CS217211B1 - Process for producing graft copolymers - Google Patents

Abstract

A method for producing graft copolymers of the ABS resin type with an improved relationship between melt fluidity and product toughness, based on the formation of thermolabile ionic bonds between functional groups in the elastomeric and glassy phases.

Description

The invention relates to the production of graft copolymers of type ABá resins by emulsion radical polymerization.

Graft copolymers of the AB3 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 3,624,183 or N3R 1,960,409. According to UJ 3,624,183, the AB8 copolymer is prepared by grafting a mixture of 40 to 55 parts by weight of a mixture of styrene or alpha-methylstyrene with acrylonitrile onto 60 to 45 parts by weight of butadiene-styrene copolymers containing 10 parts by weight of S5 styrene, the resulting grafted copolymer being 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 N3R 1,960,409, an elastomeric latex is prepared by emulsion copolymerization of butyl acrylate, acrylonitrile and a crosslinking monomer, e.g. allyl methacrylate, in the presence of 0.1 parts by weight of ammonium persulfate and 1.8 parts by weight of parts 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 styrene-acrylonitrile copolymers.

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 prepared by radical emulsion copolymerization of a mixture of monomers, the polymerization of which produces a polymer with a glass transition temperature Tg higher than 80 °C in the presence of an elastomer latex with a glass transition temperature of max. 20 °C, by using persulfate in an amount of 1.85 Í0 ^_ ^ to initiate the polymerization.

-2 , to 0.74 . 10 mol per iOO g of monomer and after completion of polymerization, the functional groups incorporated into the polymer are converted into thermolabile bonds by adding 0.1 to 5.0 parts by weight of oxide, hydroxide or salt of a polyvalent metal per 100 parts by weight of polymer.

The dosing of persulfate into the polymerization batch is usually carried out in an aqueous solution, which may also contain a buffer, e.g. sodium carbonate, the presence of which prevents the autocatalytic decomposition of persulfate during storage. Potassium or ammonium persulfate is most often used. Depending on the temperature regime of the polymerization process, in some cases it is advantageous to dose the persulfate in several doses separated by time, or continuously during the entire process. The alternatives mentioned are particularly suitable at higher polymerization temperatures and in continuous or semi-continuous process arrangements, when a single dosing of persulfate can easily lead to its premature exhaustion. Other components of the polymerization batch, such as monomers, emulsifier, electrolyte, reducing components, molecular weight regulators, or crosslinking agents, can be dosed in the process according to the invention in amounts comparable to conventional processes. When choosing the ratio between the monomer and water phases, it is desirable to take into account that the persulfate present acts as an electrolyte, i.e., that at its high concentration in the water phase, agglomeration or coagulation of latex particles may occur. These phenomena can be limited (while keeping other parameters unchanged) by increasing the volume of the water phase, i.e., increasing the water content in the batch. The formation of thermolabile ionic bonds between the functional groups of the polymer by adding a polyvalent metal in the form of an oxide, hydroxide or salt can be ensured either by dosing the aforementioned additives into the isolated polymer (which usually passes through the production cycle in powder form) or by appropriately choosing the coagulation regime, e.g., by precipitating the latex by adding salts of a polyvalent metal, possibly in the presence of an emulsifier 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 innomers. From the point of view of the effect of the invention, it is significant that the formed thermolabile bonds are significantly weakened at processing temperatures (200 to 270 °C) compared to the temperatures at which products made from these polymers are applied.

The advantage of the process according to the invention is the improvement of the relationship between melt flowability and toughness of the final polymer and often also the increase of latex stability at constant emulsifier content. The presence of bound sulfate groups, which are formed by the reaction of persulfate fragments and monomers, contributes to an increase in the polarity of the polymer, which usually allows for a reduction in costs and often an increase in heat resistance during subsequent antistatic treatment. The reduction of the emulsifier content in the latex while maintaining its stability also has a positive effect on latex demonomerization.

Example

The following components were dosed into a 15 l stainless steel polymerization reactor (parts by weight, 1 part by weight = 25 g)

recipe number 1 2 3 4 5 polybutadiene latex (dry) 17.0 17.0 17.0 17.0 17.0 K2 ^at 2°8 0 0.1 0.8 1.5 0.1 azo-bis-isobutyronitrile 0.05 0 0 0 0 KgCOj 0.5 0.5 0.5 0.5 0.5 tert-dodecyl mercaptan 0.3 0.3 0.3 0.3 , 0.45 styrene 75 75 75 75 75 acrylonitrile 25 25 25 25 25 total aqueous phase 200 200 200 200 200 sodium lauryl sulfate 0.4 0.4 0.4 0.4 0.4

The polybutadiene latex used and the turbidimetrically determined particle size D _t = 0.3 A ¹ ® β dry matter 51.5 56 were identical in all formulations. Potassium persulfate was dosed in the form of an aqueous solution after heating the remaining components in the batch to 60 °C.

After one hour of mixing the batch while simultaneously heating to 60 °C, another 0.4 parts by weight of sodium lauryl sulfate was added to the latex. After 5 hours of polymerization, the monomer conversion was determined to be higher than 95% in all cases. 0.3 parts by weight of diethylhydroxyamine was added to the latexes, unreacted monomers were removed by steam distillation, and the latexes were coagulated with a calcium chloride solution containing 0.5 parts by weight of CaCl2 per 100 parts by weight of polymer. 0.3 parts by weight of calcium stearate and 0.2 parts by weight of the antioxidant 2,6-ditert-butyl-4-methylphenol were added to the dried powder before granulation.

The following characteristics of the obtained material were determined from the granulate.

recipe number 1 2 3 4 5 Notch toughness according to UN 64 0612 (kJ/m ² ) 16 16 16 16 13 melt flow index according to Cón 64 0861 («/10 min/220 °C) 5.4 5.4 7.1 8.5 8.4

By comparing the values of melt toughness and fluidity found for recipes 3 and 4, which correspond to the process according to the invention, with the values found for recipes 1 and 2, which correspond to the known preparation method, it is clear that the process according to the invention allows for achieving higher fluidity without deterioration of the polymer toughness. Recipe No. 5, which did not correspond to the process according to the invention, demonstrates that increasing the melt fluidity in the usual way, i.e. increasing the content of the molecular weight regulator in the polymerization batch, is associated with a decrease in the polymer toughness. ..·

Example 2

In the same equipment as in example δ. i, resin latexes were prepared according to the following recipes (parts by weight, 1 part by weight = 25 g)

recipe number 6 7 8 latex copolymer of 2-ethylhexyl acrylate with ethylene glycol dimethacrylate in a mass ratio of 98:2 18 18 18 KjÍgOg 0.1 0.8 0.1 0.4 0.4 0.4 t.dodecyl mercaptan 0.05 0.05 0.2 total aqueous phase 250 250 250 styrene 75 75 75 acrylonltrile 25 25 25 sodium dodecylbenzenesulfonate 0.3 0.3 0.3

The elastomer latex used with a turbidometrically determined particle size D _t ' = 0.3 µm was identical in all cases. The persulfate was dosed into the batch, heated to 80 °C in the form of an aqueous solution. After 10 minutes from the dosing of the persulfate, another 0.3 wt. part of sodium dodecylbenzenesulfonate was dosed. After 3 hours of polymerization at 80 °C, 0.3 wt. parts of diethylhydroxylamine were dosed to the latexes, unreacted monomers were removed by steam distillation and the latexes were coagulated with an aqueous solution of aluminum sulfate containing 0.5 wt. % of aluminum sulfate based on the dry matter of the latex. Before granulation, 0.1 wt. % of 2,6-dibutyl-4-methylphenol, 0.5 wt. % of ZnO and 2 wt. % of calcium stearate were added to the dried powder. The following melt flow and polymer toughness values were determined from the granulate of the obtained polymer resins.

recipe number 6 7 8 melt flow index (g/10 min/220 °C) according to ČáN 64 0861 18 24 24 notch toughness according to ČáN 64 0612 (kJ/m^) 9 9 7

Similarly to example no. i, it is clear that in recipe no. 7, which corresponds to the process according to the invention, a more favorable relationship between melt fluidity and polymer toughness was achieved than in recipes 6 and 8, which corresponded to known processes.

Claims (2)

SUBJECT OF THE INVENTION Process for the preparation of graft copolymers of the type ABAB resins by free-radical emulsion copolymerization of monomer mixtures whose polymerization results in a polymer having a glassy temperature Tg greater than 80 ° C in the presence of elastomer latex with a glassy temperature of 20 ° C max. use persulfate in an amount of 1.85. 10 ”^ to o 0.74. 10 moles per 100 g of monomer and after polymerization, the functional groups incorporated into the polymer are converted into thermolabile bonds by the addition of 0.1 to 5.0 wt. parts by weight of polyvalent metal oxide, hydroxide or salt per 100 wt. parts of the polymer. 2. A process according to claim 1, wherein the polyvalent metal is calcium, zinc, magnesium or aluminum.