Reinforced polyester compositions and method of making same

This invention relates to a method of preparing a reinforced polyester composition comprising the steps of: I. mixing PA1 (a) at least one cyclic ester oligomer selected from the group consisting of ethylene terephthalate and cyclohexylenedimethylene terephthalate, PA1 (b) an organic initiator comprising one to five hydroxy groups which are capable of opening the cyclic ester rings, PA1 (c) a catalyst, and PA1 (d) a reinforcing material, II. heating the mixture of I at a temperature ranging from 270.degree. C. to 320.degree. C.

FIELD OF THE INVENTION 
This invention relates to a method of preparing reinforced polyester 
compositions by thermal, ring-opening polymerization of cyclic ester 
oligomers in the presence of various catalysts, initiator(s), and 
reinforcing materials. The method is useful in preparing the compositions 
of the invention which have advanced mechanical properties. 
BACKGROUND OF THE INVENTION 
The method of this invention is useful for the preparation of reinforced 
polyester compositions. There is a continuing need in various industrial 
arts for improved reinforced polyester compositions which are useful as 
composites. Composites are those materials formed by mixing extremely 
strong and stiff fibers in a polymer resin matrix or binder. The materials 
in this class have advanced mechanical properties. The fibers that 
dominate the field of advanced composites are, in order of chronological 
developmental, glass, boron on a tungsten filament core, graphite or 
carbon, and aromatic polyamides. They possess the desirable properties of 
low density and extremely high strengths and moduli. 
It is well known to those skilled in the art that composites are difficult 
to prepare from high molecular weight polymers because it is difficult to 
get adequate "wetting" or flow of the high molecular weight polymer into 
the reinforcing material. It is a distinct advantage, therefore, to have a 
low molecular weight/low melt viscosity material (such as cyclic ester 
oligomers) which can be melted, flowed into the reinforcing material, and, 
subsequently, polymerized to attain high molecular weight and good 
toughness. 
Composites based on cyclic polymers having high molecular weights, such as 
polycarbonates, polyetherimides, polyarylates, and polyketones, are known 
in the art as reported in the Newsletter of High Performance, entitled 
Advanced Materials, Vol. 11, No. 16, Sep. 25, 1989. 
Also, the superior improved moldability and improved properties of a molded 
article obtained by reinforcing poly(alkylene terephthalate) resins such 
as poly(ethylene terephthalate) (PET) and poly(cyclohexylene dimethylene 
terephthalate) (PCT) has long been established (see e.g., U.S. Pat. No. 
3,814,725). 
The relationship between high molecular weight and high melt viscosity is 
well established. See Flow Properties of Polymer Melts, 2d Ed., published 
in 1981 by J. A. Brydson, pp. 67-69. Compositions having high molecular 
weights such as those known in the art are expected to have a high melt 
viscosity. 
As described previously, a low melt viscosity is required in the 
preparation of the compositions of this invention in order to get adequate 
"wetting" or flow of the polymer into the reinforcing material. 
In J. Am. Chem. Soc., 112, pages 2399-2402, entitled "Remarkably Selective 
Formation of Macrocyclic Aromatic Carbonates: Versatile New Intermediates 
for the Synthesis of Aromatic Polycarbonates" (1990), the role of cyclic 
oligomers as intermediates in the preparation of aromatic polycarbonates 
is described. The journal article also describes the commercial importance 
of the use of ring-opening polymerization in the preparation of 
polyamides, aliphatic polyesters, silicones, and epoxide thermosets in the 
absence of reinforcing material. 
Also, it is known in the art to polymerize cyclic oligomers of ethylene 
terephthalate in the absence of reinforcing material. Japanese Patent 
Publication 48-33277 (Publication Date: Oct. 12, 1973) to Nihon Ester KK, 
and Polymer, Volume 1, pages 384-396 (1960). However, the prior art does 
not show the combination of oligomers with reinforcing materials to attain 
good wetting prior to polymerization. 
SUMMARY OF THE INVENTION 
The problems noted above with known methods of preparing reinforced 
polyester compositions of the art are overcome with the method of 
preparing a reinforced polyester composition comprising the steps of: 
I. mixing 
(a) at least one cyclic ester oligomer selected from the group consisting 
of ethylene terephthalate and cyclohexylenedimethylene terephthalate, 
(b) an organic initiator comprising one to five hydroxy groups which are 
capable of opening the cyclic ester rings, 
(c) a catalyst, and 
(d) a reinforcing material, and 
II. heating the mixture of I at a temperature ranging from about 
270.degree. C. to about 320.degree. C. 
Moreover, the invention provides compositions which comprise: 
(a) a thermoplastic polyester prepared by ring opening polymerization of a 
cyclic ester oligomer selected from the group consisting of ethylene 
terephthalate and cyclohexylenedimethylene terephthalate; and 
(b) a reinforcing material. 
The compositions and methods of the invention are useful for the 
preparation of molded articles, and for a variety of other industrial 
uses, such as making machine parts, sports equipment. 
The advantages of the compositions and methods of the invention reside in 
the fact that a low molecular weight/low melt viscosity oligomer can be 
melted, then flowed into the reinforcing material, and, subsequently, 
polymerized to attain high molecular weight and good toughness. The 
invention also provides the advantage of improved surface smoothness of 
molded objects. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention provides a method of preparing a reinforced polyester 
composition comprising the steps of: 
I. mixing 
(a) at least one cyclic ester oligomer selected from the group consisting 
of ethylene terephthalate and cyclohexylenedimethylene terephthalate. 
Component (a) is preferred to be a substance consisting essentially of at 
least one cyclic ester oligomer selected from the group consisting of 
ethylene terephthalate and cyclohexylenedimethylene terephthalate. 
Oligomers are defined for the purposes of this invention as low molecular 
weight polymers that have at least 2 repeating units, but not more than 25 
repeating units. A "cyclic" structure for purposes of this invention is 
defined as a structure which has no terminal groups or a structure which 
is essentially ring-like. 
These oligomers are selected from the group consisting of ethylene 
terephthalate and cyclohexylenedimethylene terephthalate. 
The cyclic ester oligomers of ethylene terephthalate may be obtained by 
extraction of the high molecular weight polymer for several hours with a 
solvent such as methylene chloride, filtering away the high molecular 
weight polymer so that the high molecular weight polymer is left in solid 
form and the low molecular weight polymer is liquefied. Then the methylene 
chloride solution is concentrated, and the product is dried. The product 
obtained is an oligomeric mixture containing a majority of cyclic trimer 
of ethylene terephthalate plus other cyclic species (such as tetramer, 
pentamer, etc.), bis(2-hydroxyethyl terephthalate), and other linear, low 
molecular weight polymeric species. An alternate method of obtaining the 
cyclic oligomers of ethylene terephthalate is described in Japanese Kokai 
Patent Gazette (A) 01-275-575 Application Date: 28 Apr. 1988) to Toyobo 
Company, Ltd. The method involves the preparation of polyethylene 
terephthalate having a high degree of polymerization (DP) from cyclic 
ethylene terephthalate. The cyclic oligomers of cyclohexylenedimethylene 
terephthalate may be prepared from, preferably, 0.15-0.40 inherent 
viscosity, 50% cis poly(1,3- or 1,4-cyclohexylenedimethylene 
terephthalate) by a cyclodepolymerization reaction. Cyclodepolymerization 
is defined as depolymerization of a linear polymer to form cyclic oligomer 
species. 
This cyclodepolymerization reaction involves refluxing a 2-3 w/v % solution 
of the 50% cis poly(1,3- or 1,4-cyclohexylenedimethylene terephthalate) in 
a solvent such as 1,2,4-trichlorobenzene containing 100-200 ppm titanium 
tetraisopropoxide for several days and cooling the reaction mixture to 
room temperature. The mixture is then filtered to remove high molecular 
weight polymer, and the 1,2,4-trichlorobenzene is removed by distillation. 
The waxy mixture comprising the cyclic oligomers is then washed with warm 
methanol to minimize the residual cyclohexanedimethanol, filtered, and 
dried; 
(b) an organic initiator comprising a compound containing one to five 
hydroxy groups which are capable of opening the cyclic ester; this opening 
of the cyclic ester is accomplished by alcoholysis. 
Particularly preferred organic initiators are ones comprising from one to 
three hydroxy groups. Even more preferred organic initiators are ones 
comprising two hydroxy groups. 
Examples of hydroxy compounds containing two hydroxyl groups per mole which 
may be used to prepare the new compositions of the invention include 
ethylene glycol, hexanediol, 1,4-cyclohexanedimethanol (cis or trans), 
1,3-cyclohexanedimethanol (cis or trans), the monomer of poly(ethylene 
terephthalate), sometimes called bis(2-hydroxyethyl)terephthalate, and 
various low molecular weight, linear, essentially hydroxy-terminated 
oligomers derived from poly(ethylene terephthalate), or other polymeric 
material. 
The preferred organic initiator is bis(2-hydroxyethyl terephthalate), or a 
mixture of bis(2-hydroxyethyl terephthalate) with other slightly higher 
molecular weight species which are substantially terminated with hydroxyl 
groups. 
The initiator is not always required to be added in order to successfully 
prepare the composites of the invention. This is true because there are 
times the initiator is already present in the polymer sample from which 
the oligomers are separated. Also, the amount of hydroxyl-containing 
species which may act as an initiator will vary from one lot of cyclic 
monomers to another. The optimum amount of initiator, therefore, must be 
determined for a particular lot of monomer. In general, the amount of 
initiator added will vary up to 5-6 mole % (assuming two hydroxyls per 
molecule), depending on the volatility of the initiator and the amount of 
hydroxyl-containing species present in the cyclic oligomers; 
(c) a catalyst in the presence of a reinforcing material; catalysts which 
may be used to prepare the compositions of the invention comprise one or 
more species selected from the group of catalysts known to be effective in 
esterification reactions, such as organic acid salts, carbonates, 
alcoholates, and oxides of metals such as zinc, manganese, cobalt, 
titanium, lead, and antimony. 
Preferred catalysts are titanium, lead, and antimony. Even more preferred 
catalysts are titanium and antimony. 
The amount of these catalysts required to be present will vary, depending 
on the temperatures at which the composition is being prepared, the 
thermal stabilities of the cyclic ester oligomer(s) and the composition 
product in the presence of the catalyst, the catalyst specie(s) being 
used, the rate of polymerization desired, and the acceptable level of 
residual cyclic oligomer in the composition. 
In general, as the amount of catalyst increases, the polymerization rate 
increases, the amount of residual cyclic oligomer decreases, and the 
thermal stability decreases. Useful catalyst levels include 50-5000 ppm 
(based on the metal), but the preferred range for titanium is about 
100-400 ppm, and the preferred range for antimony is about 400-2000 ppm; 
and 
(d) a reinforcing material, such as those described above for the 
compositions of the invention. Reinforcing materials which may be used to 
prepare the new thermoplastic compositions of the invention include 
unidirectional fibers or tows or woven fabrics of glass fiber, carbon 
fiber, boron fiber, and ceramic fiber. Glass fibers are preferred since 
they are less expensive to obtain. 
The glass fibers suitable for use in the present invention may be in the 
form of glass filaments, threads, fibers, or whiskers, etc. and may be 
vary in length from about 1/8 to continuous length with a diameter from 
about 5-50 microns. Glass filaments or threads in the form of ribbons or 
fabrics are preferred. The glass fibers are commercially available and are 
well known in the art. 
Carbon fibers are also preferred due to the increase in the tensile and 
stiffness properties of the composite formed. 
Preferably, the amount of fibers which are present in the composition is 
from about 15-65% by weight. More preferably, the amount of fibers should 
be from about 15-50% by weight of the composition. 
In addition to the reinforcing materials, the composition of this invention 
may also contain other fillers and additives such as mica, talc, flame 
retardants, stabilizers, and other processing aids and colorants. 
Also, the compositions of this invention may contain additives commonly 
employed with polyester resins, such as mold release agents, antioxidants, 
tougheners and nucleating agents. 
The reinforcing materials may be, optionally, treated or coated with 
materials which promote adhesion of the thermoplastic polyester matrix to 
the reinforcing material. 
In Step I, items (a)-(d) do not have to be mixed sequentially in the 
context of this invention. Also, Step II should follow Step I. However, it 
is possible for items (a)-(c) to be rapidly mixed and melted before being 
transferred into a mold. 
Further, the compositions of the invention are prepared by mixing the 
components together by any convenient means to obtain an intimate mixture, 
as long as polymerization of the cyclic oligomers does not occur before 
they can be made to flow into the reinforcing material. 
The method of the invention also includes step II which involves heating 
the mixture of Step I at a temperature ranging from about 270.degree. C. 
to about 320.degree. C.; 
Where the cyclic ester oligomers useful in the method described above are 
oligomers of ethylene terephthalate, the preferred temperature range is 
from about 300.degree. to about 320.degree. C. A more preferred 
temperature range is from about 300.degree. to about 310.degree. C. Where 
the cyclic ester oligomers useful in the method described above are 
oligomers of cyclohexylenedimethylene terephthalate, the preferred 
temperature range is from about 270.degree. to about 300.degree. C. A more 
preferred temperature range is from about 280.degree. to about 290.degree. 
C. 
The reinforced polyester compositions of the invention comprise: 
(a) a thermoplastic polyester prepared by ring opening polymerization of a 
cyclic ester oligomer selected from the group consisting of ethylene 
terephthalate and cyclohexylenedimethylene terephthalate; and 
(b) a reinforcing material. 
A thermoplastic polyester is defined herein as a polyester that is 
sensitive to heat. Even when the final form has been assumed by applying 
heat, the original material can be reformed. Thermoplastic materials 
soften upon heating without destruction of the polyester. It can then be 
pressed, molded, extruded or cast into a desired shape into which it 
solidifies upon cooling. The softening and hardening processes are 
relatively fast so that the article can be molded, hardened by cooling and 
ejected from the mold in a matter of seconds rather than minutes. 
The cyclic ester oligomers useful within the context of this invention have 
been described fully hereinabove. The reinforcing materials useful within 
the context of this invention have also been described fully hereinabove. 
Ring-opening polymerization is a term readily understood by one skilled in 
the art. For the purpose of this invention, ring-opening polymerization is 
defined as a polymerization in which a ring-like or cyclic monomer is 
opened catalytically and/or by means of an initiator to form a linear 
species which is capable of opening other monomer rings. As the rings are 
opened, they are effectively added to the growing polymer chain to 
increase its molecular weight. This reaction continues until most of the 
cyclic monomer has been used up or until the chain becomes terminated. 
The cyclic ester oligomer and the reinforcing material may be mixed in 
various ways to form the reinforced polyester composition as more fully 
described hereinafter. For example, the cyclic ester oligomer and the 
reinforcing material may be mixed before being introduced into a mold. 
They may be mixed by adding the cyclic ester oligomer to the reinforcing 
material which is already affixed into the mold. As stated previously, it 
is possible for items (a)-(c) to be rapidly mixed and melted before being 
transferred into a mold. 
Further, it is not necessary for the mixing of the cyclic ester oligomer 
and the reinforcing material to occur in a mold. They may be mixed outside 
of a mold, as long as the mixing does not cause premature polymerization. 
The reinforced polyester composition can be reheated and reformed. 
More particularly, the compositions may be prepared by several methods 
including single compression molding in which the reinforcing material is 
placed in the mold, the cyclic oligomer(s) containing the catalyst and 
initiator is spread over the reinforcing material, and the mold is closed 
and held at a sufficient temperature and time to cause polymerization of 
the cyclic ester oligomer. Other variations upon this procedure may also 
be used, such as by impregnating the reinforcing material (which had been 
earlier coated with the catalyst or the catalyst and the initiator) with 
the cyclic ester oligomer(s) by some method such as pultrusion and, 
subsequently, heating the composite (usually in a mold) at a temperature 
and time sufficient to effect polymerization.

The following examples are for illustrative purposes only, and not to limit 
the scope of the invention. All percentages are by weight, unless 
otherwise specified. 
EXAMPLE 1 
This example illustrates the preparation of a batch of cyclic oligomers 
derived from poly(ethylene terephthalate) containing bis(2-hydroxyethyl 
terephthalate) as an initiator and antimony catalyst. 
To a 2000-ml, single-necked flask are added 55 grams of cyclic oligomers 
{extracted from poly(ethylene terephthalate) with methylene chloride, 
concentrated to dryness with a rotary evaporator, and vacuum dried at 
140.degree. C. overnight} and 800 ml of methylene chloride and the mixture 
is magnetically stirred for about an hour. In a small bottle, 0.3638 gram 
(0.00143 mole) (1.5 mole %) of bis(2-hydroxyethyl terephthalate) (BHET) is 
dissolved in 25 ml of methanol, and the solution is added slowly to the 
stirred solution/suspension of oligomer in methylene chloride. Separately, 
0.080 gram (836 ppm Sb from antimony III ethylene glycoxide) is 
dissolved/suspended in 25 ml of methanol and is also slowly added to the 
stirred solution/suspension of oligomer in methylene chloride. The mixture 
(now containing cyclic oligomers, BHET, and antimony catalyst) is stirred 
for an additional 15 minutes, concentrated to dryness on a rotary 
evaporator, and vacuum dried at 140.degree. C. overnight. 
EXAMPLE 2 
This example illustrates the preparation of a glass-filled thermoplastic 
composite (50 wt % glass) from cyclic oligomers derived from poly(ethylene 
terephthalate) using bis(2-hydroxyethyl terephthalate) (BHET) as an 
initiator. 
A 2.5-in..times.2.5-in piece of unidirectional glass (Orcoweb Fiberglass 
S-500) weighing 1.32 grams is placed on a 20-mil, chrome-plated brass 
plate, a 10-mil shim (3-in..times.3-in. open space) is placed on the 
chrome-plated brass plate surrounding the glass fiber, and 1.32 grams of 
cyclic ester oligomer containing 1.5 mole % of added bis(2-hydroxyethyl 
terephthalate) and 836 ppm of antimony catalyst (prepared as described in 
Example 1) are spread over the glass fibers. A second chrome-plated brass 
plate is placed on top of the materials to complete the assembly, the 
corners of the assembly are clamped, and the assembly is placed on the 
lower platen of a Hannafin press preheated to 305.degree. C. After about 
10 seconds preheating of the assembly, the platens of the Hannafin press 
are closed, and the `sandwiched` assembly is held at 305.degree. C. for 20 
minutes. After being cooled below 250.degree. C., the assembly is opened 
and the composite is removed. The composite thus formed is tough and 
rigid. 
EXAMPLE 3 
This example illustrates the preparation of a carbon fiber-filled composite 
(42 wt % carbon) from cyclic oligomers derived from poly(ethylene 
terephthalate) using bis(2-hydroxyethyl terephthalate) (BHET) as an 
initiator. 
Example 2 is repeated except a 2-in..times.2-in. piece of carbon fabric 
(0.75 gram) (Gravitex fabric, 8 Harness Satin, from Courtaulds Advanced 
Materials, rinsed in methylene chloride and air dried) and 1.0 gram of 
cyclic ester oligomer, which is extracted as in Example I are used. The 
composite thus prepared is tough and rigid. 
EXAMPLE 4 
This example illustrates the preparation of a batch of cyclic oligomers 
derived from poly(ethylene terephthalate) containing 
cyclohexane-dimethanol (CHDM) as an initiator and antimony catalyst. 
To a 2000-ml, single-necked flask are added 75 grams of cyclic oligomers 
derived from poly(ethylene terephthalate) (obtained as described in 
Example 1) and 900 Ml of dry methanol, and the mixture is magnetically 
stirred at room temperature for about an hour. To the stirred mixture is 
added 0.4219 gram (0.00293 mole) 2.25 mole %) of 74% 
trans-1,4-cyclohexanedimethanol, and the mixture is stirred for an 
additional 30 minutes. Separately, 0.1090 gram (.about.836 ppm Sb from 
antimony III ethylene glycoxide) is dissolved/suspended in 30 ml of dry 
methanol and then slowly added to the previously-described, 
magnetically-stirred cyclic oligomers in methanol. After being stirred for 
an additional 15 minutes, the flask contents are concentrated to dryness 
with a rotary evaporator and vacuum dried at 100.degree. C./24 hours/0.5 
torr. 
EXAMPLE 5 
This example illustrates the preparation of a glass-filled thermoplastic 
composite (50 wt % glass) from cyclic oligomers derived from poly(ethylene 
terephthalate) using cyclohexanedimethanol as an initiator. 
Example 2 is repeated except the batch prepared in Example 4 is used. The 
composite obtained is tough and rigid. 
EXAMPLE 6 
This example illustrates the preparation of a glass-filled, thermoplastic 
composite from cyclic oligomers derived from 95% cis 
poly(1,4-cyclohexylenedimethylene terephthalate) and titanium catalyst. 
Cyclic oligomers of poly(cyclohexylene-dimethylene terephthalate) are 
obtained by the cyclodepolymerization of 0.25 I.V., 95% cis 
poly(1,4-cyclohexylenedimethylene terephthalate) in 1,2,4-trichlorobenzene 
in the presence of titanium tetraisopropoxide catalyst as generally 
described in the specification. A batch is then prepared from these cyclic 
oligomers and 200 ppm titanium (from tetraisopropoxide) by the general 
procedures described in Examples 1 and 4, except using dry isopropanol 
instead of methanol or methylene chloride. A tough, rigid thermoplastic 
composite is prepared in a Hannafin press (using the technique described 
in Example 2) at 285.degree. C. for 25 minutes by the procedure described 
in Example 2. 
As used herein, inherent viscosity (I.V.) is measured at 25.degree. C. 
using 0.50 g of polymer per 100 mL of a solvent consisting of 60% by 
weight phenol and 40% by weight tetrachloroethane. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention. Moreover, all patents, patent applications (published or 
unpublished, foreign or domestic), literature references or other 
publications noted above are incorporated herein by reference for any 
disclosure pertinent to the practice of this invention.