REACTIVE

&
FUNCTIONAL
POLYMERS
ELSEVIER Reactive & Functional Polymers 37 (1998) 49-56

Synthesis of polyphosphate and polyphosphate ester having pendant

amine salt groups

Chonghui Wang, Daisuke Iwami, Toshio Takayama, Shigeo Nakamura *

Department of Applied Chemistry, Faculty of Engineering, Kanagawa University, Kanagawa-Ku, Yokohama 221-8686, Japan

Received 25 June 1997; accepted 7 November 1997

Abstract

Seven cyclic and noncyclic organic phosphates have been examined for the reactivity to polycondensation. Polyphos-
phate and polyphosphate ester having pendant tertiary amine salt groups are obtained from a cyclic organic phosphate
having a primary amine salt group and a tertiary amine salt group by a molten organic phosphate phase/organic phase poly-
condensation method. A novel concept of the zwitterion polycondensation mechanism is proposed. The chemical structure
of the resulting polymers was contirmed from infrared spectra, solid state 3’P and 13CNMR spectra. 0 1998 Elsevier
Science B.V. All rights reserved.

Keywords: Cyclic phosphate; Polyphosphate; Polyphosphate ester; Inorganic-organic copolymer; Amine salt group;
Zwitterion polycondensation mechanism

1. Introduction ture of phosphorous-containing compounds. Inves-

tigation of the reaction of organic phosphates is
Recently, considerable attention has been paid important for the preparation of inorganic-organic
to phosphorus-containing polymers, especially inor- copolymers, inorganic-organic polymer blends and
ganic-organic copolymers [l-7]. The phosphorus- polymeric condensation agents.
containing polymers are expected to find various Synthesis and behavior of many polyphos-
applications such as fire retardants, adhesives, se- phate from inorganic phosphates such as LiH2P04,
lective ion-exchange resins, synthetic bilayer mem- NaHzPOd and KH2P04 have been reviewed [l 11.
branes and blood-compatible materials [8,9]. Leber and Buck reported the preparation of inor-
Activating agents containing phosphorus such ganic polyphosphate by the reaction of phospho-
as polyphosphoric acid, polyphosphate esters, rus pentoxide and ammonia [ 12,131. Van Wazer and
polyphosphoric acid trimethylsilyl ester and phos- Westman described the chemistry of some inorganic
phorus pentoxide-methanesulfonic acid have been polyphosphates [ 14,151. Although many investiga-
used for polycondensation [lo]. tions have been reported on the preparation of organic
The structure of polyphosphates is similar to that polydiesters of phosphoric acid, their monomers
of organic polymers because of the tetrahedral na- are organophosphorus compounds with three cova-
lent bonds such as bis(diethylamino)methoxyphos-
* Corresponding author. phine [16], 2-hydro-2-oxo-1,2,3-dioxophosphorinane

1381-5148/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved

PII S1381-5148(97)00167-3
50 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56

[17-191, or expensive aryl phosphorodichloridates ylenediamine (TEMED), N,N-dimethyl-1,3-propane-

and phosphonic dichlorides [20-231. diamine (DMPA), and ethylene glycol (EG) were ob-
However, few investigations have been reported tamed from Tokyo Kasei Kogyo Co. and used without
on the synthesis of organic polyphosphate or further purification.
polyphosphate ester using phosphoric acid and di- JR spectra were recorded on a JASCO JR-810.
amine or phosphoric acid, diamine and diol as start- The solid-state 31P- and 13C-NMR spectra were ob-
ing materials. tained on a JEOL EX-200WB NMR spectrometer us-
Phosphoric ester has been used as a ligand for the ing phosphoric acid and adamantane as external stan-
introduction of metal ions into monomers and poly- dards, respectively. Thermogravimetry and differen-
mers [24]. Organic polyphosphate and polyphos- tial thermal analysis (TG-DTA) were performed on a
phate ester having pendant tertiary amine salt groups Seiko SSC/5200 at a heating rate of 1OWmin.
can be used as polymer ligands with multifunc-
tional groups. This article describes the reactivity of 2.2. Preparation of organic phosphates
seven organic cyclic and noncyclic phosphates from
phosphoric acid and amine to the polycondensation, 0.01 Mole of HsP04 in 30 ml of acetone was
and also the synthesis of organic polyphosphate and added dropwise to 0.02 mole of BA (or DA, TEA or
polyphosphate ester having pendant tertiary amine DEA) or 0.01 mole of EtDA (or TEMED or DMPA)
salt groups from a cyclic phosphate. in 30 ml of acetone with stirring and cooling.
Phosphates Sl to S7 (Fig. 1) were precipitated by
2. Experimental adjusting the pH of the solutions to 5 to 6. The precip-
itates were filtered, washed with acetone, and dried.
2.1. Materials and measurements
2.3. Polymer synthesis
Phosphoric acid, benzylamine (BA), diethylamine
(DA), triethylamine (TEA), diethanolamine (DEA), 0.2 Mole of DMPA in 15 ml of N-methylpyrrol-
ethylenediamine (EtDA), N,ZV,,N,N’,-tetramethyleth- idone (NMP) was slowly added to 0.2 mole of phos-

0 -
0 NH3+CH2C6H5 7 0-NH2+(CH&H& s2
Sl P<-
‘<O- NH3+CH2CBH5 0 NH2+(CH2CH&
AH AH

0
0-NH+(CH&H& 8 0-NH,+(CH&H20H)2
s3 p< - s4
‘<O-NH+(CH&H )
33 0 NH2+(CH2CH20H)2
AH AH

0 v+
B
‘<O-NH
0-NH3+
+I
S5 ;<“““+--J S6
3
AH AH ‘:

:: ONHa+
s7
P<~NH+ 3
OH A
Fig. 1. Structure of the organic phosphates.
 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56 51

phoric acid with cooling and stirring in the course of Table 1

30 min. Then, 0.05 mole of DMPA was added and Thermal properties of organic phosphates a
heated according to the predetermined program. A Phosphate Ll Td
mixture of unreacted DMPA and resulting water was (“C) (“Cl
evaporated off during the reaction. The reaction was Sl 134
further continued for 30 min under reduced pressure s2 132
(lo-* Torr). Then the reaction mixture was cooled s3 - 89
to room temperature. When polyphosphate having s4 82 167
pendant tertiary amine salt groups (PPAS) was ob- S5 142 207
S6 114 176
tained, it was separated as precipitate from NMP Sl 70 120
and washed with acetone. Polyphosphate ester hav-
ing pendant tertiary amine salt groups (PPEAS) was a Measured by TG-DTA at 1OWmin in nitrogen.
obtained by adding 0.1 mole of EG to the reaction
mixture in the absence of NMP in the initial stage of darn tertiary amine salt groups (PPAS and PPEAS)
reaction. were prepared (Scheme 1).
Thermal properties of the organic phosphates Sl
3. Results and discussion to S7 were examined (Table 1). Noncyclic phos-
phates Sl, S2 and S3 have no melting temperature
3.1. Reactivity of organic phosphates (T,). However, the noncyclic phosphate S4 has a
melting temperature, and cyclic phosphates S5, S6
Ammonium hydrogenphosphate has been used for and S7 have a melting temperature, respectively.
the preparation of polyphosphates [ 111. Now, it was Their decomposition temperatures (Td) are much
tried to prepare polyphosphate from various cyclic higher than their T, values.
and noncyclic phosphates as shown in Fig. 1. As shown in Scheme 2, when disodium hydro-
When the organic phosphates Sl-S6 were used as genphosphate Na2HP04 was heated to sufficiently
starting materials, polymer was not obtained by the high temperature, condensation occurred with the
reaction at an atmospheric pressure. However, when neighboring HPOd*- ion with elimination of result-
the organic phosphate S7 was used as a monomer, ing water and a dimer was obtained. When sodium
polyphosphate and polyphosphate ester having pen- dihydrogenphosphate NaH2P04 was heated, conden-

1
Cl r
iT 0-NH3+ fl /p-
P( 1 -~-“-,-~;O- ,”
1 O-NH+ 3
OH /Y
HaC CH3

s7 PPAS

s7 PPEAS
Scheme 1.
52 C. Wanget al. /Reactive & FunctionulPolymers37 (1998) 49-56

Na+O-
I:
P--6Nat t
Y
Na+OT- P-O-Nat
0 0-
i 0-NH3+
B p+ <o-NH+
AH AH I 3
OH fi
- Hz0 B I:
- Nat& P-O -P-O-Nat s7 S7’
(1)
A-Nat h-Nat Fig. 2. Interconversion of 57 to zwitterion S7’.

the probability of zwitterion formation, so that the

B - Hz0 concentration of the zwitterion is increased.
Ho- P--OH - (2) As for organophosphorus compounds with five
O-Nat covalent bonds, three P-O single bonds in the S7
Scheme 2. are not coplanar. Consequently, electrophilic reaction
of the phosphorus cations in the cyclic zwitterions is
not inhibited by the steric hindrance.
sation occurred resulting in poly(sodium phosphate).
Therefore, phosphoric acid with a proton being 3.2. Polycondensation
neutralized can form a phosphate and condensation
occurs. The phosphate must be thermally stable in the Previously, we have reported the application of an
molten state, so as for the polycondensation to occur. organic phase/organic phase inter-facial method for the
The T, of the inorganic phosphate is lower than the polycondensation of diol and acid chloride [25,26].
T+ However, the T, values of most noncyclic phos- The S7 is insoluble in the reaction medium NMP and
phates obtained from primary, secondary and tertiary the monomer DMPA, so the reaction of P- N bond for-
amines, such as Sl, S2 and S3, arc usually higher than mation is very similar to that of organic phase/organic
the Td values. Although the noncyclic phosphate S4 phase inter-facial polycondensation. Namely, the
clearly melts before decomposition occurs, polycon- molten organic phosphate phase is an organic phase
densation does not occur. When the cyclic phosphates and the DMPA-containing NMP is another.
S5 and S6 were heated, polymer was not obtained. The results of polycondensation of S7 are given
However, when the cyclic phosphate S7 was heated, in Table 2. The reaction temperature is controlled
polycondensation occurred rapidly, and a glassy poly- in three stages. In the first stage, the reaction tem-
mer was obtained. The S7 contains two different types perature of 120°C was favored to remove resulting
of amine salt groups, whereas the S5 and S6have two water. If the reaction temperature is 180°C in the
amine salt groups of the same type. fist stage, the yield of PPAS will be low due to
The dissociation energy of the tertiary amine salt the thermal decomposition of S7 and the evapo-
groups is smaller than that of the primary amine salt ration of DMPA, whose boiling point is 134.9“C.
groups. Consequently, the tendency of the tertiary In the second stage, the reaction temperature was
amine salt groups to dissociate is greater than that of raised to 160°C for PPAS and 170°C for PPEAS to
the primary amine salt groups when the S7 is heated remove the resulting water and unreacted DMPA.
in the polycondensation. The polycondensation in the third stage was carried
The structure of the cyclic phosphate S7 is similar out at higher temperatures under reduced pressure
to pentacovalent organophosphorus compounds. The to remove remnant water and unreacted reactants.
phosphoryl bond (P=O) involves p,-dx bonding From the elemental analysis, the ratio of phosphate
and can be represented as a hybrid of electron-pair- to phosphinamide is 63 : 37 for PPAS4 and the ratio
ing in Fig. 2. Therefore, the P=O bond has both of phosphate : phosphinamide : phosphoric acid ester
dipolar and double bond characteristics. Obviously, is 50 : 23 : 37 for PPEAS-3.
the two cyclic amine salt groups in S7 hinder the As shown in Fig. 2, the P+-O- zwitterions are
internal rotation of P-O single bond and increase formed due to the cyclic amine salt groups of S7.
 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56 53

Table 2
Results of interfacial polycondensation

Run No. Temperature/time Evacuated temperature/time Yield

(“CW (“CW (%I
PPAS 1 180/2 + 200/l 200/0.5 62 0.24
PPAS 2 15012+ 170/l 17OIO.5 73 0.21
PPAS 3 120/2 + 160/l 160/0.5 90 0.19
PPAS 4 120/3 + 160/l 160/0.5 91 0.23

PPEAS 1 120/2 + 200/l 20010.5 88 0.21

PPEAS 2 120/2 + 190/l 19010.5 87 0.22
PPEAS 3 12012-+ 180/l 180/1.0 89 0.22

a Measured at 0.5 g/d1 in formamide at 30°C.

Consequently, the polycondensation is supposed to In the first step, the intermediate Zl is formed
proceed through a zwitterion mechanism. When in- in the same manner as for inorganic phosphate
organic phosphate Na2HP04 is heated, condensation Na#PO+ However, both ends of the Zl have very
occurs according to Scheme 2 accompanying with high reactivity due to the formation of two cyclic
the elimination of water. However, further conden- amine salt groups. The resulting P+ -O- zwitte-
sation of the resulting product does not take place rions make the positive charge of the phosphorus
because no reactive hydroxyl group remains. The higher so that it becomes a highly effective elec-
condensation of the organic phosphate S7 proceeds trophilic reagent. Moreover, the negative oxygens
differently from that of the inorganic phosphate in the amine salt groups become more reactive for
NaTHPO,, and polyphosphate are formed through nucleophilic reaction.
the reaction mechanism as shown in Scheme 3. The second step of the reaction involves the at-

+- 51
C
437
T;+Z_>,-OH
-Hz0
A
s7

+Zl

B 0NH3+
> N (CH& O- P<o-NH+
3
/\
22

-2DMPA

23
Scheme 3.
54 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56

tack of the phosphorus in the P+-O- zwitterions first step of the reaction is nucleophilic attack of Nu
on the negative oxygens in the amine salt groups (the primary amine group in DMPA and the hydroxyl
and the ring-opening dissociation of the two amine group in EG) on the phosphorus in the P+-O- zwit-
salt groups. Then, the primary amine salt groups in terion, resulting in the intermediate 24 by the disso-
one phosphate dissociate to produce primary amine ciation of the tertiary amine salt group. In the second
cations and the tertiary amine salt groups in another step, the intermediate 24 is dehydrated to form the
phosphate dissociate to yield tertiary amine groups, intermediate 25. The thermal stability of the non-
and the intermediate 22 is formed. Consequently, the cyclic amine salt group is lower than that of the cyclic
dissociation of the organic phosphate in the second amine salt group, and DMPA in the noncyclic amine
step is important. The hydroxyl group of the phos- salt group is removed when the intermediate 25 is
phoric acid is removed due to the dissociation of the heated in the third step resulting the intermediate 26
amine salt group. or 27. Both ends of the intermediate 25 or 26 are
Inorganic phosphate HP0a2- is not converted into reactive, because one end is a zwitterion group and
H2P04- and the Na$-IPOd is not condensed into the other is a nucleophilic group.
polyphosphate. In the compound 22 in Scheme 3,
one of DMPA units dissociates its tertiary amine part 3.3. Spectral identijcation of polymers
but the other does its primary amine part. Although
there is discrepancy between tertiary and primary IR spectra of these polymers exhibit strong ab-
amine salts, their thermal stability is lower than sorptions at 1170 cm-’ due to the P=O bond and at
cyclic amine salts as shown in Table 1. Thus, in the 1080 cm-’ due to P-O-H stretching vibration. The
third step, the resulting 1 mole of water and 2 mole bands at 3400 cm-’ and 2500 cm-’ are assigned to
of DMPA are removed by heating to produce the O-H and -NH+< bonds, respectively. Absorptions
intermediate 23. of P-N bond appear at 1040 and 770 cm-‘. Absorp-
When DMPA and EG are used as nucleophilic tion of P-O-C for PPEAS is not identified because
reagents, the mechanism proposed for the P-N and the absorption band due to P-N bond is overlapped
P-b bond formation is shown in Scheme 4. The at 1040 cm-‘.

C
NHs+O;>i 7 0NH3+ <
+Nu
NH+0 P-O- P<o-NH+
3
/\ /\

Zl 24

0
-H20 /- NH3+0-18 -DMPA
NH+o-)P -0 -F-O-NH3+(CH2)3N ( _
L /\ Nu

Z6, Nu=-NH(CH~)~N(CH~)~ 27, Nu= -OCH2CH20H

Scheme 4.
 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56 55

NMR spectra were recorded by high-resolution

a
2’ B 1’
I solid-state NMR. 31P-NMR and ‘3C-NMR spectra of
II
--P-O- - P-O * PPAS

b-
PPAS and ‘3C-NMR spectrum of PPEAS are shown
3 IiH, 2 in Figs. 3 and 4, respectively. The peak at S 5.80 ppm
LH~ CH 2uH+cCH3 can be assigned to Pl’ and another peak at 6 1.72
'X

---Jh--
I 1 I
4 1
ppm to F’2’in the 31P-Nh4R spectrum of PPAS in
comparison with 31P-NMR spectrum of phosphoric
acid.
20 10 0 -10 -20
The 13C-NMR spectrum of PPAS consists of the
3’P G/ppm following signals: The peak at S 59.20 ppm is con-
firmed to be the absorption of Cl of PPAS because
the attachment of tertiary amino group to the carbon
of - CHz - causes a downfield shift as compared to
that of -CHs. The peaks at 6 47.12, 38.90 and 26.0
ppm are assigned to C2, C3 and C4 of PPAS, respec-
tively. Chemical shifts of these carbons of the side
band of PPEAS in ‘3C-NMR spectrum of PPEAS
are shifted as compared to that of PPAS. Although
the absorptions of five types of carbon appear in
this spectrum, it is difficult to identify the chemical
shift of the C2 of -CHzO- or C3 of side chains of
I I I I I I I PPEAS. However, the C3 peak can be confirmed in
70 60 60 40 30 20 10 13CCP/MAS Nh4R spectrum of PPEAS using DDph
method because the carbons with attached protons
13C G/ppm
are suppressed and some methyl carbon cannot be
Fig. 3. Solid state 3’P- and 13C-NMR spectra of PPAS. eliminated entirely. Therefore, the assignment of the
peaks of carbons of PPEAS is correctly presented as
shown in Fig. 4. The 13C-NMR chemical shifts of
PPAS and PPEAS are summarized in Table 3.

3 -arc-/- %,o -J - CH2CH3--0 --

I
4 CHP 3
LH 2 CH 2 NH+<CH3
C"3
5 1

PPEAS

200 150 100 50 0 -50

13CWppm
Fig. 4. Solid state 13C-NMR spectrum of PPEAS, BG: background.
56 C. Wang et al. /Reactive & Functional Polymers 37 (1998) 49-56

Table 3 151 K. Kishore, P Kamran, K. Iyanar, J. Polym. Sci. Part A:

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WI S. Kobayashi, J. Kadokawa, I.F. Yen, S. Shoda, Macro-
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1 59.26 1 63.15
PI I. Cabasso, SK. Sahni, J. Polym. Sci. Part A: Polym.
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3 38.90 3 43.43
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5 23.80
[lOI M. Ueda, Yukigosei Kyokaishi (J. Syn. Org. Chem., Jpn.),
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[ill M. Kajiwara, Gaisetsu Mukikobunshi (Outline of Inorganic
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2398.
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