FR2574802A1 - PROCESS FOR PREPARING POLYSTYRENE SHOCK STABLE FOR AGING - Google Patents

Abstract

POLYSTYRENE PREPARATION PROCESS PRESENTING GOOD COLD AND AGING RESISTANCE. PREPARATION PROCESS CONSISTING OF APPLYING STYRENE, A RUBBERY TERPOLYMER OF PEROXIDES SHOWING GOOD THERMAL STABILITY AND ADDITIVES CHOSEN FROM MERCAPTANS, OR DIVINYLBENZENE. APPLICATION TO THE MANUFACTURE OF GARDEN FURNITURE AND CARAVANS.

Description

The present invention relates to a process for the preparation of polymers

  grafted; it more particularly relates to a method of manufacturing

  Styrene-based graft copolymers stable to aging.

  Polystyrene is a thermoplastic material which thanks to the ease with which it can be obtained and worked is widely used in the plastics industry. Unfortunately his job is limited as a result of his

  poor impact resistance and poor stability to aging.

  In order to improve its properties and in particular its impact resistance, it has been proposed to use styrene copolymers with other polymers, in particular rubbers: this is why, for example, rubbers have been proposed for the most part. saturated part, for example ethylene propylene rubbers and ethylene propylene rubbers and a polyunsaturated monomer. However, their employment presents many difficulties; in particular, these weakly unsaturated rubbers having a low double bonding rate do not favor the grafting of styrene onto the elastomer. Compositions are obtained which have a degree of grafting, that is to say a level of polystyrene grafted on the very weak elastomer to the nearest of 0.5: this low value of the grafting rate causes a weakening of the properties. mechanical properties, in particular elongation at break over time. Furthermore, a microscopic observation shows that the compositions obtained consist of large globules of rubber which are dispersed in the composition without any cohesion and whose size can reach 10 to 15 microns. Under stress the bad cohesion induces a

  Negative cavitation at the elastomeric-thermoplastic interface.

  If the manufacture of copolymers grafted with ethylene rubber, propylene and unsaturated monomer makes it possible to improve the properties-shock it seems that the known methods lead to products which have a poor stability to aging, this stability over time that can be improved by solving the problem of crosslinking of

the elastomer.

  When styrene is polymerized in the presence of elastomeric materials of the ethylene-propylene type comprising an unsaturated monomer, grafted raw products are obtained, in particular comprising a graft copolymer formed by reaction of the rubber with monomeric styrene and rubbery patterns consisting of "Bridged" patterns, that is to say rubber patterns interconnected by chemical bonds. The crosslinking density of the "bridged" rubber is expressed by the "swelling index" which is inversely proportional to the degree of crosslinking, which means that

  the lower the swelling index, the higher the crosslinking density.

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  However, it has been found that an aging-resistant resin was a resin which had a poor crosslinking density, that is to say an index of

relatively high swelling.

  It is therefore seen that it is necessary to make a compromise between the degree of grafting and the swelling index to obtain a resin which has both good impact properties, good stability to aging and also

good cohesion of the co-polymers.

  We have now found the way to solve these problems to obtain a resin that combines good impact properties with good aging stability. The present invention relates to a process for the preparation of graft polymers consisting in polymerizing in suspension in two stages the styrene in the presence of a rubbery terpolymer of ethylene, of propylene and of a third component, characterized in that it is used in the first step styrene with the rubbery terpolymer in the presence of additives selected from mercaptans and / or triallylcyanurate and / or divinylbenzene, peroxides having a high thermal stability and that in a second step the polymerization by prior addition is continued a mixture of peroxides selected from tertiobutyl perbenzoate, di-tert-butyl peroxide and 2,5-dimethyl, 2,5-di-tert-butyl peroxyhexyn-3, and in that after the two stages of polymerization of calcium, lithium or barium sterarates in an amount at most equal to 0.25% by weight

  relative to the weight of the dry polymer.

  According to another characteristic of the method of the invention is added optionally after the two polymerization stages during the granulation of the polymer metal oxides selected from zinc or titanium oxides used alone or in mixtures. These oxides are used in an amount at most equal to 2% relative to the weight of the dry polymer. The use of such compounds makes it possible to obtain polystyrene grades which are particularly suitable for product applications which must have a high degree of stability.

  white coloring: caravan elements or garden furniture.

  The implementation of the process according to the invention makes it possible to obtain graft polymers having a gel content of between 10 and 40% and a swelling index of between 10 and 20%, which indicates a high level of crosslinking. In addition, a microscopic observation of the graft polymers obtained according to the process of the invention makes it possible to observe that they have good cohesion and a microstructure such that 66% of the particles have an average size of less than 6 microns. Moreover, the process of the invention leads to

  to finished products with good resistance to cold and aging.

  It should also be noted that the process leads to polymers which have mechanical properties of the same order as those of the properties

known impact polystyrene.

  The process of the present invention consists in using, in a first step, styrene with the rubbery terpolymer in the presence of additives, peroxides having a good thermal stability. Additives

  are selected from mercaptans such as n-docedyl mercaptan and / or

  triallylcyanurate and / or divinylbenzene these transfer agents are used respectively in amounts at most equal to 0.2% relative to the organic phase constituted by the rubbery styrene terpolymer mixture. The peroxides used during the first stage of the process according to the invention are chosen from peroxides having a good graftability, for example benzoyl peroxide: they are used in

  amount equal to at most 0.2% relative to the weight of the organic phase.

  The second step of the process according to the invention consists in continuing the polymerization by prior addition of a mixture of peroxides chosen from tert-butyl perbenzoate and di-t-butyl peroxide and 2,5-dimethyl 2-5 di- tert.-butyl peroxy hexyne-3. These peroxides are used respectively in an amount at most equal to 1% by weight relative to the weight of the organic phase consisting of styrene plus rubbery terpolymer, they have a shelf life of between 1 hour to 10 hours at 135 C. After the two polymerization steps, during the granulation of the polymer, calcium, lithium or barium salts of stearic acid in an amount equal to at most 0.25% by weight relative to the weight of the dry polymer: these salts make it possible to increase the resistance to

  oxidation and improve the implementation of polymers.

  According to another characteristic of the process of the invention is added optionally after the two polymerization stages during the granulation of the polymer metal oxides selected from zinc or titanium oxides used alone or in mixture. These oxides are used in an amount at most equal to 2% by weight relative to the weight of the dry polymer: they promote the

  polymer stability in air and U.V.

  In a known manner it is possible to add also after the polymerization steps anti-U.V. agents selected from benzotriazoles and hindered amines. As benzotriazoles, for example 2 (2-hydroxy-5-t-octylphenyl) benzotriazole, 2 (2-hydroxy-5-methylphenyl) benzoltriazole may be mentioned. The hindered amines are chosen from bis (2, 2 ', 6, 6', tetramethyl 4 piperinyl) sebacate and hexadecyl-3,5-di-tert-butyl-4-hydroxybenzoate. It is also possible to use, after polymerization, antioxidants such as, for example, triethylene glycol-bis-3 (3-tert-butyl-4-hydroxy-5-methylphenyl) propionate.

  to increase the thermal stability at high temperature.

  In a known manner, the rubbery terpolymer is based on ethylene, propylene and a third component. The third component that enters into the composition of the rubber used for the production of the graft polymers according to the invention is chosen from 1,4-hexadiene and dicyclopentadiene,

  tricyclopentadiene, 5 - vinylnorbornene - 2, 5 - ethylidenenorbornene -

  2, 5 - methylene - norbornene - 2, 5 (2 propenyl) norbornene -2, 5 (50 hexenyl) norbornene -2, 4, 7, 8, 9 tetrahydroindene and isopropylidene tetrahydroindene . The process of the invention is carried out in the following manner: in an autoclave equipped with a heating device, an agitator and a cooling device, styrene, rubbery terpolymer and water are introduced. amount at most equal to 150% relative to the weight of the organic phase consisting of styrene plus rubbery terpolymer mixture. Peroxides transfer agents are then added, the rubbery terpolymer is used in an amount at most equal to 20% by weight relative to the weight of the organic phase and preferably in an amount close to 12%. The

  additives selected according to the invention from n-dodecyl mercaptan, triallyl-

  cyaurate and divinylbenzene are used respectively in an amount at most equal to 0.10% by weight relative to the weight of the organic phase and preferably in an amount at most equal to 0.10%. The peroxides used in the first step of the process of the invention are used in an amount of at most 0.4% and preferably 0.2% relative to the weight of the organic phase. This first step is carried out at a temperature at most equal to C. After the inversion of the phases which takes place after about 2 hours, the polymerization is continued by a new addition of water and by an increase of the temperature by bearings up to a temperature of 150 C

after 6 hours.

  The stearates used to carry out the process of the invention are added to the polymer when the latter is used on single-screw or twin-screw extruders or on internal mixers. Similarly, the optionally used metal oxides as well as the benzotriazoles and the hindered amines are also used during the step of

shaping of the polymer.

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  The polymers obtained according to the process of the invention have good mechanical properties as well as good aging resistance to oxidation and U-V aging. All of these properties favor these polymers in the fields of application where it is required a good stability to the weather and the sun such as use for the manufacture of garden furniture and caravans.

  The following examples illustrate the present invention.

  All quantities are expressed in parts by weight.

EXAMPLE 1

  In an autoclave equipped with a heating device, an agitator and a cooling device, are introduced: - 88 parts of styrene - 12 96 of a rubbery terpolymer consisting of 44% by weight

  ethylene, 45% by weight of propylene and 11% by weight of 2-ethylindene.

  norbornene this terpolymer has a viscosity such that 5 parts by weight dissolved in 95 parts by weight of styrene has a viscosity of 60 centipoise at 20 C - 6.7 parts of paraffin oil - 0.108 part of benzoyl peroxide - 0.08 part of tertiodeodecyl-mercaptan

- 46 parts of water.

  The reaction mixture is subjected to the first polymerization step by heating the reaction mixture to reach a temperature of 92 ° C. after 60 minutes and then stirring for 1 hour.

  minutes using a turbine stirrer.

  After this first stage, 0.31 part of tertiary butyl perbenzoate, 0.13 part of di-tert.-butyl peroxide and 0.6 part of 2,5 dimethyl 2,5 di-tert-butyl peroxyhexine are added. 3 - 0.08 part of triallylcyanurate - 69 parts of water - 0.214 part of hydroxyapathite - 0.019 part of calcium carbonate

  - 0.013 part of potassium persulfate.

  The reaction mixture is then heated stepwise so that its final temperature reaches 150 ° C. after 7 hours. We then obtain a

  organic phase that is filtered and dried.

  G of the polymer thus obtained are mixed on a screw extruder with 0.1 part of triethylene glycol-bis-3- (3-tert-butyl-4-hydroxy-5-methylphenylpropionate) 0.25 part of 2 ( 2 hydroxy 5-t-octyl phenyl) benzotriazole 0.25 part of bis 2,2 '6,6' tetramethyl 4 piperidinyl sebacate 0,125 part of lithium stearate The rubber phase of the polymer obtained has a particle size such that 80% of the particles are a size between 1 and 7 microns and an average size of 4 microns. Its characteristics are summarized in Table 1. The level of gel which expresses the level of crosslinked phase, that is to say the amount of grafted terpolymer is determined by cold stirring in toluene, the graft copolymer and then centrifuging. together to determine the amount of insoluble gel in toluene. The dry mass of the insoluble polymer is determined by vacuum treatment of the gel obtained previously. The percentage of gel in relation to the test sample expresses the

freezing rate.

  The swelling index which makes it possible to express the crosslinking density

  is equal to the ratio of the gel mass to the dry resin.

  The coefficient oL expresses the ratio of the amount of polystyrene

  grafted on the amount of terpolymer in the grafted phase.

  The melt index is determined according to ASTM D 1238.

  The Vicat point is determined according to ASTM D 1525 (method A).

  The Izod shock is determined according to ASTM D 256.

  The elongation at break is determined according to ASTM D 638.

  The tensile modulus is determined according to ASTM D 638 as well as

  as the stress at the threshold and the stress at break.

  Aging resistance has been studied at "WEATHER-O-METER" followed

  elongation at break as a function of time.

  The "WEATHER-O-METER" test consists of placing specimens in an enclosure subjected to a light source having a power of 6,000 Watts and consisting of a filtered Xenor source according to ASTM G 26-70 and G 27- 70. The chamber is maintained at a humidity of 60%, the temperature of the black body being 55 C.

  A watering cycle simulates the effect of rain.

  The measurement of YELLOX INDEX (Yellowness Index) is carried out

according to NFT 08-014.

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TABLE I

  Swelling Index 16 Frost Rate 26.4

5 .__ _ _ _ _ _ _ _ _ ___ _ _ _ _

I 1.20

  Flow rate 15 Vicat C 92.9 Izod impact 13.4 (Joules / meter) X 10 Elongation at break% 68 Tensile modulus 1 310 (Mega-Pascals) Threshold stress 12.3 (Mega-Pascals) Constraint at rupture 15.8 (Mega-Pascals) Resistance to aging Elongation initial rupture 68% Elongation at break as a function of time after 2000 h

of exposure to WEATHER-O-

METER40%

YELLOW INDEX INITIAL 2

30. After 2000h. at WEATHER-O-

METER 20

EXAMPLE 2

  Example 1 is repeated but adding triallylcyanurate in the first step and 0.8 part of di-tert.-butyl peroxide in the second

  step instead of 2,5 dimethyl 2,5 di-tert.-butyl peroxyhexyn-3.

  Table 2 gives the characteristics of the product obtained.

EXAMPLE 3

  Example 1 is repeated using the following amounts of styrene reactants: 81.45 parts - rubbery terpolymer described in example I: 11.88 parts - paraffin oil: 5.71 parts - benzoyl peroxide: 0.053 part - tertio-dodecyl mercaptan: 0.089 part triallyl cyanurate: 0.099 part - divinylbenzene: 0.009 part tert.-butyl perbenzoate 0.067 part - di-tert.-butyl peroxide 0.22 part A 100 parts of the obtained polymer is added on a screw extruder

  0.125 part of calcium stearate.

  The properties of the product obtained are summarized in Table 2.

EXAMPLE 4

  Example 3 is repeated but using 0.27 parts of peroxide of

  di-tert-butyl instead of 0.22 part.

  After the polymerization phases, 0.125 parts of lithium stearate, 1.2 parts of lithium oxide, are added to the polymer on a screw extruder.

  titanium and 0.8 parts of zinc oxide per 100 parts of polymer.

  The properties of the monomers are summarized in Table 2.

EXAMPLE 5

  Example 4 is repeated but using 0.16 part of

  di-tert.-butyl peroxide instead of 0.27 part.

  After polymerization, 0.125 parts of lithium stearate and 2.5 parts of zinc oxide are added to a screw extruder. Product properties

are summarized in Table 2.

EXAMPLE 6

  -Example 3 is repeated but after polymerization the polymer is extruded with the same additives used in Example I except that the 0.125 part of

  Lithium stearate is replaced by 0.125 part of calcium stearate.

  Table 2 summarizes the properties of the polymer obtained. EXAMPLE 7 (Comparative Example) Example 1 is repeated but replacing the rubbery terpolymer with a Ziegler-type polybutadiene which has the following characteristics: viscosity for a 5% solution in styrene 81 centipoise at C.- Mooney viscosity ML ( 1 + 4) at 100 C: 35 Tg: 98% - 1-4 isomer content cis: 98% - 1-2 vinyl content: 2% Table 2 gives the characteristics of the polymer obtained -

TABLE 2

2 3 4 5 6 7

  EXAMPLE Test 156 Test 104 Test 103 Test 105 Test 106 Index of swelling 8.2 18.8 11.9 3 30 11 Gel rate 34.3 26.3 36.4 14.8 17.5 35 cjL2 .. 0, gg 1,27 1,27 1,37 1,26 1,2 Flow rate 12 16,5 20 7 9 9,0 Vicat point * C 73 78 '74 g0 80 80 Shock Izod 8 13 11 20 28,5 16 (3m / meter) X 10 Elongation elongation 96 40 60 61 30 20 55 Tensile modulus (Moduleentraction 1370 1 670 1 340 2 400 2 220 1 500 (Mga-Pascals) _________ 1 Threshold stress 13.6 15.5 - 12 , 3 25.0 22.2 13.0 (MegaPascals) Breaking stress {(Mga-Pascals) 14.3 IS, 0 16.6 20.6 18.4 15.0 Resistance to aging Initial elongation at break 96 40 60 60 30 20 55 Elongation at break after 2000h 25 35 30 20 10 2 exposure to WEATHER-O-METER (96)

  YELLOW INDEX INITIAL 3,5 1,5 0,5 0,7 1 4

  after 2000 hours in the weather -0- METER 26 28 15 13 22 tp color / _ 1

Claims (2)

  1) Process for the Preparation of Grafted Polymers Comprising Two-Step Suspension Polymerization of Styrene and the Presence of a Rubber Terpolymer of Ethylene, Propylene and a Third Component, characterized in that the first step styrene with the rubbery terpolymer in the presence of additives chosen from S mercaptans and / or triallylcyanurate and / or divinylbenzene, peroxides having a high thermal stability and that in a second step the polymerization is continued by prior addition of a mixture of peroxides chosis among tert-butyl perbenzoate, di-t-butyl peroxide and 2,5-dimethyl, 2,5-di-tert-butyl peroxyhexyn-3, and that after the two steps of polymerization of calcium, lithium or barium stearates in an amount at most equal to 0.25% by weight relative to the weight of the dry polymer. 2) Process according to claim I characterized in that after adding the two polymerization stages during the granulation of the polymer metal oxides selected from zinc or titanium oxides used alone or in mixture.