particularly useful for packaging. Oxygen barrier properties are important in film applications such as packaging primal cuts of meat (that is, large cuts of meat which are shipped to a specific store for further cutting for specific consumer consumption). As described by Davis et al. in USP 4,886,690, the oxygen barrier layer can also be designed as "peelable" to allow removal once the packaged primal cut arrives at the butcher/grocer; a peelable construction or design is particularly useful for "case-ready" vacuum skin packages of individual portions and eliminates the need for repackaging to an oxygen permeable package for blooming to bright red. The layer or film comprising the blend or composition of this invention may optionally comprise at most 50, preferably at most 25, more preferably at most 15, most preferably at most 10 wt% of at least one other polymer.

[0034] This invention is further illustrated by the following examples. Unless stated otherwise all percentages, parts and ratios are by weight.

SPECIFIC EMBODIMENTS

[0035] A set of suspension polymerizations is conducted in a 1 -liter stirred glass vessel. Monomer mixtures used in these experiments include the three monomers, 0.406% di-(t- butylcyclohexyl)peroxydicarbonate (an initiator), and approximately 100 ppm butylated hydroxy toluene. The aqueous phase contains approximately 0.12% methylhydroxypropyl cellulose, a suspending agent. Approximately 300 grams of the monomer phase and 370 g of the aqueous phase are added to the reactor. The reactor temperature is increased to 38°C to initiate the polymerization, and then the temperature of the polymerization is ramped to 68°C over approximately 30 hours to complete the polymerization.

Example 1

[0036] A monomer mixture containing 248 g vinylidene chloride (VDC), 46.5 g vinyl chloride (VC) and 2.01 g methyl acrylate (MA) is polymerized according to the procedure described above.

Example 2

[0037] A monomer mixture containing 247 g vinylidene chloride, 46.5 g vinyl chloride and 2.16 g acrylonitrile (AN) is polymerized according to the procedure described above. Example 3

[0038] A monomer mixture containing 247 g vinylidene chloride, 46.5 g vinyl chloride and 2.75 g methyl methacrylate (MMA) is polymerized according to the procedure described above.

Comparative Example A

[0039] A monomer mixture containing 250 g vinylidene chloride and 46.5 g vinyl chloride is polymerized according to the procedure described above.

Comparative Example B

[0040] A monomer mixture containing 231 g vinylidene chloride and 65.1 g vinyl chloride is polymerized according to the procedure described above.

[0041] The results of these polymerizations are shown in Table 1. These results include the molar concentrations of the comonomer and termonomer in the monomer mixture, the temperature at which melting of the polymer is complete as measured by DSC, the percent crystallinity as measured by DSC, the average mole percent vinylidene chloride in the polymer assuming the polymerization is run to 85% conversion of monomer to polymer as calculated from reactivity ratios, and the time to complete the polymerization as determined by the rate falling below 2% conversion per hour as measured by reaction calorimetry. The results demonstrate that for a comparable melting point the terpolymers of this invention will contain a higher fraction of VDC and thus have better barrier properties. These results also demonstrate that the terpolymers have higher crystallinity than comparable copolymers leading to superior barrier and modulus. An additional benefit is that these terpolymers exhibit a faster polymerization rate than a comparable copolymer.

Table 1

Comparative Properties of VDC Copolymers and Terpolymers

[0042] A set of suspension polymerizations is conducted in an 8 ounce glass vessel. Monomer mixtures used in these experiments include the three monomers and 0.369% t-butyl peroxy-2-ethylhexanoate. The aqueous phase contains approximately 0.1% methyl- hydroxypropyl cellulose, suspending agent. Approximately 90 g of the monomer phase and 150 g of the aqueous phase are added to the reactor. The reactor temperature is increased to 71 °C to initiate the polymerization, and then the temperature of the polymerization is ramped to 84°C over approximately 6 hours to complete the polymerization.

Example 4

[0043] A monomer mixture containing 80.3 g vinylidene chloride, 9.0 g vinyl acetate (VA) and 0.675 g methyl methacrylate is polymerized according to the procedure described above.

Example 5

[0044] A monomer mixture containing 80.3 g vinylidene chloride, 9.0 g vinyl acetate and 0.675 g methyl acrylate is polymerized according to the procedure described above.

Example 6

[0045] A monomer mixture containing 80.3 g vinylidene chloride, 9.0 g vinyl acetate and 0.675 g methyl methacrylonitrile is polymerized according to the procedure described above. Example 7

[0046] A monomer mixture containing 80.3 g vinylidene chloride, 9.0 g vinyl acetate_and 0.675 g acrylonitrile is polymerized according to the procedure described above.

Example 8

[0047] A monomer mixture containing 79.7 g vinylidene chloride, 9.0 g vinyl acetate and 1.35 g methyl methacrylate is polymerized according to the procedure described above.

Example 9

[0048] A monomer mixture containing 79.7 g vinylidene chloride, 9.0 g vinyl acetate and 1.35 g methyl acrylate is polymerized according to the procedure described above.

Example 10

[0049] A monomer mixture containing 79.7 g vinylidene chloride, 9.0 g vinyl acetate and 1.35 g methacrylonitrile is polymerized according to the procedure described above.

Example 11

[0050] A monomer mixture containing 79.7 g vinylidene chloride, 9.0 g vinyl acetate and 1.35 g acrylonitrile is polymerized according the procedure described above. Comparative Example C

[0051] A monomer mixture containing 81.0 g vinylidene chloride and 9.0 g vinyl acetate is polymerized according to the procedure described above.

Comparative Example D

[0052] A monomer mixture containing 76.5 g vinylidene chloride and 13.5 g vinyl_acetate is polymerized according to the procedure described above.

Comparative Example E

[0053] A monomer mixture containing 72.0 g vinylidene chloride and 18.0 g vinyl acetate is polymerized according to the procedure described above.

[0054] Reported in Table 2 are the results of these polymerizations. These results include the molar concentrations of the comonomer and termonomer in the monomer mixture, the temperature at which melting of the polymer is complete as measured by DSC, the percent crystallinity as measured by DSC and the average mole percent vinylidene chloride in the polymer assuming the polymerization is run to 92% conversion of monomer to polymer as calculated from reactivity ratios. The results demonstrate that for a comparable melting point the terpolymers of this invention will contain a higher fraction of VDC and thus have better barrier properties. These results also demonstrate that the terpolymers have higher crystallinity than comparable copolymers leading to superior barrier and modulus.

Table 2

More Comparative Properties of VDC Copolymers and Terpolymers