GB1568632A

GB1568632A - Process for preparing vinyl or vinylidene halide polymer products

Info

Publication number: GB1568632A
Application number: GB446479A
Authority: GB
Original assignee: Hooker Chemicals and Plastics Corp
Current assignee: Occidental Chemical Corp
Priority date: 1976-11-30
Filing date: 1977-01-07
Publication date: 1980-06-04
Also published as: FR2372180B1; BR7700207A; DE2701680A1; SU799672A3; BE850890A; FR2372180A1; JPS6031848B2; IT1084901B; NL7701001A; CA1111176A; ES455205A1; JPS5369294A

Description

(54) IMPROVED PROCESS FOR PREPARING VINYL OR VINYLIDENE HALIDE POLYMER PRODUCTS (71) We, HOOKER CHEMICALS & PLAS TICS CORP., a Corporation organised and existing under the laws of the State of New York, United States of America, of Niagara Falls, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the preparation of vinyl or vinylidene halide polymer products of high impact strength and food processability by bulk polymerisation.

In our United Kingdom Specification No.

1,436,162 we describe and claim a process for the preparation of a vinyl halide polymer product, which process comprises bulk polymerising a monomer composition comprising at least 50% by weight of a vinyl halide monomer in the presence of a preformed polymer which consists essentially of a hydrocarbon polymer derived from one or more acyclic mono-olefins and optionally a cyclic or acyclic diene, has a weight average molecular weight of at least 50000, and is present in an amount of 0.005 to 20% by weight of the total weight of monomer.

In this process, the polymerisation mass proceeds after initiation from a substantially clear solution or dispersion of olefin polymer in monomer composition to a milky opaque emulsion. After about 1 hour, the reaction mass becomes a paste, and after about 1.5 hours of reaction, corresponding to 25 to 30% conversion of monomer to polymer, the reaction isotherm shows a rapid increase, with concurrent thickening of the paste, i.e.

development of a "thick paste state" in the reaction mass. After 40 to 45 /O conversion of the monomer to polymer, the thick paste becomes, in the main, a fine non-vitreous powder.

In our copending Application No. 614/77 (Specification No. 1,568,631) we describe and claim a process for the preparation of a vinyl or vinylidene halide polymer product, which process comprises bulk polymerising a monomer composition comprising at least 50% by weight of a vinyl or vinylidene halide monomer and 0 to 50% by weight of an ethylenically unsaturated monomer copolymerisable therewith, in the presence during liquid phase polymerisation of more than 3.5% by weight based on said monomer composition of at least one preformed olefin polymer having a weight average molecular weight of at least 50,000, removing from the polymerisation mass during the thick paste state thereof from 2% to less than 50% by weight of the monomer composition charged to the polymerisation, the effective concentration of said olefin polymer after monomer composition removal being above 5.3 weight percent based on monomer composition remaining in said polymerisation mass after said removal, and continuing the polymerisation to provide a finely divided particulate polymer product.

We have now found that polymer products of high impact strength and good processability can be obtained wherein there is a high portion of small size particles and a low residual vinyl or vinylidene halide monomer content even when the effective concentration of olefin polymer following monomer removal is below the minimum required in accordance with the process of Application No. 614/77 (Specification No.

1,568.631).

The present invention accordingly provides a process for the preparation of a vinyl or vinylidene halide polymer product, which process comprises bulk polymerising a monomer composition comprising at least 50 /O by weight of a vinyl or vinylidene halide monomer and 0 to 50% by weight of an ethylenically unsaturated monomer Co- polymerisable therewith, in the presence during liquid phase polymerisation of more than 1.8% by weight based on said monomer composition of at least one preformed olefin polymer having a weight average molecular weight of at least 50,000, removing from the polymerisation mass during the thick paste state thereof from 2% to less than 50% by weight of the monomer composition charged to the polymerisation, the effective concen traction of said olefin polymer after monomer composition removal being above 3.5 weight percent based on monomer composition remaining in said polymerisation- mass after said removal, and continuing the polymerisation to provide a finely divided particulate polymer product provided that if more than 3.5% by weight of the preformed olefin polymer is present during liquid phase polymerisation the effective concentration of said olefin polymer after monomer composition removal is not more than 5.3 weight percent.

Except for the above-defined improvements or modifications of the invention, the reactants and reaction conditions, e.g.

reaction temperature and pressure, are substantially the same as those for the polymerisation disclosed in Application No. 614/77 (Specification No. 1,568,631).

The vinyl or vinylidene halide monomers useful in the process of the invention are the alpha-halo-substituted ethylenically- unsaturated compounds which like vinyl chloride are capable of entering into an addition polymerisation reaction, for example, vinyl fluoride, vinyl bromide, vinyl iodide, vinylidene fluoride, vinylidene chloride, vinylidene bromide and vinylidene iodide. The polymer products of the present invention can be formed of the same or different alpha-halo-substituted ethylenically unsaturated monomers and, thus, the products can contain homopolymers or copolymers, for example, binary copolymers, terpolymers, and interpolymers formed by addition polymerisation. Illustrative of these copolymers is a copolymer of vinyl chloride and vinylidene chyloride.

The vinyl halide monomer utilised in the present process is preferably vinyl chloride, although other vinyl halides such as vinyl fluoride and vinyl bromide can be employed also.

In carrying out the process of the invention the monomer composition can be removed from the thick paste state of the agitated polymerisation reaction mass in any suitable way. For example liquid monomer may be filtered from the bulk reaction mass, e.g. by passage through a pressure filter. The filtrate can then be distillerl outside the reaction vessel with the distillation residue containing -initiator and unreacted olefin polymer being returned to the reaction vessel. However, since the polymerisation is genially carved out under at least auto ge us superatmonheric pressure. especi we vinyl chloride is employed as a removal removal of monomer is preferably y- venting the reaction mixture to a - e,- e.z the atmosphere, wherein llt subsEntially below the reaction pressure. Removal by venting is especially desirable since it promotes rapid removal of heat from the reaction mass.

Monomer removal is commenced during the above-descibed thick paste state of the reaction the duration of which generally corresponds to conversion to polymer of 25% to 45%, more typically 30% to 40 O by weight of monomer, based on monomer charged. The onset of the thick paste state is generally accompanied by a rapid increase in the heat evolved from the reaction, i.e. by a rapid increase in the reaotion isotherm as evidenced by a sharp increase in reaction pressure. Preferably monomer removal in accordance with the invention is commenced 5 to 15 minutes after beginning of the thick paste state of the polymerisation. The venting of monomer from the reaction mass accords ing to the preferred mode - of removal of monomer may be carried out in continuous fashion, or altematively and desirably, in intermittent but regular fashion with the reaction mass being restored, after each release of monomer, substantially to the temperature and pressure prevailing in the reaction mass prior to each release of monomer, The polymerisation vessel is desirably equipped with a conventional adjustable valve to facilitate venting.

The amount of monomer which is removed during the thick paste state of the polymerisation reaction in order to avoid product agglomerates according to the invention is a minor proportion of the monomer employed in the polymerisation, i.e. 2% to less than 50 weight percent of the monomer charged. Preferably, however, to retain substantially all of the benefits and advantages of the prior art polymerisation process of United Kingdom Specification No. I,436,.162 no more than 40 weight percent, typically no more than 30 weight percent, of the monomer charged to the polymerisation is removed in the process of the invention.

While some improvement in obtaining finely divided polymer product d small maximum particle size can be achieved by removing only small amounts, say 2 to 3% by weight, of monomer during the thick paste state of the polymerisation, it is preferred to remove at least 5 weight percent of the monomer charged in the process of the invention.

Preferably the percentage of monomer removed can vary from 8 to 15% up to 25 to 35%, and is more preferably 15 to 35% based on the monomer charged.

The rate of removal of monomer by venting or other removal technique can be varied over a wide range but usually is 0.1% to 1.5% preferably 0.15% to 1.2% per minute based on- the weight of monomer charged. An especially good result is generally obtained when the monomer is removed from the polymerisation mass at a rate which can range from 0.3% to 0.8 up to 1.0% or even up to 1.2% by weight per minute.

The proportion of monomer and olefin polymer charged initially to the polymerisation should be sufficient to provide, after monomer removal in the thick paste state, an effective olefin polymer concentration of above 3.5%, by weight computed on the amount of monomer remaining after removail of monomer according to the invention, i.e. on the amount of monomer charged minus the amount of monomer removed in the thick paste state of the polymerisation.

The" initial concentration of olefin polymer and monomer in the polymerisation should be' such as to provide a reaction mixture containing, before venting or other removal of the monomer, above 1.8%, and desirably at least 3% by weight of olefin polymer based on the weight of monomer charged.

Whale the exact chemical nature of the polymer product formed by the process of the present invention is not knows it is believed that a graft copolymer is formed in whioh a vinyl or vinylidene halide polymer forms upon the olefin polymer. To obtain a maximum reduction in melt viscosity which is a standard measure of procssabillty, the ,OWifl polymer used as trunk or backbone polymer in graft polymerisation should be inXpatible with the vinyl or vinylidene ide polymer formed. During the process ing of a vinyl or vinylidene halide polymer such as in moulding, the physical properties of the polymer change during the processing as a result of the polymer being held at bigh temperatures for long periods, the high temperatures arising from the internal heat built up as a result of shear forces produced the the-processing machinery. Thus, the phys- ica( properties sof a graft polymer havmg a trunk polymer which is compatible with a vinyl or vinylidene halide polymer can change during processing as the result of solubilisation of the trunk polymer into the vinyl or vinylidene halide polymer. In such a case, the impact strength would decrease during the processing. Therefore, the poly mer products of the present invention pre ferably are graft copolymers having an olefin polymer backbone which is incompatible with the vinyl or vinylidene halide polymer formed thereon. With such an incompatible polymer backbone, the physioal properties of the graft oopolymer do not change during processing, since the incompatibility prevents the soluibilisation of the trunk polymer in the vinyl or vinylidene halide polymer.

The melt viscosity is reduced by the choice of a graft copolymer and is not affected by the usual subsequent processing conditions.

The melt viscosity of the graft copolymer formed also depends upon the molecular weight of the trunk polymer, as well as the vinyl or vinylidene halide polymer formed thereon. A maximum reduction of melt viscosity can be expected from the graft copolymer where the trunk polymer is chosen so as to have low molecular weight, e.g. a weight average molecular weight of 50,000 to 150,000 and the vinyl or vinylidene halide monomer is polymerised so as to have a reasonably low molecular weight also, such low molecular weight olefin polymers being preferred for especially easy processing in the molten state. Preferably to produce polymer products of excellent impact strength, i.e. of high graft olefin polymer content or high grafting efficiency, the weight average molecular weight of the olefin polymer may range from 150,000 to 1,000,000 or higher and is especially 150,000 to 400,000.

While it is preferred that the monomer composition consist of vinyl or vinylidene halide monomer, e.g. vinyl chloride alone, the present invention is also intended to include polymer products formed by the free-radical addition polymerisation of a monomer composition containing a predominant amount, i.e. at least 50 percent, of vinyl or vinylidene halide, and a minor amount, i.e. less than 50 percent by weight, of another ethylenically unsaturated monomer composition copolymerisable therewith, Preferably, the other ethylenically unsaturated monomer is used in amounts of 20 percent or less by weight and more preferably in amounts of 10 percent or less by weight of the monomer composition used in preparing the polymer. Suitable ethylenically unsaturated compounds which can be used to form binary copolymers, terpolymers, tetrapolymers and interpolymers, are monoethylenically unsaturated hydrocarbons, i.e. monomers containing only carbon and hydrogen, such as ethylene, propylene, 3-methylbutene-l, Smethylpen- tene- 1, pentene-l, 3,3-dimethylbutene-l. 4,4 dimethylbutene-1, octene-1, decene-1, styrene and its nuclear alpha-alkyl or aryl substituted derivatives, e.g. o-, m- or p-methyl, ethyl, propyl or butyl styrene, alphamethyl, ethyl, propyl or butyl styrene, and phenyl styrene; halogenated styrenes such as alpha-chlorostyrene; monoethylenically unsaturated esters including vinyl esters, e.g. vinyl acetate, vinyl propionate, vinyl butyrate, vinyl stearate, vinyl benzoate, vinyl-p-chlorobenzoate. alkyl methacrylates. e.g. methyl, ethyl, propyl, butyl and octyl methacrylate, alkyl crotonates, e.g. octyl crotonate, alkyl acrylate e.g.

methyl, ethyl, propyl, butyl, 2-ethyl hexyl, stearyl, hydroxyethyl and tertiary butylamino acrylates, isopropenyl esters, e.g. isopropenyl acetate, isopropenyl propionate, isopropenyl butyrate and isopropenyl isobutyrate; isopropenyl halides, e.g. isopropenyl chloride; vinyl esters of halogenated acids, e.g. vinyl alphachloroacetate, vinyl alpha-chloropropionate and vinyl alpha-bromopropionate; allyl and methallyl esters, e.g. allyl chloride, allyl cyanide, allyl chlorocarbonate, allyl nitrate, allyl formate and allyl acetate and the corresponding methallyl compounds; esters of afkenyl.

alchols e.g. beta-ethy;l allyl alcohol ard beta- propyl allyl alcohol; halo-alkyl acrylates, e.g.

methyl alpha-chloroacrylate and ethyl alphachloroacrylate, methyl alpha-bromoacrylate, ethyl alpha-bromoacrylate, methyl alphafluoroacrylate, ethyl aipha-fluoroacrylate, methyl alpha-iodoacrylate and ethyl alphaiodacrylate; alkyl alpha-cyanoacrylates, e.g.

methyl alpha-cyanoacrylate and ethyl alphacyanoacrylate; maleates, e.g. monomethyl maleate, monoethyl maleate, dimethyl maleate and diethyl maleate; -fumarates e.g.

monomethyl fumarate , monomethyl fumarate, dimethyl fumarate and diethyl fumarate; diethyl glutaconate; monoethylenically unsaturated organic nitriles including, for example, fumaronitrile, acrylonitrilo, metha crylonitrile, ethacrylonitrile, 1,1 -dicyanopro- pene-l, 3-octenenitrile, crotonitrile and oleonitrile; monoethylenically unsaturated carboxylic acids and anhydrides including, for example, acrylic acid, methacrylic acid, crotonic acid; 3-butenoic acid, cinnamic acid, maleic, fumaric and itaconic acids and maleic anhydride, as well as amides of these acids, such as acrylamide; vinyl alkyl ethers and vinyl ethers, e.g. vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl n-butyl ether, vinyl isobutyl ether, vinyl 2-cthylhexyl ether, vinyl 2-chloroethyl ether, and vinyl cetyl ether; vinyl sulphides, e.g. vinyl betachloroethyl sulphide and vinyl beta-ethoxyethyl sulphide. Diethylenically unsaturated hydrocarbons containing two double bonds in conjugated relation and halogen derivatives thereof, e.g. butadiene- 1,3; 2-methylbutadiene-1,3; 2,3-dimethylbutadiene-l 3; 2 chloro-butadiene-l 3; 2,3-dichloro-butadiene- 1,3; and 2-bromo-butadiene-l,3, can also be used.

Specification monomer compositions for forming copolymers can be illustrated by vinyl chloride and/or vinylidene chloride and vinyl acetate, vinyl chloride and/or vinylidene chloride and maleic or fumaric acid esters, vinyl chloride and/or vinylidene chloride and acrylate or methacrylate esters, vinyl chloride and/or vinylidene chloride and vinyl alkyl ether. These are given as illustrative of the numerous combinations of monomers possible for the formation of copolymers. The present invention includes all combinations.

The free radical bulk polymerisation of the monomer compostion is conducted in the presence of an olefin polymer, which may be a homopolymer or copolymer, for example, binary copolymer, terpolymer, or tetrapolymer. The olefin polymers can also contain units derived from a diene.

Suitable olefin monomers are propene, butene-1, isobutene, pentene, hexens heptene, octene, 2-methyl-propene-l, 3-methylbutene-l, 4-methylpentene-1, 4-methylhex even1, 5-methylhexene-l.

Suitable comonomers for preparing olefin copolymers are those utilised to prepare homopolymers as listed above such as propene or butene-l with ethene or isobutylene with isoprene, ethene with vinylacetate, or ethene with ethyl acrylate. Suitable termonomers for preparing olefin terpolymers are those utilised to prepare homopolymers and binary copolymers as disclosed above such as propene, ethene and up to 15 percent preferably up to 6 percent by weight of a diene such as dicyclopentadiene, butadiene, cyclooctadiene and other non-conjugated dienes with linear or cyclic chains.

The olefin polymers used are characterised by being soluble, partially soluble or dispersible at normal room temperature and pressure in vinyl or vinylidene halide monomer and if a homopolymer, having monomeric units with 2 to 8 carbon atoms; if copolymers, having - monomeric units with 2 to 8 carbon atoms; and if a halogenated polymer, having monomeric units with 2 to 8 carbon atoms. Suitable halogenated olefin polymers arc the chlorinated, brominated or fluorinated olefin polymers. The weight average molecular weight of the olefin polymers and copolymers can vary from 50,000 to 100,000,000 and higher as described above.

The free radical bulk polymerisation can take place in accordance with the process of the invention at temperatures between 250 and 900, preferably 400 to 80 , and especially 500 to 75 , centigrade. The polymerisation reaction is conducted in the presence of a small initiating amount of a free radical initiator for the reaction. Useful free-radical initiators are organic or inorganic peroxides persulphates, ozonides, hydroperoxides, peracids and percarbonates, diazonium salts, diazotates, peroxysulphonates, trialkyl borane-oxygen systems, amine oxides, and azo compounds such as 2,21-azo-bis-isobutyroni- trile and 2,2'-azo-bis-2, 4-dimethyl valeronitrile. Preferably an azo compound or an organic peroxy compound, especially an organic peroxide, is used as the initiator. The initiator is used in a concentration ranging from 0.01 to 1.0% and preferably 0.05 to 0.5% based on the total weight of all monomers in the reaction mixture. Organic initiators which have particularly good solubility in the bulk polymerisation mass are especially useful in the practice of the invention and include the following representative examples: lauroyl peroxide, benzoyl peroxide, diacetyl peroxide, azobisisobutyronitrile, diisopropyl peroxydicarbonate, azo-bisisobutyramidine hydrochloride, t-butyl peroxypivalate, 2,4-dichlorobenzoyl peroxide, and 2, 2' -azo-bis-(2,4-dimethyl valeronitrile!. These and other suitable initiators are more particularly described by J. Brandrup and E.H.

Immergut, Editors "Polymer Handbook", interscience Publishers, 1966, Chapter II entitled "Decomposition Organic Free Radical Initiators". Advantageously, the initiator which is used is chosen from a group of initiators known in the prior art as the "hot catalysts" or those which have a high dgreee of free-radical initiating activity.

Initiators with a lower degree of activity are less desirable in that they require longer polymerisation times. Also, long polymerisation times may cause preliminary product degradation evidenced by colour problems, e.g.

pinking.

The present process is preferably carried out in a single stage bulk operation but, if convenient or desired, the reaction can be effected in a two stage reaction in which high speed, high shear agitation is used during a first stage, and low speed, low shear agitation is used in a second stage. Two stage bulk polymerisation processes for vinyl halide and vinyl halide-comonomer mixtures which are useful in the practice of the invention are described in United Kingdom Patent Specifications Nos. 1,047,489 and 1436162 and United States Patent Specification No.

3,522,227.

In the following abbreviated description of a typical two stage reaction configuration for carrying out the present process, for the sake of simplicity, the initial stage of the polymerisation or copolymerisation will be referred to as first stage reaction and the vessel in which this initial stage of polymerisation is carried out will be referred to as "Prepolymeriser". The final or complementary stage of the polymerisation will be called simply second stage reaction and the vessel in which it is carried out the "Polymeriser".

In the first stage reactor, the means chosen to agitate the monomer or monomers is of a type capable of providing high shear agitation and is commonly referred to as a "radical turbine type" agitator. At the start of the first stage reaction,. the Prepolymeriser is charged with a monomer composition to which an initiator has been added. Any polymerisation generally used in bulk polymerisation methods, that is, those hereinabove described, can be used to an extent which is usual for bulk polymerisation processes. After addition of the vinyl or vinylidene chloride monomer to the first stage reactor, a small amount of monomer is vented in the process of removing the air from the first stage reactor vessel. The speed of the turbine type agitator generally lies between 500 and 2,000 revolutions per minute or a tip speed of 2 to 7 metres per second in the first stage reactor. A tip speed of at least 0.1, and preferably, 0.5 to 2 metres per second is used in the second stage reactor. These figures should not be regarded as limiting values. As soon as a conversion of at least 3 to 20 percent of the monomer composition has been obtained in the first stage reactor, the contents of the vessel are transferred to a second stage polymeriser vessel equipped to provide slow speed, low shear agitation so as to ensure proper temperature control of the reaction medium. Preferably the conversion in the first stage reactor is 3 to 15 percent and is especially 7 to 15 percent. The reaction temperature in both first and second stage reactors generally ranges between 25 degrees centigrade to 90 degrees centigrade, preferably 40 to 80 degrees centigrade. The reaction pressure in the first stage reactor is also at least an autogeneous superatmospheric pressure generally in the range between 80 to 210 pounds per square inch, and preferably between 90 to 190 pounds per square inch.

Since the maximum conversion (e.g. 25 305S) of vinyl or vinylidene halide corresponding to onset of the thick paste state of the polymerisation invariably occurs in the second reaction stage of the above described two stage reaction configuration, vinyl or vinylidene halide monomer is always removed from the second stage of the two stage reaction process in accordance with the invention. Moreover, as will be evident to those skilled in the art, the conditions of temperature pressure and agitation of the second stage are substantially similar to, and hence, typify those used when carry; ing out the present improved polymerisation in a single reaction stage.

The improved polymerisation product of the invention is recovered from the polymerisation reaction vessel in conventional fashion, e.g. by expelling unreacted monomers by venting. The finely divided polymer products are easily ground or otherwise comminuted to a homogeneous powder for mixture with conventional inert additives such as fillers, dyes and pigments.

In addition, the polymerisation products can be mixed with plasticisers, lubricants, thermostabilisers and ultraviolet and light stabilisers as desired. If desired the polymer product can be directly melted for combination with the aforementioned additives and subsequent molten processing such as moulding and extrusion. The melting or fusion of the polymer products which contain predominantly, finely divided particles, occurs so rapidly as to avoid any serious decomposition or colour-degradation caused by exposure to elevated temperature during the melting or fusion operation.

The exact mechanism by which the present process effectively breaks up re action mixture agglomerates is not understood completely. but while the invention is not bound to any theory it is surmised that removal of vinyl or vinylidene halide monomer in accord with the invention increases the ratio of solid phase, i.e. polymer. to liquid phase, i.e. vinyl or vinylidene halide monomer containing dissolved or dispersed olefin polymer, in the reaction mass and hence rapidly advances the reaction mass out of the thick paste state into the fluid powder state described hereinabove.

In order to further illustrate the invention the following Examples are given. In this specification unless otherwise indicated, parts, percentages and proportions are by weight and temperatures are in degrees centigrade.

EXAMPLE 1 To a vertical type first stage reactor of 2.5 gallon capacity and stainless steel construction, equipped with a radial turbinetype agitation a pressure sensor and a venting valve, there is added 6.81 kg vinyl chloride monomer, 1.26 g of dicyclohexyl peroxydicarbonate polymerisation initiator sold under the tradename "Lupcrsol 229" and 0.75 g of a 50iso methanol solution of "Gelva" (a densifying agent which is a 2:1 copolymer of vinyl acetate and crotonic acid manufactured by Monsanto Co.) ("Lupersol" and "Gelva" are Registered Trade Marks).

About 0.908 kg of vinyl chloride monomer are vented from the reactor in order to remove entrapped air. The reaction mass is heated to about 700 under an autogeneous reaction pressure of about 167 psig. With the agitator operating at about 1500 rpm and agitated at these conditions of temperature and pressure for about 25 minutes after w initiator charged at the beginning of the second reaction stage is 3.18 kg and 5.0 g., respectively, and the monomer removal step Of the invention is omitted so that the proportion of terpolymer based on monomer in the second stage is substantially the same as that in Example 1 above subsequent to the monomer removal step, i.e. about 4.5%.

A polymer product which has satisfactory impact resistance is obtained in a yield of 7.72 kg (corresponding to a conversion of monomer to polymer of about 80% based on monomer charged to the polymerisa ben), Only about 60% of the product is capable of passing through the 10 mesh screen described in Example 1. The amount of residual vinyl chloride monomer in the product fraction which passed through the 10 mesh screen is about 990 ppm.

Many process changes can be made in the process of Example 1 which is illustrative of the invention, without departing from the scope of the invention. For example, if desired, a portion, e.g. about 10% of the vinyl chloride reactant, may be replaced by a compatible comonomer, e.g. methyl acrylate, to obtain an excellent finely divided particulate polymer product.

Also, advantageously the vinyl chloride which is allowed to escape in Example 1 can be collected by venting the vinyl chloride to a cooled receiver at atmospheric pressure or to a compressor for iiquification. The resultant recovered vinyl chloride can be reserved for later polymerisation. Futhermore, excellent results are obtained when the ethylene-propylenediene terpolymer is replaced by the following olefin polymers, polyethylene, polypropy- lene and ethylene propylene diene-modified terpolymer having an ethylene/propylene ratio of 55/45 and containing 1,4-hexadiene as the diene in an amount of 3 t 0.5 percent, a 1-butene-ethylene copolymer containing 5% ethylene, and chlorinated polyethylene sold under the trademark "Tyrin".

Moreover, instead of adding the olefin polymer directly to the polymerisation as described in Example 1, the olefin polymer can be mixed with all, or more conveniently, a portion of the vinyl or vinylidene halide monomer reactant and dissolved, partially dissolved or dispersed in said monomer with heating and/or agitation, as desired, prior to addition to the reaction vessel. While the addition of the olefin polymer to the polymerisation reaction mixture according to the invention can be carried out at the beginning of polymerisation reaction, i.e. at 0% conversion by weight of monomer to the polymer, it is desirable that the olefin polymer be added immediately after some of the monomer, i.e. up to about 20%, has been converted to polymer, preferably after 1% to 15 %, more preferably 3% to 15% conversion of monomer to polymer. When the polymerisation is operated as a two stage process in accordance with the aforementioned techniques of British Patent 1,047,489 and United States Patent 3,522,227, the olefin polymer is added to the polymerisation substantialy immediately after the completion of the first stage i.e. after preferably 3% to 15% by weight and more preferably 7% to 15% of the monomer has been converted to polymer. Conveniently, in carrying out the polymerisation in the two stage reaction configuration, the olefin polymer is added to the second stage so as to be present in the second stage reaction vessel prior to occurrence of any substantial polymerisation therein.

The addition of the olefin polymer subsequent to initiation of the polymerisation as described above provides in conjunction with the monomer venting procedure of the invention, in general, a faster polymerisation reaction, a lower concentration of residual vinyl or vinylidene halide monomer in the polymerisation product, and especially a particularly excellent distribution of product particle size, i.e. the product is characterised by an especially narrow distribution of product particle size and contains an especially large, generally predominant, fraction of the most minute particles. Such improved product particle size distribution is of especial advantage in many uses of the product such as injection moulding and extrusion of articles such as pipe and siding.

According to another preferred mode of carrying out the invention it is advantageous when operating the polymerisation according to the aforementioned two stage configuration to add to the first reaction stage only a portion, of the monomer or monomers used in the process with the balance being added so as to be present in the second reaction stage prior to the thick paste state venting operation which in the two stage reaction configuration is carried out in the second reaction stage. Generally at least 50% by weight or more of the monomer reactant (corresponding to at least about 60% by weight or more of the monomer reactant when the amount of monomer vented in the thick paste state is discounted from the amount of monomer used in the polymerisation) is added to the first reaction stage with the balance being added at about the beginning of the second reaction stage (so that it is present prior to the venting operation of the invention). Preferably 50% to 60% by weight of the monomer reactant is added in the first reaction stage (corresponding to addition of 60% to 70% of the monomer reactant when the monomer reactant which is vented is discounted as described above).

This preferred mode of charging mono mer or monomers in carrying out the polymerisation in the aforementioned two reaction stage configuration permits use of a first stage reaction vessel of smaller size than that used in the second reaction stage and also, in general, assists in providing a polymer product of excellent particle size distribution.

WHAT WE CLAIM IS 1. A process for the preparation of a vinyl or vinylidene halide polymer product.

which process comprises bulk polymerising a monomer compostion comprising at least 50% by weight of a vinyl or vinylidene halide monomer and 0 to 50% by weight of an ethylenically unsaturated monomer copolymerisable therewith, in the presence during liquid phase polymerisation of more than 1.8% by weight based on said monomer composition of a least one preformed olefin polymer having a weight average molecularweight of at least 50,000, removing from the polymerisation mass during the thick paste state (as hereinbefore defined) thereof from 2% to less than 50% by weight of the monomer compostion charged to the polymerisation, the effective concentration of said olefin polymer after monomer composition removal being above 3.5 weight percent based on monomer composition remaining in said polymerisation mass after said removal, and continuing the polymerisation to provide a finely divided particulate polymer product, provided that if more than 3.5% by weight of the preformed olefin polymer is present during the liquid phase polymerisation the effective concentration of said olefin polymer after monomer composition removal is not more than 5.3 weight percent.

2. A process according to claim 1, -where- in the monomer composition consists of vinyl halide monomer. the olefin polymer is a halogenated polyolefin, olefin homopolymer or olefin copolymer, said polymer having 2 to 8 carbon atoms in the monomeric olefin units thereof and a weight average molecular weight of 150,000 to 1,000,000, and the amount of vinyl halide monomer removed during the thick paste state is 5''', to 40esRc of the vinyl halide monomer charged to the polymerisation.

3. A process according to claim 2, wherein the olefin polymer is a terpolymer containing units derived from diene monomer.

4. A process according to claim 3, wherein the diene is dicyclopentadiene, 1,3butadiene or a non-conjugated diene with linear or cyclic chains, and is present in said terpolymer in a proportion up to 15% by weight.

5, A process according to claim 4, the diene is present in a proportion up b+6*- by weight of said terpolymer.

6. A process according to claim 3, wherein the olefin terpolymer is an ethylene propylene-ethylidene norbornene terpolymer.

7. A process according to claim 3, wherein the olefin terpolymer is an ethylene propylene-1,4-hexadiene terpolymer.

8. A process according to claim 2, wherein the olefin polymer is an ethylenepropylene copolymer.

9. A process according to claim 2, wherein the olefin polymer is a butene-1ethylene copolymer.

10. A process according to claim 2, wherein the olefin polymer is an ethylene homopolymer.

11. A process according to claim 2, wherein the olefin polymer is a propylene homopolymer.

12. A process according to claim 2, wherein the olefin polymer is a chlorinated polyethylene.

13. A process accordig to any one of claims 1 to 12 wherein the vinyl halide monomer is vinyl chloride, the polymerisation is a single stage bulk polymerisation caried out at a temperature of 25 to 900 centigrade under at least autogeneous superatmospheric pressure in the presence of an initiating amount of a free radical initiator for the reaction, the thick paste state of the polymerisation mass corresponds to a conversion of vinyl chloride to polymer of 30% to 40% by weight, and 8% to 35% by weight of the vinyl chloride is removed by venting from said pressurized polymerisation mass.

14. A process according to claim 13, wherein the vinyl chloride is vented from the polymerisation mass at a rate of 0.1 to 1.5% by weight vinyl chloride per minute based on vinyl chloride charged to the polymerisation and the polymerisation temperature is from 40 to 800 centigrade at autogeneous superatmospheric pressure.

15. A process according to claim 14, wherein the polymerisation temperature is from 500 to 75" centigrade, the initiator is an organic peroxy or azo compound added to the polymerisation mass in a concentration of 0.01% to 1.0% based on the weight of vinyl chloride and the vinyl chloride is vented from the polymerisation mixture at a rate of 0.15% to 1.2a/G per minute, said venting commencing 5 to 15 minutes after onset of the thick paste state in the polymerisation mass.

16. A process according to claim 15, wherein the weight average molecular weight of the olefin polymer is 150,000 to 400,000, the initiator is an organic peroxide, and the vinyl chloride is vented from the polymerisation mass at a rate of 0.3% to 1.2% per minute.

17. A process according to any one of claims 1 to 12, wherein the bulk polymer

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mer or monomers in carrying out the polymerisation in the aforementioned two reaction stage configuration permits use of a first stage reaction vessel of smaller size than that used in the second reaction stage and also, in general, assists in providing a polymer product of excellent particle size distribution. WHAT WE CLAIM IS

1. A process for the preparation of a vinyl or vinylidene halide polymer product.

17. A process according to any one of claims 1 to 12, wherein the bulk polymer

isation is conducted in two stages, a first stage during which the reaction mixture is subjected to high speed agitation until 3 to 200to by weight of the monomer composition has polymerised, and a second stage during which the resultant reaction mixture is sub vented to low speed agitation until polymer isatlon has been completed, the thick paste state and the removal of monomer composition taking place in the second stage.

18. A process according to claim 17, wherein a portion, amounting to at least 50% by weight of the monomer composition is charged to the polymerisation reaction in the first stage, the balance of the monomer composition being added at about the beginning of the second stage.

19. A process according to claim 18, wherein 50% to 60% by weight of the monomer composition is added in the first stage.

20. A process according to claim 17, 18 or 19, wherein 3% to 15% by weight of monomer composition is converted to polymer in the first stage.

21. A process according to claim 20 wherein 7% to 15% of monomer composition is converted to polymer in the first stage.

22. A process according to any one of claims 17 to 21, wherein the monomer composition consists of vinyl chloride.

23. A process according to any one of the preceding claims, wherein the preformed olefin polymer is introduced either before polymerisation has started or before 20% bp weight conversion of the monomer composition to polymer.

24. A process according to claim 23, wherein the olefin polymer is introduced after at least 1 % conversion of the monomer composition.

25. A process according to claim 24, wherein the olefin polymer is introduced after 3% to 15% conversion.

26. A process according to any one of the preceding claims, wherein the olefin poly; mer is introduced to the polymerisation dissolved or dispersed in a portion of the monomer composition.

27. A process according to claim 1 substantially as described in Example 1.

28. A polymer product when prepared by a process as claimed in any one of the preceding claims.