Note: Descriptions are shown in the official language in which they were submitted.
lOB~90 8-CH-2268
This invention relates to an improved process
of preparing higher molecular weight branched copoly(alkylene
terephthalates). More particularly, it provides an improved
procedure for the solid state polymerization of branched
copoly(alkylene terephthalates) of high melt viscosity in
shorter reaction times by adding a minor amount of aromatic
(poly-) or (copoly-) carbonate to the polymer before heating
the solid in an inert atmosphere.
Articles manufactured from poly(al~ylene
terephthalates) have many valuable characteristics, including
strength, toughness, solvent resistance, high gloss, and
the like. These articles may be fabricated by a number
of well known techniques, including injection molding, roto
molding, blow molding, extrusion, and the like, depending
on the shape of the desired product.
Certain of these techniques, in particular, blow
molding and extrusion, require that the molten poly(alkylene
terephthalate) have a suitably high melt viscosity, e.g.,
in excess of 10,000 poises, to prevent collapse or blow-
outs in the soft preformed state. It has been found that
poly(alkylene terephthalates) of such high melt viscosity
are obtained only with great difficulty in the conventional
bulk melt polymerization processes generally used to prepare
the polyester.
It is easier to achieve high melt viscosities if
a small amount of a tri- or higher functional ester-forming
branching component is included in the polyester, and still
easier if the branched copolyester is subjected to solid
state polymerization, i.e., heating particles of the resin
at a temperature of above 150C. and below the sticking
point of the particles, in an inert atmosphere or under a
vacuum.
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It has now been discovered that branched
copoly(alkylene terephthalates) of high melt viscosity
can be obtained in reduced reaction period if a small
amount of an aromatic (poly-) or (copoly-)carbonate resin,
e.g., a bisphenol-A (poly-)-carbonate, or a bisphenol-A/
tetrabromobisphenol-A (copoly-)carbonate, is intimately
; blended with the branched copolyester before solid state
polymerization.
The amounts of added aromatic (poly-) or
(copoly-)-carbonate can have a similar effect in different
degrees. Low concentrations, e.g., 0.1 to 5 percent by
weight, have a minimum effect on product properties, while
larger concentrations, e.g., up to 15 or even 20 percent
by weight, in addition to reducing the reaction time, lead
to interesting and important products of lower crystallinity,
higher impact strength and increased flexibility.
According to the present invention, there is
provided an improved method for the preparation of a high
melt viscosity branched copoly(alkylene terephthalate) and
from 0.01 to 3 mole percent, based on the terephthalate
units, of units of a branching component which contains at
least three ester-forming groups, said branched polyester
having a melt viscosity of greater than about 10,000 poises,
said process comprising:
(a) forming an intimate blend of a corresponding,
normally solid branched copolyester having a melt viscosity
of below about 3,000 poises and from 0.1 to 5.0 percent by
weight of an aromatic tpoly-) or a (copoly-) carbonate resin
and transforming said blend into a solid particulate st~;~te;
and
(b) heating the particles of solid branched
copolyester-aromatic (poly~-) or (copoly-)carbon~te blend
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at a temperature of above 150C. and below the melting point of
said polyester in the presence of an inert gas until the desired
degree of increase in melt viscosity is obtained.
The melt viscosity is determined under the conditions
specified in the example. Typically, a "high melt viscosity"
resin is of greater than about 7,~00 poises and generally in
excess of about 10,000 poises at 250C. A specific polyester
according to this invention is one having an melt viscosity of
greater than 15,000 poises.
The polyester resins with which this invention is
concerned are, in general, saturated condensation products of
C2-C10 glycols, e.g., ethylene glycol, propylene glycol, ~~
butanediol-1,4, hexanediol-1,6, decanediol-l,10, cyclohexane-1,4-
dimethanol, and the like, and terephthalic acid, or reactive
derivatives thereof, e.g., dimethyl terephthalate. In addition
to the terephthalic acid units, other dicarboxylic acid units,
such as adipic, naphthalene dicarboxylic, isophthalic and
orthophthalic units may be present in small amounts, e.g.,
from about 0.5 to about 15 mole percent of the total acid units.
The branched high melt viscosity poly(alkylene
terephthalate) resins include a small amount of a branching
component containing at least three ester-forming groups.
The branching component can be one which provides branching
in the acid unit portion of the polyester, or in the glycol
unit portion, or it can be a hybrid. Illustrative of such
branching components are tri- or tetracarboxylic acids,
such as trimesic acid, pyromellitic acid, and lower alkyl
esters thereof, and the like, or preferably, polyols, and
especially preferably, tetrols, such as pentaerythritol;
triols, such as trimethylolprophane; or dihydroxy
carboxylic acids and hydroxydicarboxylic acids and
derivatives, such as dimethyl hydroxyterephthalate, and the
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` like.
- The branched copolyesters are used as starting
materials because the final properties are far better than
linear polyesters for a broad number of uses where high melt
strength is important. Moreover, such branched materials
reach a higher melt viscosity more rapidly than the
unbranched materials when used in solid state processes.
The relative amount of branching component can vary,
but is always kept at a minor proportion, e.g., of up to 5
mole percent maximum, for every 100 moles of the
- terephthalate units in the branched polyester. Preferably,
the range of branching component included in the
esterification mixture (and, generally, that included in
the starting material), will be from 0.01 to 3 mole percent,
based on the terephthalate units. Especially preferably,
it will comprise from about 0.02 to about 1 mole percent,
based on the terephthalate component. -
Processes for preparing the branched polyester
starting materials used in this process are well known to
those skilled in the art. The description in U.S.
3,692,744 - dated September 19, 1972 - Domba is helpful.
The general procedure for making the starting
resins is a condensation in the melt state, using an excess
of the alkanediol to the dial~yl terephthalate or
terephthalic acid and the desired branching component. Heat
(250 to 260C.) and high vacuum (0.2 to 1.0 mm Hg) are
used for a long enough time, e.g., 3 to 12 hours, to build
the molecular weight by eliminating volatile byproducts.
It has been found that the resin used as starting material
in this solid state process should be predominantly hydroxy
terminated. It will be normally solid. The melt viscosity
will be below about 3,000 poises, typically 1,000 to 2,000
-~ poises.
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A variety of aromatic (poly-) and (copoly-)
carbonates are suitable. These are well known to those skilled
in this art. They will be resins of the general formula:
o
H ~ ORO - C -~-- OROH
wherein R is a divalent aromatic radical, mono or poly-
nuclear, like in the case of homopolymers and unlike in the
case of copolymers, and n is of such a value as to cause
the resin to be normally solid. Especially suitable is a `
bisphenol-A (copoly-) carbonate which can be made in known
ways, e.g., by condensing bisphenol-A or a mixture of
bisphenol-A and tetrabromobisphenol-A and phosgene. Such
resins are also available from several commercial sources.
As has been mentioned above, the amount used can vary from
about 0.1 to 20 percent by weight, preferably 0.5 to 2 percent by
weight, based on the combined weights of the aromatic poly-
carbonate and the branched copolyesters. Also suitable are
halo-substituted bisphenol-A polycarbonates.
The process of this invention is carried out in
two steps, first, making an intimate blend of the branched
polyester and the aromatic polycarbonate, e.g., by
co-extrusion, milling, intensive mixing, etc., and then
transforming the polyester-polycarbonate blend to a solid
particulate state and, second, heating the particles until
the desired degree of increase in melt viscosity is obtained.
Experiments have shown that pellets, e.g~,
extruded and chopped cubes, cylinders, spheres, irregular
shapes, and the like, of up to 1/4 inch maximum dimension,
react in the solid state as well as the ground polymer, in
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the long run. However, to obtain a more homogeneous polymer
when using branched polyesters, grinding of the feed is preferable.
It is convenient to grind the feed e.g., by passing it through
a mill with dry ice cooling, using a coarse screen.
Alternately, extruded pellets may be heated in a stream
of hot inert gas containing a modifying amount of diol correspond-
ing to the diol incorporated in the polyester. See, U.S.
Patent 3,953,404, dated April 27, 1976, Borman.
With respect to the heating stage, experiments
have shown that solid state polymerization proceeds readily
at temperatures above about 150C. The rate is especially rapid
at 200C. or 210C., and measurably slower at 150C. or 160C.
Heating can be carried out between 150C and 210C. The most
preferred temperature range is between 180C. and 210C. and
especially between 190C. and 210C.
The preferred inert gas is nitrogen, although
if desired, argon, helium, carbon dioxide, or mixtures
thereof with or without nitrogen may be employed. Up to
3,000 ppm of 1,4-butanediol may be added to the inert gas
(no poly(l,4-butylene terephthalate) is used) to moderate
the polymerization in order to obtain a more homogeneous
product.
The particles can be in a fixed or fluidized
bed during the heating step. The particles can be agitated
in any conventional manner, if desired. A fluidizing
stream of nitrogen can provide agitation, removal of
volatiles and an inert atmosphere.
The time required for step (b) of the process can
vary, depending on the temperature, the amount of aromatic
polycarbonate resin in the particles and the melt viscosity
desired. In general, it will be between about 1/2 hour and
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several days, e.g., up to 96 hours, or longer. In any
event, however, the time will be measurably shorter than
required with particles which do not contain any of the
aromatic polycarbonate.
The polyester products of this invention can be
combined with conventional additives, such as reinforcements,
stabilizers, antioxidants, plasticizers, lubricity promoters,
dyes, pigments, flame retardant additives, and the like.
The products are useful for all fabricating purposes, but
especially so for blow molding and extrusion and for foam
fabrication purposes.
The following non-limiting examples illustrate
the process of this invention.
A branched polyester is prepared from 1, 4-
butanediol and dimethylterephthalate, with the addition of
0.215 mole percent pentaerythritol. The melt viscosity is
1,700 poises (as measured at 250C. in a capillary
rheometer as described in ASTM D-1238).
A portion of the polyester is co-extruded with
1 percent by weight of a bisphenol-A polycarbonate resin
(General Electric Company LEXAN 140 powder) and the
extrudate is chopped into 1/8 inch cubes. The cubes are
set in fluidized motion and heated in an apparatus for solid
state polymerization at 207C. in an atmosphere of nitrogen
containing 1,400 ppm of 1, 4-butanediol. The pelletized
product which initially has a melt viscosity of 2,400
poises after solid state polymerization for 2 hours and
40 minutes reaches a melt viscosity of 56,900, which is
eminently suitable for blow molding, and similar
fabrication techniques. For comparison purposes, the solid
state polymerization is repeated on a branched copolyester
without any aromatic polycarbonate resin being added thereto.
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In this case, even after 13 hours of reaction time, the
melt viscosity has increased to only 41,400 poises
from a starting viscosity of 1,700 poises.
The branched copolyester of Example 1 is extruded
with 5 percent of the polycarbonate powder and pelletized
When subjected to the solid state polymerization process,
the melt viscosity increases from 5,700 poises to 49,300
poises in 1 hour and 15 minutes.
A branched polyester of the type used in Example
1 is extruded with 1 percent polycarbonate resin ~LEXAN 140)
and heated to 202 to 205C. in a fluidized bed in a nitrogen
stream containing 1,340 ppm of butanediol vapor. The melt
viscosity increases from 1,650 poises to 42,800 poises in
3-1/4 hours. When this example is repeated using pure N2,
free from added butanediol vapor, the melt viscosity
increases to 43,500 poises in 3 hours, but the product is
less homogeneous, resulting in greater surface roughness of
an extruded strand.
For comparison purposes, a branched copolyester
similar to the product used in Example 1, but with an initial
melt viscosity of 1,400 poises, is heated in a fluidized
bed solid state polymerization apparatus at 205 C. for 6
hours and 30 minutes. The fluidizing nitrogen gas contains
1,470 ppm 1,4-butanediol vapor. The melt viscosity of the
polymer increases t~ 16,400 poises.
The procedure of Example 1 is repeated,
substituting for the bisphenol-A (poly-)carbonate, a 1:
1 bisphenol-A/tetrabromobisphenol-A (copoly-)carbonate
prepared by a modified procedure according to A.D. Wambach,
U.S. 3,915,926 - dated October 28, 1975. Substantially
the same results are obtained.
Obviously, other modifications and variations of
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the present invention are possible in the light of the
above teachings. For example, instead of pentaerythritol
as a branching component, there can be substituted
trimethylolpropane and trimethyl trimesate. Instead of
bisphenol-A polycarbonate resin, a hydroquinone polycarbonate
or a tetrabromobisphenol-A polycarbonate resin can be used.
It is, therefore, to be understood that changes may be
made in the particular embodiment described which will be
within the full intended scope of the invention as defined
by the appended claims.
