Polyphthalamides having a useful combination of thermal and mechanical properties and excellent solvent resistance, particularly to alcohols, comprise recurring aliphatic terephthalamide and 2,6-naphthalene dicarboxylamide units and, optionally, isophthalamide units.

This invention relates to crystalline polyamide compositions and, more 
particularly, to such compositions having a desirable combination of 
thermal and mechanical properties, alcohol resistance, and low moisture 
absorbancies. 
BACKGROUND OF THE INVENTION 
Commonly assigned U.S. Pat. No. 4,603,166, issued Jul. 29, 1986, discloses 
polyphthalamide compositions which, when filled with glass fibers and 
molded, have heat deflection temperatures at 264 psi, determined according 
to ASTM D-648, above about 245.degree. C. (473.degree. F.). Included are 
compositions comprising recurring terephthalamide and adipamide or 
terephthalamide, isophthalamide and adipamide units and, preferably, 
wherein the mole ratio of dicarboxylic acid moieties provided by the 
terephthalamide, isophthalamide and adipamide units is about 
65-90:25-0:35-5, respectively. As disclosed therein, such compositions, 
including particulate- and fiber-filled compositions, exhibit desirable 
thermal properties including heat deflection temperature, high tensile 
strength and flexural modulus and are useful in various applications 
including preparation of molded articles, fibers, and laminates. 
Commonly assigned U.S. Pat. No. 4,617,342, issued Oct. 14, 1986, and 
commonly assigned, U.S. Pat. No. 4,863,991 issued Sep. 5, 1989, to Poppe 
et al., and published European Patent Application No. 84300745.1 
(Publication No. 0122688), published Oct. 24, 1984, disclose 
polyphthalamides which, when filled with glass fibers, have heat 
deflection temperatures at 264 psi, determined according to ASTM D-648, 
above 240.degree. C. Compositions according to U.S. Pat. No. 4,617,342 are 
prepared from dicarboxylic acid compounds comprising terephthalic acid and 
isophthalic acid compounds in a mole ratio of 80:20 to about 99:1 and 
diamines comprising hexamethylene diamine and trimethylhexamethylene 
diamine in a mole ratio of about 98:2 to about 60:40. Compositions taught 
in U.S. Pat. No. 4,863,991 are based on terephthalic acid and isophthalic 
acid compounds in a mole ratio of about 70:30 to about 99:1 and 
hexamethylene diamine. Such compositions have utility in various 
applications, the neat and fiber-filled compositions being particularly 
suited for molding applications. 
For certain end uses it would be desirable to modify certain properties of 
polyphthalamides such as those described above. In particular, it would be 
desirable to provide polyphthalamides with improved properties such as 
solvent resistance, especially to alcohols, and lower moisture absorption. 
Reduced moisture absorption is important because it can lead to better 
retention of mechanical properties by articles fabricated from polyamides 
when exposed to wet or humid environments. Such improvements would lead 
not only to improved performance of products fabricated from such resins 
in existing end uses, but also utility in additional applications with 
more stringent requirements. Examples of specific applications for such 
polyphthalamides where the above improvements would be beneficial include 
many injection molding and engineering applications, such as electrical 
and electronic connections, pump housings, and automobile under-hood and 
trim parts, especially those trim pieces which come in contact with 
windshield washer fluid or other fluids that contain alcohols which can 
cause cracking. 
In general, it is known that modification of polymer properties may be 
achieved in various ways. Modification of the molecular structure of a 
given composition through the use of additional monomers in polymerization 
can lead to desirable improvements in some properties. However, the same 
often are accompanied by loss of other desirable properties and use of 
additional monomers is not always practical due to process considerations. 
Addition of other materials to a polymeric composition may lead to 
property improvements without complicating a polymerization process; 
however the effects of additives often are unpredictable and, again, 
improvements in some properties often are achieved at the expense of other 
properties. Blending a given polymer with one or more other polymers may 
give blends with combinations of properties intermediate those of the 
individual components; however, processing requirements often limit the 
number of candidates that can be blended with a given polymer in an 
attempt to attain desirable property modifications and properties of a 
blend may or may not reflect those of its components depending on 
compatibility of the components with each other, reactivity thereof under 
blending or processing conditions and other factors. 
The use of 2,6-naphthalene dicarboxylic acid in the preparation of 
polyamides has been reported to result in improvements in certain 
properties. U.S. Pat. No. 4,246,395 to Mortimer, issued Jan. 20, 1981, 
discloses fiber-forming polyamides consisting of 45-75 mole % 
hexamethylene terephthalamide units, 20-40 mole % hexamethylene 
isophthalamide units and 5-20 mole % units derived from certain other 
dicarboxylic acids and diamines, examples of which include 1,3 or 
1,4-cyclohexane-bis-methylamine or dodecamethylene diamine, dodecanedioic 
acid, 2,6-naphthalene dicarboxylic acid, 4,4'-oxydibenzoic acid or 
1,4-cyclohexane dicarboxylic acid. The resulting polyamides are said to 
have improved thermal properties including glass transition temperature 
(&gt;155.degree. C.), melting points below 320.degree. C. and better thermal 
stabilities. Mortimer also mentions that his polyamides can be used for 
molding applications. 
U.S. Pat. No. 4,042,571 to Kawase et al., issued Aug. 16, 1977, discloses a 
process for preparing a fire retardant polyamide from at least one 
naphthalene dicarboxylic acid, including 2,7-naphthalene dicarboxylic acid 
and 2,6-naphthalene dicarboxylic acid or its amide forming derivative or a 
combination of the two, a halogen-substituted mono- or dicarboxylic acid 
and an aliphatic diamine. Kawase et al. discloses that the naphthalene 
dicarboxylic acid is at least 40 mole % of the total acid component. 
According to the patent, additional dicarboxylic acid components can be 
used in an amount up to 55 mole % based on the total acid component. 
Aliphatic dicarboxylic acids such as adipic acid and aromatic dicarboxylic 
acids such as terephthalic acid and isophthalic acid are mentioned as 
examples of such additional acids. The acid component is polymerized with 
a diamine, including hexamethylene diamine. The disclosed polyamides can 
be formed into fibers, films and other shaped articles. In addition to 
enhanced fire retardancy, the disclosed compositions are said to show 
superior mechanical properties, chemical resistance, water resistance and 
thermal stability, especially when the amount of naphthalene dicarboxylic 
acid compound used in preparation of the composition is at least 40 mole % 
of the total acid component. This patent discloses that if the naphthalene 
carboxylic acid component is less than 40 mole % of the total acid 
component, the above properties are sacrificed. 
U.S. Pat. No. 3,538,056 to Caldwell, issued Nov. 3, 1970, discloses 
high-melting linear polyamides prepared from an acid component of at least 
60 mole % naphthalene dicarboxylic acid and branched chain diamines. 
According to the patent, these polyamides may be modified by inclusion in 
the acid component of up to 40 mole % of another dicarboxylic acid which 
may be aliphatic, aromatic or alicyclic, including isophthalic acid and 
terephthalic acid, and a diamine including hexamethylene diamine. Uses for 
these polyamides are said to include films, fibers and molded objects. 
U.S. Pat. No. 4,012,365 to Moriyama et al., issued Mar. 15, 1977, discloses 
transparent polyamides prepared with 2,7-naphthalene dicarboxylic acid or 
its amide-forming derivative or a combination of the two, an aliphatic 
diamine component containing 4 to 13 carbon atoms and a comonomer 
component, which may be an aromatic dicarboxylic acid comonomer, including 
terephthalic, isophthalic or 2,6-naphthalene dicarboxylic acid, or a 
diamine component. The disclosed polyamides are said to have poor 
crystallinity, excellent transparency, high heat resistance and chemical 
resistance especially to methanol, ethanol, n- and iso-propanol. The 
patent requires that the 2,7-naphthalene dicarboxylic acid or its 
amide-forming derivative or a combination of the two account for 50 to 100 
mole % of the total acid component used in preparation of the polyamides, 
otherwise the polyamide has a reduced melting point and becomes easily 
soluble in alcohols. The disclosed polyamides can be melt shaped into 
films and fibers according to the patent. 
U.S. Pat. No. 3,674,752 to Ridgway et al., issued Jul. 4, 1972, discloses 
fibers with increased resistance to loss in stiffness when subjected to 
conditions of heat and moisture and low shrinkage when subjected to hot or 
boiling water. The disclosed polyamides are derived from 80-90 mole % 
adipic acid, 10-20 mole % 1,6 or 2,6-naphthalene dicarboxylic acid and 
hexamethylene diamine. 
U.S. Pat. No. 3,575,935 to Elam, issued Apr. 20, 1971, discloses polyamides 
useful as molding plastics derived from at least one aromatic or alicyclic 
dicarboxylic acid, including terephthalic, isophthalic and 2,6-naphthalene 
dicarboxylic acids, and 4,4-dimethyl-1,7-heptanediamine or 
4-methyl-4-ethyl-1,7-heptanediamine or mixtures thereof. These polyamides 
are said to have improved heat distortion temperatures, impact strength 
and clarity. 
Other patents which mention the use of 2,6-naphthalene dicarboxylic acid in 
preparation of polyamides include the following: U.S. Pat. Nos. 3,408,334; 
3,467,623; 3,505,288; 3,639,358; 4,172,938 and 4,698,414. 
Although the above patents disclose polyamides prepared from 2,6-and 
2,7-naphthalene dicarboxylic acid, none discloses the invented polyamide 
compositions comprising recurring units based on terephthalic acid, 
isophthalic acid and 2,6-naphthalene dicarboxylic acid and one or more 
aliphatic diamines, or the desirable thermal and mechanical properties 
together with improved alcohol resistance exhibited by such compositions. 
Surprisingly, polyamide compositions of the present invention have 
excellent solvent resistance (especially alcohol resistance) even when the 
naphthalene dicarboxylic acid component is only 25 mole % of the total 
acid component, contrary to the 40-50 mole % required by some of the 
patents described above. 
An object of this invention is to provide an improved polyamide 
composition. A further object is to provide a polyphthalamide composition 
having utility in injection molding and other applications. A still 
further object of the invention is to provide polyphthalamide compositions 
with improved solvent resistance and less moisture absorption resulting in 
improved retention of mechanical properties when used in applications 
involving exposure to wet or humid environments or alcohols. 
DESCRIPTION OF THE INVENTION 
The objects of this invention can be attained by providing a crystallizable 
polyamide comprising recurring units: 
##STR1## 
wherein R comprises a divalent aliphatic radical and the mole ratios of 
the dicarboxylic acid moieties of the A, B and C units is about 
45-65:0-20:25-55 respectively. For purposes hereof, the dicarboxylic acid 
moieties of the units A, B and C are defined as follows: 
##STR2## 
Generally, such polyphthalamides have melting points of about 280.degree. 
to about 330.degree. C. and glass transition temperatures ("Tgs") of about 
105.degree. to about 140.degree. C. The invented compositions provide good 
mechanical properties, superior chemical resistance, especially to 
alcohols, low moisture absorption, and low molding shrinkage. For example, 
some polyphthalamide compositions according to the invention are capable 
of retaining 95-100% of their tensile strengths after exposure to methanol 
or ammonium hydroxide. By using less 2,6-naphthalene dicarboxylic acid to 
achieve superior chemical resistance, the present invention also can 
provide a cost advantage as compared to polyamides comprising greater 
proportions of units based on 2,6-naphthalene dicarboxylic acid. In 
addition, these polyphthalamides are well suited for use in automobile 
exterior parts, especially trim pieces, which come in contact with alcohol 
(e.g., in windshield washer fluid) which can cause stress cracking. 
The polyphthalamide compositions of the present invention also exhibit 
reduced water absorption. As such, these compositions have the added 
advantage of substantially retaining their desirable mechanical and 
thermal properties, such as tensile and flexural strengths, when wet. For 
example, glass fiber-filled polyphthalamide compositions of the present 
invention prepared from 50 mole % terephthalic acid and 50 mole % 
2,6-naphthalene dicarboxylic acid and hexamethylene diamine can retain 95% 
of their tensile strengths after 5 days of exposure to boiling water. 
In addition, filled compositions of the present invention exhibit desirable 
properties such as improved tensile strength and flexural strength, high 
heat deflection temperatures and improved dimensional stability, 
properties useful for molding precision parts. 
Referring to the formulas depicted above, R comprises a divalent aliphatic 
radical. Preferably, R comprises at least one divalent straight chain or 
cyclic aliphatic radical of about 4 to about 20 carbon atoms having up to 
one methyl substituent per carbon atom because the invented compositions 
containing such radicals exhibit a desirable combination of melt 
processibility and physical properties in articles prepared therefrom. 
Examples of such preferred radicals include tetramethylene, 2- and 
3-methyl pentamethylene, hexamethylene, 2- and 3-methyl hexamethylene, 
2,5-dimethyl hexamethylene, octamethylene, 1,2-, 1,3- and 1,4-cyclohexane, 
3,3'-, 3,4'- and 4,4'-dicyclohexylmethane, dodecamethylene and 
combinations thereof. More preferably, R comprises octamethylene or 
hexamethylene because fiber-filled polyphthalamide compositions according 
to the invention containing such R groups often exhibit heat deflection 
temperatures at 264 psi of at least about 260.degree. C. Best results are 
achieved when R is hexamethylene. The invented polyphthalamides also may 
contain units as represented by formulas A, B and C above but wherein R is 
replaced by one or more other types of divalent hydrocarbyl radicals such 
as a divalent aromatic radical, e.g., phenylene, meta- or para-xylylene, 
oxybisphenylene or methylenebisphenylene. The proportion of such units 
usually should not exceed about 20-30 mole percent as greater proportions 
can lead to sacrifices in melt processibility, crystallinity and other 
properties. 
A preferred polyphthalamide according to this invention comprises recurring 
units A, B and C, as represented above, in proportions such that the mole 
ratios of the dicarboxylic acid moieties in the units A, B and C is about 
50-60:0-20:25-50. The preferred ratios result in polyphthalamide 
compositions with fast crystallization rates, thereby resulting in faster 
molding cycles, high crystallinity, high glass transition temperatures and 
superior chemical resistance, especially to alcohols. In particular, the 
invented compositions comprising a polyphthalamide component, wherein 
units A, B and C are present in such proportions and R in the above 
formulas is hexamethylene, and glass fibers are particularly advantageous 
because they exhibit heat deflection temperatures at 264 psi according to 
ASTM D-648 of at least about 260.degree. C. A particularly preferred 
composition according to the invention is that wherein the mole ratio of 
the dicarboxylic acid moieties of units A, B and C is about 50:0:50. 
If desired, the invented compositions also can comprise a fibrous or 
particulate filler component. Fibrous fillers can impart improved 
mechanical properties such as tensile strength and flexural modulus. 
Particulate fillers can also be used to obtain improvements in these 
properties as well as compositions of increased density and lower cost. 
Combinations of such materials also can be used. Typically, amounts of 
such fibers or particulates can range up to about 60 weight percent based 
on weight of the filled composition. Preferably, about 15 to about 50 
weight percent of fibers or particulates is used to achieve desirable 
mechanical properties without substantial adverse affects on melt 
processibility. Representative fibers suitable as reinforcing agents 
include glass fibers, graphitic carbon fibers, amorphous carbon fibers, 
synthetic polymeric fibers, aluminum fibers, aluminum silicate fibers, 
aluminum oxide fibers, titanium fibers, magnesium fibers, rock wool 
fibers, steel fibers, tungsten fibers, cotton, wool and wood cellulose 
fibers, etc. Representative filler materials include calcium silicate, 
silica, clays, talc, mica, carbon black, titanium dioxide, wollastonite, 
polytetrafluoroethylene, graphite, alumina trihydrate, sodium aluminum 
carbonate, barium ferrite, etc. 
Fiber-filled compositions according to this invention are particularly 
desirable because they combine the desirable polyphthalamide properties 
with improvements in tensile and flexural strength, modulus and heat 
deflection temperature imparted by the fibers, making such polyphthalamide 
compositions particularly well suited as injection molding materials. 
Glass fibers are especially preferred for molding applications. Specific 
examples of glass fibers include alkali-free, boron-silicate glass or 
alkali-containing C-glass. Suitably, average thickness of the fibers is 
between about 3 and 30 microns. It is contemplated to use long fibers 
e.g., ranging from about 5 mm to about 50 mm, and also short fibers, e.g., 
from about 0.05 mm to about 5 mm. In principle, any standard commercial 
grade fiber, especially glass fibers, can be used. 
Preferred glass fibers for injection molding applications have lengths of 
about 0.25 mm to about 25 mm. While longer or shorter fibers are suitable, 
the former can be difficult to disperse in the polyphthalamide, thereby 
lessening their reinforcing effect. Shorter fibers are easily dispersed 
but provide less reinforcement due to their low aspect ratio. 
The fibers can be sized or unsized and may include a coupling agent to 
improve adhesion of the fibers to the polyphthalamide. Commercially 
available glass fibers supplied with sizing agent applied thereto can be 
used as such or with the size removed, for example by abrasion. Sizing 
agents resistant to degradation or release of volatiles at temperatures 
employed in processing the invented compositions are preferred; examples 
include polyesters and polyester-urethanes. Examples of coupling agents 
include various silane, titanate and chromium compounds as known to those 
skilled in the art. 
Compositions according to this invention also can contain pigments, 
stabilizers, flame retardants, nucleating agents, lubricants, impact 
modifiers and other suitable additives to improve or modify properties. 
Conventional additives include lubricants such as stearyl alcohol, 
metallic stearates and ethylene bisstearamide and heat stabilizers such as 
alkali metal halides and combinations thereof with copper salts and 
phosphorous acid, sodium or alkyl or aryl phosphates, and phosphites, 
various cupric salts of organic or inorganic acids, such as cupric acetate 
and butyrate, and alkali or alkaline earth metal halides, such as sodium 
iodide and potassium iodide. 
The invented compositions also can be alloyed or blended with other 
thermoplastic resins, for example, other polyamides, polyesters, poly(aryl 
ether sulfones), polyarylene sulfides or oxides, polyamide-imides, 
polyetherimides, polyarylates, polycarbonates or combinations thereof to 
provide compositions with beneficial properties. 
The invented polyphthalamides can be prepared from the appropriate starting 
materials, e.g., a dicarboxylic acid component comprising terephthalic 
acid, 2,6-naphthalene dicarboxylic acid and, if used, isophthalic acid, or 
their derivatives, and a diamine component comprising at least one 
aliphatic diamine or derivative thereof, in suitable proportions by any 
suitable means. The dicarboxylic acid component and diamine component are 
used in essentially stoichiometric quantities although a slight excess of 
either, e.g., up to about 10 mole percent, can be used to account for loss 
of reactants or to provide final products with a predominance of acid or 
amine end groups as desired. One suitable preparation involves a salt 
preparation step, preferably conducted batchwise to achieve proper 
stoichiometry, wherein dicarboxylic acid and diamine components and 
solvent are added to a suitable reaction vessel in appropriate amounts and 
maintained under conditions effective to cause salt formation but avoid 
appreciable conversion of salts to oligomers. Water is a preferred solvent 
and temperature is preferably maintained below about 120.degree. C. to 
minimize conversion. Product of the salt preparation step can be 
introduced into a condensation section operated either batchwise or 
continuously. In the condensation section substantial conversion of salts 
to polymer takes place. The condensation product then typically is 
introduced into a finishing section, such as a twin-screw extruder, to 
obtain further conversion and increase inherent viscosity from a level of 
about 0.1 to about 0.6 dl/g typically achieved in the condensation section 
up to about 0.8 dl/g or greater. The polymeric product can be recovered 
from the finishing section and, for example, pelletized or mixed with 
fillers, additives and the like. Commonly assigned U.S. Pat. Nos. 
4,603,193, issued Jul. 29, 1986, and 4,831,108, issued May 16, 1989, both 
to Richardson et al. and incorporated herein by reference, also disclose 
suitable methods for preparation of such polyphthalamides by a process 
particularly suited for high melting polyamides. The process of the latter 
comprises forming an essentially homogeneous mixture of polyamide-forming 
starting materials, transferring the mixture to a heated preflash zone 
under pressure, passing the heated, pressurized mixture through an orifice 
into a zone of lower pressure and high heat flux to form an aerosol mist 
of reactants, passing the aerosol mist through the zone of high heat flux 
at low residence time and passing the resulting product to a finishing 
reactor to increase conversion thereof. 
Filled compositions according to this invention can be prepared by 
combining components comprising the invented polyphthalamide and a fibrous 
or particulate filler component by any suitable means. Conveniently, the 
invented polyphthalamide in powder, pellet or another suitable form is 
melt compounded with the filler component and any other additives or 
materials to be used in desired amounts, at a temperature effective to 
render the polyphthalamide molten without degradation thereof, in a high 
shear mixer, e.g., a twin-screw extruder, to obtain substantially uniform 
dispersion of filler component and any other additives in the 
polyphthalamide. Use of kneading blocks or other suitable mixing elements 
in compounding aids in achieving a high degree of dispersion of the 
components. To minimize degradation of the polyphthalamide, preferred 
temperatures when using a twin-screw mixer are equal to or up to about 
20.degree. C. greater than the melting point of the component. Mixing of 
the components in solid form prior to melt compounding can be conducted to 
facilitate melt blending. Fibers or particulates also can be incorporated 
by feeding the same to the molten polyphthalamide in an extruder or other 
compounding apparatus or by other suitable methods. 
The invented compositions are particularly useful as injection molding 
compounds for production of molded objects, for example, chemical and 
refinery equipment components, computer parts, electronic connectors, 
switch components, pump housings, pulleys, valve components and automobile 
trim and under-the-hood parts. Injection molding of such compositions can 
be conducted using standard injection molding equipment. Injection molding 
can be accomplished by heating the invented compositions to above the 
melting point of the polyphthalamide but not so high as to substantially 
degrade the same, injecting the composition into a mold maintained at a 
temperature of about 5.degree. C. or more above the glass transition 
temperature of the polyphthalamide to about 30.degree.-40.degree. C. above 
such glass transition temperature and maintaining the composition in the 
mold for a time effective to solidify the composition. A 20 second to 1 
minute cycle time, barrel temperatures ranging from about 290.degree. to 
about 340.degree. C. and mold temperatures of about 100.degree. C. to 
about 150.degree. C. are suitably employed with specific temperatures 
varying somewhat depending on melting point, degradation temperature and 
glass transition temperature of the polyphthalamide.