Polyurethane prepolvmer composition comprising an alkyl benzoate

FIELD OF THE INVENTION

The present invention relates to a polyurethane prepolymer composition comprising at least one alkyl benzoate as well as cured polyurethane made thereof and the use of alkyl benzoate as plasticizers in polyurethanes mixed, cast and cured at room temperature.

BACKGROUND OF THE INVENTION

For urethane systems comprising a polyurethane prepolymer, based on a polyisocyanate and a polyol, and a curative that are designed to be used at room temperature for cast applications, the viscosity of the individual components and the viscosity of the mixed system are critical metrics that impact the usability of such cast urethane systems. If the viscosity is too high, the system may be difficult to mix, and the mixed system may not easily flow into a cast mold. Lowering the viscosity of a cast urethane system can be achieved through the choice of the polyol backbone or higher amounts of free polyisocyanate monomer content. However, application requirements and health and safety issues limit these options, especially when the prepolymer is intended to be a low free (LF) product comprising only low amounts of free polyisocyanate monomer.

Another option for the polyurethane prepolymer composition formulator is to lower the viscosity through the addition of a diluent, generally a plasticizer. Adding a plasticizer to a urethane composition will lower viscosity; However, adding a plasticizer has a negative effect on the physical properties of the cured polyurethane elastomer. The challenge for the polyurethane prepolymer composition formulator is to only add enough plasticizer to the polyurethane prepolymer composition to ensure ease of use but not so much as to significantly lower the physical properties.

A possible solution to such an issue would be to use a low molecular weight solvent to accomplish better plasticizing efficiency. This is often not a viable approach, as the solvent may cause leaching and the odor imparted by the solvent is highly undesirable.

WO-A-2019/089237 discloses viscosity reducers for sprayable polyurethane compositions, such as triethylphosphate (TEP), tris(1-chloro-2-propyl phosphate) (TCPP), diisononyl adipate (Plastomoll® DNA), phthalate plasticizers (Palatinol®), and trimethyl pentanyl diisobutyrate (TXIB).

US-A-2016/0312090 discloses an adhesive comprising polyurethane prepolymers and plasticizers such as tris(2-ethylhexyl) trimellitate (TOTM), phthalate free C1-C20 alkylsulphonic acid ester with phenol (such as Mesamoll®), benzoate ester, biobased plasticizers such as bio succinic acid or soy based plasticizers.

EP-A-1846492 discloses the use of Cg to Cn alkyl benzoates as plasticizers for polyvinyl chloride in combination with other plasticizers. The use of such alkyl plasticizers for cast polyurethanes is not disclosed.

US-A-4365051 discloses a polyurethane polymer prepared from 4,4’-MDI and caprolactone/diethylene glycol polyester polyol and various diamino alkyl benzoates. The diamino alkylbenzoates work as a curative in these compositions. Since the isocyanate monomers are not removed from the composition, it is believed that they are still present in the composition.

CN104302685 discloses a polyurethane polymer prepared from polyether or polyester polyols and isocyanate, and plasticizers like dibasic ether (DBE) and triethyl phosphate in an amount of 11-30 wt%. Isononyl benzoate is disclosed in a list of suitable plasticizers. Since the isocyanate monomers are not removed from the composition, it is believed that they are still present in the composition.

US-A-2015/167263 discloses a polyurethane polymer prepared from polyether polyol and IPDI. In one example, the prepolymer is mixed with HDI-trimer and plasticizer in an amount of 15-50 wt%. Since the isocyanate monomers are not removed from the composition, they are still present in a relatively high amount in the composition.

EP-A-2103648 discloses a polyurethane polymer prepared from PPG and IPDI. Isononyl benzoate is used as plasticizer in one of the examples. Since the isocyanate monomers are not removed from the composition, they are still present in a relatively high amount in the composition.

However, despite of the prior art, there remains a need for plasticized polyurethane prepolymer compositions which are of low viscosity, preferably at room temperature, which have low volatility (e.g. low odor), which are not compromised on physical properties [compared to non-plasticized polyurethane prepolymer compositions], which are preferably color stable, which comprise preferably low amounts of free polyisocyanate monomer and contain as little plasticizer as possible.

SUMMARY OF THE INVENTION

It was surprisingly found that polyurethane prepolymer compositions comprising at least one polyurethane prepolymer (obtained by the reaction of at least one polyisocyanate and at least one polyol) and at least one alkyl benzoate, in particular a monoester of benzoic acid and isodecyl alcohol, as a plasticizer achieves the same viscosities as common polyurethane plasticizers such as phthalate at significantly lower amounts and that the physical properties of the cured polyurethanes are even better compared to polyurethanes comprising common polyurethane plasticizers.

DETAILED DESCRIPTION OF THE INVENTION

The features and advantages of the present disclosure will be more readily understood, by those of ordinary skill in the art from reading the following detailed description.

Each aspect so described may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

Although the preferred embodiments of the present invention are described herein, it is to be understood that the invention is not limited to that precise embodiment, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. The following examples are illustrative of a practice of the invention, but are not meant to be considered as limiting the scope of the invention.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the scope of the present invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments describe herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. The present invention disclosed herein may suitably be practiced in the absence of any element that is not specifically disclosed herein.

Embodiments of the present invention exhibit a number of advantages over the prior art. Polyurethane prepolvmer

Polyurethane prepolymers of the present invention are formed from the reaction of at least one polyisocyanate and at least one polyol, wherein the at least one polyisocyanate is used in an amount such that NCO groups are present in molar excess relative to the hydroxyl groups of the at least one polyol to obtain a polyurethane prepolymer with free NCO groups, such as an NCO-terminated PU prepolymer. Such polyurethane prepolymers, and methods for their preparation are well known in the art, many of which are commercially available.

Polvisocvanate

The term polyisocyanate, as used herein, is defined as a molecule having two or more isocyanate (NCO) groups, such as di- and poly-functional isocyanates, e.g. tri- and tetra- functional isocyanates, including oligomers, polymers and blocked isocyanates.

The present invention is not limited to a particular polyisocyanate. Any polyisocyanate having two or more isocyanate groups, is suitable for use in preparing the polyurethane prepolymers of the present invention. Obviously, no attempt is made here to provide an exhaustive list of possible polyisocyanate suitable for the practice of the present invention.

Suitable polyisocyanates of the present invention include aliphatic polyisocyanates, cycloaliphatic polyisocyanates, polycyclic polyisocyanates, aromatic polyisocyanates and aliphatic-aromatic diisocyanates.

In one embodiment, the at least one polyisocyanate to prepare the polyurethane prepolymer of the present invention comprises a diisocyanate.

“Diisocyanate monomer” is understood to mean a hydrocarbon compound of low molar mass (of less than 700 g/mol) having two isocyanate groups.

Suitable diisocyanates of the present invention include aliphatic diisocyanates, cycloaliphatic diisocyanates, polycyclic diisocyanates, aromatic diisocyanates and aliphatic-aromatic diisocyanates.

“Aromatic diisocyanate monomer” is understood to mean a diisocyanate monomer as defined above, in which one of the NCO groups is connected via a covalent bond to a carbon atom forming part of an aromatic hydrocarbon ring, such as a phenyl group.

Suitable aromatic diisocyanates of the present invention include diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), phenylene diisocyanate (PDI), tolidine diisocyanate (TODI), diphenyl diisocyanate (DPDI), dibenzyl diisocyanate, naphthalene diisocyanate (NDI), anthracene diisocyanate, benzophenone diisocyanate, xylene diisocyanate (XDI), and combinations thereof.

Preferred aromatic diisocyanate monomers suitable in the practice of the present invention include 2,4’-methylene-bis-(phenyl isocyanate) (2,4’-MDI) and 4,4’-methylene- bis-(phenyl isocyanate) (4,4’-MDI), 2,2-diphenylpropane-4,4’-diisocyanate, toluene-2, 4- diisocyanate (2,4-TDI; CAS: 584-84-9), toluene-2, 6-diisocyanate (2,6-TDI; CAS: 91-08-7), para-phenylene diisocyanate (PPDI), tolidine diisocyanate, naphthalene-1 ,4-diisocyanate, naphthalene-1 ,5-diisocyanate, stilbene-4,4'-diisocyanate, diphenyl-4, 4'-diisocyanate, benzophenone-4,4'-diisocyanate, 1 ,3- and 1 ,4-xylene diisocyanates, para- tetramethylxylene diisocyanate (p-TMXDI), meta-tetramethylxylene diisocyanate (m- TMXDI), and combinations thereof.

Suitable aliphatic and cycloaliphatic diisocyanates of the present invention include ethylene diisocyanate, propylene diisocyanate, butylene diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanates (HDI), heptane diisocyanate, octane diisocyanate, nonane diisocyanate, decane diisocyanate, undecane diisocyanate, dodecane diisocyanate, tetracene diisocyanate, isophorone diisocyanate (IPDI), cyclohexyl diisocyanates (CHDI), 2, 4, 4-trimethyl-1 ,6-hexane diisocyanate (TMDI), methylene bis(p-cyclohexyl isocyanate) (H12MDI), xylene diisocyanate (XDI), L-lysine ethyl ester diisocyanate (LDI), methylene biscyclohexyl isocyanates, bis(isocyanatocyclohexyl)cyclohexane, bis(isocyanatocyclohexyl)methane, bis(isocyanatocyclohexyl)-2, 2-propane, bis(isocyanatocyclohexyl)-1 ,2-ethane, 2- isocyanatomethyl-3-(3-isocyanatopropyl)-5-isocyanatomethyl-b icyclo[2.2.1]-heptane, 2- isocyanatomethyl-3-(3-isocyanatopropyl)-6-isocyanatomethyl-b icyclo[2.2.1]-heptane, 2- isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanatomethyl-b icyclo[2.2.1]-heptane, 2- isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethyl-b icyclo[2.2.1]-heptane, 2- isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl )-bicyclo[2.2.1 ]-heptane, 2- isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanatoethyl )-bicyclo[2.2.1 ]-heptane, 2- isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl )-bicyclo[2.2.1]-heptane, and combinations thereof.

Preferred aliphatic diisocyanate monomer suitable in the practice of the present invention include 1 ,3-trimethylene diisocyanate, propylene-1 ,2-diisocyanate, tetramethylene-1 ,4- diisocyanate, 1 ,6-hexamethylene diisocyanate, 2,2,4-trimethylhevamethylene diisocyanate, 2,4,4-trimethylheyamethylene diisocyanate, 1 ,9-nonamethylene diisocyanate, 1 ,10-decamethylene diisocyanate, dodecane-1 ,12-diisocyanate, isophorone diisocyanate, cyclobutane-1 ,3-diisocyanate, 1 ,3-cyclopentyl diisocyanate, 1 ,4’-cyclohexyl diisocyanate, 4,4’-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, 2,2’- diethylether diisocyanate, 1 -isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; the three geometric isomers of 1 ,1'-methylene-bis(4-isocyanatocyclohexane), and combinations thereof.

In a more preferred embodiment of the present invention, the at least one polyisocyanate is selected from a group consisting of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanates (HDI), para-phenylene diisocyanate (PPDI) and methylene bis(p-cyclohexyl isocyanate) (H12MDI).

In a more preferred embodiment of the present invention, the at least one polyisocyanate is toluene diisocyanate (TDI).

Polyol

The present invention is not limited to a particular polyol. Such polyols are well known in the art and more than one may be used.

A polyol suitable for the present invention used in the preparation of the present polyurethane prepolymer may be selected from any polyol known in the art. Polyols include compounds having more than one hydroxyl groups. Thus, polyols suitable for the present invention comprise diols, triols, and/or higher average hydroxyl functionality. The average hydroxyl functionality can range from 2 to 8, preferably 2 to 3 and more preferably from 2 to 2.5. The formation of such polyols is well known in the art.

In many embodiments, diols are preferred over triols or polyols with higher hydroxyl functionality.

In some embodiments of the present invention, the polyol comprises at least one polyester polyol, at least one polyether polyol, at least one polycaprolactone polyol, at least one polycarbonate polyol or combinations thereof.

The term "polyester polyol" as used herein means a polyol having ester linkages.

A polyester polyol suitable for the present invention for making a polyurethane prepolymer is a polyol having a backbone derived mainly from a polycarboxylate and a poly alcohol, e.g., a majority of the ester linkages in the backbone are derived from a polycarboxylate and a polyol, such as found in polyethylene adipate) glycol:

The hydrocarbon chain of the polyol can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups and can be either linear or branched. Some polyester polyols also employ caprolactone and dimerized unsaturated fatty acids in their manufacture. Suitable examples of polyester polyols include poly(adipate) glycol, poly(hexamethylene adipate) glycol, polyethylene adipate) glycol (PEAG), poly(diethylene adipate) glycol, poly(ethylene/propylene adipate) glycol, poly(trimethylolpropane/hexamethylene adipate) glycol, poly(ethylene/butylene adipate) glycol, poly(butylene adipate) glycol, poly(hexamethylene/neopentyl adipate) glycol, poly(butylene/hexamethylene adipate) glycol (PBHAG), poly(neopentyl adipate) glycol, ortho-phthalate-1 ,6-hexanediol, and combinations, compolymers (including block and random copolymers) and terpolymers thereof.

Suitable polyester polyols may be produced by polycondensation.

These polyester polyols are prepared by conventional methods using a combination of diacids (dibasic acids) and polyols that are known in the art. For example, polyester polyols include the reaction products of diacids such as adipic acid, glutaric acid, succinic acid, azelaic, sebacic, or phthalic or isophtalic acid with diols such as ethylene glycol, 1 ,2- propylene glycol, 1 ,3 propane diol, 1 ,4-butane diol (BDO), 1 ,3 butanediol, 1 ,6-hexane diol, diethylene glycol, polyethylene glycol, polypropylene glycols, or polytetramethylene ether glycol.

The term “polyether polyol” as used herein means a polyalkylene ether polyol represented by the general formula HO(RO)nH, wherein R is an alkylene radical and n is an integer large enough that the polyether polyol has a number average molecular weight of at least 250 g/mol.

These polyalkylene ether polyols are well-known components of polyurethane products and can be prepared by the polymerization of cyclic ethers such as alkylene oxides and glycols, dihydroxyethers, and the like by known methods.

In one embodiment, polyether polyols include polyethylene glycol (PPG), polypropylene glycol (PPG), polyhexamethylene glycol (PHMG), polyoctamethylene glycol (POMG), polyceamethylene glycol (PDMG), copolymers from propylene oxide and ethylene oxide (PPG-EO glycol), poly(tetramethylene ether) glycol (PTMEG or PTMG; also known as polytetrahydrofuran (PTHF)), mixed ether diols, such as poly ethylene propylene glycol copolymer diols, and the like.

In a preferred embodiment, the at least one polyol is selected from the group consisting of PPG and PTMEG. In a more preferred embodiment, the at least one polyol is PPG. A “polylactone polyol” suitable for the present invention for making a polyurethane prepolymer is a polyol having a backbone derived mainly from a hydroxycarboxylic acid or lactone.

Suitable polylactone polyols include those made by polycondensation of, e.g., a caprolactone such as e-caprolactone, and the like, often initiated by a small polyol such as ethylene glycol.

In one embodiment, polycaprolactone polyols include, but are not limited to, 1 ,6- hexanediol-initiated polycaprolactone, diethylene glycol initiated polycaprolactone, trimethylol propane initiated polycaprolactone, neopentyl glycol initiated polycaprolactone, 1 ,4-butanediol-initiated polycaprolactone, and combinations thereof. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

A “polycarbonate polyol” suitable for the present invention for making a polyurethane prepolymer is a polyol having a backbone comprising mainly carbonate linkages, -O- (CO)-O-, as opposed to carboxylate linkages, -0-(CO)-R wherein R is a hydrogen or an organic radical bound to the carbonyl by a C-C bond .

Polycarbonate polyols can be prepared by reaction of glycols, e.g., 1 ,6-hexylene glycol and the like, with organic carbonates, e.g., diphenyl carbonate, diethyl carbonate, or ethylene carbonate and the like. Thus, suitable polyols of the present invention are poly(hexamethylene carbonate) (PHMC) diol or Poly(1 ,6-hexyl-1 ,2-ethyl carbonate) (PHEC) diol.

Suitable polycarbonates include, but are not limited to, polyphthalate carbonate. The hydrocarbon chain can have saturated or unsaturated bonds, or substituted or unsubstituted aromatic and cyclic groups.

LF prepolymer

In one embodiment of the present invention, the at least one polyurethane prepolymer of the present invention, further comprising free polyisocyanate monomers, is a “low free monomer” polyurethane prepolymer (also known as “low free”, “LF” or “low isocyanate”). These are understood by one of ordinary skill in the art to have lower amounts of “free” polyisocyanate monomers than conventional polyurethane prepolymers, i.e. the polyurethane prepolymer compositions have less than 0.1 wt.% free polyisocyanate monomers based on the total weight of the polyurethane prepolymer. Examples of "low free monomer” polyisocyanates include, but are not limited to low free monomer MDI, low free monomer TDI, low free monomer PPDI, low free HDI and low free NDI.

Optionally the amount of free polyisocyanate in the polyurethane prepolymer composition may be at a reduced level, e.g., the polyurethane prepolymer composition may be a "low free" polyisocyanate prepolymer mixture, e.g., free polyisocyanate levels of less than 25 wt.%, less than 10 wt.%, less than 5 wt.%, less than 3 wt.%, less than 1 wt.%, less than 0.5 wt.% or less than 0.1 wt.%. As an example, free diisocyanate in the polyurethane prepolymer composition may be removed by distillation as is known in the art.

In many embodiments of the invention, the amount of free diisocyanate in the prepolymer mixture is at a reduced level, e.g., less than 10 wt.%, and in many embodiments the prepolymer mixture is a low free diisocyanate prepolymer mixture having free diisocyanate amounts of less than 5 wt.%, less than 3 wt.%, less than 1 wt.%, less than 0.5 wt.% or less than 0.1 wt.%. Such low free monomer prepolymers and methods for their preparation are also known in the art.

In the case of the low-monomer-content NCO prepolymers, a typical structure is composed of the reaction product of two isocyanates A and of a polyol B, therefore being ABA. Because of the large excess of isocyanate (high index) in relation to polyol, the probability of formation of larger units, such as ABABA, is very small. These low- monomer-content NCO prepolymers comprise only ABA units. In contrast, NCO prepolymers that do not comprise low monomer content (also termed batch prepolymers or non-thin-layer prepolymers) have a distribution of ABA, ABABA, ABABABA, etc., and also comprise free isocyanate A.

Residual monomer contents in polyurethane prepolymer compositions and polyurethanes can be disadvantageous for different reasons. Some systems are processed at elevated temperatures (e.g. hot melt adhesives at 100-170°C), a temperature range at which monomeric diisocyanates have a considerable vapor pressure.

Alkyl benzoate (benzoic acid monoester) (Plasticizer)

The polyurethane prepolymer composition of the present invention comprises at least one alkyl benzoate. In one embodiment of the invention, the at least one alkyl benzoate is an unsubstituted alkyl benzoate. In a preferred embodiment of the present invention, the at least one alkyl benzoate is a compound according to the following formula (I)

(Formula (I)) wherein R1 is a linear or branched C ₄ -C ₂₄ alkyl.

In a preferred embodiment, R1 is a linear or branched Cg-Cn alkyl.

In the most preferred embodiment, the at least one alkyl benzoate is isodecyl benzoate (also named 8-methlynoyl benzoate) CAS Nr.: 120657-54-7 as illustrated in formula (II)

Isodecyl benzoate of the present invention is available as Benzoflex™ 131 from Eastman Chemical Company or Jayflex™ MB10 from ExxonMobil Chemical.

In a preferred embodiment, the total plasticizer content of the polyurethane prepolymer composition is made up of the Cg benzoate and/or Cm benzoate and/or Cn benzoate. Thus, according to the invention the total plasticizer content may be made up of one or more Cg-Cn benzoates only.

In the polyurethane prepolymer composition of the present invention, additional plasticizers such as phthalate esters, alkyl adipate or trialkyl isobutyrate might be present. Examples of phthalate esters that are optionally used as additional plasticizers with Cg to C11 alkyl benzoate(s) in accordance with the present invention include diisobutyl phthalate, butyl benzyl phthalate, diisoheptyl phthalate, dioctyl phthalate, diisononyl phthalate, diisooctyl phthalate, diisoheptyl phthalate, di-2-ethyl hexyl phthalate (DEHP), diisononyl phthalate, di-2-propyl heptyl phthalate and diisodecyl phthalate. Typical commercial materials include the Jayflex™ plasticizers, Jayflex™ 77 (DIHP), Jayflex™ DINP and Jayflex™ DIDP available from ExxonMobil Chemical and the Palatinol plasticizers marketed by BASF and Vestinol plasticizers from Oxeno.

Examples of benzenepolycarboxylic acid esters that are optionally used as additional plasticizers with Cg to Cn alkyl benzoate(s) in accordance with the present invention include phthalates such as Palatinol® AH (di-(2-ethyl hexyl) phthalate; Palatinol® AH L (di-(2-ethyl hexyl) phthalate); Palatinol® C (dibutyl phthalate); Palatinol® 1C (diisobutyl phthalate); Palatinol® N (diisononyl phthalate); Palatinol® Z (diisodecyl phthalate) Palatinol® 10-P (di-(2-propyl heptyl) phthalate); Palatinol® 711 P (heptyl undecyl phthalate); Palatinol® 911 (nonyl undecyl phthalate); Palatinol® 11 P-E (diundecyl phthalate); Palatinol® M (dimethyl phthalate); Palatinol® A (diethyl phthalate); Palatinol A (R) (diethyl phthalate); Palatinol® K (dibutylglycol phthalate), Jayflex™ 77, Jayflex™ DINP, Jayflex™ DIDP, Santicizer® 261 (C ₇ -C ₉ alkyl benzyl phthalate), Santicizer® 261A (benzyl isononyl phthalate), Benzoflex™ 2088 (di-benzoates) and Eastman 168™ (dimethyl hexyl terephthalate).

Examples of adipates that are optionally used as additional plasticizers with Cg to Cn alkyl benzoate(s) in accordance with the present invention include Plastomoll® DOA (di-(2- ethylhexyl) adipate) and Plastomoll® DNA (diisononyl adipate).

Examples of preferred additional plasticizers include Jayflex™ DINA (di-isononyl adipate; available from ExxonMobil Chemical), di-2-ethyl hexyl terephthalate, di-2-propyl heptyl phthalate or diisodecyl phthalate.

Typically the ratio of alkyl benzoate to additional plasticizer is 1 :1 to 10:1 .

In one embodiment of the present invention, the at least onepolyurethane prepolymer is present from 60 wt.% to 95 wt.%, preferably 70 wt.% to 90 wt.%, based on the total weight of the polyurethane prepolymer composition.

In one embodiment of the polyurethane prepolymer composition of the present invention, the at least one alkyl benzoate is present from 5 wt.% to 40 wt.%, preferably from 10 wt.% to 30 wt.%, based on the total weight of the polyurethane prepolymer composition.

In a preferred embodiment, the polyurethane prepolymer composition of the present invention does not comprise additional plasticizer.

Curable polyurethane prepolvmer composition

The present invention further relates to a curable polyurethane prepolymer composition comprising

(a) at least one polyurethane prepolymer,

(b) at least one alkyl benzoate and (c) at least one curative.

Curative

Curatives, also called curing agents, coupling agents, cross linking agents or chain extenders, are well known in the art and include various polyols or polyamines.

Common curatives include C1-12 alkylene diols such as ethylene glycol, 1 ,3-propanediol,

1 .4-butanediol (BDO), 1 ,5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, trimethylol propane, 1 ,10-decanediol, 1 ,1 -cyclohexane dimethanol, 1 ,4-cyclohexane dimethanol, cyclohexane dial and the like; ether diols such as diethylene glycol; dipropylene glycol, dibutylene glycol, triethylene glycol and the like; hydroquinone-bis-hydroxyalkyl ethers such as hydroquinone-bis-hydroxyethyl ether (HQEE), diethylene glycol etc.; and diamines including ethylene diamine, hexamethylene diamine, isophorone diamine, xylylene diamine, methylenedianiline (MDA), naphthalene-1 ,5-diamine, ortho, meta, and para-phenylene diamines, toluene-2, 4-diamine, dichlorobenzidine, diphenylether-4,4'- diamine,4,4'-methylene-bis(3-chloroaniline) (MBCA), 4,4'-methylene-bis(3-chloro-2,6- diethylaniline) (MCDEA), diethyl toluene diamine (DETDA), 3,5-diethyltoluene-2,4- diamine, 3, 5-diethyltoluene-2, 6-diamine, mixtures of 3, 5-diethyltoluene-2, 4-diamine and

3.5-diethyltoluene-2, 6-diamine (Ethacure® 100) tertiary butyl toluene diamine (TBTDA), dimethyl thio-toluene diamine, monomethyl thio-toluene diamine, mixtures of dimethylthio- toluene diamine and monomethyl thio-toluene diamine (Ethacure® 300), trimethylene glycol di-p-amino-benzoate (Polacure™ 740), 1 ,2-bis(2-aminophenylthio)ethane

(Cyanacure™), methylenedianiline (MDA) and methylenedianiline-sodium chloride complexes ((MDA)3 ^* NaCI; Caytur® 21 and Caytur® 31 from LANXESS).

In one embodiment, the at least one curative is a polyol. If the polyol is selected as the curative, the polyol curative may include ethylene glycol; polyethylene glycol; propylene glycol; polypropylene glycol; lower molecular weight polytetramethylene ether glycol; 1 ,3- bis(2-hydroxyethoxy)benzene; 1 ,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene; 1 ,3-bis-12-[2- (2-hydroxyethoxy)ethoxy]ethoxy)benzene; 1 ,4-butanediol; 1 ,5-pentanediol; 1 ,6- hexanediol; resorcinol-bis(2-hydroxyethyl)ether; hydroquinone-di(2-hydroxyethyl)ether; trimethylol propane, and combinations thereof.

In one embodiment, the at least one curative is a polyamine. If the polyamine is selected as the curative, the polyamine curative may include 3,5-dimethylthio-2,4-toluenediamine (DMTDA ) and isomers thereof, 3, 5-diethyltoluene-2, 4-diamine and isomers thereof, 1 ,3- propanediol-bis-(4-aminobenzoate), 4,4'-bis-(sec-butylamino)-diphenylmethane, 1 ,4-bis- (sec-butylamino)-benzene, 4,4'-methylene-bis-(2-chloroaniline), 4,4'-methylene-bis-(3- chloro-2,6-diethylaniline), trimethylene glycol-di-p-aminobenzoate, polytetramethyleneoxide-di-p-aminobenzoate, N,N'-dialkyldiamino diphenyl methane, r,r'- methylene dianiline, phenylenediamine, 4,4'-methylene-bis-(2-chloroaniline), 4,4'- methylene-bis-(2,6-diethylaniline); 4,4'-diamino-3,3'-diethyl-5,5'-dimethyl diphenylmethane; 2,2',3,3'-tetrachloro diamino diphenylmethane; 4,4'-methylene-bis-(3- chloro-2,6-diethylaniline); isobutyl-3,5-diamino-4-chlorobenzoate; and combinations thereof.

In select embodiments, the at least one curative comprises an aromatic diamine, including a methylenedianiline, toluene diamine, xylylene diamine, phenylene diamine, and the like; specific examples include, 4,4'-methylenedianiline (MDA), 4,4'-ethylene-bis- 2,6 diethyl aniline (MDEA) ortho, meta, and para-phenylene diamines, toluene-2, 4- diamine, 4,4'-methylene-bis(3-chloroaniline) (MBCA), 4,4'-methylene-bis(3-chloro-2,6- diethylaniline) (MCDEA), diethyl toluene diamine (DETDA), 3,5-dimethylthio-2,4- toluenediamine (DMTDA), isobutyl-3, 5-diamino-4-chlorobenzoate, and trimethylene glycol di-p-amino-benzoate.

In a preferred embodiment of the present invention, the at least one curative of the curable polyurethane prepolymer composition is a polyol and more preferably an ethylene oxide-capped polypropylene oxide) (EO-PPG).

In one embodiment, the at least one curative is present from 1 wt.% to 50 wt.%, preferably 10 wt.% to 50 wt.%, based on the total weight of the curable polyurethane prepolymer composition.

Process of preparing a curable polyurethane prepolvmer composition

The present invention further relates to a process for producing curable polyurethane prepolymer compositions, comprising the step of: contacting the at least one polyurethane prepolymer of the present invention, the at least one alkyl benzoate of the present invention and at least one curative.

In preparing the curable polyurethane prepolymer composition of the present invention, the at least one polyurethane prepolymer, the at least one alkyl benzoate and the at least one curative can be combined in any order or in any manner. For example, the at least one curative can be mixed with the polyurethane prepolymer composition, e.g. adding the at least one curative to the at least one polyurethane prepolymer and the at least one alkyl benzoate or adding the at least one polyurethane prepolymer and the at least one alkyl benzoate to the at least one curative. Alternatively, a meter-mix machine may be used to meter and mix the three components simultaneously and continuously and allow continuous filling of molds to obtain higher productivity.

In one embodiment, the process comprises the step of adding the at least one curative to the polyurethane prepolymer composition of the present invention. In another embodiment, the process comprises the step of adding the polyurethane prepolymer composition of the present invention to the at least one curative.

In one embodiment, the at least one curative is present from 1 wt.% to 50 wt.%, preferably 10 wt.% to 50 wt.%, based on the total weight of the curable polyurethane prepolymer composition. Catalyst

In one embodiment of the present invention, the curable polyurethane prepolymer composition comprises no catalyst (d).

In a preferred embodiment of the present invention, the curable polyurethane prepolymer composition comprises a catalyst (d). The present invention is not limited to a particular catalyst. Examples of catalysts suitable for the present invention are trialkylamines, diazabicyclooctane, tin dioctoate, dibutyltin dilaurate, N-alkylmorpholine, lead octoate, zinc octoate, calcium octoate, magnesium octoate, the corresponding naphthenates, and p-nitrophenolate.

In a preferred embodiment of the present invention, the catalyst is a solution of triethylene diamine in dipropylene glycol.

The catalyst (d) speeds up certain reactions in the chain extension (i.e. curing) of polyurethanes. The catalysts include a range of amines and metal salts.

In one embodiment, the at least one catalyst is present in an amount of 0.0001 to 1 parts per 100 parts polyurethane prepolymer composition, preferably 0.005 to 0.5 parts per 100 parts polyurethane prepolymer composition.

Process for preparing a polyurethane

Polyurethanes of the present invention are obtained by reacting the polyurethane prepolymer composition and the curative of the present invention (such process being known as “casting” or “curing”). The curing of the polyurethane prepolymer composition with the at least one curative typically progresses in a mold. In a preferred embodiment, the curing occurs at a temperature of 10°C to 40°C, more preferably at room temperature. Curing of the curable polyurethane prepolymer composition with the curative imparts a network structure to the polyurethanes. After curing, the polyurethane formed in the mold is demolded and, optionally, postcured with additional heat and time so as to fully realize the physical properties of the polyurethane’s elastomeric network structure.

Polyurethane articles can be casted in various ways, including, but not limiting to, open casting, compression molding, centrifugal molding, liquid injection molding, reaction injection molding, Ribbon Flow® rotational casting (moldless), spraying, rotational molding, vacuum casting, transfer molding, pressure casting, solvent casting and troweling.

Polyurethane

The polyurethane (polyurethane elastomer) of the present invention can be formed into numerous useful articles by various means known such as coating, casting and milling processes. A molded product of the polyurethane elastomer composition may be optionally further subjected to secondary crosslinking under the conditions of 100°C to 150°C for 5 h to 24h after being molded.

In a preferred embodiment of the present invention, the polyurethane comprises the reaction product of at least one polyurethane prepolymer composition according to the present invention, free polyisocyanate monomer and at least one curative, wherein the amount of free polyisocyanate monomer is below 0.1 wt.% and wherein the at least one alkyl benzoate is isodecyl benzoate.

Use of an alkyl benzoate

The invention is particularly useful in the production of cast polyurethanes at room temperature. Thus, the present invention relates to the use of an alkyl benzoate as plasticizer for the production of cast polyurethanes at room temperature, preferably for the production of cast polyurethanes based on at least one polyurethane prepolymer with an amount of free polyisocyanates of below 0.1 wt.% based on the total weight of the polyurethane prepolymer. Abbreviations

The abbreviation "CAS” means Chemical Abstracts Service.

The abbreviation “DEG” means diethylene glycol. The abbreviation "DINP” means diisononyl phthalate.

The abbreviation Έ300” means Ethacure® 300.

The abbreviation “EO-PPG” means ethylene oxide-capped polypropylene glycol. The abbreviation “h” or “hrs” means hours. The abbreviation “mPa ^* s” means millipascal-second.

The abbreviation “MW” means average molecular weight.

The abbreviation "% NCO" means content of free isocyanate groups.

The abbreviation "PPG" means polypropylene glycol.

The abbreviation "PU" means polyurethane. The abbreviation “S 160” means Santicizer® 160.

The abbreviation “S 278” means Santicizer® 278.

The abbreviation “TDI” means toluene diisocyanate.

The present invention is illustrated further by means of the following Examples:

Examples

The following materials were used in the examples:

Materials:

Polyurethane prepolvmer components: TDI 80:20 mixture of toluene-2, 4-diisocyanate (CAS No. 584-84-9) and toluene-2, 6-diisocyanate (CAS No. 91-08-7) (commercially available at Covestro)

PPG-425 polypropylene glycol; Mw=425 g/mol; CAS No. 25322-69-4; (commercially available from Monument Chemical) PPG-1000 polypropylene glycol; Mw=1000 g/mol; CAS No. 25322-69-4; (commercially available from Covestro)

PPG-2000 polypropylene glycol; Mw=2000 g/mol; CAS No. 25322-69-4; (commercially available from Covestro)

DEG diethylene glycol; C ₄ H ₁₀ O ₃ ; CAS No. 111-46-6; (commercially available from Shell)

Plasticizer:

DIDP diisodecyl phthalate; CAS No. 26761-40-0; (commercially available from ExxonMobil)

DINP diisononyl phthalate; CAS No. 28553-12-0; (commercially available from ExxonMobil)

Santicizer® 278 Ci ₂ -alkyl benzyl phthalate; (commercially available from Valtris)

Santicizer® 160 butyl benzyl phthalate; CAS No. 85-68-7 (commercially available from Valtris)

Eastman TXIB trimethyl pentanyl diisobutyrate; CAS No. 6846-50-0 (commercially available from Eastman Chemical Company)

Benzoflex™ 9-88 SG dipropylene glycol dibenzonate; CAS No. 27138-31-4

(commercially available from Velsicol (Velsiflexes)) Jayflex™ MB10 isodecyl monobenzoate; C17H26O2; Mw=262,4 g/mol; CAS No. 131298-44-7 (commercially available from ExxonMobil Chemical)

Curative:

EO-PPG-1000 curative; ethylene oxide-capped polypropylene oxide); Mw=1 ,000 g/mol; CAS No. 9003-11-6; (commercially available from Monoment Chemical)

EO-PPG-2000 curative; ethylene oxide-capped polypropylene oxide); Mw=2000 g/mol; CAS No. 9003-11-6; (commercially available from Dow)

Ethacure® 300 curative; mixture of dimethyl thio-toluene diamine and monomethyl thio-toluene diamine (commercially available from Albemarle)

Catalyst:

Niax ^* A33 catalyst; 33 weight % solution of triethylene diamine in dipropylene glycol; (commercially available from Momentive Performance Materials)

The following tests were used in the following Examples.

Methods:

Free NCO content (% NCO) Free NCO content can be determined by a procedure similar to that described in ASTM D1638-70, but employing tetrahydrofuran as the solvent.

Viscosity

Viscosity was measured according to D4878.

Hardness Hardness of cured polymer samples was measured using a Type A durometer (Pacific Transducer, Model 306L) according to ASTM 2240-85.

Tensile strength

Tensile strength and elongation at break were measured according to ASTM D638. Die C tear

Die-C tear strength was tested according to ASTM D-624 (Die-C Tear).

Trouser tear

Trouser tear strength was tested according to ASTM D1938 (Trouser Tear).

Bashore rebound

Bashore rebound was tested according to ASTM-D 2632.

Compression set B

The compression set buttons were tested according to ASTM D-395 Method B. Compression set measures the ability of an elastomer to retain its elastic properties during prolong action of compressive forces. The lower the compression set the better the elastomer retains its elastic properties (less permanent deformation or viscous flow). Low compression set is important in applications such as seals, machinery mount and vibration dampening.

Preparation of the polyurethane prepolymer

LF TDI-PPG-425 polyurethane prepolymer was prepared by reacting 4073.4 g PPG-425 with excess TDI at temperatures in the range of 60°C to 100°C. The reaction mixture was held at the reaction temperature for 3 hours with agitation. Unreacted TDI monomer was then removed by a wiped film evaporator.

Polyurethane prepolymer 1 was prepared by reacting 3429.8 g PPG-1000 and 643.8 g DEG with excess TDI at temperatures in the range of 60°C to 100°C. The reaction mixture was held at the reaction temperature for 3 hours with agitation. Unreacted TDI monomer was then removed by a wiped film evaporator.

Polyurethane prepolymer 2 was prepared by reacting 6902.3 g PPG-2000 and 269.7 g PPG-4000 with excess TDI at temperatures in the range of 60°C to 100°C. The reaction mixture was held at the reaction temperature for 6 hours with agitation. Unreacted TDI monomer was then removed by a wiped film evaporator.

Making a polyurethane prepolymer dilution with plasticizer

A prepolymer dilution is made by weighing out the appropriate amount of prepolymer into a mixing vessel, followed by the appropriate amount of plasticizer. This mixing vessel is then placed into a vortex mixer and mixed at 1900 RPM for approximately 30 seconds. This mixing process is repeated until the plasticizer has been completely incorporated. If the viscosities of the prepolymer and plasticizer are exceedingly different, it is often helpful to first mix the two by hand and then utilize the vortex mixer.

Measurement of the viscosity of the polyurethane prepolvmer dilution After a prepolymer dilution has been made, the viscosity of the dilution at room temperature is measured. To do this, a Brookfield RV Viscometer equipped with an S27 spindle and Thermosel is employed. The Thermosel that has had a disposable measurement sleeve inserted is set to a temperature of 25°C and allowed to equilibrate at this temperature, prior to making a measurement. Once equilibrated, 10 mL of a plasticizer dilution are then placed into the disposable sleeve, using a disposable syringe, and the Brookfield Viscometer is then lowered into the measurement position. The viscometer is then turned on, and the rotations per minute (RPM) of the spindle are adjusted such that the torque reading on the viscometer is between 20% and 80% of full scale. The experimental setup is allowed to come to a steady-state, before recording the viscosity, approximately 30 minutes.

Table 1. Viscosity [mPa ^* s] of LF TDI-PPG-425 polyurethane prepolymer with various amounts of plasticizers

Inventive example

As shown in Table 1 , MB10 is a more efficient plasticizer than the other tested plasticizers, as the viscosity of the polyurethane prepolymer composition is the lowest when the same amounts of plasticizers are used. The efficiency of the MB10 plasticizer is in particular remarkable at low amounts of only 10-15 wt.% plasticizer based on the total weight of the polyurethane prepolymer composition.

Preparation of the cast polyurethane Three polyurethanes were prepared based on curable polyurethane prepolymer compositions. All three curable polyurethane prepolymer compositions have similar characteristics, e.g. viscosity (6,300-6,600 mPa ^* s) and %NCO (6.67). Table 2 shows the components of the curable polyurethane prepolymer compositions used to prepare cured polyurethanes.

Table 2. Curable polyurethane prepolymer compositions and characteristics nventive example; ^** parts per 100 parts polyurethane prepolymer composition Physical properties

Table 3 shows the physical properties of cast polyurethanes PU 1 to PU 3 with various plasticizers.

Table 3. Physical properties of cast polyurethanes nventive example; ^** 72 hours at room temperature

The inventive polyurethane PU 1 , comprising MB10 as plasticizer, has comparable physical properties to polyurethane PU 2, comprising DINP, although the amount of plasticizer is in PU 1 much lower (18 wt.% of the polyurethane prepolymer composition) compared to PU 2 (30 wt.% of the polyurethane prepolymer composition). PU 1 also shows better trouser tear than PU 2.

The inventive polyurethane PU 1 , comprising MB10 as plasticizer, has better physical properties than polyurethane PU 3, comprising TXIB when the same amount of plasticizer is used in both polyurethanes (18 wt.% of the polyurethane prepolymer composition).

The inventive polyurethane PU 1 shows no leaching, low odor and low discoloration.