An NMR study of chain transfer to diols containing both primary and secondary hydroxy groups in the polymerization of ε-caprolactone

Article abstract of DOI:10.1039/a810010a

ε-Caprolactone has been polymerized in the presence of various diols, viz. propane-1,2-diol (PD), butane-1,3-diol (BD) and hexane-1,5-diol (HD). ¹H and ¹³C NMR spectroscopy were used to evaluate the structures. The final products were found to be a function of the diol used. It was shown that reactions incorporating PD gave low conversions and/or low degrees of polymerizations when compared with those involving BD or HD. In polymerizations involving BD two ¹³C resonances could be seen in the carbonyl region, assignable to the ester carbonyls adjacent to the oxymethine and oxymethylene groups derived from the residues of the diol units. Thus, both primary and secondary hydroxy groups were shown to be active in the transfer reaction. Selective decoupling was used to assign the down-field resonance to the carbonyl adjacent to oxymethylene and the up-field resonance to the carbonyl adjacent to oxymethine. However, in the case of the polymerization incorporating BD, approximately 10% of end groups were shown to be secondary alcohols, which are derived from the secondary hydroxy group of BD that does not transfer. In polymerizations involving HD only one carbonyl resonance, which could be assigned to an ester adjacent to the diol residue, was observed. From COSY spectra it was possible to assign a peak due to the ester of the secondary hydroxy. The fraction of secondary chain ends was thus observed to be greater, at ca. 13%, than in the BD polymerizations.

Full text of DOI:10.1039/a810010a

J O U R N A L O F
An NMR study of chain transfer to diols containing both primary and
secondary hydroxy groups in the polymerization of e-caprolactone
Alexander Kavros, Thomas N. Huckerby and Stephen Rimmer*
The Polymer Centre, School and Chemistry, Lancaster University, Bailrigg, Lancaster, Lancs,
UK LA1 4YA. E-mail: s.rimmer@lancaster.ac.uk
C H E M I S T R Y
Received 24th December 1998, Accepted 16th February 1999
e-Caprolactone has been polymerized in the presence of various diols, viz. propane-1,2-diol (PD), butane-1,3-diol
(BD) and hexane-1,5-diol (HD). 1H and 13C NMR spectroscopy were used to evaluate the structures. The final
products were found to be a function of the diol used. It was shown that reactions incorporating PD gave low
conversions and/or low degrees of polymerizations when compared with those involving BD or HD. In
polymerizations involving BD two 13C resonances could be seen in the carbonyl region, assignable to the ester
carbonyls adjacent to the oxymethine and oxymethylene groups derived from the residues of the diol units. Thus,
both primary and secondary hydroxy groups were shown to be active in the transfer reaction. Selective decoupling
was used to assign the down-field resonance to the carbonyl adjacent to oxymethylene and the up-field resonance to
the carbonyl adjacent to oxymethine. However, in the case of the polymerization incorporating BD, approximately
10% of end groups were shown to be secondary alcohols, which are derived from the secondary hydroxy group of
BD that does not transfer. In polymerizations involving HD only one carbonyl resonance, which could be assigned
to an ester adjacent to the diol residue, was observed. From COSY spectra it was possible to assign a peak due to the
ester of the secondary hydroxy. The fraction of secondary chain ends was thus observed to be greater, at ca. 13%,
than in the BD polymerizations.
Introduction
The polymerization of e-caprolactone (CL) by ring-opening
insertion polymerization, mediated by metal alkoxides, is a
well established synthetic tool. The method is used widely in
the preparation of both high molecular weight and oligomeric
poly(e-caprolactone) (PCL). Much of the work in elucidating
the mechanism and applying ring-opening insertion polymeriz-
ation can attributed to Kricheldorf et al.,1–3 Jerome et al.4 and
Penczek et al.5–8 These authors showed that the polymerization
does in fact proceed by an insertion mechanism. Metal alkox-
ides that work well include those based on tin, titanium,
aluminium and rare-earth metals (for examples of rare-earth
catalyzed polymerizations see references 9–11).
In the case of the synthesis of telechelic oligomers the chain-
end functionality can be added in one of two ways. In the first
method a metal alkoxide is prepared and is then used as an
initiator. The molecular weight of the resultant oligomer is
inversely proportional to the metal alkoxide concentration.
Chain-end functionality, usually hydroxy, is then formed by
hydrolysis of the metal alkoxide bond that is successively
transferred to the chain end as the polymerization ensues.
Thus, if one uses a metal alkoxide prepared from a diol the
product is a dihydroxy functional oligomer. In the second,
commercially significant, variant of this methodology the metal
alkoxide is employed in catalytic amounts in the presence of
the hydroxy species,12,13 the concentration of which determines
the final degree of polymerization of the polymer. In this
method the hydroxy species acts as a transfer agent. That is,
the hydroxylic proton is transferred to the alkoxy chain end
with scission of the metal alkoxide bond and formation of a
new metal alkoxide bond. The transfer step is shown in Fig. 1.
We have used this latter technique to prepare poly(e-
caprolactone-g-methyl methacrylate) materials.14 In that work
a poly(methyl methacrylate) with diol functionality at one
chain end was prepared. This was then used as a transfer
agent in the dibutyl tin oxide (DBTO) catalyzed polymeriz-
ation of CL. The diol functionality was derived from a radical
polymerization of methyl methacrylate in the presence of the
Fig. 1 Transfer of an alcohol (R∞OH) to a tin catalysed ring-opening
insertion of Cl.
chain transfer agent, 3-mercaptopropane-1,2-diol. Thus the
end group contained both primary and secondary hydroxy
groups. In order to show that both hydroxy groups were active
in the transfer process, we determined the concentration of
secondary hydroxy end groups in the resulting poly(e-
caprolactone-g-methyl methacrylate). Since this was found to
be vanishingly low we concluded that in this case both primary
and secondary hydroxy groups were transferred. To our knowl-
edge no previous work on the transfer to similar diols has
been reported. We have therefore embarked on a study using
high field NMR spectroscopy, the results of which are reported
here, of the transfer to diols containing both primary
and secondary hydroxy groups in the polymerization of e-
caprolactone.
Results and discussion
Low molecular weight models for assignment of carbonyl
resonances
The carbonyl regions of the 13C spectra of CL synthesized
under conditions in which chain transfer to hydroxy group
J. Mater. Chem., 1999, 9, 1071–1076
1071

Fig. 2 A PCL with the carbonyl groups giving rise to resolved
resonances in 13C NMR spectra labelled (a, b, c). The polymerization
was carried out in the presence of the alcohol, ROH.
dominates chain termination, contain three resonances that
are derived from three different ester carbonyls.15 The domi-
nant resonance is due to the ester carbonyl of repeat units
that lie within the bulk of the chain. The other two resonances
are derived from ester carbonyls of an ultimate repeat unit
together with those that are formed from esterification of the
transferred hydroxy group. The carbonyls giving rise to this
pattern of resonances are illustrated in Fig. 2.
Fig. 4 Fully decoupled (a); C–H coupled (b); selectively C–H
decoupled (irradiation at d 5.15) (c) and selectively C–H decoupled
(irradiation at d 4.125) (d) 13C NMR spectra of compound 1, in the
carbonyl region.
The resonances of carbonyls b and c have been reported to
occur at 173.9 and 174.1 ppm respectively.15 The chemical
shift of b is also a function of molecular weight.15 The chemical
shift of a is a function of R. Thus if transfer to different
alcohol groups in the same transfer agent is possible then
separate resonances for each carbonyl may be observed in
medium field NMR spectra. In this work two different alcohol
groups are present in the transferring diol. No data were
available to enable the prediction of the position of the two
chemical shifts to be expected from ester carbonyls derived
from transfer to one or other of the two, primary or secondary,
hydroxy groups in the diols. Therefore the model compounds
shown in Fig. 3 were synthesized. Experiments to unambigu-
ously assign the carbonyl resonances were then carried out.
In compound 1, COSY unambiguously assigned the complex
multiplet at 4.05–4.21 ppm to the oxymethylene protons and
the multiplet at 5.15 ppm to the oxymethine protons. The
proton-noise-decoupled 13C spectrum showed carbonyl ester
resonances at 173.75 and 174.02 ppm. The peaks were of equal
intensity indicating that the NOES were the same for both
carbonyl resonances. The observed spectrum for this region is
shown in Fig. 4(a). The completely C–H coupled spectrum is
shown in Fig. 4(b); as expected the spectrum is highly complex
owing to multiple C–H couplings. Fig. 4(c) shows the spectrum
with irradiation at d 5.15, which corresponds to the resonance
position for the oxymethine protons. Clearly, the up-field
multiplet became less complex in this spectrum, while the
down-field multiplet was unaffected. Irradiation at d 4.125,
the resonance position for the oxymethylene protons, produced
the trace in Fig. 4(d). In this case the down-field multiplet
became simplified. It was therefore possible to assign the peak
at d 173.75 to an ester carbonyl adjacent to the oxymethine
group and that at d 174.02 to an ester carbonyl adjacent to
the oxymethylene group. The resonance from an ester carbonyl
resulting from transfer to the primary hydroxy of PD was
thus observed down-field of the carbonyl ester resonance
resulting from transfer to the secondary hydroxy. Similar
experiments with compounds 2 and 3 gave the assignments
given in Table 1.
The other models that were required were those for the
secondary hydroxy end groups, which are formed as a result
of transfer to only the primary hydroxy group. Spectral data
for the diols themselves were sufficient for these purposes. The
observed 1H and 13C resonances for hydroxymethine sites and
hydroxymethylene sites are given in Table 2.
NMR of PCLs: assignment of resonances and treatment of data
The main aim of this work was to examine the effect of
changing the distance between primary and secondary hydroxy
groups of diols involved in transfer during the polymerization
of CL. The first aspect to be examined was the effect on the
final conversion. The final % conversion of CL was determined
from both the 1H and 13C NMR spectra. The 1H NMR values
were determined by comparison of the 1H resonances due to
the oxymethylene protons of CL (d 4.17 (t)) and the converted
oxymethylene 1H resonances of the PCL (d~4.05 (t) and
~3.60 (t)). An example of the signals in this region and
assignment15 of the resonances from the PCL polymer is
shown in Fig. 5. Alternatively, the carbonyl resonances in the
13C spectra may be used. The resonances of interest here are
the carbonyl carbons from CL (176.1 ppm) and the four
carbonyls of PCL (labelled as C1–C4 in Tables 4 and 6).
While C–H decoupled 13C NMR must not be assumed to be
generally quantitative, these carbonyls are adjacent to similar
Table 1 Assignments of 13C resonances in the ester carbonyl region
of the model diesters. Calculated values are in parentheses
Oxymethine carbonyl
(d/ppm)
Oxymethylene carbonyl
(d/ppm)
Compound
1
2
3
174.02
174.34
174.44
173.75
173.88
174.04
Table 2 13C and 1H NMR resonances associated with the primary
and secondary hydroxy groups of the diols
–CHOH (d/ppm)
–CH OH (d/ppm)
2
Diol
13C
1H
3.861
3.991
~3.78
13C
1H
PD
BD
HD
67.96
66.43
67.36
67.44
60.04
61.86
3.369/3.555
3.730/3.780
~3.60
Fig. 3 Diesters used as models for the diol residues.
1072
J. Mater. Chem., 1999, 9, 1071–1076

Fig. 5 1H NMR spectrum for the product of the TBO catalysed
polymerization carried out at 80 °C in the presence of hexane-1,5-diol.
An example of the resonances used to determine % conversion of CL.
Fig. 7 COSY-45 spectrum for polymer formed in the presence of BD.
groups containing identical numbers of hydrogens so that
NOES are expected to be equal. This assumption is supported
by the fact that carbonyl resonances observed for the model
diester compounds (for example see Fig. 2) were indeed of
equal intensity and were derived from groups of equal
concentration.
spectra of the free BD and HD diols showed that such
oxymethine resonances should be expected at d 3.99 and
3.78 ppm respectively (see Table 2). Peaks in this region could
be observed in the relevant PCL spectra. However, these
resonances, postulated as arising from end groups at relatively
low concentration, cannot be unambiguously assigned in this
manner. Therefore COSY measurements were also employed,
so as to ensure correct identifications for these important
peaks. The COSY spectra of PCLs prepared in the presence
of BD and HD are shown in Fig. 7 and 8.
The important cross-peak connections to be made in these
spectra involve couplings between methyl of the diol residue
adjacent to the oxymethine protons of either a secondary
alcohol (secondary alcohol end group) or esterified secondary
alcohol (i.e. the residue of a diol that has transferred). Two
couplings to methyl can be observed in both spectra. These
are labelled a and b for the connections from ester methine
and hydroxymethine respectively. Clearly the resonances at d
3.84 (Fig. 6) and d 3.73 (Fig. 7) in BD and HD respectively
are coupled to the methyl protons at d 1.19 (Fig. 7) and d
1.15 (Fig. 8). The identity of these methine protons is con-
firmed by the presence of further coupling to adjacent methyl-
ene protons at ~d 1.71 (BD) and ~d 1.425 (HD) respectively.
The ester oxymethine protons derived from diol residues that
have undergone transfer show cross-peaks at d 4.89 (Fig. 6)
and d 4.995 (Fig. 8). It can, therefore, be stated with confidence
that the resonances at d 3.84 and d 3.73 are indeed due to
secondary hydroxy groups that are derived from either BD or
HD diol residues, which are located at chain ends.
A typical spectrum for the carbonyl region, showing all five
resonances is shown in Fig. 6. The PCL resonances are labelled
C1–C4 on progressing from high to low frequency. The two
resonances common to all spectra are those at 173.6 ppm (C1)
and 173.4 ppm (C2). C1 arises from carbonyl carbons on the
ultimate repeat unit while the source of C2 is the in-chain
caproate ester carbonyl.15 The two ester carbonyls derived
from transfer to each of the alcohol groups are observed at
varying chemical shifts depending upon the diol used. By
reference to the model diesters we were able to assign the up-
field resonance (C4) to the carbonyl attached to an oxygen of
the oxymethine group and the down-field resonance (C3) to
the carbonyl attached to an oxygen of the oxymethylene
group. The observed resonance positions and their signal
assignments are given in Table 3.
It was also necessary to identify the 1H resonances that
arise from the hydroxymethine protons of secondary end
groups. Such groups will arise if transfer does not occur to
the secondary hydroxy group of the diol. Examination of the
Fig. 6 The carbonyl region of a 13C NMR spectrum of a PCL prepared
at 80 °C with TBO catalyst.
Table 3 Observed resonances derived from ester carbonyls adjacent to
the transferring diols
C3
(d/ppm)
C4
(d/ppm)
Diol
PD
BD
HD
173.0
173.2
n.a.
172.8
172.8
173.0
Fig. 8 COSY-45 spectrum for polymer formed in the presence of HD.
J. Mater. Chem., 1999, 9, 1071–1076
1073

Table 4 M (SEC), DP (NMR) and % conversion data for polymerizations catalyzed by TBO
n
% Secondary
hydroxy
end groups
Reaction
temp./ °C
M
g mol−1
(SEC)/
DP
(NMR)
% Conversion
1H
% Conversion
13C
n
Diol
PD
BD
HD
PD
BD
HD
120
120
120
80
80
80
477
1690
1660
642
1390
1028
4.7
12.1
11.0
5.8
10.8
11.2
34
100
100
29
80
100
56
100
100
50
93
100
n.a.
10.0
12.7
n.a.
8.6
14.0
Tetrabutoxy titanium (TBO) catalysis
integral when compared with that of the primary oxymethylene
peak at d 3.60 indicated that only 12.7% of chain ends could
be accounted for in this manner. Table 4 indicates the fraction
of secondary hydroxy end-groups formed in the polymeriz-
ations incorporating BD and HD. It can be seen from this
table that, in BD polymerizations, ca. 10% of the end groups
were formed from secondary residual BD units. Also,
consistently higher secondary hydroxy contents were found in
polymerizations involving HD than in those with BD.
Tables 4 and 5 contain the data derived from polymer systems
formed via catalysis using TBO. The first observation to be
made from these data is that none of the polymerizations
attain degrees of polymerization (DPs) that are close to the
theoretical value of 23. Secondly, both the DP and the final
conversion of CL appear to be a function of the choice of
diol. PD in particular is a rather poor choice of diol for these
polymerizations. Both the degree of polymerization and final
conversion of CL are significantly reduced at both reaction
temperatures. No significant differences in DPs or in rates of
polymerization were observed when the polymerizations were
conducted in the presence of either BD or HD. The data imply
that the PD–Ti complex, which forms as a result of transfer
from the propagating PCL chain, is a less efficient initiator of
CL polymerization than the similar complexes formed from
transfer to either BD or HD. PD in these systems should in
fact be regarded as a degradative chain transfer agent.
DBTO catalysis
The results from DBTO catalysis are shown in Tables 6 and
7. DBTO catalysis data echoed the results with TBO. Thus,
in polymerizations involving PD, at a polymerization tempera-
ture of 120 °C, although the final conversion was high (in fact
significantly higher than in the TBO catalyzed system), the
degree of polymerization and M , as measured by SEC, was
n
low. This again indicates that the PD–DBTO complex may
Table 5 shows the relative peak sizes of components in the
carbonyl region from the PCLs polymerized by catalysis with
TBO. The degradative behaviour of PD in these systems is
again noteworthy. At neither of the polymerization tempera-
tures, 80 °C or 120 °C, are resonances due to esters adjacent
to the diol unit observed. This again implies that initiation,
following transfer to PD, by the PD–Ti complex is inefficient.
The data imply that the majority of the PCL chains present
are initiated by some process other than insertion into a PD
alkoxide–Ti bond. The second point of note is that only one
resonance due to carbonyls attached to HD units is observed.
The spectra of all the polymerizations that include BD in the
reaction mixtures show two peaks in this region of equal
intensity. From reference to the spectra of the model diesters
it is clear that two resonances should be present. It can thus
be concluded that both the primary and secondary hydroxy
groups of BD are active in transfer and in reinitiation. Two
explanations are possible for the absence of the second peak
in the polymerizations involving HD. Firstly, the down-field
resonance due to a carbonyl attached to oxymethylene, derived
from transfer to primary hydroxy, may be hidden within the
dominant main chain resonance (C3). Alternatively, transfer
may occur only to primary hydroxy sites leaving the secondary
hydroxy group as a chain end. In the latter case it should be
possible to observe the secondary alcohol end group. For
example, in the product from a reaction conducted at 120 °C,
a peak which could be assigned to the secondary alcohol
oxymethylene protons was observed at d 3.76. However, its
not be an efficient reinitiator of polymerization. The high
conversion and low degree of polymerization in this system
may indicate the existence of a chain-breaking side reaction in
this system. Significantly, when the reactions were carried out
at the lower temperature of 80 °C, but for longer reaction
times, much improved results were obtained. Thus the degrees
of polymerization (as measured by NMR) and M s (SEC)
n
were much higher. The DPs were still, however, well removed
from the theoretical value. Examination of the 13C spectrum
showed that both of the expected oxymethylene and oxyme-
thine ester carbonyls arising from esterification of both the
secondary and primary hydroxy groups were present.
Interestingly, the 1H spectrum of the product from the PD
polymerization carried out at 120 °C also showed resonances
that could be attributed to free PD. The polymerizations
involving BD and HD proceeded to high conversion and gave
polymers of degrees of polymerization between 9 and 13,
which are again below the expected value. With this catalyst,
as with TBO, polymerizations involving HD appear to give a
significantly higher fraction of secondary hydroxy. Also, the
concentration of secondary hydroxy sites found in these poly-
merizations appears to be lower than in equivalent TBO
polymerizations. No resonances that could be assigned to
secondary hydroxy sites from the PD residue were observed.
Table 7 shows the results of 13C spectroscopy in the carbonyl
region. In the case of the PD (carried out at 80 °C) and BD
containing polymerizations the carbonyls attached to both
oxymethine and oxymethylene groups of the residual diol were
observed. In each case both resonances were observed to have
equal intensity. In the case of the HD containing polymeriz-
ation only one resonance was observed. However, as discussed
above for the TBO catalyzed polymerizations, this resonance
is derived from an oxymethine carbonyl and therefore the
second resonance must lie underneath the main chain reson-
ance, C3. Thus, as with the TBO catalyzed polymerizations,
both primary and secondary hydroxy groups are active in
transfer and reinitiation. However, reference to the 1H spectra,
discussed above, indicates that, as in the TBO catalyzed
system, the primary alcohol is more reactive in the transfer
Table 5 C1–C4 integrations for TBO catalysis
Reaction
temp./ °C
Diol
C4
C3
C2
C1
PD
BD
HD
PD
BD
HD
120
120
120
80
80
80
n.a.
0.06
0.08
n.a.
0.08
0.05
n.a.
0.04
n.a.
n.a.
0.08
n.a.
0.58
0.70
0.78
0.71
0.68
0.67
0.42
0.20
0.14
0.29
0.16
0.19
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J. Mater. Chem., 1999, 9, 1071–1076

Table 6 M (SEC), DP (NMR) and % conversion data for polymerizations catalyzed by DBTO
n
% Secondary
hydroxy
end groups
Reaction
temp./ °C
M
g mol−1
(SEC)/
DP
(NMR)
% Conversion
1H
% Conversion
13C
n
Diol
PD
BD
HD
PD
BD
HD
120
120
120
80
80
80
788
1474
1445
1782
2109
1782
6.9
12
11
14
11
97
89
78
100
100
96
100
95
90
100
100
100
n.a.
10
13
0
9
14
14
Table 7 C1–C4 integrations for DBTO catalysis
(GC)) and hexane-1,5-diol (HD) (Aldrich, purity=99.9+%
(GC)) were used as supplied. Since all of the reactants gave
single peaks on analysis by GC further purification was deemed
unnecessary.
Reaction
Diol
temp./ °C
C4
C3
C2
C1
PD
BD
HD
PD
BD
HD
120
120
120
80
80
80
0.08
0.05
0.05
0.05
0.06
0.04
0.08
0.05
n.a.
0.05
0.06
n.a.
0.61
0.57
0.80
0.80
0.74
0.80
0.23
0.22
0.15
0.10
0.14
0.16
Analysis
NMR spectra were recorded at 399.78 MHz (1H) and
100.54 MHz (13C) using
a JEOL GSX400 instrument.
Magnitude-mode 2D-COSY-45 spectra of polymers were mea-
sured using a spectral width of 2718.9 Hz and 56 acquisitions
for each of 1024 increments were sampled into 1024 complex
points. Data were processed for presentation and analysis
using the software suite nmrPipe.16 The arrays were zero-filled
to 2048×2048 complex points and transformed in each dimen-
sion after application of a sinebell window function. Molecular
weights and molecular weight distributions of the PCLs were
measured by size exclusion chromatography (SEC) (calibrated
against polystyrene standards) with Styragel@ 5 mm mixed gel
columns (Polymer Laboratories) and a UV detector system.
Tetrahydrofuran was used as the eluent at a flow rate of
1.0 cm3 min−1. Sample concentrations were approximately
2 g dm−3.
reaction and this is reflected by the presence of secondary
hydroxy end groups.
Conclusions
The purpose of this work was to further investigate, following
on from our initial reports on the use of PMMA diols, the
effect of using diols with both primary and secondary hydroxy
groups as transfer agents for the preparation of PCL diols. As
in our previous report14 conditions were chosen that model
those in operation on an industrial scale. Therefore water was
removed from the system by passing a dried stream of nitrogen
through the reaction mixtures at the reaction temperature.
Water, in these insertion polymerizations, acts as another type
of transfer agent. The occurrence of significant transfer to
water would result in the formation of carboxylic acid end
groups. Since these end groups were not observed in the NMR
spectra we assume that the effect of residual water under these
conditions is negligible. The presence of small amounts of
water also has no effect on the final conversion of CL.
We have shown that under these conditions both 1,3 BD
and 1,5 HD act as transfer agents in which both hydroxy
groups are able to transfer the propagating chain end.
However, the secondary hydroxy has been shown to be less
reactive and this results in the presence of an appreciable
number of secondary hydroxy end groups. A higher fraction
of secondary end groups was found in the polymerizations
involving HD than in those with BD. PD showed anomalous
behaviour under some conditions. The results appear to indi-
cate that PD may be involved in degradative chain transfer
that may be a result of side reactions. However, at a polymeriz-
ation temperature of 80 °C, PD gave polymer of a similar
quality to that from polymerizations containing BD or HD.
Thus there are structural differences in the final PCL product
that are a function of the distance between the two hydroxy
groups in the transferred diol. These observations strongly
suggest that the structure of the catalytic site undergoing
transfer is cyclic.
Synthesis of model compounds
In order to correctly assign the 13C resonances derived from
the carbonyl carbon of the diester unit, model compounds
were prepared. Models for each diester unit were prepared by
preparing the dipropionyl ester of each diol. Thus each diol
(50 mmol) (PD, BD or HD), in turn, was mixed with propionic
acid (100 mmol) and toluene-p-sulfonic acid (0.35 mmol). The
mixture was heated using Dean–Stark conditions at 175 °C for
approximately 24 h. The products were then distilled under
vacuum. The 1H NMR (400 MHz) and mass spectrometric
(EI+) data for each diester were as follows.
Propane-1,2-diyl dipropionate (1): d 1.14 (2×t, 6H), 1.25
(d, 3H), 2.33–2.35 (2×q, 4H), 4.07 and 4.18 (2×dd, 2H),
5.15 (m, 1H); m/z 115 (1 minus –O–COCH CH ).
2
3
Butane-1,3-diyl dipropionate (2): d 1.14 (t, 6H), 1.26 (d,
3H), 1.89 (m, 2H), 2.40–2.42 (2×q, 4H), 4.12 (dd, 2H), 5.03
(m, 1H); m/z 133 (2 minus –O–COCH CH ).
2
3
Hexane-1,5-diyl dipropionate (3): d 1.13, 1.14 (2×t, 6H),
1.21 (d, 3H), 1.4–1.65 (3×m, 6H), 2.30–2.32 (2×q, 4H),
4.07 (t, 2H), 4.92 (m, 1H); m/z 157 (3 minus –O–COCH CH ).
2
3
Polymerizations
Polymerization mixtures were prepared from CL (6.3 g,
55 mmol), catalyst (0.1 mmol) (DBTO or TBO), xylene
(12 cm3) and the required diol (4.7 mmol). These mixtures
were then heated under a stream of dry nitrogen at either
120 °C for 6 h or 80 °C for 7 days. This procedure would give
a theoretical degree of polymerization (DP) of 23. The whole
reaction mixture, including the xylene solvent, was then ana-
lysed by 1H and 13C NMR and SEC.
Experimental
Materials
CL (Aldrich, purity=99.9+% (GC)), dibutyl tin oxide
(DBTO) (Aldrich), titanium tetrabutoxide (TBO) (Aldrich),
xylene (Aldrich), propane-1,2-diol (PD) (Aldrich, purity=
99.9+% (GC)), butane-1,3-diol (BD) (Aldrich, purity=99.9%
J. Mater. Chem., 1999, 9, 1071–1076
1075

2
H. R. Kricheldorf, M. V. Sumbal and I. Kreiser-Saunders,
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Assignment of carbonyl resonances in models
In order to assign the two resonances derived from the ester
carbonyls of the primary and secondary esters the following
procedure was used. A fully decoupled spectrum was first run;
this located the two carbonyl resonances from each diester.
Fully C–H coupled spectra were then obtained, displaying
complex couplings for both sites, involving interactions with
several protons. From 1H COSY spectra ester methylene
3
4
H. R. Kricheldorf and S.-R. Lee, Macromolecules, 1996, 29, 8689.
D. Tian, Ph. Dubois and R. Jerome, Macromolecules, 1996, 30,
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A. Duda and S. Penczek, Macromolecules, 1995, 28, 5981.
S. Penczek and A. Duda, Macromol. Symp., 1996, 107, 1.
J. Baran, A. Duda, A. Kowalski, R. Szymamski and S. Penczek,
Macromol. Symp., 199, 123, 93.
J. Baran, A. Duda, A. Kowalski, R. Szymamski and S. Penczek,
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W. M. Stevels, M. J. K. Ankone, P. J. Dijkstra and J. Feijen,
Macromolecules, 1996, 29, 8296.
5
6
7
8
9
(–CH O–) and methine (–CHO–) proton resonance positions
2
were identified and frequency values determined. The 13C
coupled experiment was repeated but with selective irradiation
at the resonance frequency for the methylene protons of the
primary ester. This caused the primary carbonyl response to
be partially decoupled with simplification of the multiplicity.
This procedure was repeated with irradiation at the methine
frequency; in this case the secondary ester carbonyl response
showed partial collapse.
10 Y. Shen, Z. Shen, Y. Zhang and K. Yao, Macromolecules, 1996,
29, 8289.
11 Y. Shen, Z. Shen, Y. Zhang and K. Yao, Macromolecules, 1996,
29, 3441.
12 A. Duda, Macromolecules, 1994, 27, 576.
13 Examples of patents include: UK 859 640; UK 859 642; UK
859 643; UK 859 644; UK 859 645 (all 1961).
14 S. Rimmer and M. H. George, Eur. Polym. J., 1993, 29, 205.
15 R. F. Storey and A. E. Taylor, J. Macromol. Sci., 1996, A33, 77.
16 F. Delaglio, S. Grzesiek, G. Vuister, G. Zhu, J. Pfeifer and A. Bax,
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Paper 8/10010A
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