WO2009153034A1 - Phosphoramidate flame retardants - Google Patents

Abstract

Disclosed are a group of phosphoramidate compounds, all of which have flame retardant properties, particularly on cellulosic fibers. Some of these compounds form oligomers, which are also useful as flame retardant substances.

Description

PHOSPHORAMIDATE FLAME RETARDANTS

Technical Field of the Invention The present invention relates to the general field of flame retardant substances.

Background of the Invention

Phosphorus based flame retardants with novel chemistries have recently attracted increased attention in the field of flame retardants as a suitable alterna- tive to halogen based flame retardants, which are facing increasingly stiffer environmental regulations (see S. V. Levchik, E. D. Weil, Journal of Fire Science. 2006, 24, 345, 2; and S. Lu, I. Hemmerton, Progress in Polymer Science. 2002, 27, 1661). Phosphoramidates have been found to be very suitable for application on cellulosic fibers because of their effectiveness and possible phosphorus- nitrogen synergism phenomena (see M.J. Tsafack, J. Levalois-Grutzmacher, Surface & Coatings Technology. 2006, 201, 2599). However, there is still a need for further flame retardant compounds for various applications.

Summary of the Invention According to one aspect of the invention, there is provided a group of novel phosphoramidate compounds, namely the compounds:

Phosphoramidic acid, 1 ,3-ethanediylbis-, tetramethylester (PAEDBTME);

Dimethyl 2-(2-hydroxyethoxy)ethylphosphoramidate (DMHEEP);

Phosphonic acid, 1,4-piperazinediylbis-tetramethyl ester (PAPDBTME);

Diethyl 2-(2-hydroxyethoxy)ethylphosphoramidate (DEHEEP);

and the oligomers of DMHEEP and DEHEEP:

R = CH₃, CH₂CH₃ n_{1 =}2- 10 It was found that these novel compounds have advantageous flame retardant properties and, in particular, are suitable for use as flame retardants on cellulosic fibers.

According to another aspect of the invention, it was found that a further group of compounds, which are basically known per se, also have advantageous flame retardant properties and are suitable, in particular, for use as flame retardants on cellulosic fibers. It is the following group of compounds:

Phosphoramidic acid, N-(2-hydroxyethyl)-, dimethylester (PAHEDM)

Phosphoramidic acid, N-(2-hydroxyethyl)-, diethylester (PAHEDE)

Phosphoramidic acid, N-(2-hydroxypropyl)-, dimethylester (PAHPDM)

Phosphoramidic acid, N-(2-hydroxypropyl)-, diethylester (PAHPDE)

Phosphoramidic acid, 1 ,2-ethanediylbis-, tetraethylester (PAEDBTEE)

Phosphoramidic acid, 1 ,4-piperazinediylbis-, tetraethylester (PABDBTEE).

Although all the above mentioned compounds are particularly useful as flame retardants applied on cellulosic fibers, they may also be used as flame retardants in other materials like synthetic textile fibers, polyurethanes and other synthetic polymers.

A still further aspect of the invention involves use of the following oligomeric phosphoramidates of PAHEDM, PAHEDE, PAHPDM and PAHPDE:

R = CH₃, CH₂CH₃ n = 2 - 3, (I₁ = 2 - 10

and of DMHEEP and DEHEEP:

R = CH3, CH2CH3 n₁ = 2 - 10 as flame retardants. Using non-monomeric compounds as flame retardants provides an advantageous alternative in view of forthcoming regulatory limitations.

Detailed description of the invention

1. General results for various phosphoramidates 1.1 General Synthesis Method

Mono phosphoramidates: (PAHEDM, PAHEDE, PAHPDM, PAHPDE, DMHEEP, DEHEEP):

The Atherton-Todd reaction was employed to synthesize all phosphorus compounds. A mixture of 0.1 mole of primary or secondary amines with ei- ther 0.1 mole triethyl amine or pyridine in 100 ml anhydrous tetrahydrofuran was added to a three necked flask. The mixture was then cooled to 0°C using an ice bath, and a mixture 0.1 mole of alkyl phosphite and 0.1 mole of carbon tetrachloride in 20 ml anhydrous tetrahydrofuran was added drop- wise over a period of 2 hours under nitrogen environment. The reaction mixture was then brought to room temperature and left at this temperature for further 4 hrs. The mixture was then filtered to remove the salts. The phosphoramidates were then obtained in quantitative yields by evaporating the solution under vacuum.

Bis phosphoramidates: (PAEDBTME, PAEDBTEE, PAPDBTME, PAPDBTEE):

To synthesize the bisphosphoramidates a similar procedure as described above for monophosphoramidates was followed. In this case 0.05 mole of primary or secondary amine were taken. In the case of PAEDBTME, after the reaction was over, the solution was filtered and the residue washed twice with tetrahydrofuran (50ml). PAEDBTME was then extracted from the residue left after filtration with dichloromethane. The extracted solution was then dried under vacuum to obtain PAEDBTME.

Oligomeric phosphoramidates:

During the synthesis of hydroxyl functional phosphoramidate (PAHEDM, PAHEDE, PAHPDM, PAHPDE, DMHEEP and DEHEEP) it was realized that the synthesis led to the formation of some byproducts. These byproducts were identified as the oligomers of the respective hydroxyl functional phosphoramidates and were characterized by HPLC-MS data.

For example, in PAHEDM synthesis, oligomers of PAHEDM were formed with general structure as shown below:

n = 2- 10 Oligo-PAHEDM

The general structures of oligomers of hydroxyl functional phosphorami- dates are shown below:

n = 2-3, n₁ =2- 10

and

R₁ =2 - 10 Without being bound by theory, the formation of oligomers may be due to the free hydroxyl group of phosphoramidates which may react with another molecule of phosphoramidate to form oligomers. This transesterifaction reaction may be catalyzed by the presence of small amounts of acid or base and/or heat. It was also observed that the hydroxyl functional phosphoramidates self oligomerized during storage even at room temperature.

1.2 Application and Test Procedure

Cotton fabrics were treated with various concentrations of phosphorus com- pounds from acetone solutions so as to obtain 1 , 2 and 4% phosphorus content. The fabrics were then dried at room temperature to remove acetone and conditioned overnight at 20°C and 65% relative humidity before the fire test were performed. The Limiting Oxygen Index (LOI) of treated cotton fabrics was obtained according to ASTM D 2863. A minimum of three samples were tested for each treatment and average values taken.

1.3 LOI Results

Table 1a shows the LOI results for the ten compounds described further above. It can be seen that increasing the phosphorus content on the fabric increases the LOI values.

Table 1a: LOI obtained with various phosphoramidates

The LOI values for treated cellulose with oligomeric phosphoramidates are given below in Table 1b: Table 1b: LOI obtained with oligomeric phosphoramidate

These results show that flame retardant properties obtained with oligomeric phosphoramidates are comparable to those of their monomeric counterparts.

2. Specific results for PAHEDE 2.1 Synthesis

PAHEDE was synthesized by reacting 0.1 moles of ethanol amine (EA) with 0.1 moles of diethylphosphite (DEP) in presence of 0.1 mole of triethyl amine (TEA) and 0.1 mole of carbon tetrachloride (CCI₄) in THF solvent as shown in the following scheme:

PAHEDE was further purified by filtering out the reaction mixture and evaporating the solvent. It was obtained as colorless viscous fluid. The structure of PAHEDE was confirmed from Fourier Transform Infra Red Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and Mass spectrometry data.

2.2 Application

PAHEDE was applied to cellulosic fibers from aqueous solution to have required amount of phosphorus content. Further improvement of the wash fastness of the treated cellulose was done by treating the fiber with PAHEDE in combination of crosslinking agents like methylol formaldehyde (MF) resin, dimethylol dihydroxy ethylene urea (DMDHEU) and dimethylol urea (DMU). The treated cellulose con- taining crosslinking agents were cured at 165°C for 5 minutes and rinsed with warm water and dried.

2.3 Methods LOI tests were carried out according to ATSM D2863 method using an FTT Oxygen Index apparatus. Char content of treated cotton was measured by weighing the residue left after the LOI tests. TGA studies were carried out with a Mettler Toledo instrument in which the treated samples were heated from 40 to 500⁰C at a heating rate of 10⁰C /min. Laundry tests were performed according to the ISO- 6330 method.

2.4 Results

2.4.1 Effect of PAHEDE on LOI values of treated cotton Table 2 shows the LOI values and char content of treated samples. From the table it can be seen that increasing the phosphorus content on the fabric increases the LOI values. An increase in phosphorus content of treated cotton also increases char content left after the LOI test. This further indicates the condensed phase action of PAHEDE as flame retardant.

Table 2: LOI and char content of treated Cellulose

Treatment LOI, % Char Content %

1% P PAHEDE 24.3 10.8

2% P PAHEDE 25.8 16.2

4% P, PAHEDE 28.7 23.8

2.4.2 Thermal properties of cotton treated with PAHEDE Table 3 shows the thermal properties of cotton treated with PAHEDE at different concentrations of phosphorus. Treatment of cotton with PAHEDE reduces the heat of combustion and the temperature of combustion values, indicating condensed phase flame retardant action. The TGA data indicate that the temperature of decomposition is lowered for treated cotton and that there is an enhanced char formation with increasing concentration of phosphorus. Table 3: Thermal properties of treated cotton

2.4.3 Crosslinkinp treatments on cotton

Crosslinking experiments were further carried out using various crosslinkers like 1 ,3-Dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), Melamine formaldehyde (MF) resin and 1 ,3-Dimethylolurea (DMU). Table 4 shows the effect of crosslinking treatments on durability to laundry and LOI of treated cotton.

Table 4: Crosslinking treatments

It is seen from Table 4 that DMDHEU and MF resin are able to provide better durability to laundry as compared to DMU. This may be due to lower functionality and reactivity of DMU.

Claims

Claims

1. A phosphoramidate compound, selected from the group consisting of:

O

O

-O

/ \

(PAEDBTME),

\

(DMHEEP),

(PAPDBTME),

(DEHEEP).

and the compounds of formula (I):

R — CH₃, CH₂CH₃ D₁ =2- 10

2. Use of a phosphoramidate compound selected from the group consisting of:

i) the compounds:

(PAEDBTME),

(PAEDBTEE),

(DMHEEP),

(PAPDBTME),

,0.

N^{' V}OH H (DEHEEP),

(PABDBTEE),

and

ii) the compounds of formula (I):

R = CH₃, CH₂CH₃ n_{1 =}2- 10

and iii) the compounds of formula (M):

R = CH₃, CH₂CH₃ n = 2 - 3, n-, = 2 - 10

as a flame retardant substance.

3. Use according to claim 2, comprising the application of the flame retardant substance to cellulosic fibers.

4. Use according to claim 2 or 3, wherein the flame retardant substance is PAHEDM.

5. Use according to claim 2 or 3, wherein the flame retardant substance is a mixture of PAHEDM and oligomers thereof according to formula (III)

n = 2 - 10