Process for the preparation of a polyamide from unsaturated nitrile, lactam and water

This invention relates to a new process for preparing a copolyamide comprising polymerizing an alpha, beta-unsaturated nitrile and water with a molar excess of a lactam. In one embodiment, acrylonitrile, water and caprolactam are polymerized to form a nylon-3,6.

BACKGROUND OF THE INVENTION 
This invention relates to a new process for preparing a copolyamide 
comprising polymerizing an alpha, beta-unsaturated nitrile, water and a 
lactam. 
The preparation of a polyamide from acrylonitrile and water is disclosed in 
U.S. Pat. Nos. 3,629,203 and 3,499,879. The ring opening addition 
polymerization of caprolactam is also known and is carried out by adding a 
catalytic amount of water to open the ring and then later removing the 
water at an elevated temperature. Surprisingly, applicants have discovered 
that although these polymerizations proceed by different mechanisms the 
alpha, beta-unsaturated nitrile, water and lactam can be polymerized 
together to form a copolymer under the appropriate reaction conditions. 
The process of this invention results in high yields of a copolyamide which 
has particularly good physical properties. Moreover, the percent water 
insolubility and the structure of the resultant copolyamide can be varied 
by varying the reaction conditions. 
SUMMARY OF THE INVENTION 
It has now been discovered that copolyamides can be prepared by a process 
comprising polymerizing an alpha, beta-unsaturated nitrile, water and a 
lactam. More particularly, it has been discovered that a copolyamide 
containing both three carbon and six carbon carbonamide repeating units 
can be prepared by polymerizing acrylonitrile and water with a molar 
excess of caprolactam. 
DETAILED DESCRIPTION 
The Polymer 
The copolyamides obtained by the process of this invention are generally 
defined as containing carbonamide repeating units as follows: 
##STR1## 
wherein R is a suitable substituent and n is 2-11. Each copolyamide will 
contain at least two different carbanamide repeating units. Preferred 
copolyamides are those wherein R is hydrogen and n is 2 and 5. 
The copolyamides of this invention can be polymerized with other monomers 
and/or resins. These monomers and/or resins are selected from the group 
consisting of polyamides such as nylon-3, nylon-4, nylon-6, nylon-6,6, 
nylon-6,10, nylon-11, nylon-12, or monomers thereof such as ammonium 
acrylate; esters such as methyl acrylate; unsaturated acids or salts 
thereof; and vinyl monomers such as acrylamide. 
The properties of the copolyamides obtained by the inventive process vary 
depending upon the amount and identity of the monomers used and the 
reaction conditions. The preferred polyamides are melt processable without 
decomposition and highly crystalline. 
Reactants 
The inventive process is a copolymerization of an alpha, beta-unsaturated 
nitrile, water and a lactam. 
Any alpha, beta-unsaturated nitrile can be polymerized in accordance with 
this invention. The preferred nitriles contain less than 40 carbon atoms 
and are represented by the following formula: 
##STR2## 
wherein each R.sub.1 is independently selected from the group consisting 
of 
(1) hydrogen; and 
(2) C.sub.1-30 alkyls. 
More preferred nitriles are those wherein each R.sub.1 is independently 
selected from hydrogen and C.sub.1-4 alkyls. Examples of these nitriles 
include acrylonitrile and methacrylonitrile. 
Any lactam can be used as a comonomer in the instant invention. The 
preferred lactams contain less than 40 carbon atoms and can be represented 
by the following formula: 
##STR3## 
wherein x is 3 to 11 and wherein each R.sub.2 is independently selected 
from the group consisting of: 
(1) hydrogen; and 
(2) C.sub.1-30 alkyls. 
More preferred lactams are those wherein x is 3 to 5 and R.sub.2 is 
hydrogen or a C.sub.1-4 alkyl. Examples of these lactams include 
caprolactam and pyrrolidone. 
This process works best when a molar excess of the lactam is present. 
Theoretically, all that is needed for the polymerization is one mole of 
lactam per mole of acrylonitrile and water. However, it has been found 
that at equal molar ratios, the copolyamide formed has a low molecular 
weight and takes a long time to form. Therefore, the molar ratio of the 
nitrile to the lactam is preferably less than 1 to 1, more preferably less 
than 0.5 to 1. 
The third monomer component is water. The ratio of the nitrile to the water 
is preferably about 1 to 1. 
Other monomers or polymers can also be polymerized with the nitrile, water 
and lactam in ths process. For example, ammonium acrylate, a nylon-3 
monomer, can be polymerized with the nitrile and lactam to produce a 
copolyamide. Since one mole of water is generated when one mole of 
ammonium acrylate is polymerized to a polyamide, it is only necessary to 
add enough water so that there is a total of one mole of water, from the 
ammonium acrylate polymerization and from the added water, for every one 
mole of the nitrile. Preferably, the molar ratio of the nitrile to the 
ammonium acrylate is about 1 to 1, and thus it is not necessary to add any 
water. In this monomer system, the ratio of the nitrile to the lactam can 
vary widely and ratios of less than 1 to 1 can be used to prepare 
copolyamide. It is preferred to use a ratio of less than 1 to 2. For the 
purpose of this invention, any ammonium salt of an alpha, beta-unsaturated 
carboxylic acid can be used instead of the ammonium acrylate. 
Process Conditions 
The process of this invention can be conducted under a broad range of 
process conditions. It is important to maintain suitable contact between 
the monomers so that the desired polymerization can occur. Although 
suitable contact time can be established when the monomers are in the 
solid, liquid or gaseous phase, it is preferred to perform the 
polymerization in the liquid phase. This liquid phase can be obtained by 
various methods including the use of solvents. 
In the preferred practice of the invention, the monomers are maintained at 
a temperature above their melting points but below the decomposition 
temperature of the monomers or product polymers, which is generally about 
350.degree. C. It is more preferred to conduct this process at a 
temperature between 125.degree. C. and 250.degree. C., and conducting the 
process between 150.degree. C. and 200.degree. C. is most preferred. 
The time required for the instant polymerization process will depend upon 
various process parameters. For example, at low temperatures it will take 
longer for the copolyamide to form than at high temperatures. In general, 
the reaction is conducted in less than 48 hours with times ranging from 8 
to 24 hours normally being adequate to produce polymers. 
Although the monomers can be polymerized in contact with the atmosphere, a 
more desirable group of copolyamides having high intrinsic viscosities and 
molecular weights are obtained by carrying out the polymerization in the 
absence of oxygen. This can be achieved by blanketing the reaction mixture 
with either an inert gas such as nitrogen or with gaseous ammonia. 
The instant polymerization can proceed at atmospheric, superatmospheric or 
subatmospheric pressure. Preferably, the monomers are heated under 
superatmospheric pressures. It has been found that at pressures such as 0 
to 5,000 psig are preferable with 50 to 2,000 psig being most preferable. 
The polymerization process of this invention can proceed by any of the 
generally known modes of polymerization including bulk, slurry, suspension 
or solution polymerization by batch continuous or intermittent addition of 
the monomers and other components. 
It is often convenient to carry out the instant polymerization in the 
presence of a diluent which may also be a solvent to the monomers, 
products or both. Inert diluents which can be used in the process of this 
invention include hydrocarbons such as benzene, toluene, xylene, ethyl 
benzene, solvent naphtha, n-hexane, cyclohexane, isooctane and decalin; 
ether such as dioxane, diethyl ether, dibutyl ether and dimethoxy ethane; 
aromatic halogenated compounds such as chlorobenzene and dichlorobenzene. 
In addition to these organic solvents, an anhydrous solvent such as liquid 
ammonia may also be used. 
The polymerization conditions have a large effect on the physical 
properties of the resultant copolyamide. Lower polymerization temperature, 
increased polymerization time and catalysts favor the formation of a 
copolyamide containing higher percentages of a carbanamide comprising 
three carbons. Increased polymerization time favors formation of higher 
molecular weight copolyamides. 
Certain catalysts have been found to be effective in the instant process. 
These catalysts comprise tertiary amines such as tripentylamine and 
tripropylamine. 
Recovery 
At the end of the polymerization, the unreacted monomers are removed from 
the reaction mass by suitable means, e.g. distillation, extraction with a 
solvent or mixture of solvents or by combination of such techniques. The 
unreacted material may be removed in conjunction with removal of low 
molecular weight polymers, if desired. Any suitable solvent or mixture of 
solvents may be employed in purifying the crude reaction product. The 
reaction of the solvent is more or less selective. If the polymerization 
reaction is carried out in the inert organic diluent in which the polymer 
is insoluble, the polymer will precipitate and may be removed by 
filtration, centifigation, etc. The polymer which is obtained may easily 
be purified by extracting it with a liquid that is a solvent for the 
monomer but which is not a solvent for the polymer. Frequently, water is 
used for this purpose. 
The polymers produced herein have a wide variety of applications. 
Generally, they may be used in any application calling for a polyamide. 
For example, these copolyamides can be used as fibers, plastics, films and 
molding resins.

SPECIFIC EMBODIMENTS 
In order to provide a better understanding of the present invention, the 
following working examples are presented. In each of the examples, the 
polymer formed was identified by various analytical techniques as a 
copolyamide. 
EXAMPLE 1 
The monomers, acrylonitrile and water and caprolactam, were charged into a 
1 liter non-stirred autoclave reactor in a molar ratio of 11/2. The 
autoclave was purged with nitrogen for 2 minutes and then pressurized. The 
polymerization proceeded for 2 hours at 160.degree. C. and then for 22 
hours at 210.degree. C. The reactor was cooled and opened and the polymer 
was broken into small pieces and then water extracted for 24 hours. The 
water insolubility was found to be 42.4% and the polymer comprised 20% 
3-carbon carbonamides and 80% 6 carbon carbonamides. 
EXAMPLES 2-8 
The procedure of Example 1 was repeated. The polymerization conditions and 
the structure of the resultant copolyamide is shown in Table I. 
TABLE I 
______________________________________ 
Preparation of Copolyamides 
React % 
Temp/ H2O Melt 
Molar Time In- Point % 
Ex Reactants 
Ratio (.degree.C./Hr) 
solub 
(.degree.C.) 
Struc.** 
Crystal 
______________________________________ 
1 Acrylo/ 1/1/2 160/2 42.4 155 20/80 40.30 
water/ 210/22 
capro- 
lactam 
2 Acrylo/ 1/1/2 140/2 22.5 160 24/76 43.1 
water/ 180/22 
capro- 
lactam 
3 Acrylo/ 1/1/2 189/24 45.3 155 22/78 42.4 
water/ 230/16 
capro- 
lactam 
4 Acrylo/ 1/1/3 193/24 53.1 165 16/84 42.3 
water/ 
capro- 
lactam 
5 Acrylo/ 1/1/3 160/2 60.2 155 11/89 41.6 
water/ 195/22 
capro- 
lactam 
6 Acrylo/ 1/1/3 175/24 68.0 155 19/81 42.7 
water/ 200/16 
capro- 
lactam 
7* Acrylo/ 1/1/2 160/2 37.0 145 30/70 43.5 
water/ 205/22 
capro- 
lactam 
8* Acrylo/ 1/1/3 193/24 55.7 155 26/74 39.6 
water/ 
capro- 
lactam 
______________________________________ 
*Reactor contains 5% (molar) of tripentylamine based on acrylonitrile 
concentration. 
**Ratio of 3 carbon carbonamides to 6 carbon carbonamides in polymer 
backbone. 
EXAMPLE 9 
The monomers, i.e. acrylonitrile, ammonium acrylate and caprolactam, were 
changed into a 25 ml. glass ampoule in a molar ratio of 11/3. The ampoule 
was purged with nitrogen for 30 seconds and sealed with a flame. The 
ampoule was then placed into a protective metal cage and then the cage 
containing the ampoule was placed in an air oven set at 175.degree. C. for 
24 hours. The ampoule was cooled and opened and the polymer was broken 
into small pieces and then water extracted for 24 hours. The water 
insolubility of this polymer was 30.4%, the crystallinity was 45.4% and 
the polymer comprised 32% 3-carbon carbonamides and 68% 6-carbon 
carbonamides. 
Although only a few embodiments of this invention have been specifically 
described above, it should be appreciated that many additions and 
modifications can be made without departing from the spirit and scope of 
the invention. These and all other modifications are intended to be 
included within the scope of this invention, which is to be limited only 
by the following claims: