CS257334B1 - Elastomer blend for continuous production of tough polystyrenes - Google Patents

Abstract

A mixture of polybutadiene elastomers for the continuous production of high-impact polystyrenes by block technology, containing, in addition to the main polybutadiene, a polybutadiene elastomer which is branched. The amount of branched polybutadiene in the mixture is 10 to 50 parts by weight of the elastomer mixture.

Description

The invention relates to a mixture of elastomers for the continuous production of high-impact polystyrenes by block technology.

The requirements for the technical specification of polybutadiene elastomers used for the production of high-impact polystyrenes by block continuous technology differ from the requirements for elastomers for batch technology (suspension or block suspension). In continuous technology, a solvent is added (ethylbenzene, toluene, etc.), which results in a different mode of conducting the prepolymerization of the rubber solution; polybutadiene elastomers with a higher Mooney value are used.

As is known, the butadiene molecule polymerizes in three stereospecific configurations:

cis-trans vinyl

All polybutadiene elastomers contain a mixture of these three basic structures in varying proportions.

For tough polymers, polybutadiene rubbers with low or medium content of cis-1,4 structures, mainly with a content of 35 to 55% cis, are most often used from this wide range of products.

For economic reasons, or to enhance certain properties, it is known to use an elastomeric mixture of polybutadienes with a low content of cis-1,4 structures, with polybutadiene containing more than 95% cis-1,4 structures being added as the second elastomer.

During the preparation of polybutadiene, polymerization also occurs at different degrees of chain branching.

In practice, branching is often expressed as the ratio of the measured intrinsic viscosity to the intrinsic viscosity calculated in the Mark-Houwink molecular weight distribution equation.

branching index measured intrinsic viscosity calculated intrinsic viscosity

According to this criterion, linear elastomeric polybutadiene has an index equal to 1. Elastomers with an index of 0.7 and below are highly branched.

Another, less accurate indicator of branching is the ratio of solution viscosity (5 wt% in styrene) to Mooney viscosity. The advantage is that it is based solely on measured data.

It was found that the use of branched polybutadiene elastomers improves the physical and mechanical properties of tough polystyrenes, especially notch toughness.

The above disadvantages of the current state are eliminated by the elastomer mixture for the continuous production of tough polystyrenes according to the invention, which is composed of 50 to 90 wt. % of basic polybutadiene rubber with a polydispersity coefficient Mw/Mn = 1.8 to 3.5 with a solution viscosity of 90 to 180 m Pa , carbon black 10 to 50 wt. % of polybutadiene rubber with a branching index of 0.7 to 0.95, with a polydispersity coefficient of 2.5 to 5.5 and with a solution viscosity of 40 to 100 m Pa . s.

The use of this mixture according to the invention improves in particular the impact and notch toughness, as documented by the following examples.

Comparative example

In the model unit for the production of block high-density polystyrene in a continuous process, high-density polystyrene - a type suitable for injection molding with a content of 7% by weight of polybutadiene rubber was produced. The rubber used was of the following specifications:

polydispersity coefficient Mw _ _n

Mn ^{of 2.u} solution viscosity 165 mPas Mooney viscosity 53

The following temperature and conversion profile was maintained in the reactor section:

Table

Temperature Conversion

prepolymerization boiler 125 until 128 °C 29 until 32 % mass 45 rpm I. horizontal reactor 136 until 138 °c 44 until 47 % mass 17 rpm II. horizontal reactor 153 until 156 °c 54 until 56 % mass 12 rpm III. horizontal reactor 159 until 160 °c 67 to 70 % mass 7 rpm

After degassing to a value of 0.05 wt. % free styrene, extrusion and granulation, test specimens were prepared and the physical and mechanical properties were measured, which are listed in Table I.

Example 1

An elastomer mixture according to the invention with the following composition was used:

parts by weight of elastomer according to specification in the comparative case parts by weight of polybutadiene elastomer with branching index = 0.7 polydispersity coefficient 3.7 solution viscosity 60 mPas

The elastomer mixture of the above composition was dissolved in monomeric styrene in solutions with a concentration of 7% by weight. The elastomer solution was processed in a continuous unit for the production of block-shaped high-impact polystyrene with the same temperature and conversion profile as in the comparative case.

After degassing, extrusion and granulation, the physical and mechanical properties of the prepared samples of the material thus obtained were measured. The measured data are given in Table I.

Example 2

An elastomer mixture according to the invention with the following composition was used:

parts by weight of elastomer according to specification in the comparative case parts by weight of polybutadiene elastomer with branching index = 0.95 polydispersity coefficient =2.6 viscosity 42 mPas

For further processing, the same procedure was used as for the comparative example.

Test specimens were prepared from the obtained high-impact polystyrene and the physical and mechanical properties were measured. The results are in Table I.

Example 3

An elastomer mixture according to the invention with the following composition was used:

parts by weight of polybutadiene elastomer following specifications:

viscosity 180 mPas polydispersity Mw _ , _

Mn ^3.5 parts by weight of butadiene elastomer with branching index = 0.8 with polydispersity coefficient = 5.5 with viscosity 98 mPas

The same procedure as in the comparative example was used for further processing.

Test specimens were prepared from the obtained high-impact polystyrene and the physical and mechanical properties were measured. The results are in Table I.

Example 4

An elastomeric mixture according to the invention with the following composition was used:

parts by weight of the base polybutadiene elastomer following specifications:

polydispersity coefficient ^Mw - 1 0

Mn ' solution viscosity 90 mPas parts by weight of polybutadiene elastomer with branching index = 0.8 polydispersity coefficient Mw θ

Mn' with a viscosity of 72 mPas

The same technological procedure as in the comparative example was used for further processing.

Test specimens were prepared from the obtained high-impact polystyrene and the physical and mechanical properties were measured. Results - in Table X.

Table 1

Quality indicator Method Units Cf. Example Example Example Example example 1 2 3 4 Charpy Notch Toughness ČSN 64 0612 test body No. 2 r 2 J.cm 1.06 1.17 1.39 1.24 1.56 Charpy Impact Strength ČSN 64 0612 test body No. 2 J.cm 10.3 10.7 12.0 11.2 12.5 Contractual shrinkage ČSN 64 0209 Ϊ 30 í 5 í 30-5 4 30 Í 5 % 30 Í 5% 30 - 5%

Continuation table

Quality indicator Method Units Cf. example Example 1 Example 2 Example 3 Example 4 Melt flow index ČSN 64 0861 200 C load 49 N g/lOmin 8.1 7.9 7.8 8.2 8.0 Ductility ČSN 64 0605 34 37 42 39 44

SUBJECT OF THE INVENTION

Claims (1)

Blend of elastomers for the continuous production of tough polystyrenes by block technology, characterized in that it consists of 50 to 90 wt. % of polybutadiene rubber having a polydispersity coefficient Mw / Mn of 1.8 to 3.5, a solution viscosity of 90 to 180 mPas and of from 10 to 50 wt. polybutadiene rubber having a branching index of 0.7 to 0.95, a polydispersity coefficient of 2.5 to 5.5, and a solution viscosity of 40 to 100 mPas.