摘 要

本研究利用一具長鏈狀脂肪族一級烷基胺鹽(alkylammonium)來進行蒙脫土(montmorillonite)的有機改質化，並使用此有機黏土(organoclay)加入聚醯亞胺(polyimide)中來製備聚醯亞胺/黏土奈米複合材料(polyimide/clay nanocomposites)。在本論文中，我們提出了數種製備方法以求得剝離型(exfoliated)奈米複合材料。這些方法包括有同時混合法(one-step method, O )、依序加入法(two-step method, T)及原位聚合法(in-situ polymerization, I)。同時，我們也針對聚醯亞胺的結構及有機黏土的含量對奈米複合材料的形成所造成的影響做一說明，並使用傅立葉轉換紅外線光譜儀(FTIR)及X-ray繞射儀(XRD)分別鑑定聚醯亞胺的結構及有機黏土的層間距離(basal spacing)及分散性，熱重分析儀(TGA)鑑定材料的熱穩定性。
由TGA及XRD的結果，我們可證實烷基胺鹽確實有將黏土層間的鈉離子製換出來並順利插層進入層間(gallery)。由XRD的結果，我們也可發現當黏土含量在3 wt %時由依序加入法所製備出的聚醯亞胺BPDA-ODA/黏土奈米複合材料有著最佳的黏土分散性。由TGA的測試，此奈米複合材相較於聚醯亞胺BPDA-ODA，在10 %重量損失時的溫度提升了31℃。我們也利用XRD針對界面活性劑及溶劑(DMAc)在奈米複合材的形成機制中所扮演的角色做一詳細說明，並證實在醯亞胺化(imidization)的過程中，界面活性劑的裂解及溶劑的蒸發都對黏土的分散性有著絕對的影響。

Abstract

Organically modified montmorillonite by a long chain alkylammonium surfactant was used to prepare polyimide/clay nanocomposites in this study. Several attempts were made in an effort to achieve fully exfoliated nanocomposites. These included the one-step method, two-step method and in-situ polymerization method. At the same time, the effects of polyimide structures and clay contents were studied. Two dianhydrides and two diamines were used to prepare polyimide/clay nanocomposites via the two-step method. The polyimide/clay nanocomposites with various clay contents from 1.5 ~ 10 wt % were prepared via the two-step method too. The structure of polyimides and the dispersion level of clay were identified by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Thermogravimetric analysis (TGA) was performed to demonstrate the thermal stability of the nanocomposites.
TGA and XRD results indicate the surfactants are intercalated into the layers of clay. FTIR results indicate the all polyimides in the nanocomposites are formed successfully. XRD results indicate the BPDA-ODA/clay nanocomposite within 3 % by weight of clay via the two-step method is shown to have the best dispersion level of clay. These results are consistent with observations from TGA. The temperature at 10 % by weight loss of the nanocomposite is 31 ℃ greater than that of pure BPDA-ODA. The formation mechanism of polyimide/clay nanocomposites via the two-step method can be described by three distinct steps. A polyamic acid/clay mixture with an exfoliated morphology is first formed. A portion of solvents and intercalated surfactants are then either degraded or expelled from the clay gallery under thermal imidization, resulting in a reduced gallery height of 1.32 nm. On the other hand, portion of the clay layers show an exfoliated morphology due to the effective surfactant and polyimide molecules. As a result, a partially exfoliated polyimide/clay nanocomposite is obtained.

Table of Contents

Acknowledgments
Abstract i
Abstract (in Chinese) ii
Table of Contents iii
List of Tables v
List of Figures vi

Chapter 1. Introduction 1
1.1 Polyimides 1
1.2 Clays 3
1.3 Polymer/clay Nanocomposites 5
1.4 Polyimide/clay Nanocomposites 10
Chapter 2. Experimental 12
2.1 Materials 12
2.2 Instruments 12
2.3 Samples Preparation 15
2.3.1 Preparation of Organoclay 15
2.3.2 Synthesis of Polyimides 17
2.3.3 Synthesis of Polyimide/clay Nanocomposites 17
Chapter 3. Results and Discussion 25
3.1 Characterization of Organoclay 25
3.2 Characterization of Polyimide 33
3.3 Preparation of Polyimide/clay Nanocomposites Via Different
Synthesis Methods 37
3.4 Preparation of Polyimide/clay Nanocomposites With Different
Chemical Structure in Polyimides 48
3.5 Preparation of Polyimide/clay Nanocomposites With Different
Clay Contents 56
3.6 Formation Mechanism of Polyimide/clay Nanocomposites 62
Chapter 4. Conclusion 66
Chapter 5. Suggestions and Future work 69
References 75
Appendixes 70
Appendix 1. XRD pattern of Na+-montmorillonite (JCPDS 12-204).

Appendix 2. XRD patterns of MONT/DMAc solution (M) with
different thermal process (a) 2~40º (b) 2~10º.

Appendix 3. XRD patterns of BPDA-ODA/3%MONT nanocomposite
(T) with different heating process (a) 2~40º (b) 2~10º.

Appendix 4. XRD patterns of BPDA-ODA/3%OC nanocomposite
(O) with different heating process (a) 2~40º (b) 2~10º.

Appendix 5. XRD patterns of BPDA-ODA/3%OC nanocomposite
(I) with different heating process (a) 2~40º.




List of Tables

Table 1. Codes and chemical structures of materials used in this study.14

Table 2. Codes of synthesis methods 19

Table 3. Illustration of the cation exchange ratio with organoclay 29

Table 4. Thermal stability of polyimides 36

Table 5. Thermal stability of polyimide and polyimide/clay
nanocomposites via different synthesis methods 42

Table 6. Thermal stability of polyimide and polyimide/clay
nanocomposites with different chemical structures 51

Table 7. Thermal stability of polyimide and polyimide/clay
nanocomposites with different clay contents 60










List of Figures

Figure 1. Synthesis of polyimide 2

Figure 2. The structure of 2:1 layered silicates 4

Figure 3. Orientations of alkylammonium ions in the galleries of
layered silicates with different layer charge densities 6

Figure 4. Alkyl chain aggregation models (a) short alkyl chains
(b) intermediate chain lengths (c) longer chain length 7

Figure 5. Scheme of different types of composite arising from the interaction of layered silicates and polymers (a) phase-
separated microcomposite (b) intercalated nanocomposite
(c) exfoliated nanocomposites 9

Figure 6. Conformation and estimated molecular dimensions of
Surfactant (C12Cl) 13

Figure 7. Synthesis of organoclay/DMAc suspension solution 16

Figure 8. Synthesis of polyimide thin films 18

Figure 9. Flow chart of one-step method to synthesize the
polyimide/claynanocomposite 20

Figure 10. Flow chart of two-step method to synthesize the
polyimide/clay nanocomposite 22

Figure 11. Flow chart of in-situ polymerization to synthesize the polyimide/clay nanocomposite 24

Figure 12. (a) OC (b) OC /DMAc suspension solution 26

Figure 13. TGA curves of montmorillonite (MONT)、organoclay (OC)
and surfactant (C12Cl) 27

Figure 14. XRD patterns of montmorillonite (MONT), organoclay
(OC) and surfactant (C12Cl) (a) 2~40º (b) 2~10º 30

Figure 15. XRD patterns of OC/DMAc suspension solution (O)
with different thermal process (a) 2~40º (b) 2~10º 32

Figure 16. FTIR spectra of poly (amic acid) and
polyimide (BPDA-ODA) 34

Figure 17. TGA curves of polyimides 35

Figure 18. XRD patterns of polyimides 38

Figure 19. FTIR spectra of polyimide (BPDA-ODA)/clay
nanocomposites within 3 % by weight of organoclay
via different synthesis methods 39

Figure 20. TGA curves of BPDA-ODA and BPDA-ODA/clay
nanocomposites within 3 % by weight of organoclay
via different synthesis method 40

Figure 21. XRD patterns of BPDA-ODA and BPDA-ODA/clay nanocomposites within 3 % by weight of organoclay via different synthesis method (a) 2~40º (b) 2~10º 43

Figure 22. XRD patterns of ODA/DMAc, ODA/MONT-DMAc
and ODA/OC-DMAc mixing after 48hr and remove the
DMAc (i.e. heating to 150 stage) 45

Figure 23. XRD patterns of BPDA-ODA/3%OC nanocomposite (T)
with different heating process (a) 2~40º (b) 2~10º 46

Figure 24. TGA curves of polyimide and polyimide/clay
nanocomposites within 3 % by weight of organoclay
via two-step method (T) (with BPDA series) 49

Figure 25. TGA curves of polyimide and polyimide/clay
nanocomposites within 3 % by weight of organoclay
via two-step method (T) (with 6FDA series) 50

Figure 26. XRD patterns of polyimide/clay nanocomposites within
3 % by weight of organoclay via two-step method (T)
(with different chemical structures) 53

Figure 27. Conformations and estimated molecular dimensions
of repeat unit of polyimides (a) BPDA-ODA
(b) BPDA-OODA. Molecular chain axis is indicated by
the arrow 54

Figure 28. Conformations and estimated molecular dimensions
of repeat unit of polyimides (a) 6FDA-ODA
(b) 6FDA-OODA. Molecular chain axis is indicated by
the arrow 55

Figure 29. FTIR spctra of polyimide (BPDA-ODA)/clay
nanocomposites via two-step mothod with various
clay contents 57

Figure 30. TGA curves of polyimide (BPDA-ODA)
and BPDA-ODA/clay nanocomposites via two-step
method with various clay contents 58

Figure 31. XRD patterns of polyimide (BPDA-ODA)
and BPDA-ODA/clay nanocomposites via two-step
method with various clay contents (a) 2~40º (b) 2~10º 61

Figure 32. Schematic diagram illustrating the synthesis of
organoclay/DMAc suspension solution 64

Figure 33. Schematic diagram illustrating the nanostructural evolution
during synthesis of polyimide/ clay nanocomposites via
two-step method 65

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