Amorphous polyamides are generally suitable for the manufacture of sheets, strips, tubes, and injection-molded articles. However, many amorphous polyamides have relatively low glass transition temperatures and low decomposition temperatures. Accordingly, products made from these polyamides cannot be used in high temperature environments.
Numerous crystalline polyamides are known to have high Td values, for example, the polycondensation product of hexamethylenediamine and either adipic acid or dodecane dicarboxylic acid. However, many crystalline polyamides also have low Tg values. Further, these crystalline polyamides are not transparent. If a transparent polyamide is desired, the polyamide must be amorphous rather than crystalline.
Various amorphous polyamide compositions are well known. An example of an amorphous polyamide composition, disclosed in U.S. Pat. Nos. 2,715,620 and 2,742,496, is a polyamide of isophthalic acid and hexamethylenediamine. These polyamides are reported to have a low dimensional stability at elevated temperatures. U.S. Pat. No. 4,250,297 proposed to overcome this difficulty by replacing part of the hexamethylenediamine with an isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine.
Amorphous polyamides based on mixtures of terephthalic acid and isophthalic acid or their derivatives and hexamethylenediamine also are known, as reported in U.S. Pat. Nos. 3,379,695 and 3,475,387. While such compositions are said to exhibit minor improvements in heat deflection temperatures relative to the isophthalic acid and hexamethylenediamine polyamides, transparency of products prepared from these compositions suffers and crystallization of the polymer can occur during use of the products at elevated temperatures if the mole ratio of isophthalic acid to terephthalic acid is too low.
U.S. Pat. No 3,145,193 discloses a transparent polyamide based on the polycondensation product of alkyl-substituted polymethylene diamines having at least seven methylene groups and a mixture of terephthalic acid with 5-10% isophthalic acid.
Yu et al., J. of Polymer Science, XLII, 249-257 (1960), investigated the homoadipamide and copolyamide of adipic and terephthalic acids with 4,4-dimethyl-1,7-heptanediamine. The polymer was reported to be transparent. The authors ascribed the transparent attribute to the chain packing interference contributed by the methyl groups on the diamine.
J. G. Dolden, Polymer, 17 (October), 875-892 (1976), proposed that the crystallinity found in polyamides prepared from diacids and diamines is the result of the ability of the linear chains to pack in a regular crystal lattice and of the hydrogen bonding which exists between interchain amide links. The author further noted that the introduction of asymmetry by introducing ethyl or higher substituents along the asymmetric chain or the attachment of more than one methyl group to the same in-chain carbon member acts to prevent crystallization.
U.S. Pat. Nos. 4,451,642 and 4,564,705 disclose polyamides derived from aromatic bis(neopentylamine). These references also disclose that polyamides derived from diamines which contain no hydrogen atoms in the position beta to nitrogen are superior in thermal stability to those diamines which contain such hydrogens. These references also mention that neopentyldiamine is known and that polyamides have been made from this diamine. There is, however, no disclosure of any particular neopentyldiamine polyamide or properties thereof. There is no teaching that the compositions disclosed in these patents have a high Td, nor any suggestion that the Tg can be elevated by means of a simple aliphatic diamine. Further, U.S. Pat. No. 4,831,108 describes a polycondensation process wherein an attempted polycondensation of neopentyldiamine and a 40/60 mole ratio of terephthalic acid/isophthalic acid resulted in a discolored product having a reported inherent viscosity of 0.07 dL/g. A polyamide having an inherent viscosity of less than 0.40 dL/g has insufficient mechanical properties to produce a useful product.
Other attempts have been made to produce amorphous polyamides. U.S. Pat. No. 2,766,222 discloses a polymer of meta-xylylene diamine and isophthalic acid. U.S. Pat. No. 3,294,758 discloses replacement of a portion of substituted polymethylene diamine with an unbranched, unsubstituted polymethylene diamine of the same chain length in a polycondensation with terephthalic acid and/or isophthalic acid. U.S. Pat. No. 3,382,216 discloses terephthalic acid-containing polyamides having specific proportions of 2-methylpentamethylenediamine.
Amorphous copolyamides are disclosed in U.S. Pat. No. 4,232,145. This reference discloses a diaminodicyclohexylalkane or a mixture of diaminodicyclohexylalkane with a polyamide-forming aromatic dicarboxylic acid of more than 9 carbon atoms and an omega-amino-acid or an aliphaic dicarboxylic acid-diamine. The Tg of the copolymer is increased by increasing the proportion of omega-amino-acid or aliphatic dicarboxylic acid-diamine mixture.
While these patents and publications disclose various amorphous polyamides and properties thereof, there remains a need for amorphous polyamide compositions having a desirable balance of properties, including high glass transition and decomposition temperatures, such that articles fabricated from the amorphous compositions can be used in high temperature environments.
Accordingly, it is an object of the present invention to provide improved amorphous polyamide compositions. Another object of the present invention is to provide an amorphous polyamide composition which exhibits an improved glass transition temperature. Another object of the present invention is to provide an amorphous polyamide composition which exhibits improved thermal decomposition temperature. A further object of the present invention is to provide a transparent polyamide. A still further object of the present invention is to provide copolyamide compositions having advantageous properties. These and other objects and advantages of the present invention will be apparent to those skilled in the art from the following description.