Novel hyperbranched polymer based on urea linkages

Article abstract of DOI:10.1039/a803676d

The thermal decomposition of 3,5-diaminobenzoyl azide, to generate in situ the corresponding 3,5-diaminophenyl isocyanate, was found to give hyperbranched polyureas, whose structure was established using IR and NMR spectroscopy.

Full text of DOI:10.1039/a803676d

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Novel hyperbranched polymer based on urea linkages
Anil Kumar and E. W. Meijer*†
Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600MB Eindhoven,
The Netherlands
The thermal decomposition of 3,5-diaminobenzoyl azide, to
generate in situ the corresponding 3,5-diaminophenyl iso-
cyanate, was found to give hyperbranched polyureas, whose
structure was established using IR and NMR spectros-
copy.
3,5-Diaminobenzoyl azide was prepared starting from 3,5-di-
aminobenzoic acid as described in Scheme 1. The amine groups
were protected with a Boc group34 and the carboxylic acid was
converted to carbonyl azide using the procedure described by
Ghatge and Jadhav.35 Removal of the Boc group with TFA in
CH2Cl2 followed by treatment with saturated NaHCO3 solution
gave pure 4 in an overall yield of 59%. The FTIR spectrum of
4 exhibits a strong absorption at 2136 cm21 indicating the
presence of azide groups. Thermal decomposition of the
aromatic carbonyl azides has been reported15,16 to occur at ca.
107 °C and, hence, the polymerization was carried out at 110 °C
by heating a solution of 4 in NMP. Rapid evolution of N2 was
observed during the initial stages of the reaction, after which the
solution was maintained at 110 °C for 7 h. The polymers were
precipitated into water, centrifuged, washed with acetone and
vacuum dried at 90 °C to give around 90% yields of the wholly
aromatic polyureas which are soluble in solvents like DMSO,
NMP and DMF. The FTIR spectrum of the polymer indicates
In the last decade synthesis of three-dimensional dendritic
polymers by constructing branches upon branches, either in a
stepwise fashion to get dendrimers or in a one-step process to
get hyperbranched polymers, has received much attention.
These highly branched, untangled and globular structures have
been explored because of their unusual properties.1–5 Although
dendrimers have been studied extensively for their size, shape
and surface functional group related properties, their large scale
synthesis has been limited to only a few structures because of
the inherent difficulties in the stepwise growth process.
However, whilst the one step approach for the synthesis of
hyperbranched polymers has potential for large scale prepara-
tion, it lacks well defined and monodisperse dendrimers.
Hyperbranched polymers have been synthesized by self-
condensation polymerization using an ABx type monomer in
which A and B are functional groups that react with each other
and not with themselves. These hyperbranched polymers can be
divided into two major categories depending upon the growth
process. One is the classical polycondensation involving an ABx
type monomer where the growth of the polymer starts only at
the already existing reaction sites A and B; in other words there
is no generation of a new growing site during the polymeriza-
tion. Some examples of this class are polyphenylenes,6,7
polyesters,8–12 polyethers,13,14 polyurethanes,15–17 poly-
amines,18 polyamides19 and polysiloxanes.20 The second cat-
egory is where new growing sites are generated during the
polymerization reaction and examples of this class include
polystyrene 21–23 and polyacrylates.24 The consequence of these
new reaction sites during polymerization is an increased number
of subunits in the polymer. This leads to difficulties in
estimating the degree of branching as quantification of each of
the subunit structures is not possible.
the absence of any residual azide (no absorption at 2136 cm21
)
or isocyanate (no absorption at 2200 cm21) and shows strong
absorption at 1656 and 3352 cm21 indicating the formation of
H2
N
N
BocHN
MeOH–Et3
N
CO2H
CO2H
(Boc)2O
H2
BocHN
2 (96%)
1
1. Et3N–ClCO2Et–THF, 0 °C
2. NaN3–H2
O
H2
N
H2
N
N
BocHN
BocHN
1. TFA–CH2Cl2
2. NaHCO3
110 °C
NCO
CON3
CON3
H
2N
H2
5
4 (77%)
3 (80%)
NH2
NHCONH
NH2
NHCONH
H2N
NH2
H2N
NHCONH
HNOCHN
H2
N
HNOCHN
HNOCHN
NH2
HNOCHN
NHCONH
NHCONH
NH2
Dendritic and hyperbranched structures based on amide
linkage25–31 have received considerable attention due to the fact
that polyamides are commercially important and these linkages
are the backbone of all the naturally occurring proteins and
enzymes. Linear polyureas have been studied extensively in
order to produce alternative fiber-forming polymers analogous
to the polyamides.32 There is now a much wider range of
commercial polymers containing urea groups.33 Surprisingly
there are no reports on the synthesis of hyperbranched or
dendritic polymers based on urea linkages. This could be due to
the inherent difficulties in the synthesis and purification of
monomers containing both amine and isocyanate groups, to
obtain the urea linkage, as they are not compatible. Here we
report synthesis and characterization of the first example of a
hyperbranched polymer based on urea linkages. We developed
a novel one-pot route to wholly aromatic hyperbranched
polyureas, via the in situ generation of a diaminophenyl
isocyanate monomer 5 by the thermal decomposition of the
corresponding carbonyl azide 4 (Scheme 1).
NHCONH
H2
N
NHCONH
NH2
H2
N
NHCONH
NH2
H2
N
NHCONH
HNOCHN
H
2N
HNOCHN
NHCONH
NHCONH
NH2
NH2
NHCONH
NHCONH H2
N
NH2
H2
N
HNOCHN
HNOCHN
HNOCHN
NH2
HNOCHN
NHCONH
H
2N
HNOCHN
H2
N
N
H
C
O
N
H
NHCONH
HNOCHN
NHCONH
NHCONH
NH2
HNOCHN
NH2
H2N
NHCONH
NHCONH
H2
N
NH2
H2
N
NH2
HNOCHN
NH2
H2
N
NH2
Scheme 1
Chem. Commun., 1998
1629

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Notes and References
† E-mail: tgtobm@chem.tue.nl
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urea linkages. The H NMR spectrum of the hyperbranched
polyurea (Fig. 1) was analyzed based upon the various possible
subunits (A–C) that may be present. Various peaks in the NMR
spectrum of the polymer (Fig. 1) were assigned upon the NMR
spectrum of three model compounds that resemble subunits
A–C. The degree of branching calculated based on the 1H NMR
H2N
HNOCHN
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HNOCHN
HNOCHN
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H2N
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This work was supported by the Netherlands Foundation for
Chemical Research (SON).
Received in Liverpool, UK, 13th May 1998; 8/03676D
1630
Chem. Commun., 1998