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Title:
A METHOD FOR ALTERNATIVE CROSS-LINKING OF UNSATURATED POLYESTERS VIA CATALYTIC ALKYNE COUPLING
Document Type and Number:
WIPO Patent Application WO/2005/070983
Kind Code:
A1
Abstract:
The invention comprises a method for cross-linking of unsaturated polyester chains (UPE) in a manner that they are functionalised, introducing an alkyne functionality and then cross-linked by catalytic coupling by alkyne moieties.

Inventors:
Straub, Thomas (Viljo Sohkasen katu 3 D 26, Vantaa, FI-01370, FI)
Koskinen, Ari (Huhtimonkatu 21, Karkkila, FI-03600, FI)
Application Number:
PCT/FI2005/000042
Publication Date:
August 04, 2005
Filing Date:
January 21, 2005
Export Citation:
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Assignee:
HELSINKI UNIVERSITY OF TECHNOLOGY (P.O. Box 1000, Hut, FI-02015, FI)
Straub, Thomas (Viljo Sohkasen katu 3 D 26, Vantaa, FI-01370, FI)
Koskinen, Ari (Huhtimonkatu 21, Karkkila, FI-03600, FI)
International Classes:
C08F8/42; C08F283/01; C08F290/06; C08F299/04; C08G63/91; (IPC1-7): C08F299/04; C07C211/23; C08F4/50; C08F4/80; C08F238/02
Foreign References:
US5556921A
Other References:
LIN Q. ET AL.: 'Metal catalyzed pgotocross linking of polymers containing pend' POLYMER. vol. 44, 2003, pages 5527 - 5531, XP004447580
TREGRE J. ET AL.: 'A diacetylene polymer via oxidative coupling of diapropargylfl' J.POLYM.SCI. vol. 35, 1997, pages 587 - 591, XP002989018
Attorney, Agent or Firm:
Kuosmanen, Panu (Helsinki University of Technology, Otaniemi International Innovation Centre OIIC P.O. Box 9202, Hut, FI-02015, FI)
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Description:
A method for alternative cross-linking of unsaturated polyesters via catalytic alkyne coupling An alternative process has been invented to cross-link unsaturated polyester chains after their functionalisation.

Maleic (1a, b) and fumaric (2a-c) diesters have been functionalised at room temperature by a quantitative nucleophilic addition of propargyl amine, i. e. the hydroamination of the double bond, to yield model compounds 3a-c, bearing a required alkyne group.

A subsequent Sonogashira-type, catalytic homo-coupling of two alkyne moieties of 3 leads to the well-defined'cross-linked'products 4a, b.

At room temperature, in presence of air as final oxidant, the PdCI2 (PPh3) 2/Cul/amine mixture (Sonogashira type of catalyst) is a very effective system for the catalytic oxidative homo-coupling of terminal alkynes to the corresponding diynes1 and thus, the structurally well-defined target compounds 4 are obtained in a one-pot reaction in nearly quantitative yield, based on the maleic and fumaric starting materials.

General problems for cross-linking of unsaturated polyester chains are usually the following: The commonly used vinyl-monomer-based radical cross-linking processes of polyester chains do not yield very well-defined products. For example, they give rise to different chain lengths of the linkages and direct linking of the double bonds of the polyester heterochain. Side-reactions such as homopolymerisation of styrene occur. 2 A further source of inhomogeneity arises from the maleate-fumarate isomerisation during the synthesis of the heterochain prepolymers. Since the fumarate is more reactive in the co- polymerisation, the presence of fumaric unsaturation is crucial for overall density of cross-linking, directly influencing the extent of irregular double

bond consummation and the resulting variable distance between the successive cross-links. 4 In addition, emission of vinyl monomers is a constantly growing major concern. Since environmental legislation becomes more and more stringent, constantly reducing the amount of monomeric components which can be used in unsaturated polyester products, the development of alternative cross-linking methods, reducing or completely avoiding possible emissions of harmful, volatile compounds, e. g. of styrene, is highly desirable.

State-of-the-art solutions Unsaturated polyester (UPE) resins are heterochain polymers, containing repeating ester groups and aliphatic double bonds in the backbone. 5 They are commonly prepared by polycondensation of maleic or phthaiic anhydride and diols. The chains are generally co-polymerised in a free- radical chain-growth process, with vinyl monomer, usually styrene, to yield the final product, a three-dimensional cross-linked network. 5 6 The product is not well-defined, since the radical process includes several reactions, such as inter-and intramolecular cross-linking via styrene bridges of various lengths, branching by styrene on polyester double bonds, direct cross-linking of the latter and homopolymerisation of the vinyl monomer. 2 4-6 All these side-reactions alter the properties of the final product. To tune the process and obtain the desired properties of the final products, production starts usually employing different diols and acids in mixtures of various ratios. This formation of the prepolymer and the subsequent co- polymerisation with vinyl monomer are conducted under various reaction conditions, which provides a further possibility to direct the reactions towards the formation of a product exhibiting certain properties.

However, the development of unsaturated polyesters as a product has come to its turning point. Environmental legislation is tightening all the time and the content of volatile components to dissolve and finally cross-link the

solid UPE heterochain backbones is restricted, with regulations becoming more and more stringent. As the level of monomeric components which can be used in unsaturated polyester products is coming down, more challenges are set to the design of polymer. The structures need to be perfected most compatible with monomers and the cross-linking network in the cured product must be continuous to ensure the product performance.

Namely, a highly defined structure of the three-dimensional network has to be achieved.

A literature research has been done (Sci Finder, Beilstein Crossfire) which did not yield any similar description of the process. However, the separate reactions themselves are well-documented in the literature7 8 as stated before.

The invention and solution to present problem The new process innovatively combines well-known synthetic methods to overcome some major problems of the present systems. The cross-linking of unsaturated polyester chains is no longer carried out using vinyl monomers in radical chain reactions. Instead the model compounds, maleates and fumarates, standing for the corresponding maleic and fumaric units that are characteristic for the standard polyester resins used in industry, are functionalised quantitatively by nucleophilic addition of propargyl amine. 7 In this way, the problems resulting from cis-trans isomerism of the heterochain backbone2 4-6 are solved, since the addition reaction goes to completion and yields the saturated enantiomers 3, without side product formation. Therefore purification is not needed and 3 can be used as it is. Thus, irregular and incomplete consumption of the available double bonds of the polyester prepolymer are no longer an obstacle.

However, varying the stoichiometry, i. e. use of any sub-stoichiometric amounts of amine, allows to retain a certain unsaturation in the polyester chain, if that is desired in order to tune the properties of the cured product.

The actual cross-linking is done in a second, catalytic reaction, the Sonogashira type of homo-coupling of the introduced alkyne function. In this way 3 is converted to 4 in quasi quantitative yield, with no detectable side reactions (NMR) and leads to structurally well-defined products. This is in sharp contrast to the vinyl-monomer-based method, where homopolymerisation of the vinyl monomer and different chain lengths of the linkage introduce considerable inhomogeneities into the final product. 2, 4-6 The catalyst system of choice is a PdCi2 (PPh3) 2/Cul-mixture in presence of air oxygen.

Replacing the common radical cross-linking strategy by the two-step method presented here, not only provides benefits regarding a higher structural definition of the cured product, it also avoids emissions of vinyl monomer, a distinctive plus in times of growing environmental restrictions.

Applications The field of potential applications is polymer production with its wide application for polyester resin based products. Because of the high

structural definition of potential products, speciality chemicals/materials are obvious production targets.

Since laws concerning emissions get ever more stringent, the development of new strategies for the cross-linking of unsaturated polyester prepolymers is of paramount importance.

The presented process satisfies the urge for'green chemistry'by using an emission free Pd/Cu catalysed oxidative coupling of alkynes as a potential alternative for the cross-linking of unsaturated polyester chains, once the latter have been functionalised quantitatively by facile nucleophilic addition of propargyl amine to the maleic/fumaric ester units.

In addition of being environmentally benign, the invented process circumvents several obstacles inherent in the synthesis of UPE-resin-based polyesters. Therefore, novel highly defined products will be available from any chosen UPE.

With its high technological standards but limited resources, industry could largely benefit by implementing the presented method for manufacturing novel high-tech niche products, i. e. polyesters with tailor-made properties based on the high structural definition that can only be achieved applying the invented process to the UPE of choice.

The present invention is described with following examples which do not limit its applicability but clarify its exploitation. The examples consist of two steps.

Step 1.

Model functionalisation of unsaturated polyester chains, introduction of a well-defined linker group : Nucleophilic addition of propargyl amine to maleic and fumaric diesters 1a, b; 2a-c.

Propargyl amine (605 mg, 11.0 mmol) was added to 10.0 mmol of either maleic diester 1a, a mixture of the maleic/fumaric isomers 1 b, 2b or fumaric diester 2a, 2c respectively, via syringe. The reaction mixture was stirred at rt for 6-24 h to yield the pure product quasi quantitatively (97.5-99. 9 % by NMR), with some fumaric diester as the sole by-product. 3a, c can be purified by distillation, 3b by flash chromatography. Compound 3a : 1H-NMR (C6D6, rt, 400 MHz) 8 3.73 (t, 1 H, NCH, 3J=6. 0 Hz), 3.37 (s, 3 H, OMe), 3.32 (s, 3 H, OMe), 3.27 (d, 2 H, HCCCH2N, 4J=2. 4 Hz), 2.56 (m, 2 H, NCHCH2CO), 2.05 (t, 1 H, HCCCH2N, 4J=2. 4 Hz), 1.98 (s, br, 1 H, NH).

13C-NMR (C6D6, rt, 100 MHz) 8 172.5, 170. 0 (COOCH3), 80.7 (dt, HCCCH2N, 2J=50 Hz, 2J=8. 3 Hz), 70.8 (dt, HCCCH2N, 1J=249 Hz, 3J= 4.2 Hz), 55.5 (d, NCHCH2,'J=138 Hz), 50.5, 50.2 (q, OCH3, 1J=146 Hz), 36.7 (dt, NCHCH2CO, 1J=131 Hz, 2J=4. 2 Hz), 35.9 (tt, HCCCH2NH,'J=140 Hz, 2J=4. 2 Hz, 3J=4. 2 Hz). Boiling point: 99°C/0. 2 mm. HRMS (ESI+) calcd. for CgH14NO4 200.0923 ; found 200.0925. Compound 3b : 1H-NMR (C6D6, rt, 400 MHz) 8 4.10-4. 03 (m, 4H, COOCH2CH2), 3.79 (t, 1 H, NCH, 3J=6. 0 Hz), 3.28 (d, 2 H, HCCCH2N, 4J=2. 4 Hz), 3.19-3. 10 (m, 4H, COOCH2CH2), 3.01 (s, 6 H, OMe), 2.64 (m, 2 H, NCHCH2CO), 2.21 (s, br, 1 H, NH), 1.90 (t, 1 H, HCCCH2N, 4J=2. 4 Hz). 13C-NMR (C6D6, rt, 100 MHz) 8 172.0, 169.6 (s, COOCH3), 81.0 (dt, HCCCH2N, 2J=50 Hz, 2J=8. 3 Hz), 71.1 (dt, HCCCH2N, 1J=248 Hz, 3J=4. 2 Hz), 69.9, 69.3 (t, COOCH2CH2, 1J=148 Hz), 63.0 62.7 (t, COOCH2CH2 1J=147 Hz), 57.4 (q, OCH3,'J=141 Hz), 55.6 (d, NCHCH2, 1J=138 Hz), 37.0 (dt, NCHCH2CO, 1J=131 Hz, 2J=4. 3 Hz), 35.9 (tt, HCCCH2NH 1J=139 Hz, 2J=4. 3 Hz, 3J=4. 3 Hz). HRMS (ESI+) calcd. for C13H22NO6 288. 1447; found 288.1461. Compound 3c 1H-NMR (C6D6, rt, 400 MHz) 8 3.88 (m, 2 H, COOCH2CH3), 3.84 (m, 2 H, COCH2CH3), 3.74 (t, 1 H, NCH, 3J=6. 2 Hz), 3.23 (d, 2 H, HCCCH2N, 4J=2. 4 Hz), 2.55 (m, 2 H, NCHCH2CO), 1.96 (s, br, 1 H, NH), 1.86 (t, 1 H, HCCCH2N, 4J=2. 4 Hz), 0.87 (t, 3 H, OCH2CH3, 3J=7. 2 Hz), 0.86 (t, 3 H, OCH2CH3, 3J=7. 2 Hz).

13C-NMR (C6D6, RT, 100 MHz) 8 171.9, 169.4 (s, COOCH2CH3), 80.9 (dt, HCCCH2N, 2J=48. 6 Hz, 2J=8. 0 Hz), 70.9 (dt, HCCCH2N, 1J=247 Hz, 3J=4. 2 Hz), 60.0, 59.5 (t, OCH2CH3, 1J=147 Hz), 55.7 (d, NCHCH2, 1J=137 Hz), 37.1 (dt, NCHCH2CO, 1J=130 Hz, 2J=4. 3 Hz), 36.0 (tt, HCCCH2, 1J=139 Hz,

2J=4. 3 Hz, 3J=4. 3 Hz), 13.9 (q, OCH2CH3, 1J=137 Hz). Boiling point: 112°C/0.2 mm Hg.

Step 2.

Model cross-linking of functionalised polyester chains : Catalytic oxidative homocoupling of 3a, 3b In a typical experiment, Cul (10 mol %) are added to a mixture of 3a, b (10.0 mmol) and PdCi2 (PPh3) 2 (2 mol %) in 20 ml NEt3/20 ml THF at rt under argon and the mixture is stirred for 12 h (control run). No reaction could be detected by nmr. The flask was opened to air and the reaction went to completion within 2-4 h. The solvents were removed and the target compounds 4a, b were isolated in a nearly quantitative yield (94 %-96 % based on the maleic and fumaric starting materials 1,2. Compound 4a : 1H- NMR (C6D6, rt, 400 MHz) 5 3.66 (t, 2 H, NCH, 3J=6. 0 Hz), 3.34 (s, 6 H, OMe), 3.27 (s, 6 H, OMe), 3.18 (m, 4 H, CCCH2N), 2.51 (m, 4 H, NCHCH2), 2.02 (s, br, 2 H, NH). 13C-NMR (C6D6, rt, 100 MHz) 8 172. 2,169. 8 (s, COOCH3), 75.5 (t, CCCH2N, 2J=8. 6 Hz), 67.8 (t, CCCH2N, 3J= 4.3 Hz), 55.6 (d, NCHCH2, 1J=141 Hz), 50.7, 50.2 (q, OCH3, 1J=147 Hz), 36.8 (dt, NCHCH2CO, 1J=130 Hz, 2J=4. 3 Hz), 36.6 (dt, CCCH2NH, 1J=141 Hz, 2J=4. 3 Hz). HRMS (ESI+) calcd. for C18H25N208 397. 1611 ; found 397.1609.

Compound 4b : 1H-NMR (C6D6, rt, 400 MHz) 8 4.13 (m, 4 H, COOCH2CH2), 4.06 (t, 4 H, COOCH2CH2, 3J=4. 9 Hz), 3.70 (dt, 2 H, NCH, 3J=7. 2 Hz, 3J=6. 2 Hz), 3.30 (d, 4 H, CCCH2N, 3J=6. 2 Hz), 3.25 (t, 4 H, COOCH2CH2, 3J=4. 7 Hz), 3.20 (t, 4 H, COOCH2CH2, 3J=4. 9 Hz), 3.06 (s, 6 H, OMe), 3.03 (s, 6 H, OMe), 2.61 (m, 4 H, NCHCH2CO), 2.08 (dt, 2 H, NH, 3J=7. 2 Hz, 3J=6. 2 Hz). 13C-NMR (C6D6, rt, 100 MHz) 8 171. 8,169. 4 (COOCH3), 75.8 (t, -CCCH2N, 2J=8. 6 Hz), 69.3, 69.2 (t, COOCH2CH2,'J=142 Hz), 67.7 (t, - CCCH2N, 3J= 4.3 Hz), 63.2, 62.7 (t, COOCH2CH2 1J=147 Hz), 57.3 (q, OCH3, 1J=140 Hz), 55.8 (d, NCHCH2, 1J=140 Hz), 37.0 (dt, NCHCH2CO, 1J=130 Hz, 2J=4. 3 Hz), 36.6 (dt, CCCH2NH, 1J=141 Hz, 2J=4. 3 Hz). HRMS (ESI+) calcd. for C13H22NO6Na 595.2479 ; found 595.2482.

The results summarised: Nucleophilic addition of propargyl amine to maleic acid esters (1a, 1b) or fumaric acid esters 2a-c respectively, yields 3a-c [5], bearing the desired alkyne function. The reactions are performed at rt, using neat compounds, and proceed quantitatively, 7a making further purification essentially superfluous. The synthesis of b from maleic anhydride and the alcohol3b produces a 3: 1 mixture of maleic (cis) (1b) and fumaric (trans) (2b) diester, an isomerisation well-documented for the preparation of unsaturated polyester chains from maleic anhydride and diols. 3a 5 6a Subsequent radical cross-linking using styrene favours the trans-type of unsaturation, thus introducing a source of inhomogeneity in the cured product. 4 6a This complication is eliminated here, since the addition of the propargyl amine to the acid esters yields the racemates 3a-c quantitatively, if somewhat slower for the trans-species 2a-c. All the double bonds are consumed, and can potentially contribute to the cross-linking via the introduced alkyne functionality. Using the amine in any sub-stoichiometric amount would allow to retain a defined degree of unsaturation in the heterochain backbone. It is noteworthy, that in the course of the addition reaction, the propargyl amine catalyses an isomerisation of maleic diester to fumaric diester, which can easily be followed by NMR spectrometry and by the visible temporary formation of fumaric diester crystals in the reaction mixture. However, this does not constitute an obstacle since the addition of the amine proceeds to completion. Various mechanisms have been proposed for this isomerisation.

Attempts to dimerise 3 under standard Hay conditions or with Cu (OAc) 2/MeCN9 respectively, failed. However, in presence of air, the PdCI2 (PPh3) 2/Cullamine mixture is a very effective system for the catalytic oxidative homo-coupling of terminal alkynes to the corresponding diynes1 and thus, the target compounds 4 are obtained in high yield. Control runs confirm that the combination of Pd, Cu and 02 is crucial for the success of the coupling reaction. Recently an anaerobic variant of this reaction has been reported, but it fails when acetyl or phenylsulphonyl groups are present. 10 The reaction is easily monitored by proton NMR spectrometry, the vanishing signal representing the terminal alkyne hydrogen and the collapsing doublet of the corresponding methylene group being the obvious features. The carbon NMR spectra unambiguously confirm the structure of the target compounds 4, revealing a characteristic shift and loss of multiplicity for the signals of the alkyne carbons as well as the loss of a long range coupling for the adjacent methylene group in comparison to the corresponding spectra of compounds 3.

In summary, we demonstrated that a Pd/Cu catalysed oxidative coupling of alkynes provides a potential alternative for the cross-linking of unsaturated polyester chains, once the latter have been functionalised quantitatively by facile nucleophilic addition of propargyl amine to the maleic/fumaric ester units. The procedure presents a synthesis of structurally well-defined products in high yield in a one-pot reaction. Various disadvantages of radical co-polymerisation pathways that introduce inhomogeneities into the cured product are thus avoided and emission of vinyl monomer is eliminated altogether, a distinctive plus in times of environmental awareness and legislative restrictions.

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