IL28663A - Process for the polymerization of vinyl chloride and polyvinyl chloride obtained - Google Patents

Description

28663/2 >»3 *» ism f-ii s Process for the polymerization of vinyl chloride and polyvinyl chloride obtained CHA ILLOIf Societa Anonima Italiana per le Fibre Tessili Artificiali S.p.A.

C: 27217 This invention relates to a process for the low temperature bulk-polymerization of vinyl chloride and to highly syndiotactic polyvinyl chloride thus obtained.

It is known that the low temperature polymerization of vinyl chloride results in the formation of polyvinyl chloride hich exhibits a degree of syndiotacticity exceeding 1.8, glass transition temperature (Tg) exceeding 95°C and a higher softening temperature than the polyvinyl chloride obtained at a higher polymerization temperature. Such polyvinyl chloride, usually called highly syndiotactic polyvinyl chloride, is particularly suitable to be transformed into fibres having excellent physical, mechanical and chemical characteristics and in -particular an excellent dimensional stability both in boiling water, as well as in air at higher temperature and in solvents used in dry cleaning within the temperature limits of the normal practical use of such solvents.

The degree of syndiotacticity, as understood herein, is determined in the manner disclosed by Fordham, Burleigh and Sturm in J. Polymer Sci. Vol. XLI (1959) - pages. 73-82.

The glass-transition temperature (Tg) is determined in the manner described in J. Polymer Sci. Vol. 56 (1962) - pages 225-231, from which it will also be seen that the Tg-value of a conventional polyvinyl chloride is about 78°C.

The low temperature polymerization of vinyl chloride, practically, involves serious difficulties as far as the polymerization process a d the catalyst are concerned.

In fact, the only polymerization process which can be easily carried out at low temperature is the bulk-pplymerization, because e other known polymerization processes, that is emul- A sion or solution process, involve man inconveniences such as the choice of a suitable solvent or emulsifying agent, the necessity to use voluminous equipment and great volumes of reacting compounds for obtaining an industrially interesting productivity,, hig costs for bringing the polymerization mixture down to a low temperature, etc* As to the catalyst, the usual polymerizatio initiators like inorganic peroxides, azo-bis-isobutyroHiitrile, „ persulpha-tes„ etc. are ineffective in the low temperature polymerization of vinyl chloride, because they are stable and do not produce the free radicals required to start polymerization. it is known that the Redox catalyst system constituted by an organic hydroperoxide and sulphur dioxide is capable to form Howevero ' the use of such catalysts gives rise in practice to several drawbacks. For example,, such catalysts are seif-inflararaable when in contact with air* they are difficult to syn hetize and very unstable. Furthermore they are very oxygen sensitive inasmuch as slightest oxygen traces9 riot checked du~ . ring the polymerization, cause great variations in the polymer! zation conversion and in the viscosity of the polyme 0 Furthermore» the decomposition products of' said catalysts prove to b still excellent polymerization initiators at room t mperature or at higher temperatures, consequently the unreac-ted recovered monomers„ containing the decomposition products of said catalystsp tend to polymerize during their recovery and storage,, .

Therefore the problem arises of completely eliminating those decomposition products from the unreacted monomers.

A primary object of this invention isP therefore„ to provide an advantageous and reliable process for low temperature bulk-polymerization of vinyl chlorides in which the above recalled drawbacks are avoided.

It has been surprisingly found that such drawbacks can be avoided by bulk-polymerization at a temperature below 0°C of vinyl chloride in the presence of a catalytic system consiti g of an organic hydroperoxides sulphur dioxide and at least one alcoholate ,of the general formula (R-o)^ Me wherein "R" is a alky! radical with a linear or branched chain having from 1 to 6 carbon atomse "Me" is a metal of the first or second group of the Periodic System or aluminium and "n" may be 1, 2 or 3B dep It is pointed out that the strongly effective free radical polymerization initiators which start the low temperature bulk~polymerization of vinyl chloride are produced by the cooperation of the above cited three compounds of the catalytic system^ that is an organic hydroperoxide, sulphur dioxide and an aleoholate.

The simultaneous presence of these three compounds, therefore,, is essential for carrying out the polymerization in so far as in the case that one of the three compounds is missing no polymerization would take place.

The polyvinyl chloride thus obtained exhibits a degree of syndiotacticity exceeding 1.8, a Tg- alue exceeding 95°C, excellent colour characteristics!, an excellent heat stability and surprisingly it has been found that the polymer contains monovalent sulphonic end groups in the proportion of at least one per chain. The colour characteristics are measured by means of a General Electric Integrating Spectrophotometer according to the C. I.E. System of representation and measuring of colour. (See Journal of the Optical Society of America |θ - 52 - 1938 and National Bureau of standards in "Paper Trade Journal" 103 -108 page 38 - 1936).

According to that system the colour is expressed in terms of purity index (PI) and brightness (B) , referred to standard illuminatio s, which is an emiss on source corresponding to a black body at 6.200°K.

The heat stability or, still better, heat sensitivity is given by the variation of the purity index (ΛΡΙ). and by the brightness variation (Δ B) of the polymer after heating in a forced air oven' at 110eC for one hour. A polyvinyl chloride will hereinafte be said to a high colour characteristics w e 1 it shows a purity index of at least 97 and. a brightness of at least 90? while a polyvinyl chloride will hereinafter be said to have an excellent heat stability when it will show a ά I P (purity index variation) lower than 5 and AB (brightness variation) lower than 20e " The most important, feature o this invention resides in the presence of at least one alcoholate in the Redox catalyst system containing an organic hydroperoxide and sulphur dioxide* In actg it has been surprisingly found that the presence of an alcoholate* even in traces» radically changes the course of the reaction between the sulphur dioxide and the hydroperoxide in vinyl chloride monomer at a temperature below 0eC9 insofar as sulphur dioxide acts as reducing activator o the hydroperoxide!, decomposing it immediately with the formation of free radicals which start the low temperature bulk-polymerization of vinyl chloride,, It is known that the sulphur dioxide^ at low temperatures» can act as a' monomer capable of copolymerizing with winyl chloride to foria a vinyl chloride-sulphur dioxide copolymer which' . is easily .heat-degradable* of low colour quality? very often insoluble in the solvent for highly syndiotactic polyvinyl chloride andj, therefore? not suitable to be transformed into fibres* Now0 it has been surprisingly found that the proportio of vinyl chloride-sulphur dioxide copolymer decreases as the concentration of sulphur dioxide decreases and as the ( -0)-/S02 molar ratio increases and this proportion is zero when said ratio is about 1„ and that when the (R-0)—/so molar ratio exceeds 1* — β -= the polymerization conversion markedly decreases down to a plete inhibition of the polymerization when said ratio exceeds tion as applied to the continuous stirred reactor polymerization (see Stanley walas > Reaction Kinetics for Chemical Engineers, McGraw - riill 1959 pages 79-100) . Tne polymerization conditions ; were the following: dwell time 120 min. , sulptour dioxi-de/cumene hydroperoxide molar ratio 2 , different molar ratios as reported in Table 1 and a constant concentration of cumene hydroperoxide of ,0.18¾ by weight wi£h respect to vinyl chloride. The percentage of sulfone groups (- -») is determined from the ratio; between the absorption of the band 1130 cm"1 (A 1130) and that of the band 1425 (A 1425) and between the absorption of the band 1325 cm (A 1325) and that of the band 1425 cm*"' (A 1425) respectively, wherein 1130 an"1 and 1325 cm""1 -1 are the typical absorption bands of the sulfone group and 1425 cm band is characteristic of bonding vibration of ~Cri2«= group in the polyvinyl chloride according to Shimanouchi and Tasumi-Bull Chem. Soc. Japan - 34 - 359-365 - (1961). When the absorp~ tion ratio A 1130/A 1425 is lower than 0.3 and the absorption ratio A 1325/A 1425 is lower than 1 , it is assumed that sulfone groups are practically absent.

The infrared spectra were registered by a Perkin Elmer XR 125 grating spectro-photometer on pressed disks of polymer dispersed in KBr.

TABLE 1 ./- ; The enclosed figures 1, 2, 3» 4 and 5 show the infrared spectrum of a polymer obtained by using a (R-0)-/S02 ratios o£ respectively 0.152, 0.446, 0.854, 1 and 1.82.

As it can be seen* the presence of sulfone groups is strongly evident in figures 1, 2 and their abxence is evident in figures 3» 4 and 5« The organic hydroperoxide, as used herein, is an organic compound of the formula R-O-O-H, in which R is a linear or branched chain alkyl radical* a cycloalkyl radical* an aryl radical or an alkyl-aryl radical.

Examples of such compounds are the hydroperoxides of methyl, ethyl, n-propyl, tert.butyl, n. utyl, amyl, hexyl, octyl, phenyl-ethyl , phenyl-isobutyl, phenyl-isopropyl. Particularly suitable are the cumene hydroperoxide and tert.butyl-hydroperoxide. It is to be expressly pointed out thats as distinct from the hydroperoxides above, organic peroxides of the general formula R-O-O-R are ineffective in the process of this invention.

The concentration of the organic hydroperoxides is not critical and, typically, is comprised between 0.01 and 3% by weight with respect to the monomer feed and preferably from 0.01 % to 0.4%.

The concentration of the sulphur dioxide must be such that the molar ratio sulphur dioxide/organic hydroperoxide is comprised between 1:1 and 1 :1» but preferably between 0.5:1 and 10:1.

Practically, it is preferred that the quantity of sulphur dioxide is not greater than 3% by weight with respect to the monomeric system, because a quantity exceeding 3% involves a higher polymerization rate which in the bulk-polymerization / gives rise to remarkable drawbacks of exchange of the polymerization heat.

The alcoholates having the formula (R-0)nMe, wherein "R" is an alkyl radical with a linear or branched chain having from 1 to 6 carbon atoms, "Mew is a metal of the first or second group of the Periodic System or aluminium and "n" may be 1 , and 3 depending on the valency of Me, include: methylates ethy-lates, propylates, tert . utylates, n-butylates, n-amylates, tert.amylates and the like of sodium, potassium, lithium, magnesium, calcium, zinc. and aluminium.

The short chain alcoholates, from 1 to 3 carbon atoms, are preferred for solubility reasons, and among these the alcohobetween alcohol and alkaline or alkal ne earth metals are particularly preferred for reasons of economy and ease of preparation. It has also been found that the metal linked with the alkoxy group influences the colour and the heat stability of the colour of the polymer obtained. From this point of view the alkaline earth metal a aluminium are preferred.

The proportion of the alcoholates in .the reaction mixture lies between 0.01% and 5¾» by weight referred to the monomeric system. Proportions between 0.03% and 1% are preferred.

The alcoholates may be added to the reaction mixture either in pure form or, still better, dissolved in non-reactive organic solvents. The best solvents of alcoholates are aliphatic alcohol: having from 1 to 5 carbon atoms and among these methyl alcohol and ethyl alcohol are preferred. It has been found that the solubility of alcoholates in the conventional solvents increases when sulphur dioxide is dissolved together with them. In this case- it is possible to use poor or non solvents for the alco-folates, such as aliphatic nitriles, e. g. acetonitrile, ali- ' phatic chloro. derivatives, e. g. dichloroetane or tetrachloro-ethanei esters e. g. methyl or ethyl acetate; tetrahydrofura-ηί etc. The nature and the quantity of such , solvents have no influence on the polymerization course. Practically, for economic reasons, concentrated solutions of alcoholates are preferred.

The organic solvents, preferably, have to be anhydrous in order to avoid the hydrolysis of the alcoholates.

The alcoholate solution is preferably prepared by dissolving the alcoholate in the solvent containing the desired amount of sulphur dioxide. In this way, it is possible to obtain very concentrated alcoholate solutions, with considerable saving in solvent.

The polymerization temperature is below 0°C and particularly comprised between -10° and -70°C. Such a temperature of the reaction mixture is controlled by conventional means, such as, e. g. dipping the reactor in a thermostatic bath containing cooled trichloroethylene or cooled acetone.

By the term bulk-polymerization as used herein, it must be understood not only the polymerization carried out by the catalytic system in the undiluted monomer, but also in the presence of minor amount of non-reacting organic compounds, liquid at the polymerization temperature, having a diluting action on the polymerization slurry, to render the latter more free under agitation and to facilitate the heat transfer through the reaction vessel. The following substances are suitable as diluting . agents: saturated aliphatic hydrocarbons, aryl hydrocarbons, cycloalkyl hydrocarbons, saturated halogenated hydrocarbons, etc Among these compounds, halogenated saturated hydrocarbons such as ethyl chloride, methyl chloride, dichloroethane, are preferred.

A further advantage of this invention lies in that, by the catalytic system used in this invention, it is possible to obtain very high polymerization conversion also in the absence of diluting agents without an undersired thickening occuring in the polymerization mass.

It is adviseable to conduct the polymerization in the absence of oxygen which has an inhibiting effect on the polymerization. In general, for this purpose suitable inert gases such as nitrogen or carbon dioxide are used to displace the air from the polymerization reactors The process of this invention can be carried out, in practice, in continuous, semi-continuous or batchwise mode of operation. In each case, sulphur dioxide and organic hydroperoxide are kept separated from each other until thei introduction into the monomeric system in the reactor. The alcoholate can be fed either together with the sulphur dioxide or alone. As just said, it is preferred, however, to feed the alcoholate '■· ;/ together with the sulphur dioxide in solution in a non-reactive solvent.

The polymerization can be short-stopped at the desired level that is at the desired monomer conversion and molecular weight either by known radical inhibitors such as, for example, molecular oxygen, quinone and the like, or by adding an acid for destroying the alcoholate in the catalytic system, the presence of which is essential to the progress of the polymeri- / zatiorie, or by adding further amounts of the aicoholate so as to bring (R«=-0)—/S02 molar ratio to a value exceeding 2, or by discharging the polymerization slurry into an aqueous alkaline solution having a pH value of 9-12.

The polyvinyl chloride, obtained according to the process of this invention, besides being highly syndiotactic, that is, exhibiting a degree of syndiotacticity exceeding 1.8 and a Tg-value exceeding 95°C, has a high colour characteristics that is a PI of at least 97 and a B of at least 90, an excellent heat-stability, that is a ΔΡΙ lower than 5 and a ΔΒ lower than 20, and, surprisingly, it has been found, by qualitative and quantitative analysis, that the polymer contains at least one monovalent suiphonic end group per polymer chain.

From this chemical evidence it has to be deduced that the catalytic system generates suiphonic radicals that are the chain initiators. The growing radical having a suiphonic end group as chain initiator can terminate according to three different mechanisms: disproportionation, transfer or recombination. In the first two cases the polymer chain will have one suiphonic end group only, while in the third case the polymer chain will have two suiphonic end groups. From this recognition it comes out clearly that in the polymer the suiphonic groups are only at the end of the polymer chain.

Therefore, the quantity of suiphonic groups is correlated with the molecular weight of the polymer, such as, for instance, in a polymer having a number average molecular weight of 50.000, the quantity of millEquivalent monovalent suiphonic groups must be between 20 and 40.

For these particular characteristics, such polyvinyl chloride is particularly suitable to be transformed into fibres. In this case the polymerization conditions have to be arranged in order to obtain a polymer showing a number average molecular weight comprised between 30«,000 and 120.000. Moreover, the presence of sulp onic groups imparts to the polymers as well as to the shaped articles obtained therefrom, such as fibres, films, etc. the capability to react, by ionic-type reaction, with cat 'on- . active compounds such as, for instance, antistatic agents, basic dyes etc.

This highly syndiotactic polyvinyl chloride having sulphonic end groups differs from copolymers of vinyl chloride and ethylenically unsaturated comonomers containing the sulfonic group, in as much as the sulphonic group (-SO^H) is situated at the chain end and, therefore, does not introduce any extraneous monomeric units along the polymer chain.

This highly syndiotactic polyvinyl chloride having sulphonic end groups presents, therefore, the great advantage witii respect to the vinyl chloride copolymers containing said sul-phonated comonomers and obtained at low temperature polymerization in that it does not contain any heterogeneity of structural variation along the polymer chain. In fact, it is known that the particular characteristics of the polyvinyl chloride obtained at low, temperature, are due to the possibility that its polymeric chains arrange themselves in a crystalline lattice. The sulp onated comonomers would introduce molecular structures in the polymeric chain that are incompatible with the crystalline lattice dimensions.

Therefore, the crystallinety of the system strongly decreases or becomes nil, and consequently the physical properties of the polymer are reduced. The sulphonic-grOups (-SO^H) differ from the sul one groups because the former give all the reactions of the strong acids waile the sulfone groups do not.

Therefore, he sulphonic groups can be determined quantitatively by means of potentipmetric titration. Using as a reference what is described in the "Society of Dyers and Colou-ris So 80 page 577» 1964**, a method is developed in order to determine the number of sulphonic end groups contained in this particular polyvinyl chloride.

According to this method» a solution containing 1% by weight of the polymer in cyclohexanone is percolated through an ion exchange resin column containing two equal and separate quantities of Amberlite IR 120 (cationic resin) at the top and of Amberlite IR 410 (anionic resin) at the bottom* In this manner it is possible to eliminate all the acids and inorganic salts coming out from the polymer or solvent and to substitute the possible cations bonded to the sulphonic groups with hydrogen ions* in order to mafce all the sulphonic groups titra abie.

The height of the column is 50 cm and the internal diameter is 1.9 cm. The titration of the sulphonic acid groups in the polymer, is directly carried put in the cyclohexanone solution, after ion exchange,, by means of a methanol solution of a quaternary ammonium base.

The titration is carried out potentiometrically by means of any electrode e. g. platinum. The results of the acidity titration are expressed as miiliequivalents of monovalent sulphonic groups per kg of dry polymer. (One milliequivalent corresponds to 0.032 g of elemental sulphur).

The micro analysis of this polyvinyl chloride shows the presence of carbon, hydrogen, chlorine and sulphur and it is found that the quantitative figure of the sulphur per kg of polymer is equal to the value determined as sulphonic monovalent group via potentiometric analysis.

It is understood- that the catalytic system and process of this invention can be applied as well to the copolymerization of vinyl chloride with up to 50% by weight of ethylenically unsaturated monomers copolymerizable with vinyl chloride. The only difference with respect to the process described above, is that the starting monomers are an admixture of vinyl chloride and one or more other copolymerizable ethylenically unsaturated monomers.

By the term "ethylenically unsaturated monomers" have to be understood the organic compounds containing the group C=C» Examples of these compounds are: vinylidene or vinyl compounds, such as vinylidene chloride or fluoride, vinyl fluoride; vinyl esters of carboxylic aliphatic acids containing from 2 to 16 carbon atoms, such as for instance, the vinyl esters of the acetic acid, or the propionic acid, etc.; the acrylic-type monomers, such as acrylic acid, methacrylic acid or their derivatives, as, for instance, acrylonit ile, acrylate or metha-crylate of aliphatic alcohols containing from 2 to 12 carbon atoms.

In order to further illustrate this invention, but without being limited thereto, the following examples are given. EXAMPLE 1 Into a 2 litre glass polymerisation reactor fitted with a stirrer, a cooling system and a thermometer, were continuously fed in: - vinyl chloride - cumene hydroperoxide - sulphur dioxide - an alcoholate of the type recorded on the following Table II » in alcoholic solution.

The fed in quantities of such compounds are reported in Table II o The polymerization reactor was kept at a temperature of -30°C by means of a thermostatic bath., Prom an over low pipe the suspension of the polymer thus obtained was filtered and the polymer thus obtained was washed with methanol and with ethyl ether.

On Table II are recorded: : the quantity o vinyl chloride fed-in in g/hr. , the quantity of cumene hydroperoxide fed-in in g/hre „ - the quantity of S02 fed-in in g/hr. „ - Dwell time (DT) , expressed by the ratio between the volume of the reactor in which the polymerization is carried out and the volume feed rate of the monomers , - the intrinsic viscosity ( ^ ) of the polymer obtained, determined in cyclohexanone at 3C°c and expressed in dl/g. By the intrinsic viscosity it is possible to determine the average , v -4 < molecular weight M according to the formula: (^) =2.4 . 10 x M ( see j . Pol . Sci, 41., 73, 1959) . This formula, however, is only an approximate one, the colour of the polymer expressed in terms of purity index , (Pi) and brightness (B):.' - heat sensitivity, expressed by the variation of the purity index ( Δ IP) and by the brightness variation ( Δ B) of the •A polymer after heating in a forced air oven at 110°C for one hour, syndiotacticity degree, Tg-value, monovalent sulphonic groups (MSG) expressed in milliequivalent for kg of dry polymer, determined by potentiometric titrations sulphur (S) in grams for kg of dry polymer.

A It is evident from the results thus obtained and recorded in enclosed Table II that* when an alcoholate is absent,, there is no polymerization (see tests 1 and 2) and furthermore that when the molar ratio (R-0)—/S02 is lower than 0.70 (see tests 3 and 4), substantial quantities of sulphur dioxide are copo¬ sulphur quantity per leg of polymer which is higher than the one corresponding to the monovalent sulphonic groups present therein.

It is to be recognized'.that* when the molar ratio (R-0)—/S02 is 0.70 (see test 17) « small quantities of vinyl chloride-sulphur dioxide copolymers are present, which however, do not affect remarkably the properties of the polymer.

EXAMPLE 2 By operating according to Example 1 , were fed in continuously 400 g/hr of vinyl chloride, an organic hydroperoxide and an alcoholate in methanolic solution at 12% by weight.

The polymerization temperature was maintained at -20°c by thermostatic bath.

The obtained results are recorded in folloving Table III.

T A B LfeE M l ) - 21 - EXAMPLE 3 Into a 2 litre glass polymerization reactor provided with a stirrer, a refrigeration system and a thermometer, 360 g/hr vinyl chloride, 40 g/hr ethyl chloride, 0.4 g/hr cumene hydroperoxide, 0.84 g/hr sulphur dioxide and 1 g/hr sodium ethylate, are continuously fed in.

The polymerization reactor is maintained strictly at -40°C in a thermostatic bath.

The suspension of polymer thus obtained is continuously discharged through an overflow pipe. The obtained polymer is then recovered by centrif ugation and dried. The polymerization cons to 14.9% ( corresponding to an hourly conversion ned polymer showed the following characteristics : - intrinsic viscosity 1 .35 PI $7: 5 - colour B 93 Δ ΡΙ 3.5 - heat sensitivity A B 1 3 - syndi o t act i city degree 2.1 - Tg-Value 107°C - MSG (in millie - Sulphur ( g per kg dry polymer) 0.80 EXAMPLE 4 By operating according to Example , the following substan ces were fed in: 800 g/hr vinyl chloride 0.96 g/hr tertiary-butyl -hydroperoxide 1 , 2 g/hr sulphur dioxide (methyl alcohol solution at 12% / by weight) 1 ,072 g/hr magnesium ethyl ate (methyl alcohol solution at 10% by weight) .

The sulphur dioxide and the magnesium ethyl ate ere fed-in together.

The temperature of polymerization vas strictly maintained at -30°C by means of a thermostatic bath.

The polymerization conversion amounted to 10% and the obtained polymer showed the following characteristics; intrinsic, viscosity 1 .40 dl/g ) PI 99.5 colour ) ) B 95.9 ·: ■ ' . ) ^PI - 2.9 heat seiisitivity r ) Δ B 10.7 syndiotactic degree 2.05 Tg~value 103?C MSG (in milli equivalents per kg dry polymer) 25.0 sulphur ( g per kg of dry polymer) 0.8 Similar results were obtained when substituting the methyl alcohoj, as solvent „ with ethyl alcohol , acetonitrile or tetra-hydrofuran.

EXAMPLE 5 Also here one proced s according: to Example 1 , by continuously feeding in - 800 g/hr vinyl chloride - 1 .2 g/hr tertiary-butyl hydroperoxide - 1 ,2 g/hr sulphur dioxide - .096 g/hr magnesium methylate in methanolic solution having - a concentration of 1 3% b. w.

The polymerization reactor was maintained strictly at -40°C by means of a thermostatic bath. The polymerization conversion amoun ed to 9.2% and the polymer obtained showed the following characteristics: - intrinsic viscosity 1 .32 dl/gr ) PI 99.8 - colour I ) B 96.3 - heat sensitivity - syndi ot act i city degree 2 » 30 - Tg-value 04°C - MSG (in milliequivalents per kg dry polymer) 27.

- S (in g per kg dry polymer!) 0.88 EXAMPLE 6 It was operated according to Example 1 9 by continuously feeding in: - 800 g/hr vinyl chloride - 200 g/hr ethyl chloride - 1 · 5 g/hr eumene hydroperoxide - 1 .5 g/hr sulphur dioxide ( ethyl alcohol solution at 15% by weight) - 1 g/hr magnesium ethylate ( ethyl alcohol solution at 10% by weight) .

The sulphur dioxide and the magnesium ethylate were fed in together.

The polymerization temperature was continuously maintained at -20° c by means of a thermostatic bath. The polymerization conversion amounted to I 2.3 e and the polyraer obtained showed the following characteristics: intrinsic viscosity 1 o 52 dl/gr 1 PI 99.5 colour ) B 95.8 heat sensitivity syndiotacticity degree 1 .9 Tg-value 102°C MSG (in mill! equivalents per kg dry polymer) 23.G S (in g per kg dry polymer) 0.73 Similar results were obtained by substituting the ethyl alc ohol with acetonitrile or tetrahydrofuran.

EXAMPLE 7 Into a 2 litre polymerization reactor containing 2000 gr of vinyl chloride pre-cooled at -^15°C and maintained at this temperature by a thermostatic bathe during 2 hours the following substances were fed in: - 3 3 cumene hydroperoxide - 3 g sulphur dioxide and - 2 g magnesium methyl ate.

After the feeding in was completed, the reactor was cooled and kept under stirring in an atmosphere of nitrogen for 1 hour. Thereupon the reaction mass was discharged and the polymer was recovered by filtration. The polymer thus obtained was then washed with methyl alcohol and then dried , n an oven at 0? c under vacuum for 12 hours. 360 gr polyvinyl chloride (conversion 13%) were thus ob- tained which showed the following characteristics: - intrinsic viscosity 1 .3 dl/gr - J PI 99,7 colour ) I B 96.1 - VA PI 2.5 heat sensitivity I )A B 11 .5 - syndiotacticity degree 1 .82 g- value 100°C - MSG (in railli equivalents per kg dry polymer) 27.8 - S (in g per kg . dry polymer) 0.9 When the test was repeated by operating at a temperature of -45° Cs the following results were obtained: conversion 9.5 % intrinsic viscosity 1 .15 dl/g ) PI 99.9 — colour ) ) B 96.9 - ) Δ PI 2.1 heat sensitivity } ) Δ B 11 .8 - syndiotacticity degree 2.41 - Tg-value 108°C - MSG (in milliequivalents per kg dry polymer) 32.8 - S (in g per kg dry polymer) 1 .05 EXAMPLE 8 One proceeded according to Example 7» by feeding during 2 hours into 2000 g vinyl chloride maintained at -20°C. - 3 g cum en e hydroperoxide - 3 g sulphur dioxide - - 26 - - 3.5 g zinc ethylate. 220 g polymer (conversion 11%) were thereby obtained.

EXAMPLE 9 Into a polymerization glass reactor fitted with a stirrer, a cooling system and a thermometer, were ed in continuously: - vinyl chloride - 0.145%, by weight with respect to the monomer, of cumene hydroperoxide - 0.153%, by weight with respect to "the monomer, of sulphur dioxide -.0.103%, by weight with respect to the monomer, of magnesium methylate.

The quantities of sulphur dioxide and magnesium methylate were fed in together dissolved in a solvent at concentrations reported in Table IV following.

The molar ratio S02/cumene hydroperoxide was 2.5 and the molar ratio ( -0)-/S02 was 1.

The polymerization temperature was -30°C and was maintained at this value by means of a thermostatic bath. The dwell time was 2 minutes.

On Table IV are recorded: - the type of solvent used, - concentrations of S02 and magnesium methylate in their solution, - conversion in %, - intrinsic viscosity of the obtained polymer, - syndiotacticity degree, - Tg-value, - MSG (in milliequivalents per kg dry polymer), - sulphur (in g per kg dry polymer).

•A Coneeatra~ Concentration of maSyndiotac Conversion tion of Intrinsic Solvent gnesium al- Tg-value ticity in % viscosity S02 coholate in degree % by weight Acetoni- 7,3 % 9.1 ?. trile 1.07 dl/g 105°C 2.1 Dichloro- 9.6' % 8. %. 1.02 di/g e&haa-e 106°C 2.03 Methyl 29.8 % 20 % 9.0 ¾ 1.05 dl/g 104°C 2.2 acetate Tetrahy* 31.2 % 21 % 8.7 % 1,05 dl/g 105°C 2.1 drofura EXAMPLE 10 The same process as described in Example 1 was followed by continuously feeding into the reactor: - vinyl chloride, - 20% by weight with respect to the monomer of ethyl chloride, - 3.0% by weight with respect to . the monomer of cumene hydrope r oxide, - 1 .27% by weight with respect to the monomer of sulphur dioxide, - 0 o 854% by weight with respect to the monomer of magnesium methylate in methanolic solution at 1 2% by weight.

The polymerization temperature was -40°C , and dwell time was 90 minutes. The molar ratio S02/cumene hydroperoxide was 1 and the molar ratio (R-0)-/S02 was 1 .

The polymerization conversion was 9.5%.

The obtained polymer exhibited the following characteristics : - intrinsic viscosity 0.8 dl/g - syndiotacticity degree 2. 30 - Tg-value 107°C - MSG(in milli equivalents per kg of dry polymer) 52.7 \ PI 98 - colou . 3 ) B 92 ί Δ PI 3 Δ B 1 3 EXAMPLE 1 1 By operating according to Example 9 e the f ollowing compounds were continuously fed into a polymerization reactor: - vinyl chloride, •A - by weight with respect to the monomer, of ethyl chlori- de, - 2<,53%s by weight with respect to the monomer, of cumene >hy- droperoxidee - 2.7% by weight of sulphur dioxide„ - 1.82% by weight of magnesium methylate in methanolic solution at 12% by weight* The molar ratio S02/cumene hydroperoxide was 205; and that of (je-oj-/so was 1» The dwell time was 30 minutes and the po- 2 -lymerization temperature was -40°e<, The polymerization conversion was 12.0% and the obtained polymer exhibited the following characteristics: - intrinsic viscosity , 0.86 dl/g - syndio acticity degree 2.3 - Tg-value 109°C - sulphur (in g per kg of dry polymer) 1.525 - MSG (in milliequivalents per kg of dry polymer) 48.8 ) Pi 97.5 - colour 1 ) B 91.5 - heat sensitivity EXAMPLE 12 By operating according to Example 9» the following compounds were continuously ed into a polymerizatio reactor: - vinyl chloride, - 0.01% by weight of cumene hydroperoxide - 0.022% by weight of sulphur dioxide, - 0.0148% by weight of magnesium methylate in methanolic solution at 12% by weight.

The molar ratio SOg/cumene hydroperoxide was 5» and that of ( -»0)— S02 was 1. The dwell time was 480 minutes and the polymerization temperature of -20°C. The polymer zation conversion was 2.5 and the obtained polymer exhibited the following cha ac eristics: - intrinsic viscosit 0.90 dl/g - syndiotacticity degree .1.85 - Tg~value . 102°C - sulphur (in g per kg of dry polymer) 1,41 - MSG (in milliequivalentsper kg of dry polymer) 4 «5 ) PI 99 - colour J ) B · 94 |A PI 2.5 - heat sensitivity ) ) Δ B 11 EXAMPLE 13 By operating according to Example 1 „ were ed into a glass polymerization reactor having a capacity of 2690 cc^ the follo-ving compounds: - 345 g/hr vinyl chloride - 13.45 g/hr methyl acrylate - i.345 g/hr cumene hydroperoxide, - 1.412 g/hr sulphur dioxide* - 0.948 g/hr magnesium methylate in methanolic solution at 12% by weight.

The polymerization temperature was -30°CY The polymerization conversion was 8.50¾.

The copolymer, thus obtained, contained a copolymer!zed methyl acrylate proportion of 7.0% by weight and had an intrinsic viscosity of 1.20 dl/g.

•A By doubling the quantity of the methyl acrylate, the obtain ed copolymer had a content of methyl acrylate of 1 3% by weight. EXAMPLE 14 - Example 12 was repeated by feeding* as monomers, » 1 345 g/hr of vinyl chloride and - 40.35 g/hr of vinyl acetate.

The polymerization conversion was 3 « 00%. The obtained copolymer had a proportion of copolymer! zed vinyl acetate of 3% by weight and exhibited an intrinsic viscosity of 1 .00 dl/g. EXAMPLE 15 0.1 50 g of cumene. hydroperoxide, 0.158 g of sulphur dioxide and 0.101 g of magnesium methylate in methanolic solution at 12%, were added in i hour and under agitation to an admixture of 98 g of vinyl chloride and 2 g of methyl acrylate maintained at -30°Co The temperature was strictly maintained at . this value by means of a thermostatic bath.

The polymerization started immediately and the formed polymer progressively precipitated. The agitation was stopped after about 2 ftxi and the copolymer separated by pouring the reaction mass into an aqueous solution of NaOH at pH of 10. 6 g of copolymer were obtained having a content of copolymerized methyl acrylate of 1 3% and exhibited an intrinsic viscosity of 1 dl/g. Its content of sulphur railli equivalent in the form of monovalent sulphonic groups per kg of dry copolymer was 39.2.

Claims (1)

1. - 32 - WHAT WE CLAIM IS: 1. A process for the low temperature bulk-polymerization of vi- 1 nyl chloride characterized in that the polymerization is carried out in the presence of a catalyst system consisting of an organic hydroperoxide,, sulphur dioxide and at least an alcoholate of the formula (R-o)n«Me wherein nR" is an alkyl radical with a linear or branched chain having from 1 to 6 carbon atoms, "Me" is a metal of the first or second group of the Periodic System or aluminium and "n" may be 1 , 2 or 3o depending on the valency of Me0 in which the molar ratio (R-0)-/so does not exceed ,2. ' , „ 2o A process according to Claim 1» characterized in that the molar ratio (R~o)- S02 is comprised between 0.70 and 1,8. 3. A, rocess according to Claim 2, characterized in that the molar (R~0)-/S02 ratio is comprised between 0.85 and 1.5. 4. A process according to Claims 1 , 2 o 3. characterized in that the alcoholate is a sodium alcoholate. 5. A process according to Clains 1 , 2 or 3 characterized in that the alcoholate is a potassium alcoholate. 6. A process according to Claims 1 , 2 or 3 characterized in that the alcoholate is a magnesium alcoholate. 7. A process according to Claims 1, 2 or 3 characterized in that the alcoholate is a zinc alcoholate. 8. A process according to Claims 1, 2 or 3 characterized in that the alcoholate is an &uminium alcoholate. 9» A process according to Claim 4 characterized in that the alcoholate is sodium methylate or sodium ethylate. 0o A process according to Claim 5 in which the alcoholat is ./■ potassium raethylate or potassium ethylate, o A process according to Claim 6 in which the alcoholate is magnesium raethylate or magnesium ethylate» o A process according to anyone of the preceding claims in which the alcoholate is fed in form of a solution in an a- liphatic alcohol having from 1 to 5 carbon atoms and preerably methyl alcohol or ethyl alcohol«, c A process according to anyone of the Claims from 1 to 1 1 in which the alcoholate is ed together with sulphur dio-„ sdde in form of a solution in a solvent selected from the class consisting of aliphatic alcohol having from 1 to 5 carbon atoms* aliphatic nitriles* dichloroethaner tetrachlo roethaneB methyl acetate, ethyl acetate0 and tetrahydrofu- ran0 » A process according to anyone of the preceding claims,, characterized in that the quantity of alcoholate lies, between 0 01 % and 5% by weight referred to the monomers. o A process according to Claim 1 4 » characterized in that the quantity of alcoholate lies between 0 * 03 and \% by weight referred to the monomers0 „ A process according to anyone of the preceding claims 9 characterized in that the concentration of the organic hydroperoxide is comprised between 0.01 and 3% by weight with respect to the ed monomers· « A process according to Claim 1 6* characterized in that the concentration of the organic hydroperoxide is comprised from 0 01 to 0 „ % by weight with respect to the fed monomers0 » A process according to anyone of the preceding claims* o / » , ~ 34 - characterized in thate as organic hydroperoxide, cumene hydroperoxide or ter-butyl hydroperoxide is used,, 1 9o A process according to anyone of the preceding claims, characterized in that the molar ratio sulphu dioxide/organic hydroperoxide is comprised between 1 : 15 and 1 5 : 1 . 20o A process according to Claim 1 9 » characterized in that the. raolar ratio sulphur dioxide/organic hydroperoxide is comprised between 0* 5 : 1 and 10: 0 '21 A process according to Claims 19 and 20 , characterized in that the quantity of sulphur dioxide is not greater than 3% by weight with respect to the monomers. 22 * A process according to anyone of the preceding claims, characterized in that the polymerization is conducted at a temperature below 0°C, but preferably comprised between 23. A process according to anyone, of the preceding claims, characterized in that the polymerization is carried out in the presence of a diluting agent, preferably in the presence of lialogenated saturated hydrocarbons. 24. A process according to anyone of the preceding claims, characterized in that the vinyl chloride is copolymer!zed with up to 50% of one or more other copolymerizable ethylf,¾ically unsaturated monomers. 25. Poly%di¾yl chloride exhibiting: a) a degree of syndiotact city exceeding *8 b) a Tg-value exceeding 95°C c) said polymer showing colour characteristics, according to C.I.Eo method, of: - purity index at least 97 and o/ a - brightness of at least 90 „ \ d) said, polymer showing a heat sensitivity of: - a purity inde variation lower than 5 and - a brightness variation lower than 20 e and e) said polymer containg at least one monovalent sulphonic end groups per chain. 260 Polyvinyl chloride according to Claim 25» characterized in that the polymer contains from one to two monovalent sulpho nic end groups per chain. 27» Shaped articles such as fibres, films etc. obtained from the polymers as claimed in Claim 25. Milan0 Gio/oc For the Applicants D . HWHO»COHOND