CA1136314A

CA1136314A - Molding composition and injection molded article

Info

Publication number: CA1136314A
Application number: CA000350042A
Authority: CA
Inventors: John J. Charles; Robert C. Gasman
Original assignee: GAF Corp
Current assignee: GAF Corp
Priority date: 1979-12-26
Filing date: 1980-04-17
Publication date: 1982-11-23
Also published as: JPS5693751A

Abstract

ABSTRACT OF THE DISCLOSURE

Poly (C2-C4 alkylene terephthalate) molding composition containing mica and a multiphase composite polymer. The multiphase polymer has a first elastomeric phase polymerized from a monomer system including C1-C6 alkyl acrylate as well as crosslinking and graftlinking monomers and has a final rigid thermoplastic phase polymerized in the presence of the elastomeric phase, Preferred compositions also include thermally stable reinforcing fibers such as glass fibers.

Description

~ ~-3~

BACKGROUND OF THF INVENTION
Polybutylene terephthalate (PBT) reinforced with thermally stable reinforcing fibers such as glass fibers is well known as a molding resin and is described in numerous patents and publications including for instance United States 2,814,725, United States 4,124,561, United States 3,814,786 and United States 3,625,024. Fiber reinforcement generally improves the tensile strength, flexural strength, flexural modulus and heat distortion temperature of the molding composition. However, moldings, cspecially injec-tion moldings of large fiber glass reinforced articles of PBT, nylon and other semicrystalline thermoplastics tend to display distortion or warping while glass fiber reinforced armorphous thermoplastic compo~mds do not pre-sent such problems. It is believed that strains resulting from the different degrees of volumetric contraction parallel to and transverse to the direction of plastic melt flow into the mold during the cooling of molded articles are responsible for such warping. Orientation of the glass fibers parallel to the direction of melt flow during molding produces this directional difference in volumetric contraction. The warping is thus believed due to the presence of the very reinforcing fibers which contribute to the enhanced physical characteristics of the finished product. It is known that addition of mica to fiberglass reinforced PBT reduces warping. Unfortunately, the mica also greatly reduces impact strength.
Various impact modifiers are also known which improve the impact strength of molded PBT compositions. Some of these are described for instance in United States patents 4,096,202 and 4,034,013. It is generally ~ ' X
. . ; :
, . , : . , .

believed and unEortunately true, that some modifiers which improve impact characteristics of PB~ or other poly (C2-C4 alkylene tere phthalate) molding compositions, including fiber reinforced compo-sitions, also tend to increase the warping characteristics of the compositions.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an improved poly (C2-C4 alkylene terephthalate) molding composition and method for producing same as well as molded articles of such composition. As compared with known prior art compositions, the molded compositions of the invention have an especially desirable combination of properties including less than anticipated warpage and improved impact strength.
Improved polyester molding compositions of the invention consist essentially of at least about 40 wt% poly (C2-C4 alkylene terephthalate) with at least about 50 wt% of such poly (C2-C4 alkylene terephthalate) being polybutylene terephthalate having an intrinsic viscosity between about 0.5 and about 2.0 dl/g, such composition containing:
(a) between about 1 and about 40 wt% based on total molding composition of phlogophite mica flakes having an average particle size between about 40 and 325 mesh with at least 90% of all mica flakes present in the composition having particle sizes between about 40 and about 200 mesh; and (b) between about 5 and about 30 wt% based on total mslding composition of a multiphase composite polymer comprising:
(1) about 25 to about 95 wt% of a first elastomeric phase poly-merized from a monomer system comprising about 75 to 99.8% by

- 2 -' :' ~ , , :

~3~i3~

weight Cl to C6 alkyl acrylate, 0.1 to 5% by weight crosslinking monomer, and 0.1 to 5% by weight graftlinking monomer, said cross-linking monomer being a polyethylenically unsaturated monomer hav-ing a plurality of addition polymerizable reactive groups all of which polymerize at substantially the same rate of reaction, and said graftlinking monomer beiny a polyethylenically unsaturated monomer having a plurality o~ addition polymerizable reactive groups, at least one of which polymerizes at a substantially diff-erent rate of polymerization from at least one other of said reac-tive groups; andt2) about 75 to 5 wt% of a final, rigid thermoplastic phase polymerized in the presence of said elastomeric phase.
Preferred compositions of the invention include use of glass or other thermally stable reinforcing fibers and the use of the preerred multiphase polymers described below. Preferred thermally stable reinforcing fibers are glass fibers. Where used, thermally stable reinforcing fibers are preferably present in amounts between about 3 and about 50 wt% based on total molding composition and preferably have diameters between about 5 and about 20 microns and aspect ratios of at least about 5.
DETAILED DESCRIPTION_OF T~IE IN~ENTION
As mentioned above; the invention includes a novel mold-ing composition, molded articles of such composition and method for producing such composition. The molding composition broadly com-prises poly (C2-C~ alkylene terephthalate) containing, mica, multi-phase composite polymer and preferably thermally stable reinforcing fibers, as described herein.
Polybutylene terephthalate (PBT) used in the invention may

- 3 -`:

.

3~

be produced in any suitable manner such as by reacting terephthalic acid or a dialkyl ester of terephthalic acid, e.g., dimethyl, tere-phthalate, with diols having four carbon atoms, e.g., tetramethylene glycol. PBT for use in the invention has an intrinsic viscosity (I.V.) between about 0.5 and about 2.0 dl/g measured in ortho-chlorophenol at 25C., with material having an I.V. between about 0.5 and about 1.1 dl/g being preferred. Manufacture of PBT is well known to those skilled in the art as are the techniques for obtaining PBT of desired instrinsic viscosi-ty. Such conventional production techniques - 3a -,.~ . , ~

.
,: : . , 3~

for PBT are discussed in greatar detail, for instance, in United States Patent 3,465,319.
In addition to PBT, compositions of the in~ention may also in-clude polyethylene terephthalate (PET) or polypropylene terephthalate although PBT must, as indicated above, account for at least 50 wt% of the poly (C2-C~ alkylene terephthalate) used. PET and polypropylene terephtha-late may, like PBT, be produced by any suitable conventional methods. PET
where used is preferably present in amounts between about 1 and about 35 wt% based on total composition:
Where PET is used in compositions of the invention a nucleating agent such as talc etc, is also preferably employed in amounts between about .01 and about 10 wt% based on total composition. The PET function is to reduce warpage probleMs and reduce cost. PET having an intrinsic viscosity between about 0.4 and about 1.2 dl/g as measured in orthochlorophenol at 25C is preferred.
Thermally stable reinforcing fibers used in the invention may be any such fibers which are thermally stable at the conditions normally used in the production of products from PBT molding compositions and include, for instance, fibers of materials such as glass, aramid, calcium sulfate, aluminum metal, boron, asbestos, carbon, fibrous potassium titanate, iron whiskers, etc. Such fibers should normally have diameters between about 5 and about 20 microns and aspect ratios (ratio of length of fiber to diameter of fiber) of at least about 5. Glass fibers are preferred for use in the invention. Glass fibers, where used, preferably have diameters between about 10 and about 15 microns and aspect ratios of at least about 20.
Reinforcing fibers used in the invention are normally used in amounts between about 3 and about 50 wt% based on total weight of molding .
.
: .
-, , : - .

composltion, more preferably in amounts between about 3 and about 20 wt% on the same basis. As is commonly recognized, the use of such fibers improves substantially such physical properties as tensile strength, flexural strength, flexural modulus and heat distortion temperature of the molding composition. Glass or other fibers for use in the invention may be manu-factured and incorporated into the molding composition in any suitable manner, such as by separate extrusion blending with the PBT, extrusion blend-ing with other ingredients of the compositions of the invention or incorporat-ing into the PBT or PBT containing composition during injection molding of products from the molding composition of the invention.
Molding composition of the invention contains between about 1 and about 40 wt% phlogophite mica flake having an average particle size between about 40 and about 325 mesh (i.e. passing through a 40 mesh screen but retained on a 325 mesh screen~ with amounts between about 10 and about 30 wt%
being preferred. Such mica is readily obtainable from a number of suppliers and is sold for instance by ~arietta Resources International under the trade name Suzorite ~R in various size grades. One commonly used grade of such mica, is for instance identified as ~IAR 60-S and has at least about 90%
particles in the size range between about 40 and about 200 mesh.
As mentioned, the invention also required the presence of between about 5 and about 30 wt% based on total molding composition of a multiphase composite polymer comprising:
(1) about 25 to about 95 wt% of a first elastomeric phase polymeriz-ed from a monomer system comprising about 75 to 99.8% by weight Cl to C6 alkyl acrylate, 0.1 to 5% by weight crosslinking monomer, and 0.1 to 5% by weight graftlinking monomer, said crosslinking monomer being a polyethylenical-ly unsaturated monomer having a plurality of addition polymerizable reactive groups all of which polymerize at substantially the same rate of reaction, : , . ~:: , ; , ;

~13~

and said graftlinking monomer being a polyethylenically unsaturated monomer having a plurality oE addition polymerizable reaction groups, at least one of which polymerizes at a substantially different rate o:E polymerization from at least one other of said reactive groups; and (2) about 75 to 5 wt% of a final, rigid thermoplastic phase polymerized in the presence of said elastomeric phase.
The multiphase composite polymer used in compositions of the invention comprises from about 25 to about 95 wt% of a first elastomeric phase and about 75 to 5 wt% of a final rigid thermoplastic phase. One or more intermediate phases are optional, for example, a middle stage poly-merized from about 75 to 100 percent by weight styrene. The first stage is polymerized from about 75 to 99.8 wt% Cl to C6 acrylate resulting in an acrylic rubber core having a glass transition temperature below about 10C
and crosslinked with 0.1 to 5 percent crosslinking monomer and further containing 0.1 to 5 percent by weight graftlinking monomer. The preferred alkyl acrylate is butyl acrylate. The crosslinking monomer is a poly-ethylenically unsaturated monomer having a plurality of addition polymerizable reactive groups all of which polymerize at substantially the same rate of reaction. Suitable crosslinking monomers include poly acrylic and poly methacrylic esters of polyols such as butylene diacrylate and dimethacrylate, trimethylol propane trimethacrylate, and the like; di- and trivinyl benzene, vinyl acrylate and methacrylate, and the like. The preferred crosslinking monomer is butylene diacrylate. The graftlinking monomer is a poly-ethylenically unsaturated monomer having a plurality of addition poly-merizable reactive groups, at least one of which polymerizing at a sub-stantially diferent rate of polymerization from at least one other of said reactive groups. The function of the graftlinking monomer is to provide a residual level of unsaturation in the elastomeric phase, particularly in .

~3~i31~

the latter stages oE polymerization and, consequently, at or near the surface of the elastomer particles.
When the rigid thermoplastic phase is subsequently polymerized at the surface of the elastomer, the residual ~msaturated addition poly~
merizable reactive group contributed by the graftlinking monomer participates in the subsequent reaction so that at least a portion of the rigid phase is chemically attached to surface of the elastomer. Among the effective graftlinking monomers are allyl group-containing monomers of allyl esters of ethylenically unsaturated acids such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, allyl acid maleate, allyl acid fumarate, and allyl acid itaconate. Somewhat less preferred are the diallyl esters of polycarboxylic acids which do not generally have a favorable polymerization rate. The preferred graftlinking monomers are allyl methacrylate and diallyl maleate. A most preferred interpolymer has only two stages, the first stage comprising about 60 to 95 percent by weight of the interpolymer and being polymerized from a monomer system comprising 95 to 99.8 percent by weight butyl acrylate, 0.1 to 2.5 percent by weight ; butylene diacrylate as crosslinking agent, 0.1 to 2.5 percent by weight allyl methacrylate or diallyl maleate as a graftlinking agent, with a final stage polymerized from about 60 to 100 percent by weight methyl methacrylate.
The final stage monomer system can be comprised of Cl to C16 methacrylate, styrene, acrylonitrile, alkyl acrylates, allyl acrylates, allyl methacrylate, diallyl methacrylate, and the like, as long as the over-all glass transition temperature is at least about 20C. Preferably the final stage monomer system is at least about 50 wt% Cl to C4 alkyl meth-acrylate. In a preferred embodiment the final stage monomer system may also contain epoxy functionality. By "epoxy functionality" is meant epoxy : : , : :............. , : ., . . ' , - . . -lmits which are pendant from the final stage polymer. The preferred way of incorporating epoxy functionali~y into the final stage polymer is by use of epoxy containing monomer such as glycidyl acrylate of glycidyl methacrylate in the final stage monomer mixture. Alternate epoxy cont~ining monomers are butadiene monoepoxide, allyl glycidyl ether, 4, S-epoxy pentyl methacrylate or acrylate, 10, ll-epoxy undecyl methacrylate, or other opoxy-containing ethylenically unsaturated monomers. Other ways of introducing epoxy unctionality into the final stage of the mul~iple stage pulymer are possible, such as post epoxidation. It is further preferred that the final stage polymer be free of units which tend to degrade poly ~alkylene terephthalates), for example, acid, hydroxyl, amino, and amide groups.
For futher descriptions and e~amples of various multiphase polymers suitable for use in the present invention, reference may be had to the aforementioned llnited States Patent 4,096~202 the disclosure of hich is incorporated herein by reference. Additional examples of multi-phase polymers suitable for use in the invention may be found in United States Patent 4,034,013.
The multiphase polymer serves as an impact modifier to improve impact characteristics of molded articles made from molding composition of the invention. The mica flakes serve a completely unexpected function in eliminating or very substantially reducing the warpage of molded parts ~hich would normally be expected because of the presence of the multiphase polymer of the combination of multiphase polymer and thermally stable reinforcing fibers in molding composition and products of the invention.
In addition to the ingredients mentioned above, compositions ~Id products of the invention may contain suitable flame retardant additives in amounts up to about 25 wt% based on total molding composition and may ;

~ -8-` ~.'''- : ~ `

contain relatively minor amounts of other materials which do not unduly affect the desired characteristics o the finished product. Such additional materials, may, depending upon the particular compositionsemployed and products desired, include for instance, colorants and lubricants. Where present, such additional materials normally comprise no more than about 20 wt~ of the total composition or finished product.
In preparing molded compositions of the invention, the rein-forcing fibers may be intimately blended into the PBT by any suitable means such as by dr~ blending followed by melt blending, blending in extruders, heated rolls or other types of mixers, etc. Conventional master batching techniques may also be used. The same considerations apply to addition of the other essential or optional ingredients of the composition of the invention. Suitable blending and molding techniques are well known in the art and need not be described in detail herein. In a preferred embodiment of the invention, the composition of the invention is compounded by dry blending followed b~ melt mixing in an extruder with barrel temperatures between about 240 and about 270C. Likewise, in molding products o the invention from molding compositions o the invention,linjection molding is preferred. When injection molding is used~ barrel temperatures between 20 about 250C and 265C are preferred. In a preferred embodiment, the molding composition of the invention is formed by extrusion and pelletized.
Products of the invention are then produced by injection molding the pel-letized extrudate.
As mentioned above, one of the major advantages of th~ compositions and products of the invention is that the use of mica in molding compositions of the invention substantially reduces shrinkage and warpage otherwise associated with the use of the multiphase polymer or combination of multi-phase polymer and reinforcing fibers without substantial harm to the _g ., ~ , .

desirable improvements in physical propert:ies associated with the use of such fibers.
While warpage is frequently determined by visual inspection, a quantitative definition can be expressed in terms of percent warp equals ~dm TtXloo where "dm" equals maximum distance from a flat surface to a point on a warped side of the article being evaluated, and "t" equals the thickness of the warped side of the article. This equation defines warp in terms of wall thickness without regard to length of the part. Since some absolute deviation from a straight line gives the same percent warp, a correction for part length must also be included to more accurately define warpage of a part in terms of the visual effect of the warp. Part warp (PW) may therefore be defined as PW = ~ = (dmtT~XlLoo wherein PW equals part warp, "L" equals total length of the warp member and the other values are as stated immediately above. In evaluating warpage of samples and products, and average warpage value for a five sided plain box is frequently calculated based upon measurements of warpage of the right, left, front and back sides of the box.
The follo~ing examples are intended to illustrate the application and usefulness of the invention without limiting the scope ~hereof, In the example, all quantities are given in terms of wt% based on total com-position unless otherwise specified. Physical properties, including ~arpage, were measured by the following criteria and reported as an average for samples of each composition tested:

~ .,.

,: : , . :. :

:
::

~3~

Property Test Procedures Tensile Yield Strength ASTM D-638 Flexural Yield Strength ASTM D 790 Flexural Modulus ASTM D-790 Notched Izod Impact Strength Cantilever Beam Reversed Notch Izod Impact Strength AS'~ D 256 Percent warp As de~ined above ~e~
PBT (0.8 I.V.) was compounded on a Midland Ross 1.5 inch extruder with various amoun~s of phlogophite mica and other ingredients as specified below to form various molding compositions as specified in Table I below.
The mica used was Marietta Resources International Suzorite HAR 60-S mica flake having the following size distri'bution.
trace - 20 + 40 mesh ~U.S. sieve) 76% - 40 + 100 mesh 19% -100 ~ 200 mesh 3% -200 + 325 mesh 2% -325 mesh Marietta Resources International Suzorite ~IAR 200-S mica flake was also used. This material had the following size distribution:
trace - 20 + 40 mesh (U.S. sieve) 1% - 40 + 100 mesh 55% -100 + 200 mesh 20% -200 + 325 mesh 24% -325 mesh The following conditions were employed:

.: .:
;~. . - ' .:: ., ; .:
: , :: :: ~ : : :
: ' : ': . ' ~ :

Extruder Zone Températures Back Pressure 0-200 1 270C Amperage 12-25 2 265C Screw rpm 90 3 260C.

4 255C. Melt temperature 243-251C.
250C.
Each of the experimental molding compositions specified in Table I and produced as described above was then molded on a 50 tOII 3 ounce recipro-cating screw injection molding machine to provide ASTM test specimens. Parts suitable for measuring warpage ~camera slide storage box wi~h four large flat sides) were molded on a 250 ton 36 ounce Impco screw ram machine. Molding conditions were:
3 oz., 50 ton molding machine Barrel temperature --- front 480F.
rear 480F.
nozzle 480F.
Injection pressure 1100 psi Screw rpm 75 Injection time 10 sec.
Mold time 20 sec.
Total cycle time 30 sec.
Mold temperature 100F
36 oz., 350 ton molding machine 20 Barrel temperature --- front 480P
center 480F.
rear 480F.
nozzle 490F.
Measured melt temperature 420F.
Screw rpm 80 Total cycle time 94 sec.
Mold temperature 175F.
Mold time 40 sec.
Injection pressure 1100 psi Physical properties were as shown in Table II below.

"

. .
.

, . : :: :. .
: :, : :. : - :

~3~

TABLE I
__ EXPERIMENTAL MOLDING COMPOUNDS
Wt %
Ingredient _ 2 3_ PBT (0.8 I.V) 25 25 30 PET ~0.8 I.V) 20 20 20 60-S Mica Flake 20 200-S Mica Flake 20 15 Glass Fibers ~OCF 419 AA
3/16 inch) 20 20 20 KM 330 Acrylic Impact Modifier 14.3 14.3 14.3 Acrawax C Lubricant 0.2 0.2 0.2 Epon 815 Uiepoxy Modifier 0.5 0.5 0.5 TABLE II
PHYSICAL PROPERTIES OF EXPERIMENTAL MOLDING COMPOSITIONS
- -Wt %
_ 2 3 % Warp Annealed 100 120 % ~arp Unannealed 81 97 Notched IZod Impact Strength ~Foot Pounds per Inch) 1.8 1.7 1.4 : 20 Cantilever Beam Reversed Notch Izod Impact Strength (Foot Pounds per Inch) 7.8 8.2 7.5 : Flexural Strength (psi)1&~000 19,100 16,300 Flexural Modulus (psi) x 106 1.23 1.27 .90 Tensile Strength (psi)11,430 12,308 10,000 - : : ~ , .::, :, -: ,- : :

~, . .:,. . : . :: ::
.. ..~, . . . .

~3~

In order to evaluate the effect of various additives and combina-tions of additives or warpage characteristics of injection molded PBT arti-cles, a number of molding compositions were prepared from which parts were molded and tested for warpage, all as described in Example 1. The composi-tions tested and warpage data obtained are shown in table III. To simplify comparisons, table III also shows warpage as a percent of the warpage obtained using PBT molding compound with no additives.

:,.

.:
. .
: ~

~ a ~ ~ 0~O
~ U~ ¢ o ¢ ~ oo ~ ~ D ~ O~D O
~ ~ I ~ ~ ~ ~ ~ cor~ ~ u~
:3 z; ~ ~ ~ + + I + , + + , + t Z ~Y
~ o\ O
U~
~ 1~ In 00r~ l H00 ~ _I r~ H \O
¢o\ ~
G ~:) ¢
~ ~ LLl o\
~ ~ Cl~ Ln 00 ~ ~ O 00 ~ ~
¢ FO. I ~ ~ ~ N L17 0 u~
U~ ~ Z t~ 0~ ~ ~`I + I + I + ~ I + + +
0\o ~
a a H a ~ o cn H ~ ." ~a~ H o ~o o O~o ~ ~ a~ ~ o1~ ~ O ~ O r~
¢ O ~ H ~ H H .~ `J H N
¢ H E--~ H Ul 1/~ 11'1 It) Lr7 ¢ H ~ ~t t~ ~ Q r-l i~ ~ H ~
~Y ¢
~_ ~ ~_ o\o H ~ --E-l ~ _i ~ o o O O O O o 3 Cl~ ~ N N N N N N
~_ V~ P., ~
U~ ~O
Z
H ~L1 a u~ ¢ x o O o 1~ O H ,_~ N N N
Z N
H .
¢ ~
¢ O O O O

O H .--1 N N N N
:4 r_ ~ U) u~
E~ ~ O O u~ O O
P:~ o ~ oO oO O O o u oo ~ ~ ~ co ~ ~D
`_ O ~ H N ~ ~ Lfl ~ t`00C~) O ._1 N
&
t~

. , - ~ `:- : , :. , :.. - ~;

,:: :
.: " ;,:: : ~::; , i:
: : : .

3 ~ ~

~ rom table III it can be seen that the presence of mica flakes, especially the 60-S grade, resulted in much less warpage of molded parts than would have been expected based on warpage of parts containing multiphase poly-mer or a combination of multiphase polymer and glass fibers.
As mentioned above, flame retardant additives may be used in compo-sitions and products of the invention. Pre:Eerred flame retardant additives for this purpose include decabromodiphenyl ether, brominated phenylene oxide, brominated polycarbonate, brominated polystyrene, tctrabromo phthalic anhy-dride and antimony trioxide.
Between about 5 and about 40 wt% based on total molding composition of Poly(C2-C4 alkylene terephthalate-co-alkylene-oxide) is also preferably used in compositions of the invention. Preferred Poly(C2-C4 alkylene tere-phthalate-co-alkylene-oxide) for use in the invention is poly(butylene tere-phthalate-co-tetramethylene oxide). Suitable Poly(C2-C4 alkylene terephtha-late-co-alkylene-oxide) elastomers and their pre~aration are well known as described for instance in United States patent 3,766,146. Poly(butylene tere-phthalate-co-tetramethylene-oxide) having a Shore D hardness between about 50 and about 60 and a melt index between about 7 and about 9 is particularly preferred.
While the invention has been described above with respect to certain preferred embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit or scope of the invention.

, :

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Polyester molding composition consisting essentially of at least about 40 wt% poly (C2-C4 alkylene terephthalate) with at least about 50 wt% of such poly (C2- C4 alkylene terephthalate) being polybutylene terephthalate having an intrinsic viscosity be-tween about 0.5 and about 2.0 dl/g, such composition containing (a) between about 1 and about 40 wt% based on total molding com-position of phlogophite mica flakes having an average particle size between about 40 and 325 mesh with at least 90% of all mica flakes present in the composition having particle sizes between about 40 and about 200 mesh; and (b) between about 5 and about 30 wt% based on total molding com-position of a multiphase composite polymer comprising:
(1) about 25 to about 95 wt% of a first elastomeric phase poly-merized from a monomer system comprising about 75 to 99.8% by weight C1 to C6 alkyl acrylate 0.1 to 5% by weight crosslinking monomer, and 0.1 to 5% by weight graftlinking monomer, said cross-linking monomer being a polyethylenically unsaturated monomer hav-ing a plurality of addition polymerizable reactive groups all of which polymerize at substantially the same rate of reaction, and said graftlinking monomer being a polyethylenically unsaturated monomer having a plurality of addition polymerizable reactive groups, at least one of which polymerizes at a substantially different rate of polymerization from at least one other of said reactive groups; and (2) about 75 to 5 wt% of a final, rigid thermoplastic phase poly-merized in the presence of said elastomeric phase.

2. Molding composition according to claim 1 which contains between about 1% and about 40% wt% based on total molding compo-sition of polyethylene terephthalate.

3. Molding composition according to claim 2 which also con-tains between about 0.01 and about 10% wt% based on total molding composition of a nucleating agent.

4. Molding composition according to claim 1 which also con-tains between about 3 and about 50 wt% based on total molding composition of thermally stable reinforcing fibers having diameters between about 5 and about 20 microns and aspect ratios of at least about 5 and wherein at least a majority of the mica flakes present in the composition having particle sizes between about 40 and about 100 mesh.

5. Molding composition according to claim 4 wherein the reinforcing fibers are glass fibers.

6. Molding composition according to claim 5 wherein the glass fibers have diameters between about 10 and about 15 microns and aspect ratios of at least about 20.

7. Molding composition according to claim 1 wherein the final rigid thermoplastic phase of the multiphase polymer contains epoxy groups.

8. Molding composition according to claim 7 wherein epoxy groups are derived from glycidyl acrylate or glycidyl methacrylate.

9. Molding composition according to claim 1 wherein said graftlinking monomer is allyl methacrylate or diallyl maleate.

10. Molding composition according to claim 1 wherein the crosslinking monomer is butylene diacrylate.

11. Molding composition according to claim 1 wherein the final rigid thermoplastic phase of the multiphase polymer is polymerized from a monomer system comprising from about 50 to 100 wt% of a C1 to C4 alkyl methacrylate.

12. Molding composition according to claim 1 wherein the final phase monomer system is free of acid, hydroxyl, amino and amide groups and wherein the glass transition temperature of the final thermoplastic phase is at least about 20°C.

13. Molding composition according to claim 1 which also contains between about 3 and about 50 wt% based on total molding composition of glass reinforcing fibers having diameters between about 5 and about 20 microns and aspect ratios of at least about 5, and wherein at least a majority of the mica flakes present in the composition have particle sizes between about 40 and about 100 mesh and wherein said first phase of the multiphase polymer comprises between about 60 and about 95 wt% of said multiphase polymer, said first phase is polymerized from monomer system comprising between 95 and about 99.8 percent by weight butyl acry-late, between about 0.1 and about 2.5 wt% butylene diacrylate as a crosslinking agent, and between about 0.1 and about 2.5% allyl meth-acrylate or diallyl maleate as a graftlinking agent and said final phase of said multiphase polymer is polymerized from about 60 to 100 wt% methyl methacrylate.

14. Molding composition according to claim 1 wherein the poly (C2-C4 alkylene terephthalate) is essentially polybutylene terephthalate.

15. Molding composition according to claim 14 which also includes between about 3 and about 50 wt% based on total molding composition of glass reinforcing fibers having diameters between about 5 and about 20 microns and aspect ratios of at least about 5.

16. An injection molded article molded from molding composi-tion of claim 1.

17. An injection molded article molded from molding composi-tion of claim 2.

18. An injection molded article molded from molding composi-tion of claim 4.

19. An injection molded article molded from molding composi-tion of claim 5.

20. An injection molded article molded from molding composi-tion of claim 13.

", j, .. ..