CS222740B1 - Process for producing graft copolymers - Google Patents

Abstract

A method for producing grafted copolymers of the ABS resin type with improved melt flow and product toughness, based on the formation of thermolabile ionic bonds between persulfate fragments bound in a glassy polymer phase.

Description

The invention relates to the production of grafted copolymers of the ABS resin type by emulsion radical polymerization.

Graft copolymers of the ABS resin type are prepared by grafting a polymer that is in a glassy state at normal temperature and usually has a glass transition temperature _{Tg of} 90 to 120 °C onto a polymer that is in a rubbery state at normal temperature and usually has a _Tg in the range of -100 to 20 °C. Grafting is most often carried out using emulsion, suspension or emulsion-suspension polymerization and the resulting polymer is then isolated, dried and usually shipped after the addition of suitable additives.

An example of an emulsion process for preparing these polymers is US Patent No. 3,624,183 or NSR 1,960,409. According to US 3,624,183, an ABS copolymer is prepared by grafting a mixture of 40 to 55 parts by weight of a mixture of styler or alpha-methylstyrene with acrylonitrile onto 60 to 45 parts by weight of a butadiene styrene copolymer containing 10% by weight of styrene, the resulting grafted copolymer being able to be mixed with a separately prepared copolymer of 60 to 80 parts by weight of styrene or alpha-methylstyrene with 40 to 20 parts by weight of acrylonitrile. According to NSR 1,960,409, an elastomeric latex is prepared by emulsion copolymerization of butyl acrylate, acrylonitrile and a crosslinking monomer, for example allyl methacrylate, in the presence of 0.1 part by weight of ammonium persulfate and 1.8 parts by weight of acrylonitrile. part of sodium oleate per 100 parts by weight of monomers. The rubbery latex obtained is grafted with a styrene-acrylonitrile mixture and, before isolating the polymer, is mixed with a separately prepared latex of a styrene-acrylonitrile copolymer.

From the point of view of the processing and utility properties of the resulting material, it is necessary to choose a compromise between the fluidity of their melt and the toughness of the resulting product when producing these polymers; increasing the molecular weight of the polymer, which in the range of practically used molecular weights improves the toughness of the material, is associated with a decrease in the fluidity of the melt. Similarly, increasing the degree of grafting of the elastomer with a glassy polymer usually leads to an increase in toughness and a decrease in the fluidity of the melt.

This deficiency of the known methods can be substantially reduced by using the process according to the invention.

According to the invention, grafted copolymers of the ABS resin type are obtained by radical emulsion polymerization of monomers whose polymer has a glass transition temperature _Tg higher than 80 °C, in the presence of an elastomer with a temperature _Tg of max. 20 °C, in such a way that an elastomer containing 1.4 to 1.4.10 ^-2 g of carboxyl groups per kg of elastomer or an elastomer prepared by emulsion polymerization using at least 0.3 wt. % persulfate on the monomers is grafted with a monomer mixture containing 50 to 80 wt. % vinylaromatic monomers, 20 to 50 wt. % monomers from the acrylonitrile and methyl methacrylate group and 0.1 to 10 wt. % of a monomer, initiator or regulator with at least one carboxyl group in the molecule, the weight ratio of monomers to elastomer being 95:5 to 50:50, the elastomer used contains 20 to 99% of insoluble fraction and at least 70% by weight of a bonded diene or alkyl acrylate with 2 to 10 carbon atoms in the alkyl and after completion of the polymerization, the carboxyl and sulfate groups present in the polymer are converted into thermolabile bonds by adding oxide, hydroxide or salt of a polyvalent metal in an amount of 0.1 to 10% by weight per polymer.

The use of mercaptostearic acid is particularly advantageous for introducing carboxyl groups into the polymer.

As a starting elastomer latex, a latex of an elastomer with a carboxyl group content in an amount of 1.4 to 1.4. . ^10_2 moles is generally applicable. A suitable method for preparing starting elastomer latexes is described, for example, in Czechoslovak patent No. 148,982 or Czechoslovak patent No. 126,932. Suitable monomers for ^the preparation of an elastomer latex are, for example, butadiene, isosporene, butyl acrylate, octyl acrylate, monooctyl maleate, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, cinnamic acid, and ketanoic acid. Carboxyl groups in both polymer components (i.e. elastomeric and glassy) can be located both inside the polymer chains and at their ends; in general, their introduction into the polymer can be done either by direct incorporation of carboxyl monomers or molecular fragments from initiators or carriers into macromolecules, or by functional conversion of suitable groups present in the polymer, for example hydrolysis of ester, amide or nitrile groups, or oxidation of aldehyde groups. To prepare a suitable elastomeric latex, it is also possible to use the introduction of sulfate groups into the polymer by initiating emulsion polymerization with an increased amount of persulfate. The primarily formed sulfate groups are partially hydrolyzed during polymerization to hydroxyl groups, whose oxidation by the present persulfate produces carboxyls. In terms of the formation of thermolabile bonds, in addition to carboxyl, the primarily formed sulfate groups are also useful. The appropriate amount of persulfate is most often 0.3 to 2 wt. % per monomer, used to prepare the elastomer latex. Compared to the use of a carboxyl monomer, this method of preparing a functionalized elastomer is limited to relatively low functional group contents because the high concentration of persulfate can disrupt the colloidal stability of the resulting latex.

When choosing specific conditions for emulsion grafting, it is possible, as in the case of elastomeric latexes, to use procedures known for the preparation of carboxyl latexes, which are described, for example, in the above-cited Czech patents. Suitable monomers for the glassy polymer component are, for example, styrene, methyl methacrylate, acrylonitrile, alpha-methylstyrene, acrylic acid, methacrylic acid, monobutyl maleate. Anionic, cationic and nonionic surfactants can be used as emulsifiers in an amount of usually 0.5 to 5% by weight per monomer mixture. Grafting can be carried out in the presence of molecular weight regulators, for example, xanthogen disulfides or mercaptans, or crosslinking agents, for example, divinylbenzene or glycol dimethyl acrylate, the concentration of which is closely related to the molecular characteristics of the resulting polymer.

The formation of thermolabile ionic bonds between the functional groups of the polymer by the addition of a polyvalent metal in the form of an oxide, hydroxide or salt can be ensured either by dosing the above additives into the isolated polymer (which usually passes through the production cycle in powder form), or by a suitable choice of coagulation mode, for example by precipitation of latex by the addition of a polyvalent metal salt, or in the presence of emulsifiers based on carboxylic acid soaps. Ca, Zn, Cd, Mg, Al are particularly suitable as polyvalent metals, the use of which is common in the vulcanization of ionomers. component

From the point of view of the effect of the invention, it is significant that part of the thermolabile bonds are formed between the elastomeric and glassy phases, and that at processing temperatures (200 to 270 °C) the thermolabile bonds are significantly weakened compared to the temperatures at which products made from these polymers are applied.

The advantage of the process according to the invention is both an increase in the toughness of the resulting product compared to similar materials prepared by conventional methods, and an improvement in the heat resistance and appearance characteristics of the product. From a technical point of view, a favorable factor is the possibility of reducing the content of emulsifiers while maintaining sufficient stability of the latex during the production process.

Example 1

ABS resin was prepared by emulsion polymerization in a 151 polymerization kettle according to the following procedure:

a) the following components were added to the reaction vessel:

(parts by weight, 1 part by weight — 30 g) recipe

No. 2 latex of a copolymer of butadiene with methacrylic acid, containing 0.35 moles of carboxyl groups, the particle size of which was determined by fluorometry

D _t = 0.25 ,um, with a polymer content of 50 wt. % and containing

heme gel 92% per polymer 35.0 35.0 K2S2O8 0.2 0.2 K2CO3 0.1 0.1 styrene 37.0 36.7 acrylonitrile 13.0 12.7 methacrylic acid 0 1.0 target dodecyl mercaptan 0.40 0.62 sodium dodecylbenzenesulfonate 0.30 0.30

total water phase

200

200 b J batch was heated to 70 °C and after 2 hours of polymerization with constant stirring and temperature control at 70 °C, the same amount of monomers as in the starting batch and 0.5 wt. parts of sodium dodecylbenzenesultonate in the form of a 16% aqueous solution were dosed into the reaction mixture. After another 3 hours of polymerization, 0.2 wt. parts of diethylhydroxylamine were dosed into the latexes and the latexes were coagulated by adding an aqueous solution of calcium chloride in an amount of 0.5 wt. % CaCl 2 per polymer. The obtained pulp was washed with water, dried at 80 °C and mixed with 0.2 wt. % 2,6-ditert.butyl-4-methyl phenol and 3 wt. % calcium stearate. The following melt flow properties and notch toughness were found for the polymer samples:

melt flow index (g/10 min) according to ČSN 64 0861 at

220 °C 15.3 15.8 volatilization heat (kJ/m ² J according to ČSN 64 0612

This example demonstrates the beneficial effect of the process according to the invention (formulation no. 2) on the toughness of the polymer. Formulation no. 1, which does not correspond to the process according to the invention, is given for comparison.

Example 2

In a stainless steel polymerization kettle with a diameter of

recipe number 3 4 5 6 7 8 9 latex A (in dry matter) 20 20 20 20 20 20 20 benzoyl peroxide 0.01 0.01 0.01 0.01 K2S2O8 0.2 0.2 0.2 K2CO3 0.1 0.1 0.1 tert.dodecyl mercaptan l 0.13 0.10 0.05 0.29 0.05 0.05 0.05 styrene 75 75 50 50 75 75 70 acrylonitrile 25 25 25 25 25 25 25 mercaptostearyl 1.0 acid itaconic acid 2.0 methacrylic acid lily 0.5 0.5 0.5 alphamethylstyrene 25 25 methyl methacrylate 5.0 lauryl sulfate sodium 3.0 3.0 3.0 3.0 water 150.0 150.0 150.0 150.0 dodecylbenzenesulfonate sodium nan 1.5 1.5 1.5 For recipes 3 to 6 was like "latex" "And" For recipes No. 3 and 4 was dosed

used a latex of a copolymer of 2-ethylhexylacrylate, styrene, ethylene glycol dimethacrylate, divinylbenzene and acrylic acid in a weight ratio of 90/7/1/1/1, whose turbidimetrically determined latex particle size D _t was 0.17 μτη and the gel content in the polymer was 36%.

For recipes No. 7 and 9, a polybutadiene latex with a turbidimetrically determined size D = 0.3 µm was used as latex A, in the synthesis of which 0.5 wt. % potassium persulfate per monomer was used as initiator. The gel content in the polymer was 95%.

For recipe No. 8, a polybutadiene latex with a turbidimetrically determined particle size D = 0.3 μπι was used as latex A, in the synthesis of which 0.2 wt. % azo-bis-isobutyrlonitrile was used per monomer. The gel content in the polymer was 72 %.

15 l of grafted polymer latexes were prepared by emulsion polymerization at 60 °C according to the following recipes (doses are given in parts by weight, 1 part by weight equals 30 grams).

monomer mixture once at the beginning of polymerization, for recipes no. 5 and 6 it was dosed continuously at a uniform rate for 6 hours, for recipes 7 to 9 the monomer mixture was dosed in two equally large doses at the beginning and after 2 hours of polymerization. After 6 hours of polymerization, 0.1 wt. part of diethylhydroxylamine per monomer was added to the latexes and by coagulation with an aqueous CaCl2 solution, powdered polymers were isolated from the latexes, which were mixed with 1 wt. part of calcium stearate and 0.5 wt. part of magnesium oxide after drying. for samples 3 to 6 wt. parts of calcium stearate for samples 7, 8 and 9. The following values of the Melt Flow Index according to ČSN number 64 0861 and the notch toughness of the proportion ČSN 64 0612 were found for the samples.

IQ number· recipe 3 4 5 melt flow index (g/10 min/ /220°C) 7.1 7.6 9.2 notch toughness (kj/m ² ) 16 9 21

7 8 9

9.3 7.1 7.1 8.5

25 18 23

The results given in Example 2 demonstrate the effect of the process according to the invention on the fluidity of the melt and the toughness of the polymer by various methods of sample preparation. The amount of the mol. weight regulator was deliberately chosen so that in the individual pairs 3 and 4, 5 and 6, 7 and 8 the samples obtained according to the invention (marked with odd numbers) and by the known process (samples with even numbers) always had practically the same fluidity. The toughness values found for samples with odd recipe numbers are in all cases significantly higher than for the corresponding samples with even recipe numbers. Recipes No. 3, 7, 8 represent the incorporation of carboxyl groups into ^{the 1} glassy phase of the copolymerization, recipe No. 5 using a carrier (regulator) that has a carboxyl group in the molecule, i.e. at the end of the polymer chain. Formulation No. 7 uses an elastomeric latex that was synthesized using an increased amount of persulfate. Formulations No. 4 and 6 do not meet the condition of the presence of carboxyl groups in the glassy phase, and formulation No. 8 does not meet the condition of the presence of functional carboxyl or sulfate groups in the elastomeric polymer.

Recipe No. 9 demonstrates the possibility of applying the process according to the invention to monomer mixtures containing methyl methacrylate.

Claims (2)

1. A process for producing the grafted ABS resin type kopoilymerů radical emulsion pOlymeriací monomer whose polymer has a glass transition temperature T _g higher than 80 degrees Celsius in the presence of an elastomer with a maximum temperature T _g of 20 ° C, characterized in that the elastomer containing one, 4 to 1.4.10 ^-2 moles of carboxyl groups or elastomer prepared by emulsion polymerization using at least 0.3 wt. % of persulfate to monomers is grafted with a monomer mixture comprising 50 to 80% by weight of vinyl aromatic monomers, 20 to 50% by weight of monomers from the group acrylonitrile and methyl methacrylate and 0.1 to 10% by weight of a monomer, initiator or regulator with at least one carboxyl group per molecule; wherein the weight ratio of monomers to elastomer of the invention is 95: 5 to 50: 50, the electrolyte used contains 20 to 99% insoluble and at least 70% by weight of the bound diene or alkyl of 2 to 10 carbon atoms in the alkyl and and the sulfate groups in the polymer are converted to thermolabile bonds by the addition of an oxide, hydroxide or polyvalent metal salt in an amount of 0.1 to 10% by weight per polymer. 2. A process for the production of graft copolymers of the ABS resin type according to claim 1, characterized in that rcercaptostearic acid is used to introduce the carboxyl groups into the copolymers.