Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-10
2002-12-24
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S420000, C525S430000, C525S431000
Reexamination Certificate
active
06498217
ABSTRACT:
The present invention is related to branching of high-molecular-weight polyamides using aliphatic or aromatic esters of carbonic acid.
There are few examples in both patent and academic literature concerning branching of polyamides (PA) and related polymers. Branching of polymers causes broad molecular weight distribution and generally leads to change of melt flow behavior in comparison with linear analogous polymers. Such polymers show non-Newtonian (structural viscous) melt flow in the broad range of shear rates. This is important for the processing of plastics since it extends their processing window. Such polymers can be applied for processing requiring high strength of the melt (e.g. blow extrusion) as well as for processing, where high flow is necessary (e.g. fast injection molding).
Branching of polyamides is a way to extend a processing window of polyamides. For instance, for extrusion, which operates at shear rates 10
2
-10
3
1/s order of magnitude, high polymer melt strength is necessary. On the other hand, for injection molding which operates at shear rates 10
3
-10
4
1/s order of magnitude, higher flow is desired in order to produce large articles and replicate fine details. It means that we need polymer, which shows high melt viscosity at low shear rates (or at low red. radial frequencies) and low melt viscosity at high shear rates (or at low red. radial frequencies). Such behavior is typical for structural viscous melts. Since structural viscosity is common for branched polymers, branching of polyamides makes possible to apply various processing techniques to these polymers.
Both ring opening polymerization of lactams and polycondensation reactions were used for syntheses of branched polyamides.
Melt polycondensation using low concentration of multifunctional comonomer is a common way of preparing branched polyamides. Bishexamethylenetriamin (GB 749479), compounds of the general formula H
2
N—R—NH—R—NH
2
(DE-2732329), (H
2
N—(CH2)
n
)
2
N—(CH
2
)x-N—((CH
2
)
n
—NH
2
)
2
(DE-19654179), amino- groups containing dendrimers (DE-19654179) are used as multifunctional amines. Also tri- and tetracarboxylic acides were used as a branching agents: 3,5,3′,5′-biphenyl-tetracarboxylic acid, 1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridintricarboxylic acid, 3,5,3′,5′- bipyridyltetracarboxylic acid, 3,5,3′,5′- benzophenonetetracarboxylic acid; 1,3,6,8-acridintetracarboxylic acid, trimesic acid and pyromellitic acid (EP-774480). Polyacids or polyamines are described as branching agents for syntheses of polyamides via polycondensation of nylon salts or co-aminoacids, and for polymerization of lactams (EP-345648). Other branching agents used for analogous syntheses of branched polyamides are pyrandicarboxylic acids and their esters (DE-4100909) or &agr;-amino-&egr;-caprolactam (DE-3714607) or amino acid containing more than one amino- or carboxylic groups (Polymers for advance technologies 6, 1995 pp. 373-382).
Application of multifunctional initiator on the polymerization of lactams leads to formation of star branched polyamides (WO-9746747, WO-9724388, Chem. Mater.4, 1992, pp.1000-1004). Termination of hydrolytic polymerization of &egr;-caprolactam with tetra- and octacarboxylic linking agents leads to formation of star shaped nylon-6 polymer. On the other hand activation of anionic polymerization of lactams with trimesoyl-tris-caprolactam leads to three armed polymer. Similar structure can be obtained by cationic polymerization of lactams initiated by ammonium cations of tris-2-aminoethylamine neutralized with HCl (ACS Symp. Ser. 30 (1) 1989, pp.117-118).
Anionic polymerization of lactams on the polyamide chains containing N-benzoyl-side groups makes it possible to manufacture polyamides with branches of other chemical structure than the main chain (Polymer 37, 1996 pp. 2541-2545).
Most of the described methods, although leading to high molecular weight branched polyamides, are difficult to carry out in large-scale productions. Moreover, besides reaction control difficulties, these methods can hardly produce materials of desired branched structures. They need solvent and often also special equipment is necessary. These drawbacks increase in consequences the production costs and the manufacturing is more complicated.
The branching affects properties of polymers both in the molten state and in solution and therefore it is a useful way to improve the processibility of polymers. Especially for the production efficiency of fiber forming technologies and injection molding processes, the decrease of the production cycle time is essential. Therefore, in the case of semicrystalline polyamides, there is a demand to improve flow properties of polyamide melt without negative impact on crystallisation time.
Branching reactions should not lead to low-molecular-weight side chains in the case of semi-crystalline polyamides, since short branches causes decreases of crystallinity. Low content of crystalline phase leads to deterioration of mechanical properties. Polymer stiffness decreases dramatically, but also tensile strength, modulus, hardness and abrasion resistance are negatively affected by decrease of crystallinity. Also water- and gas-barrier properties depend on the content of crystalline phase.
It was now surprisingly found that commercially available polyamide can be easily branched using diesters of carbonic acid e.g. diphenylcarbonate (DPC) and dimethylcarbonate (DMC) as branching compounds.
The new high-molecular weight polyamides branched by diesters of carbonic acid have surprisingly excellent flow properties and a high degree of crystallinity, which results in excellent mechanical properties, especially high stiffness. In the case of fully amorphous polyamides the above described branching can improve the flow properties.
The invention also concerns a process to synthesise branched polyamides by reaction of commercially available linear polyamides with dimethylcarbonate and diphenylcarbonate (or by other ester of carbonic acid). Such a process makes it possible to retain high degree of crystallinity after polymer branching and the polymers exhibit structural viscous behavior. The reaction proceeds under similar conditions as those used for the melt synthesis of polycarbonates (high temperatures and low pressures). Temperatures range between 250-350° C. and pressures are adjusted to 0,05 to 30 mbar, preferred 0,05 to 10 mbar and most preferred 0,5 to 1 mbar. The reaction proceeds according to the Scheme I.
Branching can be carried out in the reactor made out of glass, metal or other material as well as in the kneader or extruder. The combination of these reaction conditions is also possible. For instance, a polymer is at first extruded in order to obtain a granulate with regular distribution of the branching agents and then the reaction is completed in the glass reactor. Special attention must be paid in order to prevent oxidation of the molten polyamide by air oxygen which leads to dark product with obviously poor mechanical properties. Provided that the reaction takes place in the glass reactor, intensive stirring using appropriate stirrer prevent deposition of polyamide onto the wall of the reactor, which could cause irregular branching and deterioration of the polymer color.
Blanketing the reactive melt with nitrogen is preferred. The danger of product deterioration is high especially when the reaction is over and the reaction mixture cools down. Therefore cooling is preferred to be carried out in nitrogen (or other inert gas) stream.
Amide-bond containing polymers are suitable for such a reaction, e.g.: poly(&egr;-caprolactam) (PA-6), polyhexamethyleneadipamide (PA-6,6), polyhexamethyleneazelainamide, polyhexamethylenesebacinacidamide, polyamide PA-11; PA-12; PA-4,6; PA-6,12, poly(amide-imide)s, poly(amide-ester)s, their copolymers and their mixtures.
In the case of aramides, those prepared from isophthalic acid and/or terepthtalic acid (or their derivatives) or their mixtures (or mixtures of their derivatives) are preferred f
Bruder Friedrich-Karl
Douzinas Konstadinos
Marek Miroslav
Bayer Aktiengesellshaft
Gil Joseph C.
Mrozinski, Jr. John E.
Woodward Ana
LandOfFree
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