Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2000-01-26
2002-04-23
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C525S457000
Reexamination Certificate
active
06376637
ABSTRACT:
The present invention relates to dendritic and highly branched polyurethanes, to a process for preparing them and to their use.
Dendrimers, arboroles, starburst polymers and hyperbranched polymers are terms for polymeric structures which have a branched structure and a high functionality. These structures have been described in different variants for many classes of polymeric compounds, for example for polyamines, polyamides, polyethers, polyesters, polyphenylenes and polysiloxanes. A comprehensive review of this field is given, for example, in E. Malmstrböm and A. Hult, J.M.S. -Rev. Macromol. Chem. Phys., 1997, C 37(3), 555-579 and in Dendritic Molecules, R. Newkome, C. N. Moorefield and F. Vögtle, Verlag Chemie, Weinheim 1996.
Dendritic and highly branched polyurethanes are accorded only little importance in the literature at present. The preparation of such compounds is described, for example, in R. Spindler and J. M. J. Frechet, Macromolecules 1992, 4809-4813. In the process described there, highly branched polyurethanes are prepared by an intermolecular polyaddition reaction of monomers of the formula (I)
This monomer, which may be regarded as phenol-capped 3,5-diisocyanatobenzyl alcohol, is prepared from 3,5-dinitrobenzyl alcohol in a four-stage reaction by means of various protective group techniques. On heating, phenol is eliminated and the polyaddition of the monomers (I) onto one another commences. Disadvantages of this process are that the monomer (I) is not commercially available and the preparation of the highly branched polyurethanes described in thus very expensive and that the required elimination of phenol is associated with toxicological and occupational hygiene problems.
A. Kumar and S. Ramakrishnan, J. Chem. Soc., Chem. Commun. 1993, 1453, describe the preparation of highly branched polyurethanes by a single-vessel synthesis. Here, a dihydroxybenzoyl azide is first generated and this polymerizes intermolecularly under the action of heat with elimination of nitrogen. The monomer described in this process is also not commercially available and the phenyl urethanes are thermally unstable, which restricts the possible use of the products. In addition, azides are difficult to prepare and to handle.
R. Spindler and J. M. J. Frechet, J. Chem. Soc., Perkin Trans. I, 1993, 913, describe a synthesis of structurally uniform polyurethanes in which dendrite branches are built up from a diisocyanatobenzyl chloride and a protected 3,5-dihydroxybenzyl alcohol and are coupled to a polyfunctional alcohol as center. Here too, the monomers described are not commercially available and the preparation of the dendrimers is thus expensive.
R. T. Taylor and U. Puapaiboon, Tetrahedron Lett. 39(1998)8005, describe a dendrimer synthesis via a Curtius reaction. Here, dendritic urethane branches are first gene rated from aromatic phenoldicarboxylic acids by treatment with alcohol and diphenylphosphoryl azide using protective group techniques and these are then coupled convergently to a triurethane derived from benzenetricarboxylic acid. The disadvantages of this process are the same as those mentioned above.
WO 97/02304 describes a process for preparing dendritic and highly branched polyurethanes in which compounds customary in polyurethane chemistry are used as starting materials. Isocyanate components used are, for example, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), p-phenylene diisocyanate, hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). As polyol component, use is made, for example, of glycerol, trimethylolpropane (TMP) or pentaerythritol. To prepare the dendrimers, monomers which have one NCO group and two protected OH groups are produced in a first reaction step. Addition of these monomers onto an OH or NH containing initiator molecule and removal of the protection on the OH groups gives polyurethane polyols which grow into dendritic structures by divergent (shell-like) buildup. Modification of this reaction scheme also enables the dendrimers to be prepared by the convergent method, i.e. generation of the dendrite branches and subsequent coupling to a center. Highly branched polyurethanes can also be prepared from the monomers mentioned by means of an intermolecular reaction. The important disadvantage of this process is the use of protective group chemistry. The introduction and removal of the protective groups makes this process cumbersome and expensive.
It is an object of the invention to develop a simple process for preparing dendritic and highly branched polyurethanes which can be carried out using readily available raw materials and which, in particular, can be carried out without the incorporation of protective groups.
We have found that this object is achieved by exploiting the differences in the reactivity of the isocyanate groups of diisocyanates or polyisocyanates or of the functional groups in the compounds which are reactive toward isocyanates in order to control a selective buildup of the polymers.
The present invention accordingly provides a process for preparing dendritic or highly branched polyurethanes by reacting diisocyanates and/or polyisocyanates with compounds containing at least two groups which are reactive toward isocyanates, wherein at least one of the reactants contains functional groups having a different reactivity compared to the other reactant and the reaction conditions are selected so that only certain reactive groups react with one another in each reaction step.
Usually, the in each case most reactive groups of the monomers react with one another or the most reactive groups of the monomers react with the end groups of the dendrimers.
The invention also provides the dendritic and highly branched polyurethanes prepared by this process.
For the purposes of the present invention, dendritic polyurethanes are macromolecules which contain urethane groups, are structurally and molecularly uniform and have branched molecular chains going out from a central molecule. For the purposes of the present invention, the branched molecular chains themselves are also included under the term dendritic polyurethanes.
For the purposes of the present invention, highly branched polyurethanes are uncrosslinked macromolecules which contain urethane groups and are both structurally and molecularly nonuniform. They can, on the one hand, be built up going out from a central molecule in a manner similar to dendrimers, but with a nonuniform chain length of the branches. On the other hand, they can also be built up linearly with functional side groups or else, as a combination of these two extremes, have linear and branched parts of the molecule.
Preferred diisocyanates and/or polyisocyanates having NCO groups of differing reactivity are, for example, aromatic isocyanates such as tolylene 2,4-diisocyanate (2,4-TDI), diphenylmethane 2,4′-diisocyanate (2,4′-MDI), triisocyanatotoluene, or aliphatic isocyanates such as isophorone diisocyanate (IPDI), 2-butyl-2-ethylpentamethylene diisocyanate, 2-isocyanatopropylcyclohexyl isocyanate, dicyclohexylmethane 2,4′-diisocyanate and 4-methylcyclohexane 1,3-diisocyanate (H-TDI).
Preference is also given to isocyanates whose NCO groups initially have the same reactivity but in which a first addition of an alcohol or amine onto an NCO group enables a decrease in the reactivity of the second NCO group to be induced. Examples are isocyanates whose NCO groups are coupled via an electronic system, e.g. 1,3- and 1,4-phenylene diisocyanate, naphthylene 1,5-diisocyanate, biphenyl diisocyanate, tolidine diisocyanate and tolylene 2,6-diisocyanate.
It is naturally also possible to use mixtures of the abovementioned isocyanates.
As compounds having at least two groups which are reactive with isocyanates, preference is given to using bifunctional, trifunctional or tetrafunctional compounds whose functional groups have differing reactivities toward NCO groups. Preferred compounds have at least one primary and at least one secondary hydroxyl group, at least one hydroxyl group and at least one er
Bruchmann Bernd
Ehe Ulrike
Stiefenhöfer Konrad
Treuling Ulrich
Wingerter Frank
BASF Corporation
Borrego Fernando A.
Cameron Mark K.
Gorr Rachel
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