Case 00269(2)1
VINYL ACETATE POLYMERS METHODS OF MAKING THEM
AND USES THEREOF
This invention relates to vinyl acetate polymers, methods of making them and uses of them. More especially but not exclusively the invention relates to partially hydrolysed vinyl acetate polymers for use as primary granulating agents in the production of polyvinyl chloride (PVC) by the polymerization of vinyl chloride (VCM).
PVC is a commercially very important polymer. Much PVC is prepared by free radical addition polymerization of VCM suspensions. The VCM suspensions are stabilised by primary granulating agents which stabilize the VCM droplets and allow the droplet size to be regulated.
Typical primary protective agents are partially hydrolysed polyvinyl acetate polymers and copolymers which have been prepared by polymerizing vinyl acetate monomer (VAM) in the presence of an aldehyde as a chain transfer agent and then partially hydrolysing the resulting product. For example GB 2 002 789 describes a primary granulating agent. Vinyl acetate monomer (VAM), methanol, acetaldehyde and azobisisobutyronitrile (AIBN) are heated together until about 75% of the VAM has been polymerized. The principal role of the methanol is as a solvent. The principal role of the acetaldehyde is as a chain transfer agent (CTA) and the principal role of the AIBN is as a radical initiator. The acetaldehyde and unreacted VAM are removed using methanol vapour to give a solution of polyvinyl acetate (PVAc) in methanol. The PVAc is partially hydrolysed to give a polymer having a degree of hydrolysis of 70.1% and a degree of polymerization of 350. The resulting polymer has a strong absorbance at 280nm demonstrating the presence of unsaturated carbonyl functionality in the polymer (Lloyd, D. G., J. Applied Polymer Sci., 1959, 1, 70-72) introduced from the acetaldehyde.
It has now been unexpectedly found that it is not essential to use aldehydes as chain transfer agents to introduce unsaturation when making partially hydrolysed polyvinyl acetate (co)polymers for use as primary granulating agents for VCM polymerization.
In accordance with an aspect of the invention it has been found that partially hydrolysed polyvinyl acetate polymers having a relatively high ethylenic unsaturation are useful as primary granulating agents.
Furthermore it has been unexpectedly found that using selected organic halides such as organic chlorides and bromides as chain transfer agents during the polymerization of VAM leads to relatively high ethylenic unsaturation in the eventual partially hydrolysed polymer, even if the selected chloride or bromide does not contain ethylenic unsaturation itself. This is demonstrated by trichloroethylene which inherently having ethylenic unsaturation introduces little ethylenic unsaturation into the polymer in view of its low chain transfer constant for vinyl acetate.
According to the invention therefore there is provided a partially hydrolysed polyvinyl acetate polymer or copolymer having a degree of hydrolysis in the range 65 to 95% and at least 53µmoles preferably at least 54µmoles of ethylenic unsaturation per gram of polymer. The molecular mass Mn of the polymer or copolymer can be in the range 10 000 to 100 000 such as 15 000 to 50 000, preferably 17 000 to 40 000. In some embodiments the copolymer comprises no more than 5wt% preferably no more than 2wt% of the co- monomer. A co-monomer can have allyl functionality preferably wherein the allyl group containing co-monomer is of structural formula I
R2R3C=CR1CR4R5X
I
where X is selected from Cl, Br, OR6 and CO2R7
R1, R2, R3, R6 and R7 are independently selected from H and C1-6 straight chain or branched alkyl, and CO2R8 where R8 is selected from H and C1-6 straight chain or branched alkyl and
R4 and R5 are independently selected from H, C1-6 straight chain or branched alkyl, OC1-6 straight chain or branched alkyl or where R4 and R5 taken together are =O or
or where X is H or C1 to C6 straight chain or branched alkyl, R1, R2 and R3 are as hereinbefore defined and R4 and R5 are independently -OR9 or –OOCR10 where R9 and R10 are independently selected from C1-6 straight chain or branched alkyl.
In embodiments R1, R2 and R3 are independently selected from H, methyl and ethyl and X is Cl or OR7 where R7 is H or methyl. In these embodiments R4 and R5 are preferably H.
In embodiments R1 and R3 are independently selected from H and CO2R8 where R8 is H, methyl or ethyl, R2 is H, methyl or ethyl, X is CO2R7 where R7 is H, methyl or ethyl. In these embodiments R4 and R5 can be H.
In embodiments R2 and R3 are independently selected from H and CO2R8 where R8 is H, methyl or ethyl, R1 is H, methyl or ethyl, X is CO2R7 where R7 is H, methyl or ethyl. In these embodiments R4 and R5 can be H.
A co-monomer can have di-olefin functionality and may be selected from vinyl norbornene, ethylidene norbornene, norbornadiene, dicyclopentadiene, 1,5 cyclooctadiene, tetrahydroindenes, 1,4 hexadiene and 1,4 pentadiene.
A co-monomer can have acryl functionality preferably selected from monomers of structural formula II
R11R12C=CR13COZ
II
where R11, R12 and R13 are independently selected from H, C1-6 straight chain or branched alkyl OC1-6 straight chain or branched alkyl and
Z is OH, OR14 or NR14R15 where R14 and R15 are independently selected from H and C1-8 straight chain or branched alkyl or aromatic groups such as phenyl.
In embodiments R11, R12 and R13 are independently selected from H, methyl and ethyl and Z is OR14 where R14 is H, methyl, ethyl or 2-ethylhexyl.
Embodiments of the invention further provide a partially hydrolysed polyvinyl acetate polymer or copolymer having a molecular mass Mn in the range 10 000 to 100 000, a degree of hydrolysis in the range 65 to 95%, at least 40 µmoles of ethylenic unsaturation per gram of polymer and a polydispersity index less than 2.3.
Polymer or copolymers of the invention can be used as a primary granulating agent in the polymerization or copolymerization of VCM.
The invention further provides a method of preparing PVC comprising polymerizing VCM optionally in the presence of a co-monomer in the presence of a polymer or copolymer of the invention.
The invention further provides PVC obtainable by a process of the invention.
The invention still further provides a method of preparing a polymer or copolymer of the invention by reacting VAM and optionally a co-monomer in the presence of a chlorine or bromine containing chain transfer agent having a polyvinyl acetate polymerization chain transfer value in the range 0.01 to 5, preferably 0.2 to 3 more preferably 0.25 to 1.2, and subjecting the resulting material to partial hydrolysis. In embodiments of the invention the chlorine or bromine containing chain transfer agent is at least one of carbon tetrachloride, chloral, ethylidene bromide, hexachloroethane, trichloroacetaldehyde, E-1-chloro-butene, Z-1-chloro butene, E-1-chlorobut-2ene, Z-1-chlorobut-2-ene, 2-chlorobut-1-ene, 3-chlorobut-1-ene, E-3-chlorobut-2-ene, Z-3-chlorobut-2-ene, 1-chloro-2-methylpropene, 3-chloro-2-methylpropene-, vinyl bromide, allyl chloride and ethyl dichloroacetate. The VAM may be polymerized in the presence of an allyl group containing co-monomer. The allyl group containing co-monomer can be of structural formula I
where X is selected from Cl, Br, OR6 and CO2R7
R1, R2, R3, R6 and R7 are independently selected from H and C1-6 straight chain or branched alkyl, and CO2R8 where R8 is selected from H and C1-6 straight chain or branched alkyl and
R4 and R5 are independently selected from H, C1-6 straight chain or branched alkyl or where R4 and R5 taken together are =O or
or where X is OH or C1 to C6 straight chain or branched alkyl, R1, R2 and R3 are as hereinbefore defined and R4 and R5 are independently -OR9 or –OOCR10 where R9 and R10 are independently selected from C1 to C6 straight chain or branched alkyl or aromatic groups. In embodiments of the invention the allyl group containing monomer is selected from one or more of allyl acetate, allyl chloride, allylidene diacetate,
The invention yet further provides the use of a partially hydrolysed polyvinyl acetate polymer or copolymer as a dispersion stabilizer in suspension polymerization of a vinyl compound, the polymer or copolymer being characterised by the ratio of absorbance at 280nm of a 0.2wt% aqueous solution of the vinyl alcohol polymer to the absorbance at 320nm of a 0.2wt% aqueous solution of the vinyl alcohol polymer is more than 0.7 at 30°C and a Yellow Index of 40 or lower according to JIS K 7105 (1981) as measured on a dry powder, the absorbance being measured with an optical path length of 1cm.
The invention still further provides the use of a partially hydrolysed polyvinyl acetate polymer or copolymer as a dispersion stabilizer in suspension polymerization of a vinyl compound, the polymer or copolymer being characterised by the absorbance at 280nm being no more than 0.36 and the absorbance at 320nm being no more than 0.36 the absorbance being measured of a 0.2wt% aqueous solution at 30C with an optical path length of 1cm. In embodiments the absorbance at 280nm is no more than 0.2 preferably no more than 0.1. In embodiments the absorbance at 320nm is no more than 0.15 preferably no more than 0.1.
Throughout this disclosure where values are mentioned it is intended that they may form the upper or lower limit of a range of values especially in combination with another mentioned value.
The invention is not especially limited as to the nature of the organic halide provided that it has a chain transfer constant for vinyl acetate of at least 0.01, more preferably at least 0.02, yet more preferably in the range 0.02 to 5 and still more preferably in the range 0.02 to 2 such as 0.25 to 1.2. Throughout this disclosure where values are mentioned it is intended that they may form the upper or lower limit of a range of values especially in combination with another mentioned value. Chain transfer constants can be determined by performing a series of low conversion, bulk vinyl acetate polymerisations at a constant initiator/ monomer ratio but varying transfer agent / monomer molar ratios at constant temperature. Typically polymerisation is performed at 60°C to less than 15% conversion using AIBN as the initiator. Molecular weights of the isolated polymer are obtained by either GPC or viscometry. Plotting 1/Pn (the degree of polymerisation) against the transfer/monomer ratio gives the chain transfer constant as the gradient for minimally rate retarding agents asThe chain transfer constant can be determined by methods described by Clarke, Howard and Stockmayer, Macromol. Chem, 1961, 44, 427-447.
By way of non-limiting example suitable organic chlorine or bromine compounds include carbon tetrachloride, hexachloroethane, chloral, vinyl bromide, ethylidene bromide, allyl chloride, methallyl chloride, 1-chloro-but-2-ene (ie crotyl chloride) and ethyl dichloroacetate. The invention need not be restricted to a single chain transfer agent and optionally more than one could be used. It is also possible to use other chain transfer agents which need not have a chain transfer constant within the preferred range nor indeed to be organic halides provided that at least some organic halide chain transfer agent, preferably having a chain transfer constant in the above ranges is present such that the resulting PVA has sufficient unsaturation. The chain transfer agents could also be added all at once at the beginning of the polymerization or discontinuously or continuously during part or all of VAM polymerization. Consequently, the concentration of agent can be varied during the polymerization arbitrarily in order to make a specific molecular weight or molecular weight distribution or polymer blend.
Those skilled in the art will have no difficulty in devising methods of polymerizing the VAM. In general VAM is stirred with the organic halide and an initiator in the substantial absence of oxygen.
A solvent can be present. The solvent should be a solvent for both the VAM and the produced polyvinyl acetate and compatible with the other materials present. Examples of suitable solvents include methanol, ethanol, toluene, methyl acetate and diethyl ether. Methanol is generally preferred. The purpose of the solvent is to allow polymerization to proceed further before the mixture becomes too viscous to stir effectively than would otherwise be the case. The precise amount of solvent present is not of the essence of the invention. In general since the solvent may participate in chain termination it is desirable, but not essential, to keep the amount of solvent at a low level.
Conventional free radical initiators such as AIBN, di-benzoyl peroxide and lauroyl peroxide may be used. Conveniently the free radical initiator is added in solution form for example in a toluene or xylene solution of concentration of about 0.2M. The amount of free radical initiator used depends on the desired rate of reaction.
If desired a co-monomer can be present. Those skilled in the art will have no difficulty in devising suitable co-monomers nor in devising methods of co-polymerization. Particularly preferred co-monomers are those with allyl functionality such as allyl acetate, allylidene diacetate and allyl chloride or substitution variants thereof. It will be apparent to the skilled worker that allyl chloride can function both as a chain transfer agent and a co-monomer. Suitable co-monomers can be added in varying quantities according to the levels of incorporation desired and can be added continuously or discontinuously. Other suitable co-monomers include olefins such as propylene and butenes, di-olefins particularly those having at least one allylic hydrogen such as vinyl norbornene, ethylidene norbornene, norbornadiene, dicyclopentadiene, 1,5 cyclooctadiene, 1,6 octadiene, tetrahydroindenes 1,4 hexadiene and 1,4 pentadiene which are typically used in the production of EPDM rubbers, acrylic acid and its salts, acrylates such as methyl acrylate and ethyl acrylate; methacrylic acid and its salts, methacrylates such as methyl methacrylate and ethyl methacrylate; acrylamide and its derivatives such as N-methyl acrylamide, or N-ethyl acrylamide or N,N dimethyl acrylamide; vinyl ethers such as methyl vinyl ether or ethyl vinyl ether, nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride and vinyl fluoride; allyl compounds such as (meth)allyl chloride, crotyl chloride and their derivatives, allyl acetate, allyl ethers, (meth)allyl ethers, (meth)allyl esters such as 1-methallyl acetate or ethers or crotonic esters and crotonic ethers such as 3-methallyl acetate; allylidene compounds such as allylidene diacetate or allylidene diethers such as dimethoxyacrolein or diethoxyacrolein; or unsaturated carboxylic acids such as crotonic acid, fumaric acid, maleic acid or itaconic acid and their salts and esters such as dimethyl fumarate or diethyl itaconate.
The precise temperature at which polymerization is performed is not of the essence of the invention. If the temperature is too low then the reaction time will be too long. If the temperature is too high then the initiator will decompose at too high a rate. In general terms the temperature should not exceed 75°C and preferably is in the range 60 to 70°C but the skilled worker can by routine experimentation devise ways of operating outside this range and above 75°C. The initiator is chosen to have a suitable half-life in the temperature range and solvent mix selected. Those skilled in the art will have no difficulty in selecting appropriate initiators and reaction temperatures. Initiators can be added at the start of the polymerization, intermittently or continuously, depending upon the choice of initiator used. Suitable examples include benzoyl peroxide, lauryl peroxide, hydrogen peroxide and AIBN.
The reaction is allowed to proceed until the desired proportion of the VAM has been polymerized. Typically this will be of the order of 50 to 80% such as 60 to 70%. At this point the polymer may have Mw of about 10 000 to 500 000 preferably about 15 000 to 100 000 such as 20 000 to 70 000.The polymer may have a polydispersity of about 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.2, 3.5, 3.7, 3.9, 4.1,4.3,4.5, 4.7, 4.9 or 5.1.
The polymer is then separated from unreacted VAM. Those skilled will have no difficulty in devising suitable ways of doing this. One way of achieving this is to add methanol as either liquid or vapour and distil off the VAM/methanol azeotrope leaving a solution of the polymer in methanol. At least some methanol can be removed from the polyvinyl acetate polymer solution. Optionally additives can be added in small quantities such as mild bases (for example pyridine or di-isopropylamine or sodium bicarbonate) as well as polymerization inhibitors.
The polyvinyl acetate polymer is then subjected to partial hydrolysis. Those skilled in the art will have no difficulty in devising suitable ways of hydrolysing the polymer. Acid catalysed hydrolysis can be used but base catalysed hydrolysis is preferred. A way of hydrolysing the polyvinyl acetate is to add a small amount of base for example a solution of sodium methoxide in methanol to a solution of the polyvinyl acetate in methanol with vigorous mixing. Other bases which could be used include hydroxides or alkoxides such as ethoxides of sodium, potassium, lithium, magnesium, calcium or ammonium and any combination thereof. Other solvents can be used such as THF, toluene, methyl acetate provided adequate solubility is achieved. By changing the types of solvent (and thus the dielectric constants of the mixture) changes to the block factor (η, or “blockiness”) can be made (Moritani and Fujiwara, Macromol. Chem, 1977, 10, 532-535). A wet solid gel rapidly forms which can be aged and/or kneaded and/or extruded until the desired degree of hydrolysis is obtained. The hydrolysis reaction is then stopped for example by addition of water or acetic acid, optionally in the presence of an active amine material such as hydroxylamine, semicarbazide or hydrazine and in the presence of a suitable diluent such as methyl acetate, water, methanol, ethanol or mixtures thereof. In an embodiment of the invention the gel is finely chopped and mixed with a dilute solution of acetic acid for example in water or methyl acetate optionally in the presence of hydroxylamine.
Hydrolysis is allowed to continue until the desired degree of hydrolysis is achieved. Typically degrees of hydrolysis are in the range 65% to 90%, preferably between 69 and 75% more preferably in the range of 68-73% such as about 70%. 70% hydrolysis means that 70% of the acetate groups have been hydrolysed from the polyvinyl acetate.
After hydrolysis and “termination” of the hydrolysis reaction, the mixture should be freed of the supernatant liquid. Various methods can be used such as filtration or centrifuging to leave a swollen polymer gel. The hydrolysed polymer can then be dried for use. Those skilled in the art will have no difficulty in devising suitable drying techniques. Examples include heating under reduced pressure, or heating with hot inert gas such as nitrogen or carbon dioxide or heating in air. Drying with hot gas with less oxygen than is present in air such as less than 5% oxygen could be used. Where oxygen is present it is preferred that the flammability limit of the polymer, or indeed any volatiles given off during drying, should not be exceeded. Optionally some water or steam can be present in the gas stream.
In general the polymer will not be dried to absolute dryness but rather volatiles are generally removed down to a low level such as below 5wt% such as 3wt%. Drying is typically performed on a polymer which has been ground or chopped with a graded particle size, or it has been produced in a small particle size during hydrolysis and is typically performed over a period of 0.5 hours to 20 hours. Typically drying is performed at temperatures between 100°C and 150°C, such as 110-140°C more preferably 125-135°C for example at 130°C. During drying additional dehydration of the polymer backbone can occur leading to increased levels of conjugated and unconjugated unsaturation being developed as measured by a variety of means. This procedure is described in US3220992.