Transesterification of Oligomeric Dialkyl Phosphonates,
Leading to the High-Molecular-Weight
Poly-H-phosphonates
JULIA PRETULA, KRZYSZTOF KALUZYNSKI, RYSZARD SZYMANSKI, STANISLAW PENCZEK
Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, ul. Sienkiewicza Nr 112,
90-363 Lo ´ dz, Poland
Received 11 August 1998; accepted 11 September 1998
ABSTRACT: Polycondensation of 1,10-decanediol with dimethyl-H-phosphonate taken
in excess leads to oligomers with methyl-H-phosphonate end groups. The polytranses-
terification of the resulting oligomer as well as the related model reactions were
studied. The synthesis of poly(decamethylene-H-phosphonate) was analyzed and the
final product had M
n
= 1.4 –1.9 10
4
(from end groups, vpo, and M
n
of the derived
polymers). The exchange of the ester groups between two homoesters (dimethyl and
diethyl phosphonates) used as models, conducted at r.t. and catalyzed by metal alkoxide
provides mixed (hetero) ester in a few minutes. If the concentration of the catalyst is not
high enough, then the reaction does not go to equilibrium, because the alcoholate anions
are converted into the anions of monoesters of the H-phosphonic acid, catalytically
inactive at this temperature. However, these monoesters become catalytically active at
higher temperature, i.e., at the conditions used for preparing higher molecular-weight
products by transesterification. The apparent rate constants ( k) of the ester exchange
catalyzed by monoester salt (modeling the propagation step in polytransesterification)
were determined by two independent methods; at 130°C k 1.0 10
-2
mol
-1
L s
-1
.
The detailed study of the model polytransesterification, and particularly of the polymer
end groups appearance and disappearance (studied by
1
H-,
13
C-, and
31
P-NMR) allowed
postulation of the reaction mechanism and confirmed our previous work, describing
formation at these conditions of polymers with M
n
10
4
. © 1999 John Wiley & Sons, Inc.
J Polym Sci A: Polym Chem 37: 1365–1381, 1999
Keywords: polycondensation; polytransesterification; phosphonate; polyphospho-
nate; NMR
INTRODUCTION
In this article the model mechanistic studies ex-
plain how and why the polytransesterification of the
oligomeric poly(alkylene H-phosphonates) R[OP(O-
)(H)OR']
n
OP(O)(H)OR (called later polyphospho-
nates) leads to the products with M
n
over 10
4
.
ROP(O)(H)OR is removed from the oligomer end
groups and distilled off together with some other
low molecular-weight side products from the chain
ends.
Several methods have been explored in the
past in the preparation of the polyphosphonates
(1): polymers with backbones containing the
—ROP(O)(H)O— unit, where R is the residue of
the corresponding glycol [cf. eq. (3)].
1,2
These poly-
mers are hydrolytically unstable, but the highly
reactive P—H bond can be converted into the, for
example, P—C or P—O bonds, providing hydro-
lytically stable structures.
3,4
The first documented high-molecular-weight 1
M
n
10
5
) was prepared in our laboratory over 20
years ago by ring-opening polymerization:
5,6
Correspondence to: S. Penczek
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 37, 1365–1381 (1999)
© 1999 John Wiley & Sons, Inc. CCC 0887-624X/99/091365-17
1365