characterization of phase structures of … · characterization of phase structures of novel...

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

luciocb@inta.es, mlcerrada@ictp.csic.es, fuentegj@inta.es

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)