Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-06-21
2002-03-12
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S170000, C528S324000, C528S329100, C528S330000, C528S332000, C528S335000, C528S336000, C528S338000, C528S339000, C528S347000, C528S349000
Reexamination Certificate
active
06355769
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the manufacture of partially aromatic polyamides. In particular, the present invention relates to a process for making a partially aromatic polyamide from an aliphatic diamine and the dialkyl ester of an aromatic dicarboxylic acid.
BACKGROUND OF THE INVENTION
Partially aromatic polyamides consist of aromatic dicarboxylic acid and aliphatic diamine monomer units. Such polyamides are generally characterized by high melting points, high glass transition temperatures, low moisture absorption and, unlike aliphatic polyamides such as nylon 6 and nylon 66, good dimensional stability under moist conditions. The combination of high temperature and dimensional stability render partially aromatic polyamides particularly suitable for use in electronics, engineering plastics, films and fibres.
Unfortunately, however, the majority of partially aromatic polyamides are difficult to manufacture using the conventional melt polycondensation process that is successfully used in the manufacture of aliphatic polyamides. These processes generally involve admixing a dicarboxylic acid and a diamine to form a salt in aqueous solution. The salt is heated to a temperature that is higher than the melting point of the polyamide being formed but that does not result in excessive thermal degradation of the desired polyamide. U.S. Pat. No. 5,502,155 to Ng, issued Mar. 26, 1996, does, however, describe such a process for making partially aromatic polyamides. The process involves heating an admixture of an aromatic dicarboxylic acid and an aliphatic diamine to a temperature of at least 270° C. at a pressure of at least 1.2 MPa in the presence of a monocarboxylic acid such as formic acid. Water is added incrementally during heating. This process is particularly suitable for making polyamides from 2,6 naphthalene dicarboxylic acid, and cannot be universally applied to all partially aromatic polyamides.
Partially aromatic polyamides are characterized by melting points of at least about 275° C. and in some instances, melting points of greater than 300° C. Such high melting points generally result in significant thermal degradation during the synthesis of the desired polyamide. Moreover, branching formation side reactions compete with the polymerization reaction at the high temperatures required to maintain the partially aromatic polyamide in the form of a melt. These side reactions lead to serious melt viscosity build-up as the molecular weight of the polyamide increases. The viscous melt traps gaseous condensate within the polymeric molecule. This causes voids to form in the polymer which make subsequent processing of the polyamide difficult.
Processes have been developed which resolve some problems associated with making partially aromatic polyamides by conventional means. For example. Wittbecker and Morgan (Journal of Polymer Science, 40:280 (1959)) describe an interfacial polycondensation process in which an acid chloride, such as a dicarboxylic acid chloride, is reacted with a compound containing an active hydrogen atom (—OH, —NH and —SH) near the interface of the two phases of a heterogeneous liquid system, for example benzene in water. Yamazaki et al. (Journal of Polymer Science, 13:1373-1380 (1975)) describe a low-temperature method of reacting the phosphite and phosphonate salts of aromatic diamines and aliphatic dicarboxylic acids in a pyridine solution in the presence of metal salts such as LiCl or CaCl
2
. However, both of these methods are too costly for practical use on a commercial scale, and nevertheless, would be difficult to conform to continuous operations.
U.S. Pat. No. 3,642,710 to Keen, which issued Feb. 15, 1972, describes a process for making high molecular weight polyamides such as polydodecamethylene terephthalamide, which is a partially aromatic polyamide, at a decreased temperature. Specifically, the reactant, dodecamethylene diammonium terephthalate, is heated at a temperature of about 255-275° C., in the presence of a viscosity stabilizer, a reagent capable of controlling the molecular weight of the polyamide when the polymerization reaction attains equilibrium. In this process, the reaction mass remains solid and can subsequently be melt spun into filaments.
U.S. Pat. No. 3.917,561 to Chapman and Pickett, which issued Nov. 4, 1975, teaches another process for making polydodecamethylene terephthalamide in which a cation-exchange treated dodecamethylene diammonium terephthalate salt is melt polymerized in the presence of a sterically hindered phenol, benzenephosphinic acid, copper acetate in combination with an alkali metal halide or a mixture of any of these additives. In this process, the additives cooperate with the cation-exchange treated salt to provide a melt-stable polyamide. Both this method and the method of Keen described above undesirably involve the step of forming a salt from the diacid and diamine reactants and the use of special additives such as stabilizers. The Chapman and Pickett method further requires the costly step of salt purification by ion-exchange.
Processes for making high molecular weight polyamides at lower temperatures have also been developed. In this regard U.S. Pat. No. 4,131,712 to Sprauer, which issued Dec. 26, 1978, describes a process in which a dicarboxylic acid-rich (diacid-rich) component and a diamine-rich component are combined with heating in the absence of water to form a polyamide. The diacid- and diamine-rich components each have melting points which are depressed in comparison to the pure diacid and diamine compounds, advantageously allowing the polymerization to be conducted at a lower temperature, and thereby minimizing thermal degradation. Such a process cannot be used in the manufacture of partially aromatic polyamides for a number of reasons. At the outset, the aromatic dicarboxylic acid reactants used to synthesize partially aromatic polyamides have an extremely high melting point and often cannot be melted without themselves being thermally degraded. Further, these reactant mixtures are not stable under anhydrous conditions, conditions which are central to the Sprauer process.
SUMMARY OF THE INVENTION
It has now been found that partially aromatic polyamides can be manufactured by combining an aromatic dicarboxylic acid component, at least a portion of which is in the form of an alkylated ester, with a diamine component in the presence of water. Esterification of the dicarboxylic acid advantageously lowers its melting point to a temperature that allows melting of the acid while avoiding, or at least minimizing, thermal degradation thereof. Admixture of the dicarboxylic acid component and the diamine component in the form of a melt is thereby facilitated. Further, the partially aromatic polyamide formed by these reactants likewise contains the alkyl sidechains and these sidechains function also to depress the melting point of the polyamide, yielding a polyamide that is more readily processed than the corresponding polyamide that lacks such alkyl sidechains.
Accordingly, the present invention provides a process for making a partially aromatic polyamide from at least one aromatic dicarboxylic acid component and at least one aliphatic diamine component comprising a diamine having from 6-12 carbon atoms, wherein 20-100% by weight of the dicarboxylic acid in said acid component is in the form of an alkylated ester, said process comprising the steps of:
(a) admixing non-stoichiometric amounts of the acid component with the diamine component in the presence of water;
(b) heating the admixture to a temperature at which it forms a melt while discharging therefrom volatile matter;
(c) further heating the admixture to a temperature above the melting point of the partially aromatic polyamide to form a polyamide oligomer;
(d) adding sufficient amounts of an aliphatic diamine having from 6-12 carbon atoms, or an aromatic dicarboxylic acid, at least a portion of which is in the form of an alkylated ester, so that the total amounts of the acid component and diamine component in the admixture of
DuPont Canada Inc.
Hampton-Hightower P.
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