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Journal of Polymer Research

ISSN 1022-9760

Volume 19

Number 11

J Polym Res (2012) 19:1-7

DOI 10.1007/s10965-012-9994-2

Preparation, tensile, damping and thermalroperties of polyurethanes based on

various structural polymer polyols: effects ocomposition and isocyanate index

Shoubing Chen, Qihua Wang & Tingmei

Wang

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13

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ORIGINAL PAPER

Preparation, tensile, damping and thermal properties

of polyurethanes based on various structural polymer

polyols: effects of composition and isocyanate index

Shoubing Chen & Qihua Wang & Tingmei Wang

Received: 25 March 2012 /Accepted: 4 October 2012# Springer Science+Business Media Dordrecht 2012

Abstract A series of polyurethanes (PUs) based on poly

(tetramethylene glycol) (PTMG), poly (ethylene adipate)

(PEA) diol, polycaprolactone (PCL) diol and castor oil (CO)were synthesized. The tensile, damping and thermal properties

were studied systematically in terms of the composition and

isocyanate index (R). Results showed that when R is 2, the

PUs exhibit a relatively high tensile strength more than

30 MPa. The PTMG-PU, PCL-PU and PEA-PU show high

elongation at break compared to the cross-linked CO-PU.

When R is 1.5, tensile strengths decrease compared to R is 2.

But, the elongations of PTMG-PU, PCL-PU and CO-PU

increase. DMA analysis showed that the glass transition tem-

perature (Tg) is increasing as the sequence of PTMG-PU,

PCL-PU, PEA-PU and CO-PU. TheTgof CO-PU is as high

as 60.6 C when R is 1.5 and 93.4 C when R is 2. The Tgranges of the other linear PUs are between 50 and 12 C.

The damping temperature ranges of these PUs are relatively

broad. Further, TG results showed the start degradation tem-

peratures of them are approx 260 C. These results show a

good guidance to select a kind of PU when prepare the

PU-polymer composites for given properties.

Keywords Polyurethanes. Polyols . Tensile properties,

Damping properties

Introduction

Polyurethanes (PUs) are organic polymers that contain the

urethane group in the structure. PUs are produced in the

form of foamed plastics, structural elastomers and coating

elastomers, adhesives and auxiliary agents, for their struc-

tural versatility [14].The PU is made by the reaction of a polyol with a diiso-

cyanate. The isocyanates form the major part of the hard or

rigid phase of the polyurethane. Polyols provide the soft seg-

ment of the polymer and are capped with a hydroxyl group.

The multiformity of PU comes from the different Polyols [1,

5]. PU can be available both as relatively rigid plastomers and

as flexible elastomers with compact or foamed structures. PU

as flexible elastomers especially the polymer composites con-

taining PU (PU used as the component of polymer matrix or

used as modifier) has received considerable attention in recent

years for the increasing demand of functional and structural

polymer composites. Spirkova [6] studied PU elastomers madefrom linear polybutadiene diols. The polybutadiene-based PU

prepared from isophorone diisocyanate exhibited very good

elastic properties and good oil resistance. Oprea [7] investigat-

ed high molecular weight polyethylene glycol based PU and

the results showed that the prepared PU had very good tensile

properties. Bae et al. [8] prepared PU from 4,4-methylene bis

(phenylisocyanate), poly(tetramethyleneglycol) and studied

their dynamic mechanical behaviour. Gite et al. [9] presented

a study on the effect of NCO/OH ratio and an increase in

hydroxyl content of acrylic polyols on the properties of PU

coatings. Further, the PU-based polymer composites were

researched extensively recent years. For e.g. the preparation

and properties of PU modified by carbon nanotubes [10],

silicate nanoclay [11, 12], zeolite particulate [13], nanofiber

filaments [14], polystyrene [15], chitin [16], vinyl ester [17],

epoxy resin [18, 19], wood flour [20], etc. Though diffident

kinds of PU and PU composites were studied, most of

researchers only focused one or two types of PU. The compar-

ison of performance between different types of PU is limited.

In this paper, we focused on the castable PU elastomers

and presented the comparison of performance between

S. Chen :Q. Wang (*) : T. Wang

State Key Laboratory of Solid Lubrication, Lanzhou Institute

of Chemical Physics, Chinese Academy of Sciences,

Lanzhou 730000, China

e-mail: [email protected]

J Polym Res (2012) 19:9994

DOI 10.1007/s10965-012-9994-2

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different types of them. The polyether diol-based PU, poly-

ester diol-based PU and triol-based PU were prepared with

2,4-toluene diisocyanate and the 3, 3-dichloro-4, 4-dia-

mino diphenyl methane was taken as chain extender. Their

mechanical, damping and thermal properties were studied

systematically in terms of composition and isocyanate in-

dex. The results could be a reference for making PU elasto-

mer and related PU composite with specific performance.

Experimental

Raw materials

Poly (tetramethylene glycol) (PTMG) (Mn02000) was sup-

plied by Mitsubishi Chemical Corporation (Japan). Poly

(ethylene adipate) (PEA) diol (Mn02000) was purchased

from Qingdao Huayuan Polymer Co., Ltd. (Shandong, Chi-

na). Polycaprolactone (PCL) diol (Mn02000) was supplied

by Daicel Chemical Industries Co. Ltd. (Japan). Castor oil(CO) was obtained from Laiyang Shuangshuang Chemical

Co., Ltd. (Shandong, China). Figure 1shows structures of

the polyols. 2, 4-Toluene diisocyanate (TDI) was supplied

by Shanghai Sanyou Chemical Reagent Co., Ltd. (Shanghai,

China). 3, 3-Dichloro-4, 4-diamino diphenyl methane

(MOCA, Chemtura, Shanghai, Co., Ltd.) was used as curing

agent. The PTMG, PEA, PCL and CO were dried under

vacuum at 100 C for 8 h before use.

Synthesis of PUs based on various polymer polyols

The synthetic method was developed as follows: the

isocyanate-terminated polyurethane prepolymer was pre-

pared by reacting polyols (PTMG, PEA, PCL, CO) and

TDI with continuous mechanical stirring for 2 h at about

70 C under dry nitrogen atmosphere [22]. The isocyanate

index (R, NCO/OH molar ratio) was 1.50 and 2.0, respec-

tively. Then the melt curing agent MOCA for the PU was

added and mechanical stirred uniformly. The mixture was

degassed under vacuum and poured into preheated Teflon

moulds. They were cured at 100 C for 12 h. In present

study, PTMG-based PU (PTMG-PU), PEA-based PU (PEA-PU), PCL-based PU (PEA-PU) and castor oil-based PU

(CO-PU) with the two isocyanate indices (1.5 and 2) were

prepared, respectively.

Characterization

Fourier transform infrared(FTIR) spectra were obtained on

a FTIR spectrometer (Bruker Instruments, Germany) in the

wave number range 4000500 cm1.

Tensile properties were studied on an Electron Omnipo-

tence Experiment Machine SANS-CMT5105 (Shenzhen

Sans Testing Machine Co., Ltd., China), according to GB/T1040.2/1A-2006 (ISO527-2/1A:1993) under ambient con-

dition. The sample (length 150 mm, preferred thickness

4 mm, gauge length 50 mm) was tested at the strain rate of

10 mm/min and five specimens were tested for each sample

compositions.

Scanning electron microscopy (SEM) imaging was

performed on a JSM-5600 (JEOL, Japan) operated at

20 kV. The samples were coated with gold before

observation.

Dynamic mechanical analysis(DMA) was carried out on

a DMA 242 C analyzer (NETZSCH Instruments, Germany)

with double-cantilever mode (3.2 cm1.0 cm) over a tem-

perature range from 100 C to 150 C at a heating rate of

3 C/min at 1, 10, 20, and 50 Hz, respectively.

Fig. 1 Chemical structures of the polymer polyols

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Thermogravimetric analysis (TGA) was performed on a

STA 449 C Jupiter Analyst (NETZSCH Instruments, Ger-

many), with a heating rate of 10 C/min from room temper-

ature to 750 C under a nitrogen atmosphere.

Results and discussion

FTIR analysis

Figure2shows the FTIR spectra of PTMG, TDI, PTMG-PU

prepolymer and cured PTMG-PU (NCO/OH molar ratio Ris

2). The absorption at about 1113 cm1

is the characteristic

absorption of aliphatic ether. An intense sharp absorption

band for the NCO group is observed at ca. 2270 cm1for the

isocyanate terminated PTMG-PU prepolymer. In addition,

the PU prepolymer spectrum show characteristic absorption

bands at 1734 and 3286 cm1 corresponding to the C0O

group of the urethane linkage and the NH stretching of

urethane amide. In the spectrum of cured PTMG-PU, thecharacteristic absorption band at ca. 2270 cm1 disappears,

which indicates that the PU prepolymer is cured completely

by MOCA. The spectra confirm the formation of PTMG-PU

prepolymer and the completely cured of PTMG-PU.

The other FTIR spectra of the PEA, PCL, CO and their

corresponding PU prepolymers we studied in this paper are

shown in Fig. 3. The characteristic absorption bands for

PEA-PU prepolymer are C0O group of the urethane linkage

(1737 cm1), N-H of urethane amide (3348 cm1) and

terminated NCO (2273 cm1). The characteristic absorp-

tion bands for PCL-PU prepolymer are C0O group of the

urethane linkage (1726 cm1), N-H of urethane amide

(3348 cm1) and terminated NCO (2273 cm1). The char-

acteristic absorption bands for CO-PU prepolymer are C0O

group of the urethane linkage (1709 cm1), N-H of urethane

amide (3294 cm1) and terminated NCO (2273 cm1). The

spectra confirmed the formation of PU prepolymer.

Tensile properties

Tensile properties of PU based on various polyols are shown

in Fig. 4(isocyanate index, R, is 2) and Fig. 5(R is 1.5).

WhenR is 2, PUs based on each polyols exhibit a relatively

high tensile strength (more than 30 MPa). The PTMG-PU,

PCL-PU and PEA-PU are linear PUs and thus show high

elongation at break compared to the cross-linked CO-PU.

Further, for the cross-linked networks exist in CO-PU, the

tensile strength of it is much higher than the others. WhenR

is 1.5, the tensile strength of each kind of PU decreases

compared to the PU when R is 2. Nevertheless, the elonga-

tion at break of PTMG-PU, PCL-PU and CO-PU increaseby 47 %, 16 % and 348 % compared to when theR of PU is

2, respectively.

Figure6 gives the stressstrain curves of the various PU

when R is 2. For the linear PU, we can see the stress is

increase with the increasing strain until the sample is break.

The rate of stress increases sharply and then slowly. And

Fig. 2 FTIR spectra of PTMG, TDI, PTMG-PU prepolymer and cured

PTMG-PU(R02)

Fig. 3 FTIR spectra of PEA, PCL, CO and their corresponding PU

prepolymers (R02)

Fig. 4 Tensile properties of PU based on various polyols withR is 2

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during the test, significant stress-whitening phenomena are

observed. Therefore, crystallizing induced during the tensile

testing in linear PU polymers. For the cross-linked CO-PU,

a type stressstrain curve of noncrystal polymer can be seen.

A yield point exists in the curve.The tensile properties of PU are dependent on the chem-

ical composition and content of the soft segment, and also

on the hard segment content [21]. Generally, PU has higher

tensile strength but lower elongation at break when the

content of hard segment is higher. For each kind of PU,

the hard segment content is higher and thus the tensile

strength is stronger when R is 2. In present study, the

different of chemical composition comes from the different

chemical structures of polyols (Fig. 1). For CO-PU, the

castor oil is a triol, cross-linked networks can be formed in

CO-PU [22]. Compared to linear PU, it exhibits higher

tensile strength but lower elongation. The PTMG-PU,PCL-PU and PEA-PU have same hard segment content for

the molecular weight of them is same. However, more

hydrogen bonding could be formed easier in polyester-PU

(PCL-PU and PEA-PU) compared to polyether-PU (PTMG-

PU) [23]. The polyester-PU has better tensile properties. It is

noticed that only the PEA-PU show relatively low tensile

strength and elongation when R is 1.5, which is not consis-

tent the discussion. The possible reason will be discussed in

SEM analysis.

SEM analysis of tensile fracture PUs

Figure7 shows the surface morphologies of tensile fracture

PUs based on various polyols. The fracture surface of

PTMG-PU (Fig. 7 A and a) presents a smooth, homoge-

neous microstructure and a little small ridges exist on the

fracture plane. However, the fracture surface of PEA-PU

shows a most heterogeneous microstructure. Large cracks

and many small substances similar to bulge exist in the

fracture plane especially when R is 1.5 (Fig. 7b). The

reasons may be that the hydrogen bonding is much stronger

than the other PU. Many rigid phases exist in it which

impaired the elasticity of the PEA-PU. Thus, it shows nota-ble lower tensile strength and lower elongation. The surface

morphologies of PCL-PU (Fig.7 C and c) are a little more

heterogeneous and much small ridges compared with the

morphologies of PTMG-PU. It could be attributed to the

hydrogen bonding in PCL-PU. That is why the tensile

strength of PCL-PU is a little higher whereas elongation at

break of PCL-PU is a little lower than the corresponding

property of PTMG-PU. The SEM of CO-PU shows ho-

mogeneous, glassy morphologies (Fig. 7 D and d) be-

cause of the cross-linked network structure. It is the

special structure determines the properties of high strength

and low elongation of it.

Dynamic mechanical analysis

The storage modulus (E) and loss modulus (E) are the

quantities of energy stored through elastic behavior and

energy lost through conversion to heat, respectively. The

loss tangent, tan , defined by the ratioE/E, is usually used

as a measure of the damping properties (dissipation of

vibration energy) of materials [24]. The glass transition

temperatures (Tg) were obtained as a large maximum in

the tan curves [25] and the temperature range with tan>

0.2 is taken to evaluate damping capacity called damping

temperature range in present study.

Figure 8 and 9 show DMA traces of PTMG-PU, PCL-

PU, PEA-PU and CO-PU at 10 Hz; the corresponding

characteristic data are given in Table1. It can be seen that

the glass transition temperatures (Tg) is increasing as the

sequence of PTMG-PU, PCL-PU, PEA-PU and CO-PU.

CO-PU is a three dimension cross-linked network structure.

The chain segments of it need more quantity of heat to

move. The Tg of CO-PU is as high as 60.6 C when R is

Fig. 5 Tensile properties of PU based on various polyols withR is 1.5

Fig. 6 Stressstrain curves of the various PU with R is 2

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Fig. 7 SEM micrographs of

tensile fractured surface of (A)

PTMG-PU, (B) PEA-PU, (C)

PCL-PU, (D) CO-PU whenR is

2; (a) PTMG-PU, (b) PEA-PU,

(c) PCL-PU, (d) CO-PU when

R is 1.5

Fig. 8 DMA traces of PTMG-PU and PCL-PU with different R at

10 Hz Fig. 9 DMA traces of PEA-PU and CO-PU with differentR at 10 Hz


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1.5 and 93.4 C when R is 2. And the damping temperature

range (tan >0.2) is approx 50 C. It can be used in damp-

ing polymer composites with polymers has higher (for ex-

ample epoxy resin [18]) or lowerTg to further broaden the

temperature range. PTMG-PU, PCL-PU and PEA-PU pres-

ent as elastic state in ambient temperature. TheTgof them is

lower than zero C. The Tg of PCL-PU and PEA-PU is

higher than PTMG-PU because of the affections of the

hydrogen bonding. The Tg range of them is between 50

and 12 C and the damping temperature range (Table1) is

relatively broad. The results show a good guidance to select

a kind of PU when prepare the PU-polymer composites for

given properties (either mechanical or damping properties).

In practical application, the influence of frequency must

be considered. Four test frequencies are applied to PEA-PU

(R02) are shown in Fig.10. TheTgof the PU becomes higher

and the damping temperature range becomes wider when the

higher frequency is applied. The reason for the Tgshift was

that at a fixed temperature, when the frequency was low

enough and 1/ ( delegates frequency)>>(chain segment;

the relaxing speed of chain segment from one equilibrium

position to another was expres sed with ), the polymer

showed high-elastic state. When the frequency was high

enough and 1/

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Conclusions

(1) The polyether diol-based PU (PTMG-PU), polyester

diol-based PU (PEA-PU and PCL-PU) and triol-based

PU (CO-PU) were synthesized and studied. When R is

2, PU based on each polyols exhibits a relatively high

tensile strength more than 30 MPa. The PTMG-PU,

PCL-PU and PEA-PU show high elongation at breakcompared to the cross-linked CO-PU. When R is 1.5,

the tensile strength of each kind of PU decreases com-

pared to R is 2. Nevertheless, the elongations at break

of PTMG-PU, PCL-PU and CO-PU increase by 47 %,

16 % and 348 %, respectively.

(2) The DMA analysis shows that theTg is increasing as

the sequence of PTMG-PU, PCL-PU, PEA-PU and

CO-PU. The Tg ranges of PTMG-PU, PCL-PU and

PEA-PU are between 50 and 12 C and the damping

temperature range is relatively broad. The Tgof CO-PU

is as high as 60.6 C whenRis 1.5 and 93.4 C when R

is 2. Its damping temperature range is approx 50 C.They can be used in damping polymer composites with

polymers which has lowe r or highe r Tg to further

broaden the temperature range. Further, the TG results

show the start degradation temperatures of them are

approx 260 C. These results show a good guidance to

select a kind of PU when prepare the PU-polymer

composites for given properties.

Acknowledgements The financial supports from the National Sci-

ence Foundation for Distinguished Young Scholars of China (Grant

No. 51025517), the Innovative Group Foundation of NSFC (Grant No.50721062), and the 973 Project of China (2007CB607606), the Na-

tional Defense Basic Scientific Research Project (A1320110011) are

duly acknowledged.

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