DD161028A1 - METHOD FOR PRODUCING ETHYLENE VINYL ACETATE COPOLYMERISES - Google Patents

Abstract

A one-step process for the preparation of ethylene-vinyl acetate copolymers with 5-20 mol% of vinyl acetate in tubular reactors having at least three reaction zones and high degrees of conversion, narrow molar mass distribution and high chemical homogeneity is described. The reaction conditions in the individual reaction zones are characterized by the established relationships between the maximum reactor temperature, the one-minute half-temperature of the lowest-decomposing peroxide, the maximum reactor temperature and the initiator feed, and the vinyl acetate concentration of the individual zones. The dependencies are expressed in the form of formulas.

Description

YEB Leuna-Werke Leuna, d. 15/9/79

"Walter Ulbricht" Dr.Btl / Zö

LP 7972 Title of the invention

Process for the preparation of ethylene-vinyl acetate copolymers

Field of application of the invention

The invention relates to a process for the preparation of copolymers of ethylene with 5 to 20 Mo1-% vinyl acetate in tubular reactors having at least three reaction zones.

Characteristic of the known technical solutions

In the preparation of copolymers of ethylene with vinyl acetate by radical high-pressure polymerization, there is a high chain-transferring effect of the comonomer and thus a reduction in the average molecular weight of the polymer. This reduction in molecular weight is undesirable if it exceeds a certain level. Therefore, a number of methods have been proposed which allow the preparation of copolymers of ethylene with 5 to 20 Uol-% vinyl acetate and high degree of reaction of the reaction mixture.

It is thus known to add to the Raktionsgemiach polyfunctional polymerizable compounds and thus increase the average Molmaaee of the copolymer (DE-OS 1495 787, DD-PS 117 077).

In these methods, it proves to be disadvantageous that relatively expensive substances must be used and the chemical composition of the resulting multipolymer is usually changed in an undesirable manner. It is also known to carry out the polymerization in multizone reactors at low temperatures, wherein a complicated division of the reaction mixture and a considerable technical effort for initiator dosing is necessary (DE-AS 1520 227).

It is also known to carry out the polymerization of ethylene-vinyl acetate mixtures of different composition in individual, successive reaction zones, both in the flow direction decreasing and increasing vinyl acetate concentrations have been described · disadvantageous in these methods is adjusting vinyl acetate concentration of the unreacted reaction mixture, the whole It is also known to prepare copolymers of ethylene with 5 to 20 mol% of vinyl acetate by a two-stage process by synthesizing copolymers with a low molecular weight in a 1-stage and reacting them in a 2-stage process. However, this effective process has the disadvantage that residues of the peroxide or its decomposition products further processing in special fields, such as in Schlagzhmhmung of PVC, can adversely affect ·

Object of the invention

The aim of the invention is the preparation of copolymers of ethylene with 5 to 20 mol% of vinyl acetate without crosslinking, which enable use in special fields.

Explanation of the essence of the invention

It was the object to develop a process that allows the preparation of copolymers with 5 to 20 mol% of vinyl acetate with high degrees of conversion, narrow molar mass distribution and high chemical homogeneity in a single-stage process

This object is achieved by a method in tubular reactors having at least three reaction zones at pressures above 50 MPa and temperatures above 350 K in the presence of initiating substances, according to the invention, the difference between the Reaktormaximaltemperatur the 1st zone and the one-minute half-temperature of the lowest decomposing peroxide used in the first zone, according to Equation 1

P TjIAX ₁ - TH, 1 = 30 4- TTJ. Ig SI ± 10 K, (equation 1)

the reactor maximum temperature of each further reaction zone by initiator dosing according to equation 2

% AXi ^{= 3} ^ AXi + 20 (i-1) І 10K (G1.2)

and the vinyl acetate concentration in each zone according to Equation 3

(V) i '= (V) ₁ (1 - ijTj-! ·) - 1 mol% (Eq. 3)

with the one-minute half-life temperature of the lowest-decomposing peroxide used in the first zone being above 36K, the temperature of the tempering medium of each zone between the one-minute half-temperature of the lowest-decomposing peroxide of each zone and the respective maximum reactor temperature is set and the formula symbols used in equations 1-3 have the following meaning:

(K) reactor maximum temperature of 1, zone (K) reactor maximum temperature of the i th zone Th (K) one-minute half-temperature of the am

lowest decomposing peroxide, 1 (K) one-minute half-temperature of the lowest decomposing peroxide of the 1st zone reactor inlet pressure

Vinyl acetate concentration of the copolymer Vinyl acetate concentration of the reaction mixture of the 1, zone

(V) j_ mol% vinyl acetate concentration of the reaction mixture of the ith zone SI g (10 min) melt index of the copolymer determined

at 463 K and 2.16 kp load in zone number. with i = 1,2,3, ..,. *, n

P MPa (V) Mo 1-% (V) ₁ Mo 1-%

EXAMPLES

Three- or four-zone reactors with approximately the same zone length were used, which were surrounded by jacket pipes, through which a temperature control medium was pumped in countercurrent at the temperatures (W W) indicated in the examples. Adjustment of the indicated vinyl acetate concentrations in each zone was effected by metering the total vinyl acetate consumed by copolymerization into the unreacted monomer mixture upstream of the suction side of the reaction pressure compressor of the strand fed into the first zone. The setting of the specified MaximaItemperatüren was achieved by metering of peroxide mixtures in a known manner.

As the lowest decomposing peroxides in the first zone, the following substances were used:

Peroxide 'Tjj (K) designation

Diisopropylperoxidikarbonat dilauryl 3,3,5-trimethyl tert "- BuJtyl-peroxy ~ 2-ethylhexanoate tert-butyl perbenzoate _#

368 A 393 B 388 C 403 D 441 e

Examples 1 - 5 dimension Beisp.1 B _e isp, 2 Ex. - C 3 B _e isp. 4 Ex _e 5 Three-zone reactor MPa 230 220 _230 9.5 230 230 parameter 8.7 P e C 7.8 B A Peroxide, mol% 6.0 7.4 441 13.1 21.4 "!•Zone Mo 1-% 5.2 7.1 465 11.9 20.4 (V) ₁ Uol-% 4.6 6.2 481 10.7 19.1 (V) ₂ ' K 502 460 425 435 426 (V) ₃ K 531 490 427 466 441 TMAX, 1 K 549 505 430 470 456 ТМАХ, 2 K 460 428 8.5 415 404 tmax, 3 K 462nd 430 4.5 418 415 TTM, 1 K * 464 433 18.2 422 418 ^T TM, 2 Mo 1-% 5.0 6.8 2.7 11.5 20.0 TTM, 3 g / 10min 3.0 12.1 4.1 121.0 (V) % 27.4 23.1 20.7 16.1 SI, 463K 4.3 2.4 2.2 1.7 Implementation degree MW_ ₁ Mn

Examples б - ю four-zone reactor

P ^ч * MPa peroxide, 1st zone

MoI JS

¹ MAX, 1 ¹ MAX, 2

³ UAX, 3

ТМАХ, 4

, 3

, 4

Mol-Jg MoI-JS

230 'D 8.1 7.4 6.7 6.1 458 482 489 508

445 446

448,450

240 A

9.9 8.7 8.0

7.5 420

441 453 470

408 410 425 428

230

10.1 9.4 8 _t 3 7.6 455 471 486 506 438 440 443 445

240 С

13.1 12.4 11.1 10.4 444 464 480 498 428 432 448 449

250 A

21.8 20.4 18.3 17.1 412 430 451 463 405 408 420 424

(V)

SI, 463K

Implementation degree

- 1

hn

g / 10min

в, 8 2.4 22.1

2.6

8.2

2.8 18.2

3.1

8.4 15.0 22.3

2.0

11.2 25.1 20.7

1.7

18.6 50.1 17.8

1.5

As results from the preceding examples, with the method according to the invention relatively low mass immunity can be achieved with a high degree of conversion of the monomer mixture.

By elution fractionation, the copolymers were decomposed according to Examples 1 to 10 in 10 to 15 fractions and determined by saponification of the vinyl acetate content of the fractions. All fractions of a series had within the error range of the determination method (-0.3 mol%) the same vinyl acetate content, whereby the high chemical homogeneity of the Kopolymerisa invention produced te was detected.

Claims (1)

claim A process for the preparation of ethylene-vinyl acetate copolymers containing 5 to 20 mol% of vinyl acetate in tubular R _e actuators having at least three reaction zones at pressures above 50 MPa and temperatures above 350 K in the presence of initiating substances, characterized in that the difference between the reactor maximum temperature of the 1 # zone and the one-minute half-life temperature of the lowest decomposing peroxide used in the first zone, according to Equation 1 ΪΜΑΧ1 - ^T H, 1 = 30 + ^ j . Ig SI ί 10 K, (G1.1) the reactor maximum temperature of each further reaction zone by initiator dosing according to equation 2 ¹ MAZi = Тіідх 1 + 20 (i - 1) t 10 K (Eq.2) and the vinyl acetate concentration in each zone according to Equation 3 (V) i = (V) ₁ (1 - ^ t -) - 1 mol% (Eq, 3) The one-minute half-life temperature of the lowest-decomposing peroxide used in the first zone is above 36K, the temperature of the tempering medium of each zone is between the one-minute half-temperature of the lowest-decomposing peroxide Set the zone and the respective reactor maximum temperature and the formula symbols used in dep equations 1 to have the following meaning: (K) Maximum reactor temperature of the first zone (K) Maximum reactor temperature of the ith zone TH (K) One-minute half-life temperature of the lowest lowest-decomposed peroxide am- ^v TH, 1 (K) one-minute half-life temperature of the am lowest decomposing peroxide of the 1 zone P MPa Raktoreingangsdruck (V) Mol% vinyl acetate concentration of the copolymer (V) -j mol% vinyl acetate concentration of the reaction mixture of the 1st zone (V) i 'mol% vinyl acetate concentration of the i-th zone reaction mixture SI (g / 10min) melt index of the copolymer at 4b'z K and 2.16kp at SI> 1 i number of hours with i = 1,2,3 »···· η