DD158248A1 - METHOD FOR PRODUCING IMPACT-RESISTANT AND AGING-STABLE COMPOSITIONS - Google Patents

Abstract

Preparation of the molding compositions by radical graft copolymerization of styrene, substituted styrenes or mixtures thereof in the presence of ethylene-propylene-diene terpolymer rubber using at least two free radical initiators of different grafting activity with respect to the grafting base. Concentration ratios and time of addition of the free-radical formers are prescribed as well as the stirring shear of the reaction mass. D. Preparation can be carried out after pure bulk polymerization or mass-suspension polymerization, lowering the shear pot by reducing the Rührerdrehzahl, addition of inert solvents or other suitable measures. The object of the invention is to improve the reaction and the radical graft copolymerization of styrene, substituted styrenes or mixtures thereof in the presence of EPT elastomers in such a way that property-changing changes in morphology are largely avoided when the polymer in the melt or solution shears. The invention is of importance in the production of impact-molding compounds and moldings intended to have an increased service life in durable products.

Description

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Title of the invention

Process for the production of impact-resistant and aging-stable molding compositions

Area of application of the invention

The invention relates to a process for the preparation of impact-resistant and aging-stable molding compositions by radical cationic graft copolymerization of styrene, substituted styrenes or mixtures thereof in the presence of ethylene-propylene-diene terpolymer rubbers.

Characteristic of the known technical solutions-

Impact-resistant polystyrenes of the type mentioned are known to be prepared by reacting styrene and / or substituted styrenes in the presence of a suitable ethylene-propylene terpolymer rubber (EPT rubber) and; In the presence of suitable radical formers (free-radically) polymerized, the reactants may be present in aqueous emulsion or suspension. It is also possible to use the mass or solution / solution technology in which the rubber in the monomer is dissolved, optionally an inert solvent Finally, it is known that one starts first by the mass process and the reacting system · when a certain conversion is reached, converts into an aqueous suspension and the Reaction so terminated "It is also well known that good mechanical properties of the final product are linked to a range of reaction and processing conditions

Thus, the concentration of actual Pfropfcopolytnorisat within the total product must reach a certain minimum level.

It was suggested that this goal be achieved by a specific choice of peroxidic initiators by type and quantity. reach (DT-OS 2400495) «

On the other hand, however, it is known that a sufficient impact resistance of the end product is bound to an optimum particle size of the dispersed Elastphas.e 'The previously described way of increasing the Pfropfeopolytnerenanteils usually leads in this regard to an inadmissible strong drop in Elastpartikelgröße, in particular because

1 HK / * J \ J «J /

In the interest of a sufficiently rapid heat dissipation and uniform distribution of the EPT-rStyrol phase in the initial phase of the polymerization, a high energy input should be ensured, so that the application of this proposed solution are limited * It has been proposed, the formation of the desired Elastpartikelgröße already Start of the polymerization by premixing a blast monomer solution with polyacrylate monomer solution (DT-OS 1770353V This measure, however, means the introduction of an additional process step "Moreover, it is extremely problematic under these conditions to set the required minimum graft It is known that the production of impact-resistant graft polymers of the type described here is still linked to a further condition. The elast particles must remain as unvarnished as possible in the course of the preparation, work-up and preparation process in size and size However, under the conditions of mass, mass / mass or mass suspension polymerization described herein, the EPT elastules show an increased shear susceptibility, so that either during the polymerization under the influence of stirring at high polymerization conversions or under conditions In these cases, the impact resistance of the final product u _e U # drops very sharply, rendering the plastic material useless for the intended use.

It has therefore been proposed to crosslink the discrete elast phase, which still contains free double bonds, after their formation by adding special peroxides (DAS 1694585s DT-OS 2536262). In this procedure can

However, it can not be ruled out that the plastic phase is also crosslinked in an undesired manner. Crosslinking of the elastomer as described in US Pat. No. 3,435,093 brings about problems in dissolving the EPT in the monomer.

Although a certain improvement in the corresponding disadvantages in the manufacturing process can be achieved by each of the known solutions mentioned, but the fact remains unsatisfactory that each of these measures are relatively narrow limits and that the interaction of several measures, a conflict of effects. shows·

So. it is possible, through the use of di-tert-butyl _e ~ ~ peroxide as an initiator a sufficiently high degree of grafting to. On the other hand, it is true that with increasing grafting activity of the initiator also an increasing cross-linking of the elast phase is observed, which had a positive effect on the particle strength on the other page causes the formation of a high .Pfropfpolymerisatanteils the increased production of inclusions of the plastic phase in the Elastpartikeln}, so-called _s Elastphaseninklusionen _e These inclusions are known to be important for the formation of a high impact resistance levels without simultaneously Elast "having to increase concentration in unwanted V / else "However, If the inclusion proportion too strong to _9, · the effective Elastphasenvolumen (= turn leads to increased instability despite adequate -Pfropfung the Elastteilchen to shear stress" originally used Elastmenge i- Elastphaseninklusionen · " Wagner, E _e R," Robeson, L ₈ M ·; Rubber Chem * and Technol · 43; 1970, 1129)

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Thus, even when the temperature increases and then during the processing of the end product, it becomes disadvantageous.

Object of the invention

The object of the invention is to improve the free-radical graft polymerization of styrene, substituted styrenes or mixtures thereof in the presence of EPT elastomers in an economical manner such that the described disadvantages of the known processes, such as the undesired change in the morphology in particular .by reducing the "elast particles in shear of the polymer solution or melt, avoided and aging-stable molding compositions are obtained with improved impact resistance, which can be processed without degrading property morphology · ·. "

Explanation of the essence of the invention The technical task

The invention has for its object to develop a process for the production of impact-resistant and aging-stable molding compositions by radical graft copolymerization of styrene, substituted styrenes or mixtures thereof in the presence of ethylene-propylene-diene terpolymer rubbers, which by mutually tunable measures the Adjustment of favorable elast particle sizes, grafting degrees, elastic phase volumes u »a <. Sizes, allow the above goal.

Features of the invention

According to the invention, this object is achieved by combining at least two radical formers having different transfer activity with respect to the graft base in such a way that the addition of the radical generator (s) with a lower transfer activity in a concentration of 0 _? 01 ⁹ 10 ~ ³ to 0.2 ^β 10 "^ mol % based on the monomer and of the radical generator (s) ^ with higher transfer activity in a concentration of 0.15 * 10-3 _{bia s s} tO" 3 Mol % based on the monomer before the start of the polymerization to the reaction mixture takes place 'and during the polymerization in a conversion range of 5 - 50%, preferably 20 - 35 % * of the radical generator (s) with higher transfer activity up to a total concentration of 2.0 After reaching a conversion of 20-35 %, the shear gradient set in the course of the polymerization is maintained or reduced by 10 % to 10 % by mole. A solution of the rubber is used in a known manner the monomers _from? sets the Polymerisationshilfsatoffe to and the procedure is otherwise one of the known polymerization technologies "

The polymerization initiators which can be used according to the invention are peroxide-containing and azo-containing free-radical formers from the group of compounds customarily used for the stated purpose. According to the invention, at least two free-radical generators which differ in the transfer activity of their radicals relative to the grafting base EPT are combined with each other, in each case also mixtures from two or more. Radicals of the same or similar relative transfer activity can be represented. "Relative levels of transfer activity (or grafting activity) are for many

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known radical generator or the radicals resulting from them in the relevant literature. Radical formers which can be used in the context of the invention are, for example, azo-diisobutyronitrile, · 2.2 ^{l of} azo-bis (2,4-dimethyl) -valeronitrile, diisopropyl peroxydicarbonate, di-n-butyl peroxydicarbonate, dicetyl peroxydicarbonate, t-butyl peroxyacetate, di- t-butyl peroxide, di-lauroyl peroxide, t-butyl perbenzoate, dibenzoyl peroxide and its substitution products, t-butyl peroxyneodecanoate, t-butyl peroxypivalate, dicumyl peroxide, t-butyl hydroperoxide, di-isopropylbenzene monohydroperoxide, cumene hydroperoxide, without limiting this enumeration Character has ··

Combinations of free radical generators with different transfer activity which can be used in the context of the invention are 'zV B *. Azo-diisobutyronitrile / dibenzoyl peroxide, azo-diisobutyronitrile / di-lauroyl peroxide, azo-diisobutyronitrile / di-tert-butyl peroxide, dibenzoyl peroxide / tert-butyl perbenzoate, dibenzoyl peroxide / di-t-butyl peroxide, dibenzoyl peroxide / t-butyl lydroperoxide, 2,2'- Azo-bis (2,4-dimethyl) valeronitrile / di-n-butyl peroxydicarbonate, 2,2'-azo-bis (2,4-dimethyl) valeronitrile / di-t-butyl peroxide.

The assignment of the radical formers to one another depends on the strength of the desired effect with regard to degree of grafting, degree of crosslinking of the elastase phase, particle size and stability to elastomers, but also according to which temperature stages are chosen during the polymerization process. The latter are based on the requirements of the rate of application and of the optimum shear rate to be set. Under grafting is the ratio

Mass of the grafted monomers. Mass of the graft base

understood

As is known, the degree of cross-linking of the dispersed elast phase is of decisive influence on its mechanical stability. It is therefore also to be taken into account in the selection of the free-radical formers, the attainable degree of crosslinking being known to be approximately parallel with the transfer activity of the initiator radicals.

The usable in the context of the invention monomers include not only styrene its substitution products, such as ck-methylstyrene, KernalkyIstyrole, core halostyrenes, Cyanstyrole, methoxystyrenes, Atropanitril u * ae also styrenes with multiple different substituents * According to the invention usable EPT rubbers are usually on ethylene-propylene-diene rubbers having diene contents of between 0.5 and 15 % used in this field. The diene component responsible for sufficient grafting belongs to the series of compounds commonly used in this field, such as cyclopentadiene, ethylidene norbornene, butadiene, isoprene.

The maintenance required in the context of the invention, in parallel with the use of a suitable radical generator combination, or the setting of the necessary shear rate after the achievement of a turnover of. 20 - 35 % $ in each case after the phase inversion has been completed, can be carried out in various ways, depending on the polymerization technology used. When pure bulk polymerization or mass / solution polymerization is used, the desired purpose is achieved

a) by throttling the stirrer speed, optionally to 0, '.

b) by addition of inert solvents,

c) by raising the temperature,

d) through a combination of all three individual measures _e

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The lowering of the shear rate does not need to happen abruptly, it can be adapted to the portability of the. Polymerization process also be carried out stepwise or continuously ·

In any case, it is recommended that because of the necessary in the first Star dium of the polymerization process to the completed phase reversal high shear rate to operate this first stage as a mass or Maase solution Polytnerisation. The inventive lowering of the shear rate for a conversion of 20-35 % can also be achieved by transferring the polymerizing composition to the state of an aqueous suspension and polymerizing it out there. The suspension stabilizers which are suitable are the dispersants conventionally used in this context. The impact-resistant and age-resistant graft polymers prepared by the process according to the invention. possess improved overall mechanical properties compared to products which are prepared by known methods, especially a largely insensitive to processing influences morphology and thus improved toughness.

Version is beepie -

Example 1

• Suitable ethylene-propylene-dicyclopentadiene terpolymer (ethylene: 44 »7 Gevn-%, propylene: 46.0 wt" - #, dicyclopentadiene: 9 _f ~ 3 Gevu%) is dissolved with stirring at 40 ⁰ C in styrene · Before and during the dissolving process is purged with nitrogen and evacuated several times · Thereafter, the addition of a Initiatorgemisch.es carried consisting of 0.22 "10""^ mol% of dibenzoyl peroxide and 1.0" 10 "" ^ Di-t-butyl peroxy the prepolymerization is carried out in a unter'Rühren V _p a-jacketed vessel at 105 ⁰ C up to. a turnover of 32 %

Thereafter, the'Vorpolymerisat is transferred to a heated reaction tube and the polymerization without shear stress in several temperature stages (120 ⁰ C, 140 ⁰ G, 150 ⁰ C) continued

At the end of the polymerization, the temperature is raised to 170 ^° C. within 30 minutes and then the viscous mass is discharged.

The product is comminuted and freed of residual monomers under vacuum. Thereafter, stabilization is carried out with 0 _s 2 % of di-tert-butyl-p-cresol

The mechanical test gave the values _? which are put together in Tab »1«

Dissolution process and Vorpolyrnerisation were carried out as described in Example 1. * In contrast to Example 1, an ethylene-propylene-ethylidenenorbornene elastomer was (ethylene 48 Gewe-%, propylene 45 5 percent? "-% _s norbornene _6} 5 GEWC *» ») in The prepolymerization takes place only up to a conversion of 28 %. Thereafter, the viscous mass is dissolved in an aqueous dispersant solution containing methoxyhydroxypropylcellulose of Oj.sub.1 Gew.sub.2. -%, based dispersed on water so that the Elastpartikel a direct shear stress are withdrawn "the polymerization is carried out under pressure at 110 ⁰ C and 120 ⁰ G until a conversion of 93% is reached" the Suspen "sionspolymerisate are filtered off, crushed and. dried (test values in Tab. 1) _e

The example illustrates the variability of the process in terms of the Elastzusamniensetzung used and the te.ch »nologische solution. The demand for reducing the shear stress of the Elastteilchen above a turnover of 20 ~ 35 % *.

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Example 3

Dissolution process and prepolymerization are carried out as described in Example 1. By way of derogation from Example 1, at 28 % conversion 20 parts by weight of solvent are added and the monomer / elast mixture is transferred to a reactor with lower stirring speeds. After addition of an initiator mixture consisting of 0.3 × 10 ^-2 dicumyl peroxide and 0.9 x 10 "- ³ mole% di-t-butyl peroxide, the polymerization is successively at temperatures of 100, 125 and 140 ⁰ C, at the same time the stirring speed is lowered, so that at the end of the polymerization, a stirring speed of <10 U / min is realized.

Thereafter, the polymer mixture is discharged, the monomer and solvent eliminated and. the polymer was worked up as usual (test values in Tab. 1).

The example illustrates the variability of the process with respect to the addition of solvents, a possible change, the components within the initiator mixture and the methods and. Method for gradual lowering of the shear rate.

Comparative Example A

The polymerization takes place in a stirred tank with stirrer made of stainless steel, which is directly comparable to that of Example 1.

Are presented 90 (wt .-) Tle, styrene, in the 11 TIe. of an ethylene-propylene-dicyclopentadiene terpolymer gem. Example 1 have been resolved. The monomer Elast solution are 0.9 x 10 "~ added to 3 mol% of dibenzoyl peroxide and the reaction mixture heated to 78 ⁰ C. The polymerization is carried out up to a • 52% conversion, after which the reaction mixture is transferred into a tube reactor without a stirrer and at different positions

Polymerization temperatures (2 h at 120 ⁰ C, 2 h at 140 ⁰ C, 2 h at 160 ⁰ C) polymerized to a conversion of 88 % ''.

The viscous .A composition is at 180 ⁰ C discharged (test values in Table "1) _e Comparative Example shows that although already after 52% conversion, the shear rate is lowered to 0 and a temperature stages program is connected, it is impossible to products with sufficient mechanical level If one further condition, the application of a combination of different radical formers required in the invention claim, is not obtained, the tests have a comparatively high impact resistance. The impact resistance (without notch), however, is very low.

The Pm process in the 1 * stage is carried out as described in Example 1. "Deviating from Example 1, the co- and. Graft copolymerization to continued to a conversion of 68% with stirring, is then polymerized without stirring effect up to a conversion of 95%, so that ultimately a solid block formed * laugh cooling, the polymer mass is machined product, ground and chinen over processing slides. processed to test bars «The result of the mechanical test is contained in Tab © 1«

The example documents that the mechanical properties are inadequate, in particular an excessive susceptibility to shear stress occurs if the stirring is continued at unacceptably high conversions with undiminished agitation intensity, although a mixture according to the invention of radical formers of different grafting reactivity.

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is used, so that only the combination of all the conditions specified in the claim of the invention leads to products which meet increased requirements.

Comparative Example C

The polymerization is carried out as described in Example 1. It is presented a 10% EPT-styrene solution, which will be added to 0.2 x 10 * "· 'mole% di-t-butyl peroxide · The polymerization is effected initially at · 105 ° C · At 35% conversion to 115 ⁰ C and the shear rate gradually lowered, so that at 50 % conversion no direct shear action .on the elast particles takes place »V / eeere 2 h is polymerized at 135 ⁰ C and then for 1 1/2 h at 150 ⁰ C. The conversion is 96 %. The mechanical properties are shown in Table 1.

The example shows that, although a free-radical generator with high transfer activity is used with respect to the elastomer and the shear rate is lowered during the polymerization, inadequate impact strength is achieved, especially after processing in the extruder.

In my opinion _{i i}

The polymerization is carried out as described in Example 1 with the difference that 0.25 ° 10 " ^-3 mole % dibenzoyl peroxide and 0.1 × 10 -4 mole % di-tert-butyl peroxide are added as free-radical formers 97 % <> The mechanical properties are shown in Table 1 »The example shows that despite the shear rate set according to the invention but with an unfavorable ratio of the initiators having different transfer activity, poor mechanical values and very poor processing stabilities are obtained.

Table 1: Summary of the properties characterizing the examples

Impact resistance

Impact-Vicat bending strength-temperature

/ k "J / m ² 7

Changes during processing 'on a twin-screw extruder

Impact resistance

/ k "J / m ² 7

Impact bending strength

/ ET / m ² 7

Remaining portion of the original BIAS phase PVumen

r%

example 1 92/18 X 30 Example 2 20 χ 25 Example 3 95/18 X 22 Comparative example Λ 48 22 For example B 75/10 X 18 Comparative Example C 92/18 X 12 Comparative example D 65 25

98

101

97

95 88 90/16 χ 95/19 x 88/15 χ

27 23

20

18

12

10

93 95 91

56 48 57 50

χ = unbroken number of test bars totaling 20

Claims (1)

Process for the preparation of impact-resistant and aging-stable molding compositions by free-radical grafting of styrene, substituted styrenes or their mixtures in the presence of ethylene-propylene-diene-terpoly- ned rubbers as grafting base according to known poly-. tnerisationstechnologie, characterized in that at least two radical generators with different transfer activity with respect to the graft base are combined with each other so that the addition of the or the radical generator (s) with lower transfer activity in a concentration of 0.01 x 10 "x ⁵ to 0.2 x 10 "* - ⁵ mol% ₉ based on the monomers and or the free radical generator (s) with higher transfer activity at a concentration of O5I5 'x 10" - ³ to 1.0 x 10 "- ⁵ mol% _t based on the monomer j before the start of the polymerization to the reaction mixture and during the polymerization in a Unisatzbereich of 5 to 50 % _t preferably 20 to 35 % _} of the radical generator (s) with higher transfer activity up to a total concentration of 2.0 * 10 " ( % ), And after reaching a conversion of 20 to 35 %, maintain the previously set shear rate in the further course of polymerization or lowered «. For this purpose-1 ropes tables