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Патент USA US3035045

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May 15, 1962
Filed Dec. 12, 1957
.Sé/rene -me/A nary/1b
8 Ho
‘3 100 -
90 _
mefh acry/afe)
Fabr'lcaflon Temp. ( F)
Wi/?am K. Sc/zwe/(ger; Jr.‘
Robert‘ L’. L 66
C/IF/‘ord Jones; Jr: .
United States Patent 0
Patented May 15, 1962
of the faster monomer and proceeds only for the limited
time until the point is reached where substantially only
the homopolymer of the slower monomer is capable of
William Kenmore Schweitzer, Jr., and Robert Edward
Lee, Midland, Clilford Jones, Sr., Linwood, and John
Lester Lang, Midland, Mich, assignors to The Dow
Chemical Company, Midland, Mich, a corporation of
being formed. The result is a polymeric mixture of ho
mopolymers and copolymers. As can be readily ap
preciated, the makeup of the conglomeration will usually
be found to vary with the initial ratio of monomers pres
ent in the reaction mass, the conditions of polymerization,
Filed Dec. 12, 1957, Ser. No. 702,376
8 Claims. (Cl. 260—88.1)
the purity of starting materials, and many other factors
10 that will be apparent to those skilled in the art. Repro
ducibility of the conglomeration from batch to batch is
very di?icult, if not entirely impossible. It is frequently
necessary to blend batches of such inconsistent polymers
to provide products having the desired properties. Such
proved physical properties. The invention additionally
contemplates the process by which these copolymers are 15 techniques, of course, are costly and time consuming.
Many of the prior attempts to minimize compositional
heterogeneity of copolymerization products have involved
Polystyrene and other homopolymers of monovinyl
This invention relates to improved thermoplastic co
polymers useful in thermal molding procedures. More
particularly it relates to such copolymers exhibiting im
continuous polymerization processes. In most of those
processes, it has been attempted to adjust the feed stock
tions. The articles so prepared are characterized by ex 20 to that which would give a particular copolymer product
desired. While suitable products can be made by follow
ceptional properties that make the articles Well adapted
ing the prior processes, such processes, almost without
for a wide variety of uses. However, those homopoly
aromatic monomers are among the most widely used
materials in preparing articles by thermal molding opera
mers are not without disadvantages.
One of the prin
cipal disadvantages involves the rheological properties of
exception involve delicate control and, despite meticulous
execution, still leave room for considerable improvement
the polymers. In order to obtain the requisite tensile and 25 in compositional heterogeneity. Thus, it would be de
sirable to have a process which would provide composi
tional homogeneity and easy control of copolymerization.
Among the copolymers which have appeared to have
to employ a polymer of certain minimum average molecu
unique properties for use in molding are those of the
lar weight. When it is desired to obtain enhanced prop
erties in the polymer product, it is then necessary to in 30 vinyl aromatic monomers, such as styrene, with the alpha
beta unsaturated carboxylic acids, such as acrylic and
crease its average molecular weight. However, as the
methacrylic acids. Even when prepared by the conven
average molecular weight of such homopolymers is in
tional batchwise processes, the copolymers exhibit im
creased, the temperatures and/ or pressures required for
proved physical properties, such as increased heat dis
thermal fabrication are, accordingly, proportionately in
creased. Thus, in preparing such homopolymers it has 35 tortion temperatures over either of the homopolymers.
However, the monomers involved in the preparation of
always been necessary to reach a compromise in the
such products result in so much heterogeneity in the prod
molecular weight between that which gives optimum
uct that it is dif?cult to reproduce the properties of the
physical properties of the copolymer and that which
product from batch to batch. Also, in the batchwise
permits the most convenient fabrication temperatures and
40 processes, the copolymers tended to cross-link at high
conversions. When the copolymers are prepared by the
In order to circumvent such problems, attempts have
aforementioned continuous processes, the properties of
been made to copolymerize styrene with a wide variety
the resulting product are somewhat improved, but the
of comonomers, such as butadiene, acrylonitrile, alkyl
copolymers tend to exhibit a thermal instability, as evi
acrylates, and the like, to modify some property of homo
polystyrene or for some other reason. None of those 45 denced by a progressive decrease in melt viscosity upon
continuous exposure to elevated temperatures. Signi?
copolymer products so obtained, however, has overcome
cant evidence that the heretofore available processes re
the di?iculties due to the physical properties-fabrication
sult in heterogeneous compositions resides in the appear
temperature contradiction which is believed to be caused
ance of molded sections prepared from the copolymer
by the rheological properties inherent in the linear or
branched copolymer products generally obtained by con 50 products of such processes. Such sections are usually
translucent or opaque. Thus, it would be particularly
ventional procedures. Copolymerization also introduces
desirable to have an improved process for preparing
other vexatious complications. For example, the prod
styrene-acrylic and the like copolymers, so that their full
ucts of conventional copolymerizations are generally ob
potential as molding materials could be easily re?ized
tained as conglomerations, mixtures, or blends of com
positional variants resulting from the di?erences in co 55 and readily achieved.
The provision of an improved continuous polymeriza
polymerizability of various monomers. The substituents
impact strength, elongation, and similar properties, of a
minimum for general acceptability it has been necessary
tion process for mixtures of copolymerizable monomers
attached to the terminal carbon atoms of the ole?nic un
is the principal object of this invention.
saturation determine to a great extent the ability of a
It is a further object to provide such a process for
particular monomer to polymerize or to copolymerize.
They also in?uence the rate at which a particular mono 60 preparing copolymer products of improved compositional
mer will copolymerize with another. Thus, when two
It is a still further object to provide such a process for
di?erent monomers are intermixed and caused to copoly
preparing copolymer products of improved thermal sta
merize, one of the monomers will ordinarily be found
bility and clarity.
to have greater polymerizability. As a consequence, the 65
Another object is the provision of a facile process for
more polymerizable monomer in a mixture of monomers '
may polymerize with itself in the initial portion of the
preparing molding grade copolymer products of premium
reaction to form a homopolymer until its concentration
Still another object is to provide an improved class of
in the reaction mass has dropped appreciably. Only then
copolymers from vinyl aromatic monomers and acrylic
will the less polymerizable monomer be able to actually 70 co-monomers which exhibit the aforementioned improved
copolymerize with the faster monomer.
The actual co
polymerization further depletes the relative concentration
properties and characteristics.
The above and related objects are accomplished by
means of the process of the present invention wherein a
about 160° C.
homogeneous monomeric material consisting essentially of
said mixture at a rate and in a proportion such as to main
a vinyl aromatic monomer and an acrylic monomer is
tain in said mixture a constant equilibrium ratio of the
monomeric materials to each other and to maintain the
proportion of copolymer in the mixture constant at not
prepared and heated together with not more than about
60 percent of the copolymer product resulting therefrom
at an elevated temperature while maintaining the propor
The monomeric materials are fed into
tions of said monomeric material and said copolymer
more than about 60 percent by weight.
These conditions are readily attained by feeding con
product substantially constant ‘by feeding additional
tinuously, and at steady rates, the copolymerizable mon ‘
amounts of said monomeric material to the mixture at
meric materials to the polymerizing system in a polymeri
substantially the same rate at which it is polymerized 10 zation zone which is maintained Within the indicated
While Withdrawing said copolymer product at about the
range of temperature While continuously withdrawing
Same rate at which said monomeric material is fed to the
‘from said polymerization zone a portion of the polymer
mixture, all of said steps being conducted in the substan
izing system or polymerization mass at a rate correspond
tial absence of iron.
ing to the volumetric feed rate of monomeric materials.
The copolymers contemplated by the invention are 15 When equilibrium is attained in such a system, the ratio
' those containing recurring units of polymerized mono
of monomeric materials to one another in the polymeri
vinyl aromatic monomers of the benzene series and also
zation zone, the concentration of polymer in the poly
merizing system, and the chemical composition of the
copolymer product are generally found to be substantially
containing in the same copolymer chain recurring units
of copolymerized acrylic monomers. Among the mono
vinyl aromatic monomers, styrene is preferred. However, 20 constant. It should be apparent that the relative propor
other monomeric alkenylaromatic compounds, such as
tions in which the monomeric materials ‘are chemically
combined in the copolymer are not necessarily the same
as the relative proportions of the monomeric materials
in the homogeneous mixture from vwhich the copolymer
styrene 'or ortho-para-dichlorostyrene, or comonomeric 25 was formed. The proportions of monomeric materials
mixtures of styrene with alpha~methyl styrene or of
which are necessary in a {feed mixture in order to produce
styrene with any of the above-named compounds may
a copolymer having a particular empirical structure may
also be used. Thus, the term “monovinyl aromatic mon
be determined from the pertinent reactivity ratios or, if
omer” as used herein is intended to include the com
such ratios are not avail-able, the suitable proportions may
pounds having a vinyl radical directly attached to a carbon 30 be found by simple preliminary tests. As a practical;
para-methyl styrene, meta-ethyl styrene, ortho-para-di
methyl styrene, ortho-para-nl'ethyl styrene, para-chloro
styrene, isopropyl styrene, ortho-methyl-para-isopropyl
atom of an aromatic nucleus.
By arcylic monomer it is meant to include acrylic acid
and methacrylic acid. The acrylate esters, such as the
alkyl acrylates when used as the sole acrylic monomer,
matter, once the equilibrium has been established, it is
most conveniently continued by maintaining a heat bal
ance on the system through ‘adjustment of the feed rates
of monomeric material and rate of withdrawal of the
do not provide the outstanding properties desired herein. 35 mixture of copolymer product and unpolymerized
However, small amounts of alkyl acrylates and alkyl
methacrylates may be used if desired to form a terpoly
mer. It has also been found that crotonic acid and
' itaconic acid are generally not satisfactorily operable in
For successful operation of the process, it is essential
that all steps up to the withdrawal of the portion of the
polymerizing system be conducted in the substantial ab
the process ‘for the primary reason that each is insoluble 40 sence of iron. Best results are obtained when all iron
in the monovinyl aromatic monomer. Solubility is a pre—
is effectively excluded from the polymerization system.
requisite for successful operation, since only ‘when such
Thus the use of apparatus constructed of ordinary iron
condition-is achieved is it possible to achieve a homoge
and steel is prohibited. Elemental or ionic iron even in
neous monomeric material and consequently the desired
a concentration of 10 parts per million or less has such a
polymer products.
retardant effect on the rate of polymerization as to pre
Excellent molding grade copolymers can be manufac 45 elude acceptable polymerization rates. Even the com
tured by the present process when the monovinyl aromatic
mon stainless steels, when used as materials of construc
monomer is employed in the homogeneous monomeric
tion, retard the rate of polymerization somewhat, al
material in a concentration of from about 70 to about 99
though not prohibitively. A further disadvantage of the
percent of the total weight of monomeric material with
presence of iron is the discoloration of the resultant co
the remainder being made up of the acrylic monomer.
polymeric product and also the increase in the thermal
There is no signi?cant advance in copolymeric properties
instability of the product. For the latter reasons it is
when the base polymer is composed of less than about
preferred to exclude iron from all steps of the process in
one percent of acrylic monomer. Copolyrners composed
cluding those relating to withdrawal of the copolymeric
of appreciably, more than about 30 percent of acrylic 55 product and subsequent processing steps, such as de
monomer are dif?cult and expensive to prepare, have a
volatilization, grinding and the like. Materials of con
signi?cantly reduced polymerization rate, and are so
struction, such as non-ferrous alloys, nickel, glass-lined
‘cross-linked as to be of little utility as molding materials.
steel, and the like, are well-adapted for use in carrying
Any advantage obtained from such copolymers by way of
' out the process and, when so carried out, the copoly
their inherent properties is not proportional to that ob
meric product has maximum and reproducible properties.
tained when smaller amounts of acrylic monomer are
When operating in accordance with the process of this
used. In addition such advantage, even when achieved,
invention at the expressed temperature range of from
seems to be o?-set by an undesirable reduction in some
about 130° C. to 160° C., it has been found that the
‘other property of the product, and by the increased corro
pressures encountered are in the range of from about 25
sive tendencies of the monomers, which increase the dif? 65 to 75 pounds per square inch gauge. Those pressures
culties, incurred in successfully accomplishing the poly
will maintain the monomeric materials in the liquid state.
Because the process operates under equilibrium con
The copolymers of this invention are made by heating a
ditions, it is preferred to conduct it so that the polymeriza
homogeneous mixture of the monomeric material and the
tion system continuously contains less than about 60 per
copolyr'ner'ic product thereof in bulk, i.e., in the sub ‘
70 cent of solids. By 60 percent or less solids content in the
tial absence of other polymerizable substances, soh le
polymerization system is meant that. the polymerization
diluents or insoluble dis ersants , or in the
p rcsence
of r
small amounts of solvents for the polymer at a pressure
su?'icient to preserve the liquid state.
temperature is maintained betweenabout 130° C. and
mixture or mass contains not more than 60 percentrby
' weight of copolymer product. When the process is op
erated such that the polymerization system contains sub
stantially more than 60 percent solids, the desirable con-
system. Fitted into the outlet pipe 14 is a metering pump
15 for withdrawing a metered portion of the polymeriz
ing materials. The outlet pipe 14 is connected to a conven
tional devolatilizer such as that described in US. 2,804,
920 issued September 3, ‘1957, to 'C. C. Perkins or other
ditions of equilibrium are found to be more di?cult to
achieve and maintain and the copolymer product is less
subject to precise control. Additionally, when higher
solids concentrations are involved, practical problems
such as uniform heat transfer and pumping of the viscous
polymerizing system, become quite serious. Although
similar devolatilizing apparatus (not shown) which is
adapted for handling viscous ?uids.
A temperature regulating control 16 is installed in the
solids of less than 60 percent may be utilized as the equili
brium, the full potential capacity of the apparatus is not
realized and the subsequent devolatilization is prolonged.
system. -A thermocouple -17 is inserted in a well in coil
In order to maintain an equilibrium it follows that the 10 10 and connected to control 16. A valve 18 is fitted into
inlet line 12 between metering pump 13 and coil 10. The
percent solids at any moment will be greater than the per
control is adjusted so that an increase of temperature
cent conversion of monomer to polymer. In practice, it
within the coil 10 will open the valve 18 and cause more
is preferred to adjust the rates of feed and withdrawal
monomer to be introduced into the polymerizing system.
so as to operate at very low conversions of about 1 to 5
A pressure regulating control 19 is also inserted into
percent or less. That results in greater compositional 15
the system. Connected to the control 19 is a valve 20
which is ?tted into the outlet line 14 between the coil 10
Although minor amounts of the usual free radical poly
and the metering pump 15. The control 19 is also con
merization catalysts may be employed in the process,
nected to inlet line 12 at the point designated by the
they are not essential to its successful operation. Ac
cordingly, it is preferred to operate without any added 20 numeral 21. The control 19 is adjusted so that an in
crease in pressure in the inlet line 12 will open ‘the valve
catalyst. As will be later described, however, catalysts
20. This causes a portion of the polymerizing system to
may be employed in adjusting the process to provide the
be withdrawn.
copolymer products having the desired viscosity.
The use of the temperature regulating control 16 and
The copolymer product can be isolated from the un
polymerized components of the polymerization mixtures
by any of the known methods, such as by precipitation
in a non-solvent or by devolatilization. vIt is preferred
the pressure regulating control 19 permits the process
to be subject to automatic control.
Once the coil 10 is
hydrostatically ?lled and equilibrium has been established,
to devolatilize the mixture mechanically by heating the
a slight increase in temperature within the coil 10, as may
mixture under reduced pressure whereby the volatile un
be caused by the exothermic polymerization reaction,
opens the valve 18. In this way, fresh, relatively cold
polymerized components are vaporized leaving the co
polymer product as a residue. If immediate devolatiliza
tion is impractical upon withdrawal of the mixture from
the polymerization zone, the mixture may advantageously
be chilled to stop or to retard subsequent polymerization
monomer is automatically introduced to the polymeriza
tion system to lower its temperature. Simultaneously,
the valve 20 opens to allow the discharge of an equal
volume of monomer-copolymer mixture.
If desired a part of the coil 10 may have a jacket 24
to the greatest possible extent. If polymerization is al
lowed to continue beyond withdrawal of the polymeriza
tion system from the polymerization zone, it generally
through which heat exchanging ?uids may be passed by
tion and of the conventional batch-polymerized product.
of manufacture. The products exhibit improved proper
ties, particularly with regard to thermal stability and to
means of inlet 22 and outlet 23. Such means allows the
polymerization to be controlled at any desired solids.
does not proceed according to and under the necessary
The copolymer products produced in accordance with
conditions of the present process but will ordinarily fol
low the usual batchwise polymerization mechanism and 40 the present process are thermoplastic and capable of being
formed by conventional thermal fabrication methods, such
kinetics. The results in such instances will e?ectively be
as compression and injection molding, into useful articles
a blend of the desired copolymeric product of this inven
Such a blend is, of course, likely to be obtained with the
aforementioned disadvantages of compositional hetero 45 the transparency of the molded articles over the copoly
mers and products of similar monomer composition but
geneity, thermal instability, translucence, gels due to
prepared by prior processes. In addition, the copolymers
cross-linking, and others. As a generally in?exible rule,
of this invention are free of gels and the like which are
only the products resulting from the present process are
found to exhibit the indicated desirable properties.
To afford further illustration, a preferred embodiment
of an apparatus which is well-adapted for the manipula
tive steps of the process will be described. It should be
understood that the invention is not limited to any
particular apparatus and that known mechanical equiva
commonly present when a copolymer is partially cross
linked, highly branched, or of highly heterogeneous com
position. The lack of such defects is of paramount im
portance in achieving commercially successful moldings,
particularly transparent moldings. Still further, the im
proved properties of the copolymer products obtained by
lents may be substituted in the preferred embodiment 55 practice of the present invention are more easily and
consistently reproducible than when the prior processes
without departing from the spirit and scope of the inven
are employed for their preparation.
tion. In the drawings:
It is believed that the aforementioned improvements
FIG. 1 is a schematic plan of the apparatus and
FIG. 2 is a plot of heat distortion temperature versus
fabrication temperature and will be described in Exam
ple 6.
In the preferred embodiment there is provided a loop
16 of pipe forming a torus, hereinafter referred to as coil
in the copolymeric product are the result of a more regu
lar and uniform molecular architecture of the .copolymer
than that of copolymers prepared by the prior known
processes. In the prior processes the resulting polymeric
products had highly irregular, non-uniform, heterogeneous
architecture which depended upon the amount of pre
10. A recirculating pump is provided in the coil 10 to
recirculate the polymerizing mixture through the coil. 65 mixing of the monomers and the relative chemical re
activities of the monomers. In the process of this inven
An inlet pipe 12 is attached to the coil 10, preferably near
tion, however, it is believed that there are produced co~
the recirculating pump 11. The pipe 12 causes dispersion
polymers Whose architecture very closely resembles the
of monomeric materials within the polymerizing system
theoretical recurring groups that could be drawn from
as rapidly as possible so as to maintain the polymeriza
tion equilibrium. Fitted into inlet pipe 12 is a metering 70 an examination of the starting monomeric mixtures.
Because of the molecular architecture, the copolymer
pump 13 for metering a homogeneous monomeric ma
products obtainable by practice of the present invention
terial into the coil 10. The inlet pipe 12 is connected
generally exhibit a rheological behavior which is excep
to conventional inventory tanks (not shown). At a point
tionally well-adapted for thermal fabrication. It is be
on the coil 10 remote from the inlet pipe 12 is an outlet
pipe 14 for withdrawing a portion of the polymerization 75 lieved that the carboxylic groups are capable of such an
alignment or orientation that they hydrogen bond with
in the liquid state.
one another.
polymers exhibit strengths approaching those of copoly
polyerization mixture was fed into a devolatilizer where
the mixture was heated under reduced pressure and the
mers which are cross-linked by primary valence bonds.
unpolymerized monomers vaporized leaving the copoly
However, at elevated temperatures the copolymers of
the present invention exhibit the ?uidity or plasticity which
is usually associated with linear polymers. As a result.
they can be easily formed or shaped into practically any
mer product as a residue containing approximately 1
Thus, at ordinary temperatures, the co
desired article. Upon cooling from an elevated tem
perature, the “pseudo-cross-linking” of the present co
The withdrawn portion of the
percent of volatile material.
Using the above apparatus, copolymers were prepared
from styrene and both acrylic acid and methacrylic acid
in various compositional ratios. The temperature of the
10 coil was maintained throughout each of the polymeriza
polymers caused by the hydrogen bonding is generally
tions at 145 ° C.
observed to recur. This behavior likewise'results in higher
heat distortion temperature for the copolymers. How
ever, although the heat distortion temperature is increased
then fed ‘into the coil, wherein they were allowed to
polymerize to about 50 percent conversion, after which
appreciably, there is only a slight elevation of the tem
a portion of the copolymer-monomer mixture was con
15 tinuously withdrawn at the same rate at which the
perature required to fabricate the copolymers thermally.
monomers were being introduced. After equilibrium
was established, the withdrawn polymer-monomer por
tions were devolatilized. The following results were
This behavior is in contrast to the prior experience in
the polymerization art, where a modi?cation which would
cause an increase in the heat distortion temperature would
necessarily result in a proportional increase in the fabri
The monomers were ?rst intermixed,
cation temperature. This effect is of readily apparent
commercial signi?cance.
For use in molding applications the copolymers should
Monomer Feed
have a solution viscosity of from 4 to 20 centipoises, and
preferably from 5 to 10 centipoises, as measured from 25
Polymer Composi- Volatiles
Thus, for a
ity 2
at 440° F.
a 10 percent by weight solution of copolymer in methyl
95/5 acrylic acid____ ill/8.5 acrylic acid__
ethyl ketone at room temperature. The solution viscosity
90/10 methacrylic
82/18 mcthacrylic
is a parameter of the molecular weight for any given
copolymer wherein the polymer chains are of similar
spatial con?guration. By that is meant that all the chains 30
are linear or branched or cross-linked.
tion 1 (styrene/
0. 75
0. 40
8. 3
7. 7
4, 180
10, 760
1. 25
8. 3
13, 000
1 Polymer composition determined by titration with alcoholic NaOH.
'1‘ Viscosity of 10 percent of copolymer in methyl ethyl ketone at 25° 0.
given copolymer an increase in solution viscosity indicates
an increase in molecular weight. In any molding opera
tion there must be a compromise between the physical
Each of the samples was compression molded into a
properties of the molded article and the melt viscosity 35 specimen of a thickness of about 0.1 inch. ' In each in
of the polymer from which the article is molded. Both
stance the molding was completely transparent and with
the physical properties and the melt viscosity are de
out any discernible discoloration. When feed stocks
pendent, in the case of linear polymers, upon the molecu
were employed containing ‘greater than 30 percent by
lar weight of the polymer. The above-stated range of
weight of acrylic acid or of methacrylic acid, the result
solution viscosities provides copolymers having the opti-'
mum properties and workability and is accordingly pre
ferred. The desired range is attained by operating within
the aforementioned temperature range of from about 130°
ing products were so cross-linked that the solution vis
cosities were impossible to obtain. Those compolymers
could not be molded into clear {gel-free moldings.
By way of contrast the same feed stocks were placed
in tubes, allowed to polymerize batchwise to about 50
C. to 160° C. Within the expressed range it may be
desirable to employ minor amounts of the conventional
percent conversion, and subsequently devolatilized. The
free radical catalysts to achieve the desired viscosity at
samples were molded under the same conditions and the
molded specimens found to be translucent to opaque.
the temperature which gives optimum polymerization
By way of further contrast the monomers were
Although the copolymer products of the present inven
polymerized to completion under conventional mass
tion may, per so, be formed into useful molded articles, 50 polymerization conditions. The samples were highly
it is most common in the polymer art to employ formula
cross-linked, as evidenced by a large number of gels
tions consisting of many ingredients. Thus, the copoly
being observed in them when they were molded as well
mers may be dyed, pigmented, ?lled, plasticized or formu
as vwhen they were dissolved in methyl ethyl ketone.
lated in any conventional or desired manner.
The following examples are oifered for purposes of 55
illustrating and exemplifying the operation of the process
and advantages of the copolymers. In the examples, all
parts and percentages are by weight.
Example 1'
Example 2
Several copolymers were prepared using the continu
ous polymerization apparatus described in Example 1.
By varying the temperature of polymerization from about
100° C. to about 170° C. copolymers resulted having so
60 lution viscosities in the range of from 4 to 20 centipoises
A polymerization reactor was constructed from a loop
as measured at 25° C. from a 10 percent solution in
of coiled standard 1 inch pipe about 100 inches in length.
The ends of the pipe were connected to a pump for
methyl ethyl ketone, as well as copolymers outside of
a that solution viscosity range. ,
'rapidly circulating the contents of the coil. Means were
-provided for continuously feeding, at a measured uni
form’ rate, a homogeneous mixture of'liquid monomeric
materials. Means were also provided'for maintaining
‘These copolymer products, having solution viscosities
higher than 20 centipoises, required such high tempera
the temperature of the coil at a temperature of from
about 130° C. to about 160° C. At a point in the coil
V'I‘hose copolymers having solution viscosities of less than
remote from the point of vintroduction of the feed mix
ture there was provided means for continuously with
drawing a portion of the polymerizationmixture at the
prepared from them had very poor tensile strengths and
. same rate as the rate'of feed into the coil and under
conditions that the contents of the coil were maintained
tures and pressures for their fabrication as to preclude
their use in conventional thermal fabricating equipment.
4 centipoises molded easily, 7 However, molded sections
were noticeably inferior in other of their physical prop
V erties.
The copolymer products’ falling within the range of so
75 lution viscosities of from 4 to 20 'centipoises were easily
The heat distortion temperatures in degrees centigrade
were plotted against the fabrication temperatures in de
grees Fahrenheit. In the resulting plot, point A is poly
styrene and the lines leading therefrom represent, in each
molded into clear sections having good physical proper
Example 3
Using the continuous polymerization apparatus de
case, a copolymer product with decreasing styrene con
scribed in Example 1, a monomer feed of 90 parts sty
rene and 10 parts acrylic acid was polymerized by the
method therein described. After devolatilization to
about a 1 percent volatiles content, the sample was
heated to 280° C. for 75 minutes. At intervals the melt
tent and a correspondingly increasing comonomer content.
In all instances the result was found to be an essentially
linear function with increasing acrylic monomer. These
results are shown in the graph of FIGURE 2 of the here
to annexed drawing. The slope of the styrene-acrylic co
viscosity of the polymer product was determined. After
polymer product is +1.25; that of the styrene-methacryl
about 15 minutes, the melt viscosity of the product was
ic acid copolymer product is +0.75; and that of styrene
found to drop at a rate of about 23 percent per hour.
‘By way of contrast the same monomers were copoly
methyl-methacrylate copolymer product is —‘0.45.
The signi?cance of these results is of considerable
merized under conventional mass polymerization condi
commercial importance. With the copolymers of the
tions to about 50 percent conversion. After devolatiliza 15 present invention, it is possible to prepare articles having
tion, the product was exposed to the identical conditions
exceptional dimensional stability which can be fabricated
as above described. In this instance, the melt viscosity
on conventional apparatus at the usual temperature.
was found to drop at the rate of 35 percent per hour.
What is claimed is:
This indicated that considerably less thermal stability
1.A process for preparing thermoplastic copolymers
was obtained than had been achieved in the product pre
of molding grade comprising, as continuous steps ('1) the
pared in accordance with this invention.
preparation of a homogeneous monomeric material con
sisting essentially of a monovinyl aromatic monomer of
Example 4
the benzene series and from 1 to 30 percent by weight
Several attempts were made to repeat the process of 25 of said monomeric material of an unsaturated carboxylic
Example 1 using iron pumps in place of the stainless
acid selected from the group consisting of acrylic and
steel pumps. In most instances no polymerization was
methacrylic acids, (2) the exposure in a polymerization
initiated. In the few runs where polymerization started,
zone of a mixture of said homogeneous monomeric ma
the rates of polymerization were prohibitively low for
terial and the copolymer product of polymerization there
commercial operation. When the copolymeric product 30 of
in the liquid state to a polymerization temperature
was devolatilized and examined it was found to be dis
between about 130° C. and about 160° C., the propor
colored badly and to have little thermal stability.
tion of said copolymer product being not more than about
When the stainless steel pumps were again replaced,
60 percent by weight of said mixture, (3) the maintenance
the polymerization rates and the product returned to that
of the proportions of said monomeric material and Said
previously prepared.
Example 5
A kettle was ?tted with a turbine-type agitator and
with inlet and outlet tubes for introducing liquid mo
nomeric materials and withdrawing ?uid copolymer
copolymer product in said mixture substantially constant
by feeding additional of said monomeric material to the
mixture while withdrawing said mixture of copolymer
product and unpolymerized monomers from said zone
‘at about the same volumetric rate at which said mono
monomer mixtures. Means were provided for pumping 40 meric material is being fed to said mixture, all of said
the materials into and out of the kettle. The kettle was
steps being carried out in the substantial absence of iron,
jacketed for thermal control. All materials of ‘construc
and ?nally (4) isolating said copolymer product from
tion which were in contact with the monomers or co
said mixture.
polymers were of stainless steel.
2. The process claimed in claim 1 wherein said continu
The process of Example VI was repeated in this ap 45 ous steps are in sequential order.
paratus. The results were found to be identical to those
3. The process claimed in claim 1 wherein said mono
obtained with the coil apparatus of that example.
meric material is fed into said polymerization zone at
a rate to maintain the polymerization temperature sub
Example 6
stantially constant.
Several copolymers were made in the apparatus of 50
4. The process claimed in claim 1 wherein the propor
Example 1 and in accordance with that process. After
tion of said copolymer product in said polymerization
devolatilization the polymeric materials were checked for
zone is maintained constant at from about 15 to about
heat distortion temperature and for fabrication tempera
The term, “heat distortion temperature,” for present 55
purposes, should be construed as that temperature which
results when a sample of speci?ed dimensions is loaded
in a prescribed manner and heated at a ?xed rate until the
sample is deformed to a stated value. Such a test method
60 percent by weight of said mixture.
5. The process claimed in claim 1 wherein said poly
merization step (2) is conducted at a pressure of from
about 25 to 75 pounds per square inch gauge.
6. The process claimed in claim 1 wherein said co
polymer product is isolated by devolatilization of said
is described in A.S.T.M. Tentative Method of Test for 60 mixture.
7. The process claimed in claim 1 wherein said mono
Heat Distortion Temperature of Plastics (D—648—44T) in
the 1944 Book of A.S.T.M. Standards, Part III, page 1627.
viny-l ‘aromatic monomer is styrene.
A modi?cation of that method is described in A.S.T.M.
8. The process claimed in claim 1 wherein the concen
Bulletin No. 134, May 1945. In the modi?ed test, a com
tration of iron in the system at any time does not exceed
pression molded sample is cut into a test specimen having 65 10 parts per million.
dimensions of 1.75 by ‘0.5 by 0.375 inch. The load is
applied until a given deformation is obtained. The tem
References Cited in the ?le of this patent
perature at which that deformation results is considered to
be the heat distortion temperature.
The fabrication temperature, for purposes of this ex 70 2,420,330
Shriver et .al ___________ __ May 13, 1947
ample, is that temperature which is 25° F. above the tem
Chaney _______________ __ Jan. 9, 1951
penature at which a mold will just ?ll when a ram pres
sure of 10,000 pounds per square inch is applied. For
this example, a 1 oz. standard Watson-Stillman injection
molding machine was used.
De Nie _______________ __ Ian. 9, 1951
Leary ________________ __ June 9, 1953
(Other references on following page)
Tobolsky et 211.: Organic Peroxides, pp. 795-103, Inter
Barrett _______________ __ Apr. 13, 1954
McDonald et a1 ________ __ Dec. 20, 1955
science (1954)
Schildknecht: Polymer Processes, Interscience (1956).
D’Alelio: Fundamental Principles of Polymerization,
Boundy-Boyer: Styrene, Its Polymers, Copolymers and
Derivatives, pp. 865-866, 885-886, Reinhold (1952).
5 John Wiley, pp. 413-424, 434-5 (1952).
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