Single step preparation of block copolymer of polyamides

Process for forming block copolymer involves mixing dry salt of a prepolyamide and a molten melt-spinnable polyamide. Mixture is heated to a temperature in the range of between from the melting point of higher melting component of the mixture to below amide-interchange temperature of a blend of the melt-spinnable polyamide and the homopolymer which would result from the polymerization of the salt. Mixing and heating is continued until substantially all of the salt and the polyamide are converted into a block copolymer. The latter can be used to make fibers. One example of a suitable salt is a 30203-6 salt.

CROSS REFERENCE TO RELATED APPLICATIONS 
This application is related to U.S. patent application Ser. No. 740,159 
filed same date by applicant. Subject matter of related application is a 
low energy method for forming block copolymers of polyamide. 
BACKGROUND OF THE INVENTION 
1. Field of Invention 
A new and useful process is directed for forming a block copolymer. The 
process is more directed to the forming of a block copolymer of two 
different polyamides having utility, after further processing for example, 
as a fiber. The copolymer comprises blocks of many monomeric repeating 
units of each of the different polyamides. By way of comparison, a 
copolymer can comprise random sequences of repeating units of each of the 
different polyamides. The latter can be referred to as a random copolymer. 
Furthermore, a block copolymer and a random copolymer formed from the same 
two different polyamides are known to possess different properties. 
2. Description of the Prior Art 
Block copolymers of polyamides and methods for preparing said copolymers 
are known, see U.S. Pat. No. 3,683,047, Honda et al., issued Aug. 8, 1972. 
One disclosed method for producing a block copolymer involves mixing two 
different polyamide polymers at a temperature above an amide-interchange 
temperature of the mixed polyamides until a block copolymer is formed. By 
way of comparison if the aforementioned mixing at said temperature is of 
further duration the resulting product is a random copolymer. 
The molecular weight of each of the polyamides used to make a block 
copolymer via amide-interchange can be relatively high, for example, 
50,000-100,000. It is believed that at above an amide-interchange 
temperature an exchange can occur between the two different polyamide 
molecules at any location where 
##STR1## 
exists. Thus it is possible that with two different polyamides, each of 
50,000 molecular weight, the amide-interchange occurs right in the middle 
of the two molecules. As such a copolymer will have formed with one block 
having a molecular weight of 25,000 and the other block having an equal 
molecular weight while the copolymer still has a molecular weight of 
50,000. Equally, the amide-interchange could occur towards one end of a 
polyamide and thus a copolymer could result having one segment, of say, 
49,000 molecular weight derived from one polyamide, attached to another 
segment, of say, 200 molecular weight derived from the other polyamide. 
Because of apparent lack of control of where the amide-interchange will 
occur other methods have been suggested. 
Honda et al suggests using two different low molecular weight, i.e. 
1000-4000, polyamides. The polyamides are different, in part, in that one 
is an aminoterminated polyamide whereas the other is a 
carboxylic-terminated polyamide. The other difference resides in that the 
balance of polyamides are also different. The aforementioned different 
polyamides are copolymerized at a temperature where amide-interchange or 
transamidation is nominal while the reaction of amino-terminated groups 
with carboxylic-terminated groups occur almost completely. The resulting 
product is a block copolymer wherein the blocks have essentially a 
molecular weight of the starting polyamide, i.e. 1000-4000. 
The aforementioned methods require separate preparation of each of the 
starting components followed by remelting and mixing to make a block 
copolymer. This is a disadvantage. 
SUMMARY OF THE INVENTION 
Contrary to expectations based on the prior art it has now been found that 
a block polyamide copolymer can be formed using a prepolyamide salt and a 
molten meltspinnable polyamide as the starting components. Thus the 
separate preparation of one of the starting polyamides can be bypassed as 
well as its remelting. 
Present process involves mixing the dry salt and the molten polyamide at a 
temperature in the range of between from the melting point of the higher 
melting component to below the amide-interchange temperature of a blend of 
the melt-spinnable polyamide and the homopolymer which would result from 
the polymerization of the salt. The mixing at the elevated temperature 
continues until substantially all of the salt and the polyamide are 
converted into a block copolymer. 
The resulting block copolymer can be converted into a fiber or monofilament 
which can be further converted to yarn or fabric, for example.

DESCRIPTION OF THE INVENTION 
One of the components used as a starting material in this process is a salt 
selected from the group consisting of prepolyamides represented by the 
following formula: 
##STR2## 
wherein R.sub.1, R.sub.2 and R.sub.3 are selected from the group 
consisting of H, C.sub.1 -C.sub.10 alkyls and C.sub.3 -C.sub.10 isoalkyls; 
R.sub.4 is selected from the group consisting of C.sub.1 -C.sub.10 
alkylenes and C.sub.3 -C.sub.10 isoalkylenes; and 
R.sub.5 is selected from the group consisting of C.sub.6 -C.sub.14 
arylenes, C.sub.0 -C.sub.10 alkylenes and C.sub.3 -C.sub.10 isoalkylenes. 
The foregoing solid salt can be referred to as a prepolyamide because upon 
heating under suitable conditions the salt loses water and forms 
##STR3## 
linkages to form a polyamide. 
The other component used as a starting material in this process is a 
melt-spinnable polyamide. The term "melt-spinnable polyamide" as used 
herein excludes the polyamide which could be formed by the aforementioned 
prepolyamide salt. Melt-spinnable refers to a process wherein the polymer, 
a polyamide, is heated to above its melting temperature and while molten 
forced through a spinneret. The latter is a plate containing from one to 
many thousands of orifices, through which the molten polymer is forced 
under pressure. The molten polymer is a continuous filament and depending 
on the number of orifices many filaments can be formed at the same time. 
The molten filaments are cooled, solidified, converged and finally 
collected on a bobbin. This technique is described in greater detail in 
ENCYCLOPEDIA OF POLYMER SCIENCE AND TECHNOLOGY, Vol. 8, Man-Made Fibers, 
Manufacture. 
Polyamides which are crystallizable and have at least a 30.degree. C 
difference between melting point and the temperature at which the molten 
polymer undergoes decomposition can be melt spun. Examples of melt 
spinnable polyamides are as follows: nylon-6,6 (also known as poly 
(hexamethylene adipamide); nylon-6,10(poly(hexamethylene sebacamide)); 
nylon-6 (poly(pentamethylene carbonamide)); nylon-11 (poly(decamethylene 
carbonamide)); MXD-6 (poly (methaxylylene adipamide)); M-9 
(bis(paraminocyclohexyl) methane azelamide)); M-10 
(bic(paraminocyclohexyl) methane sebacamide)); and M-12 
(bis(paraminocyclohexyl) methane dodecanoamide)); others are listed in 
ENCYCLOPEDIA OF POLYMERS SCIENCE AND TECHNOLOGY, Vol. 10, Section 
Polyamide Fibers, table 12. Methods for preparing these polyamides are 
well known and described in numerous patents and trade journals. 
The amount of salt present relative to the amount of the melt-spinnable 
polyamide can vary within a broad range. If however, too much of either 
component is used then the resulting copolymer is not a block copolymer. 
Rather it is a copolymer consisting of mostly long chains of the most 
prevalent component bridged together by relatively short segments of the 
lesser component arranged in a statistically random fashion. And 
difference between a random and a block copolymer can be demonstrated by 
comparing physical properties of the two. In this invention an operative 
range of the amount of salt to the total weight of the components is 
between from about 10 weight % to about 75 weight % with about 20 weight % 
to about 40 weight % preferred. 
The process involves mixing in an inert atmosphere e.g. nitrogen, carbon 
dioxide, and the like, the prepolyamide salt with the molten 
melt-spinnable polyamide. The molten polyamide is prepared by heating it 
to a temperature above its melting point but below its decomposition 
temperature. It too is heated to in inert atmosphere. The resulting 
mixture of the salt and the molten melt-spinnable polyamide is heated to a 
temperature in the range of between from the melting point of the higher 
melting component to below about the amide-interchange temperature of a 
blend of the meltspinnable polyamide and the polyamide which would result 
from the polymerization of the salt. The lower temperature is defined by 
the melting point of either the melt-spinnable polyamide or the salt 
whichever is higher. 
The upper temperature for the process is an amide-interchange temperature. 
In this process one of the polyamides which could have such an interchange 
is the melt-spinnable polyamide. The other material would be a polyamide 
formed from the prepolyamide salt. Thus if the latter polyamide was formed 
and mixed with the melt-spinnable polyamide there would be a temperature 
below which amide interchange would not occur between the two or be so 
nominal as not to form a block copolymer. 
Amide-interchange refers to the reaction where an 
##STR4## 
(labeled A in the following illustration) reacts with a different 
polyamide (labeled B in the following illustration) so that the following 
is representative of the end result: 
##STR5## 
Amide-interchange is the mechanism by which a block copolymer is formed by 
a process known as melt blending. 
The mixture of salt and the molten melt-spinnable polyamide is maintained, 
while being mixed, within the aforementioned temperature range and under 
an inert atmosphere. The mixing at the elevated temperature continues 
until substantially all of the salt and the polyamide are converted to a 
block polymer. Samples of the mixture can be taken during processing and 
tested to determine when the conversion is essentially completed. One of 
the testing methods is described in the Examples. 
When substantially all of the salt and the polyamide are converted to a 
block copolymer the resulting polymer can be represented by the following 
structure: 
##STR6## 
wherein the R's are as heretofore defined. The subscripts n and m refer to 
the relative amounts of each present. Thus the percentage, 
##EQU1## 
is between from about 10 weight % to about 75 weight % as the operative 
range. Nominal amounts of unreacted salt or melt-spinnable polyamide can 
remain, however, its effect on the resulting properties of the block 
copolymer would be negligible. Furthermore, any unreacted component could 
be converted during further processing of the block copolymer, for 
example, conversion to a fiber. On the other hand it could be removed by 
various means. 
As shown in the foregoing structure for the block copolymer the 
melt-spinnable polyamide is present in its bivalent radical form. The 
bivalence results from the coupling of 
##STR7## 
groups within the melt-spinnable polyamide with the 
##STR8## 
of the salt. 
The following examples describe how certain block polyamide copolymers were 
prepared using present invention. Also described are comparisons with 
block copolymers of similar polyamides prepared by other methods. Also 
comparisons are made with polyamides and random polyamide copolymers. 
EXAMPLE 
A salt having the following structure: 
##STR9## 
which can be referred to as a 30203-6 salt, was used as a component and 
was prepared in the following manner. First, 1,2-bis 
(.beta.-cyanoethoxyethane), having the following structure: 
NC--(CH.sub.2).sub.2 --O--(CH.sub.2).sub.2 --O--CH.sub.2).sub.2 --CN, was 
prepared. To prepare it a 5 liter double walled (for water cooling) glass 
reactor with a bottom drain and stopcock was charged with 930 grams (15 
moles) of ethylene glycol and 45.6 grams of 40% aqueous KOH solution. Some 
1620 grams (30.6 moles) of acrylonitrile (NC--CH=CH.sub.2) were then added 
dropwise with stirring at such a rate that the temperature was kept below 
35.degree. C. After the addition was completed the mixture was stirred an 
additional hour and allowed to stand overnight. The mixture was 
neutralized to a pH of 7 by the addition of 6 molar HCl. After washing 
with a saturated NaCl solution three times, the product was separated from 
the aqueous layer, dried over CaCl.sub. 2 and passed through an Al.sub.2 
O.sub.3 column to insure that all basic materials had been removed. The 
yield was 90% of theoretical. 
The next step was preparation of 4,7-dioxadecamethylenediame (NH.sub.2 
(CH.sub.2).sub.3 --O--(CH.sub.2).sub.2 --O--(CH.sub.2).sub.3 --NH.sub.2). 
Into an 800 milliliter hydrogenation reactor was charged 150 grams of 
1,2-bis (.beta.-cyanoethoxyethane), 230 milliliters of dioxane and about 
50 grams Raney Co. After purging the air, the reactor was pressurized with 
hydrogen to 2000 p.s.i. and heated to 110.degree. C. As the hydrogen was 
consumed additional hydrogen was added until the pressure remained 
constant. Upon cooling, the pressure was released and the catalyst was 
filtered. The dioxane was removed by atmospheric distillation. The 
remaining mixture was distilled using a 3 foot spinning band distillation 
unit. The diamine distilled at 123.degree.-124.degree. C and 3.75 mm Hg. 
About 98 grams of 99.95% pure material were obtained. The resulting 
material can be referred to as a 30203 diamine. 
The next step was the preparation of the salt. To a solution of 41.50 grams 
of adipic acid dissolved in a mixture of 250 milliliters of isopropanol 
and 50 milliliters of ethanol were added, with stirring, 50 grams of the 
30203 diamine dissolved in 200 milliliters of isopropanol. An exothermic 
reaction occurred. Upon cooling, a polymer salt crystallized out of 
solution. The salt was collected on a Buchner funnel and subsequently 
recrystallized from a mixture of 400 milliliters of ethanol and 300 
milliliters of isopropanol solution. The product, dried in vacuo overnight 
at 60.degree. C, had a melting point of 127.degree.-128.degree. C and a pH 
of a 1% solution was 6.9. 85 grams (92% yield of theoretical) of the salt 
was obtained. 
The block copolymer was prepared in the following manner. A suitable 
container was purged with dry nitrogen and while under nitrogen 40 grams 
of dry powdered nylon-6 were added to the container. The nylon-6 was a 
commercially available material. The container and its contents were 
heated to 245.degree. C by a vapor bath. The nylon-6 used had onset 
melting point of 210.degree. C. To the molten nylon-6 were added 17.1 
grams of the 30203-6 salt previously prepared. While the addition of the 
salt was made the container was kept under a positive pressure of nitrogen 
and during and after the addition the resulting mixture was constantly 
stirred. The container and its contents were maintained at a temperature 
of 245.degree. C for one hour. After cooling the resulting polymer was 
analyzed as to its structure. 
The method used to analyze the polymer structure involved the fractional 
precipitation of the polymer in formic acid. Generally the method was as 
follows: one gram of dry polymer (copolymer; random or block or 
homopolymer) was weighed to the nearest tenth of a milligram. The one gram 
sample was dissolved in a standardized formic acid (i.e. 90% formic acid). 
The resulting solution was diluted with distilled water to a given % 
formic acid, e.g. 55% formic. The solution was allowed to stand at ambient 
temperature for three hours and then filtered. The collected precipitate 
was then washed with water, dried and weighed to give the % sample 
recovered at that particular formic acid concentration. A graph was then 
constructed by plotting the % of the sample recovered vs. formic acid 
concentration. The different polymers, i.e. random copolymer, block 
copolymer, homopolymer (e.g. nylon-6) each have different solubilities in 
formic acid. Thus each gave a different characteristic curve. 
Accompanying Table I, contains the recovery data for nylon-6, polymerized 
30203-6 salt, and a physical mixture of equal amounts of nylon-6, 
polymerized 30203-6 salt, and block 30203-6/6 polymer prepared by melt 
blending; and random 30203-6/6 copolymer. Also shown for the mixture are 
calculated values based on what the expected values would be based on the 
recovery curves for the individual polymers. 
TABLE I 
__________________________________________________________________________ 
Precipitation of Various Polyamides in Formic Acid 
% Recovered 
Polymerized 
Mixture of 
Nylon 6.sup.+ 
30203-6.sup.+ 
3 Polyamides* 
Random 
% Formic Acid 
1 2 1 2 Observed 
Calculated 
30203-6/6 
__________________________________________________________________________ 
60 0 0 -- -- 0 0 
57 -- 0 -- -- -- -- 
56 95.4 
-- -- -- -- -- 
55 -- 92.2 
-- -- 36.1 31.9 0 
50 96.5 
93.8 
-- -- 39.3 32.2 0.2 
47 -- -- -- -- -- -- 0.4 
45 97.5 
95.1 
-- -- 53.7 44.0 -- 
44 -- -- -- -- -- -- 5.1 
41 -- -- -- -- -- -- 11.7 
40 -- -- -- -- 61.4 61.1 -- 
38 -- -- -- -- -- -- 23.8 
35 -- -- -- -- 62.2 62.1 -- 
32 -- -- -- -- -- -- 62.2 
30 98.4 
96.4 
0 0 -- -- -- 
29 -- -- -- -- -- -- 71.1 
26 -- -- -- -- -- -- 79.7 
25 -- -- -- -- 63.8 62.8 -- 
23 -- -- -- -- -- -- 81.5 
20 -- -- -- 0.4 
63.9 63.3 82.8 
15 -- -- 0.7 
0.7 
67.5 64.2 -- 
10 -- -- ** 47.8 
69.6 69.4 -- 
5 -- -- 86.7 
83.6 
86.5 80.6 -- 
2 -- -- ** 89.4 
86.5 81.0 -- 
__________________________________________________________________________ 
Notes 
.sup.+ Sample 1 based on 2 grams whereas sample 2 is based on 1 gram 
*Mixture consists of 1 gram each of nylon 6, polymerized 30203-6 and bloc 
30203-6/6 
**Sample taken but result was believed to be erroneous. 
Accompanying Table II contains recovery data for four 30303-6/6 block 
copolymers prepared by melt blending and two block 30203-6/6 copolymers 
prepared by this invention. 
Both the data in Table I and the representative curve (line A) in the 
FIGURE shows that almost all of the nylon-6 is recovered when the % of 
formic acid is decreased to about 55-56%. In contrast with the polymerized 
30203-6 salt, represented by line F, none of the polyamide precipitates 
until the formic acid concentration is down to about 15%. The data for the 
polymerized salt is given in Table I. 
Both the data in the Table I and the representative curve (line D) in the 
FIGURE, also indicates that the precipitation of a random 30203-6/6 
copolymer does not occur until about a 45% of concentration of formic acid 
is reached. Furthermore, in contrast to the nylon-6, which has an almost 
perpendicular recovery line (except for the top portion), the slope of the 
recovery curve for the random copolyamide is much more gradual. 
The DSC (Differential Scanning Calorimeter) curves for the block 
copolymers, prepared by the process, showed the absence of endothermic 
peaks corresponding to either the melting of 30203-6 salt or 30203-6 
polymer. Further the block copolymer, prepared by this process, had 
endothermics which corresponded to those shown by 30203-6/6 block 
copolymers prepared by melt blending. Finally the block copolymers had 
melting points more than 40.degree. C above that observed for a random 
copolymer of the same overall composition. Thus this comparison indicates 
that block polyamide copolymers can be prepared by this invention. 
Some of the foregoing polymers were also characterized by DSC melting 
points. In particular melting points were obtained for nylon-6, random 
30203-6/6 and the block 30203-6/6 copolymers prepared by the invention. 
The DSC and inherent viscosities are given in the accompanying Table III. 
TABLE III 
______________________________________ 
Physical Constants 
DSC - .degree. C 
Inherent 
Material Onset Peak Viscosity 
______________________________________ 
Nylon-6 210 222 1.03 
Random 30203-6/6 
138 161 0.81 
Block 30203-6/6 
Sample 7 198 213 0.60 
Sample 8 193 210 0.85 
______________________________________ 
Differences in sample melting temperatures reflect differences in block 
sizes whereas differences in viscosities reflect differences in molecular 
weights. 
Recovery line E represents what happens when a mechanical blend of nylon-6, 
polymerized 30203-6 salt, and block 30203-6/6 is precipitated from a 
solution in formic acid. The actual recovery data for the blend is almost 
equal to a calculated recovery amount based on the actual recovery data 
for the individual polymers when taking into consideration the amount of 
each polymer used to make the mechanical blend. The actual recovery data 
and calculated values are shown in Table I. 
TABLE II 
______________________________________ 
PRECIPITATION OF VARIOUS BLOCK POLYAMIDE IN 
FORMIC ACID 
% Recovered 
By this invention 
Melt Blend 
30203-6/6* 30203-6//.sup. (+) 
% Formic Acid 
3 4 5 6 7 8 
______________________________________ 
55 58.5 0 0 0 0 0 
50 73.2 53.1 0 0 40.5 9.3 
47 82.9 69.9 24.7 0.9 67.1 52.0 
44 86.5 84.7 58.7 6.7 74.2 77.5 
41 87.9 ** 77.7 62.2 81.8 84.6 
38 88.5 89.9 85.2 72.5 84.2 88.7 
35 88.9 92.2 88.5 79.2 85.9 ** 
32 89.5 93.1 89.5 82.5 88.1 90.3 
29 90.0 93.5 90.5 86.1 88.4 93.0 
26 90.7 93.5 91.6 ** 89.5 93.5 
23 89.3 94.0 ** ** 90.3 94.0 
20 90.1 94.5 93.3 87.6 90.3 ** 
______________________________________ 
*Samples prepared by melt blend of 70% nylon-6 and 30% 30203-6 Polymer. 
Samples 3, 4, 5 and 6 were melt blended at 283.degree. C for 15, 60, 180 
and 360 minutes respectively. 
**Indicates sample taken but result was believed to be erroneous. 
.sup.+ Samples prepared using 70% nylon-6 and 30% 30203-6 salt. 
In general then the foregoing comparison of the different recovery curves 
for the different polyamides indicate that the different polymers can be 
characterized by their solubility in formic acid. 
Table II contains data for four different block 30203-6/6 copolymers. The 
latter, samples 3, 4, 5 and 6, were prepared by melt blending of nylon-6 
and 30203-6 polymer for various lengths of time. Table II also contains 
the recovery data for two block 30203-6/6 copolymers, samples 7 and 8, 
prepared by this invention. 
Comparison of recovery lines for 30203-6/6 copolymers prepared by melt 
blending with those by present invention indicate that the latter method 
results in a block copolymer. The recovery lines are representative lines 
B and C in the FIGURE. Line B represents a composit recovery curve of a 
30203-6/6 block copolymer prepared by melt blending 30203-6 polyamide and 
nylon-6 at 282.degree. C for about 2-3 hours. Line C represents the 
recovery curve of a block copolymer prepared by this invention. The small 
difference between lines B and C are believed to represent an experimental 
difference rather than a difference of structure. Changes in processing 
for either or both of the block copolymers could change the % recovery. 
Support for this resides in the fact that other block copolymers prepared 
by this invention have recovery curves which were to the left of line B. 
Analogous results, as described heretofore, will be obtained when different 
salts, other than a 30203-6 salt, such as 30403-6, 30603-8, and 30103-14 
are used. Also similar results will be obtained when other temperatures 
are also used. Also, similar results will be obtained when some other 
C.sub.0 -C.sub.10 alkylene or a C.sub.3 -C.sub.10 isoalkylene or a C.sub.6 
-C.sub.14 arylene is used in place of the tetramethylene (R.sub.5) used in 
the example. Examples of the heretofore mentioned C.sub.0 -C.sub.10 
alkylenes and C.sub.3 -C.sub.10 isoalkylenes include ethylene, 
trimethylene, isopropylidene, isobutylidene, and the like. Examples of the 
heretofore mentioned C.sub.6 -C.sub.14 arylenes include naphthylene, 
phenylene, tolylene, and the like. The previously mentioned C.sub.1 
-C.sub.10 alkyls include methyl, ethyl, propyl, butyl, pentyl, hexyl, 
heptyl, octyl, nonyl, and decyl and use of such groups, in place of the 
hydrogen used in R.sub.1, R.sub.2, and R.sub.3, in the example, along with 
isoalkyls will also yield similar results. Use of any one of the 
aforementioned alkylenes or the isoalkylenes in place of the ethylene used 
in R.sub.4 in the example will also yield similar results.