Impact modification of polyamides

Details Impact modification of polyamides Impact modification of polyamides

1993-06-07

2001-10-16

Mullis, Jeffrey C. (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...

C525S179000, C525S182000, C525S183000, C525S184000, C525S240000

Reexamination Certificate

active

06303691

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a novel class of impact modifiers which can improve the impact strength of polyamides with little adverse affect on the flexural modulus of the polyamide.
BACKGROUND OF THE INVENTION
Toughened thermoplastic polyamide compositions are known. See for example, U.S. Pat. No. 4,174,358 which discloses a polyamide matrix and at least one other phase containing particles ranging from 0.01 to 10 microns of at least one specified polymer.
U.S. Pat. No. 4,350,794 discloses a polyamide composition by melt blending of a polyamide resin and a halobutyl composition.
There is still a need to improve the impact strength of polyamide compositions, without substantial loss of the high flexural modulus of the polyamide.
It has now been found that the incorporation of certain polymer blends in polyamide compositions will produce toughened polyamide compositions having improved impact strength without substantial loss of the high flexural modulus of the polyamide.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a polymer blend useful as an impact modifier for polyamide compositions comprising:
(a) a halogen-containing copolymer of a C
4
to C
7
isomonoolefin and a para-alkylstyrene; and
(b) a polyolefin component comprising an elastomeric polyolefin, a crystalline polyolefin or mixture thereof.
DETAILED DESCRIPTION OF THE INVENTION
The Copolymer Component
Suitable copolymers of a C
4
to C
7
isomonoolefin and an alkylstyrene which may be a mono or polyalkylstyrene. For elastomeric copolymer products, the alkylstyrene moiety may range from about 0.5 to about 20 weight percent preferably from about 1 to about 20 weight percent and most preferably about 2 to about 20 weight percent of the copolymer. The preferred copolymers are copolymers of a C
4
to C
7
isomonoolefin and a para-alkylstyrene.
The copolymers of the isomonoolefin and para-alkylstyrene suitable for use in the present invention include copolymers of isomonoolefin having from 4 to 7 carbon atoms and a para-alkylstyrene, such as described in European patent application 89305395.5 filed on May 26, 1989, (Publication No. 0344021 published Nov. 29, 1989). The copolymers have a substantially homogeneous compositional distribution and include the para-alkylstyrene moiety represented by the formula:
in which X is halogen (preferably bromine) or hydrogen, and in which R and R
1
are independently selected from the group consisting hydrogen, alkyl preferably having from 1 to 5 carbon atoms, primary haloalkyl, secondary haloalkyl having from 1 to 5 carbon atoms and mixtures thereof. The preferred isomonoolefin is isobutylene. The preferred para-alkylstyrene comprises para-methylstyrene.
Suitable copolymers of an isomonoolefin and a para-alkylstyrene include copolymers having a number average molecular weight (M
n
) of at least about 25,000, preferably at least about 30,000, and most preferably about 100,000. The copolymers, preferably, also have a ratio of weight average molecular weight (M
w
) to number average molecular weight (M
n
), i.e., M
w
/M
n
of less than about 6, preferably less than about 4, more preferably less than about 2.5, most preferably less than about 2.0.
The brominated copolymer of the isomonoolefin and para-alkylstyrene obtained by the polymerization conditions now permit one to produce copolymers which comprise the direct reaction product (that is, in their as-polymerized form), and which have unexpectedly homogeneous uniform compositional distributions. Thus by utilizing the polymerization set forth herein, the copolymers suitable for the practice of the invention can be produced. These copolymers, as determined by gel permeation chromatography (GPC) demonstrate narrow molecular weight distributions and substantially homogeneous compositional distributions, or compositional uniformity over the entire range of the compositions thereof. At least about 95 weight percent of the copolymer product has a para-alkylstyrene content within about 10 weight percent, and preferably within about 7 weight percent, of the average para-alkylstyrene content for the overall composition, and preferably at least 97 weight percent of the copolymer product has a para-alkylstyrene content within about 10 weight percent and preferably about 7 weight percent, of the average para-alkylstyrene content for the overall composition. This substantially homogeneous compositionally uniformity thus particularly relates to the intercompositional distribution. That is, with the specified copolymers, as between any selected molecular weight fraction the percentage of para-alkylstyrene therein, or the ratio of para-alkylstyrene to isoolefin, will be substantially the same, in the manner set forth above.
In addition, since the relative reactivity of para-alkylstyrene with isoolefin such as isobutylene is close to one, the intercompositional distribution of these polymers will also be substantially homogeneous. That is, these copolymers are essentially random copolymers, and in any particular polymer chain the para-alkylstyrene to isoolefin, will be essentially randomly distributed throughout that chain.
Suitable halogen-containing copolymers of a C
4
to C
7
isomonoolefin and a para-alkylstyrene useful in the blends of this invention are the halogenated copolymers corresponding to the previously described iosmonoolefin-alkylstyrene copolymers which may be obtained by halogenating the previously described copolymers. The suitable halogenated copolymers comprise at least 0.5 weight percent of the alkylstyrene moiety. For elastomer copolymer products, the alkylstyrene moiety may contain from about 0.5 to about 20 weight percent, preferably from about 1 to about 20 weight percent, more preferably 2.0 to about 20 weight percent of the copolymer. The halogen content of the copolymer may range from above zero to about 7.5 weight percent, preferably from about 0.1 to about 7.5 weight percent.
The preferred halogen-containing copolymers useful in the practice of this invention have a substantially homogeneous compositional distribution and include the para-alkylstyrene moiety represented by the formula:
in which R and R
1
are independently selected from the group consisting of hydrogen, alkyl preferably having from 1 to 5 carbon atoms, primary haloalkyl, secondary haloalkyl preferably having from 1 to 5 carbon atoms, and mixtures thereof and X is selected from the group consisting of bromine, chlorine and mixtures thereof, such as those disclosed in European patent application 89305395.9 filed May 26, 1989 (Publication No. 0344021 published Nov. 29, 1989). Preferably, the halogen is bromine.
Various methods may be used to produce the copolymers of isomonoolefin and para-alkylstyrene, as described in said European Publication. Preferably, the polymerization is carried out continuously in a typical continuous polymerization process using a baffled tank-type reactor fitted with an efficient agitation means, such as a turbo mixer or propeller, and draft tube, external cooling jacket and internal cooling coils or other means of removing the heat of polymerization, inlet pipes for monomers, catalysts and diluents, temperature sensing means and an effluent overflow to a holding drum or quench tank. The reactor is purged of air and moisture and charged with dry, purified solvent or a mixture of solvent prior to introducing monomers and catalysts.
Reactors which are typically used in butyl rubber polymerization are generally suitable for use in a polymerization reaction to produce the desired para-alkylstyrene copolymers suitable for use in the present invention. The polymerization temperature may range from about minus 35° C. to about minus 100° C., preferably from about minus 40° C. to about minus 80° C.
The processes for producing the copolymers can be carried out in the form of a slurry of polymer formed in the diluents employed, or as a homogeneous solution process. The use of a slurry process is, however, preferred, since in that case, lower viscosity mixtures are produced in

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