Molecularly miscible polymer blends

Abstract: A molecularly miscible polymer blend of polyvinyl phenol and polyacetal exhibits useful properties.

Description: Field of the Invention This invention is concerned with molecularly miscible polymer blends of polyvinyl phenol and polyacetal. Background of the Invention The mixing together of two or more polymers has attracted interest as a means of arriving at new property combinations without the need to synthesize novel structures. In most cases, when two polymers are mixed, the components tend to segregate into separate phases, forming a non-adhering, heterogeneous mixture that exhibits inferior overall properties. Only occasionally do polymers blend to form a single homogeneous amorphous phase. The term polymer blend refers to an intimate mixture of two or more polymers. Blends of polymers are often described as miscible or compatible, and the terms are sometimes considered to be equivalent. The term miscible will be used herein to describe a mixture of two or more polymers that form a single-phase solution (solid or liquid) on a molecular scale within the amorphous phase. Miscibility can be achieved by selecting components that interact with one another in an attractive mode (e.g. which mix exothermically). Several methods can be used to determine miscibility in polymer blends. For example, when a film is prepared from a miscible blend, it is usually optically clear, while immiscible blend films are usually opaque. However, this criterion is not useful when one of the blend components is crystallizable. The most commonly used criterion for miscibility is the existence of a single glass transition temperature for a given miscible blend. This parameter is relatively easy to measure for amorphous systems, and rapid if a technique such as differential scanning calorimetry is used. Greater sensitivity, especially useful for semi-crystalline blends, can be obtained when dynamic mechanical methods are employed to measure the glass transition temperature. As the relative proportion of components changes, a smooth change between the glass transition temperatures for the pure blend components and the glass transition temperatures for the various blends will be observed over the miscible range for the blends. JP-A-60-10250 discloses resist compositions comprising an alkali soluble resin and a polyacetal-type dissolution inhibitor. The composition becomes alkali-soluble upon electron beam exposure. Summary of the Invention The present invention is a molecularly miscible blend of polyvinyl phenol and polyacetal comprising at least 85 mole percent, based on the total polyacetal, of polyoxymethylene; wherein the terms miscible blend are defined as a mixture of two or more polymers that form a single-phase solution (solid or liquid) on a molecular scale within the amorphous phase. Detailed Description of the Invention Molecularly miscible blends are herein defined as blends which can be mixed such that they exhibit only one glass transition temperature, indicating a single amorphous phase. More specifically, molecularly miscible blends exhibit one glass transition temperature (T g ) as measured by dynamic mechanical testing. In this procedure, polymers are subjected to an oscillatory mechanical deformation to detect changes in the modulus and visco-elastic response of the polymer blend as a function of temperature. It has been found in accordance with the instant invention that the desired molecularly miscible blends can be obtained by blending together a compatible mixture of (a) a polyvinyl phenol, with (b) a polyacetal. A preferred molecular miscible blend comprises components (a) and (b) blended in relative proportions by weight within a range of from 1:99 to 99:1 parts based on 100 parts of (a) and (b) combined. The most preferred molecular miscible blend is prepared from 80 to 20 parts of (a) and, correspondingly, from 20 to 80 parts of (b). Blends of components (a) and (b) which are also usable can range in relative proportions from 40:60 to 60:40, or be, approximately equal proportions by weight, i.e. (a):(b) = 50:50. The polyvinyl phenols employed as the first component in the molecularly miscible blends of the invention are homopolymers and copolymers of ortho-, meta- and para-vinyl phenols. Polyvinyl phenols may be illustrated by the following formula for poly(para-vinyl phenol): The polyvinyl phenols may optionally carry any of various substituents that do not markedly affect the phase behaviour of the polymer blend. The molecular weight of the polymer does not appear to be a critical factor. Those having a number averaged molecular weight of between 2,000 and 75,000 are preferred, but the polymers having molecular weights lower or higher than this range may also be used. The polyvinyl phenol may be prepared by bulk polymerization, emulsion polymerization or solution polymerization of the corresponding monomers in the presence of a cationic catalyst such as boron trifluoride etherate. Such procedures are well known in the art. High purity poly(para-vinyl phenol) may be prepared by several methods known in the art. It may be produced by polymerizing para-vinyl phenol in the presence of phenols without unsaturated side chains, and in the presence of a polymerization accelerator. It may also be produced by dehydrogenating crude para-ethylphenol, polymerizing the resulting crude para-vinyl phenol without purification, and then purifying the resulting polymerization product. Preferably, a high purity poly-(para-vinyl phenol) is used as produced (by Hoechst Celanese) by polymerization of a high purity para-acetoxystyrene, followed by hydrolysis to para-vinyl phenol. Vinyl phenols useful for the production of polymers may be prepared, for example, by hydrolysis of commercially available coumarin or substituted coumarins, followed by decarboxylation of the resulting hydroxy cinnamic acids. Useful vinyl phenols may also be prepared by dehydration of the corresponding hydroxy alkyl phenols or by decarboxylation of hydroxy cinnamic acids resulting from the reaction of substituted or non-substituted hydroxybenzaldehydes with malonic acid. Various processes suitable for production of vinyl phenol are well known in the art. Suitable polyvinyl phenols useful in the present invention are described in U.S. Patent Nos. 3,869,292 and 4,439,516, and in European Patent Application 138,609. The production of suitable high-purity para-vinyl phenols useful in the present invention is described in U.S. Patent Nos. 4,028,340 and 4,517,349. The polyacetal employed as the second component in the blends of the invention is a polyoxyalkylene polymer which is composed of at least 85 mol % of polyoxymethylene. The polymer is illustratively produced by polymerization of formaldehyde, provided as such or from a formaldehyde source. One preferred formaldehyde source is 1,3,5-trioxane which is viewed as a formaldehyde trimer. The polymer has a high molecular weight and a structure typified by the following: where terminal groups are derived from controlled amounts of water and the x denotes a large (typically 1500) number of formaldehyde units linked in head-to-tail fashion. To increase thermal and chemical resistance, terminal groups are typically converted to esters or ethers. Optionally the polyacetal has polymerized therewith a small proportion of a second compound such as a low molecular weight cyclic ether which is not a formaldehyde source. The cyclic ether which is preferred as an optional comonomer of the polyacetal is a low molecular weight cyclic ether of up to 10 carbon atoms inclusive and up to 2 oxygen atoms inclusive. One class of such cyclic ethers is the group of compounds known as oxirane compounds or olefin oxides having two carbon atoms and one oxygen atom in a cyclic three-membered ring. Such olefin oxides have up to 10 carbon atoms inclusive and are suitably hydrocarbon olefin oxides such as ethylene oxide, propylene oxide, 2-butylene oxide and 1-octene oxide, or are halogenated olefin oxides, preferably chlorinated olefin oxides such as epichlorohydrin. Other cyclic ethers with one oxygen but more than two carbon atoms in the ring are the oxacycloalkanes such as oxacyclobutane (oxetane), oxacyclopentane (oxolane) and oxacyclohexane (oxane), as well as halogenated, preferably chlorinated oxacycloalkanes such as 2,2-di(chloromethyl)oxetane. Preferred cyclic ethers for copolymerization with formaldehyde are ethylene oxide, 1,3-dioxolane and 1,4-dioxane. The polyacetals comprise at least 85 mole percent, preferably at least 90 mole percent, based on total polyacetal of polyoxymethylene, the unit derived from formaldehyde, with an optional amount of no more than 15 mole percent, preferably no more than 10 mole percent, based on total polyacetal, of a cyclic ether polymerized with the polyoxyalkylene. Although block copolymers of formaldehyde are known wherein a polyoxymethylene block is attached to a block of a second polymerized monomer, e.g., the cyclic ether, the preferred polyacetals, when copolymers are employed, are the more typical random copolymers, wherein the monomers are copolymerized and the moieties of cyclic ether occur randomly throughout the polymer chain. Although such copolymers are suitable for the blends of the invention it is generally preferred to use homopolymers of (the) formaldehyde (source) without any substantial amount of comonomer. Preferred polyacetal (co)polymers, are represented by the repeating formula wherein each R₁ and R₂ independently is a hydrogen atom, an alkyl radical containing up to 4 carbon atoms, or a haloalkyl radical of up to 4 carbon atoms and 2 halogen atoms inclusive, preferably a haloalkyl radical of up to 1 halogen atom wherein the halogen atom is a chlorine atom, and n is an integer from 0 to 3 inclusive, with n being 0 in at least 85% of the repeating units. These polyacetal (co)polymers are produced by polymerizing at least 85 mole percent of formaldehyde with up to 15 mole percent, based on total polyacetal, of the cyclic ether as described above. The polyacetals are produced by polymerization of formaldehyde (or a formaldehyde source) and, optionally, up to 15 mole percent of the cyclic ether comonomer in the presence of a Friedel Crafts catalyst, preferably complexed with an electron-rich molecule. The Friedel Crafts catalysts are metal halides having acidic properties. This class of catalysts include the halides but preferably the fluorides or chlorides of boron, aluminium, iron, tin and other metals as is known in the art. The catalysts are often provided as a complex of an electron-rich oxygen compound such as an ether, but complexes with an alkanol or an alkanoic acid are also suitable. The production of polyacetals is well known in the art and is taught by U.S. Patent Nos. 2,947,727, 2,947,728, 3,027,352, and 3,072,609. Also included in the term polyacetal resins are the polyacetal copolymers, such as those listed in British Patent No. 807,589, which include other monomers capable of providing active hydrogens, such as alkylene glycols, polythiols, vinyl acetate/acrylic acid copolymers, or reduced butadiene/acrylonitrile polymers. The method of blending the polyvinyl phenol and the polyacetal is not material so long as a uniform mixture of the two components is obtained without undue degradation of the components or the resulting blend. For example, the components may be blended in a corotating twin-screw extruder, or in a mixing device which exhibits high shear. The blends of the invention may also contain additives and stabilizers, fillers and fire retardant materials, mould release agents, colorants and other materials which are designed to improve the processability of the blend or its components or to improve the properties of the resulting blend. Such additives are incorporated within the blend or blend components prior to, together with or subsequent to the blending of the polyvinyl phenol with the polyacetal. The polyvinyl phenol/polyacetal blends of the invention are miscible blends having unique properties. The blends are of particular utility in instances where moulded parts are desired which exhibit strength when exposed to conditions of high temperature. The blends are processed by conventional methods, such as extrusion or injection moulding, into sheets, plates, films and moulded objects. The blends find particular utility in the production of both internal and external parts for the automotive industry and structural parts for application in the construction industry. The miscible blends of the invention, when filled with reinforcing materials such as metal or glass, will exhibit good adhesion due to the high reactivity and hydrogen-bonding capability of the blends. The blends of the invention could also be used as coatings for materials such as glass or metal. The invention is further illustrated by the following Examples, which should not be construed as limiting the invention. Example 1 Melt blends were prepared containing a polyvinyl phenol having a number average molecular weight of 8700 and a density of 1.16 g/cm³, and a moulding grade polyacetal copolymer (Celcon M-90, a trademark) with a density of 1.42 g/cm³ (both purchased from Hoechst Celanese). The blends prepared are shown in Table 1. The blends were compounded on a 15mm Baker-Perkins co-rotating, intermeshing twin screw extruder operating at 235°C. Subsequent to blending, specimens of the blends were compression moulded at 225°C into plaques. The moulded specimens were stored over desiccant prior to testing. Miscibility of the two blend components was demonstrated by determining the glass transition temperature (T g ) and melting point (T m ) for each blend. The T g of the blends was determined by the temperature at which the dynamic mechanical loss tangent, tan delta, reached a maximum value in mechanical torsion at 1 Hz frequency and low strain amplitude. The T g of polyvinyl phenol was measured by differential scanning calorimetry (DSC) at 20°C/min heating rate. The pure polyvinyl phenol sample was too brittle for dynamic mechanical testing. The T g of polyacetal is a continuing matter of controversy (not unusual for highly crystalline polymers), but is thought to correspond to a loss peak at -6°C. Melting point analysis was performed by DSC at 20°C/min on compression moulded samples. Reported melting temperatures correspond to the peak temperature of the DSC melting endotherm. As noted in Table 1, the glass transition temperatures for the blends decline in a nearly linear fashion from the T g for polyvinyl phenol (153°C) upon adding polyacetal to the blend. The melting point temperatures of the polyacetal crystalline phase decrease in a smooth transition from the T m for pure polyacetal (170°C). As polyvinyl phenol was added to the polyacetal, the morphology, viewed by optical microscopy, changed considerably. The spherulites became larger and developed a marked "ringed" or "bonded" texture (caused by a periodic twisting of the lamellae) which is not present in the neat polyacetal. This phenomenon has previously been reported for the polycaprolactone/polyvinyl chloride and polyvinylidene fluoride/poly-3-hydroxy butyrate blend systems which are known to be miscible systems. It may also be pointed out that the blend spherulites were space-filling (and therefore included the polyvinyl phenol component). Scanning transmission electron microscopy (STEM) showed no evidence of a dispersed, discrete phase, also suggesting miscibility. Thus, the observation of a single intermediate glass transition accompanied by a depression of the melting point of the crystalline component, combined with morphological observations, provides compelling evidence that the blends of the invention are miscible. Example 2 Melt blends were prepared containing a polyvinyl phenol having a number average molecular weight of 50,500 and a density of 1.16 g/cm³ (purchased from Hoechst Celanese), and a moulding grade polyacetal copolymer with a density of 1.42 g/cm³ as described in Example 1. The blends prepared are compared with the individual polymers in Table 2. Miscibility of the blends is again demonstrated by the single and intermediate glass transition temperatures and depressed melting point temperatures for the blends.

Claims: Claims for the following Contracting States : BE, DE, FR, GB, IT, NL, SE A composition comprising a miscible blend of i) a polyvinyl phenol; and ii) a polyacetal comprising at least 85 mole percent, based on the total polyacetal, of polyoxymethylene; wherein the terms miscible blend are defined as a mixture of two or more polymers that form a single-phase solution (solid or liquid) on a molecular scale within the amorphous phase. The composition of claim 1, wherein the polyvinyl phenol is produced by polymerizing a high purity para-acetoxystyrene monomer, followed by hydrolysis to form a high purity para-vinyl phenol. The composition of claim 1 or 2, wherein the polyacetal is produced by the polymerization of 1,3,5-trioxane. The composition of claim 1 or 2, wherein the polyacetal is represented by the formula wherein each R₁ and R₂ is a hydrogen atom, an alkyl radical of up to 4 carbon atoms inclusive, or a haloalkyl radical of up to 4 carbon atoms and 2 halogen atoms inclusive, and n is an integer from 0 to 3 inclusive with n being 0 in at least 85% of the repeating units. The composition of anyone of claims 1 to 4, wherein the polyacetal is at least 85 mole percent of polymerized formaldehyde (source), and up to 15 mole percent of ethylene oxide, 1,3-dioxolane, or 1,4-dioxane is copolymerized therewith. The composition of anyone of claims 1 to 5, comprising from 99 to 1 parts of polyvinyl phenol and from 1 to 99 parts of polyacetal. The composition of anyone of claims 1 to 5, comprising from 80 to 20 parts of polyvinyl phenol and from 20 to 80 parts of polyacetal. The composition of anyone of claims 1 to 5 comprising from 40 to 60 parts of polyvinyl phenol and from 60 to 40 parts of polyacetal. An article prepared from the composition of anyone of claims 1 to 8 and a filler. An article coated with the composition of anyone of claims 1 to 8. Claims for the following Contracting State : ES A process for the preparation of a miscible blend by blending together i) a polyvinyl phenol; and ii) a polyacetal comprising at least 85 mole percent, based on the total polyacetal, of polyoxymethylene; wherein the terms miscible blend are defined as a mixture of two or more polymers that form a single-phase solution (solid or liquid) on a molecular scale within the amorphous phase. A process as claimed in claim 1, wherein the components are blended in a co-rotating twin screw extruder or in a high shear mixing device. A process as claimed in claim 1 or 2, wherein the polyvinyl phenol is produced by polymerizing a high purity para-acetoxystyrene monomer, followed by hydrolysis to form a high purity para-vinyl phenol. A process as claimed in any one of claims 1 to 3, wherein the polyacetal is produced by the polymerization of 1,3,5-trioxane. A process as claimed in any one of the claims 1 to 3, wherein the polyacetal is represented by the formula wherein each R₁ and R₂ is a hydrogen atom, an alkyl radical of up to 4 carbon atoms inclusive, or a haloalkyl radical of up to 4 carbon atoms and 2 halogen atoms inclusive, and n is an integer from 0 to 3 inclusive with n being 0 in at least 85% of the repeating units. A process as claimed in any one of claims 1 to 5, wherein the polyacetal is at least 85 mole percent of polymerized formaldehyde (source), and up to 15 mole percent of ethylene oxide, 1,3-dioxolane, or 1,4-dioxane is copolymerized therewith. A process as claimed in any one of claims 1 to 6, wherein from 99 to 1 parts of polyvinyl phenol and from 1 to 99 parts of polyacetal is used. A process as claimed in any one of claims 1 to 7, wherein from 80 to 20 parts of polyvinyl phenol and from 20 to 80 parts of polyacetal is used. A process as claimed in any one of claims 1 to 8, wherein from 40 to 60 parts of polyvinyl phenol and from 60 to 40 parts of polyacetal is used.

Inventors: FRENCH RAYMOND NICHOLAS, MACHADO JOSEPH MICHAEL, FRENCH, RAYMOND NICHOLAS, MACHADO, JOSEPH MICHAEL
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1991
Main classification: C08L25
IPC codes: C08L59, C08F12, C08F8, C08L25