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CHARACTERIZATION OF PHASE STRUCTURES OF NOVEL
METALLO-POLYURETHANES
Polyurethanes (PUs) are widespread used in chemical and building industries due to the fact that a large variety of starting materials with specific properties can be used for their
formation. In other advanced applications, such as in the aerospace field, they are used as polymeric matrix of energetic composite materials. Butacene is a functional polyol, with a
ferrocene group grafted onto the main chains of an OH-terminated polybutadiene (HTPB). Thus, new organometallic PUs with relevant catalytic properties can be obtained from this
prepolymer.
It is well-known that segmented PUs have phase-separated morphology giving rise to nanodomains. The physico-chemical differences between two families of PUs, one synthesized
with HTPB and the other one obtained from Butacene (soft segments, SS) are studied in this contribution. Different diisocyanates have been used at a given family forming the hard
segments (HS), either aliphatic (isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (HMDI)) or aromatic (toluene-2,4-diisocyanate (TDI) and methylene diphenyl
diisocyanate (MDI)). The chemical structures of diisocyanates greatly affect the final micro-structure as well as the nanodomains formation and their ordering through hydrogen bonds
between urethane groups dispersed within an amorphous matrix of flexible segments of polybutadiene. The presence of hydrogen bonds has been evaluated by Fourier transform
infrared (FTIR) spectroscopy, while the existence of phase separation either by Differential Scanning Calorimetry (DSC) or Dynamic Mechanical Analysis (DMA) and the organization of
those domains by X-ray diffraction.
R:
Isophorone diisocyanate (IPDI) Toluene -2,4- diisocyanate (TDI)
Methylene diphenyl diisocyanate (MDI) Hexamethylene diisocyanate (HMDI)
OCN
NCONCO
NCO
NCOOCN
OCN
NCO
OHHOHO
OH
NCOOCN
HO
OH
HO
OH
HO
OH+
OHHO
NCOOCN
HO
OH
HO
OH
HO
OH
HO
OH+
OH OH0.2 0.2 0.6 + OCN R
RNCO N
H
O
NH
OO
O
n
HTPB
n
PU
Metallo-PUButaceneFe
Si
OHyHO x
Fe
Si
OyxO
O
HN
+ R
HN
OOCN R NCO
Beatriz Lucio1, María Luisa Cerrada2 and José Luis de la Fuente1
1Instituto Nacional de Técnica Aeroespacial “Esteban Terradas” (INTA)
Ctra. de Ajalvir, Km. 4, Torrejón de Ardoz, Madrid, 28850 2Instituto de Ciencia y Tecnología de Polímeros (ICTP). Consejo Superior de Investigaciones Científicas (CSIC)
C/ Juan de la Cierva 3, Madrid, 28006
[email protected], [email protected], [email protected]
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
-125 -100 -75 -50 -25 0 25 50 75 100 125
1E-5
1E-4
1E-3
0,01
0,1
1
10
100
1000
10000
Sto
rag
e m
od
ulu
s, M
Pa
Lo
ss m
od
ulu
s, M
Pa
Temperature, ºC
HTPB-TDI , Multifrequency
Ta
ng
en
t D
elta
tan
E´´
1 Hz
3 Hz
10 Hz
30 Hz
E´
-80 -60 -40 -20 0 20 40 60
0,00
0,25
0,50
0,75
1,00
1,25
Ta
ng
en
t D
elta
Temperature, ºC
MDI
0,00
0,25
0,50
0,75
1,00
1,25
TDI
0,00
0,25
0,50
0,75
1,00
1,25
Butacene-isocyanate, 1 Hz
HTPB-isocyanate, 1 Hz
HMDI
0,00
0,25
0,50
0,75
1,00
1,25
HSSS
HSSS
IPDI
-80 -60 -40 -20 0 20 40 60 80
IPDI
HMDI
TDI
MDI
Temperature, ºC
Butacene-isocyanate, 10 ºC/min
HTPB-isocyanate, 10 ºC/min
SS HS
BUTACENE
Tg o SS1 (°C)
Tg f SS1 (°C)
ΔCp SS1
(J/g°C)
Tg m SS1 (°C)
ΔCp SS2
(J/g°C)
Tg m SS2 (°C)
Tg o HS1 (°C)
Tg f HS1 (°C)
ΔCp HS1
(J/g°C)
Tg m HS1 (°C)
ΔCp HS2
(J/g°C)
Tg m HS2 (°C)
IPDI -50 -44 0,24 -47 - - -14 -4 0,17 -9 - -
HMDI -54 -46 0,34 -50 <0,1 -38 - - <0,1 54 - -
TDI -55 -47 0,34 -51 - - - - <0,1 -28 - -
MDI -53 -43 0,33 -48 - - - - <0,1 -21 <0,1 2
Abstract
Materials
Results and discussion
DMA and DSC analysis confirms the phase segregation in both systems. The relaxation time distribution associated with the SS mechanism is narrower than that ascribed to the HS
relaxation, i.e., it involves a broader temperature range.
Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane HS were obtained by
the deconvolution of C=O region and analysis of the relative absorbances. This quantification suggests different degrees of HS phase separation which depend on the macroglycol and
chemical structure and the symmetry of the diisocyanate
Interdomain ordering between hard domains is observed in those macromolecular architectures containing HTPB as soft segments. The spacing values are dependent on the
diisocyanate used.
Conclusions
Acknowledgments: Beatriz Lucio is grateful to INTA for the financial support through the FPI fellowship program.
Quantitative information
regarding the relative amounts
of non-hydrogen bonded (1738-
1725 cm-1), loosely hydrogen
bonded (1715-1700 cm-1) and
strongly bonded and ordered
urethane hard segments (1700-
1680 cm-1) were obtained by
the deconvolution of C=O
region (A) and analysis of the
relative absorbances (B).
HTPB BUTACENE
IPDI (cm-1) A (%) B (%)
1737 32,5 31,4
1714 34,1 37,2
1689 33,4 31,4
1725 46,7 37,3
1699 36,9 36,5
1679 16,4 26,2
HMDI (cm-1) A (%) B (%)
1727 46,1 40,2
1708 35,6 37,3
1693 18,3 22,5
1723 50,5 46,2
1699 37,0 36,8
1678 12,5 17,0
TDI (cm-1) A (%) B (%)
1739 49,1 45,4
1717 31,8 33,5
1699 19,1 21,1
1737 48,3 44,3
1711 32,0 33,5
1687 19,7 22,2
MDI (cm-1) A (%) B (%)
1737 49,7 46,5
1715 31,7 32,7
1697 18,6 20,8
1736 53,4 51,3
1712 29,2 30,7
1691 17,4 18,0
0.5 1.0 1.5 2.0
200
300
400
500
600
700
800
900
1000
HTPB_HMDI
HTPB_IPDI
HTPB_TDI
HTPB_MDI
norm
. in
t. (
a.u
.)
q (1/nm)
HTP
B_M
DI
HTP
B_T
DI
HTP
B_I
PDI
HTP
B_H
MDI
0
3
6
9
12
inte
rdom
ain
spacin
g (
nm
)
0.5 1.0 1.5 2.0
200
300
400
500
600
700
800
900
1000
BUT_HMDI
BUT_IPDI
BUT_TDI
BUT_MDI
no
rm. in
t. (
a.u
.)
q (1/nm)
Ordering capability seems to be dependent on the lack or presence of Butacene in the macromolecular
architecture. Furthermore, the mean interdomain spacing between hard domains (d = 2π/qmax) is also strongly
dependent on the nature of diisocyanate, those aliphatic ones showing values higher than the spacing obtained
for hard segments containing aromatic diisocyanates.
The relaxation of soft segments exhibits in the
Butacene systems an intensity in tan much higher
than in the HTPB samples, implying a greater energy
dissipation capacity at this temperature range in the
former specimens. The relaxation time distributions
associated with the SS mechanism and,
consequently, its width, are narrower than those
involved in the relaxation of the rigid segments.
DMA analysis shows the existence of phase separation and, then,
two different glass transitions regions: the related to cooperative
motions of the soft and hard segments, respectively. At a given
family, the relaxation of soft segments takes place at similar
temperatures (Tmax at around -75 °C for HTPB samples and at
about -50 ºC for Butacene specimens, at 1 Hz in E″ basis). The
storage modulus is about 1000 MPa for all of them at the lowest
temperatures.
HTPB
Tg o SS1 (°C)
Tg f SS1 (°C)
ΔCp SS1
(J/g°C)
Tg m SS1 (°C)
ΔCp SS2
(J/g°C)
Tg m SS2 (°C)
ΔCp HS1
(J/g°C)
Tg m HS1 (ºC)
ΔCp HS2
(J/g°C)
Tg m HS2 (°C)
IPDI -77 -70 0,55 -73 <0,1 -43 <0,1 -12 - - HMDI -76 -70 0,40 -72 <0,1 -57 <0,1 -10 <0,1 49
TDI -74 -68 0,45 -71 <0,1 -40 <0,1 -11 - - MDI -75 -68 0,41 -72 <0,1 -56 <0,1 -8 - -
DSC results are in a good agreement with those obtained by DMA analysis.
Phase separation is observed and, then, two different glass transitions
regions appears: the ascribed to generalized motions of the soft and hard
segments, respectively. It should be commented that only the glass
transition located at the lowest temperatures and related to SS is possible to
be accurately determined since the one ascribed to HS involves a very small
specific heat increment (lower than 0,1 J/g ºC).
Deconvolution results indicate the presence of a substantial
amount of the free carbonyl (around 50%, except for HTPB-
IPDI with a value close to 30%), a reasonable amount of
hydrogen bonded, disordered carbonyl (around of 35%,
except for the samples based on aromatic diisocyanates, with
a value close to 30%) and small amount of strongly hydrogen
bonded carbonyl groups (around 20% for those PU samples
containing aromatic rings as hard segments, and low values
for the other ones). However, independing on these data, the
more significant differency between both series is determined
by the lower wavenumbers for the signals representative of
well-ordered hydrogen bonded structure for the PUs based
on Butacene (for PUs from HTPB ≥ 1690 cm-1 vs from
Butacene ≤ 1690 cm-1).
DMA
FTIR
DSC SAXS
1679
1699
Butacene-IPDI1725
1678
1699
1723Butacene-HMDI
168017201760
1687
1711
1737Butacene-TDI
168017201760
1691
1712
1736 Butacene-MDI
Ab
so
rba
nce
(a
.u.)
16891714
HTPB-IPDI
1737
1693
1708
1727
HTPB-HMDI
168017201760
1699
1717
1739HTPB-TDI
Wavenumber (cm-1)
168017201760
1697
1715
1737HTPB-MDI
Wavenumber (cm-1)