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2,408,426
Patented Oct. 1, 1946
“ UNITED STATE 5
i PATENT OFFICE
2,408,426 ~
PREPARATION OF MODIFIED METHYL
METHACRYLATE COMPOSITIONS
Frederick L. Johnston, Claymont, Del., assignor to
E. I. du Pont de Nemours & Company, Wil
mington, DeL, a corporation of Delaware
'
.
No Drawing. Application January 12, 1943,
Serial N0. 472,161
(CL 260-83)
2 Claims.
1
This invention relates to the preparation of"
modi?ed methyl methacrylate compositions and,
more particularly, to such compositions adapted ,
to give molded articles characterized by high re
sistance to distortion by heat.
Heretofore methyl methacrylate monomer has
been polymerized to yield thermoplastic molding
compositions. When such polymers are prepared
In the preferred method of, carrying out this
small amounts of benzoyl peroxide and
the selected halo-ole?n are dissolved in methyl
. invention,
methacrylate monomer. This solution is sus
pended in about twice its volume of water.
water contains a small proportion of a mild dis
persing agent such as the 65% sodium salt of poly
methacrylic acid and is buffered to a pH of about
7.5 by means of a suitable inorganic salt. This
by heating methyl methacrylate monomer in the
mixture is agitated vigorously in a closed reac
10
absence of catalysts or in the presence of small
tion vessel capable of withstanding moderate
concentrations of peroxide-type catalysts, the re
pressures. The polymerization is carried out by
sulting molding compositions are difficult to fuse
heating at a temperature in the neighborhood
into optically homogeneous masses under heat
of 125° C. under a pressure of about 50 lbs/sq. in.
and pressure, and, when hot, are too viscous for
15 for twenty to thirty minutes until the essential
satisfactory molding by injection.» In the past
these objections have been partly overcome by
completion of polymerization is indicated by a
various means but an outstanding dif?culty has
been to obtain a product which can be molded into,
articles that do not tend to distort at undesirably
appearance of monomeric methyl methacrylate.
sudden drop in pressure due to the essential dis
It is preferable to prevent the reaction from be
coming too violent by suitable cooling of the ves
low temperatures; particularly, has this been the 20 sel. The mixture is then cooled and discharged
case where the articles have been injection mold
from the reaction vessel. The granular product
ed although it also holds to a considerable extent
with respect to compression molded articles. A
further di?lculty is to obtain a product improved
in this characteristic and at the same time char
acterized by good moldability and yielding mold
ed products having optical homogeneity and being
is separated from the mother liquor, washed, cen
trifuged, and dried by heating at 70° C to 100°
C. in a circulating air oven or under vacuum, and
25 this dried granular polymer is then masticated
on hot mixing rolls for ten to ?fteen minutes, re
moved from the rolls, cooled and comminuted to
pass a %" screen. Thev resulting product is suit
free from discoloration.
An object of the present invention is to provide 30 able for compression or_ injection molding and
an improved methyl methacrylate composition
shows special advantages when used for the lat
characterized by good moldability and adapted to
be molded into articles having high resistance to
distortion by heat, optical homogeneity, and free
ter purpose.
‘
The following examples illustrate speci?c em
bodiments of the composition and the method of
dom from discoloration. A further and more
preparing same according to the present inven
particular object is to provide a composition 35
tion, all parts being given by weight unless other- _
adapted to be injection molded into articles hav
‘ wise specified:
ing high resistance to distortion by heat. A still
Exmu: I
further object is to provide a practical and eco
nomical method of preparing such compositions. 40
Other objects will be apparent from the descrip
tion of the inventiongiven hereinafter.
The above objects are accomplished according
(a)
The following solutions are made up of:
>
Parts
Distilled water _________________________ __
to the present invention by polymerizing mono
NazHPO4.12H2O
meric methyl methacrylate in the presence of very 45 1% Water solution of
‘small amounts, of unsymmetrical alpha-ole?nic
4800
'56
polymethacrylic acid --_,_____________ __
‘compounds in which one of the carbon atoms of
the double bond carries a single, halogen atom.
More speci?cally, the polymerized methyl meth
acrylate composition of the present invention is 50
prepared by polymerizing a dispersion of mono
meric methyl methacrylate in a non-solvent liq
uid such as water in the presence of 0.01% to
3.0%, by weight of the monomer, of an unsym
(b)
.
‘
Parts
Methyl methacrylate monomer __________ .._ 2786
Octadecyl alcohol (lubricant) ___________ .._
56
Trichloroethylene _________ __l____.'. _____ __~
14
(c)
Benzoyl peroxide _______________________ -_
'l
metrical alpha-ole?nic compound in which one
of the carbon atoms of the double bond carries a 65 The ingredients in (a) are dissolved together
- single halogen atom, at a temperature of 100° C.
and charged into a glass enamel‘ vlined closed re
150° C. under autogenous pressure.
9,408,426
3
action kettle capable of withstanding pressures
up to 300 lbsJsqin. and ?tted with a stainless
steel anchor shaped stirrer, stainless steel ba?les,
thermocouple for observing the temperature of
the contents, and an outlet through the head to a
tioned in this speci?cation are determined by this
pressure ‘gauge. The catalyst (c) is freshly dis
solved in (b) and the resulting solutionis charged
at once into the reaction kettle.
method.
\
A similar methyl methacrylate polymer poly
The kettle is
sealed and the stirrer operated at 575 R. P. M.
throughout the run. External heat is applied to
bring the kettle contents, to a temperature of
110° C. within ?fteen to twenty minutes at which
time the pressure gauge shows about 45 lbs./sq.in.
pressure. The heat is then shut oil". Within one
to two minutes the exothermic polymerization re 15
action begins and there is a surge of‘ temperature
and pressure to 114° C. and 53 lbs./sq.in., re
spectively, where the bulk of the polymerization
takes place. Within about. ?ve minutes there is
a rapid decrease in pressure to about 15 lbs./sq.in. 20
and the temperature begins to drop. Stirring is
continued until the kettle contents have cooled
to 40° C. or. below at which time the pressure
The above example is repeated using varying
quantities of trichloroethylene. When the prod
ucts are worked up and molded as above, injection
molded softening temperature specimens are ob
tained which soften vas shown in the following
table:
Softening-tom ra
Oonocntmtion of trichlmoethylcno
(based on methyl methacrylate monomer)
gauge shows zero pressure and the kettle is
opened. The product, in the form of crystal clear 25
spherical granules up to about 1/64" diameter, is
removed from the mother liquor on ?lter cloth
0.0
.
(blank for control).................... --
0.25%
_____ __
0.75%
2.00%’.
cction
° C.
64
82
0.50”
86
_-
85
1.00% ________________________________________ __
the washings are clear. This requires a total of
ture of
molded sinj en
84":24' x0.065"
.... -_
91
85
about 20,000 parts of wash water. Excesswater 30
is removed by means of a centrifuge and the prod
not is dried at 100° C. for‘24 hours under high
vacuum.
I
a
The ?ne granular product is converted to mold
ing powder suitable for injection molding by hot 35
pressing into sheets at 160° 0., followed by chop
ping into particles which will pass a %” screen.
Exam: I!
The ingredients for a granular polymerization
are assembled as follows‘ '
l\
(in
Parts
Distilled water________________________ __,- 4800
NazHZPO4J2HzO ______________________ __
This molding compound is then injection molded
in an injection molding machine, suitably a
1% Water solution of 65% sodium salt of
l-ounce capacity De Mattia vertical injection 40
molding machine built by the De Mattie. Machine
and Tool Company, Clifton, N. J. The machine‘
polymethacrylic acid. ______________ ..-__
(b) _
480
Parts
Methyl methacrylate monomer__________ __ 2786
2-Chloropropene
is supplied with a die capable of molding test
specimens whose measurements are 21/2" x 1/z" x
0.065". The polymer is injected into the die 45 Benzoyl peroxide
___.._.._ ______ __....____.,-_
'
Cc)
14
Parts
'7
through agate at the end of the‘ cavity ‘with the
die closing and injection taking place during a
The ingredients are charged into a kettle as de
scribed in Example I and polymerization is con
period of 1.25 seconds. The machine is timed
ducted in a similar manner. Heat is applied as in
to maintain piston pressure on the molding pow
der and clamping pressure on the die simultane 50 Example I and after the heat has been cut off
the exothermic polymerization reaction causes a
ously for ?fteen seconds to enable the molding to
surge of temperature and pressure to 125° C. and
set up in the die. A new injection is made every
70 lbs/sq. in., respectively. The bulk of the poly
sixty seconds. The polymer may be molded under
merization takes place under ' these conditions.
several temperature conditions to yield speci
mens of attractive appearance. ~ When the heat 55 The resulting polymeris worked up and converted
to molding powder and injection molded in the
ing cylinder delivers polymer. at 220° C. into the
manner described in Example I.’ When the heat
cold die, satisfactory moldings are produced un
ing cylinder delivers polymer at 230° C. into the
der 22,700 lbs./sq.in. piston pressure.‘ Moldings
cold die, satisfactory moldings are produced un
of excellent clarity and surface characteristics are
obtained which are faithful reproductions of the 60 der 25,700 lbs./ . in. piston pressure. The mold
ings obtained are brilliantly clear and are faith
die cavity. Injection moldedstrips molded as
ful reproductions of the die cavity. Injection
above are found to “soften’? at 86° C. according
to the following method.
molded strips from the 2%“1: K" x 0.065" die
soften at 99° C. according to the softening te The strip 2%" x 1/2''' x 0.065" is mounted
perature
determination
described
under Exam
horizontally by one end in a clamp, cantilever 65 pie
1
"
.
.
fashion, the supported end sticking 14" into a
A similar methyl methacrylate polymer poly
vertical slot in the clamp so that the strip is sup
ported 34;" from the end. At a spot 1A" from the - merized as above but without the addition of
2-chloropropene and converted to molding powder
opposite end on the upper edge a weight of 27.5 g.
is placed so that it rests entirely on-the test strip 70 in the same manner yields injection molded test
strips which soften at 74° C. by the above deter
and is free to move up or down with the strip.
The assembly (excepting the weight) is immersed
in a bath of circulating mineral'oil which is uni
formly heated at a‘ steady rate of 2° C. per minute.‘
The “softening” temperature is observed-as that
mination.
Example II is repeated using
vof 2-chloropropene. When the
quantities
products are '
worked up and molded as above, injection molded
75 softening temperature specimens are obtained
3,403,490
.
5
6
It will be understood that the above examples
are merely illustrative and that the present in
vention comprises, in its broader. aspects, the
whose softening temperatures
to the
method decribed under Example I are as follows:
polymerization of monomeric, methyl methac
.
soitcnlngtemnew 5 rylate
in the presence of small amounts of any
unsymmetrical aipha-ole?nic compound in which
w“ ° mm‘
'
Oonoentrationoi
methyl mstbm
(baled
mine!) on
gl?jflsd‘lp?w?
one of the carbon atoms of ‘the double bond
carries a single halogen atom‘, to obtain a prod
uct especlally'suited for injection and compres
' c.
10
:1 (blank for control) ...................... --
‘a:
.i "f, ........................................ -_
w
so
'
sion molding.
unsymmetrical alpha-ele?nic compound as here-'
in de?ned. The structure and constitution of
the rest of the molecule of the halo-ole?n is rela
w
mam-l III
(0)
tively immaterial as long as it does not contain
chromophoric structures which would impart
is-
A polymerization is carried out using the follow
ing ingredients:
Distilled water
'
The invention contemplates the use of any
color to the product or functional groups that
inhibit the polymerization of methyl methac
rylate. In order to avoid the cumbersome and
Parts
4800
Na:HPO4.l2HaO _____________________ ..
56 20
impractical use of gaseous modi?ers, it is pre
ferred to employ halo-ole?ns of molecular weight
above 70 and chloro-ole?ns are preferred.
Compounds which are closely related chemi
((1))
Parts
cally to the herein speci?ed halo-ole?ns but
Methyl methacrylate monomer__________ __ 2772
which do not fall within the speci?c de?nition
1-Chloro-3-hydroxypropene-1 __________ __
28 25 of being unsymmetrical alpha-ole?nic com
1% Aqueous solution of the 65% sodium salt
of polymethacrylic acid ________ m _____ .._
(c)
600
Parts
Benzoyl peroxide
__-_
pounds in which one of the carbon atoms of the
double bond also carries a single halogen atom,
7
fail to produce signi?cant improvements in
The above ingredients are polymerized accord 3“ methyl methacrylate polymers. Thus if the
ing to the general method described in Example
process of Example II is ‘repeated using small
I. ' The bulk of the polymerization takes place at
a temperature of 121° C. under a pressure of 48
‘ concentrations
of
other
chlorine
containing
compounds closely related to 2-chloropropene,
trichloroethylene, etc., the following results are
is worked up and injection molded according to
the general me od described in Example I, poly 35 obtained:
granular polymer
mer delivered from the heating cylinder at 220°
C. is readily injection molded into specimens of
excellent appearance under a piston pressure of
23,300 lbs/sq. in. Aspecimen 2%" x 1b" x 0.065"
is found to soften at 87° according to the method
described in Example I. A correspondingun
modi?ed control polymer softens at 74° C.
Exmnl IV
The following solutions are made up:
(a)
~
,
Softening tempera
ture of injection
moldedspecimen
2%”x%’ X0065”
Concentration of modi?er
(based on methyl methacrylate monomer)
40
'
I
.0% (blank ior control) ...................... _.
.507 tetrachloroethylene __________ __
.15‘?a
dlcbloroethylene.
4% symmetrical
symmetrical dichioroethylenen
2
as’;
_
carbon tetrachloride ...... .
Parts
Distilled water_________________________-- 4800
NamPOamHsO __._ ____________________ __
56
1% Aqueous solution of the 65% sodium salt
of polymethacrylic acid. ____________ _._.__
(12)
600
Parts
Methyl methacrylate monomer_________ ..._.. 2772
Methyl alpha-chloracrylate monomer ____ __
28
In general, the use of the speci?c halogenated
50 ole?ns de?ned above as modi?ers for methyl
methacrylate according to this invention leads
to polymers that show superior heat resistance
in injection molded specimens. However, the
concentration of the particular halogenated ole
on the properties
Parts 55 ?n has an important bearing
and equivalent e?ects are '
of
the
molded
product,
Benzoyl peroxide
7
obtained with different concentrations for each
The above ingredients are polymerized in the
speci?c halogenated ole?n. This is obvious in
general manner described in Example 1. During
view of the differences in activity of the various
the exothermic polymerization reaction the bulk e0 modi?ers contemplated and their di?ering rela
of the polymerization takes place at a temperative molecular weights. In general, the concen
ture of 126° C. under a pressure of 55 lbs./sq. in.
tration of speci?c halogenated ole?n required is
when the resulting granular polymer is worked '
greater the higher the molecular weight of the
up and injection molded, polymer delivered from
speci?c halogenated ole?n. But only relatively
the heating cylinder into the injection die at 200° 65 small amounts of the modi?ers de?ned above
- C. molds readily under a piston pressure of 23,300
are required, and the present invention contem
lbs/sq. in. An injection molded specimen
plates the use of these modifiers in concentra
21/2" x 9611' x 0.065" is ‘found to soften at 89° C.
tions only up to about 3% by weight of the methyl
according to the softening temperature determi
methacrylate monomer. Particularly with very
nation described under Example I.
70 active modi?ers, concentrations as low as 0.01%
The above example is repeated using 2% of
produce signi?cant improvements.
methyl alpha-chloracrylate monomer (based on
It is preferredto carry out the present inven
tion by polymerizing methyl methacrylate com- _
' methyl methacrylate monomer) instead of 1%
and an injection molded specimen 21/2" x Vi" x
positions'while dispersed in a non-solvent such
0.065" is found to soften at 95° C. as compared 75 as water. Temperatures of polymerization may
to 74° C. for an unmodi?ed control.
(c)
2,408,426
7
8
be from 100° 0. up to temperatures of 150° C. or
higher, with a temperature oi.’ at least 125' C.
size may be used on products oi’ the present in
vention.
-
preferred, in closed reaction equipment suitably
designed to withstand the autogenous pres-
Plasticizers or lubricants may be added to the
products of this invention either during poly
sures developed. As the reaction temperature is 5 merization as in Example I or during subsequent
increased,_ the‘concentration ot benzoyl peroxide
mastication of the polymer 'on heated rolls. Suit
about 1%, (based on methyl methaerylate monomer) at 100° C. to 0.5% in the range of 110° C.
similar manner for imparting special appearance
concentration is further decreased, and at temperatures of 150° C. and above the catalyst may
articles by the known methods of compression
or, injection molding commonly used for shaping
eil'ects to the polymer.
to 115° C. and to 0.25% in the range of 120° C. 10
The products of this invention are useful as
to 130° 0. Above this temperature the catalyst
molding powders for the preparation oi’ valuable
.8 catalyst concentration is selected which yields 15 processloi’ injection molding, the products of this
tion for optimum molding properties.
Catalysts other than benzoyl Peroxide are
used in corresponding amounts- V'I'hus didodecyl‘
ously known methyl methaerylate polymers in‘
‘that the molded articles show a much greater
resistance to distortion by heat while at the
peroxide, diethyl peronide, hydrogen peroxide, 20 same time being optically horn
and free
and similar‘/ catafrom discoloration. The products of this inven
~
persuli'uric
and its
salts,
lysts
may beacid
suitably
used.
The use of dispersants such as the 65% sodium
rods.
'
‘
salt of polymethacrylic acid is‘ optional. The
As many apparently widely diirerent embodi
amount required generally varies in inverse ratio 25 ni'ents of this invention may be made without
to the effectiveness of agitation during polymerdeparting from the spirit and scope thereof, it is
ization. The amount and eifectiveness of the disto be understood that the invention is not lim
persant selected, if any.>is preferably so limited
ited to the speci?c embodiments thereof except a
as to prevent the formation ofa permanent sus, as de?ned in the appended claims. _
pension and merely suincient to keep droplets 30 ,I claim:v
‘
_
of the methyl methacrylate compositions‘ from
coalescing during polymerization. The water
1. Process of preparing a modi?ed methyl
methacrylate omposition which comprises poly
dispersant is the most effective. A pH of less 35 3.0% by weight of the monomer of trichloroethyl;
than 4 or above 10 is generally to be avoided
because of the tendency of methyl methacrylate
ene at a temperature 01 100? C.-150° C. under .
autog'enous pressure.
-
monomer to hydrolyze under these conditions.
2. A modi?ed methyl 'methacrylate molding
The products of this invention can also‘ be precomposition adapted to be molded into articles
pared by other methods of polymerization, such 40 having a high resistance to distortion by heat
Any of the customary methods for converting
weight of the monomer of trichloroethylene while
granular I thermoplastic polymers to injection
dispersed in water, said polymerimtion being car
molding compositions such as by masticatingon a ried out at. a temperature oi’ 100° C.-150° C. under
heated rolls or by --= w - 1 thrzmgh a screw stutter
followed vby cooling and chopping to convenient
autogenous ‘pressure.
s
FREDERICK L-JOHNSTON.
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