Process for preparing extrusion grade ABS polymer

Details Process for preparing extrusion grade ABS polymer Process for preparing extrusion grade ABS polymer

2001-04-16

2003-03-04

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S316000

Reexamination Certificate

active

06528591

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for making extrusion grade ABS polymers, more particularly, a continuous mass polymerization process.
SUMMARY OF THE INVENTION
A continuous mass polymerization process for making an extrusion grade ABS resin having desirable properties and suitable for making refrigerator liners is disclosed. The process comprise charging a reaction mixture into a first in a series of reactors under conditions promoting polymerization, the mixture comprising diene rubber, a mixture of monomers, inert solvent and a chemical initiator to form a reaction mixture. The mixture is then transferred into a subsequent reactor operating at a temperature of 130 to 155° C. with no addition of chemical initiator and the resulting product is then devolatilized. The ABS thus produced contains about 10 to 16 pbw of dispersed rubber particles having an average particle diameter of 0.3 to 0.7 microns.
BACKGROUND OF THE INVENTION
ABS polymer materials are known and have long found utility in a wide variety of applications. Thermoplastic compositions, most notably extrusion grades, containing ABS polymers alone or in conjunction with other resinous components are commercial products that are globally available. Refrigeration components, most notably refrigerator liners are one industry segment where ABS polymers have found considerable acceptance.
In its continued search for improvements, the refrigeration industry has been seeking material systems having a particularly desirable balance of properties; no single property renders a material system suitable for this demanding application. Material having such desirable properties would feature a high level of mechanical properties and good processability. Such desirable material would meet certain values of shear viscosity, tensile modulus, elongation-to-fail, resistance to impact, melt strain hardening and melt strain at the onset of visible necking. The melt strain hardening (stress growth) and strain to onset of visible necking are properties indicating the stability of the melt under high strains and are predictive of the uniformity of the thickness of parts that are thermoformed at high draw ratios. The materials that are currently available, although meeting some of the desirable properties, fall short in respect to others.
The ABS polymers of the current invention are preferably produced by continuous mass polymerization. Continuous mass polymerization is a well-known process for making ABS polymers. The process has been disclosed in, among others, U.S. Pat. Nos. 3,243,481, 3,337,650, 3,511,895 and 4,417,030, the specifications of which are incorporated herein by reference. U.S. Pat. No. 3,438,971, wherein a mixture of a diene-rubber-nitrile copolymer with unsaturated triglycerides is disclosed, is presently relevant.
DETAILED DESCRIPTION OF THE INVENTION
In the present context, the term “ABS polymers” refers to the genus entailing (i) a grafted diene rubber wherein grafted phase comprises the (co)polymerization product of a monoalkenyl aromatic monomer (exemplified by and sometimes referred to below as “styrene”) and an ethylenically unsaturated nitrile monomer (exemplified by and sometimes referred to below as “acrylonitrile”) and (ii) a matrix which comprises the (co)polymerization product of a monoalkenyl aromatic monomer and an ethylenically unsaturated nitrile monomer (hereinafter exemplified by and referred to as “SAN”).
The monoalkenyl aromatic monomer may be represented as
wherein Ar is selected from the group consisting of phenyl, halophenyl, alkylphenyl and alkylhalophenyl and mixtures thereof and X is selected from the group consisting of hydrogen methyl and ethyl groups.
Exemplary of the monoalkenyl aromatic monomers that can be employed in the present invention are styrene and substituted styrenes such as the o-, m-, and p-methyl styrenes, 2,4-dimethylstyrene, the corresponding ethyl styrenes, p-tert-butyl styrene, alpha-methyl styrene, alphaethylstyrene, alpha ethyl-p-methylstyrene, vinyl naphthalene, an ar-halo monoalkenyl aromatic monomer such as o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-bromostyrene and 2,4-dibromostyrene, and ring-alkyl, ring-halo-substituted styrenes, e.g., 2-methyl-4-chlorostyrene and 2,6-dichloro-4-methylstyrene. Mixtures of monoalkenyl aromatic monomers may also be used.
Exemplary of the unsaturated nitriles or alkenyl nitrile monomers which may be used are acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof.
Optional additional monomers may be polymerized along with the monoalkenylaromatic monomer and unsaturated nitrile monomer. These include alpha- or beta-unsaturated mono-basic acids and derivatives thereof, e.g., acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid and the corresponding esters thereof, such as methyl methacrylate, acrylamide and methacrylamide; vinyl halides such as vinyl chloride, vinyl bromide and vinylidene chloride, vinylidene bromide; vinyl esters such as vinyl acetate and vinyl propionate, dialkyl maleates or fumarates such as dimethyl maleate, diethyl maleate, dibutyl maleate; and maleic anhydride.
The mixture of monomers used in the inventive process comprise at least 40%, preferably at least 50%, relative to the weight of the mixture of the monoalkenylaromatic monomer. The mixture also contains at least 5%, preferably at least 10%, relative to the weight of the mixture of the unsaturated nitrile. In practice, it is desirable that the monomer mixture contains 40 to 95% and preferably 60 to 85%, by weight of the alkenyl aromatic hydrocarbon and 60 to 5% and preferably 60 to 15% and most preferably from 60 to 25% by weight of the unsaturated nitrile.
The rubber suitable in the present invention is at least one conjugated diene rubber having a glass transition temperature of at most −85° C. as determined by ASTM Test D-746-52T, selected from among 1,3-dienes, e.g., butadiene, isoprene, 2-chloro-1,3-butadiene, 1-chloro-1,3-butadiene, piperylene, etc. Also suitable are copolymers and block copolymers of conjugated 1,3-dienes with up to an equal amount by weight of one or more copolymerizable monoethylenically unsaturated monomers, including monoalkenyl aromatic hydrocarbons such as styrene and substituted styrenes such as aralkylstyrenes, including o-, m- and p-methylstyrenes, 2,4-dimethylstyrene, the corresponding ar-ethylstyrenes, p-tert-butylstyrene, etc.; alphamethylstyrene, alphaethyl-styrene; alphamethyl-p-methyl styrene, vinyl naphthalene; arhalomono-alkenyl aromatic hydrocarbons such as o-, m- and p-chlorostyrene, 2,4-dibromostyrene, and 2-methyl-4-chlorostyrene; acrylonitrile, methacrylo-nitrile; ethacrylonitrile; alpha or beta-unsaturated mono-basic acids and derivatives thereof, e.g., acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid and the corresponding esters thereof, such as methyl methacrylate, acrylamide and methacrylamide; vinyl halides such as vinyl chloride, vinylidene bromide; vinyl esters such as vinyl acetate and vinyl propionate, dialkyl maleates or fumarates such as dimethyl maleate, diethyl maleate, dibutyl maleate; and maleic anhydride.
A useful group of rubbers are the stereo-specific poly-butadiene rubbers formed by the polymerization of 1,3-butadiene. These rubbers have a cis-isomer content of about 30 to 98% and a trans-isomer content of about 70 to 2%. A preferred group of rubbers are those consisting essentially of 75 to 100% by weight of butadiene and/or isoprene and up to 25% by weight of a monomer selected from the group consisting of monovinylidene aromatic hydrocarbons (e.g., styrene) and unsaturated nitriles (e.g., acrylonitrile), or mixtures thereof. The diene rubber may contain crosslinking agent in an amount of up to about 2% based on the weight of the rubber monomer or monomers. The crosslinking agent may be any of the agents conventionally employed for crosslinking diene rubbers, e.g., divinylbenzene, diallyl maleate, diallyl fumarate, diallyl adipate, al

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