Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1996-12-31
2002-07-23
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, C528S322000, C528S323000, C528S332000, C528S335000, C528S336000, C525S142000, C525S195000, C525S327600, C525S375000, C524S099000, C524S103000, C524S538000, C524S600000, C524S606000, C428S357000, C428S364000, C428S394000, C428S395000, C442S049000, C442S181000
Reexamination Certificate
active
06423817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improved polyamides. More particularly, the present invention relates to inherently light- and heat-stabilized polyamides. The present invention further relates to a process for preparing these polyamides and to their use.
2. Description of the Related Art
The heat stability of polyamides, including nylon 6 and nylon 66, is insufficient for some applications. For instance, coloration problems can arise as a result of chemical changes (oxidative/thermal damage) to the polymer during carpet yarn or textile fabric heat setting. Both continuous filaments and staple fibers may be affected. It is known to add stabilizers to the polyamide to improve these properties. Such an addition can take place before, during or after the polymerization, for example during the processing. The customary known stabilizers are mixed into the polymer and are not bonded to the polymer chain. During processing or use they can migrate, evaporate or wash out of the polymer more or less readily, so that the effectiveness of the stabilization decreases in an undesirable manner and the surroundings (air, dyebath) may become contaminated.
DE-A-20 40 975, Sankyo Co. Ltd., describes the stabilization of synthetic polymers, including polyamides, with 4-aminopiperidine derivatives. Among the multiplicity of 4-aminopiperidine derivatives disclosed therein is 4-amino-2,2,6,6-tetramethylpiperidine (ef. No. 32 on page 8 of the document). However, this piperidine derivative is neither particularly singled out nor used in any Example. According to this reference, the 4-aminopiperidine derivatives are mixed with the ready-prepared polymer without becoming attached to the polymer chain.
DE-C-39 32 912, Sandoz, concerns polyamides containing radicals with sterically hindered amino groups, especially 2,2,6,6-tetramethyl-4-piperidyl radicals, incorporated in the molecule. The number of radicals is from 5 to 200 per polyamide molecule on average. According to this reference, these polyamides are useful, inter alia, for improving the dyeability of polyamides and as light stabilizers for plastics; they are to be incorporated in amounts of 1-10% by weight, particularly in the melt.
A paper in Poly. Deg. and Stab. 21, 251-262 (1988), states that the light stability of nylon 66 is improved on addition of 2,2,6,6-tetramethyl-4-piperidinol (TMP). The authors assume (see p. 259) that the TMP has reacted with the carboxyl end groups of the polyamide during a melt postcondensation of the TMP-including nylon 66 at 275° C. under a water vapor atmosphere. But, they say, there are signs of (undesirable) crosslinking during the later stages of irradiation.
It is known to use amines or mono- and dicarboxylic acids as chain regulators in the polymerization of polyamides, and monocarboxylic acids are very predominantly used for this purpose in practice.
It is an object of the present invention to provide inherently light- and heat-stabilized polyamides and processes for preparing them.
We have found that this object is achieved when a triacetonediamine compound of the formula
where R is hydrogen (4-amino-2,2,6,6-tetramethylpiperidine) or hydrocarbyl having from 1 to 20 carbon atoms, preferably alkyl (4-amino-1-alkyl-2,2,6,6-tetramethylpiperidine) having from 1 to 18 carbon atoms, or benzyl, is added before or in the course of the polymerization of the polyamides.
SUMMARY OF THE INVENTION
The present invention accordingly provides a process for preparing polyamides, which comprises effecting the polymerization of starting monomers in the presence of at least one triacetonediamine compound of the formula
where R is hydrogen or hydrocarbyl having from 1 to 20 carbon atoms, preferably alkyl having from 1 to 18 carbon atoms, or benzyl. Preferred embodiments of the process of this invention are described in subclaims. The present invention further provides an inherently light- and heat-stabilized polyamide containing an amine radical of the formula
where R is as defined above, chemically bonded to the polymer chain. Preferred polyamides of this invention are defined in corresponding subclaims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The triacetonediamine compound is added to the starting monomers or the polymerizing reaction mixture and becomes bonded to the end of the polymer chain through reaction of its primary amino group with the starting monomers or with the carboxyl groups of the polyamide being formed. The secondary amino group of the triacetonediamine compound does not react because of steric hindrance. Thus, the triacetonediamine compound also acts as a chain regulator.
The chemical bonding of the triacetonediamine compound to the polymer chain of the polyamide results in inherently stabilized polyamides being obtained. The process of this invention thus offers the advantage of obviating the otherwise necessary separate step of mixing a stabilizer into the polyamide. This eliminates problems or quality reductions as can arise on incorporation of a stabilizer following surface application to the polyamide granules as a result of incompatibility, viscosity degradation, migration, vaporization or washoff of the stabilizer or a twofold stress as with compounding, for example. The use of the triacetonediamine compound in the process of this invention protects the polyamides against damage by the action of heat and thermal oxidation in processing and use.
The polymerization of the starting monomers in the presence of the triacetonediamine compound is preferably carried out according to customary processes. For instance, the polymerization of caprolactam in the presence of triacetonediamine (R=H) can be carried out for example according to the continuous processes described in DE 14 95 198 and DE 25 58 480. The polymerization of 66 salt in the presence of triacetonediamine can be carried out by the customary batchwise process (see: Polymerization Processes p. 424-467, especially p. 444-446, Interscience, New York, 1977) or by a continuous process, for example as described in EP 129 196. In principle, the triacetonediamine compound and the starting monomers can be introduced into the reactor separately or as a mixture. The triacetonediamine compound is preferably added according to a predetermined amount/time program.
In a preferred embodiment of the process of this invention, the starting monomers used for polymerization are caprolactam or at least one dicarboxylic acid A selected from adipic acid, sebacic acid and terephthalic acid and at least one diamine selected from hexamethylenediamine and tetra-methylene-diamine, or dicarboxylic acid-diamine salts thereof. Caprolactam is particularly preferred. Dicarboxylic acid A is particularly preferably adipic acid or terephthalic acid. Given the appropriate choice of starting monomers, the polymerization will lead to the preferred polyamides nylon 6, nylon 66, nylon 46 or nylon 610.
In a preferred embodiment, the triacetonediamine compound is added to the starting monomers in an amount of from 0.03 to 0.8 mol %, preferably from 0.06 to 0.4 mol %, based on 1 mol of carboxamide groups of the polyamide. This statement of quantity relates for example to 1 mole of caprolactam when nylon 6 is to be prepared or to 0.5 mol of 66 salt when nylon 66 is to be prepared. It was found that amounts below 0.03 mol % do not ensure sufficient stabilization, whereas amounts above 0.8 mol % make it impossible to achieve the desired degree of polymerization owing to the regulating effect of the triacetonediamine compound.
In a preferred embodiment of this invention, the triacetonediamine compound is combined with at least one customary chain regulator. Examples of suitable chain regulators are monocarboxylic acids such as acetic acid, propionic acid and benzoic acid. The chain regulator combination and the amounts used are selected inter alia according to the amino end group content desired for the end product and according to the desired melt stability. The amino end group content depends on the dyeability desired for the
Beer Ludwig
Matthies Paul
Mell Karlheinz
Weinerth Klaus
BASF - Aktiengesellschaft
Hampton-Hightower P.
Keil & Weinkauf
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