Method for making branched polyesters reproducibly

A method for preparing branched polyesters in melt or solid phase comprises reacting together diols, diacids and polyfunctional modifiers having at least three functional radicals to form a condensation polymer. This condensation polymer is polycondensed to form a polyester by linear extension and branching while correlating catalyst activity, reaction temperature and pressure to restrain the extent of reaction for linear extension to within about 0.1 percent of the extent of reaction for branching.

FIELD OF THE INVENTION 
This invention relates to a method of preparing branched polyesters. In 
particular, this invention provides a method of reproducing a branched 
polyester having a pre-selected combination of properties for a specific 
use. 
BACKGROUND OF THE INVENTION 
Polyesters can be modified during their preparation with polyfunctional 
modifiers to obtain branched polyesters having particular chemical or 
physical properties. These polyfunctional modifiers are also known as 
branching agents. These modifiers generally have different molecular 
weights, volatilities, chemical reactivities and other properties. In the 
prior art, when a polyester is modified with a polyfunctional modifier to 
form a branched polyester, it appears that no attempt is made to insure 
that all of the modifier reacts to the same degree each time a batch of 
polyester is made. As a result, the amount of modifier incorporated into 
the branched polyester varies from batch to batch. 
Branched polyesters are known to be useful in a variety of products. 
However, practical manufacture of branched polyesters has been hindered 
because it is difficult to consistently reproduce such polyesters from one 
batch to another using prior art methods. Prior art methods do produce 
ways for preparing branched polyesters having the same or similar inherent 
viscosities. However, branched polyesters having the same or similar 
inherent viscosities do not necessarily have the same physical or chemical 
properties. For example, I have observed that two branched polyesters 
which are prepared from the same materials and have the same inherent 
viscosity can have such different physical and chemical properties, due to 
different amounts of branching, that one polyester is suitable for use as 
a film support while the other is not. 
It is well known that the inherent viscosity actually measured for a 
branched polyester is really an "overall" inherent viscosity. Such 
"overall" viscosity is the sum of an inherent viscosity due to the linear 
portion of the polyester plus an inherent viscosity due to branched 
portions of the polyester. In a method for reproducibly preparing branched 
polyesters, the "overall" inherent viscosity at a given time in the 
preparation contains a component that is due solely to the branched 
portions of the polyester and is substantially the same from batch to 
batch at such given time. 
Methods for reproducibly preparing branched polyesters have eluded workers 
in the art because of the inherent difficulty encountered in controlling 
the competing rates of linear extension and branching during the formation 
of such branched polyesters. Typically, for polyesters useful as films or 
fibers, the rate of linear extension during polycondensation is 
significantly greater than the rate of branching. When polycondensation is 
carried out under conventional conditions, that is, under conditions which 
"drive" the reaction to completion, this difference in rates is so great 
that little or no branching occurs. In general, the prior art methods 
compensate for this effect by using high concentrations of polyfunctional 
compounds for preparing branched polyesters. However, the use of high 
concentrations of polyfunctional compounds often results in undesirable 
gelation or crosslinking of the polyester. 
Branched polyesters and methods for making them are known, as disclosed for 
example, in U.S. Pat. No. 3,576,773 (issued Apr. 27, 1971 to Vaginay) and 
British Pat. No. 1,027,613 (published Apr. 27, 1966). Typically, such 
methods use polyfunctional compounds which have three or more reactant 
functional radicals, such as hydroxyl and carboxyl radicals. These 
polyfunctional compounds are also known as branching agents. U.S. Pat. No. 
4,013,624 (issued Mar. 22, 1977 to Hoeschele) relates to the preparation 
of high molecular weight branched copolyesters using a "critical" 
concentration of branching agent. This reference suggests that use of this 
concentration provides high molecular weight polyesters in the shortest 
possible time. But like the rest of the prior art, it lacks any teaching 
or suggestion of controlling polycondensation conditions in order to 
prepare branched polyesters reproducibly. 
Hence, it would be desirable to have a method of preparing branched 
polyesters whereby one could practically reproduce branched polyesters 
having a pre-selected combination of properties. Further, it would be 
desirable to have such a method wherein the concentration of 
polyfunctional modifier would be varied in a wide range without fear of 
undesired gelation or crosslinking. 
SUMMARY OF THE INVENTION 
This invention provides a method for reproducible preparation of branched 
polyesters. This method enables one to avoid gelation or crosslinking in 
the preparation of a branched polyester even when a relatively high 
concentration of polyfunctional modifier is used. In general, this method 
involves controlling the competing rates of linear extension and branching 
which occur during polycondensation whereby the resulting branched 
polyesters have a desired amount of branching batch after batch. 
More specifically, the method of this invention allows a worker skilled in 
polymer chemistry to prepare a branched polyester having a pre-selected 
inherent viscosity and other physical and chemical properties batch after 
batch. 
In practicing the method of this invention, a condensation polymer is 
formed by reacting together a diol, a diacid and a polyfunctional modifier 
which has at least three functional radicals. This polymer is then 
polycondensed in the presence of a transesterification catalyst at a 
reaction temperature and reaction pressure effective to form a polyester 
by linear extension and branching. During polycondensation, the catalyst 
activity, temperature and pressure are correlated to restrain the extent 
of reaction for linear extension to within about 0.1 percent of the extent 
of reaction for branching.

In both figures, the term "theoretical" means that all functional groups of 
all reactants, including those on polyfunctional modifiers, react at the 
same rate at the indicated viscosity values. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In general, the practice of this invention comprises reacting together a 
diol, a diacid and a polyfunctional modifier to form a condensation 
polymer. Such materials are sometimes called polymer precursors. 
Conditions for condensation of such polymer precursors are known in the 
art. Typically, condensation occurs in the presence of a 
transesterification catalyst at a temperature in the range of from about 
125.degree. to about 300.degree. C. Reaction pressure is typically in the 
range of from about 0.1 mm Hg to about one or more atmospheres. 
Condensation is generally continued for from about 30 to about 300 minutes 
or until the polymer has an inherent viscosity in the range of from about 
0.4 to about 1.0. Unless otherwise stated herein, the inherent viscosities 
were determined in a mixture of 60:40 (percent, by weight) 
phenol:chlorobenzene at 25.degree. C. and a concentration of 0.25 grams 
polymer per deciliter of solution. Low-molecular weight by-products of 
condensation, such as water, alcohols, glycols, acids and esters, are 
removed during condensation by distillation or another standard technique. 
Generally, at least about 1.1 moles of diol are present for each mole of 
diacid, and preferably from about 1.3 to about 2 moles of diol are present 
for each mole of diacid. The concentration of polyfunctional modifier used 
in the reaction mixture is the concentration required to obtain a desired 
ratio of linearization to branching at a given inherent viscosity. This 
concentration can be conveniently determined by routine experimentation. 
Typically, such concentration is in the range of from about 0.001 to about 
10 molar percent, preferably from about 0.1 to about 5 molar percent, and 
more preferably from about 0.1 to about 1 molar percent, based on moles of 
diacid. The concentration of polyfunctional modifier used will, of course, 
depend upon the number of functional groups in the modifier molecule. In 
general, the more functional groups a modifier has, the less modifier is 
needed to achieve a desired amount of branching. As is understood in the 
art, the chemical and physical properties of resulting branched polyesters 
can be varied by the use of different concentrations of polyfunctional 
modifier. 
In practicing my invention, the polymer initially obtained from 
condensation of the polymer precursors is subsequently polycondensed to 
form a desired branched polyester. Polycondensation proceeds while 
correlating polycondensation conditions, i.e. catalyst activity, reaction 
temperature and reaction pressure, to restrain the extent of reaction for 
linear extension to within about 0.1 percent of the extent of reaction for 
branching. Preferably, the extent of reaction for linear extension is 
restrained to within about 0.05 percent of the extent of reaction for 
branching. Throughout this specification and in the claims, the term 
"correlating" means that one or more of the indicated polycondensation 
conditions are changed as required, to achieve an interrelationship among 
such conditions such that a restraint is placed upon the extent of 
reaction for the linear extension of polymer chains. 
As known and understood in the art, extent of reaction refers to the 
fraction of polymer precursor molecules which have undergone reaction at a 
particular time in the polymerization. In other words, extent of reaction 
is a measure of the extent of completion of polycondensation. Extent of 
reaction is generally referred to in the art as "p". 
Under conventional polycondensation conditions, the rate of linear 
extension is generally much greater than the rate of branching. It is 
believed that this difference in rates exists because the third and 
additional functional radicals on polyfunctional modifiers react more 
slowly than the first and second functional radicals on such modifiers or 
on bifunctional polymer precursors. Thus, control of polycondensation and 
the resulting reproducibility appear to depend upon slowing down the 
linear reaction so that the extent of reaction for linear extension at any 
given time during polycondensation is substantially equal to the extent of 
reaction for branching. That is, the extent of reaction for the linear 
extension is within about 0.1 percent of the extent of reaction for 
branching. 
The practice of my invention can be illustrated in the following manner: 
In the first step of the preparation, polymer precursors, including a 
polyfunctional modifier, such as pentaerythritol (at, e.g. 0.35 mole %), 
are reacted together to form a condensation polymer. Typical reaction 
conditions for this step are described herein. Condensation is completed 
when either a particular inherent viscosity is reached or condensation 
by-products are no longer being generated. 
Upon completion of the condensation reaction, the resulting condensation 
polymer is polycondensed to form a branched polyester. Instead of 
polycondensing under conventional conditions which "drive" the linear 
polycondensation reaction forward rapidly, polycondensation is carried out 
under conditions which restrain the linear reaction to an appropriate 
degree, as described herein. Such restraining conditions include a 
decrease in catalyst activity, a decrease in temperature, an increase in 
pressure or any combination of such changes. The particular conditions 
employed in a specific instance will depend upon the specific branched 
polyester desired. These conditions can be conveniently determined with a 
reasonable amount of routine experimentation. Polycondensation is 
continued until the resulting branched polyester has a desired inherent 
viscosity. 
When polycondensation is carried out under the described conditions whereby 
the rate of linear extension is substantially equal to the rate of 
branching, inherent viscosity can be plotted in graphical form as a 
function of extent of reaction. FIGS. 1 and 2 are examples of such 
graphical plots. These plots are prepared from standard equations which 
relate inherent viscosity to degree of polymerization and degree of 
polymerization to extent of reaction. The basis for use of these equations 
is an assumption that the functional groups on all polymer precursors for 
the branched polyester have equal reactivities. These equations and 
typical calculations using them are illustrated, for example, in Rafikov 
et al, "Determination of Molecular Weights and Polydispersity of High 
Polymers," 1964, Daniel Davey and Co., Inc., pp. 345-357; Gordon et al, 
Proc. Roy. Soc., 191, 380-402 (1966); Gordon et al, Trans Faraday Soc., 
60, 604-621 (1964); Luby, J. Polymer Sci.:Symposium No. 53, 23-28 (1975); 
Flory, "Principles of Polymer Chemistry," 1953, Cornell Univ. Press, 
Ithaca, N.Y., p. 260; Lenz, "Organic Chemistry of Synthetic High 
Polymers," 1967, Interscience Publishers, Chapter 3; and Maneresi et al, 
Polymer, 17, pp. 595-600 (1976). 
If an inherent viscosity is measured during the course of a 
polycondensation reaction in the practice of my invention, this measured, 
or "actual", inherent viscosity will be substantially equal (within 
.+-.0.04, and preferably within .+-.0.02 of each other) to a calculated, 
or "theoretical", inherent viscosity which can be determined by examining 
a graphical plot, such as in FIG. 1 or 2. 
The relationship between an "actual" inherent viscosity and a calculated 
"theoretical" inherent viscosity is useful in confirming that the rate of 
linear extension in polycondensation has been effectively restrained. This 
desired restraint occurs when the the extent of reaction for linear 
extension is within about 0.1 percent of the extent of reaction for 
branching. Thus, an extent of reaction is determined for the "actual" 
inherent viscosity during the course of polycondensation, e.g. after 1.0 
or 1.5 hours. This extent of reaction is determined from the appropriate 
graphical plot, e.g. FIG. 1 or 2. Using the same graphical plot, at the 
same extent of reaction, a "theoretical" inherent viscosity is determined 
for an unbranched polyester made under the same conditions as the 
corresponding branched polyester. This unbranched polyester is then 
prepared under those same conditions. After, for example, 1.0 or 1.5 hours 
of polycondensation, the "actual" inherent viscosity of the unbranched 
polyester is measured. If this "actual" inherent viscosity is 
substantially equal to the "theoretical" value for the same unbranched 
polyester, the relationships predicted by the graphical plots are true. By 
substantially equal, I mean the inherent viscosities are within .+-.0.04, 
preferably .+-.0.02, of each other, since this takes into account 
experimental error. 
Branched and unbranched polyesters can also be characterized by 
polydispersity. Polydispersity is a measure of molecular weight 
distribution for a polyester. It can be determined by standard techniques, 
including gel permeation chromatography. Gel permeation chromatography is 
described, for example, in Bannister et al, Analytical Chemistry, Vol. 26, 
No. 9, 1954, pp. 1451-1454. 
In brief the technique comprises passing a solution of polyester in a 
suitable solvent, such as N,N-dimethylformamide, through a tower packed 
with a molecular sieve type of absorption material. Polyester molecules 
are fractionated by being absorbed into the openings of the material in a 
distribution depending upon the sizes of the molecules. The smallest 
molecules are absorbed first whereas the largest molecules are absorbed 
last, or not at all. The number of molecules in each gradient of the 
column is measured and a number average (N.A.) is calculated. The 
molecular weights of the molecules in each gradient are measured by known 
methods, e.g. viscosity measurements, and a weight average (W.A.) is 
calculated. Polystyrene is used as a standard for comparison of its number 
average and weight average molecular weights with those obtained with the 
polyester being fractionated. The values for the polyester are then 
recorded as number average polystyrene equivalent molecular weight (N.A. 
PSEW) or weight average polystyrene equivalent molecular weight (W.A. 
PSEW). Polydispersity (PD) is then defined by the following equation: 
##EQU1## 
As known in the art, a polymer having a high weight average molecular 
weight and a low number average of different sized molecules will have a 
high polydispersity. Conversely, a polymer having the same high weight 
average molecular weight but a higher number average will have a lower 
polydispersity. Polydispersity can be used as a measure of the amount of 
branching in a polyester. Reproducibility is achieved if branched 
polyester polydispersity is substantially the same batch after batch with 
a branched polyester prepared under the same polycondensation conditions. 
If polydispersity varies significantly, say greater than .+-.1.0 (at a 
polydispersity up to 4.0), the extent of reaction for linear extension has 
not been sufficiently restrained to obtain reproducibility. At 
polydispersities greater than 4.0, reproducibility is achieved with 
variations greater than .+-.1.0. 
Theoretically, a random homopolyester has a polydispersity of 2.0. In 
general, the branched polyesters prepared by the method of this invention 
have polydispersities in the range of from about 3 to about 50. The 
polydispersity, of course, can vary with the particular polyester made and 
use contemplated. 
Branched polyesters are prepared by the method of this invention in the 
presence of one or more transesterification catalysts. Each catalyst can 
be characterized with both a second order rate constant per equivalent per 
liter at a given temperature and an energy of activation. For purposes of 
this invention, catalysts are also characterized as "highly reactive" or 
"poorly reactive". As used in this specification and in the claims, highly 
reactive catalysts are those having rate constants in the range of from 
about 0.1 to about 5, and preferably from about 0.5 to about 2.5 per 
equivalent-second at 190.degree. C. These catalysts also generally have 
energies of activation in the range of from about 5 to about 35, and 
preferably from about 10 to about 20 kcal/mole. Poorly reactive catalysts 
are those having rate constants less than and energies of activation more 
than these values, respectively. Typical highly reactive catalysts include 
titanium, zinc and magnanese. Typical poorly reacive catalysts include 
antimony, sodium, magnesium, calcium and lithium. 
Mixtures of catalysts can be used, including, for example, the mixtures of 
catalysts described in U.S. Pat. No. 3,806,468 (issued Apr. 23, 1974) and 
3,830,759 (issued Aug. 10, 1974) both to me. Catalysts useful in the 
method of this invention are generally available in the form of organic or 
inorganic compounds, e.g. tetraisopropyl titanate, titanium dioxide, zinc 
acetate, zinc acetyl acetonate, calcium oxide, manganese oxide and the 
like. The acetates, chlorides, nitrates, sulfates, oxides and alkoxides of 
metals such as zinc, manganese, tin, titanium, antimony, cobalt and 
lithium are preferred. The catalyst is generally present in the reaction 
mixture in a concentration in the range of from about 0.01 to about 0.1 
percent, and preferably from about 0.02 to about 0.06 percent, by weight, 
based on the total weight of polymer precursors. Buffering compounds, such 
as alkaline salts of organic acids, can be included with the catalysts if 
desired. 
During polycondensation, catalyst activity, reaction temperature and 
pressure are correlated to restrain the extent of reaction for linear 
extension in the practice of this invention. Catalyst activity is 
generally controlled to restrain extent of reaction for linear extension 
thereby allowing reproducibility. This control can be exercised alone or 
accompanied by a change in temperature or pressure. Catalyst activity can 
be controlled by specifying the type and concentration of catalyst. For 
example, poorly reactive catalysts which slow the rate of linear extension 
can be used. Alternatively, the effectiveness of highly reactive catalysts 
can be reduced by adding end capping agents, poorly reactive polymer 
precursors, or catalyst "poisons" or deactivators. 
End capping agents are also known as chain terminating agents. Exemplary 
end capping agents are disclosed in U.S. Pat. No. 2,895,946 (issued July 
21, 1959 to Huffman) including, for example, monohydric polyalkylene 
oxides and polyalkylvinyl ethers each having one terminal hydroxyl 
radical. Poorly reactive polymer precursors include such materials as 
1,2-propylene glycol, dimethyl o-phthalate, 1,2-butylene glycol, neopentyl 
glycol, 2,2-ethylbutyl-1,3-propanediol. These compounds are generally less 
readily added to the polyester chain because of steric hindrance or other 
characteristics which decrease their reactivity. Exemplary catalyst 
"poisons" or deactivators include phosphoric acid, tributylphosphate, 
phosphorous acid, trimethylphosphate, etc. The amount of end capping 
agent, poorly reactive precursor or catalyst "poison" added will vary 
depending upon the amount and type of catalyst used, the type of polymer 
precursors reacted, the amount of branching desired, whether temperature 
or pressure conditions are changed, etc. Typically, however, from about 
0.1 to about 0.5 percent, by weight, of one or more of these materials is 
added, based on total polymer precursor weight. A moderate amount of 
experimentation may be useful to determine the optimum amount of catalyst 
"poison", poorly reactive precursor or end capping agent needed to achieve 
reproducibility. 
A change in reaction temperature during at least part of the 
polycondensation can also be used to restrain linear extension in 
preparing branched polyesters. Typically, for melt polymerization, 
reaction temperature is lowered from that used in polymer condensation and 
maintained in the range of from about 120 to about 240.degree. C. and 
preferably from about 200 to about 220.degree. C. For solid phase 
polymerization, the temperature can be lowered to within the range of from 
about 120.degree. C. to about 190.degree. C., depending upon the normal 
polymerization temperature. The point is that the temperaure is lowered 
below that normally used to "drive" the polymerization reactions forward. 
Again, the specific temperature reduction depends upon many variables 
including temperatures at which the polyesters crystallize and can be 
determined for a given reaction with limited experimentation. 
Reaction temperature can be increased as long as other reaction conditions, 
i.e. catalyst activity or pressure, are correlated with the increase to 
effect a restraint on linear extension. A change in temperature can be 
accompanied by a change in reaction pressure during at least part of the 
polycondensation. Generally, during polycondensation, pressure is 
maintained in the range of from about 5 to about 100 mm Hg and preferably 
from about 10 to about 50 mm Hg for melt polymerization reactions. The 
pressure can be higher for solid phase polymerization. In the practice of 
my invention, polycondensation pressure is generally higher than the 
pressures allowed in polycondensation procedures of the prior art. The 
reaction pressure can be changed while keeping other conditions unchanged. 
Typically, in solid phase polymerization, the reaction pressure is 
provided by the partial pressures of evolved reaction by-products, e.g. 
glycols. Regulation of these partial pressures corresponds to a regulation 
of reaction pressure needed to achieve restraint of linear extension. 
The polymer precursors mixed together and reacted to form a condensation 
polymer in the practice of this invention include diols, diacids, and 
polyfunctional modifiers. As used throughout this specification and in the 
claims, the terms "a diol", "a diacid" and "a polyfunctional modifier" 
include a mixture of diols, a mixture of diacids and a mixture of 
polyfunctional modifiers, respectively. 
Diols useful in the practice of this invention are typically dihydric 
alcohols or functional derivatives thereof, such as esters, which are 
capable of condensing with diacids or their functional derivatives to form 
condensation polymers. These diols can be represented, for example, by the 
formula RO--R.sup.1 --OR.sup.2 wherein each of R and R.sup.2 is hydrogen 
or alkylcarbonyl, preferably of from 2 to 7 carbon atoms, and R.sup.1 is 
an aliphatic, alicyclic or aromatic radical, preferably of from 2 to 12 
carbon atoms and including carbon and hydrogen atoms, and optionally, 
oxygen atoms. An alkylcarbonyl can be represented by the formula 
##STR1## 
wherein R" is alkyl preferably of from 1 to 6 carbon atoms. Representative 
alkylcarbonyl radicals are acetyl, propionyl, butyryl, etc. More 
preferably, each of R and R.sup.2 is hydrogen. 
R.sup.1 is an aliphatic, alicyclic or aromatic radical, preferably of 2 to 
12 carbon atoms and more preferably of 2 to 6 carbon atoms. Typical 
aliphatic, alicyclic and aromatic radicals include alkylene, 
cycloalkylene, alkylidene, arylene, alkylidyne, alkylenearylene, 
alkylenecycloalkylene, alkylenebisarylene, cycloalkylenebisalkylene, 
arylenebisalkylene, alkylene-oxy-alkylene, 
alkylene-oxy-arylene-oxyalkylene, etc. Preferably, R.sup.1 is hydrocarbon, 
such as alkylene, cycloalkylene, cycloalkylenebisalkylene or arylene. 
Exemplary diols useful in the practice of this invention includes ethylene 
glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 
1,4-butanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 
1,4-cyclohexanedimethanol, 1,4-bis(.beta.-hydroxyethoxy)-cyclohexane, 
quinitol, norcamphanediols, 2,2,4,4-tetraalkylcyclobutane-1,3-diols, 
p-xylene glycol, and corresponding alkyl esters thereof. 
Diacids useful in the practice of this invention are typically dicarboxylic 
acids or functional derivatives thereof, such as esters, acid halides or 
anhydrides, which are capable of condensing with diols or their functional 
derivatives to form condensation polymers. These diacids can be 
represented, for example, by the formula 
##STR2## 
wherein n is 0 or 1, each of R.sup.3 and R.sup.5 is hydroxy, halogen, e.g. 
fluoro, chloro, etc., or alkoxy, preferably of from 1 to 12 carbon atoms, 
such as methoxy, ethoxy, t-butoxy etc., or R.sup.3 and R.sup.5 taken 
together form an oxy linkage, and R.sup.4 is an aliphatic, alicyclic or 
aromatic radical, preferably of from 1 to 12 carbon atoms and including 
carbon and hydrogen atoms and, optionally, oxygen atoms. More preferably, 
each of R.sup.3 and R.sup.5 is hydroxy or alkoxy of 1 to 4 carbon atoms. 
R.sup.4 is an aliphatic, alicyclic or aromatic radical, preferably of 1 to 
12 carbon atoms. The definition of R.sup.1 given hereinbefore applies here 
as well for R.sup.4. Preferably, R.sup.4 is hydrocarbon, such as alkylene, 
cycloalkylene or arylene. 
Exemplary diacids which are useful in the practice of this invention 
include sebacic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, 
glutaric acid, succinic acid, carbonic acid, oxalic acid, azelaic acid, 
4-cyclohexane-1,2-dicarboxylic acid, 2-ethylsuberic acid, 
2,2,3,3-tetramethylsuccinic acid, 4,4'-bicyclohexyldicarboxylic acid, 
terephthalic acid, isophthalic acid, dibenzoic acid, 
bis(p-carboxyphenyl)-methane, 1,5-naphthalenedicarboxylic acid, 
phenanthrene dicarboxylic acid, 4,4'-sulfonyldibenzoic acid and other 
similar acids including those disclosed, for example, in U.S. Pat. No. 
3,546,180 (issued Dec. 8, 1970 to Caldwell), U.S. Pat. No. 3,929,489 
(issued Dec. 30, 1975 to Arcesi et al) and U.S. Pat. No. 4,101,326 (issued 
July 18, 1978 to me). Alkyl ester, acid halide and anhydride derivatives 
of these acids are also useful in the practice of this invention. 
Polyfunctional modifiers useful in the practice of this invention are also 
known as branching agents. These modifiers contain three or more 
functional radicals, such as hydroxyl or carboxyl radicals or functional 
derivatives thereof, such as esters and anhydrides. Exemplary modifiers 
include polyols having three or more hydroxyl radicals, polycarboxylic 
acids having three or more carboxyl radicals and hydroxy acids having 
three or more hydroxyl and carboxyl radicals. As used in this 
specification and in the claims, the terms "polycarboxylic acid" and 
"hydroxy acid" also include functional equivalents, such as anhydrides and 
esters. 
Representative polyfunctional modifiers are trimesic acid, trimellitic 
acid, trimellitic anhydride, pyromellitic acid, butanetetracarboxylic 
acid, naphthalenetricarboxylic acids, cyclohexane-1,3,5-tricarboxylic 
acid, glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, 
1,2,6-hexanetriol, 1,3,5-trimethylolbenzene, malic acid, citric acid, 
3-hydroxyglutaric acid, 4-.beta.-hydroxyethylphthalic acid, 
2,2-dihydroxymethylpropionic acid, 10,11-dihydroxyundecanoic acid, 
5-(2-hydroxyethoxy)-isophthalic acid and others known in the art as 
disclosed, for example, in U.S. Pat. No. 4,013,624 (issued Mar. 22, 1977 
to Hoeschele). Preferred polyfunctional modifiers include modifiers having 
three or four functional radicals, such as trimellitic anhydride and 
pentaerythritol. 
The method of this invention is useful as applied to both melt and solid 
phase polycondensation techniques. The details for using these techniques 
are known in the art. 
The branched polyesters prepared by this method can also contain various 
stabilizers, anti-oxidants, fillers, pigments, ultraviolet radiation 
absorbers, plasticizers and other addenda known to be useful in polyesters 
as disclosed, for example, in U.S. Pat. No. 4,101,326 (issued July 18, 
1978 to me). Branched polyesters are useful in a variety of products 
including, for example, photographic film supports, molded articles, 
fibers, adhesives, electrophotographic toners, lacquers, etc. The 
advantage of the method of this invention is that the method allows one to 
reproducibly make branched polyesters having particular properties for 
particular uses. 
The method of this invention is further illustrated by the following 
examples of its practice. 
EXAMPLE 1 
As discussed hereinabove, it is conventional to prepare branched polyesters 
using reaction conditions during polycondensation which "drive" the linear 
polymerization reaction forward. Very little branching occurs under such 
conditions because the reaction of more reactive linear functional groups 
prevails. In the methods of the prior art, there is no attempt to 
correlate the reaction conditions to restrain the extent of reaction for 
linear extension. For example, in a conventional preparation of branched 
polyesters, polycondensation is carried out at a temperature which is at 
least as high or higher than that used in the condensation stage, at a 
lower pressure and which unchanged catalyst activity. 
In practicing my invention, reaction conditions, e.g. temperature, pressure 
and catalyst activity, are correlated to restrain the extent of reaction 
for linear extension. In this example, the rate of linear extension is 
restrained by polycondensing at a pressure greater than that typically 
used for conventional polycondensation. In conventional polycondensation, 
the reaction pressure is kept very near vacuum in order to "drive" the 
polycondensation reaction forward. 
A branched polyester was prepared by the following procedure: 
CONDENSATION STEP 
Dimethyl terephthalate (388 g, 2 moles), ethylene glycol (188 g, 3 moles), 
cyclohexanedimethanol (89 g, 0.6 mole), diethylene glycol (21 g, 0.2 mole) 
and pentaerythritol (6.8 g, 0.05 mole, 2.5 mole %) were reacted in the 
presence of tetraisopropyltitanate catalyst (0.45 g). The reaction was 
carried out at 252.degree. C. for about 100 minutes at atmospheric 
pressure. 
POLYCONDENSATION STEP 
The resulting condensation polymer was then polycondensed in the melt phase 
in the same reactor at 252.degree. C. and 40 mm Hg for 110 minutes. The 
resulting branched polyester had an inherent viscosity of 0.45 and a 
polydispersity of 10.4. 
From the graphical plots of FIG. 2, it was determined that the extent of 
reaction for a branched polyester having an inherent viscosity of 0.45 and 
prepared with 2.5 mole % pentaerythritol is about 0.958. This same 
graphical plot shows that at such extent of reaction, the reaction 
conditions used to prepare the branched polyester should provide an 
unbranched polyester having an inherent viscosity of 0.21. This follows 
only if the polycondensation reaction conditions have been correlated 
according to this invention to restrain the extent of reaction for linear 
extension to within about 0.1% of the extent of reaction for branching. 
PREATION OF UNBRANCHED POLY(ETHYLENE TEREPHTHALATE) 
An unbranched polyester was prepared using the same materials and procedure 
in this Example for a branched polyester except that pentaerythritol was 
omitted. After 110 minutes of polycondensation, the inherent viscosity of 
the polyester was about 0.18. This value is substantially equal to the 
value of 0.21 predicted from the graphical plot of FIG. 2. 
EXAMPLE 2 
The following comparative example illustrates polyester preparation wherein 
no attempt was made to restrain linear extension during polycondensation. 
Condensation Step 
Dimethyl terephthalate (388 g, 2 moles), ethylene glycol (188 g, 3 moles), 
cyclohexanedimethanol (89 g, 0.6 mole), diethylene glycol (21 g, 0.2 mole) 
and trimellitic anhydride (19.2 g, 0.1 mole, 5 mole %) were reacted in the 
presence of tetraisopropyltitanate catalyst (0.45 g). The reaction was 
carried out at 252.degree. C. and atmospheric pressure for about 100 
minutes. 
Polycondensation Step 
The resulting condensation polymer was then polycondensed at 251.degree. C. 
for about 325 minutes. The reaction rate was very slow, so the pressure 
was reduced to 0.8 mm Hg for 30 minutes to promote reaction. No attempt 
was made to restrain linearization during this final stage of reaction. 
The resultant branched polyester had an inherent viscosity of 0.47 and a 
polydispersity of 3.02. 
Referring to the graphical plots of FIG. 2, I determined the extent of 
reaction for this branched polyester to be about 0.959. From this same 
Figure, at this same extent of reaction, the inherent viscosity for 
unbranched polyester was determined to be about 0.22. An unbranched 
polyester was not made in this procedure. However, a comparison of this 
polyester can be made with the branched polyester of Example 1. That 
comparison indicates that little branching occurred in this 
polycondensation. The branched polyester of Example 1 had an inherent 
viscosity of 0.45 and a polydispersity of 10.4. The supposedly branched 
polyester of this procedure had a similar inherent viscosity (0.47), but a 
markedly different polydispersity of 3.02. This low polydispersity 
indicates that very little branching occurred (a polydispersity of 2.0 
indicates no branching). Most of the inherent viscosity must then be due 
to linearization rather than branching. How much of the 0.47 value, of 
course, is not known, but it is believed that the portion due to 
linearization is much greater than 0.22, the inherent viscosity determined 
from the graphical plots of FIG. 2. Promoting reaction during the last 30 
minutes of polycondensation by reducing the pressure allowed linearization 
to occur while essentially inhibiting the branching reaction. 
EXAMPLE 3 
This example illustrates that the rate of linear extension is restrained by 
lowering polycondensation reaction temperature below the temperature used 
in the condensation stage and in conventional polycondensation. 
Branched poly(ethylene terephthalate) was prepared by the following 
procedure: 
Condensation Step 
Dimethyl terephthalate (388 g, 2 moles), ethylene glycol (248 g, 4 moles) 
and pentaerythritol (0.95 g, 0.007 moles, 0.35 mole %) were reacted in the 
presence of a catalyst mixture of lithium acetate dihydrate (14 ppm Li), 
zinc acetate dihydrate (65 ppm Zn), cobalt acetate tetrahydrate (20 ppm 
Co), manganese acetate tetrahydrate (55 ppm Mn), tetraisopropyltitanate 
(12 ppm Ti) and antimony oxide (325 ppm Sb). The reaction was carried out 
at atmospheric pressure and 270.degree. C. for 95-100 minutes. The 
resulting condensation polymer had an inherent viscosity of 0.37. 
Polycondensation Step 
Samples of the condensation polymer were subsequently polycondensed in a 
conventional six-stage fluidized solid phase reactor at several 
temperatures and 1 mm Hg for times up to 120 minutes at a rate of about 
1.4 kg/hr. Table I below lists the resulting "actual" inherent viscosities 
for each branded polyester. 
From the graphical plots of FIG. 1, an extent of reaction was determined 
for the branched polyester at each "actual" inherent viscosity value. At 
each such extent of reaction, a "theoretical" inherent viscosity was then 
determined for unbranched polyester prepared under the same set of 
conditions. These values of "theoretical" inherent viscosity were also 
recorded in Table I below. 
Unbranched poly(ethylene terephthalate) was prepared using the same 
materials and procedure described in this example for the branched 
polyester except that pentaerythritol was omitted. Table I below lists the 
"actual" inherent viscosities determined for samples taken during 
polycondensation. 
Table I 
______________________________________ 
Polycon- 
Polycon- Inherent Viscosity 
densation 
densation 
Branched Unbranched 
Unbranched 
Temp- Time PET PET PET 
eratures 
(min) (actual) (actual) (theoretical) 
______________________________________ 
170.degree. C. 
30 .36 .36 .32 
60 .40 .38 .35 
90 .49 .43 .41 
120 .52 .45 .43 
180.degree. C. 
30 .38 .38 .34 
60 .41 .40 .36 
90 .49 .42 .41 
120 .54 .48 .45 
190.degree. C. 
30 .41 .40 .36 
60 .55 .46 .45 
90 .76 .51 .59 
120 .93 .54 &gt;.60** 
210.degree. C. 
30 .69 .51 .55 
60 *-- .60 
90 *-- .69 
120 *-- .69 
______________________________________ 
*sample insoluble in solvent (phenolchlorobenzene mixture) 
**approximated value from extrapolation of curves in FIG. 1 
Solid phase polymerization is typically carried out at a temperature above 
about 200.degree. C. It is apparent from the results listed in Table I 
above, that lowering the polycondensation temperature restrains the rate 
of linear extension. As the temperature is lowered further, greater 
restraint is achieved at longer polycondensation times. 
This invention has been described in detail with particular reference to 
certain preferred embodiments thereof, but it will be understood that 
variations and modifications can be effected within the spirit and scope 
of the invention.