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Radical copolymerization of methyl О-acyloxyacrylates with some vinyl monomers

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Polymer International
Polym Int 48:495±501 (1999)
Synthesis and properties of polyimides
containing polybutadiene blocks
Miroslav Marek, Jr,1* Petr Holler,1 Pavel Schmidt,1 Bohdan Schneider,1
Jana Kovářová,1 Ivan Kelnar,1 Jindřich Pytela2 and Miloslav Sufčák2
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic
Kaučuk Co, 278 52 Kralupy and Vltavou, Czech Republic
Abstract: Polyimides containing polybutadiene blocks were prepared by copolycondensation of
benzophenone-3,3',4,4'-tetracarboxylic dianhydride, diphenylmethane-4,4'-diisocyanate and isocyanate-endcapped polybutadiene LBD-3000. 13C NMR CP-MAS and FTIR spectroscopies were used
to determine the chemical structure of the copolymers. TGA showed that the thermal stability of the
copolymers in inert atmosphere is almost independent of the polybutadiene content in the copolymer
(as follows from the temperature of 10% and 20% weight loss). Stress±strain experiments showed that
copolymers containing amounts of polybutadiene higher than 59 wt% exhibited elastomeric behaviour.
# 1999 Society of Chemical Industry
Keywords: polyimides; polybutadiene; block copolymers
Polyimides rank among the most important highperformance polymers because of their excellent
thermal stability and very good mechanical properties.1±4 High values of modulus and tensile strength are
retained even at elevated temperatures, because
relaxation transitions are markedly high compared
with most other common polymers.5,6 Therefore polyimides are attractive for modi®cations of thermal and
high-temperature mechanical properties of various
polymers. Such modi®cations can be carried out either
by blending or by syntheses of copolymers7±14 to
prepare new materials with unique properties.
In addition to the frequently used synthesis of
polyimides from diamines and dianhydrides (or other
derivatives of aromatic tetracarboxylic acids), the
reaction of dianhydrides with diisocyanates can also
be used for preparation of these polymers.15 Such a
synthetic route, which has already been applied to
manufacture commercially available polyimides,16
makes it possible to prepare polyimides from various
oligomer blocks end-capped with isocyanate groups.
Special attention was paid to poly(amide-imide)s,17
poly(urethane-imide)s,18 and urethane-modi®ed polyimides synthesized from diisocyanate end-capped
blocks containing soft polyether chains.19
Application of dilithiumorganic initiator to living
anionic polymerization of butadiene, and subsequent
termination and chemical modi®cation of the chain
ends led to a low-molecular-weight polybutadiene
end-capped with aromatic isocyanate groups.20
Therefore, there exists a possibility of modifying
properties of polybutadienes by incorporation of stiff
polyimide structures. Such molecular reinforcement
should lead to modi®cation of mechanical properties
of polybutadiene without macroscopic demixing
which is typical of polymer blends.21 This communication reports our effort to develop poly(butadieneimide)s using commercially available liquid polybutadiene LBD-3000 (Scheme 1) end-capped with isocyanate groups and shows some basic physicochemical
and physical properties of such copolymers.
The isocyanate end-capped polybutadiene LBD-3000
was obtained from KaucÏuk Kralupy Co, Czech
Republic. Its Mn ranged between 3200 and 3800,
the polydispersity index Mw/Mn, was 1.3, and the
concentration of isocyanate groups was 0.730 or
0.719 mmol gÿ1. The oligomer contained 60% 1,2-,
25% 1,4-trans and 15% 1,4-cis structures.
dianhydride (BTDA; Aldrich, Milwaukee, WI, USA) was
puri®ed by crystallization from acetic anhydride, and
diphenylmethane-4,4'-diisocyanate (MDI; Aldrich)
was puri®ed by pressure ®ltration22 at 60 °C. Anhydrous N-methylpyrrolidone (NMP; Aldrich, Milwaukee, WI, USA) was used as received.
* Correspondence to: Miroslav Marek, Jr, Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06
Prague 6, Czech Republic
Contract/grant sponsor: Kraučuk Co, Kralupy
(Received 18 June 1998; revised version 26 October 1998; accepted 10 February 1999)
# 1999 Society of Chemical Industry. Polym Int 0959±8103/99/$17.50
M Marek et al
Scheme 1
Diisocyanates (MDI, LBD-3000) were dissolved in
NMP in a glass reactor equipped with a nitrogen inlet
and CaCl2 drying tube, an equimolar amount of solid
BTDA was added, and the reactor was heated in an oil
bath at 70 °C for 90 min. The concentration of
monomers was 15 wt%. Triethylamine was then added
(0.03 g lÿ1) into the reaction mixture and the temperature was raised to 90 °C. After 60 min, when evolution
of CO2 ceased, the reaction mixture was poured into
water, the precipitated polymer was ®ltered off and
dried at low pressure (0.5 mmHg) at 70 °C. The
polymer was extracted with THF at 65 °C for 30 min
and at 25 °C for 24 h.
on a Perkin-Elmer TGA-7 instrument with a heating
rate of 10 °C minÿ1.
Both number and weight average molecular weights
were determined by gel permeation chromatography
(GPC) (UV detection, column 600 7.5 mm PSS
Ê , PSS, Mainz, Germany) using THF as a mobile
104 A
phase. Calibration was carried out with polybutadiene
standards (Polymer Laboratories Inc, Amherst, MA,
USA) and chromatographic data were processed using
a DataMonitor integration system (Watrex, Prague,
Czech Republic).
Stress±strain experiments were carried out at a
speed of 20 mm minÿ1 using an Instron Model 6025
(Instron Corp, Canton, MA, USA) with samples
having a gauge width of 2 cm.
Solid-state 13C NMR spectra were measured at
50.32 MHz with a DSX 200 spectrometer (Bruker
AG, FaÈlanden, Switzerland) by the cross-polarization
magic-angle spinning method (CP-MAS).23±26 The
samples were placed in ZrO2 cells for spinning in a
double-bearing system, as supplied by Bruker AG.
The magic angle was adjusted by minimizing the width
of the carbonyl band of a glycine sample. Typical
measuring parameters were as follows: 90 ° HF pulse
5±6 ms, pulse frequency repetition time 4 s, number of
scans 5000, MAS frequency 7000 Hz, spectral width
30 kHz, acquisition time 25 ms. 13C chemical shifts are
referred to the carbonyl signal of glycine
( = 176.03 ppm), measured separately.
Infrared spectra were obtained on a Bruker IFS 55
FTIR spectrometer using KBr pellets.
Viscometric measurements were carried out in an
Ubbelohde viscometer at 25 °C in m-cresol, using
solutions of concentration 0.001 g cmÿ3.
Glass transition temperatures Tg were measured
using a Perkin Elmer DSC-2 (Perkin-Elmer, Norwalk,
CT, USA) differential scanning calorimeter at a
heating rate of 10 °C minÿ1 in nitrogen atmosphere.
Thermogravimetric analysis (TGA) was carried out
Synthesis and chemical structure of polymers
Copolymers containing polyimide and polybutadiene
structures were prepared by well-established reaction
of diisocyanates with dianhydrides as is shown in
Scheme 1.
There was no special effort needed to prepare
polymers with de®ned polyimide blocks, because we
added a dianhydride into a mixture of diisocyanates
(LBD-3000, MDI) and the formation of statistical
distribution of polyimide structures was expected. The
polybutadiene contents, yields and other basic characteristics of the polymers obtained are summarized in
Table 1. In addition to polyimides with polybutadiene
blocks, polyimides BTDA/MDI (Sample 1) and
BTDA/LBD-3000 (Sample 10) were also prepared.
Partial precipitation occurred during polycondensation if the content of polyimide was higher than
59 wt%. In Fig 1, curve a, an FTIR spectrum of
polyimide BTDA/MDI is shown which contains
typical peaks of the imide structure27,28 at 1779 and
1720±1725 cmÿ1 (C=O) and 1375 cmÿ1 (CÐN). In
Fig 1 curve b, a spectrum of polybutadiene±polyimide
(Sample 4) containing typical absorption bands of
Polym Int 48:495±501 (1999)
Polyimides containing polybutadiene blocks
Table 1. Polybutadiene contents, inherent viscosities, yields and glass transition temperatures of polyimide–polybutadiene block copolymers
LBD-3000 content
LBD-3000 content
inh a (dl/gÿ1)
Residue after extraction (%)
Yield (%)
Tg ( °C)
Inherent viscosity of the soluble part of the end-product only.
The viscometric experiments were carried out in NMP at 25 °C.
Figure 1. FTIR spectrum of copolymers BTDA/MDI (no. 1) (curve a), polybutadiene–polyimide no. 4 (curve b) and BTDA-LBD-3000 (No. 10) (curve c).
both polyimide and polybutadiene is shown. 1,2Polybutadiene absorbs at 3074 cmÿ1 (CÐH stretching), 1640 cmÿ1 (C=C stretching), 910 and 995 cmÿ1
(out-of-plane CÐH vibration29 of the vinyl group).
The bands near 1665 and at 968 cmÿ1 can be assigned
to C=C stretching and out-of-plane CÐH vibration
of the trans-1,4-polybutadiene structure, respectively.29,30 Polymer BTDA/LBD-3000 (Fig 1 curve
c), which contains no MDI-based structures, also
shows, in addition to the polybutadiene bands, the
bands of the imide structure, which are much less
intense than with the other samples because the
content of polybutadiene is high (90 wt%).
Polym Int 48:495±501 (1999)
CP MAS NMR spectra of the same polymers
(Samples 1, 4 and 10) are shown in Fig 2. The BTDA/
MDI spectrum contains peaks typical of the imide
structure which were also observed in other BTDA- or
MDI-based polyimides.31,32 The peak of the imide
C=O group can be observed at 192 ppm and the
carbon adjacent to N is located at 128 ppm. Peaks at
140, 138, 136, 132, 124 and 119 ppm are attributed to
aromatic carbons. The peak at 165 ppm is located in
the region where the carbonyl carbon of the benzophenone structure usually occurs.32 The peak of
methylene carbon is at 41 ppm. Spectrum 2b, corresponding to polybutadiene±polyimide, shows, in
M Marek et al
Figure 2. 13C NMR-CP-MAS spectra of
copolymers BTDA/MDI (no. 1) (curve a);
polybutadiene–polyimide (no. 4) (curve b)
and BTDA-LBD-3000 (no. 10) (curve c).
addition to peaks related to the BTDA/MDI structure,
dominant peaks at 143, 130 and 115 ppm and a few
peaks in the aliphatic region at 55±10 ppm. Because all
these peaks are observed in the spectrum of LBD3000, we conclude that they belong to polybutadiene
sequences. The spectrum of 2c corresponds to
polymer BTDA/LBD-3000 and contains more intense
peaks of LBD-3000 at 143, 130 and 115 ppm,
compared with the spectrum of polybutadiene±polyimide, whereas the peaks of polyimide aromatic
carbons are relatively weak because of the absence of
MDI-related polyimide structures and, therefore, low
concentration of imide moieties. The absence of peaks
(except for side bands) other than those corresponding
to polyimide and LBD-3000-related structures in both
solid-state 13C NMR and FTIR spectra excludes the
possibility of the existence of side reactions, at least to
the extent detectable by these methods. Therefore, the
reason for precipitation during polycondensation in
the case of Samples 1±5 seems to be a higher content of
poorly soluble polyimide sequences and not side
reaction leading to a change of chemical structure.
Inherent viscosities are comparable with other
similar systems18 and no dependence of inh on the
content of polybutadiene or on the polycondensation
yield was observed (Table 1). This can be explained by
a very complex behaviour of dilute solutions of these
polymers, because many factors (segment length
distribution, interaction between unlike chain segments, solvent±segment interactions, micellization,
etc.) must be taken into account.33
The absence of an intense infrared absorption band
at 2300 cmÿ1 (ÐN=C=O) can hardly be taken as
evidence that LBD-3000 ef®ciently reacted with
BTDA and thus was incorporated into polyimide
chains, because the residual isocyanate groups might
be hydrolysed during isolation and subsequent drying
of the polymers at elevated temperatures. LBD-3000
is very soluble in THF (in contrast to polyimide
BTDA/MDI), so we extracted the polymers with this
Figure 3. Plot of GPC molecular-weight averages for oligomer THF
extracts versus LBD-3000 content. Mn (&) is the number-average
molecular weight, Mw (*) is weight-average molecular weight.
solvent and determined extractable portions of the
polymers and molecular weights of solutes. As shown
in Table 1, the content of the polymer soluble in THF
strongly depends on the composition of the reaction
mixture. The extractable portion of the polymer
considerably increased if the LBD-3000 content was
higher than 60 wt%. This may be explained by high
polybutadiene structure contents in the polymers,
which are very soluble in THF. In Fig 3, the
dependence of molecular weight of the extract
(measured by GPC) on the LBD-3000 content in
the reaction mixture is shown. Because all extractable
fractions have higher Mn values than LBD-3000, it is
Polym Int 48:495±501 (1999)
Polyimides containing polybutadiene blocks
Figure 4. Thermogravimetric analyses of copolymers (a) BTDA/MDI (no 1).
(– - – - –); (b) polybutadiene-polyimide (no 4) (– – –); and (c) BTDA-LBD3000 (no 10) (——).
clear that this monomer reacted with BTDA. Both
number and weight averages of molecular weights
increase with the content of LBD-3000. This indicates
that the molecular weight of fractions extractable with
THF increases with the LBD-3000 content.
GPC experiments con®rmed that LBD-3000 reacts
with the dianhydride because molecular weights of the
THF extracts were in all cases higher than the
molecular weight of LBD-3000; however, they could
not give any evidence that polybutadiene sequences
were distributed in the BTDA/MDI polyimide. Therefore, FTIR spectra of Sample 9 before and after
extraction were recorded. No signi®cant differences in
the relative intensities of the polybutadiene and
polyimide bands were observed, and probably only
molecular weight affects the solubility of the polymers
produced from the same composition of monomers.
Thermal stability
As expected, the thermal stability of polyimide
decreased upon incorporation of polybutadiene
blocks. A 10% weight loss of copolymers in the TGA
experiments (in nitrogen) was observed at approximately 140 °C lower than that of neat polyimide
BTDA/MDI. Differences in temperatures of 10%
and 20% weight losses (T10 and T20, respectively)
are about 40 °C with Samples 2±10, i.e. considerably
higher than with a polybutadiene-free polyimide
(Sample 1). Decomposition temperatures T10 and
T20 are independent of the polybutadiene content but,
as follows from Fig 4, the residual weight of samples at
higher temperatures strongly re¯ects the composition
of the polymers. While neat polyimide lost only 10% of
its weight at 550 °C, Sample 3 lost half its original
weight, and Sample 10 (which contains no MDI
structures) has an even lower residual weight at this
temperature. In spite of some decrease in the thermal
stability of Polymers 2±10 compared with highly
aromatic polyimides, their T10 values are just slightly
lower than those of polypyromellitimides containing
dodecamethylene groupings in the repeating unit34
and of polyimides prepared by nitro group displacement polyreaction.35 Small differences between TGA
Polym Int 48:495±501 (1999)
thermal stabilities in nitrogen and air were observed.
Sample 3 exhibits almost the same weight loss at
550 °C both in nitrogen and air; a 5% difference in
weight loss was found only at 700 °C. This result
probably re¯ects a relatively slow decomposition of
polybutadiene structures which is almost imperceptible in a dynamic TGA experiment under standard
conditions (heating rate 10 °C minÿ1).
Glass transition temperatures of polyimide
sequences are just observable in the case of neat
polyimide BTDA/MDI (Tg = 293 °C as shown in Table
1). Other samples did not show any change in heat
capacity which could be reliably taken as a glass
transition temperature. A low-temperature transition
of the polybutadiene block could just be estimated in
samples with their contents higher than 66 wt%
(Polymers 8±10). These glass transition temperatures
decrease with increasing content of ¯exible polybutadiene, obviously because the sample chain ¯exibility
Mechanical properties
Stress±strain measurements were performed only with
NMP-soluble samples (7±10) from which cast ®lms
can easily be produced. The results were compared
with those for Sample 4 (soluble fraction) containing
considerably more imide structures. We are aware that
the soluble fraction cannot entirely represent Sample
4, especially with respect to the molecular weight, but
we believe that this approach at least enables us to
estimate the in¯uence of high polyimide contents on
mechanical properties of the polymers. Deformation
of Polymers 7±10 took place in all regions of samples
and no necking, typical of amorphous plastics,36 was
observed. In contrast, the ®lm of Sample 4 was hard
and brittle. As follows from Fig 5, Young's moduli of
samples with low imide contents do not exceed
Figure 5. Plot of Young’s modulus versus LBD-3000 content in
polybutadiene–polyimide copolymers.
M Marek et al
break decreases with increasing content of polybutadiene structures in the range 10±20 MPa (Fig 7); a
slightly higher value (22 MPa) was found for the
polymer containing 73 wt% of polybutadiene (Sample
8). A value higher than expected on the basis of
molecular composition might indicate a more complex
physical structure (ordering) at a speci®c polyimide/
polybutadiene ratio; therefore a detailed study of
physical structure±property relationships will be the
subject of our future research.
Financial support of this work by KaucÏuk Co, Kralupy
is highly appreciated.
Figure 6. Plot of elongation versus LBD-3000 content in polybutadiene–
polyimide copolymers.
6.5 MPa, whereas this value was one order of
magnitude higher for Sample 4. This indicates that a
high content of imide structures drastically increases
the modulus, probably because the content of BTDA/
MDI structures is already high enough to develop
strong intermolecular interactions (in particular
charge-transfer complexes) which are typical of polyimides.37
Incorporation of 44% polybutadiene into the polymer chain causes a decrease in Young's modulus of
two orders of magnitude compared with wholly
aromatic polyimides.38±40 The polymers with high
polybutadiene contents (>60 wt%) showed elongation
around 350% and, as shown in Fig 6, higher contents
of polyimide sequences lead to its decrease by one
order of magnitude (37% for Sample 4). Stress-at-
Figure 7. Plot of stress-at-break versus LBD-3000 content in
polybutadiene–polyimide copolymers.
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methyl, monomerl, acyloxyacrylates, vinyl, copolymerization, radical
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