Cross-linking of modified engineering thermoplastics

Details Cross-linking of modified engineering thermoplastics Cross-linking of modified engineering thermoplastics

2001-01-16

2003-04-22

Zitomer, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S525000, C525S359100, C525S535000, C526S286000, C526S287000

Reexamination Certificate

active

06552135

ABSTRACT:

The present invention pertains to a process for the cross-linking of modified engineering thermoplastics, in particular, of polymeric sulfinic acids or sulfinic acid salts.
Various ways for preparing cross-linked polymers and membranes are known in the prior art. Some of these may be mentioned here:
1) Preparation of cross-linked membranes by the copolymerization of mono- and bifunctional monomers (example: copolymerization of styrene and divinylbenzene in thin layers, followed by sulfonation of the cross-linked polymer membrane produced). This method has the disadvantage that the cross-linked ionomer membranes produced thereby have limited oxidation stabilities since both styrene and divinylbenzene contain tertiary C—H bonds which are sensitive to oxidation. (For a comparison of the oxidation sensitivities of styrene having a tertiary C—H bond and of &agr;-methylstyrene without a tertiary C—H bond, see, for example: Assink, R. A.; Arnold C.; Hollandsworth, R. P., J. Memb. Sci. 56, 143-151 (1993).)
2) Functionalization of ion-exchanging groups of ionomers, followed by reaction with bi- or oligofunctional cross-linking agents to yield a cross-linked membrane (example: functionalization of sulfonic acid groups to yield the reactive acid chloride or imidazolide, followed by reaction with (aromatic) amines; Nolte, R.; Ledjeff, K.; Bauer, M.; Müllhaupt, R.; J. Memb. Sci. 83, 211 (1993)). In these cross-linking methods, cross-links (sulfonamide groups) are formed in the membrane which are not sufficiently stable to hydrolysis.
3) Chemical activation of ion-exchanging groups of ionomers, followed by reaction of the activated group with other groups of the polymer main chain to yield a cross-linked membrane (example: conversion of part of the sulfonic acid groups of sulfolated PEEK (polyetheretherketone) to sulfochloride groups, attack of the sulfochloride groups during membrane formation in the hydroquinone region of the PEEK repeating unit under Eriedel-Crafts acylation and formation of hydrolysis-stable —SO
2
— links (EP 0 574 791 A2). This method has the disadvantage that it can be employed only with certain aryl polymers, such as PEEK.
From Kice, J. L.; Pawlowski, N. E: J. Org. Chem 28, 1162 (1963), it has been known that low-molecular sulfinic acids can disproportionate according to the following scheme of reactions;
From Quaedvlieg, M., in: Houben-Weyl, Methoden der Organischen Chemie, Vol. II, 606, Thieme Verlag, Stuttgart (1957); Ashworth, M. R. F., in: The Chemistry of Sulphinic Acids, Esters and their Derivatives (Ed.: S. Patai), chapter 4, 97-98, John Wiley Ltd., New York (1990); Allen, P.: J. Org. Chem. 7, 23 (1942), it has been known that sulfinate can readily be alkylated to the sulfonate. The reaction was performed, inter alia, in alcohols having different chain lengths:
It has, been the object of the present invention to provide novel processes for cross-linking modified engineering thermoplastics, in particular, of polymeric sulfinic acids or salts thereof.
The above object is achieved, in a first embodiment, by a process for the preparation of cross-linked polymers, characterized in that solutions of polymeric sulfinic acids or sulfinic acid salts (—SO
2
Me), optionally in the presence of organic di- or oligohalogeno compounds [R(Hal)
x
], are liberated from solvent and cross-linked to polymers,
wherein Me stands for a monovalent or polyvalent metal cation;
R stands for an optionally substituted alkyl or aryl residue containing from 1 to 20 carbon atoms; and
Hal stands for F, Cl, Br or I.
It is particularly preferred that the sulfinic acids or salts thereof is derived from structures comprising aromatic nuclei having R
1
or R
2
structures of the following formulae as the repeating unit wherein
R
3
stands for hydrogen, trifluoromethyl or C
n
H
2n+1
, with n being from 1 to 10, in particular methyl;
R
4
stands for hydrogen, C
n
H
2n+1
, with n being from 1 to 10, in particular methyl or phenyl; and
x stands for 1, 2 and 3,
which are linked through bridging groups R
5
or R
6
wherein
R
5
stands for —O—, and
R
6
stands for —SO
2
—.
It is particularly preferred according to the present invention that the solvent is selected from dipolar-aprotic solvents, such as NMP, DMAc, DMSO or DMF.
The polymer or one of the blend components is a polymer modified with sulfinic acid groups (—SO
2
H) and/or sulfinic acid salt groups (—SO
2
Me) (Me=Li, Na, K, Rb, Cs or other mono- or di-valent metal cations). The choice of basic materials (polymeric sulfinic acids/sulfinic acid salts) is not limited; all polymeric or oligomeric sulfinic acids can be employed as the basic materials. The advantage of the cross-linking method according to the invention over the prior art is characterized by the following items:
The processes can be universally employed: all polymeric sulfinates and sulfinic acids can be cross-linked according to this process.
A wide variety of polymers can be blended with the polymeric sulfinic acids/sulfinic acid salts. Cross-linked polymer blends are obtained having blend morphologies (microstructures) and cross-linking densities which can be adjusted within wide ranges.
The cross-linked polymers have improved thermal and chemical resistance as compared with the basic substances.
The hydrolytic stabilities of the cross-linked polymers and membranes are substantially improved over the hydrolytic stabilities of other cross-linkings, for example, the cross-linking of polymeric sulfonates through sulfonamide links.
It has now been surprisingly found that the per se known disproportionation reaction can be made use of for cross-linking polymers by preparing sulfinic acid containing polymers according to a known method (Kerres, J.; Cui, W.; Neubrand, W.; Springer, S.: Reichle, S.; Striege, B.; Bigenberger, C.; Schnurnberger, W.; Severs, D.; Wagner, N.; Bolwin, K.: lecture (lector: J. Kerres), Euromembrane '95 Congress, Bath (UK), Sep. 18 to 20, 1995, Proceedings, pages 1-284 (1995)) or other methods and cross-linking the same via the above disproportionation reaction, wherein other polymers may be added to the solution of the polymeric sulfinic acid in an appropriate solvent (for example, DMSO, DMAc, DMF, NMP) which polymers are then integrated in the forming polymeric network.
The microstructure of the generated cross-linked polymer blend depends on the compatibility of the blend components. If all blend components are compatible with each other, an interpenetrating network will form in which the polymeric chains of the blend components are entangled to such an extent that the blend components can hardly be separated any more. If the blend components are immiscible with each other, a microphase structure will form in which some of the components are dispersed in a continuum of the other components. The microphase structure is dependent on the kind of the blend components and the mixing ratio of the blend components. By appropriately selecting the blend components and their mixing ratio, cross-linked blend structures can be produced as desired.
The cross-linking process according to the invention can be employed, for example, for the preparation of cross-linked cation-exchange membranes. There are two ways of proceeding:
A polymeric sulfinic acid and a polymeric sulfonic acid are dissolved together in the same solvent (DMSO, DMAc, DMF, NMP) and then further processed.
A polymer the sulfinic acid groups of which have partially been oxidized to sulfonic acid groups (oxidation level 0 to 100%; the oxidation level can be adjusted through the quantity of oxidant added to the polymeric sulfinate) is dissolved in the solvent and then further processed.
This polymer solution is then cast on a substrate (glass plate, polished aluminum sheet, woven or non-woven fabric). Thereafter, the plate is placed in a drying oven and the solvent evaporated at elevated temperature, in particular above the boiling point of the solvent under the pressure conditions chosen, During the evaporation process, cross-linking of the polymeric sulfinic acid occurs. It

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