Polyimide Membranes Modified by Polyhedral Oligomeric Silsesquioxane

doi:10.7503/cjcu20130812

Abstract

Abstract:

Four kinds of polyimide(PI)/Si membranes were prepared using PI with octaphenylsilsesquioxane(OPS), octa(aminophenyl)silsesquioxane(OAPS), polyphenylsilsesquioxane(PPSQ) of ladder structure, and nano-silica(SiO₂), respectively. Their morphologies were studied by scan electron miscroscope(SEM) and the mechanical properties were measured by tensile testing and the thermal properties were studied by differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and limited oxygen index(LOI). The SEM and XRD results of the PI/Si composites proved that there were good compatibility between PI and OAPS because the aminophenyl groups in OAPS could participate in the polymerization process of PI. The mechanical properties of PI/OAPS membrane were nearly the same with that of PI. And the addition of OPS or PPSQ decreased the PI mechanical properties sharply. DSC analysis implied that the additives could increase the glass-transition temperature(T_g) a little and the T_g of PI/OAPS was the highest because the Si—O caged structures existed in the PI main chain. The addition of OAPS, PPSQ or SiO₂ would improve the thermal stability a little according to the TGA results. One interesting result is that the LOI of PI/Si membranes significantly increased compared with pure PI membrane. The LOI for PI/OPS membrane was 57%, while that for PI was 46.5% only. The improvement was caused by the formation of a well covered silicate char structures after burning. And the LOI of the membranes of PI with polyhedral oligomeric silsesquioxanes are higher than PI/SiO₂.

Key words: Polyimide, Polyphenylsilsesquioxane, Octa(aminophenyl)silsesquioxane, Nano-silica, Thermal property, Flame retardancy

CLC Number:

O633.21

TrendMD:

FAN Haibo, YANG Rongjie. Polyimide Membranes Modified by Polyhedral Oligomeric Silsesquioxane[J]. Chem. J. Chinese Universities, 2014, 35(1): 180.

Figures/Tables 11

Table 1 Compositions of PI/Si composites*

Material	m(BTDA)/g	m(ODA)/g	m(Additives)/g	Material	m(BTDA)/g	m(ODA)/g	m(Additives)/g
PI	6.168	3.832	0	PI/OPS	6.016	3.739	0.245
PI/OAPS	6.117	3.610	0.273	PI/PPSQ	6.016	3.739	0.245
PI/SiO₂	6.097	3.789	0.114

Scheme 1 Structures of OPS, OAPS and PPSQ

Fig.1 SEM images PI/Si composites(A) PI; (B) PI/OAPS; (C) PI/PPSQ; (D) PI/POS; (E) PI/SiO2.

Fig.2 XRD patterns of PI/Si compositesa. PI; b. PI/OAPS; c. PI/OPS; d. PI/PPSQ.

Table 2 Mechanical properties of the composite PI/Si membranes

Sample	Strength/MPa	Strain at yield(%)	Young’s modulus/GPa
PI	107.1±4.8	5.9±0.2	2.6±0.1
PI/OAPS	107.9±4.0	5.7±0.2	2.7±0.1
PI/SiO₂	110.5±3.3	6.2±0.3	2.7±0.1
PI/OPS	80.6±4.5	3.1±0.2	2.2±0.1
PI/PPSQ	73.2±3.6	2.4±0.3	2.6±0.1

Table 3 TGA and DSC data of the composite PI/Si membranes

Sample	T_g /℃	T_onset/℃	T_max/℃	Residues at 800 ℃(%)
PI	281	547	590	61.5
PI/OAPS	286	538	592	63.0
PI/SiO₂	284	548	590	62.2
PI/OPS	285	496	590	57.7
PI/PPSQ	284	545	594	62.4

Fig.3 TGA curves of the composite PI/Si membranes(A) PI, PI/OAPS, PI/SiO2; (B) PI, PI/OPS, PI/PPSQ, OPS, PPSQ. Inset of (B): TGA curves of PI, OPS and PPSQ.

Fig. 4 LOI of composite PI/Si membranesa. PI; b. PI/OAPS; c. PI/SiO2; d. PI/OPS; e. PI/PPSQ.

Fig.5 Photographs of the char residues after the tests of LOI

Fig.6 SEM images of the char residues of the extinguishing composite PI/Si membranes(A) PI; (B) PI/OAPS; (C) PI/SiO2; (D) PI/PPSQ; (E) PI/OPS.Inset of (A): Picture of the char residues of the extinguishing PI membranes.

Fig.7 Photographs of the char residue surfaces of PI(A), PI/OAPS(B) and PI/PPSQ(C)

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