WO1993002116A1

WO1993002116A1 - Process for the preparation of particle form ethylene-propylene copolymers

Info

Publication number: WO1993002116A1
Application number: PCT/FI1991/000219
Authority: WO
Inventors: Jukka Veli SEPPÄLÄ; Jari Juhani KOIVUMÄKI
Original assignee: Neste Oyj
Current assignee: Neste Oyj
Priority date: 1990-01-18
Filing date: 1991-07-17
Publication date: 1993-02-04
Anticipated expiration: 1994-01-17
Also published as: FI900301A0; FI900301L; FI87360C; FI87360B

Abstract

The present invention relates to a process for the preparation of an elastomeric ethylene-propylene copolymer which is obtained in the form of particles which do not tend to adhere to each other nor on the parts of the polymerization reactor or the treatment apparatus during the later treatment. The copolymer is prepared by polymerizing with the aid of a Ziegler-Natta catalyst system ethylene in a liquid propylene at a low terperature below 15 °C. The particle form nature of the product is further pronounced when the content of the ethylene units in the copolymer obtained is more than 35 %, preferably more than 50 %.

Description

Process for the preparation of particle form ethylene- propylene copolymers

The present invention relates to a process for preparation of elastomeric ethylene-propylene copolymers in particle form.

The ethylene-propylene elastomers or EPR gums can be divided into two groups: the saturated ethylene-propylene copolymers (EPM) and the ethylene-propylene-diene terpolymers (EPDM) . These are mainly amorphous co- or terpolymers, the statisti¬ cal structure of the repeating units of which has an influence on the crystallinity of the polymer and its behavior in different weather conditions, such as on its resistance to atmospheric oxygen and ozone.

In the copolymerization of these olefin elastomers a Ziegler-Natta catalyst system generally is used comprised of a so-called procatalyst and a co-catalyst. The procatalyst is based on a compound of a transition metal belonging to some of the groups IVB-VII of the periodic system of the elements, and the co-catalyst is based on an organometallic compound of a metal belonging to some of the groups IA-IIIA of the periodic system of the elements. The catalyst system can also comprise a carrier on which the transition metal compound has been superposed, and electron donating compounds enhancing and modifying the catalytic properties.

U.S. Patent No. 4,013,823 describes the preparation of an elastomeric ethylene-propylene copolymer with aid of a catalyst mixture containing Al halide and Ti halide and wherein the Ti-compound has been superposed on an anhydrous Mg halide carrier, which catalyst mixture has then been co plexed with an electron donor. G.B. Patent No. 1,492,864 (= FI Specification No. 750,367) describes the preparation of a thermoplastic ethylene- propylene copolymer having elastomeric properties in the unvulcanized state, by copolymerizing propylene and ethylene which is present in an amount of 10-50 wt%, by using a mixture of a catalyst system comprising an optionally with a donor complexed Al alkyl and a Ti halide, which has been complexed with a donor and supported on an activated, anhydrous Mg halide carrier.

In U.S. Patent No. 4,331,561 (= FI Specification No. 762,643) catalysts are described which are suited for homo- or co-polymerizing of α-olefins and which are formed with a donor from a complexed Al alkyl and a reaction product of a donor-complexed Mg halide and a quadrivalent Ti halide. The copolymer obtained contains 40-60 wt% propylene and has both polyethylenic and polypropylenic crystallinity.

EP Patent Application 60,090 described an ethylene-propylene copolymer which is prepared by polymerizing monomers at a temperature of 22-27°C (according to the examples) with the aid of a catalyst mixture which is obtained by reacting one ore more of an Al trialkyl and/or an Al alkyl monohalide and a Ti halide which is on a MgCl₂ or MgBr₂ carrier. The product obtained comprises 40-60 wt% propylene units, no polypropylenic crystallinity and less than 10 % polyethyle¬ nic crystallinity.

In the processes of the types mentioned above for the preparation of elastomeric ethylene-propylene copolymers the problem is that in the formation of a particle form product the particles are adhered to each others and polymer is precipitated also on the inner walls of the reactor and other apparatus co ing into contact with the reaction mixture such as mixers. It is thus necessary to clean the reactor apparatus often, a tedious and time consuming procedure. The present invention has as a goal to provide such a process for the preparation of elastomeric, particle form ethylene-propylene copolymer wherein the particle form copolymer particles built up in the polymerization are not adhering to each others nor the walls of the polymerization reactor or the other surfaces in the apparatus coming into contact with the reaction mixture. This has now been achieved with a novel process which is mainly characterized by what is said in the characterizing part of claim 1. It has thus been realized that the adhesion of the polymer on the surfaces of the reaction apparatus can be avoided by carrying out the polymerization in liquid propylene and at a temperature below 15°C. The adherence is further reduced by a high ethylene unit content of the copolymer which is preferably more than 35 wt%, and most preferably more than 50 wt%.

The most preferred monomer combination is comprised of propylene and ethylene. In addition to these monomers, anyhow, a diene can also be used as a third monomer. Typical dienes are dicyclopentadiene, ethylidene-norbornene and hexa-1,4-diene.

The co-polymerization is thus carried out with aid of a Ziegler-Natta catalyst composition consisting of a so-called procatalyst and a co-catalyst. The procatalyst is based on a compound of a transition metal belonging to some of the groups IVB-VIII of the periodic system of elements, and the co-catalyst is based on an organometallic compound of a metal belonging to some of groups IA-IIIA of the periodic system of the elements. To the catalyst system usually also belongs a carrier on which the transition metal has been superposed, and electron donating compounds which enhance and modify the catalytic properties of the system.

As the procatalyst can be for example a quadrivalent Ti halide which has been superposed on a Mg halide carrier, and as the co-catalyst can be for example an organoaluminum compound such as an Al trialkyl. Specific homogenous catalyst systems can also be used. The ratio procatalyst to co-catalyst is about 20-200 and preferably about 100.

The polymerization is carried out as a precipitation polymerization wherein the polymer is not dissolved in the medium. As the medium preferably propylene in a liquid form can be used. The reactor used is an autoclave provided with a mixer, which autoclave is purged with gaseous nitrogen in order to reduce the oxygen content in a very essential degree before the polymerization. Hydrogen can preferably be used to regulate the chain length of the copolymer thus obtained.

The elastomeric copolymer of ethylene and propylene is obtained in a particle form when the amount of units originating from ethylene in the co-polymer exceeds 35 wt% (cf. Fig. 1) . The adhesion of the product is reduced with growing sequences of crystalline polyethylene and reducing amount of sequences of atactic polypropylene, but first when at the same time the polymerization temperature is kept low, ie. below 15°C, the particles obtained do not adhere on the different parts of the reactor.

The ethylene-propylene copolymer in a particle form is easy to handle so it can be used for a myriad of purposes which can gain profit of this property. The copolymer can be vulcanized, especially when it contains as a ter-monomer component some diene compound, by known methods with elementary sulphur, different sulphur compounds, peroxy compounds, azo compounds, by radiation, etc. The low degree of adhesion is an advantage both by the preparation of the polymer and by its vulcanization or other treatment, resulting in savings both in the investment and running costs of the production. The invention is illustrated in the following with examples the obtained products of from which were analyzed with methods mentioned below.

The crystallinity and the glass transition temperature of the product were determined with the DSC method. The intrinsic viscosity was determined with a capillary visco- meter at 135°C in decaline. The ethylene content of the product was determined by IR spectroscopy using the absorption at 1,150 cm"¹ and 720 cm"¹. The content correlation was calibrated with the ¹³C NMR analysis. The density of the product was determined in a mixture of ethanol and water in a density gradient column.

Example 1

An EPM elastomer was produced in a liquid propylene in a 2 L autoclave provided with a mixer, which autoclave had two small windows at the sides in order to observe the particles formed in the polymerization.

Before beginning of the polymerization the reactor was evacuated and purged four times with nitrogen. Thereafter 6 mmoles hydrogen was added as a chain transfer agent, whereafter 500 grams of liquid propylene was conducted to the reactor.

The polymerization was started by adding a catalyst system comprised of TiCl₄ on a magnesium chloride carrier and triethyl Al (a 10-wt% solution in heptane) in a mole ratio of 100. The catalyst components were mixed before feeding to the reactor. After the addition of hydrogen, propylene and the catalyst the pressure was raised to 8.0 bars by leading gaseous ethylene to the reactor (the over pressure of the ethylene was 0.5 bars). The pressure was kept constant by the continuous addition of ethylene, and the reaction mixture was stirred with a constant speed of 600 rp . The temperature was 0°C. The polymerization was stopped after 30 minutes by letting the unreacted monomer out from the reactor.

The activity of the catalyst was 14 kg copolymer/g-h. The copolymer contained 37 wt% ethylene according to IR analysis. According to the DSC analysis there were no polyethylene type crystallinity in the copolymer, its intrinsic viscosity in decaline was 2,53 at 135°C, the Shore A hardness according to ASTM D 2240-81 was 49, and as density a gradient column revealed 0.861 g/cm². The product was in a particle form and the particles didn't adhere to each others after removal of the monomers.

Examples 2-15 The process explained in example 1 was repeated, but in these examples the partial pressure of ethylene and the polymerization temperature were changed. The temperature was

1, 14 and 25°C and the total pressure was 8.0 and 18 bars. The polymerization conditions are given in Table 1 and the properties of the products thus obtained are given in Table

2. The dependence of the particle form of the polymerization temperature and the ethylene content is set forth in Fig. 1.

Examples 16 and 17 These examples were carried out as example 1 but by copolymerizing ethylene and propylene at temperatures of -5°C and -10°C. The results are presented in Table 3.

Example 18 This example was carried out as example 1 but the temperature was 14°C and the total pressure was 12.6 bars. In the polymerization as an external donor diphenyldimethyl- silane was used and the TEA/donor mole ratio was 10. The product was in a particle form and its properties were like the ones given in Table 3. From Fig. 1, it can be seen that when the ethylene content of the product varied between 37 wt% and 64 wt% (correspon¬ dingly, its polyethylene type crystallinity varied between 0% and 13%, and the glass transition temperature between 27°C and -30°C, cf. Tables 1 and 2) and the product was polymerized at a temperature below 14°C, the product obtained was in form of particles which were not tacky nor tended to adhere to each others or to reactor parts.

Example 19

It was proceeded as in example 1 but the temperature was 14°C and the total pressure 12.6 bars. In the polymerization a catalyst of the same type as previously was used except that it also contained an internal donor. As an external donor diphenyldimethylsilane was used, the TEA/donor mole ratio being 10. All other values were as in example 1. The product still was in particle form.

Results of the analysis: Density: 0.879 g/cm"¹

Hardness: 70 Shore A units

Ethylene content: 57 wt%

Intrinsic viscosity: 8.3 dl/g

Crystallinity: 19% Activity: 1.8 kg/(g catalyst * h) .

Example 20

The terpolymerization of ethylene, propylene and 5- ethylidene-2-norbornene was carried out as in example 1 except that the total pressure was 12.6 bars and the polymerization temperature was 15°C. As a medium 450 grams of propylene was used to which 22 grams of 5-ethyliden-2- norbornene had been added. A particle form EPDM elastomer with an activity of 3,5 kg/g cat.*h was obtained.

Claims

Claim

A process for the preparation of an elastomeric ethylene- propylene copolymer or ethylene-propylene-diene terpolymer in particle form wherein the content of ethylene units is more than 35 wt%, characterized in that the polymerization of the monomers is carried out at a temperature below 15°C in the presence of a Ziegler-Natta catalyst composition which is formed of a quadrivalent Ti halide procatalyst superposed on a Mg halide carrier, and an Al trialkyl co- catalyst.