Non-Aromatic Polyimides Derived from Alicyclic Monomers - American

Chapter 23

Non-Aromatic Polyimides Derived from Alicyclic Monomers

Downloaded by YORK UNIV on September 20, 2016 | http://pubs.acs.org Publication Date: December 21, 2007 | doi: 10.1021/bk-2007-0978.ch023

Toshihiko Matsumoto, Risa Takahashi, Motoaki Kaise, and Shuichi Kawabata Center for Nano Science and Technology, Tokyo Polytechnic University, Atsugi, Kanagawa 243-0297, Japan

Nonaromatic polyimides were synthesized by the polycondensation of cyclopentane-1, 2, 3, 4-tetracarboxylic 1, 2; 3, 4-dianhydride (CpDA) and bicyclo[2. 2. 1 ]heptane2, 3, 5, 6-tetracarboxylic 2, 3; 5, 6-dianhydride (BHDA) with alicyclic diamines. The poly(amic acid)s had inherent viscosities (η ) in the range from 0. 1 to 0. 4, and they formed free-standing and flexible films after being cast then cured. The nonaromatic polyimide prepared from polyalicyclic monomers PI(BHDA+ BBH) had good thermal stability with no significant weight loss up to 350 °C, and the T5 is around 430 °C. The high-temperature stability can be explained by the introduction of a bicyclic structure. The nonaromatic polyimide films had the temperatures with a maximum rate of the decomposition in N in the range of 450-490 °C. Char yields at 545 °C of the nonaromatic polyimides were lower than those of semi-aromatic and aromatic polyimides. The nonaromatic polyimide films exhibited a cutoff around 230 nm, and they were transparent even in the near IR region. Optically estimated dielectric constant ε's of the polyimides were approximately 2. 6 and the polyimides possessed negligibly small birefringence below 10- . All the polyimide films exhibited broad dispersive peaks of diffraction around 16 °(2Θ) and they were insoluble in common organic solvents. The PI(BHDA+BBH) film had a tensile modulus of 2. 1 GPa and a tensile strength of 52 MPa. inh

2

4

© 2008 American Chemical Society

Celina and Assink; Polymer Durability and Radiation Effects ACS Symposium Series; American Chemical Society: Washington, DC, 2007.

277

278


Introduction Nonaromatic polyimides are derived from aliphatic dianhydrides and aliphatic diamines, and only a few papers have been reported on these polyimides. Pioneer research was done in 1962 by Wu using bicycle[2. 2. 2]oct7-ene-2, 3, 5, 6-tetracarboxylic 2: 3, 5: 6-dianhydride derivatives and aliphatic diamines having a straight chain. fl] Volksen et al. reported the synthesis of a nonaromatic polyimide from cyclobutane-1, 2, 3, 4-tetracarboxylic dianhydride (CBDA) and l , l-bis(4-aminocyclohexyl)methane and investigated the optical properties such as the light transmittance and the refractive index. [2] They also pointed out that nonaromatic diamines formed salts during the initial stages of the polymerization, involving pendant carboxylic acid groups from the amic acid moieties along with unreacted amino-fiinctionalities and that in the case of insoluble quaternaized oligomers, only low molecular weights would predominate. Recently, Ueda et al. synthesized the nonaromatic polyimides by the polymerization of Af-trimethylsilylated alicyclic diamines with CBDA. [3, 4] In the present article, the synthesis and the properties of nonaromatic polyimides derived from alicyclic monomers will be described.

Experimental Materials Cyclopentane-1,2,3,4-tetracarboxylic 1,2;3,4-dianhydride (CpDA) was prepared from c/5,c«,c«,c«-l,2,3,4-cyclopentanetetracarboxylic acid by thermal dehydration reaction then sublimation at 170-190 °C. Bicyclo[2.2.1]heptane2,3,5,6-tetracarboxylic 2,3;5,6-dianhydride (BHDA) was synthesized according to the previous paper.[5] Bis(aminomethyl)bicyclo[2.2.1]heptane (BBH) was donated by Mitsui Chemical Co. Ltd, and used without further purification. BBH consists of four isomers; 2-exo,5-exo- (30 wt %), 2-endo,5-exo- (35 wt %), 2-exo,6-exo- (20 wt %), 2-endo,6-exo- (15 wt %). 4,4 -Methylenebis(2methylcyclohexylamine) (MCHM) and hexamethylphosphoramide (HMPA) were purchased from Aldrich Chemical Co Inc and Tokyo Kasei Kogyo Co. Ltd, respectively, and used as received. ,

General Procedure for Polymerization and Film Preparation Poly(amic acid)s were prepared by the polycondensations of dianhydrides (4 mmol) with alicyclic diamines (4 mmol) in HMPA (20 wt-% solid content) at room temperature for two days. An aliquot of the polymerization solution was


279 cast on a glass plate and the plate was heated in vacuum. The temperature was elevated from room temperature to 250 °C at a heating rate of 2 Κ min* , and then kept for 1 hour. After curing, the glass plate was immersed into boiling water to facilitate removal of thefree-standingpolyimide film. 1

Measurements Thermal analyses were carried out using a Seiko SSC 5200-TG/DTA 220 instrument at a heating rate of 10 Κ min" in a nitrogen atmosphere for the thermogravimetric analysis (TGA). Thermomechanical analyses (TMA) were made using a Seiko Instruments TMA/SS equipped with a penetration probe of 1.0 mm diameter and using an applied constant load of 10 g (stress, 0.125 MPa) at a heating rate of 10 Κ min' in air. Infrared spectra were recorded using a JASCO FT/IR-460 plus Fourier transform infrared spectrometer. Transmission and reflection UV-Vis-NIR spectra were measured using a JASCO V-570 UV/Vis/NIR spectrophotometer with a SLM-468 reflection unit. Refractive index of a polyimide film at 589 nm was recorded on an ATAGO Abbe refractometer at room temperature. The birefringence of sample films was evaluated by means of ellipsometry. The mechanical properties were examined at room temperature in air using a specially made machine at a drawing rate of 1 mm/min; the sample size (film) was 10-mm length, 10-mm width, and about 20μιη thick. The wide-angle X-ray diffraction measurements (WAXD) were performed on a Rigaku Rint 2500 X-ray diffractometer with graphite monochromated Cu Κα radiation and a 12 kW (40 kV, 300 mA) rotating anode generator. The film thickness was measured using a G-6 dial gauge (Ozaki Mfg. Co. Ltd). Inherent viscosities (r| ) were measured with an Ostwald viscometer in a 0.5 g dl' HMPA solution of poly(amic acid) at 30 °C.


1

1

inh

1

Results and Discussions Monomer and Polymer Synthesis The cyclopentane-type dianhydride CpDA was synthesized by thermal dehydration of cw,cw,cw,c/5-l,2,3,4-cyclopentanetetracarboxylic acid at 170190 °C. The norbornane-type dianhydride BHDA was prepared from endonadic acid via three steps.[5] The H-NMR spectrum revealed that BHDA consisted of the two isomers, bicyclo[2.2.1]heptane-2-e«rfo,3-e«i/o,5-ejco,6-ejcotetracarboxylic dianhydride and the M-exo derivative. The ratio was estimated to be 1:1 from the spectrum. The structures and abbreviations of alicyclic monomers are illustrated in Figure 1. !


280 The polyimides were prepared ο ο -nh according to the previous report. [6] ο Poly(amic acid)s were obtained by reacting BHDA or CpDA with CpDA MCHM and BBH in HMPA at room temperature for 2 days under a nitrogen atmosphere. Although in ^Çff' MCHM \ Ο Ο the initial stage of the BHDA polymerization a solid appeared, the solid was gradually dissolved and Figure 1. The structures and the mixture yielded a clear solution. abbreviations of alicyclic monomers. The resultant viscous poly(amic acid) solutions were cast on glass plates, and the poly(amic acid)s were transformed into the corresponding polyimides by curing the plates. Inherent viscosities (r) ) of the poly(amic acid)s were as low as 0.08-0.23, however, they formed flexible and tough films. In the IR spectra of nonaromatic polyimides, characteristic imide absorptions at 1767 cm" (asym C=0 str.) and 1699-1703 cm" (sym C=0 str.) were observed, and the absorptions of amic acid groups have practically disappeared. 2


0

0

Β

Β

Η

inh

1

1

Properties of Polymers The transmission and reflection UV-Vis-NIR spectra of the free-standing films are shown in Figure 2 together with that of a Kapton®-type polyimide PI(PMDA+DDE) which was prepared from pyromellitic dianhydride and 4,4'diaminodiphenyl ether in our laboratory. The nonaromatic polyimide films exhibit cutoffs in the range of 226-238 nm, and are transparent even in the near IR region. A cutoff wavelength is defined here as a point where the transmittance becomes below 1 % in the spectrum. The aromatic polyimide PI(PMDA+DDE) absorbs visible light due to the charge transfer, and the cutoff wavelength is 412 nm. In the reflection UV-Vis-NIR spectra of polyimide films, the reflectance of nonaromatic polyimides is smaller than that of an aromatic one. Film refractive index η was determined using an Abbe refractometer at room temperature. The dielectric constant ε of the material at afrequencynear 1 MHz is evaluated roughly from the refractive index to be ε =1.1 η . [7] These results are listed in Table 1. Optically estimated s's of the nonaromatic polyimides were approximately 2.6, whereas those of semi-aromatic and aromatic polyimides were around 2.8 and 3.1, respectively.[6] The birefringence An (optical anisotropy) of sample films was evaluated by means of ellipsometry. All the nonaromatic polyimides examined in this study possessed small birefringence below 10" . The thermal properties of the polyimide film were evaluated by the 5 % weight loss (T5), 10 % weight loss (T10), the decomposition temperatures 2

4


281

1 : M(BHDA+MCHM) 2 : PI(BHDA+BBH)


3 : ΡΙ(€ρΟΑ*ϋ€Ηϋ) 4 : ΡΙ(ΡϋΟΑ*ΰΟΕ)

200

700

1200

1700

2200

Wavelength (nm)

Figure 2. Transmission and reflection UV- Vis-NIR spectra of the free-standing polyimide films.

(Tdec), the temperatures for maximum degradation rate (Tmax), and char yield at 545 °C (CY) measured using the thermogravimetric analyses (TGA), and by the Tg measured using a thermomechanical analyzer (TMA) with a penetration probe. Tdec is noted as the point where the extrapolations of the two slopes in the TGA curve intersect. The Tg was measured using a thermomechanical analyzer (TMA) with a penetration probe. The TGA profiles of the polyimide films measured in nitrogen atmosphere with a heating rate of 10 Κ min* are shown in Figure 3. The nonaromatic polyimide prepared from polyalicyclic monomers PI(BHDA+BBH) has good thermal stability with no significant weight loss up to 350 °C, and the T5 is around 430 °C. The high-temperature stability can be explained by the introduction of a bicyclic structure, which would foster less probability of main chain scission because of the presence of multiple main-chain bonds in the cyclic units. The degradation of polymers in an inert atmosphere is caused by homolytic C-C bond scission. If the polymer backbone consists of a singlechain like that of poly(ethylene), the scission results in direct decreasing of the molecular weight. In most cases, volatile compounds are produced and released as a decomposed gas. On the other hand, in the case of step-ladder type polymers bearing double strands like the alicyclic polyimides, even if the C-C bond scission occurs, it does not lead to a significant decrease in the molecular 1


282 Table 1. Synthesis and the properties of nonaromatic polyimide films." r,

b

polyimide

film quality

film thickness

Xcut-off

(Mm)

(nm) 226

1

(dig ) PI(BHDA+MCHM)

0.23

flexible

20

PI(BHDA+BBH)

0.13

flexible

13 15

PI(CpDA+MCHM) 8

b

c


d

e

0.08

flexible

c

An* 2.55

Non-Aromatic Polyimides Derived from Alicyclic Monomers - American

Recommend Documents