MOLDING COMPOUNDS AND METHOD OF MAKING SAME

COMPOSES DE MOULAGE, ET METHODE DE PREPARATION CONNEXE

English Abstract

ABSTRACT OF THE DISCLOSURE
An improved method of producing a molding compo-
sition comprising a polyester resin prepolymer, a generally
immiscible thermoplastic resin and a mutual monomeric solvent
for both resins which will crosslink the polyester. The
improvement is had by mixing thermoplastic polymer while
still dispersed in the monomer from which it was polymerized
with the thermosetting prepolymer. During crosslinking of
the thermosetting prepolymer the immiscible thermoplastic
resin separates out in major separated phase bodies having
but a small amount of a secondary separated phase therein.
A sizable percentage of major separated phase bodies have
voids therein believed to be produced by vaporized pockets
of unreacted monomer, and the major separated phase bodies
have a more diffused interface with the matrix than the prior
art materials. The diffused interface is believed produced
at least in part by reason of the improved affinity which
the thermoplastic molecules have for the polyester. The
thermoplastic molecules are of a narrow band of intermediate
molecular weight so that they all leave the polyester at
about the same time and carry a sizable amount of monomer
with them into the separated phase

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In the process of producing low-shrink thermosetting
polyester molding compounds wherein an unsaturated thermosetting
polyester prepolymer, an unsaturated solvent therefor, and a
minor amount of a thermoplastic polymer that is also miscible in
said solvent is mixed therewith, the improvement comprising:
initiating polymerization of an unsaturated monomer composed
principally of styrene at a temperature between 40°C and 90°C
to produce a non-highly branched thermoplastic polymer, stopping
the polymerization reaction when less than 50% of the monomer
has reacted to give a polystyrene having a narrow band of
intermediate molecular weight between approximately 75,000 and
approximately 500,000 and having a dispersity between 1.0 and
2.8, maintaining said polystyrene dispersed in the styrene as a
solution thereof, and mixing said solution of polystyrene and
styrene with the thermosetting polyester prepolymer to form a
hardenable mixture, whereby the hardenable mixture during cure
forms nonspherical thermoplastic bodies of a separated phase
having a diffuse interface tightly bonded with the cured thermoset
resin.
2. The process of claim 1, wherein said initiating step
is performed with the aid of a free radical catalyst having a
dissociation constant between 8 x 10-6 to 5 x 10-5 at 75°C.
3. The process of claim 1, or 2, wherein the stopping of
the polymerization step is accomplished at least in part by
an inhibitor.
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4. In the process of producing low-shrink thermosetting
polyester molding compounds wherein an unsaturated thermosetting
polyester prepolymer, an unsaturated solvent therefor, and a
minor amount of a thermoplastic polymer that is also miscible in
said solvent is mixed therewith, the improvement comprising:
initiating polymerization of an unsaturated monomer composed
principally of styrene at a temperature between 40°C and 90°C
and with a free radical catalyst having a dissociation constant
between 8 X 10-6 and 5 X 10-5 at 75°C to produce a non-highly
branched thermoplastic polystyrene polymer or copolymer, stopping
the polymerization reaction when less than 50% of the monomer has
reacted to give a polystyrene having a narrow band of intermediate
molecular weight between approximately 175,000 and approximately
250,000 and having a dispersity between 1.0 and 2.6, maintaining
said polystyrene dispersed in the styrene as a solution thereof,
mixing the solution with the thermosetting polyester prepolymer to
form a hardenable mixture, and reacting said solvent with said
thermosetting polyester prepolymer to crosslink the prepolymer
and liberate bodies of said thermoplastic polymer therein which
have a diffuse interface tightly bonded with the crosslinked
polymer.
5. The process of claim 4, wherein said polymerization
step is carried out until from between 20 and 50% of the
unsaturated monomer has been converted to polystyrene.
6. The process of claim 5, wherein said polymerization
step is started with a free radical catalyst and is stopped by
the addition of an inhibitor.
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7. The process of claim 6, wherein the stopping of the
polymerization step is accomplished with toluhydroquinone
addition.
8. In the process of producing low-shrink thermosetting
molding compounds wherein an unsaturated thermosetting polyester
prepolymer, an unsaturated solvent therefor, and a minor amount
of a thermoplastic polymer that is also miscible in said solvent
is mixed therewith, the improvement comprising: initiating poly-
merization of a styrene-containing monomer at a temperature
between 40° and 90°C and with a free radical catalyst having a
dissociation constant between 8 X 10-6 and 5 X 10-5 at 75°C to
produce a non-highly branched polystyrene, stopping the polymer-
ization reaction when less than 50% of the monomer has reacted
to give a polystyrene having a narrow band of intermediate molec-
ular weight between approximately 75,000 and 500,000 and having
a dispersity between 1.0 and 2.6 with an inhibitor, maintaining
said polystyrene dispersed in the styrene as a solution thereof,
mixing the solution with the thermosetting polyester prepolymer
to form a hardenable mixture and reacting styrene with said
thermosetting polyester prepolymer to crosslink the prepolymer
and liberate bodies of said polystyrene therein which have a
diffuse interface with the crosslinked polymer.
9. The process of claim 8, wherein said polymerization
step is carried out until from between 20 and 50% of the
unsaturated monomer has been converted to polystyrene.
10. The process of claim 9, wherein the stopping of the
polymerization step is accomplished with toluhydroquinone
addition.
19

11. The process of claim 8, 9, or 10, wherein the molecular
weight of the polystyrene is between approximately 175,000 and
250,000.
12. In a molding compound of the type comprising an unsat-
urated thermosetting polyester prepolymer, an unsaturated cross-
linking solvent therefor, and a minor amount of a thermoplastic
polymer that is also miscible in said solvent, the improvement
wherein said thermoplastic polymer is a polystyrene having a
narrow band of intermediate molecular weight polymer molecules
having a dispersity between 1.0 and 2.8 and an average molecular
weight between 75,000 and 500,000.
13. The molding compound of claim 12, wherein said unsatur-
ated solvent is styrene.
14. The molding compound of claim 12, wherein said thermo-
plastic polymer is dissolved in unsaturated solvent containing
less than 0.05% by weight of unreactive solvent, 0.2% by weight
of emulsifiers and 0.1% of moisture.
15. The molding compound of claim 12, 13, or 14 wherein
said thermoplastic polymer has been prepared by polymerization
of a styrene containing monomer in which the polymerization react-
ion was stopped when less than 50% of the monomer had reacted by
deactivation with toluhydroquinone.

16. A molding compound comprising the following
materials in percent by weight:
<IMG>
said polystyrene resin being an essentially linear polymer
consisting of a narrow band of intermediate molecular weight
polymer molecules having a dispersity between 1.0 and 2.8 and
an average molecular weight between 75,000 and 500,000, whereby
said thermoplastic resin separates from said crosslinking resin
during its cure to produce bodies having a diffuse interface
with the crosslinking resin.
17. The molding compound of claim 16, wherein the
polystyrene has been deactivated by a free radical inhibitor.
18. The molding compound of claim 17, wherein the
inhibitor was toluhydroquinone.
19. The molding compound of claim 16, 17, or 18, wherein
said mutual solvent is predominantly unsaturated molecules
containing less than 0.05% by weight of saturated molecules,
and said thermoplastic resin contains less than 0.2% by weight
of emulsifiers and less than 0.1% by weight of water.
21

20. The molding compound of claim 16, 17, or 18,
containing glass fibers as a reinforcement.
22

Description

S~4~
The present invention relates to new and improved
sheet molding compounds and/or bulk molding compounds, par~
ticularly of the polyester type, which do not shrink appre-
ciably during cure or crosslinking of the thermosetting resin
prepolymer, and which have greater strength, less water
absorption, better efficiency of pigmentation and other
physical properties than do prior art materials.
Thermosetting resin prepolymers which cro~slink
during their cure to the thermoset condition invariably shrink
during the crosslinking, and this is particularly true of un-
saturated polyester resins which crosslink by the condensation
with unsaturated solvents. ~hen such materials are mixed with
glass fibers and cured in a mold, the resin between -the fibers
shrinks during cure leaving the imprint of the fibers on the
surface of the part produced. Over a decade ago it was dis-
covered that if a solution of a thermoplastic resin were
mixed with the thermosetting prepolymer prior to cure, the
particles of the thermoplastic resin would separate out, and
thus volumetrically decrease the amount of the total shrink
of the cured part. Patents can be found teaching substan-
tially every known type of thermoplastic polymer additive to
polyester resins. Some of these polymers are more compatible
with the polyester prepolymer when combined with a monomer
than are others, but all of the systems suggested will undergo
a shrinkage o the polyester prepolymer while it is cross-
; linking. The thermoplastics suggested for combination with
the polyester prepolymers interfere with the strength, pig-
mentation, and other properties of the finai product, and
many will bleed over the surface of the heated molds in which
the final products are formed, such that the surfaces of the
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molds must be cleaned repeatedly.
An object of the present invention is the provis-
ion of a new and improvecl low shrink thermosetting molding
material which produces a more diEfuse interface between the
separated thermoplastic phase and the thermoset matrix than
do prior art materials.
According to one aspect of the inventionO in the
process of producing low shrink thermosetting polyester
molding compounds wherein an unsaturated thermosetting
polyester prepolymer, an unsaturated solvent ther~or, and a
minor amount of a thermoplastic polymer that is also
miscible in the solvent is mixed therewith, there is pro-
vided the improvement which comprises initiating polymeriza- :
tion of an unsaturated monomer composed principally of
styrene at a temperature between 40C and 90C to produce a
non-highly branched thermoplastic polymer, stopping the
polymerization reaction when less than 50~ of the monomer
; has reacted to give a polystyrene having a narrow band of
intermediate molecular weight between approximately 75,000
and approximately 500,000 and having a dispersity between 1.0
and 3.5, maintaining the polystyrene dispersed in the
styrene as a solution thereof, and mixing the solution of
polystyrene snd styrene with the thermosetting polyester
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prepolymer to form a hardenable mixture, whereby the
hardenable mixture during cure ~orms non-spherical
thermoplastic bodies of a separated phase having a
diffuse interface tightly bonded with the cured thermoset
resin.
Another aspect of the invention, in a molding
compound of the type comprising an unsatured thermosetting
polyester prepolymer, an unsaturated crosslinking solvent
therefor, and a minor amount of a thermoplastic polymer
that is also miscible in the solvent, provides the improve-
ment in which the thermoplastic polymer is a polystyrene
having a narrow band of intermediate molecular weight poly-
mer molecules having a dispersity between 1.0 and 3.5 and
an average molecular weight between 75,000 and 500,000.
Thus, b~ means o the present invention a low
shrink molding compound is produced of a thermosetting
resin prepolymer and a thermoplastic resin which during
cure separates to provide a thermoplastic phase whose
interface with the thermoset phase is diffused by reason of
more pronounced bonding therebetween than has been produced
heretofore. This bonding between the two major phases
produces cured materials having less water absorption,
better pigmentability, and dispersion of filler than has
been produced heretofore.
The precise mechanism by which all this is
obtained is not fully known, but an understanding of how
it is obtained and its true significance will be had from
the following description of the preferred embodimènts
as compared with the
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prior art as exemplified by the material of the U.S. Kroekel
Patent 3,701,748.
Embodiments of -the invention will be described, by
way of example, with reference to the accompanying drawings,
in which: -
Bigure 1 is a photomicrograph of a material
embodying principles of the present invention, and which was
made by an electron microscope at a magnification of 450;
Figure 2 is a photomicrograph of a portion of the
material shown in Figure 1 but made at a magnification of
1800;
Figure 3 is a photomicrograph of a prior art
material not according to the present invention, and which
was made by an electron microscope at a magnification of
; 2200; and
Figure 4 is a photomicrograph of a portion of the
material shown in Figure 3 but at a magnification of 22000.
The following Bxamples also illustrate the invention.
EXAMPLE 1
A thermoplas-tic additive material for low shrink
thermosetting polyester molding compound was prepared
according to an embodiment of the present invention using
the following procedure.
A reactor that was equipped with an agitator, a
nitrogen sparge and an internal cooling coil was charged with
, 7,410 parts of styrene, 90 parts of acrylic acid, and 15
parts of benzoyl peroxide. After 30 minutes of sparging
with nitrogen, the temperature was raised to 70C and was
held at this temperature until a slight exotherm began. After
the exotherm began, a flow of cooling water was passed through
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the cooling coil to maintain the temperature at 70C plus or
minus 0.5~C. The reac-tion was allowed to continue until the
solids reached 40% by weight. At this time 3 parts of an
inhi~itor (toluhydroquinone) was added to short stop the
reaction and the batch was discharged. A final solids check
was made of the batch and enough styrene was added to pro-
duce a syrup of the thermoplastic containing 33.3~ solids.
The polystyrene so produced had a dispersity of 2.8, and an
average molecular weight of 240,000. The syrup had no per-
ceptible nonreactive monomer or emulsifiers and had only 0.05percent by weight of waterO The polystyrene also had a number
; average molecular weight of 150,000 and peak molecular weight
of 270,000.
A polyester was made in another reactor from the
following materials in parts by weight:
Materials Parts by Weight
Propylene glycol 573.2
Maleic anhydride 674.4
Toluhydroquinone (25~
solution in styrene) ~.8
The polyester was made by charging all the
propylene glycol, one third of the maleic anhydride and 1.6
grams of toluhydroquinone into the reactor using a continuous
nitrogen sparge. The temperature was raised to 190F and
after about 4 hours, the acid number was 35. Thereafter the
remainder of the maleic anhydride was added at the rate of
100 to 150 parts per minute to control the temperature at
300F, Thereafter the temperature of the ingredients was
held at 310 to 320F for 60 minutes, following which the
temperature was increased to 400F. The material had an acid
number of 29 to 32 and a sample cut 2 to 1 in styrene had a

~0~5~4~
Saybold viscosity of 21 to 25 seconds at 350F. Thereafter
the contents were cooled to 340F. The polyester prepolymer
when cut with styrene in a 90 to 10 ratio was stable at 120C
for 30 minutes before gelling.
In another tank 486.4 parts of styrene, 2.0 parts
of MEHQ (methyl ether of hydroquinone) is added and the
mixture held at a temperature between 130 to 145F. There-
after 1,138 parts of the polyester resin prepolymer produced
as above-described and at a temperature of 330 to 355F was
added with agitation to provide a thinned polyester syrup
which was then cooled to a temperature of 180F. The vis-
cosity of the thinned polyester syrup was 1 t 500 to 2,000
Brookfield cps and had a water content of 0.08 and a monomer
content within the range of 30 to 3~% by weight.
A matrix resin mix was made from the following
ingredients:
Polyester resin syrup made
as above-described 1200
; Thermoplastic polymer syrup
made as above-described800
Tertiary Butyl Perbenzoate 13.2
Benzoyl Peroxide 6.0
Zinc Stearate 80.0
The resin mix was produced by charging the polyester
resin to a Cowles mixer~ and thereafter slowly adding the
other ingredients while the mixer was running to thoroughly
disperse the ingredients throughout the resin.
A molding premix was made from the following
ingredients:
Above resin mix 1763.0
Calcium carbonate filler~15.0
Clay filler 2832.0
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One quarter inch chopped 1080.0
glass fibers produced
according to Example 1
of Ward Patent 3,702,276
The Molding Premix was made by adding the resin mix
to a Baker-Perkins single blade ~ype mixer, followed by the
clay and calcium carbonate filler while the mixer was running.
After the above ingredients were dispersed into the resin,
the mixer was run for an additional two minutes to assure a
- uniform dispersion. Thereafter the 1/4 inch chopped glass
fibers were blended in, and the mixer was run for an
additional one minute period to assure a uniform dispersion
of the strand throughout the other ingredients. The Molding
Premix produced as above-described has approximately 18
glass by weight.
A test specimen is rnade by weighing out a sufficient
amount of the premix to fill a flat bottom mold to a depth of
0.100 inch and bringing a cover die down upon the resin with
, sufficient force to provide a loading of 2,000 pounds per
`~ square inch on the resin. The premix was cured under this
- compression for 3 minutes at a temperature of 280 to 300F,
following which the molded sheet was removed and cooled. The
surface of the molded article was smooth with no evidence of
fiber imprint, and had a dark grey color. A test specimen
approximately 1/2 inch wide and 2 1/2 inch long was cut from
the material and the test specimen was notched, all in
accordance with the procedure set forth in ASTM test speci-
fication D256. The test specimen was placed on an Izod
impact strength testing machine, and the weighted pendulum
was allowed to strike the cantilevered end of the specimen.
The test specimen has an impact strength of between 8.0 and
10.0 foot pounds per inch of width.
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By way of control, and not according to the invention,
the process above-described was repeated excepting that the ther-
moplastic polystyrene resin used was not bulk polymerizad to low
conversion. The polystyrene used was made using the same propor-
tion of monomers given above excepting that the polymerization
was carried out to nearly 100% conversion. The polystyrene had
an average molecular weight of 600,000 and a dispersity of 4.5.
The solid resin was dissolved in styrene to give a syrup having
33.3% solids. This syrup was then combined with the polyester
syrup and a molding compound made using the procedure above-
described. The test specimens produced had an impact strength
of bet~een 6 and 8 foot pounds per inch of width; and they had a
dull, light grey color. Pigmentability and filler dispersion
were noticeably inferior to Example 1 because of the presence of
the higher molecular weight polymer and because of greater
spread in molecular weight.
Example 2
Sheet molding compounds are made of the following
materials according to the procedure given in the U.S. Davis,
Wood and Miller Patent 3,615,979:
Materials Desirable ~ Preferred %
By Weight By Weight
Linear thermoplastic resin 1-20
of low dispersity and
average molecular weight
Polystyrene of Example 1 4.0
Resin having crosslinkable 20-90
olefinic double bonds
Polyester of Example 1 24.0
Mutual solvent 5-40
Styrene 20.0
Catalyst for crosslinking 0.001-5
double bonds
Dicumyl peroxide 0.85
2-5-dimethyl hexyl
2,5 di (peroxybenzoate) 0.09
Mold release agent 0-5
Zinc stearate 1.71
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Gelling agent (Alkaline
Earth Metal Oxide) 0-10
Ca(OH)2 1.28
Fillers and/or fibers 0~75
CaCO3 40.0
Chopped glass fibers ~.07
The sheet molding compound that was made using the
preferred percentaye by weight of materials given above had very
good properties including high strength and there was substan-
tially no fiber imprint in the surface of the molded article.
Sheet molding compounds can be made using the desirable
percentages by weight ingredients given above. The mold release
agents, gelling agents, and fillers are not essential, but are
usually used in sheet molding compounds for the well known
functions which they perform. The fillers cheapen the product
and provide coloration, and the fibers strengthen the product.
A combination of fillers and fibers is usually used to provide
optimum strength at a minimum cost. The upper percentage of
the ranges given above for the crosslinking resin is the maximum
perctange used in resin mixes that are devoid of fillers and
fibers. The lowest percentage of the range given is that used
when fillers and/or fibers are utilized. The same is true for
~ the percentage ranges given for the thermoplastic resin, and the
.
mutual solvent.
In order to determine the reasons for the improved
properties of the materials of the present invention, a study
of the morphology of the materials was made. Photomicrographs
of the materials of Example 1 are given as exemplary. The
matrix forming resin syrup of Example 1 was used in the neat
form, and was cured under positive pressure at 400 psi and 250F
in a press. The cured resin was cut into strips approximately
1/2 inch
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wide and these strips were then broken in half to reveal the
internal structure. A photomicrograph was made of a portion
of the surface of the fracture at a magnlfication of ~50
using a scanning electron microscope. A copy of the photo-
micrograph is given in Figure 1 of the drawings, and the
morphology thereof will now be described.
The photomicrographs of Figures 1 and 2 show a
matrix (designated B) of the polyester material having
irregularly shaped pockets therein (designated A) of the
thermoplastic material and which were broken in generally the
same plane as was the matri~ resin when the test specimen
was fractured. The fact that the fracture extended across
the separated thermoplastic phase A demonstrates that the
; thermoplastic phase A was tightly bonded to the matrix
material B. Observation of the fracture of the test specimens
shows that this is typical, and -that there are no voids
between the thermoplastic phase A and the matrix B. Further
observation of the fracture of the test specimens shows that
a sizable number of the thermoplastic bodies A have a void
~ 20 in the center thereof as shown in the lower left of Figure 1.
The upper middle portion oE the area shown in Figure 1 was
enlarged at a magnification of 1800, and a copy of this
photomicrograph is shown in Figure 2 of the drawings.
Figure 2 of the drawings clearly shows the void
designated C within the center of the thermoplastic body A.
Figure 2 further indicates still other phases designated by
the parallel arrows to be present within the major thermo-
plastic phase A. These other major phases are minute and
are believed inconsequential in producing the improved
properties of the present invention. On the other hand, the
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fact that -these other phases are maintained at such a minor
particle size and amount is believed beneficial relative to
the improved properties of the present invention.
In order to exemplify the difference in the
morphology between the materials of the present invention and
the best prior art as represented by its most recent develop-
ment described in the U. S. Kroekel Patent 3,701,748,
photomicrographs were made of a material prepared in accor-
dance with Example 1 of the Kroekel patent. A matrix resin
syrup prepared in accordance with Example 1 of that patent
and containing 37.5 parts of unsaturated polyester, 12.5
parts of the methyl methacrylate thermoplastic polymer, and
50 parts of styrene was cured in the neat form using 1~
t-butyl-peroctoate under a positive pressure of 400 psi and
250F in a press. A test specimen was prepared as above-
described and broken in half. A photomicrograph was made of
the fracture at a magnification of 2,200 using a scanning
electron microscope. A copy of this photomicrograph appears
in the drawings hereof as Figure 3. In Figure 3 of the
drawings the separated thermoplastic phase is designated by
the arrow A. This area of the fracture was selected because
-there also appears a fracture of one of the bodies A as
designated by the arrow B. Figure 3 clearly shows that the
fracture for the most part passes around and along the inter-
face between the major separated thermoplastic phase A and
the matrix. The major bodies A, as shown at B, comprise a
plurality of smaller thermoplastic particles which are knit
together but which do not constitute a homogeneous phase.
This fact is further shown by Figure 4 of the drawings which -
30 is a photomicrograph at a magnification of 22,000 and which
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was made by a scannin~ electron microscope of the area B
shown in Figure 3. Figure 4 shows a smaller dispersed phase
in the form of particles B surrounded by a matrix of the
thermoplastic resin designa-ted A.
In general, the materials of the present invention
have an interface between the major separated thermoplastic
phase and the matrix which is much more difEuse than occurs
in prior art ma-terials. This fact indicates that the
materials of the present invention have a much better bond
between the matrix and the separated thermoplastic phase.
The better bonding produced by the present invention is
believed to cut down the opacity of the materials by reason
; oE a reduction in the scattering of transmitted light as it
passes across the interface between the matrix and the
separated phase and to reduce clumping or aggregation of
pigmen-t. Because there is less light scattering and more
even distribution of pigment in the materials of the present
invention, the pigments therein are more observable, and the
products have deeper coloration.
From the above description and photomicrographs it
will now be apparent that the improved properties oE the
materials of -the present invention are had by reason of a
more diffused bond between -the major thermoplastic separated
phase and the polyester matrix resin, and a generally more
homogeneous matrix. It is further apparent that the more
diffused bond between -the thermoplastic separated phase and
the matrix resin is had by the use of a thermoplastic
polymer the molecules of which are all of about the same
in-termediate molecular weight so as to still have some
compa-tibility with polyester prepolymer and be moderately

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soluble in its monomer. A sizable percent of the monomer is
carried with the thermoplastic molecules as they leave the
polyester during its cure. Because the thermoplastic
molecules are of a controlled low to intermediate molecular
weight they have some affinity ~or the polyester when agglom-
erated to bond tightly to the crosslinked polyester. Because
the molecules are all of about the same molecular weight
(low dispersity), all molecules start to leave the polyester
at about the same time during its cure; and because they all
are of a low to intermediate molecular weight, they have a
high degree of affinity for the monomer and carry along more
than can be polymerized during molding. Because the thermo-
plastic molecules still have some affinity for the cured
polyester, the agglomerated thermoplastic molecules plate
out at the interface leaving the excess monomer at the
center of the agglomerated bodies.
Upon release of the molding pressure, the monomer
vaporizes to expand and form the voids that are evident at
the center of the agglomerate bodies. It is apparent that
such a morphology can on]y be had by a particular narrow
band molecular weight of the thermoplastic resin.
Experience has shown that the thermoplastic resins
should be of a narrow band of molecular weight having an
average molecular weight between 75,000 and 500,000,
preferably between 175,000 and 250,000 and most preferably
at about 200,000. The dispersity shoulld be between 1.0 and
3.5; and should preferably be between 1.0 and 2.6. In order
to give the low porosity and absence of blistering of the
invention, the thermoplastic should have less than 0.10% by
weight of nonreactive solvents present, and preferably less
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than 0.05~. :
In order to give the improved surface brightness
and gloss, there should be less than 0.5% by weight of
emulsifiers and colloidal solvents, and preerably less than
0.2%.
The thermoplastics of the invention also produce
less pregelation and give improved uniform viscosity of the
molding compound. This is believed to be due in part to the
low moisture content of the thermoplastic as is achieved by
keeping the thermoplastic in its own monomer throughout its
format.ion and use. The moisture content should be less than .
0.20% by weight, and should preferably be less than 0.10%.
In order to obtain the desired narrow band of
molecular weight, the polymerization is preferably carried
out at a temperature between 40C and 90C, and should be
stopped before reaching 50~ conversion. Preferably a low
activity-free radical catalys-t is used having a dissociation
constant at 75C of between 8 X 10 6 and 5 X 10 5 moles per
mol per second in order that the intermediate length
molecules are grown ~neither too low molecular weight nor
too high). Without producing an encycloped.ia of mater.ials,
a partial list of the initiators will include: Benzoyl
peroxide, Azo bis (isobutyronitrile), t-Butyl perpivolate,
Bis (~-t-butylcyclohexyl) peroxydicarbonate, 2,2' azo-bis-2-
methylbutyronitrile, 2,2' azo-bis-2-cyclopentylpropionitrile,
4-chlorobenzoyl peroxide. The reaction must be stopped
before 50% conversion is reached to prevent a broad range
(large dispersity) of molecular weight material from being
formed, and to prevent appreciable branching of the molecules
from taking place. The use of the inhibitor to stop the

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reaction beEore 50% conversion is reached also aids in prevent-
ing high moleculax weight molecules from being formed. Without
producing an encyclopedia of these materials, a partial list of
-the inhibitors will include: Toluhydro~uinone, hydroquinone,
Methyl ether of hydroquinone, m-dinitro benzene, chlorobe~zo-
quinone, diphenylamide, etc..
It will further be apparent that the resin system
can include any matrix resin that is crosslinked by reason of
the condensation of olefinic double bondsl along with poly-
styrene, both of which are soluble in a mutual solvent $ystem.The preferred mutual solvent is styrene, such that the thermo-
plastic is made by polymerization thereof. Crosslinking
polyester resins are a preferred matrix-~orming resin prepolymer,
and preferred monomers are those having at least one polymeriz-
able reactive CH2=C group. The styrene copolymer is produced
to less than 50% conversion, and preferably is kept mixed with
- the monomer from which it is made.
Experience seems to indicate that polymer molecules
which are kept in the monomer in which they are made, stay
individually dispersed and surrounded by monomer solvent
molecules better than do polymer molecules which have been
concentrated to a solid which is then dissolved in the solvent.
Where the solid polymer has been dissolved, it is believed
that many polymer molecules stay together as a ~roup with the
group then solvated by the solvent monomer. Such grouped
'
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.

~S74~
polymer molecules do not separate from the polyester at the
same time that individually solvated molecules do. Solid
thermoplastic polymers which have been redissolved therefore
are not to be preferred.
While the polymerization reaction of the monomer
can be stopped before completicn and at substantially any
percent solids, preferred syrups are had when the reaction is
from 20~ to 50~ complete. The reac~ion is preferably stopped
with an inhibitor which stays with the thermoplastic and is
added therewith to the thermosetting prepolymers where it
delays its further polymerization until the final stages of
the crosslinking of the matrix resin.
While the inven-tion has been described in con-
siderable detail, we do not wish to be limited to the
particular embodiments shown and described, and it is our
intention to cover hereby all novel adaptations, modifi-
cations, and arrangements thereof which come within the
practice o~ those skilled in the art, and which are covered
by the appended claims.
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