New diamine phosphonate monomers as flame-retardant additives for polymers

Article abstract of DOI:10.1080/10426507.2010.514307

Three new phosphonate-amine monomers were synthesized in high yields starting from commercially available aldehydes. Complete NMR and FAB-MS mass spectrometry characterization is reported for all compounds, which are useful monomers for the synthesis of p

Full text of DOI:10.1080/10426507.2010.514307

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Phosphorus, Sulfur, and Silicon and the
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New Diamine Phosphonate Monomers as
Flame-Retardant Additives for Polymers
Salvatore Failla a , Giuseppe Consiglio a & Paolo Finocchiaro a
a Dipartimento di Metodologie Fisiche e Chimiche per Ingegneria ,
Università di Catania , Catania , Italy
Published online: 25 Apr 2011.
To cite this article: Salvatore Failla , Giuseppe Consiglio & Paolo Finocchiaro (2011) New Diamine
Phosphonate Monomers as Flame-Retardant Additives for Polymers, Phosphorus, Sulfur, and Silicon and
the Related Elements, 186:4, 983-988, DOI: 10.1080/10426507.2010.514307
To link to this article: http://dx.doi.org/10.1080/10426507.2010.514307
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Phosphorus, Sulfur, and Silicon, 186:983–988, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.514307
NEW DIAMINE PHOSPHONATE MONOMERS AS
FLAME-RETARDANT ADDITIVES FOR POLYMERS
Salvatore Failla, Giuseppe Consiglio, and Paolo Finocchiaro
Dipartimento di Metodologie Fisiche e Chimiche per Ingegneria,
Universita` di Catania, Catania, Italy
Abstract Three new phosphonate-amine monomers were synthesized in high yields starting
from commercially available aldehydes. Complete NMR and FAB-MS mass spectrometry char-
acterization is reported for all compounds, which are useful monomers for the synthesis of
phosphorus-containing flame-retardant polymers.
Keywords bis-α-Amino-phoshonate; characterization; FAB; monomers phosphonated; NMR
INTRODUCTION
The most commonly used approach for enhancing the fire safety performance of
polymeric materials is the use of flame-retardant additives in commercial polymers. The
physical incorporation of additives has several disadvantages. The additive is often required
in high loadings to be effective, which may result in undesired changes of the physical and
mechanical properties of the polymer. Additives can also be leached from the polymer with
aging and, as a result, reduction in any flame-retardant effect.
An alternative approach is the chemical incorporation of the flame-retardant species
in the polymeric chain by copolymerization or by some other type of chemical modification.
In this case the flame retardant is not easily lost from the polymer; thus one of the major
problem associated with the additive is eliminated.
Phosphorus-containing components have already been used in the synthesis of several
flame-retardant step reaction polymers.1–4 However, their use in the synthesis as monomers
is much less developed; therefore, there exists a need to develop the synthesis of new
monomers containing reactive selected functional groups in order to introduce phosphorus
derivatives into the polymer chain.
In a previous paper5 we reported the syntheses of new phosphonated derivatives
of bis-phenols and used them to reduce flammability of thermosetting DGEBA epoxy
resins.6–8
Moreover, N-substituted α-aminophosphonic acid derivatives, as well as their
cognate-bearing free amino groups, can be used as curing agents for epoxy resins and
Received 1 July 2010; accepted 5 August 2010.
We thank the Italian Ministry for University and Research (MIUR) for financial support.
Address correspondence to Salvatore Failla, Dipartimento di Metodologie Fisiche e Chimiche per Ingegneria,
Universita` di Catania, Viale A. Doria, 6, Catania, I-95125 (CT) Italy. E-mail: sfailla@dmfci.unict.it
983

984
S. FAILLA ET AL.
other polycondensates in order to impart thermal resistance and/or fire-proofing and
fire-retardant proprerties.9–12
Furthermore, considering the great interest in reactive phosphorus-containing
compounds as anti-flammable agents, we decided to synthesize a new bis(α-
aminophosphonates) monomer of type 1 and the 1,4-diamino benzyl phosphonates
monomer 2 (Scheme 1) in order to fully characterize them by NMR analyses and to use
such compounds for the purpose described above.
Scheme 1
RESULTS AND DISCUSSION
The adopted synthetic approach for the preparation of compounds of type 1 is sketched
in Scheme 2. It is based on a three-component condensation reaction with benzylcarbamate,
Scheme 2
aldehydes, and triphenylphosphite in the presence of acetic acid, adapted from the paper
by Oleksyszyn et al.13 The white solid obtained was filtered and, before its purification by
crystallization from methanol, NMR spectra were measured to determine the diastereomeric
ratio. We observed a complexity of the 1H-NMR spectra for compounds 3a–c, arising from
the presence of the two chiral centers, due to the formation of both racemic and meso
diastereomers. The presence of both diastereomers and their relative population was more
easily detected by 31P-NMR analyses on the crude mixture (see Table 1), although we did not
assign the signals to the relative diastereomers. After crystallization, only one diastereomer

FLAME-RETARDANT ADDITIVES FOR POLYMERS
985
Table 1 Diagnostic NMR signals of bis-carbamate derivativesa 3
1
1H-NMR (DMSO-d6)
31P{ H}-NMRb
No.
R
δCH-P (ppm)
δCH2-O-CO (ppm)
δNH-CO (ppm)
δP (ppm)
(2JPH; 3JHH, Hz)
5.63 (dd, 21; 10)
(2JHH, Hz)
5.10 (q, 12)
(3JHH, Hz)
8.91 (d, 10)
3a
3b
3c
H
15.91(5%)
15.77(95%)
16.15(50%)
15.98(50%)
14.61(50%)
14.49(50%)
CH3
5.71 (dd, 21; 10)
6.11 (dd, 20; 10)
5.08 (q, 12)
5.10 (q, 12)
8.3 (d, 10)
OCH3
8.75 (d, 10)
aFull characterization of all compounds is reported in the Experimental section.
bDiastereomeric ratio is determined by 31P-NMR of the crude mixture.
was recovered for compounds 3a–b, whereas both diastereomers* were recovered for
compound 3c.
After isolation and characterization, the benzyl (1,4-phenylene)bis((diphenoxyphosp
horyl)-methylene)dicarbamate derivatives were hydrolyzed to the free bis-α-amino-
phoshonate derivative salts 1a–c and in Table 2 the observed diasteremeric ratio is reported.
Yields are good for both the first step and the second step. Analytical characterization is
reported in Tables 1 and 2, as well in the Experimental section.
As far as the proton NMR characterization is concerned, we observed that for com-
pounds 3a–c most diagnostic peaks are due to:
• the methyne hydrogen linked to the phosphonic group, which appears as a doublet of
doublet because of the coupling with the phosphorus atom (2JHP ∼ 21 Hz) and the NH
group (3JHH ∼ 10 Hz) and whose chemical shift is sensitive to the electronic environment
present in the molecule ranging from 5.6 to 6.1 ppm;
• the benzyloxymethylene group, which appears as an AB quartet due to the chirality of
the molecule and whose chemical shift is roughly centered at 5.10 ppm;
• the NH-CO group, very sensitive to hydrogen bond formation, appearing as a doublet in
the region above 8.3–8.9 ppm.
Comparing the proton chemical shift values of compounds 1a–c (Table 2) and 3a–c
(Table 2) only a small change due to the electron-withdrawing (NH3+) effect on the aromatic
ring is observed. On the contrary, a significant change in chemical shifts value between
the amine monomer 1a–c and the cognate benzyl dicarbamate 3a–c is observed in the 31P-
NMR spectra. In fact, the phosphorus signal of monomers 3a–c is present at 16.15–14.49
ppm (Table 1), whereas for compounds 1a–c the 31P singlet appear at 11.80–11.53 ppm
(Table 2).
*We can exclude, in the room temperature spectra of our samples, the presence of conformers arising
from the restricted rotation of the Cbz (carbamate) group because in previous work14 dealing with mono benzyl
(diphenoxyphosphoryl)(phenyl)methylcarbamate derivative we did not detect any additional complexity signals
arising from the presence of this group. Moreover, in the case of bis-Cbz derivatives (3a–c), if restricted rotation
is present, more complex NMR spectra should be noticed, due to the presence of (Z,Z), (Z,E), and (E,E) rotamers,
and this is not the case for our compounds. Furthermore, the hydrolysis of 3c yields the two expected diasteremers
(racemo and meso, Table 2). Thus, all data clearly indicate that the NMR spectra are well explained by the
formation of the two possible diastereomers.

986
S. FAILLA ET AL.
Table 2 Diagnostic NMR signals of bis-amine derivativesa 1
1
1H-NMR (DMSO-d6)
31P{ H}-NMR
No.
R
δCH-P (ppm)
δNH3+ (ppm)
δP (ppm)
(2JPH; Hz)
5.78 (d, 18)
5.68 (d, 18)
5.60 (d, 18)
1a
1b
1c
H
CH3
OCH3
9.57
9.45
9.45
12.22
11.80
11.64(50%)
11.53(50%)
aFull characterization of all compounds is reported in the Experimental section.
The aromatic diamine monomer 2 was synthesized through a three-step route as
already reported by us.15 In the first step the halo-benzyl derivative was quantitatively con-
verted by the Arbuzov synthetic procedure into the phosphonate benzyl derivative, which
was nitrated and subsequently the dinitro compound was converted by Pd-catalyzed H2
reduction to diamine monomer 2. Using monomer 2 and adipoyl chloride, as well tere-
or iso-phthaloyl chloride, phosphonated polyamides were prepared by solution conden-
sation.15 All of the phosphonated polyamides were fully characterized by spectroscopic
techniques. Interestingly enough, MALDI-TOF mass spectra of polyadipamides reveals
that although we started from stoichiometric amounts of reagents, only amine-terminal
chains are present in the polymer mixture formed by the condensation reaction along with
a small amount of cyclic oligomers. Cyclic oligomers were also observed in the MALDI-
TOF mass spectrum of polyamides obtained from tere- or iso-phthaloyl chloride, whereas
in these cases three families of peaks corresponding to linear oligomers were detected. In
particular, the most intense mass peak series corresponds to the oligomers bearing amine
groups at both ends, whereas the other two series of peaks corresponds to the oligomer
chains terminated with amine and carboxyl groups and to the oligomers bearing carboxyl
groups at both ends.
The thermal properties and the thermal stability of phosphonated polyamides ob-
tained using monomer 2 were studied by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA) techniques. The TGA analyses show that the thermal
stability of our synthesized phosphonate polyamides is strongly determined by the presence
of the pendant phosphonate groups along the polymer chains.15
Now, we dispose of a variety of monomers containing phosphonate groups and
reactive NH2 groups that can be used in the polycondensation reaction to prepare a large
variety of polyamides and can be useful as hardeners in the curing process of epoxy resins.
EXPERIMENTAL
Aldehydes, triphenyl phosphite, benzyl carbamate, acetic acid, as well as solvents
used were high-purity commercial products from Aldrich. Amine monomer 2 was synthe-
sized as already reported.15
1H- and 31P-NMR spectra were recorded, in DMSO-d6, on a Varian-Inova 500 MHz
instrument operating at 500 and 200 MHz, respectively, using SiMe4 as internal reference
and 85% H3PO4 as external reference. Melting points were determined on a Bu¨chi 530
melting point apparatus and are uncorrected.

FLAME-RETARDANT ADDITIVES FOR POLYMERS
987
General Synthetic Procedure for Compounds 3a–c
To a stirred solution of the aldehyde precursor (0.10 mol) and triphenyl phosphite
(0.20 mol) in glacial acidic acid (50 mL) was added over a period of 30 min to solid
benzyl carbamate (0.20 mol) in small portions. After the addition was completed, the
reaction mixture was warmed to 80◦C and stirred for one hour. The solvent was then
evaporated in a vacuum, the oil residue was diluted with methanol (50 mL), and the
solution left at room temperature for 24 h. The white solid obtained was filtered and, before
its purification by crystallization from methanol, a 31P-NMR spectrum was measured
to determine the diastereomeric ratio. After crystallization only one diastereomer was
recovered for compounds 3a–b, whereas both diastereomers were recovered for compound
3c.
General Synthetic Procedure for Compounds 1a–c
To a solution of HBr/CH3COOH 45% (w/w) was added to the corresponding solid
benzyl (1,4-phenylene)bis((diphenoxyphosphoryl)-methylene)dicarbamate derivatives at
room temperature and stirred overnight. For the hydrolysis of 3a and 3b we used one
single diastereomer, whereas for 3c the mixture of both diastereomers was employed. Then
150 mL of diethyl ether was added and a solid was formed, which was filtered off and
washed several time with ether to give the diamine salts 1a–c.
Spectroscopic Characteristics of Compounds Listed in Table 1
Benzyl 1,4-phenylenebis((diphenoxyphosphoryl)methylene)dicarbamate
1
3
3a. H-NMR (DMSO-d6, 27◦C, ppm) δ: 8.91 (d, JHH = 10 Hz, 2H, NH), 7.68 (s, 4H,
3
ArH), 7.3 (m, 18 H, ArH), 7.16 (m, 4H, ArH) 7.06 (d, JHH = 8 Hz, 4H, ArH), 6.94(d,
3
3JHH = 8 Hz, 4H, ArH), 5.63 (dd, JHP = 21.5 Hz, JHH = 10 Hz, 2H, ArCHP), 5.10 (q,
2JHH = 12 Hz, 4H, OCH2Ar). 31P-NMR (DMSO-d6, ppm) δ: 15.77. White powder, 83%
yield, mp 249–250◦C. Anal. Calcd. for C48H42N2O10P2 (868.80): C, 66.36; H, 4.87; N,
3.22. Found: C, 66.50; H, 4.93; N, 3.20. FAB MS: m/z 869.6 [M + H]+1
.
Benzyl (2,5-dimethyl-1,4-phenylene)bis((diphenoxyphosphoryl)methyle
1
ne)dicarbamate 3b. H-NMR (DMSO-d6, ppm) δ: 8.83 (d, 3JHH = 10 Hz, 2H, NH) 7.59
3
(s, 2H, ArH), 7.31 (m, 18 H, ArH), 7.17 (m, 4H, ArH), 7.06 (d, JHH = 8 Hz, 4H, ArH),
6.91(d, 3JHH = 8 Hz, 4H, ArH), 5.71(dd, JHP = 21.5 Hz, 3JHH = 10 Hz, 2H, ArCHP), 5.07
(q, 2JHH = 12 Hz, 4H, OCH2Ar), 2.32 (s, 6H, ArCH3). 31P-NMR (DMSO-d6, ppm) δ: 15.98.
White powder, 73% yield, mp 246–248◦C. Anal. Calcd. for C50H46N2O10P2 (896,26): C,
66.96; H, 5.17; N, 3.12. Found: C, 67.01; H, 5.20; N, 3.15. FAB MS: m/z 897.9 [M +
H]+1
.
Benzyl (2,5-dimethoxy-1,4-phenylene)bis((diphenoxyphosphoryl)methy
1
lene)dicarbamate 3c. H-NMR (DMSO-d6, ppm) δ: 8.75 (d, 3JHH = 10 Hz, 2H, NH),
3
7.48 (s, 2H, ArH), 7.32 (m, 18H, ArH), 7.18 (m, 4H, ArH), 6.96 (d, JHH = 8 Hz, 4H,
ArH) 6.89 (d, 3JHH = 8 Hz, 4H, ArH), 6.1(q, JHP = 21.5 Hz, 3JHH = 10 Hz, 2H, ArCHP),
2
5.1 (dd, JHH = 12 Hz, 4H, OCH2Ar), 3.71 (s, 6H, OCH3). 31P-NMR (DMSO-d6, ppm).
δ: 14.61 (50%), 14,49 (50%). White powder, 75% yield, mp 220–240◦C. Anal. Calcd. for
C50H46N2O12P2 (928,85): C, 64.65; H, 4.99; N, 3.02. Found C, 64.71; H, 5.06; N, 3.06.
FAB MS: m/z 929.8 [M + H]+1
.

988
S. FAILLA ET AL.
Spectroscopic Characteristics of Compounds Listed in Table 2
1
Tetraphenyl 1,4-phenylenebis(aminomethylene)diphosphonate 1a. H-
NMR (DMSO-d6, ppm) δ: 9.57 (bs, 6H, NH3+), 7.86 (s, 4H, ArH), 7.38 (m, 18H, ArH),
7.20 (m, 4H, ArH), 7.12 (m, 4H, ArH), 6.98 (m, 4H, ArH), 5.78 (d, JHP = 18 Hz, 2H,
ArCHP). 31P-NMR (DMSO-d6, ppm). δ: 12.22. White powder, 85% yield, mp > 250◦C.
Anal. Calcd. for C32H32Br2N2O6P2 (762,36): C, 50.41; H, 4.23; N, 3.67. Found C, 50.49;
H, 5.27; N, 3.61. FAB MS: m/z 601.5 [M − 2HBr + H]+1
.
Tetraphenyl (2,5-dimethyl-1,4-phenylene)bis(aminomethylene)diphosp
1
honate 1b. H-NMR (DMSO-d6, ppm) δ: 9.45 (bs, 6H, NH3+), 7.81 (s, 2H, ArH), 7.39
(m, 18H, ArH), 7.24 (m, 4H, ArH), 7.11 (m, 8H, ArH), 5.68 (d, JHP = 18 Hz, 2H, ArCHP),
2.44 (s, 6H, ArCH3). 31P-NMR (DMSO-d6, ppm). δ: 11.80. White powder, 83% yield, mp
> 250◦C. Anal. Calcd. for C34H36Br2N2O6P2 (790,41): C, 51.66; H, 4.59; N, 3.54. Found
C, 51.71; H, 4.63; N, 3.51. FAB MS: m/z 629.4 [M − 2HBr + H]+1
.
Tetraphenyl (2,5-dimethoxy-1,4-phenylene)bis(aminomethylene)diphos
1
phonate 1c.. H-NMR (DMSO-d6, ppm) δ: 9.43 (bs, 6H, NH3+), 7.66 (s, 2H, ArH), 7.37
(m, 18H, ArH), 7.23 (m, 4H, ArH), 7.05 (m, 4H, ArH), 6.98 (m, 4H, ArH), 5.60 (d, JHP
=
18 Hz, 2H, ArCHP), 3.74 (s, 6H, ArOCH3). 31P-NMR (DMSO-d6, ppm). δ: 11.64 (50%),
11,53 (50%). White powder, 83% yield, mp > 250◦C. Anal. Calcd. for C34H36Br2N2O8P2
(822,41): C, 49.65; H, 4.41; N, 3.41. Found C, 49.70; H, 4.47; N, 3.40. FAB MS: m/z 661.6
[M − 2HBr + H]+1
.
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