Polyurethane-imide elastomers (PUIEs) are formed from isocyanate, polyol, acid anhydride, and diamine by liquid polymerization. Unfortunately, many of the diamines have rarely been applied to the formation of PUIEs. Hence, investigating the effect of diamines on PUIEs remains a challenge in polymer chemistry. Herein, PUIEs prepared from 4,4 ' -diphenylmethane diisocyanate (MDI), polytetramethylene glycol (Mw: 1000), pyromellitic dianhydride, and aromatic diamines (such as p-phenylene diamine, 4,4 ' -oxydianiline, and 1,3-bis(4-aminophenoxy)benzene), and aliphatic diamines (such as 1,2-ethylene diamine, 1,6-hexamethylene diamine, and 1,12-dodecamethylene diamine) were synthesized by liquid polymerization. The morphologies and the chemical, thermal, and mechanical properties of the various PUIEs were investigated. The obtained elastomeric sheets were characterized in terms of the following tests and methods: solubility and swelling tests, X-ray diffraction and differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis, tensile tests, nuclear magnetic resonance spectroscopy, infrared spectroscopy, atomic force microscopy, contact angle microscopy, and scanning electron microscopy
Polyurethane (PU) is easily synthesized from isocyanates and polyols by the polyaddition reaction. Hence, PU has been widely used in a variety of applications in many different fields. PU can be synthesized with customized specifications for rubber elasticity, abrasion resistance, and adhesion. In general, PU has a basic problem in terms of heat resistance. However, by improving this fundamental property, PU may gain some industrial advantages. Therefore, chemists have actively conducted multiple studies on the heat resistance of PU. Polyurethane-imide (PUI), which has stability in high-temperature environments, excellent electrical and mechanical properties, and good chemical resistance, is prepared via an organic-organic hybrid between urethane and imide [
Polytetramethylene glycol (Mw: 1000) (PTMG1000) was supplied by Invista Industry, Texas, USA. PTMG1000 was dehydrated in vacuo at 80˚C for 24 h before use. 4,4'-Diphenylmethane diisocyanate (MDI) was supplied by Tosoh Industry, Tokyo, Japan. MDI was purified by distillation under reduced pressure (267 - 400 Pa) at 135˚C before use. Pyromellitic dianhydride (PMDA) was purchased from Nacalai Tesque, Inc., Kyoto, Japan (Nacalai), and used without further purification. The following compounds were purchased from Tokyo Chemical Industry (TCI), Tokyo, Japan: ethylene diamine (EDA); 4,4'-oxydianiline (ODA); 1,3-bis(4-aminophenoxy)benzene (BAPB); and 1,12-dodecame-thylene diamine (DMDA). EDA was purified by distillation (trap to trap) under reduced pressure (267 - 400 Pa) before use. p-Phenylene diamine (PPDA) and 1,6-hexamethylene diamine (HMDA) were purchased from Kanto Chemical, Tokyo, Japan. PPDA was recrystallized from toluene before use. Tetrahydrofuran (THF) and benzene were purchased from Nacalai and distilled over calcium hydride in an Ar atmosphere. N,N-Dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) were purchased from Nacalai and stored over 4 Å molecular sieves before use. The following compounds were purchased from commercial suppliers and used as received: hexane (Nacalai), and acetone (Nacalai). N-methyl-2-pyrrolidone (NMP) (Nacalai) was kept over a 4 Å molecular sieve. Methanol was supplied by Toyota Kagaku Kogyo Co. Ltd., Toyota, Japan.
Scheme 1 shows the procedure for PUIE preparation. The PUIE compositions are listed in
NMR spectra were recorded on a Bruker (Massachusetts, USA) AVANCE III HD 400 (13C, 75.4 MHz) NMR spectrometer using the 13C CP/MAS method.
Scheme 1. Synthesis of polyurethane-imide elastomers by the solution method.
Sample | MDIa (×10−3 mol) | PTMG1000b (×10−3 mol) | Diaminec (×10−3 mol) | PMDAd (×10−3 mol) |
---|---|---|---|---|
PUIE-AL1 | 4.71 | 2.50 | 2.25 | 4.50 |
PUIE-AL2 | 4.60 | 2.50 | 2.08 | 4.20 |
PUIE-AL3 | 4.40 | 2.50 | 1.90 | 3.80 |
PUIE-AR1 | 4.64 | 2.50 | 2.11 | 4.23 |
PUIE-AR2 | 4.40 | 2.50 | 1.90 | 3.80 |
PUIE-AR3 | 4.24 | 2.50 | 1.72 | 3.42 |
aMDI: Mw = 250.25; bPTMG1000: Mw = 1000; cDiamines: AL1 = ethylene diamine (EDA) Mw = 60.1, AL2 = 1,6-hexamethylene diamine (HMDA), Mw = 116.21, AL3 = 1,12-dodecamethylene diamine (DMDA) Mw = 200.37, AR1 = p-phenylene diamine (PPDA), Mw = 108.14, AR2 = 4,4'-oxydianiline (ODA) Mw = 200.24, AR3 = 1,3-bis(4-amino-phenoxy)benzene (BAPB) Mw = 292.34; dPMDA: Mw = 218.12.
13C NMR spectra of the PUIEs were measured using the solid-state method. The 13C CP/MAS NMR spectrum of PUIE-AR2 is shown in
FTIR spectra were recorded on a JASCO (Tokyo, Japan) FTIR-5300 spectrometer equipped with an attenuated total reflection (ATR) system, which used an ATR500/M with ATR prism KRS-5.
XRD patterns were measured from 5˚ to 50˚ (2θ value) with Cu K (conditions: λ = 0.154 nm, 40 kV, 100 mA) on a Rigaku (Tokyo, Japan) RINT 2500 V/PC.
Scanning Electron Microscopy (SEM) was used to observe the surface morphology of PUIEs using a JEOL (Tokyo, Japan) JSM-6335 FM. All micrographs were taken at a magnification of 30 k×.
Atomic force microscopy (AFM) measurements were performed on dried sheets at room temperature in air using an OLYMPUS (Tokyo, Japan) NV2000. Most of the images were obtained in tapping-mode (ACAFM) with a silicon nitride cantilever (OMMCL-AC 240TS-C2; Olympus optical) using a spring constant of 15 N/m and a resonating frequency of 20 KHz. The scanning rates varied from 1 to 2 Hz. All images presented here were reproduced from images obtained for at least three points on each sample surface.
Contact angle (CA) measurements were performed on dried sheets at room temperature (23˚C ± 2˚C) in air using an Excimer Inc. (Yokohama, Japan) Simage Standard 100 instrument. Samples were dripped of 5 μL.
Swelling tests were performed using 0.1000 g test pieces. The degree of swelling (Rs) was calculated using the formula Rs (%) = W' − W/W × 100, where W' is the weight of the test piece soaked in benzene for 24 h and W is the weight of the test piece after drying at 30˚C for 24 h in vacuo.
Solubility tests were performed using 0.1000 g test pieces. Each test piece was soaked in a solvent (methanol, benzene, hexane, acetone, THF, DMF, DMSO, or NMP; 30.0 mL) at room temperature for 24 h.
Hardness tests were performed using a KOUBUNSHI KEIKI (Kyoto, Japan) Asker durometer (type A durometer (shore A)) with test pieces stacked to achieve a thickness of 6 mm.
Tensile tests were performed on an ORIENTEC (Tokyo, Japan) RTC-1225A Universal Tensile Testing Instruments equipped with model-U-4300 extensometer using a JIS K 6251-3-dumbbell as the standard sample and a crosshead speed of 100 mm/min.
Differential scanning calorimetry (DSC) measurements were performed on a Rigaku (Tokyo, Japan) Thermo-Plus DSC-8230 instrument at 10˚C/min from −120˚C to 200˚C under an Ar atmosphere. Approximately 5.0 mg of each PUIE was weighed and sealed in an aluminum pan. The samples were rapidly cooled to −120˚C and then heated to 200˚C at 10˚C/min.
Dynamic mechanical analyses (DMA) were performed on a Seiko Instruments (Chiba, Japan) DMS 6100 instrument at 5˚C/min from −100˚C to 300˚C at 20 Hz under an N2 atmosphere.
Thermogravimetric analyses (TGA) were performed on a Seiko Instruments TG/DTA6200 instrument (Chiba, Japan) at a heating rate of 10˚C/min from 30˚C to 500˚C under an N2 atmosphere.
13C NMR spectra of the PUIEs were measured using the solid-state method. The 13C CP/MAS NMR spectrum of PUIE-AR2 is shown in
The FTIR spectra (ATR method) of the PUIEs are shown in
The XRD patterns of the PUIEs are illustrated in
aromatic diamines, were observed at around 20˚. However, broad diffraction peaks of the PUIEs with aliphatic diamines (PUIE-AL2 and PUIE-AL3) were not observed.
Generally speaking, molecular angles are smaller on smooth surfaces than on rough surfaces. In order to understand the distinction between the PUIEs with
various diamine components, it was necessary to observe and investigate the surface wettability of the PUIE sheets. The contact angles of water on the surface of PUIE sheets were measured at room temperature and atmospheric pressure.
The surface topographies of the PUIEs were examined by AFM (
SEM micrographs of the PUIE surfaces are depicted in
long-molecular-length diamine-containing PUIEs. This may be caused by the increase in compatibility between the hard segments and soft segments. These phase separations are quite different from that of PU. The hard domains are considered to correspond to the imide portions and are in agreement with the AFM results.
The solvent resistances of PUIEs were tested by immersing each of the PUIE sheets in various solvents, such as benzene, hexane, THF, acetone, methanol, DMF, DMSO, and NMP. The results are presented in
Sample | Benzene | Hexane | THF | Acetone | Methanol | DMF | DMSO | NMP |
---|---|---|---|---|---|---|---|---|
PUIE-AL1 | × | × | × | × | × | × | × | ○ |
PUIE-AL2 | × | × | × | × | × | × | × | △ |
PUIE-AL3 | × | × | × | × | × | × | × | △ |
PUIE-AR1 | × | × | × | × | × | × | × | △ |
PUIE-AR2 | × | × | × | × | × | × | × | △ |
PUIE-AR3 | × | × | × | × | × | × | × | × |
○: completely dissolved; △: slightly dissolved; ×: undissolved; aMeasurement conditions: benzene, hexane, acetone, THF, NMP, methanol, DMF, or DMSO as the solvent at room temperature (23˚C ± 2˚C).
PUIE-AR2 dissolved slightly. PUIE-AR3 did not dissolve in NMP at room temperature.
The swelling test results are summarized in
The hardness results of the PUIE sheets with different hard segment contents are also summarized in
Sample | Hardnessa (Shore A) | Swelling rateb (%) | Tgc (˚C) | T5d (˚C) | T50d (˚C) |
---|---|---|---|---|---|
PUIE-AL1 | 75 | 164 | −45 | 351 | 431 |
PUIE-AL2 | 76 | 166 | −50 | 350 | 433 |
PUIE-AL3 | 76 | 165 | −45 | 356 | 435 |
PUIE-AR1 | 76 | 157 | −38 | 345 | 435 |
PUIE-AR2 | 81 | 154 | −57 | 351 | 437 |
PUIE-AR3 | 84 | 146 | −49 | 344 | 436 |
aMeasurement conditions: shore A type, total thickness = 6 mm, room temperature (23˚C ± 2˚C). bMeasurement conditions: benzene solvent at room temperature (23˚C ± 2˚C) for 24 h. cDSC was performed at a heating rate of 10˚C/min from −100˚C to 300˚C under an Ar atmosphere. dTGA was performed at a heating rate of 10˚C/min from 30˚C to 500˚C under an N2 atmosphere.
Samplea | σ10 (MPa) | σ50 (MPa) | σ100 (MPa) | σ200 (MPa) | σ300 (MPa) | σ400 (MPa) | σb (MPa) | Ebc (%) |
---|---|---|---|---|---|---|---|---|
PUIE-AL1 | 3.51 | 9.30 | 12.9 | 24.6 | 42.3 | - | 56.2 | 380 |
PUIE-AL2 | 3.52 | 7.46 | 10.0 | 17.4 | 35.9 | 68.0 | 63.9 | 406 |
PUIE-AL3 | 4.12 | 8.11 | 10.4 | 16.0 | 28.8 | 55.9 | 66.7 | 449 |
PUIE-AR1 | 5.13 | 11.9 | 16.0 | 27.5 | 46.3 | - | 51.7 | 336 |
PUIE-AR2 | 7.04 | 10.0 | 12.9 | 20.5 | 35.3 | 53.0 | 54.6 | 413 |
PUIE-AR3 | 5.01 | 9.61 | 12.8 | 23.3 | 38.8 | 63.1 | 68.8 | 416 |
aTensile properties measured at room temperature (23˚C ± 2˚C) with a strain speed of 100 mm/min. bTensile strength at breaking point. cElongation at breaking point.
the series of PUIE sheets with aliphatic diamine attained even better mechanical properties than PUIE sheets with aromatic diamines, except for the case of PUIE-AR3. These results suggest that PUIEs with aliphatic diamines have well-ordered and very strong intermolecular hydrogen bonding, whereas PUIEs with aromatic diamines do not allow this. Moreover, the tensile strengths and elongation at break values of PUIEs with aliphatic diamines increased as the molecular length of the diamine increased. The tensile strength of PUIE-AR3 shows the strongest value (68.8 MPa) in this series of PUIEs. PUIE-AR3 was considered to have better well-ordered packing and stronger intermolecular hydrogen bonding.
DSC analyses for the composites were performed over −120˚C to 200˚C under Ar atmosphere. From the data in
The results of DMA analyses for the composites are shown in
The TGA curves of the PUIEs in
A series of PUIEs with various diamines were synthesized. The influences of diamine on the chemical, mechanical, and thermal properties, and the surface morphology of the PUIEs were investigated through DSC, DMA, TGA, CA, AFM, SEM, and XRD. The results prove the existence of diamines in the molecular structure, and the diamines contribute to their morphologies and chemical and physical properties. However, the degree of phase separation is not proportional to the properties of the PUIEs. In addition, the mechanical properties demonstrate that the PUIEs were elastic. Moreover, the moduli of the PUIEs with aliphatic and aromatic diamines increased as the molecular length of the diamine increased. The moduli of PUIEs with DMDA and BAPB are especially high. The cohesive forces between imide segments of PUIEs with aromatic diamines are stronger in comparison with PUIEs with aliphatic diamines. The dynamic, mechanical, and thermal properties suggested that networks between the imide and the urethane segments occurred uniformly in the composites. The properties of the PUIEs had a great influence on the molecular strength or mobility of the diamine contents in the network. However, TGA analyses of PUIEs with various diamines did not show any diamine content dependence.
We found that the cohesive forces of the imide segments, which are formed from diamine and pyromellitic dianhydride, had a great influence on the properties of the PUIEs.
The authors are grateful to the ceramic laboratory of AIT for providing access to the X-ray instruments, to Mr. YuzoIshigaki for NMR spectroscopy measurements, and to Mr. Tomohiro Nishio for the dynamic mechanical analysis.
Ueda, T., Nishio, T. and Inoue, S. (2017) Influences of Diamines on the Morphologies and the Chemical, Thermal, and Mechanical Properties of Polyurethane-Imide Elastomers. Open Journal of Organic Polymer Materials, 7, 47-60. https://doi.org/10.4236/ojopm.2017.74004