Process for increasing stability of poly(esteramides)

Process for treating poly(esteramides) to improve the heat and storage stability thereof. Polymer is optionally suspended in a liquid medium, treated with an amide group-containing solvent, and then separated from the solvent and liquid medium (if any). Also, poly(esteramides) treated in this process and devices and articles comprising such poly(esteramides).

FIELD OF INVENTION 
The present invention relates to a process for treating poly(esteramides) 
to increase the heat and storage stability thereof. 
BACKGROUND OF THE INVENTION 
Poly(esteramides) are known to be useful bioabsorbable polymeric materials 
derived from reacting diamidediols with dicarboxylic acids, derivatives 
thereof or bischloroformates. Such polymers and some of their uses are 
described in U.S. Pat. Nos. 4,343,931; 4,529,792; 4,534,349; 4,669,474; 
4,719,917; 4,883,618; and 5,013,315 (all Barrows et al.). 
An increasing number of surgically implantable devices that only function 
for a relatively short period of time in vivo are being designed from 
synthetic polymers that are eliminated from the body by hydrolytic 
degradation and subsequent metabolism after serving their intended 
purpose. The molecular weight of such "bioabsorbable" polymers is an 
important parameter in determining whether or not a particular lot of 
polymer will perform properly for an adequate length of time in any 
specific application. Thus, if significant loss of molecular weight occurs 
during processing of the polymer to fabricate a device, such as by melt 
extrusion, then the device may fail prematurely in vivo as hydrolysis 
shifts the molecular weight distribution below a minimum range required 
for the device to function properly. Some causes which may lead to 
reduction in molecular weight and premature device failure include 
degradation due to melt processing conditions (e.g., the high temperature 
and shear conditions encountered during extrusion processing), due to 
moisture in the polymer, and due to synthesis residues (e.g., unreacted 
precursor materials and reaction by-products) in the polymer, e.g., acid 
chlorides. 
Loss of molecular weight upon extrusion is commonly encountered with 
polyesters even when moisture in the resin has been reduced to the lowest 
possible level. For example, poly-L-lactide, a well known bioabsorbable 
polyester has not yet been melt extruded into fiber with molecular weight 
much higher than 100,000 since the extrusion process typically degrades 
higher molecular weight fractions to this relatively constant maximum 
value. 
Bioabsorbable poly(esteramides) described in U.S. Pat. Nos. 4,343,931 and 
4,529,792 offer an advantage over poly-L-lactide and related polyesters in 
that a lower molecular weight is adequate to achieve comparable fiber 
strength due to the intermolecular hydrogen bonding provided by the amide 
linkages. Fibers made of such polymers exhibit comparable strength to 
those made of poly-L-lactide while providing lower modulus (and thus 
greater flexibility) and greater toughness and durability. Compared to 
poly-L-lactide such fibers are also more rapidly bioabsorbed. A 
disadvantage with poly(esteramides), however, results from the unreliable 
method of synthesis in which intermediate molecular weight material must 
be heated as a solid to advance the molecular weight to an acceptable 
value. If continued too long, this treatment yields excessively 
crosslinked or "gelled" material which is unsuitable for extrusion. On the 
other hand, if the process is not continued long enough, the polymer lacks 
storage and thermal stability due to the presence of unreacted acid 
chloride functionality. 
SUMMARY OF INVENTION 
The present invention provides a process for treating body absorbable 
poly(esteramides) (referred to herein as "PEA") to improve the heat and 
storage stability thereof. Previously available poly(esteramides) did not 
provide the excellent heat and storage stability provided by 
poly(esteramides) treated in accordance with the present invention. 
In brief summary, the preferred process of the invention comprises: 
a) providing a poly(esteramide) polymer as defined below; 
b) suspending the polymer in a non-reactive liquid medium, e.g., an aprotic 
liquid such as toluene; 
c) treating the suspended polymer with an amide group-containing solvent; 
d) separating the polymer from the solvent, e.g., precipitating by cooling; 
e) removing the solvent; and, typically, 
f) removing the liquid medium and drying the polymer to yield the 
stabilized polymer in powder form. 
In some instances, a poly(esteramide) in solid form may be stabilized by: 
a) providing a poly(esteramide) polymer as defined below; 
b) treating the polymer (e.g., extracting or dissolving) with an amide 
group-containing solvent; and 
c) separating the polymer from the solvent; 
thus omitting the suspension of the polymer in the liquid medium. 
Suspension with a liquid medium as described above is preferred, however, 
because lesser amounts of solvent may be used (and as noted below the 
solvent can be a source of moisture) and because PEA will precipitate at a 
higher temperature from a mixture of solvent and medium than from solvent 
above, thereby facilitating removal of polymerization of by-products such 
as HCl which have a higher affinity for the solvent at higher temperature. 
Poly(esteramides) treated in accordance with the invention are suitable for 
use in a variety of devices, for example sutures and other fiber 
containing devices. In particular, polymers treated in accordance with the 
invention may be used to advantageous result in devices whose construction 
entails rigorous conditions, e.g., melt processing such as extrusion. 
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
In general, poly(esteramide) polymers treated by the process of the present 
invention have the general formula: 
##STR1## 
wherein: 
a) R.sup.1 and R.sup.6 are identical or different and are hydrogen or 
methyl; 
b) R.sup.3 and R.sup.5 are identical or different and are selected from the 
group consisting of the following, which are linear or branched, alkylene, 
alkylene having 1 or 2 nonadjacent catenary oxygen or sulfur atoms, 
alkenylene, cycloalkylene and arylene; the members of the group having up 
to 25 carbon atoms in the cyclic compounds and from 2 to 25 carbon atoms 
in the non-cyclic compounds; 
c) R.sup.2 and R.sup.4 are identical or different and are hydrogen or alkyl 
having 1 to 4 carbon atoms or R.sup.2 and R.sup.4 together are linear or 
branched alkylene having one to four carbons forming with N--R.sup.3 --N a 
heterocyclic group having 5 or 6 ring atoms; 
d) a and b are independently zero or one; and 
e) n having an average value from about 10 to about 400. 
To manufacture fibers which have nylon-like flexibility and strength 
properties, R.sup.2 and R.sup.4 are preferably both hydrogen so as to 
facilitate hydrogen bonding. 
We have observed that when at least one of R.sup.3 and R.sup.5 is 
relatively short (i.e., about 2 to 4 carbon atoms), fibers made from the 
resultant polymer offer superior results; whereas if both R.sup.3 and 
R.sup.5 are relatively long (i.e., about 6 to 14 carbon atoms), the 
resultant fibers do not provide comparable results. Polymers of the 
invention where R.sup.3 is linear alkylene of 2 to 14 carbon atoms are 
presently preferred. Polymers of the invention where R.sup.5 is linear 
alkylene of 2 to 14 carbon atoms are presently preferred, and most 
preferred is alkylene of 4 to 12 carbon atoms. 
Polymers of the invention wherein a and b are zero are presently preferred 
because it is easier to manufacture polymers with higher molecular weight. 
Polymers of the invention wherein n is 10 to 400 are presently preferred 
because such polymers provide a more generally useful combination of 
strength and rate of in vivo absorption. Most preferred are polymers 
wherein n is about 50 to 200 because such polymers provide what is 
generally an optimal balance of strength and rate of in vivo absorption. 
Polymers with relatively lower molecular weight (i.e., relatively smaller 
n) provide lower strength with faster absorption whereas polymers with 
relatively higher molecular weight (i.e., relatively larger n) provide 
greater strength and with slower absorption. 
It has been found that polymers (and fibers formed therefrom) based on 
diamidediols formed from 1,2-ethanediamine and glycolic or lactic acids 
manifest particularly significant improvements in properties when treated 
in accordance with the process of the invention. Unless treated in 
accordance with the invention, such polymers have been observed to be more 
subject to breakdown during melt processing than some other 
poly(esteramides). 
As mentioned above, in brief summary, the process of the invention 
comprises: 
a) providing a PEA as described above; 
b) preferably suspending the polymer in a non-reactive liquid medium; 
c) treating, preferably dissolving, the preferably suspended polymer with 
an amide group-containing solvent; 
d) separating the polymer, e.g., precipitating it; 
e) removing the solvent; and, typically, 
f) removing the liquid medium if any and drying the polymer to yield the 
stabilized polymer in powder form. 
The treatment may be applied to PEA which is initially in dry form, or may 
be incorporated as part of the initial PEA synthesis process. 
When synthesizing PEA, in order to obtain the regular sequence shown in the 
formula above, it is typically desirable to first form the amide linkages 
prior to PEA-forming or stage 2 polymerization. This can be accomplished 
by combining about two moles of glycolic or lactic acid, or a combination 
thereof, with about one mole of diamine and heating at a temperature 
between about 150.degree. and about 220.degree. C. until distillation of 
water is complete. Alternatively, combination of hydroxy acid and diamine 
will produce a salt which can be purified by recrystallization and then 
subjected to the above condensation. In either case, a high yield of 
diamidediol is obtained which should be purified by recrystallization. 
Synthesis of preferred PEA polymers with an inherent viscosity suitable to 
obtain fibers with adequate strength is preferably carried out as 
described herein. The preferred process for forming poly(esteramides) 
having a suitably high molecular weight (i.e., n is 10 or more) comprises: 
a) suspending one or more diamidediols, preferably in powder form, in an 
aprotic liquid (referred to herein as a "synthesis solvent") which: 1) is 
a nonreactive solvent for acid chlorides, 2) is nonsolvent for 
diamidediols, 3) has a boiling point of 100.degree. C. or higher, and 4) 
is preferably substantially free of water; 
b) adding a stoichiometrically equal amount of one or more diacid 
chlorides; 
c) heating the mixture to a moderate temperature, e.g., about 60.degree. to 
about 90.degree. C., until low molecular weight, i.e., an inherent 
viscosity between about 0.3 and about 0.6, is achieved; and then 
d) rapidly refluxing with vigorous mechanical mixing (e.g., motor driven 
paddle), preferably until the polymer has an inherent viscosity of about 
1.0 to about 1.2; 
yielding PEA of the desired formula. By "nonsolvent" it is meant that the 
subject liquid, at its boiling point, will not solvate more than 2 weight 
percent of the subject material. Preferably, the liquid will solvate 
substantially none of the subject material. By "nonreactive" it is meant 
that the subject liquid will not react with any of the species 
(precursors, intermediates, and reaction products) of the subject 
reaction. 
The resultant PEA, still suspended in the synthesis solvent, may then be 
immediately treated in accordance with the process of the invention as 
described below or it may be reduced to powder form. It is typically 
preferred to treat the PEA within a week of its synthesis, more preferably 
immediately after its synthesis, to avoid degradation during storage. If 
necessary to delay treatment for a time after synthesis, removal of the 
synthesis solvent is generally preferred to reduce degradation during 
storage. An advantage of the treatment process of the invention is that 
typically the PEA can be treated in the same vessel it was synthesized in, 
typically using the synthesis solvent as the liquid medium. 
Preferably the inherent viscosity of the polymer is frequently or 
continuously monitored throughout the PEA synthesis. As used herein, 
inherent viscosity is measured at 30.degree. C. in 2,2,2-trifluoroethanol. 
If the synthesis is halted while the inherent viscosity is still at too 
low a level, the molecular weight of the resultant polymer will be too low 
and it will exhibit poor strength and tend to be brittle; whereas if the 
synthesis is not halted soon enough and the inherent viscosity reaches too 
high a level, the resultant polymer may gel, at least in some portions. 
Gelled portions typically lead to weak points in fibers made from such 
polymers. 
Illustrative examples of suitable synthesis solvents, which exhibit 
desirable nonreactivity and sufficiently high boiling points, include 
methyl chloroacetate, high boiling ketones, toluene, chlorobenzene, 
xylene, 1,1,2-trichloroethane, and 1,4-dioxane. The preferred synthesis 
solvents for use with a diacid chloride are chlorobenzene and toluene 
because of their useful boiling points. Toluene is most preferred because 
of its generally held status as a toxicologically safe agent. If desired, 
mixtures of synthesis solvents may be used. Typically, solvents and 
solvent mixtures which have boiling points (at 1 atmosphere) of between 
about 70.degree. C. and about 150.degree. C., preferably between about 
90.degree. C. and about 120.degree. C., are useful. 
The preferred synthesis process has the advantages of not requiring 
catalyst, of yielding product in a relatively short period of time, and of 
producing high molecular weight polymer, typically free of crosslinking, 
in an easy-to-manipulate form. In addition, moisture which would otherwise 
react with the acid chloride can be readily excluded from the system by 
azeotropic distillation prior to addition of the diacid chloride. 
Dicarboxylic acid chlorides and the dimethyl or diethyl esters of 
dicarboxylic acids useful in the synthesis of polymers by the above 
methods include those derived from dicarboxylic acids listed below. In 
addition, the free acids can also be used. The term "dicarboxylic acid" as 
used herein includes dicarboxylic acids, their methyl and ethyl esters, 
their acid chlorides and anhydrides. The dicarboxylic acids are, for 
example, oxalic acid; malonic acid, succinic acid; 2,3-dimethylsuccinic 
acid; glutaric acid,; 3,3-dimethylglutaric acid; 3-methyladipic acid; 
adipic acid; pimelic acid; suberic acid; azelaic acid; sebacic acid; 
1,9-nonanedicarboxylic acid; 1,10-decanedicarboxylic acid; 
1,11-undecanedicarboxylic acid; 1,12-dodecanedicarboxylic acid; 
1,13-tridecanedicarboxylic acid; 1,14-tetradecanedicarboxylic acid; 
1,15-pentadecanedicarboxylic acid; 1,16-hexadecanedicarboxylic acid; 
maleic acid; trans-.beta.-hydromuconic acid; fumaric acid; diglycolic 
acid; 3,3'-oxydipropionic acid; 4,4'-oxydibutyric acid; 5,5'-oxydivaleric 
acid; 6,6'-oxydicaproic acid; 8,8'-oxydicaprylic acid; 6-oxaundecanedioic 
acid; 5-oxaazelaic acid; 5-oxasebacic acid; 5-oxaundecanedioic acid; 
5-oxadodecanedioic acid; 5-oxatetradecanedioic acid; 5-oxahexadecanedioic 
acid; 6-oxadodecanedioic acid; 6-oxatridecanedioic acid; 
6-oxapentadecanedioic acid; 6-oxaheptadecanedioic acid; 
7-oxapentadecanedioic acid; 10-oxanonadecanedioic acid and other 
oxa-aliphatic dicarboxylic acids; 1,2-cyclobutanedicarboxylic acid; 
1,4-cyclohexanedicarboxylic acid and the like. Linear diacids containing 
two to twelve --CH2-- groups are preferred as they degrade into agents 
known to be metabolically satisfactory. In the presently most preferred 
polymer, R.sup.5 is preferably decane, e.g., formed by the removal of the 
chloride from dodecanedioyl chloride. It is highly preferred that the acid 
chlorides be carefully purified, e.g., by fractional distillation. 
Diamidediols useful in synthesizing polymers of this invention can be 
prepared by the above methods from diamines such as 1,2-ethanediamine; 
1,3-propanediamine; 1,3-(2-methylpropane)diamine; 
1,3-(2,2-dimethylpropane)diamine; 1,2-(1,2-dimethylethane)diamine; 
1,4-butanediamine; 1,5-pentanediamine; 1,6-hexanediamine; 
1,7-heptanediamine; 1,8-octanediamine; 1,9-nonanediamine; 
1,10-decanediamine; 1,11-undecanediamine; 1,12-dodecanediamine; 
1,13-tridecanediamine; 1,14-tetradecanediamine; 1,15-pentadecanediamine; 
1,16-hexadecanediamine; 3-oxapentane-1,5-diamine; 
4-oxaheptane-1,7-diamine; 5-oxanonane-1,9-diamine; 
6-oxaundecane-1,11-diamine; 7-oxatridecane-1,13-diamine; 
8-oxapentadecane-1,15-diamine; 9-oxaheptadecane-1,17-diamine; 
10-oxanonadecane-1,19-diamine; 11-oxahendecacosane-1,21-diamine; 
12-oxatricosane-1,23-diamine; 13-oxapentacosane-1,25-diamine; 
4,9-dioxadodecane-1,12-diamine; 3,6-dioxaoctane-1,8-diamine and other 
analogs of oxa-aliphatic diamines and the corresponding thia-aliphatic 
diamines; cyclohexane-1,4-diamine; cyclohexane-1,3-diamine; 
cyclohexane-1,2-diamine; 1,4-bis(aminomethyl)cyclohexane; 
1,3-bis(aminomethyl)cyclohexane; 1,4-bis(2-aminoethyl)-cyclohexane; 
1,4-bis(3-aminopropyl)cyclohexane; bis(4-aminocyclohexyl)methane; 
p-phenylenediamine; o-phenylenediamine; m-phenylenediamine; 
p-xylylene-alpha, alpha-diamine and other aromatic diamines; piperazine; 
4,4'-trimethylenedipiperidine; 4,4'-bipiperidine; 
N,N'-bis(3-aminopropyl)piperazine; 2,5-dimethylpiperazine; 
2,6-dimethylpiperazine; 2-methylpiperazine; imidazolidine; 
2-methylimidazolidine; and 4,5-dimethylimidazolidine. 
In the process of the invention, PEA polymer is suspended preferred in a 
liquid medium. The liquid medium should be a nonreactive, nonsolvent for 
the PEA. If desired, the liquid medium may be the synthesis solvent 
described above. In addition, lower boiling point liquids, e.g., ethyl 
acetate, not considered suitable for use as synthesis solvents may be used 
as liquid mediums. PEA in dry form may be suspended in the medium, or the 
synthesis product, still suspended in the synthesis solvent, may be used. 
As discussed above, it is preferable to treat the PEA as described herein 
shortly after synthesis. Improved storage stability of PEA is one of the 
advantages of this invention. 
Preferably, the PEA is treated before the polymer crosslinks to a gel. This 
can be achieved by monitoring the inherent viscosity of the PEA during the 
synthesis and stopping the synthesis reaction at an appropriate point. It 
has been observed that PEA tends to aggregate before gelling, the 
aggregation being observable during inherent viscosity monitoring. In the 
event that aggregation or slight gelling has occurred, it is often 
possible to reverse the aggregation or gelling in the course of heating 
and dissolving the polymer in the solvent. 
The suspended PEA is then treated with, e.g., by extracting with, 
preferably dissolving in, an amide group-containing solvent. Illustrative 
examples of amide group-containing solvents suitable for use in the 
treatment process of the invention include N-methylpyrrolidone, 
N-methylformamide, N-methylacetamide, N,N-dimethylacetamide, formamide, 
N,N-dimethylformamide, tetramethylurea and the like. Tetramethylurea and 
N-methylpyrrolidone are preferred, with N-methylpyrrolidone being most 
preferred, because these solvents are considered toxicologically safe 
compounds. Typically, PEA treated in accordance with the invention, 
sometimes referred to herein as stabilized polymer, will retain small 
quantities of the amide group-containing solvent, e.g., typically 5.0 
weight percent or less, preferably about 1.0 weight percent or less, 
sometimes about 0.05 weight percent or less. Also, PEA treated in 
accordance with the invention will typically retain only small quantities 
of liquid medium, e.g., typically about 1.0 weight percent or less, 
sometimes 0.05 weight percent or less. 
The ratio of liquid medium and amide group-containing solvent is typically 
preferably about 1:1. It will be understood that other ratios of liquid 
medium and solvent may be used in accordance with the present invention. 
Amide group-containing solvents are typically very good solvents for PEA 
but may contain trace amounts of moisture. Because the moisture may lead 
to degradation of the polymer, thereby tending to limit the in vivo 
performance of a device incorporating the polymer, it is typically 
desirable to minimize how much of the solvent is used, using only enough 
to fully dissolve the PEA. Minimizing the amount of solvent used, e.g., by 
first suspending the PEA in a liquid medium, also facilitates 
precipitation of the polymer from the solvent and removal of the solvent 
as well. 
The solution is heated, typically while stirring, to the boiling point of 
the liquid medium, to facilitate dissolving the PEA. It has been observed 
that while the PEA is dissolving in the amide group-containing solvent 
some bubbling or foaming may be observed. This action ceases once the PEA 
is fully dissolved. Also, the liquid mixture tends to turn clear once the 
PEA is fully dissolved. After the PEA is fully dissolved, it is 
precipitated from solution. Illustrative means of causing the PEA to 
precipitate include one or more of 1) allowing the solution to cool 
slowly, 2) adding additional amounts of liquid medium, preferably at the 
same temperature as the solution, and/or 3) pouring the solution into 
liquid medium (perhaps a different liquid than was used for suspension). 
To avoid agglomeration of polymer and obtain uniform treatment, stirring 
speed may be increased. Small amounts of hot liquid medium may be added to 
control or temper the rate of cooling and rate of precipitation (by 
reducing the solubility of the PEA in the amide group-containing solvent 
fraction) to help prevent coagulation of polymer. It has been observed 
that a smoother transition of dissolved PEA to a uniform dispersion of 
precipitated PEA is most readily achieved when the solution is cooled in 
such a manner (e.g., via controlled cooling rate, continuous mixing, 
addition of hot liquid medium, etc.) that a substantially uniform 
temperature gradient is maintained throughout. Preferred results have been 
obtained when precipitation was performed in a controlled manner such that 
the resultant precipitated PEA was in a smooth slush-like dispersion. When 
cooling for precipitation was performed too rapidly, a solid, wax-like 
build up of material on the walls of the vessel was observed. 
In instances where the polymer has merely been extracted or washed with the 
amide group-containing solvent, separation can typically be achieved by 
filtration. As used herein, "extraction" refers to the process of 
contacting, possibly while heating and/or mixing the mixture, the PEA with 
an amide group-containing solvent but substantially not dissolving the PEA 
in the solvent. An advantage of treating the PEA in this manner is that 
separation of the polymer from the solvent is easier and does not require 
precipitation. Treating by dissolving in the solvent typically provides 
better stabilization results as compared to mere extraction, however. 
Substantially all of the synthesis residues, e.g., acid chloride 
functionalities, remain dissolved in the solvent. The PEA, still suspended 
in the liquid medium can be separated, e.g., by filtering, permitting 
removal of the solvent. It can then be dried, e.g., by tumbling under a 
vacuum, thereby removing the liquid medium and remaining portions of 
solvent, leaving the stabilized PEA in powder form. As mentioned above, 
PEA polymers treated in accordance with the invention may contain trace 
amounts of the amide group-containing solvent and liquid medium. An 
advantage of the invention is that toxicologically acceptable liquid 
mediums and amide group-containing solvents may be used. 
In order to evaluate thermal stability, PEA polymers were melted using an 
Instron Model 4202 Melt Rheometer. A 10 gram sample was used each time and 
each sample was held for 10 minutes in the rheometer. Inherent viscosity 
was determined after each melting and the data were recorded. Melt samples 
at elevated temperatures of poly(esteramides) with and without treatment 
in accordance with the invention were analyzed for molecular weight 
distribution using gel permeation chromatography (GPC). It has been found 
from such data that the treatment of poly(esteramides) in accordance with 
the invention results in a significant improvement in retention of 
molecular weight after melt processing in the temperature range of 
greatest utility (i.e., 170.degree. to 180.degree. C.). 
The polymeric materials of this invention can be fabricated into films and 
fibers by melt extrusion. When the polymer is fabricated into fibers, it 
is preferred that n of the general formula have an average value from 
about 50 to about 200. Such fibers have been implanted subcutaneously in 
rats and have been found to be non-irritating and compatible with the 
living tissue over the time span of many months. 
The polymers of the present invention are also useful in the manufacture of 
cast and/or extruded films and molded solid surgical aids. Thus, 
cylindrical pins, screws, reinforcing plates, etc. may be machined from 
the cast or molded polymer having the aforementioned in vivo absorption 
characteristics. 
In many applications, it is preferred that the polymer have a relatively 
high molecular weight, i.e., corresponding to an inherent viscosity of 
about 1.3 to about 1.5. One particularly useful class of poly(esteramide) 
polymers are those made with ethylenediamine, i.e., R.sup.3 is an ethylene 
group. Such polymers have been found to provide good strength retention 
properties while providing relatively rapid absorption. However, such 
polymers have also been observed to be subject to substantial molecular 
weight degradation during storage and under melt processing conditions 
except when treated in accordance with the invention. In that instance, 
they have exhibited marked improvement in storage and heat stability.

EXAMPLES 
The invention will be further explained by the following illustrative 
examples which are intended to be nonlimiting. 
EXAMPLE 1 
Synthesis and Treatment of 
Poly[decane-1,10-di(carbonyloxy)ethane-1,2-di(amidocarbonylmethylene)] 
Exactly 500 grams ("g") of 1,2-di(hydroxyacetamido)ethane was mixed well 
with 1.5 liters ("l" ) of dry toluene and placed in a 22 l flask. To this 
mixture was added 3.5 l of toluene and then 758.29 g of distilled 
dodecanedioyl chloride. The mixture was heated and stirred under nitrogen 
at 90.degree. C. for six hours, then at reflux for about three hours. 
About 1.5 l of hot toluene was added. The inherent viscosity of the 
resultant PEA polymer was measured periodically until it reached 1.2, then 
exactly two liters of dry N-methylpyrrolidone was added. The mixture was 
heated to and held at 115.degree. C. until the polymer dissolved (20 to 30 
minutes). The solution was then allowed to cool to 90.degree. C. and 4 l 
of hot toluene were added in portions when the solution appeared to change 
from lustrous to grainy as precipitation of polymer began. The slurry was 
then heated at 100.degree. C. and mixed for 15 minutes before filtration. 
The polymer was separated by filtration under nitrogen, then dried in a 
vacuum oven tumble drier for about three hours to remove solvent, then 
dried in the dryer over 16 hours at 90.degree. to 100.degree. C. to remove 
N-methylpyrrolidone. 
The product having an inherent viscosity of about 1.1, was stored in a dry 
box. The thermal stability of this polymer was evaluated by melting the 
polymer in a rheometer at different temperatures and holding it at the 
temperature for a period. The following results were obtained: 
TABLE I 
______________________________________ 
Temperature Inherent Viscosity.sup.1 
(.degree.C.) 
10 20 30 
______________________________________ 
165 1.05 1.02 1.02 
170 0.97 0.93 0.91 
175 0.93 0.87 0.83 
180 0.84 0.77 0.61 
185 0.78 0.66 -- 
190 0.73 -- -- 
______________________________________ 
.sup.1 In deciliters/gram after the indicated number of minutes had 
elapsed. 
This indicates that the polymer was relatively stable at temperatures up to 
about 175.degree. C. The polymer exhibits improved stability at all 
temperatures relative to the same polymer which had not been treated in 
accordance with the invention. 
EXAMPLE 2 
Synthesis and Treatment of 
Poly[decane-1,10-di(carbonyloxy)ethane-1,2-di(amidocarbonylmethyl-methylen 
e)] 
Exactly 30 g of 1,2-di(alpha-hydroxypropionamido)ethane prepared from 
L-lactic acid and ethylenediamine was mixed well with 0.35 l of dry 
toluene and placed in a large flask. To this mixture was added 39 g of 
distilled dodecanedioyl chloride. The mixture was heated and stirred under 
nitrogen at 90.degree. C. for about one hour, then at reflux for about one 
hour. The inherent viscosity of the polymer samples was measured until it 
reached 1.2, then the reaction mixture thickened to a solid and 0.030 
liters of dry N-methylpyrrolidone was added. The mixture was heated to 
115.degree. C. while hydrogen chloride evolved and more 
N-methylpyrrolidone (0.020 liter was added) until the polymer dissolved 
(20 to 30 minutes). The solution was then poured into 3 l of ethyl acetate 
with mixing to cause precipitation of the polymer. The snow-white polymer 
was separated by filtration under nitrogen, then dried in a vacuum oven 
for 16 hours at 90.degree. to 100.degree. C. to remove ethyl acetate and 
N-methylpyrrolidone. 
The product having an inherent viscosity of about 1.5 was stored in a dry 
box. Fibers made from the polymer of this Example were found to be more 
resistant to hydrolysis than were fibers made from the polymer of Example 
1. 
EXAMPLE 3 
Synthesis and Treatment of 
Poly[hexane-1,6-di(carbonyloxy)ethane-1,2-di(amidocarbonylmethylene)] 
Exactly 10 g of 1,2-di(hydroxyacetamido)ethane was mixed well with 0.15 l 
of dry toluene in a 0.25 l flask. About 0.050 l of toluene was distilled 
off while heating the mixture to remove moisture and disperse the diamide 
diol. To this mixture at about 60.degree. C. was added 11.98 g of 
distilled suberoyl chloride. The mixture was heated and stirred under 
nitrogen at 60.degree. C. for one hour, then at 70.degree. C. for one 
hour, then at 80.degree. C. for one hour and finally at reflux for 0.5 
hour. The inherent viscosity of a polymer sample was measured after drying 
as 0.95, then exactly 0.2 l of dry N-methylpyrrolidone was added. The 
mixture was heated to and held at 115.degree. C. until the polymer 
dissolved (20 to 30 minutes). The solution was then allowed to cool to 
90.degree. C. and 0.4 l of hot toluene were added in portions when the 
solution appeared to change from lustrous to grainy as precipitation of 
polymer began. The slurry was then heated at 100.degree. C. and mixed for 
15 minutes before filtration. The polymer was separated by filtration 
while hot, then dried under vacuum at 80.degree. C. 
The product having an inherent viscosity of about 0.95 was stored in a dry 
box. 
EXAMPLE 4 
Synthesis and Treatment of 
Poly[tetradecane-1,14-di(carbonyloxy)ethane-1,2-di(amidocarbonylmethylene) 
Exactly 4.89 g of 1,2-di(hydroxyacetamido) ethane was mixed well with 0.05 
l of dry toluene and placed in a large flask. To this mixture was added 
8.975 g of distilled hexadecanedioyl chloride. The mixture was heated and 
stirred under nitrogen at 70.degree. C. for two hours and then at 
90.degree. C. for about two hours, then at reflux for about 0.75 hour. To 
this reaction mixture was added 0.080 l of dry N-methylpyrrolidone. The 
polymer dissolved (20 to 30 minutes). To the solution was then added hot 
toluene with mixing to cause precipitation of the polymer. The white 
polymer was separated by filtration under nitrogen, then dried in a vacuum 
oven for 16 hours at 80.degree. C. to remove toluene and 
N-methylpyrrolidone. 
The product was not soluble in 2,2,2-trifluoroethanol due to its increased 
hydrocarbon content therefore its inherent viscosity could not be 
determined by that method. Based on its smooth, uniform appearance and the 
lack of lumps, it is believed that the polymer did not gel during 
synthesis. Filaments pulled from a melted sample of polymer were easily 
cold drawn by hand to give tenacious fiber indicating that a satisfactory 
inherent viscosity (and therefore molecular weight) had been obtained. 
EXAMPLE 5 
Synthesis and Treatment of 
Poly[oxysuccinoyloxydodecane-1,12-di(amidocarbonylmethylene)] 
Exactly 40 g of 1,12-di(hydroxyacetamido)dodecane was mixed well with 0.5 l 
of dry toluene and placed in a large flask and heated to obtain a 
solution. To this solution was added slowly 19.6 g of distilled succinoyl 
chloride. The mixture was heated and stirred under nitrogen at 70.degree. 
C. for three hours, then at reflux for about two hours. The toluene was 
removed by filtration. The polymer was dried in vacuum at 80.degree. C. 
overnight. A portion (24 g) of the solid polymer was placed in a flask and 
heated on an oil bath at 120.degree. C. under nitrogen with overhead 
stirring, then 100 milliliters ("ml") of dry N-methylpyrrolidone and an 
equal volume of dry toluene was added. The mixture was maintained at 
120.degree. C. until the polymer dissolved (about 10 minutes). Hot toluene 
(100 ml) was added. The solution was allowed to cool to 85.degree. C. and 
150 ml of hot toluene was added slowly when the solution appeared to 
thicken. The slurry was then heated at 120.degree. C. and mixed for 15 
minutes before filtration. The polymer was separated by filtration under 
nitrogen, then dried in a vacuum oven tumble drier for about 16 hours at 
80.degree. C. to remove solvent. The product having an inherent viscosity 
of about 1.16, was stored in a dry box. 
Using a sample of the polymer which had not been treated with 
N-methyprrolidone (NMP) and a sample of the same polymer which had been 
synthesized in the same way but not treated with NMP, a comparison of the 
inherent viscosities was made at various temperatures as follows: 
TABLE II 
______________________________________ 
Temperature Inherent Viscosity (dl/g) 
(.degree.C.) NMP Treated 
Untreated 
______________________________________ 
150 1.16 1.05 
170 1.04 0.80 
180 1.04 0.71 
190 0.82 0.69 
200 0.78 0.65 
210 0.72 0.53 
220 0.64 0.50 
______________________________________ 
These results indicate that treated polymer could be successfully extruded 
at 180.degree. C. with no substantial deterioration. 
EXAMPLE 6 
Synthesis and Treatment of 
Poly[oxysuccinoyloxyhexane-1,6-di(amidocarbonylmethylene)] 
A dispersion of 40 g of 1,6-di(hydroxyacetamido)hexane in 100 ml of toluene 
was added to 250 ml of toluene dried by distilling off 100 ml of an 
initial portion of 350 ml. The mixture was allowed to cool to about 
60.degree. C. and 26.7 g of succinoyl chloride was added. The temperature 
of the mixture was maintained at 65.degree. C. for 2.5 hours, then raised 
to 90.degree. C. for two hours. The mixture was then heated at reflux for 
about 1.5 hours. The inherent viscosity of samples of the reaction mixture 
was measured at the end of each temperature run and was observed to 
increase gradually. After the completion of reflux the mixture was 
filtered hot to isolate the solid polymer and the polymer was dried in 
vacuo at 100.degree. C. overnight. The inherent viscosity was measured to 
be 1.1. A 24 g portion of the polymer was mixed under a nitrogen 
atmosphere with 100 ml of toluene and 60 ml of N-methylpyrrolidone. The 
mixture was heated to 110.degree. C. and maintained at that temperature 
until the polymer dissolved (about 0.5 hour). The mixture was then allowed 
to cool until it began to solidify. Hot toluene was added to the mixture 
and the polymer solidified. The solid polymer was separated from the hot 
liquid by filtration and dried in vacuo overnight at 100.degree. C. 
The inherent viscosity was measured after drying to be 1.1. 
The effect upon heat stability achieved by the present invention in 
Examples 1, 3, 5, and 6 was evaluated by measuring the inherent viscosity 
dl/g of the polymer produced in each example before and after heating to 
170.degree. C. for 10 minutes. The same measurements were taken of 
polymers of the same composition but not treated with an amide 
group-containing solvent in accordance with the invention. 
TABLE III 
______________________________________ 
Without Treatment 
With Treatment 
Example Initial Final Initial 
Final 
______________________________________ 
1 1.2 0.31 1.2 1.18 
3 1.1 0.67 1.2 1.18 
5 1.05 0.8 1.16 1.04 
6 1.1 0.55 1.1 0.64 
______________________________________ 
EXAMPLE 7 
Synthesis and Treatment of 
Poly[decane-1,10-di(carbonyloxy)ethane-1,2-di(amidocarbonylmethylene)] 
Exactly 500 g of 1,2-di(hydroxyacetoamido)ethane was mixed well with 1.5 l 
of dry toluene and placed in a 22 l flask. To this mixture was added 3.5 l 
of toluene and then 758.29 g of distilled dodecanedioyl chloride. The 
mixture was heated and stirred under nitrogen at 90.degree. C. for 6 
hours, then at reflux until the inherent viscosity of the polymer was 
greater than 1.2. About 1.5 l of hot toluene was then added and the 
mixture heated at reflux for 2 hours. The inherent viscosity of the 
polymer was measured periodically until it reached 1.2 when 1.3 l of dry 
N-methylpyrrolidone and 1.3 l of dry N,N-dimethylformamide were added. The 
mixture was heated to and held at 115.degree. C. until the polymer had 
completely dissolved (taking about 20 to 30 minutes). The solution was 
allowed to cool to 90.degree. C. and 4 l of hot toluene were added in 
portions when the solution appeared to change from lustrous to grainy 
appearance as precipitation of polymer began. The slurry was then heated 
at 100.degree. C. and mixed for 15 minutes before filtration under 
nitrogen, then dried in a vacuum oven tumble drier for about 3 hours to 
remove solvent, then dried for 16 hours at 90.degree. to 100.degree. C. to 
remove the amide group-containing solvents. 
The resultant product, a white powder, had an inherent viscosity of about 
1.16 and was stored in a dry box. After melting to 170.degree. C., the 
product had an inherent viscosity of 1.12 and appeared to be whiter than 
the polymer of Example 1 after melting. 
EXAMPLE 8 
To a mixture of 20 g of 1,2-di(hydroxyacetamido)ethane in 200 ml of dry 
toluene was added 7.58 g of dodecanedioyl chloride, 5.995 g of suberoyl 
chloride, 6.79 g of sebacoyl chloride, and 5.198 g of adipoyl chloride. 
The mixture was heated to 80.degree. C. and held at that temperature for 6 
hours. The mixture was then heated to boiling and polymer began to 
precipitate. To this hot mixture was added 100 ml of N-methylpyrrolidone 
in which the polymer dissolved. The mixture was heated to reflux for 2 
hours. The polymer was then precipitated by the addition of hot toluene. 
After being allowed to precipitate, the polymer was separated from the 
composition by filtration. It was then dried in a vacuum oven at 
100.degree. C. 
The inherent viscosity was determined to be 0.85. 
EXAMPLE 9 
A mixture of about 300 ml of dry toluene and 9.9 g of 
1,2-di(hydroxyacetoamido)ethane suspended in about 100 ml of toluene was 
distilled to remove about 100 ml of toluene. The mixture was cooled to and 
held at 90.degree. C. while adding 30.0 g of dodecanedioyl chloride. The 
mixture was heated at 90.degree. C. for 2 hours then 11.39 g of 
1,2-di(alpha-hydroxypropionamido)ethane was added. The mixture was heated 
for an additional 2 hours at 90.degree. C., then heated to 100.degree. C. 
After one hour at 100.degree. C. the inherent viscosity was 1.19. To this 
mixture was added 100 ml of N-methylpyrrolidone. The solution was then 
held at 100.degree. C. for 1.5 hours. The mixture was then cooled to 
80.degree. C., then reheated to and held at 100.degree. C. for 0.5 hour. 
The polymer was precipitated by addition of ethyl acetate, separated by 
filtration, and dried under vacuum at 100.degree. C. 
The inherent viscosity was determined to be 1.25. 
Various modifications and alterations of this invention will become 
apparent to those skilled in the art without departing from the scope and 
spirit of this invention.