US 5,179,166 AGranted

Monovinylidene aromatic polymers with improved properties and a process for their preparation

AssigneeThe Dow Chemical Company

InventorMehmet Demirors

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Abstract

There is disclosed a monovinylidene aromatic polymer resin having a specific rubber particle size distribution that provides surprisingly improved combinations of product properties, such as gloss, impact resistance and tensile strength. Such resin has a first group of smaller particles having a volume average particle diameter of from about 0.2 to about 0.6 micrometers and a second group of larger particles having a volume average particle diameter of from about 2.5 to about 5 micrometers. In these resins it is further necessary in this specific rubber particle size distribution, based on 100 parts by weight rubber or rubber equivalent, that (a) particles constituting from about 20 to about 60 parts by weight of the rubber have diameters of from about 0.1 to about 0.8 micrometers, (b) particles constituting from about 60 to about 20 parts by weight of the rubber have diameters of from about 2 to about 6 micrometers, and (c) that there be a specific amount of intermediate size particles constituting from about 10 to about 30 parts by weight of the rubber and having diameters between about 0.8 and about 2 micrometers. Also disclosed is a process for preparing such resins in a simplified production process wherein the rubber which is used has distinct high and low molecular weight components, the high molecular weight component having a weight average molecular weight at least about two and one half times greater than the weight average molecular weight of the low molecular weight component.

A process for preparing a rubber-reinforced monovinylidene aromatic polymer comprising the steps of:

(a) continuously supplying a reaction mixture comprising monovinylidene aromatic monomer and a dissolved rubber to a reactor means,
(b) continuously polymerizing the monovinylidene aromatic monomer in the presence of the dissolved rubber in the reactor means under conditions whereby phase inversion subsequently occurs,
(c) continuously removing from the reactor means a rubber-reinforced monovinylidene aromatic polymer, which process is characterized in that:
(d) the rubber which is dissolved in the reaction mixture has distinct high and low molecular weight components, the high molecular weight component having a weight average molecular weight at least two and one half times greater than the weight average molecular weight of the low molecular weight component, and
(e) the process conditions prior to phase inversion are adjusted to produce different groups of rubber particles from the high and low molecular weight components of the rubber, each group having a different average rubber particle size such that the product rubber-reinforced monovinylidene aromatic polymer has dispersed therein a first group of smaller particles having a volume average particle diameter of from about 0.2 to about 0.6 micrometers and a second group of larger particles having a volume average particle diameter of from about 2.5 to about 5 micrometers, and the rubber particle size distribution is such that, based on 100 parts by weight rubber or rubber equivalent:
(i) particles constituting from about 20 to about 60 parts by weight of the rubber have diameters of from about 0.1 to about 0.8 micrometers,
(ii) particles constituting from about 60 to about 20 parts by weight of the rubber have diameters of from about 2 to about 6 micrometers, and
(iii) particles constituting from about 10 to about 30 parts by weight of the rubber have diameters between greater than about 0.8 and less than about 2 micrometers.

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Abstract

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