Isocyanate-free route to caprolactam-blocked oligomeric isocyanates via carbonylbiscaprolactam- (CBC-) mediated end group conversion

Article abstract of DOI:10.1021/ma0258861

Blocked isocyanate functional oligomers and liquid rubbers are prepared by a novel, solvent-free carbonylbiscaprolactam (CBC) mediated end group conversion reaction of amine-terminated oligodimethylsiloxanes (PDMS) and oligopropyleneoxides (PPO), with molar masses varying between 400 and 3140 g/mol, and of hydroxy-terminated oligoethylene oxide (PEG), oligopropyleneoxide (PPO) and oligotetrahydrofuran (PTHF), with molar masses of around 1000 g/mol. The key reaction is the carbonylbiscaprolactam (CBC) mediated amino or hydroxy end group conversion yielding carbamoyl caprolactam functional polymers, without requiring addition of either phosgene or isocyanates. The quantitative CBC conversion of amine end groups occurred in bulk at 100 °C in the absence of catalysts, yielding N-carbamoyl caprolactam terminated oligomers and caprolactam (ring elimination, pathway RE). The reaction of hydroxy end groups at 100 to 150 °C in the presence of catalysts such as zirconium alcoholates, magnesium bromide or dibutyltindilaurate (DBTDL) produced N-carbamoyl caprolactam end groups via nucleophilic attack of the hydroxy group at one of the CBC caprolactam rings and subsequent ring opening (ring opening, pathway RO). The CBC reactions were monitored by means of ReactIR, ¹H NMR and ¹³C NMR spectroscopy. The molecular masses of the oligomers and liquid rubbers with caprolactam-blocked isocyanate end groups were measured by means of MALDI-ToF mass spectroscopy and size exclusion chromatography (SEC). The thermal behavior and deblocking temperatures of the caprolactam-blocked isocyanates obtained were examined by means of thermogravimetric analysis (TGA).

Full text of DOI:10.1021/ma0258861

Macromolecules 2003, 36, 4727-4734
4727
Isocyanate-Free Route to Caprolactam-Blocked Oligomeric Isocyanates
via Carbonylbiscaprolactam- (CBC-) Mediated End Group Conversion
,|
Steffen Ma ier ,† Ton Loon tjen s,‡,§ Bou d ew ijn Sch olten s, a n d Rolf Mu1 lh a u p t*,†,#
Institut fu¨r Makromolekulare Chemie und Freiburger Materialforschungszentrum der
Albert-Ludwigs-Universita¨t Freiburg, Stefan-Meier-Strasse 21, D-79104 Freiburg, Germany,
DSM Research, PO box 18, 6160 MD Geleen, The Netherlands, and
DSM Venturing & Business Development, PO box 18, 6160 MD Geleen, The Netherlands
Received November 28, 2002; Revised Manuscript Received April 25, 2003
ABSTRACT: Blocked isocyanate functional oligomers and liquid rubbers are prepared by a novel, solvent-
free carbonylbiscaprolactam (CBC) mediated end group conversion reaction of amine-terminated
oligodimethylsiloxanes (PDMS) and oligopropyleneoxides (PPO), with molar masses varying between 400
and 3140 g/mol, and of hydroxy-terminated oligoethylene oxide (PEG), oligopropyleneoxide (PPO) and
oligotetrahydrofuran (PTHF), with molar masses of around 1000 g/mol. The key reaction is the
carbonylbiscaprolactam (CBC) mediated amino or hydroxy end group conversion yielding carbamoyl
caprolactam functional polymers, without requiring addition of either phosgene or isocyanates. The
quantitative CBC conversion of amine end groups occurred in bulk at 100 °C in the absence of catalysts,
yielding N-carbamoyl caprolactam terminated oligomers and caprolactam (ring elimination, pathway RE).
The reaction of hydroxy end groups at 100 to 150 °C in the presence of catalysts such as zirconium
alcoholates, magnesium bromide or dibutyltindilaurate (DBTDL) produced N-carbamoyl caprolactam end
groups via nucleophilic attack of the hydroxy group at one of the CBC caprolactam rings and subsequent
1
ring opening (ring opening, pathway RO). The CBC reactions were monitored by means of ReactIR, H
NMR and 13C NMR spectroscopy. The molecular masses of the oligomers and liquid rubbers with
caprolactam-blocked isocyanate end groups were measured by means of MALDI-ToF mass spectroscopy
and size exclusion chromatography (SEC). The thermal behavior and deblocking temperatures of the
caprolactam-blocked isocyanates obtained were examined by means of thermogravimetric analysis (TGA).
1. In tr od u ction
paper and textile treatment, foams, rubbers, and rein-
forced plastics. Typical blocking reagents are bisulfites,
which produce water-soluble blocked isocyanates, phe-
nols, pyridinols, thiophenols, mercaptopyridines, mer-
captans, oximes such as methyl ethyl ketoxime, amides,
cyclic amides such as caprolactam, imidazoles, amidines,
pyrazoles, 1,2,4-triazoles, and secondary amines. An-
other simple method of blocking an isocyanate repre-
sents the reversible formation of uretdiones by dimer-
ization of isocyanates in the presence of trialkylphosphine
catalysts.
Control on polymer structures and safety require-
ments are an important objective in polyurethane
research and development. This makes it necessary to
explore isocyanate- and phosgene-free routes to blocked
isocyanates via end group conversion of amine and
hydroxy end groups. Here we report the use of carbo-
nylbiscaprolactam as a new very versatile, nontoxic
reagent that can convert terminal as well as pendant
hydroxy- and amine-groups of functional polymers into
the corresponding caprolactam-blocked isocyanates with-
out requiring the use of isocyanates.
The property profiles of polyurethanes are tailored to
meet the diversified demands of various industries.
Traditional intermediates are di- and polyfunctional
isocyanate resins, most of which are obtained via the
phosgene-mediated conversion of the corresponding
amines, or via the isocyanate-mediated conversion of the
corresponding hydroxy-functional intermediates, re-
spectively. Special safety and processing precautions are
required for such reactions because phosgene and low
molecular weight isocyanates are very toxic and very
sensitive to the presence of water. Moreover, isocyanate-
mediated oligomer formation via the conversion of
polyols requires addition of a large excess of diisocyan-
ates in order to prevent undesirable molar mass buildup
via chain extension or premature gelation, especially in
the case of multifunctional branched polyols and
polyamines. The excess diisocyanate is either left in the
resins or must be removed by vacuum stripping.
To circumvent problems related to the presence of free
isocyanates, isocyanates are blocked by reacting them
with various blocking groups. Deblocking can be induced
thermally or by reacting blocked isocyanates with
polyols. Comprehensive reviews on the chemistries and
applications of blocked isocyanates were published by
Wicks.1,2 Today, the applications of blocked isocyanates
range from automotive coatings to adhesives, sealants,
2. Exp er im en ta l Section
Ma ter ia ls. Carbonylbiscaprolactam (CBC, ALLINCO) was
supplied by DSM and used as received (purity >99%). The
prepolymers polytetrahydrofuran (PTHF, Mn ) 1010 g/mol,
bis(hydroxy) terminated, DuPont), poly(ethylene glycol) (PEG,
Mn ) 910 g/mol, bis(hydroxy) terminated, Merck), poly-
(propylene oxide) (PPO, Mn ) 990 g/mol, bis(hydroxy) termi-
nated, Aldrich), J effamines (M-600: Mn ) 590 g/mol, mono-
(amine) terminated, D-400: Mn ) 430 g/mol, bis(amine)
terminated, D-2000: Mn ) 1950 g/mol, bis(amine) terminated,
all from Fluka and Aldrich), and poly(dimethylsiloxane)
(PDMS, Mn ) 3140 g/mol, bis(3-aminopropyl) terminated,
† Institut fu¨r Makromolekulare Chemie und Freiburger Mate-
rialforschungszentrum der Albert-Ludwigs-Universita¨t Freiburg.
‡ DSM Research.
§ E-mail: ton.loontjens@dsm.com.
DSM Venturing & Business Development.
| E-mail: boudewijn.scholtens@dsm.com.
#
E-mail: rolf.muelhaupt@makro.uni-freiburg.de.
10.1021/ma0258861 CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/07/2003

4728 Maier et al.
Ta ble 1. Un ca ta lyzed Rea ction s of CBC w ith
Macromolecules, Vol. 36, No. 13, 2003
Ch a r a cter iza tion . The reaction products were identified,
and the CBC and end group conversions were determined by
means of 1H and 13C NMR spectroscopy (Bruker ARX 300, 300
and 75 MHz, respectively) and with ReactIR spectroscopy
(Mettler, Applied Systems, ReactIR1000). The molecular masses
were measured with SEC (Knauers Mikrogelset A22, CHCl3,
30 °C, with UV/RI and low angle laser light scattering
detectors, calibration vs PS standards) and MALDI-ToF mass
spectrometry (Bruker REFLEX 2, reflex mode, dithranol
matrix, LiBr and KCl as cationizing agent). The thermal
behavior of the caprolactam-blocked oligomers was measured
with TGA (Netzsch STA 409).
Isop r op ylen a m in e Ter m in a ted Oligop r op ylen eoxid es
(J effa m in es w ith M ) Mon o- a n d D ) Difu n ction a l) a n d
w ith Bis(N-p r op ylen ea m in e) Ter m in a ted
P oly(d im eth ylsiloxa n e) (P DMS)a
Mn
T
t
CBC
reaction
oligomer
(g/mol) (°C) (min) convn (%)
SMA353 J effamine M-600
560
450
100
100
100
100
15
30
60
15
30
60
30
60
120
30
83
90
95
89
95
99
83
89
92
SMA354 J effamine D-400
KS44
J effamine D-2000
1870
3. Resu lts a n d Discu ssion
The carbonylbiscaprolactam (CBC) represents an
activated derivative of carbonic acid. It is a nontoxic
(LD50 > 2000 mg/kg) white crystalline product that
melts at 118 °C. The CBC is readily obtained by reacting
phosgene with caprolactam. This route to CBC was
pioneered in 1956 by Meyer, who used CBC together
with hexamethylenediamine to produce low molecular
weight ureas and amides with rather ill-defined struc-
tures.3 In 1962 Fawcett et al. reported that CBC was
obtained as a byproduct when they studied the reaction
of caprolactam with COF2.4 In 1967, the synthesis of
CBC as an intermediate for the synthesis of lysine was
disclosed in a J apanese patent.5 As difunctional N-
acyllactam, CBC was used successfully as activator for
the anionic ring-opening polymerization of various
lactams.6-10 In 1996, BASF claimed the use of a large
variety of heterocyclic substances, among them CBC,
as activators for organic peroxides in washing and
bleaching agents.11 Since 2000, DSM and others have
filed patents concerning the preparation of CBC and its
use as coupling agent, chain extender, or cross-linker.12-19
SMA340 PDMS(-NH2)2
3140
100
a
Molar ratio of CBC:NH2 groups ) 1:1.
Aldrich) were dried before use. The catalysts MgBr2 from
Aldrich and dibutyltin dilaurate (DBTDL) from Fluka were
used without further purification. Zr(O-n-C3H7)4 was available
as 70 wt % solution in n-propanol from Aldrich. Toluene p.a.
(Merck) and CaCl2 (Gru¨ssing) were also used as received.
En d Gr ou p Con ver sion s w ith CBC. Am in e-ter m in a ted
oligom er s such as mono-, di-, and tri-isopropyleneamine-
terminated oligopropyleneoxides (J effamine) and bis(n-propy-
lene-amine) terminated poly(dimethylsiloxane) (PDMS) were
reacted in bulk with CBC at 100 °C without catalyst.
Rea ction of CBC w ith J effa m in es. The J effamines were
dried by stirring for 16 h at 60 °C in oil pump vacuum. For
example, 10.08 g (40 mmol) of CBC was reacted with 22.4 g
(40 mmol) of J effamine M-600 (Mn ) 560 g/mol). CBC and the
J effamine were mixed together and then stirred under argon
for the duration of 1 h at 100 °C. To remove the caprolactam
formed, the product mixture was dissolved in 40 mL of toluene
and extracted three times with 30 mL of an aqueous solution
of CaCl2 (40 g/L). After drying (4 d, 50 °C, oil pump vacuum),
23.89 g (85%) of a slightly yellow liquid was obtained. Proper-
ties are listed in Table 1.
As illustrated in Scheme 1, there exist two very
different reaction pathways for CBC reaction with
nucleophiles: first, the ring elimination (pathway RE)
associated with caprolactam formation, and second, ring
opening (pathway RO), which does not produce capro-
lactam as side-product. The reaction pathway RE is
typical for the reaction of phosgene and many other
phosgene derivatives such as carbonyldiimidazole. Ac-
cording to pathway RE the reaction of CBC with amines
(R-XH in Scheme 1 is R-NH2) affords formation of
either N-carbamoyl caprolactam and caprolactam or
ureas, accompanied by elimination of both caprolactam
molecules. In contrast, CBC also offers the opportunity
of nucleophilic attack at the carbonyl group of the
caprolactam ring followed by ring opening (pathway
RO). In pathway RO no caprolactam is eliminated. One-
fold ring opening converts hydroxy groups into ester-
functional N-carbamoyl caprolactams. Two-fold ring
opening yields polyesterureas. The reaction pathway RO
represents a very special feature of CBC chemistry and
is very attractive with respect to reduced emission of
low volatile organic compounds such as caprolactam.
The predominance of reaction pathway RO with respect
to pathway RE depends primarily upon the choice of
the nucleophile and is also affected by catalyst addition
and reaction conditions. Both reaction pathways are
very attractive with respect to the end group conversion
of hydroxy- and amine-terminated oligomers and the in
situ formation of reactive oligomers containing capro-
lactam-blocked isocyanate end groups without requiring
the addition of either phosgene or isocyanates during
end group conversion. The end group conversion of
amine- and hydroxy-terminated oligomers was investi-
Rea ction of CBC w ith Dia m in e-Ter m in a ted Oligod im -
eth ylsiloxa n e (P DMS). A mixture of 1.84 g (7.32 mmol) of
CBC and 11.5 g (3.66 mmol) of PDMS (Mn ) 3140 g/mol) was
stirred under argon for 30 min at 100 °C. At certain time
intervals, samples were removed from the reaction. The
caprolactam formed was removed by extracting three times
with an aqueous solution of CaCl2 (40 g/L). After drying (60
°C, 2 d, oil pump vacuum) 9.66 g (77%) of a slightly yellow
liquid was obtained. Reaction conditions and polymer proper-
ties are listed in Table 1.
Dih yd r oxy-ter m in a ted oligom er s such as PTHF, PEG,
and PPO with molecular masses of around 1000 g/mol were
reacted in bulk with CBC at 100 and 150 °C in the absence
and the presence of the catalysts Zr(OR)4, MgBr2, and DBTDL.
The reactions were carried out under argon on a 50 g scale.
The resulting oligomers were dried by stirring for 1 h at 100
°C at oil pump vacuum. In a typical experiment, the Zr-
alcoholate-catalyzed reaction of CBC with PTHF is described
below.
Rea ction of CBC w ith P THF in th e P r esen ce of a
Zr )Alcoh ola te Ca ta lyst. First, 16.75 g (66.5 mmol) of CBC,
33.25 g (32.9 mmol) of PTHF and 0.224 mL (0.234 g) of a 70
wt % solution of Zr(O-C3H7)4 in n-propanol (i.e., 0.5 mmol of
Zr(O-C3H7)4, 0.75 mol % with respect to CBC) were employed.
The Zr-propylate solution was added to 5 g of the PTHF, and
then the n-propanol was removed by stirring for 30 min at 80
°C in oil pump vacuum. The CBC was dissolved in the
remaining PTHF and was heated to the reaction temperature.
Subsequently the PTHF-catalyst-mixture was added via a
syringe. The reaction was stirred for a given time at the
reaction temperature and stopped by cooling to room temper-
ature. The reaction was monitored with a ReactIR, and the
products were analyzed by 1H and 13C NMR spectroscopy.
Reaction conditions and properties are listed in Tables 2 and
3.

Macromolecules, Vol. 36, No. 13, 2003
Caprolactam-Blocked Oligomeric Isocyanates 4729
Ta ble 2. F u n ction a liza tion Rea ction s of P THF (Mn ) 1010 g/m ol), P EG (Mn ) 910 g/m ol) a n d P P O (Mn ) 990 g/m ol) w ith
CBC (Mola r Ra tio of -OH:CBC ) 1:1)a
% of CBC converted into
[catalyst]
(mol %)
[catalyst]
(wt %)
T
(°C)
t
1x
1x
2x
OH
convn (%)
reaction
oligomer
PTHF
catalyst
(min)
ROb
REb
urethane
REb
∑
SMA224
SMA223
SMA225
SMA236
SMA238
SMA231
SMA231
none
0
0
200
100
150
100
150
100
150
75
120
20
120
70
0
82
85
0
65
8
33
0
0
0
15
0
13
0
0
0
4
17
6
6
0
6
63
88
91
0
90
12
36
93
94
97
0
100
16
54
Zr(OR)4
Zr(OR)4
MgBr2
MgBr2
DBTDL
DBTDL
0.75
0.75
0.75
0.75
0.5
0.33
0.33
0.18
0.18
0.42
0.42
170
50
0
11
4
7
0.5
18
0
SMA315
SMA316
SMA322
PEG
PPO
Zr(OR)4
Zr(OR)4
MgBr2
0.75
0.75
0.75
0.33
0.33
0.18
100
150
150
120
20
70
75
85
79
0
0
4
5
10
9
7
3
4
87
98
96
90
100
99
SMA323
SMA324
Zr(OR)4
MgBr2
0.75
0.75
0.33
0.18
150
150
20
20
70
86
23
36
0
0
0
7
11
32
0
0
0
93
34
68
99
45
99
a
b
No urea was found under the reaction conditions applied. RO ) ring opening; RE ) ring elimination.
Ta ble 3. Mola r Ma ss Distr ibu tion of P THF a n d Its CBC
Rea ction P r od u cts, As Deter m in ed by Mea n s of Size
Exclu sion Ch r om a togr a p h y (SEC)
the band area at the end of the reaction with the final
CBC conversion, as measured by means of 1H NMR
spectroscopy. It can be seen in Figure 2 that the reaction
rate of CBC with amines is quite high. The 1H NMR
spectra of caprolactam blocked isocyanate functionalized
J effamine and PDMS are shown in Figures 3 and 4. The
conversions were calculated from the integrals of the
1H NMR-signals of the caprolactam blocked isocyanate
(3.93, 2.62 ppm), caprolactam (3.11, 2.39 ppm) and CBC
(3.8, 2.45 ppm).
T
t
Mn
Mw
sample
catalyst (°C) (min) (g/mol) (g/mol) Mw/Mn
PTHF
1670
3470
3000
4630
2130
3290
5700
5190
7845
3400
2.0
1.6
1.7
1.7
1.6
SMA223 Zr(OR)4 100
SMA225 Zr(OR)4 150
SMA238 MgBr2
120
20
70
150
SMA231 DBTDL 150
50
The CBC conversion with time depends on the nul-
ceophilicity of the amine and the amine concentration.
As is apparent from Table 1 and Figures 1 and 2, the
amine conversion is very high and quantitative at
appropriate reaction times. For the diamine J effamine
D-400, the conversion amounted 99% after 1 h, whereas
for M-600, 95% was reached after 1 h. The reaction with
J effamine D-2000 yielded only 89% after 1 h and 92%
after 2 h. This is in accord when taking into account
the different concentrations of the amine end groups,
which is 4.44 mmol/g for D-400, 1.79 mmol/g for M-600,
and only 1.07 mmol/g for D-2000. In comparison to the
CBC reactions of the J effamines, the reaction of CBC
with diamine-terminated oligodimethylsiloxane (PDMS)
was considerably faster and gave quantitative conver-
sion in less than 1 h, although the PDMS amine
concentration was only 0.64 mmol/g. Most likely, this
remarkable difference in reactivity is closely associated
with the nucleophilicity of the amine end groups. The
isopropylene-amine end groups of the J effamines are
sterically more hindered and less nucleophilic with
respect to the n-propylene-amine end groups of PDMS.
Higher steric hindrance requires either higher temper-
atures or longer reaction times, respectively, to achieve
quantitative conversion of the end groups. The ReactIR
analysis of J effamine reactions performed at different
temperatures allowed the determination of the activa-
tion enthalpy of the CBC amine end group conversion
which was found to be 55.2 kJ /mol.
gated using spectroscopic methods including ReactIR
spectroscopy.
Rea ction s of CBC w ith Am in e-Ter m in a ted Oli-
gom er s. Amine-terminated oligomers such as the bis-
(n-propylene-amine)-terminated oligodimethylsiloxane
(PDMS) and the mono-, di- and tri- isopropylene-amine-
terminated oligopropyleneoxide (also known under the
trade name of J effamine) were reacted with CBC in bulk
at 100 °C. Reaction conditions and properties are listed
in Table 1. According to the spectroscopic studies the
reaction of CBC with amine groups proceeds in the
absence of catalyst exclusively via the ring elimination
mechanisms shown as pathway RE in Scheme 1. The
N-carbamoyl caprolactam end groups are equivalent to
the corresponding reaction products of the isocyanate
with caprolactam. The byproduct caprolactam can be
removed by means of vacuum stripping, thin film
evaporation or extraction using an aqueous 4 wt %
calcium chloride solution. Interestingly, as evidenced by
the absence of urea groups, the N-carbamoyl caprolac-
tam is obtained in almost quantitative yield without any
indication of elimination of the second caprolactam ring.
Thus, although during the synthesis blocked isocyanates
and amines are present simultaneously, no sign of the
consecutive reaction forming ureas was noted, meaning
that the reaction is very selective. This reaction does
not require excess CBC and is a very clean stoichiomet-
ric end group conversion. The end group conversion of
the isopropylene-amine-terminated oligopropyleneox-
ides (J effamines) is displayed in Scheme 2.
Rea ction s of CBC w ith P olyols. To examine the
possibility of forming N-carbamoyl caprolactam from
hydroxy-terminated oligomers via the ring opening
mechanism (pathway RO in Scheme 1), the reactions
of R,ω-dihydroxy-terminated polyols such as oligoeth-
ylene oxide (PEG), oligopropylene oxide (PPO), and
oligotetrahdyrofuran (PTHF) were investigated. The
reaction with CBC was performed in bulk at 100, 150,
The CBC conversions of amine end groups were
1
monitored by ReactIR spectroscopy and by H and 13C
NMR spectroscopy. Figure 1 shows the ReactIR spectra
of the uncatalyzed bulk reaction of CBC with J effamine
M-600 at 100 °C. The CBC conversion was calculated
from the area of the amide II band at 1520 cm-1. The
calibration of this method was carried out by correlating

4730 Maier et al.
Macromolecules, Vol. 36, No. 13, 2003
Sch em e 1. Rea ction s of Ca r bon ylbisca p r ola cta m (CBC) w ith Nu cleop h ilesa
a
Pathway RE: Ring elimination mechanism associated with caprolactam formation. Pathway RO: Ring opening reaction of
the CBC caprolactam ring.
Sch em e 2. CBC Rea ction w ith Am in e En d Gr ou p s of
Isop r op ylen a m in e-Ter m in a ted Oligop r op ylen eoxid es
(J effa m in e) Accor d in g to th e Rin g Elim in a tion
Mech a n ism
F igu r e 2. CBC conversion to blocked isocyanates as a
function of time. The reaction of CBC with J effamine M-600
was carried out at 100 °C in bulk without catalyst. After 60
min, 95% of the amine end groups of the J effamine were
transferred into caprolactamblocked isocyanates. The conver-
sion was determined by ReactIR spectroscopy (evaluation of
the amide II band at 1520 cm-1, calibration with 1H NMR
spectroscopy).
RE, similar to the reaction pathways established for
phosgene and other carbonic acid derivatives such as
carbonyldiimidazole and similar to the reaction with
amines. In the absence of ring opening, CBC conversion
of hydroxy groups gave mainly N-carboxylate caprolac-
tam (denoted as 1x ring elimination in Table 2) in
conjunction with urethane and carbonate, both of which
F igu r e 1. ReactIR spectra of reaction of CBC with J effamine
result from subsequent reaction of the N-carboxylate
M-600 at 100 °C (SMA353) in the absence of catalyst. In
caprolactam with hydroxy groups. In sharp contrast,
back: CBC, bands at 1708 and 1684 cm-1. In front: 95%
catalyst addition promoted reaction pathway RO involv-
ing ring opening of one or even two of the CBC
caprolactam rings. While the tin catalyst DBTDL was
less effective, zirconium alcoholate and Lewis acids such
as magnesium bromide gave high conversion and pre-
dominant ring opening (cf. Table 2). This ring-opening
reaction of CBC with hydroxy-terminated oligomers
represents a very attractive new, isocyanate-free route
to blocked isocyanates derived from polyols!
N-carbamoyl caprolactam termninated J effamine, bands at
1706, 1673, and 1520 cm-1
.
and 200 °C in the absence and in the presence of
catalysts such as Zr(OR)4, MgBr2, and dibutyltindilau-
rate (DBTDL). The reaction compositions and the
product properties are summarized in Tables 2 and 3.
An unexpected effect of the catalyst addition was
discovered. In the absence of catalyst the reaction of
CBC proceeded mainly via ring elimination pathway

Macromolecules, Vol. 36, No. 13, 2003
Caprolactam-Blocked Oligomeric Isocyanates 4731
F igu r e 3. 1H NMR spectrum of the caprolactam-blocked
isocyanate derived from CBC and the isopropyleneamine
terminated oligopropyleneoxide (J effamine M-600). Reaction
conditions: 100 °C, 60 min, and conversion ) 95%.
F igu r e 6. 1H and 13C NMR spectra of the caprolactam-blocked
isocyanate derived from PTHF, synthesized in the presence
of Zr-alcoholate (0.75 mol % Zr with respect to CBC) at 100
°C (composition: 82% caprolactamblocked isocyanate, 6%
carbonate, 12% ꢀ-caprolactam, and 12% CBC (all with respect
to total amount of CBC employed as educt)).
In the absence of catalyst addition the thermal
reaction of CBC with PTHF at 200 °C yielded after 75
min 33% N-carboxylate caprolactam terminated PTHF
obtained via elimination of one caprolactam (values are
with respect to the employed amount of CBC) together
with 17% carbonate via 2-fold caprolactam elimination
and 13% urethane via caprolactam elimination followed
by ring opening. In the absence of catalyst no ring
opening of the caprolactam rings of CBC with hydroxy
groups occurred! This is strong experimental evidence
that thermal reaction of CBC caprolactam ring proceeds
exclusively via the ring elimination pathway (pathway
RE in Scheme 1). According to Table 2, the total
conversion of CBC amounted only to 63% in that case.
For stoichiometric reasons (CBC:hydroxy end group
molar ratio of 1 mol:1 mol !), the total conversion of the
CBC cannot reach 100% when a part of CBC reacts
twice with hydroxy groups. The total conversion of the
hydroxy end groups was 93%.
F igu r e 4. 1H NMR spectrum of the caprolactam-blocked
isocyanate derived from CBC and the bis(propyleneamine)-
terminated poly(dimethylsiloxane).
F igu r e 5. ReactIR spectra of the reaction of CBC with PTHF,
catalyzed by 0.75 mol % Zr(OR)4 with respect to CBC at 100
When catalyst was added, the reactivity of CBC
increased drastically. In the presence of catalyst the
predominant reaction is ring opening according to
pathway RO, thus producing the ester-functional N-
carbamoyl caprolactam, which is equivalent to a blocked
isocyanate end group. The obtained N-carbamoyl ca-
prolactam can react with hydroxy groups either via ring
elimination or ring opening, thus producing either
urethane or urea, respectively. Predominantly urea
formation was observed when using sodium or potas-
sium alcoholates at room temperature. Also carbonates
were encountered as minor side products, formed via
the 2-fold ring elimination reactions according to path-
way RE.
°C (SMA223). In back: CBC, bands at 1706 and 1673 cm-1
.
In front: product mixture containing 82% 1x ring-opened CBC,
bands at 1735, 1705, 1656, and 1536 cm-1
.
The reactions of CBC with polyols were also moni-
tored by means of ReactIR. Typical ReactIR traces are
displayed in Figure 5. The conversion of CBC with
hydroxy groups to produce caprolactam-blocked isocy-
anate end groups was calculated from the area under
the amide II band at 1536 cm-1. The calibration of this
method was accomplished by correlating the final
conversion, as determined by 1H NMR spectroscopy,
with the area of this IR band at the end of the reaction.
1
A typical H NMR spectrum of a CBC reaction with a
Scheme 3 shows the catalytic reaction of CBC with
PTHF. In this reaction, catalyzed by Zr(OR)4 at 100 °C,
polyol is displayed in Figure 6.

4732 Maier et al.
Macromolecules, Vol. 36, No. 13, 2003
Sch em e 3. Rea ction of CBC w ith P THF P r od u cin g
N-Ca r ba m oyl Ca p r ola cta m En d Gr ou p s, Equ iva len t to
Ca p r ola cta m -Block ed Isocya n a tes, via Ca ta lytic Rin g
Op en in g Rea ction sa
F igu r e 7. CBC conversion as a function of time. The reactions
of CBC with PTHF were catalyzed by 0.75 mol % (with respect
to CBC) Zr(OR)4 at 150 °C and 100 °C (SMA225 and SMA223)
and by 0.75 mol % (with respect to CBC) MgBr2 at 150 °C
(SMA238). The conversion was determined by ReactIR spec-
troscopy (evaluation of the amide II band at 1536 cm-1
calibration with 1H NMR spectroscopy).
,
a
Minor side reactions represent molar mass build up via
SMA323, catalyzed by Zr(OR)4 at 150 °C, gave complete
CBC conversion already after 20 min and yielded 86%
of the ester-functional N-carbamoyl caprolactam via 1x
ring opening, whereas SMA234, catalyzed by MgBr2 at
the same temperature, needed 70 min for reaching a
CBC conversion of 68%. The reaction mixture obtained
in the presence of MgBr2 contained similar amounts of
the N-carbamoyl caprolactam and urethane. Again, the
addition of MgBr2 appears to be much less effective than
Zr(OR)4 with respect to the catalytic formation of the
ester-functional N-carbamoyl caprolactam via ring open-
ing of exclusively one of the CBC caprolactam rings.
Ch a r a cter iza tion of th e Oligom er s w ith Ca p r o-
la cta m -Block ed Isocya n a te En d Gr ou p s. Several of
the oligotetrahydrofurans with caprolactam-blocked iso-
cyanate end groups, prepared by reacting CBC with
PTHF, were analyzed by means of MALDI-ToF mass
spectroscopy.
The MALDI-ToF spectra of the samples produced in
the absence and presence of various catalysts are
displayed in Figure 8. In the spectrum of SMA223
(PTHF/2 CBC/Zr(OR)4/100 °C) the three main signals
correspond to bis(N-carbamoyl caprolactam)-terminated
PTHF, obtained via conversion of both hydroxy end
groups according to the 1x ring-opening reaction. No
signal of residual PTHF or PTHF containing only one
N-carbamoyl caprolactam end group were detected.
Clearly, as byproduct carbonate-mediated chain exten-
sion occurred.
For MALDI-ToF spectrum of SMA238 (PTHF/2 CBC/
MgBr2/150 °C) a very similar signal pattern was ob-
served, although three additional weak signals indicate
the occurrence of other side reactions which were not
identified. In contrast to the spectra of oligomers
produced in the presence of catalysts, the spectrum of
SMA224 (PTHF/2 CBC/no catalyst/200 °C) was very
different and confirmed the predominant formation of
the bis(N-carboxylate caprolactam)-terminated PTHF,
resulting from caprolactam elimination occurring at
both chain ends. The MALDI-ToF measurements are
in accord with the above-mentioned measurements
performed by means of 1H NMR and ReactIR spectros-
copy: In the absence of catalysts, CBC mainly reacts
with hydroxy end groups via the ring elimination
reaction (pathway RE), thus producing N-carboxylate
carbonate chain extension resulting from ring elimination
reactions.
82% of the CBC was converted after 120 min via the 1x
ring opening pathway into N-carbamoyl caprolactam
(caprolactam-blocked isocyanate). This corresponds to
a hydroxy conversion of 94%. At 150 °C, 85% (with
respect to CBC) N-carbamoyl caprolactam was formed
already after 20 min. This corresponds to a hydroxy end
group conversion of 97%. Carbonate was formed in both
reactions to a small extent of only 6% (with respect to
the amount of CBC employed). Carbonate byproduct
formation is tolerated in many applications, since it is
associated with the chain extension reaction which does
not affect end group functionality. The Lewis acidic
catalyst MgBr2 showed almost no activity as catalyst
at 100 °C However, at 150 °C it yielded 65% (with
respect to CBC) of the N-carbamoyl caprolactam via the
1x ring-opening reaction (pathway RO). This corre-
sponds to 100% conversion of the hydroxy groups. Here
byproducts were found to be 15% of N-carboxylate
caprolactam (1x ring elimination), 4% urethane and 6%
carbonate (all with respect to CBC). In comparison to
Zr(OR)4, MgBr2 was less active and somewhat less
selective. In Figure 7, the addition of Zr(OR)4 and MgBr2
catalysts is compared with respect to the CBC conver-
sion and formation of the ester-functional N-carbamoyl
caprolactam. Clearly, the zirconium catalyst is more
active than the magnesium catalyst, especially at lower
temperatures.
The data of the reactions of CBC with PEG and with
PPO are summarized in Table 2 as well. The CBC
reactions with PEG proceeded similarly to reactions of
CBC with PTHF. Zr(OR)4 catalysis led to 75% or 85%
of N-carbamoyl caprolactam via 1x ring opening at 100
or 150 °C, respectively. MgBr2 catalysis led also to a
product distribution quite similar to the CBC/PTHF
reaction. Main product was N-carbamoyl caprolactam
via 1x ring opening, byproducts were urethane, N-
carboxylate caprolactam via 1x ring elimination, and
carbonate. The reactions SMA323 and SMA324 listed
in Table 2 confirm that the Zr(OR)4 catalyst is also more
effective than MgBr2 for PPO containing the less reac-
tive secondary hydroxy end groups. The reaction of

Macromolecules, Vol. 36, No. 13, 2003
Caprolactam-Blocked Oligomeric Isocyanates 4733
F igu r e 8. MALDI-ToF mass spectra of (a) PTHF and (b) its
reaction products with CBC from reaction SMA223, catalyzed
by Zr(OR)4, and (c) SMA238, catalyzed by MgBr2, and (d) the
corresponding reaction product obtained in the absence of
catalyst. The signals in parts b and c belong to PTHF with
two blocked isocyanate end groups (ring-opening reaction) and
0, 1, or 2 carbonate units in the chain (2x ring elimination
reaction). The signals of part d belong to bis(N-carboxylate
caprolactam)-terminated PTHF (1x ring elimination reaction).
F igu r e 9. Thermogravimetric analysis of PTHF and the
corresponding caprolactamblocked isocyanate, synthesized in
the presence of Zr-alcoholate (SMA223) and MgBr2 (SMA238)
as catalysts.
Figure 9 displays the temperature-dependent weight
loss of dihydroxy- and bis(N-carbamoyl caprolactam)-
terminated PTHF. The dihydroxy-terminated PTHF
degraded in a single step with an onset degradation
temperature of around 270 °C. For the bis(N-carbamoyl
caprolactam)-terminated PTHF, prepared via CBC-
mediated end group conversion of dihydroxy-terminated
PTHF in the presence of zirconium and magnesium
catalysts, the degradation process exhibited two differ-
ent steps. Above 180 °C the weight loss of approximately
20% is likely to be associated with the thermal deblock-
ing of the end groups, involving formation of caprolac-
tam and isocyanate. The magnesium and zirconium
catalyst addition appeared to have little influence on
this deblocking temperature. The thermal degradation
of the bis(N-carbamoyl caprolactam)-terminated PTHF
occurred at a higher temperature of 320 °C compared
with only 270 °C for the dihydroxy-terminated PTHF.
This increase of thermal stability is likely to be associ-
ated with isocyanurate ring formation resulting from
trimerization of the isocyanate intermediates resulting
from the deblocking reaction.
caprolactam together with carbonate and urethane via
elimination or opening of the other ring. In contrast,
the catalyst addition promoted ring opening of mainly
one caprolactam ring of CBC, thus producing N-car-
bamoyl caprolactam end groups, which are equivalent
to caprolactam-blocked isocyanates. In comparison to
the Zr(OR)4 catalyst, the MgBr2 catalyst is somewhat
less active and less selective. In the presence of catalyst
the CBC-mediated end group conversion proceeds
smoothly and is accompanied by formation of small
amounts of carbonates.
In addition to MALDI-ToF mass spectrometry also
the size exclusion chromatography (SEC) was applied
to examine molar masses and molar mass distributions.
The polymers obtained in the reactions SMA223 and
SMA238 were analyzed by SEC in CHCl3 solution at
30 °C using linear polystyrene as molar mass standard.
The results are listed in Table 3. The N-carbamoyl
caprolactam terminated PTHF obtained exhibited some-
what higher molar masses with respect to that of PTHF
starting material. This is due to the end group formation
via CBC reaction and also to chain extension, e.g., via
carbonate formation. In fact, molar mass buildup was
less pronounced for N-carbamoyl caprolactam blocked
PTHF prepared in the presence of the Zr(OR)4 catalyst
than in the presence of MgBr2 catalyst, due to more
molar mass buildup via carbonate chain extension as
side reaction.
Samples of dihydroxy-terminated and of the corre-
sponding bis(N-carbamoyl caprolactam)-terminated
PTHF were analyzed by means of thermogravimetric
analysis (TGA) in order to examine their thermal
degradation behavior in view of the deblocking temper-
atures indicating the decomposition of the N-carbamoyl
caprolactam into free caprolactam and isocyanate. As
a function of isocyanate type and catalysts, the deblock-
ing temperature of conventional caprolactam-blocked
isocyanates is known to vary from 160 to 200 °C.1 At
temperatures above 300 °C, PTHF depolymerizes, thus
yielding THF. The ceiling temperature for the depolym-
erization of PTHF with active end groups is approxi-
mately 80 °C. It is well-known that metal ions such as
Zr4+ or Mg2+ can promote chain scission and subsequent
depolymerization via an unzipping reaction.
4. Con clu sion s
The stoichiometric end group conversion of amine-
and hydroxy-terminated oligomers by means of the
nontoxic carbonylbiscaprolactam (CBC) represents a
very convenient phosgene- and isocyanate-free route to
the preparation of a wide range of bis- and poly(N-
carbamoyl caprolactam)-terminated oligomers which are
equivalent to caprolactam-blocked isocyanate resins. A
great variety of oligomers and reactive liquid rubbers
with caprolactam-blocked isocyanate end groups are
readily available in solvent-free CBC-mediated end
group conversion reactions and do not require safety
precautions typical for handling toxic isocyanates. The
CBC-mediated end group conversion in bulk can be
controlled via end group type and catalyst addition. In
the absence of catalysts, amine end group react exclu-
sively via ring elimination (pathway RE), thus produc-
ing N-carbamoyl caprolactam-terminated oligomers which
are equivalent to caprolactam-blocked isocyanate-
terminated oligomers. This reaction proceeds smoothly
at elevated temperatures around 100 °C.
In contrast to other derivatives of carbonic acid such
as carbonyldiimidazole, CBC offers new opportunities
for tailoring reactive oligomers via selective ring-open-

4734 Maier et al.
Macromolecules, Vol. 36, No. 13, 2003
ing reaction of either exclusively one or both CBC
caprolactam rings. The ring-opening reaction (pathway
RO) was demonstrated for the CBC-mediated end group
conversion of hydroxy-functional oligomers. Only in the
presence of catalysts such as alcoholates or Lewis acids,
ring opening of the CBC caprolactam ring occurs, thus
producing ester-functional N-carbamoyl caprolactams.
It would be rather difficult to produce such oligomers
via phosgenation because the conventional synthesis
would require formation of aminocapronic acid esters
of the hydroxy-terminated oligomers followed by phos-
genation. The catalytic promotion of ring opening re-
duces the caprolactam emission during the reaction,
thus reducing volatile organic compounds. The forma-
tion of chelating complexes with catalysts represents the
key to control the reactivity of both carbonyl groups of
the CBC caprolactam rings independently. While so-
dium alcoholates catalyze ring opening of both CBC
caprolactam rings to form ester ureas, the addition of
zirconium alcoholate or magnesium halides promote the
predominant formation of ester-functional N-carbamoyl
caprolactam resulting from mainly ring opening of only
one CBC caprolactam ring. As a function of the catalyst
choice and reaction temperatures it is possible to reduce
the amount of carbonate formed via the ring elimination
mechanism. The selective ring opening of the CBC
caprolactam rings is very effective for the coupling
reactions without emission of caprolactam. The very
versatile CBC mediated hydroxy and amine group
conversion uses stoichiometric amounts of CBC and can
be applied to end groups as well as amine and hydroxy
groups attached to the main and side chains.
respectively. Since various other functional groups are
tolerated, it is possible to prepare a large variety of new
functional polymers with tailor-made property profiles.
Refer en ces a n d Notes
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sives, and sealants to special isocyanate-free polyure-
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