CA2254231A1 - Reaction mixture and process for producing polyisocyanate polyaddition products - Google Patents

Abstract

A reaction mixture comprises (a) isocyanates, (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries and/or additives, wherein the isocyanates (a) comprise aliphatic and/or cycloaliphatic isocyanates and the ratio of the isocyanate groups present in (a) to the isocyanate-reactive groups present in (b) plus, if used, (c) is from 1 : 0.98 to 1 : 0.8.

Description

CA 022~4231 1998-12-09 Reaction mixture and process for producing polyisocyanate polyaddition products The present invention relates to reaction mixtures comprising (a) isocyanates, (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain 10 extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries and/or additives.
Furthermore, the invention relates to a process for producing polyisocyanate polyaddition products by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries and/or additives, and also to polyisocyanate polyaddition products which are obtainable by such 20 a process.
The production of polyisocyanate polyaddition products, for example thermoplastic polyurethanes, hereinafter also abbreviated to TPUs, is generally known.

TPUs are partially crystalline materials and belong to the class of thermoplastic elastomers. A characteristic of polyurethane elastomers is the segment structure of the macromolecules. Owing to the different cohesion energy densities of the segments, in 30 the ideal case phase separation into crystalline "hard" and amorphous "softN regions occurs. The resulting two-phase structure determines the property profile of products which are produced from these polyurethane systems. The soft phase is, owing to the entropy elasticity of the long-chain soft segments, 35 responsible for the elasticity and the hard phase is responsible for the strength, distortion resistance and heat resistance of the polyurethane fibers. In the hard phase, the polymer chains are fixed by means of intermolecular interactions of the hard segments. The structure is a physical network held together 40 mainly by hydrogen bonds. Under mechanical loading, these interactions are partly overcome, so that irreversible restructuring of the hard segments occurs within the hard phase.
This has an adverse effect on the hysteresis behavior.
Particularly melt-spun polyurethane fibers here display large 45 working and tension losses and also high permanent extensions.
for this reason, better fixing of the rigid segments is necessary to improve the fiber properties. Furthermore, known TPUs based on CA 022~4231 1998-12-09 .

aromatic isocyanates have an undesirable tendency to discolor on irradiation and storage.

It is an object of the present invention to develop a reaction 5 mixture comprising (a) isocyanates, (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries 10 and/or additives, which mixture is suitable for producing polyisocyanate polyaddition products by reaction of the abovementioned components. The polyisocyanate polyaddition products should, in particular, have an improved thermal stability, measurable by means of the heat distortion 15 temperature, and improved hysteresis behavior after loading, and should also be stable to light.

We have found that this object is achieved by the isocyanates (a) 20 comprising aliphatic and/or cycloaliphatic isocyanates and the ratio of the isocyanate groups present in (a) to the isocyanate-reactive groups present in (b) plus, if used, (c) being from 1 : 0.98 to 1 : 0.8.

25 According to the present invention, an excess of isocyanate groups over the groups which are reactive toward the isocyanate groups is used in the reaction mixture. This excess can be expressed by the molar ratio of the isocyanate-reactive groups in the components (b) plus (c) to the isocyanate groups in the 30 component (a). According to the present invention, this ratio is from 1 : 0.98 to 1 : 0.8, preferably from 1 : 0.95 to 1 : 0.85.
As a result of this excess of isocyanate groups, these isocyanate groups form, during and possibly after the formation of the urethane groups by reaction of (a) with (b) and, if used, (c), 35 crosslinks in the form of, for example, allophanate and/or isocyanurate structures which lead to the improved properties of the polyisocyanate polyaddition products. The formation of the crosslinks can, if desired, be promoted by addition of catalysts, e.g. alkali metal acetates or formates, which are generally known 40 for this purpose. Processing of the reaction product, i.e. the polyisocyanate polyaddition product, to produce the desired films, moldings, injection-molded articles, hoses, cable sheathing and/or fibers should preferably be carried out during and/or immediately after the formation of the urethane groups and 45 before complete reaction of the reaction mixture, since thermoplastic processing of the polyisocyanate polyaddition products to produce films, moldings or fibers is preferably CA 022~4231 1998-12-09 carried out at low temperatures before and/or during the formation of the crossllnks. Isocyanates used according to the present invention are aliphatic and/or cycloaliphatic isocyanates, preferably diisocyanates, particularly preferably 5 hexamethylene diisocyanate. These isocyanates according to the present invention can, if desired, be used in combination with customary further isocyanates, for example known aromatic isocyanates. Preference is given to using from 50 to 100%, particularly preferably from 75 to 100%, of the isocyanate groups 10 used as (a) in the form of aliphatic isocyanates.

The reaction of the reaction mixture of the present invention in the process for producing polyisocyanate polyaddition products can be carried out by known methods, for example by the one-shot 15 process or the prepolymer process, for example by reacting an NCO-containing prepolymer which can be prepared from (a) and parts of the components (b) and, if desired, (c) with the remainder of (b) and, if desired, (c), on a customary belt unit, using a known reaction extruder or equipment known for this 20 purpose. The temperature in this reaction is usually from 60 to 250~C, preferably from 60 to 180~C, particularly preferably from 70 to 120~C.

25 During and, if desired, after the formation of the polyurethane groups by reaction of (a) with (b) and, if desired, (c), the reaction products can be pelletized, granulated or processed by generally known methods, for example by extrusion in known extruders, by injection molding in customary injection molding 30 machines or by generally known spinning processes, for example by melt spinning, to produce moldings of all types, films or, in the case of the spinning processes, to form fibers.

Preferably, the reaction mixture is processed on extruders or 35 injection molding machines to produce films or moldings or by a spinning process to form fibers during and, if desired, after the formation of the urethane groups by reaction of (a) with (b) and, if desired, (c), particularly preferably from the reaction melt and before complete formation of allophanate and/or isocyanurate 40 crosslinks. This direct further processing of the reaction mixture without granulation or pelletization and without substantial or complete reaction of the reaction mixture offers the advantage that crosslinking by formation of, for example, allophanate and/or isocyanurate structures has occurred to only a 45 slight degree or not at all and the reaction mixture can CA 022~4231 1998-12-09 .

therefore be processed at a desirably low temperature to form the end products such as films, moldings or fibers.

The processing of the reaction mixture is thus preferably carried 5 out by processing the reaction mixture in a softened or molten state on extruders or injection molding machines to form films or moldings or by a spinning process to form fibers at from 60 to 180~C, preferably from 70 to 120~C, during the reaction of (a) with (b) and, if desired, (c), particularly preferably from the 10 reaction melt and before complete formation of allophanate and/or isocyanurate crosslinks.

The process product from the extruder, the injection molding 15 machine or the spinning process is preferably heated at from 20 to 120~C, preferably from 80 to 120~C, for at least two hours, preferably from 12 to 72 hours, under otherwise customary conditions to partially or completely form, particularly preferably completely form, the allophanate and/or isocyanurate 20 crosslinks. This subsequent heating of the moldings, films or fibers makes it possible to obtain the crosslinks in the polyisocyanate polyaddition products, which crosslinks lead to the very advantageous properties of the products in respect of the thermostability and the hysteresis behavior after loading.

If unsaturated components (b) and/or (c), for example cis-1,4-butenediol, are used, the moldings, films or fibers can, after they have been produced, be treated by irradiation, for example by irradiation with electron beams.

Examples of the components (a) to (e) are given below. In the following, molecular weights have, unless indicated otherwise, the unit g/mol.

35 a) Suitable organic isocyanates (a) are, according to the present invention, aliphatic and/or cycloaliphatic and, if desired, additionally aromatic diisocyanates. Specific examples are: aliphatic diisocyanates such as hexamethylene 1,6-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene 1,4-diisocyanate or mixtures of at least two of the C6-alkylene diisocyanates mentioned, pentamethylene -1,5-diisocyanate and butylene 1,4-diisocyanate, cycloaliphatic diisocyanates such as 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate), cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and 2,6-diisocyanate and also the corresponding isomer mixtures, dicyclohexylmethane 4,4'-, . . .

CA 022~4231 1998-12-09 2,4'- and 2,2'-diisocyanate and also the corresponding isomer - mixtures, 1,4- and/or 1,3-di(isocyanatomethyl)cyclohexane, 1,4- and/or 1,3-di(isocyanatoethyl)cyclohexane, aromatic diisocyanates such as 1,3- and/or 1,4-di(isocyanatomethyl)benzene, tolylene 2,4-diisocyanate, mixtures of tolylene 2,4- and 2,6-diisocyanate, diphenylmethane 4,4'-, 2,4'- and/or 2,2'-diisocyanate (MDI), mixtures of diphenylmethane 2,4'- and 4,4~-diisocyanate, urethane-modified liquid diphenylmethane 4,4'- and/or 2,4'-diisocyanates, 1,2-di(4-isocyanatophenyl)ethane and naphthylene l,5-diisocyanate. Preference is given to using hexamethylene l,6-diisocyanate.

b) Suitable substances (b) which are reactive toward isocyanates and have a mean functionality, i.e. a functionality averaged over the component (b), of from 1.8 to 2.5, preferably from 1.9 to 2.2, particularly preferably from 1.95 to 2.1, are, for example, polyhydroxyl compounds having molecular weights of from 500 to 8000, preferably polyetherols and polyesterols. However, other suitable compounds are hydroxyl-containing polymers, for example polyacetals such as polyoxymethylenes and especially water-insoluble formals, e.g. polybutanediol formal and polyhexanediol formal, and aliphatic polycarbonates, in particular those prepared from diphenyl carbonate and 1,6-hexanediol by transesterification, having the abovementioned molecular weights. The polyhydroxyl compounds mentioned can be employed as individual components or in the form of mixtures.

The mixtures for producing the TPU or TPUs have to be based at least predominantly on bifunctional isocyanate-reactive substances.

Further isocyanate-reactive substances (b) which can be used are polyamines, for example amine-terminated polyethers, e.g.
the compounds known under the name Jeffamine~ (Texaco Chemical Co.); the mean functionality of the component (b) should be in the range according to the present invention.

Suitable polyetherols can be prepared by known methods, for example from one or more alkylene hydroxides having from 2 to 4 carbon atoms in the alkylene radical and, if appropriate, an initiator molecule containing two reactive hydrogen atoms in 45 bound form by anionic polymerization using alkali metal hydroxides such as sodium or potassium hydroxide or alkali metal alkoxides such as sodium methoxide, sodium or potassium ethoxide CA 022~4231 1998-12-09 or potassium isopropoxide as catalysts or by cationic polymerization using Lewis acids such as antimony pentachloride, boron fluoride etherate, etc., or bleaching earth as catalysts.
Examples of alkylene oxides are: ethylene oxide, 1,2-propylene 5 oxide, tetrahydrofuran, 1,2- and 2,3-butylene oxide. Preference is given to using ethylene oxide and mixtures of 1,2-propylene oxide and ethylene oxide. The alkylene oxides can be used individually, alternately in succession or as a mixture. Suitable initiator molecules are, for example: water, aminoalcohols such 10 as N-alkyldialkanolamines, for example N-methyldiethanolamine, and diols, e.g. alkanediols or dialkylene glycols having from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms, for example ethanediol, 1,3-propanediol, 1,4-butanediol and 1,6-hexanediol. If desired, mixtures of initiator molecules can 15 also be used. Other suitable polyetherols are the hydroxyl-containing polymerization products of tetrahydrofuran (polyoxytetramethylene glycols).

Preference is given to using polyetherols derived from 20 1,2-propylene oxide and ethylene oxide in which more than 50%, preferably from 60 to 80%, of the OH groups are primary hydroxyl groups and in which at least part of the ethylene oxide is arranged as a terminal block, and in particular polyoxytetramethylene glycols.

Such polyetherols can be obtained by, for example, first polymerizing the 1,2-propylene oxide onto the initiator molecule and subsequently polymerizing on the ethylene oxide or first 30 copolymerizing all the 1,2-propylene oxide in admixture with part of the ethylene oxide and subsequently polymerizing on the remainder of the ethylene oxide or, stepwise, first polymerizing part of the ethylene oxide onto the initiator molecule, then polymerizing on all of the 1,2-propylene oxide and then 35 polymerizing on the remainder of the ethylene oxide.

The polyetherols, which are essentially linear in the case of the TPUs, usually have molecular weights of from 500 to 8000, preferably from 600 to 6000 and in particular from 800 to 3500.
40 They can be employed either individually or in the form of mixtures with one another.

Suitable polyesterols can be prepared, for example, from dicarboxylic acids having from 2 to 12 carbon atoms, preferably 45 from 4 to 8 carbon atoms, and polyhydric alcohols. Examples of suitable dicarboxylic acids are: aliphatic dicarboxylic acids such as succinic acid, glutaric acid, suberic acid, azelaic acid, ~ . .

CA 022~4231 1998-12-09 sebacic acid and preferably adipic acid and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used individually or as mixtures, e.g. in the form of a succinic, glutaric and adipic 5 acid mixture. Likewise, mixtures or aromatic and aliphatic dicarboxylic acids can be used. In place of the dicarboxylic acids, it may be advantageous to use the corresponding dicarboxylic acid derivatives such as dicarboxylic esters having from 1 to 4 carbon atoms in the alkohol radical, dicarboxylic 10 anhydrides or dicarboxylic acid chlorides for preparing the polyesterols. Examples of polyhydric alcohols are alkanediols having from 2 to 10, preferably from 2 to 6, carbon atoms, e.g.
ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 2,2-dimethylpropane-1,3-diol, 15 1,2-propanediol and dialkylene ether glycols such as diethylene glycol and dipropylene glycol. Depending on the desired properties, the polyhydric alcohols can be used alone or, if desired, in mixtures with one another.

20 Also suitable are esters of carbonic acid and the diols mentioned, in particular those having from 4 to 6 carbon atoms, e.g. 1,4-butanediol and/or 1,6-hexanediol, condensation products of w-hydroxycarboxylic acids, for example ~-hydroxycaproic acid, and preferably polymerization products of lactones, for example 25 substituted or unsubstituted ~-caprolactones.

As polyesterols, preference is given to using alkanediol polyadipates having from 2 to 6 carbon atoms in the alkylene 30 radical, e.g. ethanediol polyadipates, 1,4-butanediol polyadipates, ethanediol-1,4-butanediol polyadipates, 1,6-hexanediol-neopentyl glycol polyadipates, polycaprolactones and, in particular, 1,6-hexanediol-1,4-butanediol polyadipates.

35 The polyesterols usually have molecular weights (weight average) of from 500 to 6000, preferably from 800 to 3500.

c) Preferred chain extenders (c) which usually have molecular weights of less than 500 g/mol, preferably from 60 to 499 g/mol, particularly preferably from 60 to 300 g/mol, are alkanediols and/or alkenediols and/or alkyne diols having from 2 to 12 carbon atoms, preferably having 2, 3, 4 or 6 carbon atoms, e.g. ethanediol, 1,2- and/or 1,3-propanediol, 1,6-hexanediol and in particular 1,4-butanediol and/or cis-and/or trans-1,4-butenediol, and dialkylene ether glycols such as diethylene glycol and dipropylene glycol. However, diesters of terephthalic acid and alkanediols having from 2 CA 022~4231 1998-12-09 to 4 carbon atoms, e.g. bis(ethanediol) terephthalate or bis(1,4-butanediol) terephthalate, and hydroxyalkylene ethers of hydroqulnone, e.g. 1,4-di(~-hydroxyethyl)hydroqulnone, are also suitable.

It may also be advantageous to use small amounts, i.e. up to 15% by weight of the amount of chain extenders used, of trifunctional compounds such as glycerol, trimethylolpropane and/or 1,2,6-hexanetriol.

To adjust the hardness and melting point of the TPUs, the molar ratios of the formative components (b) and (c) can be varied within a relatively wide range. It has been found to be useful to 15 employ molar ratios of polyhydroxyl compounds (b) to chain extenders (c) of from 1 : 1 to 1 : 12, in particular from 1 : 1.8 to 1 : 6.4, with the hardness and the melt point of the TPUs increasing with increasing diol content.

20 d) Suitable catalysts which, in particular, accelerate the reaction of the NCO groups of the diisocyanates (a) with the hydroxyl groups of the formative components (b) and (c) are the customary catalysts known from the prior art, for example tertiary amines such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo[2.2.2]octane and the like and also, in particular, organic metal compounds such as titanate esters, iron compounds such as iron(III) acetylacetonate, tin compounds such as tin diacetate, tin dioctoate, tin dilaurate or the dialkyltin salts of aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate or the like. The catalysts are usually used in amounts of from 0.002 to 0.1 part per 100 parts of polyhydroxyl compound (b).

e) Apart from catalysts, customary auxiliaries and/or additives (e) can also be added to the formative components (a) to (c).
Examples which may be mentioned are surface-active substances, fillers, flame retardants, nucleating agents, oxidation inhibitors, stabilizers, lubricants and mold release agents, dyes and pigments, inhibitors, stabilizers against hydrolysis, light, heat or discoloration, inorganic and/or organic fillers, reinforcing materials and plasticizers.

CA 022~423l 1998-l2-09 More detailed information on the abovementioned auxiliaries and additives may be found in the specialist literature.

The process of the present invention is illustrated by the 5 following examples.

Example 1 (Ratio NCO:OH = 1.1:1):

10 100 g (0.051 mol) of polytetrahydrofuran having a molecular weight of 2000 and a hydroxyl number of 57.3 mgKOH/g were placed in a Teflon vessel and heated to T=100~C. While stirring vigorously, the following were added at 10 minute intervals, 8.99 g (0.102 mol) cis-1,4-butenediol, 28.3 g (0.1683 mol) of 15 hexamethylene diisocyanate (HDI) and 3 mg of dibutyltindiacetate as catalyst. About 5 minutes after addition of the catalyst, the viscosity of the reaction mixture increased greatly as a result of the increase in molecular weight. To complete the reaction, stirring was continued for another 20 minutes at 100~C.

The polyurethane melt which still contains free NCO groups due to the excess of HDI was immediately afterward, without granulation, used as spinning polymer for the melt spinning process.

25 The spinning process was carried out using a piston-type spinning unit. The spinning temperature was 80~C and the residence time was 30 minutes. The fiber obtained was not sticky and could be wound without problems. After storage for two days at room temperature, the fiber was heated at 100~C for 24 hours, giving a significant 30 property improvement.

The polyisocyanate polyaddition products produced by this method were no longer soluble in DMA/DMF and accordingly contained 35 allophanate and/or isocyanurate crosslinks; they displayed significantly improved fiber properties.

Comparative Examples 2-4:

40 Polyurethane fibers were produced as described in Example 1, except that the molar ratio of polytetrahydrofuran: butenediol:
HDI was 1:1.5:2.5 (Example 2), 1:2:3 (Example 3) or 1:3:4 (Example 4).

~5 The fiber properties of the TPU fibers are shown in the following table:

CA 022~4231 1998-12-09 .

Table 1:

Example 1 2 3 4 NCO/OH 1.1:1 1:1 1:1 1:1 ~ rell)insoluble 1.35 1.34 1.37 Permanent 35 110 95 120 extension 1st cycle [%]
Permanent 45 130 115 140 extension 5th cycle [%]
Tenacity 7.0 3.0 3.4 3.2 [cN/tex]
Extension at700 1100 800 800 break [%]
Tension loss0.115 0.24 0.24 0.22 bw5 HDT [~C] 125 80 90 95 20 1) 0.5 % strength by weight of solution in DMA, ~: viscosity The fiber properties were determined in accordance with DIN
53835.

Compared to conventional melt-spun TPU fibers, the allophanate-crosslinked TPU fiber of the present invention displays significantly improved fiber properties.
The covalent crosslinking of the hard segments by means of 30 allophanate links made it possible to achieve a significant improvement in the hysteresis behavior (lower permanent extension and tension loss), a doubling of the tenacity and an increased HDT.

Claims (10)

1. A reaction mixture comprising (a) isocyanates, (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries and/or additives, wherein the isocyanates (a) comprise aliphatic and/or cycloaliphatic isocyanates and the ratio of the isocyanate groups present in (a) to the isocyanate-reactive groups present in (b) plus, if used, (c) is from 1 : 0.98 to 1 : 0.8.

2. A reaction mixture as claimed in claim 1, wherein the isocyanate (a) present is hexamethylene diisocyanate.

3. A process for producing polyisocyanate polyaddition products by reacting (a) isocyanates with (b) compounds which are reactive toward isocyanates and have a mean functionality of from 1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and, if desired, (c) chain extenders having a molecular weight of less than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries and/or additives, wherein the isocyanates (a) used comprise aliphatic and/or cycloaliphatic isocyanates and the ratio of the isocyanate group present in (a) to the isocyanate-reactive groups present in (b) plus, if used, (c) is from 1 : 0.98 to 1 : 0.8.

4. A process as claimed in claim 3, wherein the isocyanate (a) used is hexamethylene diisocyanate.

5. A process as claimed in claim 3, wherein the reaction mixture is processed during and, if desired, after formation of the urethane groups by reaction of (a) with (b) and, if desired, (c) on extruders or injection molding machines to form films or moldings or in a spinning process to form fibers.

6. A process as claimed in claim 3, wherein the reaction mixture is processed in a softened or molten state during the reaction of (a) with (b) and, if desired, (c) at from 60 to 180°C on extruders or injection molding machines to form films or moldings or in a spinning process to form fibers.

7. A process as claimed in claim 5, wherein the process product from the extruder, the injection molding machine or the spinning process is heated at from 20 to 120°C for from 12 to 72 hours to form the allophanate and/or isocyanurate crosslinks.

8. A polyisocyanate polyaddition product obtainable by a process as claimed in claim 3.

9. A polyisocyanate polyaddition product comprising allophanate and/or isocyanurate structures and obtainable by a process as claimed in claim 3.

10. A molding, injection-molded article, hose, cable sheeting or film obtainable by a process as claimed in claim 3.