Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-06-01
2001-06-19
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S313000, C528S324000, C528S329100, C528S332000, C528S335000, C528S336000, C528S337000
Reexamination Certificate
active
06248861
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the manufacture of branched polyamides. In particular, the invention relates to a multi-stage process for the manufacture of branched polyamides from dinitrile and diamine reactants.
BACKGROUND OF THE INVENTION
The conventional process for manufacturing polyamides is known as the “salt-strike” process. In this process, aliphatic dicarboxylic acid monomer is admixed with aliphatic diamine monomer in aqueous solution to form a salt. The salt is fed into a reactor in which both temperature and pressure are elevated. With the emission of water and volatile matter, molten polymer is formed and discharged from the reactor.
Alternative routes to the manufacture of polyamides have been developed. For example, processes in which a dinitrile and a diamine are polymerized to form linear polyamide are described in a number of patent references such as U.S. Pat. No. 2.245,129 to Greenwalt, U.S. Pat. No. 3,847,876 to Onsager, U.S. Pat. No. 4,436,895 to Hoffman et al., and U.S. Pat. No. 4,520,190 to Coffey et. al.
More recently, U.S. Pat. No. 4,739,035 to Shyu et al., describes a two-step process for the manufacture of a polyamide from diamine and dinitrile reactants in which the dinitrile is initially reacted with water in the presence of a catalyst at a temperature sufficient to cause substantial hydrolysis of the dinitrile. Subsequently, the diamine is added to the reaction mixture at a temperature sufficient to cause polymerization.
In a further U.S. Patent, U.S. Pat. No. 5,109,104 to Marks, a process for making polyamide is taught in which an omega-aminonitrile is heated with water and an oxygenated phosphorus catalyst at a pressure of between 200-350 psig. Upon reaching a temperature of 200° C.-260° C., water is added continuously, to a total amount of 15-75 grams/100 grams of omega-aminonitrile, and once the temperature is above 240° C., water vapor and ammonia are continuously removed from the reactor. The resultant mixture is then polymerized at a temperature between 240° C.-330° C.
There are, however, disadvantages associated with the processes described above. Firstly, processes in which dintrile and diamine monomers are reacted tend to yield lower molecular weight polymers due to incomplete hydrolysis of the dinitrile functionality. Moreover, these processes can lead to the formation of organic by-products which causes discoloration of the polymer product. In the manufacture of branched polymers, these problems are accentuated in the polymer product. Alkyl branched monomers are generally more volatile than their linear counterparts and this makes them more prone to by-product formation. As a result, problems of lower molecular and discoloration in the polymer product are enhanced. Accordingly, there is a need for improved methodology, particularly in the manufacture of branched polyamides.
SUMMARY OF THE INVENTION
It has now been found that branched homopolyamides and copolyamides can be formed by combining a dinitrile with a diamine, and optionally combining aliphatic dicarboxylic acids and nitriles and other aliphatic diamines and dinitriles with the dinitrile/diamine mixture, while minimizing the adverse effects of prior methods.
Accordingly, in one aspect the present invention provides a multi-stage process for the manufacture of a branched aliphatic polyamide comprising the steps of:
(a) feeding an admixture of aliphatic dinitrile, aliphatic diamine and water to a reactor, wherein the amount of water is at least the stoichiometric amount required for conversion of dinitrile and diamine to polyamide and wherein at least one of said dinitrile and said diamine are branched;
(b) heating the admixture in the reactor to a temperature of at least about 270° C. under a pressure of at least about 1.2 MPa in the presence of a catalyst with the incremental addition of water;
(c) venting water ammonia and other volatile matter from the reactor while maintaining said temperature and pressure for a period of time of at least about 30 minutes;
(d) maintaining said temperature for a further period of time while reducing the pressure in the reactor to atmospheric pressure; and
(e) discharging the polyamide so obtained from the reactor.
The present process advantageously provides a one-pot, multi-stage polycondensation process for the manufacture of branched polyamides. The incremental addition of water and the continuous removal of water and ammonia from the reaction mixture during the elevated temperature stage of the reaction minimizes discoloration of the polyamide product. Moreover, the reaction is conducted under relatively low pressure, which also allows effective purging of undesirable by-products such as ammonia. The effective purging of ammonia speeds the rate of hydrolysis of the dinitrile reactant thereby minimizing the loss of volatile branched reactant monomers. In this way, the dinitrile and diamine reactants are approximately maintained in stoichiometric ratio resulting in a polyamide product of good molecular weight.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a multi-stage process for manufacturing branched polyamide from a dinitrile and a diamine in which at least one of the dinitrile and diamine is branched.
There is no particular requirement with regard to dinitriles that are suitable for use in the present process of making branched polyamides, with the exception that at least one of the dinitrile and the diamine is branched. In the event that the dinitrile used is to be branched, examples of suitable branched dinitriles include, but are not limited to, 2-methyl glutaronitrile, 3-methyl glutaronitrile, n-methyl 1, 4-dicyanobutane where n is 1 or 2 n-methyl 1,5-dicyanopentane where n is 1, 2 or 3, n-methyl dicyanohexane where n is 1, 2 or 3, and n-methyl 1,10 dicyanodecane where n is 1-5. Other branched dinitriles can also be used in the present method, and particularly dinitriles comprising alkyl branches of from 1-3 carbon atoms, i.e. methyl-, ethyl- and propyl- branches. Examples of suitable unbranched dinitriles include, but are not limited to, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane and 1,10-dicyanodecane. Preferred dinitriles in accordance with the present invention, however, have six carbon atoms such as adiponitrile, 2-methyl glutaronitrile and other dinitriles derived from butadiene and hydrogen cyanide (HCN).
Similarly, any diamine can be used in the present process with the exception that it must be a branched diamine when the dinitrile used is not branched. Examples of suitable branched diamines include, but are not limited to 2-methyl pentamethylene diamine, 3-methyl pentamethylene diamine. n-methyl 1,6-hexamethylene diamine where n is 2 or 3, n-methyl 1,7-heptamethylene diamine where n is 2-4, n-methyl 1,8-octamethylene diamine where n is 2-4 and n-methyl 1,12-dodecamethylene diamine where n is 2-6. Other branched diamines can also be used in the present method, and particularly diamines comprising alkyl branches of from 1-3 carbon atoms. In the event that a branched diamine is not required, examples of suitable unbranched diamines include, but are not limited to, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-hexamethylene diamine, 1,7-heptamethylene diamine. 1,8-octamethylene diamine and 1,12-dodecamethylene diamine. Preferred diamines in accordance with the present invention have six carbon atoms such as 2-methyl pentamethylene diamine, hexamethylene diamine and other diamines derived from butadiene and HCN.
The dinitrile and diamine may optionally be admixed with one or more aliphatic dicarboxylic acids; lactams; alpha, omega aminocarboxylic acids; alpha omega amino nitrites; alpha, omega alkylene dinitriles; and/or other aliphatic diamines. Examples of suitable aliphatic dicarboxylic acids that can optionally be combined with the dinitrile and diamine to form a branched polyamide include 1, 6-hexanediol acid (adipic acid), 1, 7-heptanedioic acid (pimelic acid), 1,8-octanedioic acid (suberic acid), 1,9-nonanedioic acid (azelaic ac
Dupont Canada Inc.
Hampton-Hightower P.
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