Synthesis, fabrication, characterization, properties and thermal degradation kinetics study of low k poly(ether imide)s and co poly(ether imide)s, and poly(ether imide) MMT clay nanocomposites

ABSTRACT The objective of the PhD thesis research was the synthesis, film fabrication, characterization, and structure properties study of series of partially fluorinated polyether imi

SYNTHESIS, FABRICATION, CHARACTERIZATION, PROPERTIES AND THERMAL DEGRADATION

KINETICS STUDY OF LOW-K POLY(ETHER IMIDE)S AND CO-POLY(ETHER IMIDE)S, AND POLY(ETHER

IMIDE)/MMT CLAY NANOCOMPOSITES

ROHIT KUMAR H VORA

Degree: Doctor of Philosophy (PhD), 1998-2003

Department: Chemistry

PhD Thesis Title: Synthesis, Fabrication, Characterization, Properties, and Thermal

Degradation Kinetics Study of Low-K Poly(ether imide)s, Copoly(ether imide)s, and Poly(ether imide)/MMT Clay Nanocomposites

ABSTRACT

The objective of the PhD thesis research was the synthesis, film fabrication, characterization, and

structure properties study of series of partially fluorinated poly(ether imide) (6F-PEI),

copoly(ether imide)s (6F-CoPEI) and (6F-PEI)/organosoluble MMT clay nanocomposite from

commercially available monomers and materials The approach involved the polymerization of

2,2’-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) with a variety of

di-ether-containing (non-fluorinated) diamines: bis(3-aminophenoxy)diphenyl sulfone (m-SED),

4,4-bis(4-aminophenoxy)diphenyl sulfone (p-SED), and 4,4-4,4-bis(4-aminophenoxy)diphenyl propane

(BPADE) The films of these melt processable (6F-PEI) and (6F-CoPEI) polymers from p-SED

and BPADE having trifluoromethyl groups showed excellent electrical properties

Fluoro-poly(ether imide)s [6FDA + p-SED] and [6FDA + BPADE] had dielectric constants (ε’) of 2.74

and 2.65 at 10MHz respectively Mathematical model equations were developed to estimate the

dielectric constant (ε’ co ) of copolyimides For the copoly(ether imide)s, the dielectric constant values were in the range between 3.05 to 3.10 at 1 kHz These values are lower than the

commercially available poly(ether imide) ULTEM1000 (ε’=3.15), and polyimide Kapton 

H

films (ε’=3.5) at 1 kHz In addition, (6F-PEI)s, (6F-CoPEI)s, and nanocomposite films not only showed extraordinary long-term thermo-oxidative stability (TOS), but also exhibited excellent

reduced water absorption relative to commercial polyimides The transparencies of polymer films

were in the range between 80-90% at 500nm solar wavelength The nanocomposites showed

excellent solvent resistance, increased glass transition (Tg) values with increasing clay content, a

sharp lowering of the coefficient of thermal expansion (CTE), and improved surface energy

Keywords: Fluoro-poly(ether imide), Fluoro-copoly(ether imide), Fluoro-poly(ether imide)/MMT clay

nanocomposites, Low-dielectric, Estimation of dielectric constant, Thermal degradation kinetics, oxidative stability, Surface properties.

Thermo-DEDICATION

“We measure ourselves by many standards Our strengths and our intelligence, our wealth and even our good luck, are things which warm our heart and make us feel ourselves a match for life But deeper than all such things and able to suffice unto itself without them is the sense of the amount of effort we can put forth… He who can make none is but a shadow; he who can make much is a hero.”

-Prof William James [A prominent American psychologist of the 19th century (1898).]

I would like to dedicate this dissertation to my beautiful wife, Neela R Vora, who is

my better half and a very good friend, and to my two extraordinarily special teenage children, son Ashish and daughter Amee, for their all-out encouragement, support, and unconditional love during the course of this long research They are my heroes, who patiently and lovingly accepted my long and late hours at work at the Institute of Materials Research and Engineering (IMRE)’s laboratory during those years, at which time, I almost became a weekend husband and father, but never did they ever fail to let

me know that they loved me I owe them my deepest gratitude and thanks from the bottom of my heart I love you, guys

ACKNOWLEDGEMENTS

“Mind is a terrible thing to waste”

-Rev Martin Luther King, Jr

“Poverty is the greatest form of ‘Violence and Sin’ of mankind”

-Mahatma Gandhi

I would like to express my sincere appreciation and profound gratitude to my doctoral thesis advisor, distinguished Professor Suat Hong Goh at the Dept of Chemistry for his time, resources support, valuable guidance and mentorship throughout my graduate studies, and also to my co- advisor Prof Tai-Shung (Neal) Chung, for allowing me a complete creative freedom in deciding

my thesis research topic and objectives, and for his continuing encouragement

I would like to express my heartfelt thanks to the President of the National University of Singapore, Prof Fong Choon Shih, then the founding director of the Institute of Materials Research and Engineering (IMRE) for giving me his permission in 1998 to enroll for PhD studies

at the Dept of Chemistry at NUS, and for also allowing me to carry out a simultaneous PhD research work at IMRE in the Advanced Polymers Group’s lab while working at IMRE

I would also like to thank distinguished professor emeritus Prof Huang Hsing Hua for his willingness to accept me as his PhD student and, also to allow me to use his laboratory at S9-03-

03 at the Dept of Chemistry during the early years (1997-1999) of IMRE

With the blessings of these wonderful teachers and mentors, I initiated my PhD thesis research work in November 1998 at IMRE During the last five years, their patience and helpful suggestions have kept me going in carrying out sustained vigorous research work, because of which I was successfully able to meet the objectives of my thesis

I would like to acknowledge and sincerely thank Dr Motonori Takeda, Senior Managing Director and Chief Technical Officer of Wakayama Seika Kogyo Co Ltd., Japan for his friendship, and for providing various diether-containing diamine monomers free of charge for my research work I also would like to thank the wonderful staff of the Advanced Polymers and Chemicals Cluster at IMRE for many meaningful discussions on analytical techniques

I must not forget to thank Prof Syamal K Lahiri of IMRE, Assoc Prof B V R Chowdari of the Dept of Physics, Assoc Prof Jagdese J Vittal of the Dept of Chemistry, Assoc Prof Madapusi P Srinivasan and Assoc Prof Ajay Kumar Ray from the Dept of Chemical & Environmental Engineering and Assoc Prof L C Lim from Dept of Mechanical Engineering for their friendship and intellectually stimulating discussions and moral support

I would also like to thank Prof Neal Chung and Prof En-Tang Kang of the Dept of Chemical

& Environmental Engineering for the research collaborations and allowing me to co-supervise their PhD students, who used my fluoro-polyimides in their research work Similarly, I would

year to teach a 2 year undergraduate level module ‘Polymeric Engineering Materials’ in his department, thus giving me a unique opportunity to provide manpower training, and have real experience and feel for an academic teaching, which I enjoyed very much, and at the same time I was able concentrate on writing this thesis

In addition, I would like to take this opportunity to thank several of my colleagues and wonderful friends at IMRE: Dr Ramam Akkipeddi, Dr Wang Huimin, Mr Subramanian Veeramani, Dr P Santhana Gopala Krishnan, Dr Pramoda Kumari Pallathadka, Dr Liu Song Lin, Mr Sunil Bhangale, Mr Suresh Kumar Donthu, Mr Mithilesh Shah, and also to Mr Rajamani Lakshminarayanan, Mr Chinnappan Baskar, Mr Vetrichelvan Muthalagu, Mr Venkataramanan Balasubramaniam, Mr Goh Ho Wee, Mr Li Xuedong from the Dept of Chemistry; Dr Prashant D Sawant and Mr Siddharth Joshi from the Dept of Physics; Dr Igor Goliney, Dr Rengaswamy Jayaganthan, Dr Santhiagu Ezhilvalavn from the Dept of Materials Science, for sharing their ideas and for their valuable friendship Working and/or socializing with all of them has always been a special privilege for me for all these years

I would like to acknowledge the National University of Singapore for sponsoring my trip to attend and present an invited technical paper, and to chair a session at the 6th European Technical Symposium on Polyimides and High Performance Functional Polymers (STEPI-6), held in Montpellier (FRANCE), during May 13-15, 2002

Last, but not least, I would like to thank my dear and loving mother Mrs Hiralaxmi H Vora, who taught me how to read, and to my 77 year old dear father, Mr Harkisondas A Vora, a Chemical Engineer (from the UDCT-Bombay University, INDIA) and a very successful technopreneur and businessman, who got me interested in the subject of science at an early age I also thank my dear brother Mayur H Vora, and sisters Mrs Chhaya Acharya, Late Mrs Maya Parikh, and Mrs Jayshree Doshi Also thank my respected parent-in-laws: Late Mrs Ramabahen

B Kanakia and Mr Babubhai M Kanakia, brother-in-laws: Rashesh B Kanakia and his wife Mrs Rupal Kanakia, and Himanshu B Kanakia and his wife Mrs Hiral Kanakia, sister-in-laws: Mrs Meena Muni, Mrs Asha Shah and Mrs Manisha Vora, and my family for their continual loving support, and understanding and prayers

Finally, remembering last three lines from the last stanza of the all-time masterpiece poem

‘Stopping by the woods on a snowy evening’ by the great American poet:

“ But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep.”

-Robert Frost

I am happy to state that my journey for higher learning will not end with getting a PhD degree, as

I truly believe that learning is a life long process May Lord Shree Krishna, the merciful, bless and guide my wisdom in the pursuit of knowledge and happiness in this journey

1.1.2.2 Brief history on polyimide R&D and worldwide major

commercial product introduction

11

1.1.2.3 Brief summary of polyimide market size and growth

projection (year 2000 to 2010)

20

polyimide R&D activities

21

1.1.3.1 Monomers 28

1.1.3.2.2 Chemical mechanism of polymerization reaction 32

1.1.5.1 Characterization of polyimide’s chemical characteristics 48

1.1.5.2 Characterization for polyimide’s physical characteristics 48

1.1.6.2.4 Thermo-oxidative stability (TOS) of polyimides 57

1.1.6.3 Electrical and optical properties, dimensional stability

and coefficient of thermal expansion (CTE)

1.1.7 Applications of polyimides 63

IMIDE)S (6F-PEI) PROJECT

2.2.2.1.A Synthesis of fluoro-poly(ether imide) polymers 100

2.2.2.1.A.1 Synthesis of [6FDA + m-SED] fluoro-poly(ether imide)

polymer

100

2.2.2.1.A.1.a.1 Step-1: Condensation polymerization procedure 100

2.2.2.1.B Synthesis of non-fluorinated poly(ether imide) polymers 104

2.2.2.1.B.1 Synthesis of [PMDA + p-SED] poly(ether imide) polymer 104

2.3.2 Poly(amic acid) film preparation for FT-IR analysis 106

exclusion chromatography (SEC)]

110

2.4.16 Dielectric analysis (DEA) 117

CHAPTER - 3 SYNTHESIS AND PROPERTIES OF

DESIGNED LOW-K FLUORO-

COPOLY(ETHER IMIDE)S

152

3.1.2 Research objectives 157

3.2.2.1.1 Synthesis of fluoro-poly(ether imide) (6F-PEI) polymers 162

3.2.2.1.1.A Synthesis of [6FDA + p-SED] fluoro-poly(ether imide)

polymer

162

3.2.2.2 Synthesis of fluorinated copoly(ether imide) polymers 164

3.2.2.2.1 Synthesis of fluoro-copoly(ether imide) (6F-CoPEI)

polymers

164

3.2.2.2.1.A Series 1: Synthesis of [6FDA + (n Mole %) p-SED + (m

Mole %) BPADE ] fluoro-copoly(ether imide) polymer

165

3.2.2.2.1.A.1 Synthesis of [6FDA + 75 mole% p-SED + 25 mole%

BPADE ] fluoro-copoly(ether imide) polymer

165

3.2.2.2.1.B Series 2: Synthesis of [6FDA + (n Mole %) p-SED + (m

Mole %) BDAF ] fluoro-copoly(ether imide) polymer

167

3.2.2.2.1.B.1 Synthesis of [6FDA + 75 mole% p-SED + 25 mole%

BDAF] fluoro-copoly(ether imide) polymer

167

3.2.2.3.1 Synthesis of [ODPA + m-Tolidine] poly(amic acid) (PAA) 169

3.2.2.4 Synthesis of fluoro-polyimides (6F-PI) 170

3.2.2.4.1 Synthesis of [6FDA + m-PDA] fluoro-polyimide polymers 171

3.2.2.5.1 Synthesis of [6FDA + 50 mole% m-PDA + 50 mole%

p-PDA] fluoro-copolyimides polymer

3.5.6 Moisture uptake 187

3.5.12.1 Dielectric properties of polyimides and copolyimides 200

3.5.12.1.1 Dielectric behavior of non-fluorinated polyimide (PI) 201

3.5.12.1.2 Dielectric behavior of fluorine-containing polyimide

(6F-PI)

202

3.5.12.1.3 Dielectric behavior of fluoro-copolyimides (6F-CoPI) 204

3.5.12.2 Estimation of dielectric constant (ε’) of polyimides and

copolyimides

206

3.5.12.2.1 Estimation of dielectric constant of polyimides (PI) 207

3.5.12.2.1.1 Calculation of ‘Molar Polarization’ of ‘Phthalimide’

groups

207

3.5.12.2.1.1.A Estimation of dielectric constant of ULTEM-1000

[BPADA + m-PDA] polyimide polymer

3.5.12.2.2 Estimation of dielectric constant of copolyimides (Co-PI) 217

3.5.12.2.2.1 Dielectric constant of fluorine-containing copolyimides

(6F-CoPI)

219

3.5.12.2.2.2 Dielectric constant of fluoro-poly(ether imide)s (6F-PEI)

and fluoro-copoly(ether imide)s (6F-CoPEI)

219

3.5.12.2.2.2.A Dielectric constant as a function of fluorine content in

copoly(ether imide) polymers

222

3.5.12.2.2.3 Additional ‘Molar Polarization’ values for calculation of

dielectric constants by additive groups contributions

CHAPTER - 4 PREPARATION AND CHARACTERIZATION

OF 4,4-BIS (4-AMINOPHENOXY) DIPHENYL

SULFONE BASED [FLUORO-POLY(ETHER

4.2.2.1 Preparation of p-SED (Diamine) modified MMT clay 241

4.2.2.1.1 Procedure of making p-SED (Diamine) modified MMT

clay

243

4.2.2.1.2.1 Master batch of fluoro-poly(ether amic acid) (6F-PEAA) 244

4.2.2.1.3 Preparation of p-SED treated MMT clay suspensions in

NMP

245

4.2.2.1.4 Preparation of fluoro-poly(ether amic acid)/MMT clay

nanocomposites pre-formulations

245

4.3.1 [6FDA + p-SED] Fluoro-poly(ether imide), and [6FDA +

p- SED]/MMT clay nanocomposite film preparation

4.5.1.3 Solubility of [6FDA + p-SED] (6F-PEI) and [(6F-PEI)/

MMT clay] nanocomposite films

A-2 Synthesis of fluoro-poly(ether imide)s 292 A-2.1 Reaction scheme of synthesis of fluoro-poly(ether imide)

A-2.2.1 Reaction scheme for synthesis of poly(ether imide) (PEI) 295 A-2.2.2 Synthesis of [PMDA + m-SED] poly(ether imide) polymer 295 A-2.2.3 Synthesis of [PMDA + BPADE] poly(ether imide) polymer 296 A-2.2.4 Synthesis of [PMDA + BDAF] poly(ether imide) polymer 296 A-2.2.5 Synthesis of [BPDA + p-SED] poly(ether imide) polymer 297 A-2.2.6 Synthesis of [BPDA + m-SED] poly(ether imide) polymer 298 A-2.2.7 Synthesis of [BPDA + BPADE] poly(ether imide) polymer 298 A-2.2.8 Synthesis of [BPDA + BDAF] poly(ether imide) polymer 299 A-2.2.9 Synthesis of [BTDA + p-SED] poly(ether imide) polymer 299 A-2.2.10 Synthesis [BTDA + m-SED] poly(ether imide) polymer 300 A-2.2.11 Synthesis of [BTDA + BPADE] poly(ether imide) polymer 301 A-2.2.12 Synthesis of [BTDA + BDAF] poly(ether imide) polymer 301 A-2.2.13 Synthesis of [ODPA + p-SED] poly(ether imide) polymer 302 A-2.2.14 Synthesis of [ODPA + m-SED] poly(ether imide) polymer 302 A-2.2.16 Synthesis of [ODPA + BPADE] poly(ether imide) polymer 303 A-2.2.16 Synthesis of [ODPA + BDAF] poly(ether imide) polymer 304 A-2.3 Synthesis of fluorinated copoly(ether imide) (6F-CoPEI)

polymers

304

A-3.1 Reaction scheme for synthesis of fluoro-copoly(ether imide)

(6F-CoPEI)

305

A-3.2.1 Series-1: Synthesis of [6FDA + (n Mole%) p-SED + (m

Mole%) BPADE] fluoro-copoly(ether imide) polymer

305

A-3.2.1.1 Synthesis of) [6FDA + (50%) p-SED + (50%) BPADE]

fluoro-copoly(ether imide) polymer

305

A-3.2.1.2 Synthesis of [6FDA + (25%) p-SED + (75%) BPADE]

fluoro-copoly(ether imide) polymer

306

A-3.2.2 Series-2: Synthesis of [6FDA + (n Mole%) p-SED + (m

Mole%) BDAF fluoro-copoly(ether imide) polymer

307

Fluoro-copoly(ether imide) polymer

307

A-3.2.2.2 Synthesis of [6FDA + (25%) p-SED + (75%) BDAF]

fluoro-copoly(ether imide) Polymer r

308

A-3.3 Synthesis of polyimides and copolyimides for electrical

properties studies

308

A-3.3.1.2 Synthesis of [PMDA +3,3-ODA] poly(amic acid) (PAA) 310

A-3.3.2.1 Synthesis reaction scheme for fluoro-polyimide (6F-PI) 311 A-3.3.2.2 Synthesis of [6FDA + p-PDA] fluoro-polyimide polymer 311

A-3.3.2.3 Synthesis of 6FDA + 1,4-Diamino Durene]

A-3.3.3.1 Synthesis reaction scheme for fluoro-copolyimides

(6F-CoPI)

314

A-3.3.3.2 Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%)

p-PDA] fluoro-copolyimide polymer

315

A-3.3.3.3 Synthesis of [6FDA + (50%) 1,4-Diamino Durene + (50%)

m-PDA] fluoro-copolyimide polymer

315

APPENDIX - B ESTIMATION OF DIELECTRIC CONSTANT

( ε ’) OF POLYIMIDE POLYMERS

317

B.1.1 Estimation of dielectric constant of [ODPA + m-Tolidine]

B-3.1 Estimation of dielectric constant of [6FDA + (50%) m-

PDA + (50%) p-PDA] fluoro-copolyimide

327

B-3.2 Estimation of dielectric constant of [6FDA + (50%) m-

PDA + (50%) 1,4-Diamino Durene] fluoro-copolyimide

328

B-3.3 Estimation of dielectric constant of [6FDA + (50%) p- PDA

+ (50%) 1,4-Diamino Durene] fluoro-copolyimide

B-5.1 Estimation of dielectric constant of [6FDA + (75%) p-SED

+ (25%) BPADE] fluoro-copoly(ether imide)

333

B-5.2 Estimation of dielectric constant of [6FDA + (50%) p-SED

+ (50%) BPADE] fluoro-copoly(ether imide)

334

B-5.3 Estimation of dielectric constant of [6FDA + (25%) p-SED

+ (75%) BPADE] fluoro-copoly(ether imide)

335

B-5.4 Estimation of dielectric constant of [6FDA + (75%) p-SED

+ (25%) BDAF] fluoro-copoly(ether imide)

336

B-5.5 Estimation of dielectric constant of [6FDA + (50%) p-SED

+ (50%) BDAF] fluoro-copoly(ether imide)

337

B-5.6 Estimation of dielectric constant of [6FDA + (25%) p-SED

+ (75%) BDAF] fluoro-copoly(ether imide)

338

SUMMARY

Polyimides are one of the important classes of versatile engineering polymers as they exhibit reasonably good mechanical properties, chemical resistance, low dielectric constant and thermal stability, when compared to other polymeric materials They are therefore, prominent polymers amongst high performance, high temperature stable organic materials The higher glass transition temperatures (Tg) of polyimides are due to structural rigidity of dianhydrides The Tgs of these polyimides are in the range of 250 to 410°C However, high softening points and intractability of polyimides have limited their direct usage in electronic applications Hence the search for new polyimides with improved processability and higher continuous use (200°C) temperatures than the commercially available polyimides, and poly(ether imide) has received a significant attention from both academia and industries The approach involving the modification of the backbone structure of polyimides, such as an incorporation of a flexible ether linkage

and meta oriented phenylene rings into polymer backbone has provided an increase in

chain flexibility and solubility, but has also lowered the effective upper use temperature More importantly, in microelectronic device circuitry, the propagation velocity of signal is inversely proportional to the square of the dielectric constant (ε’) of the propagation medium Therefore, a low dielectric constant is necessary for a faster signal propagation in microelectronic devices without cross-talk, especially for newer multilevel high-density and high-speed electronic circuits as the geometry is further miniaturized A desirable value should be below 3.1 at 1 kHz The dielectric constant of commercially available polyimides, such as Kapton-H, [PMDA + p-ODA], Upilex-S

[BPDA + p-PDA], poly(ether imide) ULTEM-1000, [BPADA + m-PDA] and fully

fluorinated poly(ether imide) EYMYD [6FDA+BDAF], is in the range of 2.99 to 3.5

Even though, EYMYD met the requirements of low ε’, high thermal stability and continuous use temperature in the range of 170-200°C, but it was commercially available for a short time only in its amic acid solution form (an unstable material with short shelf life), and it was prohibitively expensive Both Kapton-H and Upilex-S (Tg >400°C) having higher ε’ (~3.5) and higher moisture absorption in the range of 1.5-2.8%, are available only in non-thermoplastic film forms Whereas, ULTEM1000, a melt processable resin (Tg 218°C) due to its higher moisture absorption (~1.5%), lower continuous use temperature (~170°C) and higher ε’ (3.15) is unattractive for newer 200°C continuous use temperature microelectronics fabrication applications

During the last 15 years, clay-polymer nanocomposites and hybrids have become an emerging field of research and development because of their unique microstructures, and enhanced properties These organic polymer/inorganic hybrid or nanocomposite materials (Ceramers) are expected to exhibit unique characteristic and synergistic properties of both ceramics and organic polymers Presently, perfect ‘Ceramer’ materials with all the desired properties, (Viz mechanical property retention at high temperature, low thermal expansion, toughness, ductility, and processebility, etc.) based on

‘polyimides’ chemistry have not been developed or marketed yet When developed, these new materials would provide unique properties for potential applications for electronics, electrical, aerospace, life science, separation membranes, MEMS, etc industries

The objective of the present research work was to synthesize, fabricate, characterize, and to study the properties and thermal degradation kinetics of ‘low-K’ poly(ether imide)s and copoly(ether imide)s, and poly(ether imide)/organo-soluble MMT clay nanocomposites film

The effort for the thesis research work as reported in Chapter 2 was focused on the synthesis, characterization, and study of a series of high-performance partially

fluorinated poly(ether imide) (6F-PEI) from commercially available monomers The approach involved the polymerization of 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) with a variety of diether-containing non-

fluorinated diamines, viz 4,4-bis(3-aminophenoxy)diphenyl sulfone (m-SED), aminophenoxy)diphenyl sulfone (p-SED), 4,4-bis(4-aminophenoxy)diphenyl propane

4,4-bis(4-(BPADE) by a simplified one-pot two-step solution polymerization process These PEI) polymers were characterized for their chemical properties, solubility, morphology nature, hydrolytic stability, thermal behavior, thermo-oxidative stability (TOS), thermomechanical, mechanical, electrical, transparency and melt rheology properties in order to understand their structure-property relationships

Chapter 3 describes the synthesis, characterization and study of designed low-K fluoro-copoly(ether imide)s (6F-coPEI) The synthesis methodology of these polymers was similar to that described in Chapter 2 However, before the actual synthesis of (6F-coPEI)s, several polymer compositions were first designed and their dielectric constant (ε’) values were pre-estimated by means of mathematical equations defined by the Lorentz-Lorenz’s theory, the Vogel’s theory, and Vora-Wang equations Then, a series

of (6F-PEI) and selected few (6F-coPEI)s having low dielectric constant values (by estimation) were successfully synthesized and their films were similarly characterized as discussed in Chapter 2, to study their thermal degradation kinetics, electrical, TOS and hydrolytic stability, etc properties, and to understand the effect of chemical structure of co-monomer (diamine) on their thermal stability

A series of (6F-PEI)/organo-soluble MMT clay nanocomposite formulations were also

prepared from the [6FDA+p-SED] poly(ether amic acid) having blended with varying

concentration of organo-soluble clay, and their films were characterized to understand

the effect of varying concentration of organo-soluble clay on the nano-composite’s thermal, mechanical and surface properties as reported in Chapter 4

The FTIR study confirmed that poly(ether amic acid)s (6F-PEA) were successfully converted to (6F-PEI) by chemical imidization method The inherent viscosities of these (6F-PEA), (6F-coPEA), (6F-PEI), and (6F-coPEI) were determined by viscometry The XRD measurements confirmed that (6F-PEI), and (6F-CoPEI) were amorphous polymers Glass transition temperatures (Tg) of copolymer films were predicted from the Fox equation, and compared with the results of differential scanning calorimetry (DSC) measurements Thermogravimetric analysis (TGA) measurement data and the Coats & Redfern equation were used in the thermal degradation kinetics calculation for the

determination of activation energy (E a) of polymer degradation The thermal stability results were comparable to the TOS data obtained by isothermal heating of films in air at 315°C for 300 hr The films (6F-PEI), (6F-CoPEI) and nanocomposites having trifluoromethyl groups not only showed extraordinary long-term TOS, but also exhibited excellent reduced water absorption relative to non-fluorinated polyimides Estimated ε’ values for (6F-CoPEI)s films were verified against actual measured values obtained by dielectric analysis (DEA) at 1 kHz The estimated values were in good agreement with experimental as well as literature values

The films of the [6FDA+p-SED]/MMT clay nanocomposites showed excellent solvent

resistance, also increased Tg and a sharp lowering of coefficient of thermal expansion (CTE) with increasing clay content Modulus of elasticity determined by an Instron mechanical analyzer, on an average, increased for the nanocomposite films relative to

neat fluoro poly(ether imide) [6FDA+p-SED], and films of ‘control’ non-fluorinated

polyimides The surface energy measurements by the One-Liquid and Two-Liquid Geometric Mean methods showed comparable trend of decreasing contact angle which is

an indication of improved wettability and/or adhesion, a desirable property for microelectronic applications

LIST OF PUBLICATIONS

Journal Publications: (* Corresponding author)

1 Rohitkumar H Vora*, Suat Hong Goh, Tai-Shung Chung, “Synthesis and

Properties of Fluoro-Poly(ether imide)s”, Polymer Engineering & Science, 40(6)

(2000), 1319-1329

2 Rohitkumar H Vora*, P Santhana Gopala Krishnan, Suat Hong Goh,

Tai-Shung Chung, “Synthesis and Properties of Designed Low K

Fluoro-Copoly(ether-imide)s -Part 1.”, Advanced Functional Materials, 11(5) (2001),

361-373

3 P Santhana Gopala Krishnan, Rohit H Vora*, S Veeramani, Suat Hong

Goh, Tai-Shung Chung, “Kinetics of Thermal Degradation of 6FDA Based

Copolyimides-I”, Polymer Degradation and Stability, 75(2) (2002), 273-285

4 Rohitkumar H Vora*, Pramoda K Pallathadka, Suat Hong Goh, Tai-Shun

Chung, Yong Xiong Lim, Toong Kiang Bang “Preparation and

Characterization of 4,4’-Bis(4-aminophenoxy) Diphenyl Sulfone Based

Fluoro-Poly(ether imide)/Organo-modified Clay Nanocomposites”, Macromolecular

Materials and Engineering, 288(4) (2002) 337-356

Book Chapters: (* Corresponding author)

1 Polyimide Syntheses, Characterization, Blends and Applications, T S Chung, J

Pan, S L Liu, S Mullick, R H Vora in Advanced Functional Molecules and

Polymers, H S Nalwa, (Ed.) Vol 4, p 157, Gordon & Breach Publishers, New Yoyk, 2001

2 Measurement and Theoretical Estimation of Dielectric Properties of Polyimides,

Rohit Vora*, Huimin Wang, Tai-Shung Chung in Polyimides and Other High

Temperature Polymers, K L Mittal, (Ed.) Vol 1, p 33, VSP Utrecht, The

Netherlands, 2001

3 Polyamic Acids and its Ionic Salt Solution: Synthesis, Characterization and its

Storage Stability Study, Rohit H Vora*, P Santhana Gopala Krishnan, S

Veeramani, Suat Hong Goh, in Polyimides and Other High Temperature

Polymers, K L Mittal, (Ed.), Vol 2, p 3, VSP Utrecht, The Netherlands, 2003

Conference Presentations: (# Invited paper,* Corresponding author, $ Session

Chair)

1 Rohit Vora #, * , $ , Tai -Shung Chung, “Development of Fluoro-Poly(ether

imide)s for Electronics Applications: Synthesis and Characterization”, in proceedings of the 5th Symposium on Polyimides and High Performance Functional Polymers (STEPI-5), in Polyimides and High Performance Polymers,

M J M Abadie, B Sillion (Eds.), STEPI-5, ISIM, Montpellier, FRANCE, 1999,

p 52

2 Rohit H Vora #, * , $ , P Santhana Gopala Krishnan, Suat Hong Goh, T-S

Chung, “Low K Fluoro-Copoly(ether imide)s derived form Di-ether containing

Diamines and 6FDA: Synthesis and Properties,” in proceedings of the 7th International Conference on Polymers for Electronics Packaging–RETECH 2000,

in Advances in Low-k Dielectric and Thermally Stable Polymers for Microelectronics, H Sachdev, M M Khojasteh, D McHerron (Eds.), Society of Plastics Engineers, Brookfield, USA, 2002, p-71

3 Rohit H Vora #, * , $ , P Santhana Gopala Krishnan, S Veeramani, Suat

Hong Goh, Tai-Shung Chung, “Thermal Degradation Studies of 6FDA Based

Copolyimides,” in proceedings of the 7th International Conference on Polymers for Electronics Packaging–RETECH 2000, in Advances in Low-k Dielectric and Thermally Stable Polymers for Microelectronics, H Sachdev, M M Khojasteh,

D McHerron (Eds.), Society of Plastics Engineers, Brookfield, USA, 2002, p

355

4 Rohit H Vora #, * , $ , Pramoda K Pallathadka, Suat Hong Goh,

“Development of Fluoro Poly(ether imide)s/MMT Clay Nanocomposites:

Synthesis and Characterization”, in proceedings of the 6th Symposium on Polyimides and High Performance Functional Polymers (STEPI-6), in Polyimides and High Performance Functional Polymers, M J M Abadie, B Sillion (Eds.), STEPI-6, ISIM, Montpellier, FRANCE, 2003, p 191

CHAPTER - 1

INTRODUCTION

1.1.1 High performance polymeric materials

In aerospace applications, highly specialized spacecraft structural components, cryogenic rocket engines parts, military aircraft components, etc are made up of light weight, mechanically stronger and high temperature stable composites These composites are made from special graphite, carbon, glass, or ceramic fibers matrix prepregs impregnated with the advanced high performance thermosetting and/or thermoplastics polymeric materials

Such advanced high performance polymeric materials, resin alloys and hybrid systems possess long-term ‘service temperature’ capabilities in the range from room temperature

to >150 °C The service temperature is based upon the ‘Thermal Index’ rating assigned

by the Underwriters’ Laboratories (UL) of USA The UL relative Thermal Index is an indication of the thermal stability of a polymer Underwriters’ Laboratories addresses this phenomenon with the UL Temperature Index The temperature indices are used by

UL as a guideline when they compare hot spots on devices and appliances made from these materials Higher ‘Thermal Index’ rating for a particular polymeric material means that it would continuously provide a long term thermal stability in terms of good mechanical strength, good environmental stability, dimensional stability, solvent

resistance, and electrical properties at the elevated temperature for which it is rated UL defines the end of service life as the aging time required to produce a 50% drop in the property compared with the initial value [8]

A typical list of high service temperature polymers (thermoset and thermoplastics) including linear, and heterocyclic types that are commercially used in current electronics, aerospace, automotive, electrical industries is given below [1-5, 9-10]

These factors typically include, material selection based on final product usage, product life time, polymer’s properties, processability, and of course, the cost (a main factor for most industries) of making that product using that particular polymer

Table-1: Neat resin mechanical and fracture toughness properties of high performance Thermoplastics [10-11]

Tensile Properties @ 25 °C POLYMER

Yield Strength (Kpsi) (MPa)

Modulus (Kpsi) (GPa)

Strain to Break (%)

Fract Energy (G I C ) Lb/in2 (kJ/m2) PEEK 14.5 (100) 450 (3.1) > 40 > 23 ( > 4) PXM 8505 12.7 (88) 360 (2.5) 13 PPS 12.0 (83) 630 (4.3) 5 0.6-1.4 (0.1-0.2) PAS-2 14.5 (100) 470 (3.2) 7.3 TORLON C 20.0 (138) 550 (3.8) 15 19.4 (3.4) TORLON 696 13.0 (90) 400 (2.8) 30 20.0 (3.5) ULTEM100 15.2 (105) 430 (3.0) 60 19.0 (3.3)

NR 150B2 16.0 (110) 605 (4.2) 6 13.7 (2.4) Avimid K-III 14.8 (102) 546 (3.8) 14 11.0 (1.9) LARC-TPI 17.3 (137) 540 (3.7) 4.8 10.0 (1.8) PISO2 09.1 (63) 719 (5.0) 1.3 8.0 (1.4) P-1700 10.2 (70) 360 (2.5) > 50 14.0 (2.5) SIXEF-44* 13.8 ( ) 405 ( ) 7.8 Epoxy (3501-6) 12.0 (70) 620 (4.3) 1.2 19.4 (3.4)

19.4 (3.4) BMI(HG89107) 450 ( 3.1) 7 19.4 (3.4)

* [10]

The illustrative chart, given below in Table 2, shows the relative importance of factors that a product development engineer would take into consideration according to his/her final industry products applications and end-uses [3-7, 9]

1.1.1.1 Thermosets resins

For aerospace composites applications, thermosetting resins have shown some advantages over the thermoplastic counterpart, such as low initial melt viscosity, which provide uniform wetting, tack, and ease of handling In addition, their good solvent resistance, good interfacial adhesion, good mechanical performance and durability and good damage tolerance also have ensured their use in the aerospace industries for over 50 years

However, it was also found that these resins had some disadvantages For example,

Table -2: Relative importance of factors affecting high performance resin selection by end user

the application of epoxies required complex formulations, and the resins provided poor prepregs stability and required a long processing cycle which was economically costly

In the case of BMI and PMR-15 type resin chemistry, the composites showed poor toughness and thermal cracking in endurance test, indicating questionable durability However, extensive efforts were made in the development of processes for fabrication of aerospace structural components by the contractors of NASA and U.S defense industries under DARPA funded projects Some of the most effective processes came out of this development are now also used commercially as discussed below

1.1.1.2 Manufacturing process technology for thermosetting polymers

There are several processes used in the aerospace and composites industries to manufacture large dimensioned and complex- shaped glass, ceramics, graphite, carbon, aramide, even polyimide-fiber reinforced composites Mostly thermosetting resins such as BMI, PMR, epoxy, or their special blends, have been used as matrix resins Now due to the need for very complex geometric requirements, several high temperature thermoplastics, such as polyaramides, polyimides, polyamideimides, polyetherimides, etc or their specially formulated blends are also widely used, allowing

Industrial

Electronics/

Electrical

Aerospace Automotive

prepreggers to closely match the dimensions of shaped components, and also to repair the final composites products Typical processing methods are briefly given below [3-5]:

o Wet lay-up and autoclave molding

It is generally used for larger and complex aircraft composites parts The process employs prepregs, such as tapes, mats or woven cloth forms and cured using vacuum bag under controlled heating and pressure in an autoclave

o Filament winding

It is generally used for the fabrication of cylindrical parts: rocket fuel tanks, helicopter blades, etc It involves the mechanical winding of continuous fiber strands either pre- or post-resin impregnation stage

o Compression molding

It involves the manufacturing of parts from Sheet Molding Compounds (SMC) under very high pressure and high temperature in controlled condition in an inert atmosphere or in vacuum

o Pultrusion

Precision parts of constant cross section, such as rectangular beams; tubes, angles, etc are made by this process Continuously pulling resin-coated fibers through a heated die results in partially or fully cured parts The former ones are cured in the final conversion stage in an autoclave

1.1.1.3 Trends in R&D related to high performance polymers

Since the early 1990s, there has been a definite worldwide trend towards the R&D spending for the further development high performance polymers, and extending such polymers’ usage to the electronics sector, which put forth large efforts in the application product development This has lead to the high usage of performance polymers in the electronic industries increasing faster than in the aerospace and military hardware

industry sector However, due to specific favorable processing conditions, thermoplastics polymers took lead in R&D efforts over thermosetting polymers

Market survey showed that beside thermosetting epoxies, condensation polymers having thermoplastic nature such as thermoplastic polyimide (TPI), liquid crystal polymers (LCP), polyetheretherketone (PEEK), polyetherimides (PEI), fluoro-polyimide, had been used in the product development of very large scale integrated (VLSI) circuits, micro ball greed array (BGA) packages, flex circuit substrates, etc Of course, the development of high-temperature service applications continues to be funded by major

US and foreign Government’s defense industries

The illustrative chart given in Figure 1 below shows the major trend in high performance polymer R&D efforts [6-7, 9, 12]

Figure-1: Trends in high performance polymers development [6-7, 9, 12]

Today polyimide and related chemistry based polymeric materials are used in electronics and aerospace industries The market has been driven by performance, and more recently by the life cycle of products, and ultimate cost considerations [6-7, 9, 12-13]

1.1.2 Polyimides

Ceramic, graphite, carbon, even glass fiber reinforced composites using polyimides as

Addition Polyimides

EPOXY

Silicones

LOW TEMPERATURE HIGH TEMPERATURE

BM I

a matrix resin are increasingly being used in military engineering and aerospace applications because of their high strength-to-weight ratios and corrosion resistance A variety of these polymers including polyimides and copolyimides have been synthesized

by NASA, DuPont, M&T Chemicals, Ciba Geigy, National Starch, Hoechst Celanese, and others as high performance materials, for example, as matrices for fiber reinforced composites, foam and fibers, electronics substrate films, packaging encapsulants, adhesives, and protective coatings [1-2, 9-10, 14-39]

Ongoing development of improved synthesis methods has yielded a new generation of thermosets and thermoplastic polyimides that offer broader processebility and enhanced physical properties Some new high temperature polymers eliminated the tendency to brittleness and other limitations that were present in earlier products While established market sectors continue to account for most of the volume, the newer polymers are making inroads in such fast-growing and exciting areas as microelectronics and aerospace [13]

One of the key advantages of polyimides in these markets is that they can be used in a range of -450°F (-230°C) to more than 800°F (approx 426°C), well beyond the capability of most organic plastics [2, 13, 15]

As mentioned earlier, polyimides constitute a very important class of advanced materials because of the combination of many unique chemical (good hydrolytic stability, chemical resistance, adhesion property), thermal (high stability to thermal oxidation and irradiation), mechanical (good planarization and processability, low thermal expansion, high mechanical strength), and electrical properties (low dielectric constants, high breakdown voltage, low losses over a wide range of frequency) [1, 3, 16].Polyimides can be used for applications where bismaleimides are no longer useful thermally

Through the last 50 years of research and development, numerous polyimides and monomers for preparing polyimides have been identified and synthesized and introduced

in the market Over 60 polyimide products, such as, Kapton [40], and Pyralin 3002 [41], Vespel [42], NR-150 [43], PMR-15, [44], LARC-TPI [10], ULTEM [45-47], Polyimide-2080 [48-49], M&T-2065 [50], SOLIMIDE-Foam [21], XU-218 [24], SIXEF-PI [25-38], THERMID

-IP and THERMID-AF [23, 51], to name a few, have been successfully commercialized and today play a very important role in devices for aerospace, defense, and the electronics industry However, polyimides also have some inherent problems that limit their further development These include high monomer cost, toxicity and complex processing techniques The synthesis of appropriate aromatic dianhydrides and diamines with suitable functional structures is not trivial, and their costs are prohibitive, resulting in the higher costs of polyimides, and a greater hurdle to commercialize novel polymers Additionally, some of the aromatic diamines and aromatic dianhydrides are suspect carcinogens, and their restricted sale contributes to the increased cost This further disrupted research and development in polyimides Processing of polyimides was another challenge for most polymer engineers Fully imidized polyimides are often insoluble and infusible, rendering them difficult to be processed

Although polyimides have service temperature up to 700°F (371°C), they suffer from their poor processability But for certain electrical and electronic applications, due to their unique properties and performance, polyimides still continue to gain applications, and are widely used along with other polymeric materials in aerospace, electrical/electronics insulation and defense industries today [12-16, 52-53]

The electronics and aircraft/aerospace industries are the largest current markets for such advanced polymeric materials The military market includes fighter, attack and

large transport aircraft [2-7, 9-10, 13, 20, 52] However, by the year 2010, large markets for ceramic and nanocomposite materials will be found mostly in microelectronics, military, aerospace, automotive, medical, and building and construction applications [2-

7, 9, 20]

Illustrative Figure 2 shows the processing and performance requirements of polyimide resin alloys (blends), hybrids & nanocomposites to compete against other polymers for cost effective industrial applications

Figure-2: High performance polymeric materials for industrial applications

1.1.2.1 History of commercial development of polyimides

Historically, polyimide was first reported in 1908 [1-2], when it was thrown away as a useless oligomer In 1955, DuPont successfully developed high molecular weight aromatic polyimide [1-2] The first patent for polyimide was applied by DuPont in 1959 [3] The company also developed the first commercial polyimide, Kapton, in 1960 and marketed in 1962 [4-5] Since then, polyimides have seen more rapid development due to the large demands of high performance polymers for aerospace projects’ requirements

PEI

PAI

6F- PEI Polymeric Alloy Hybrids

PEI

PAI

6F- PEI Polymeric Alloy Hybrids

Nanocomposites

In this history of polyimides section, only the history of their commercial

developments including some of the very well known and important polyimide products introductions are highlighted Since there were over 60 polyimide chemistry

based products in the high performance polymer market segment by the year 1990, it is, therefore, beyond the scope of this brief introduction to include each one of them Besides, there were several thousands of technical papers published by hundreds of academic institutions around the globe since 1955 in the polyimide area In most cases these research works just remained as an academic interest only However, they did enhance the overall scientific knowledge on polyimides and their properties and potential applications From these papers, a few selected papers were reviewed in appropriate chapters of the thesis

1.1.2.2 Brief history on polyimide R&D and worldwide major commercial product introduction

Early 1959 to 1970

DuPont introduced the first polyimide product, Kapton-H based on pyromellitic dianhydride (PMDA) and oxy-dianiline (ODA) chemistry By mid 1960’s DuPont had three major polyimide products: Kapton (film), Vespal (molding), and Pyre-ML(wire-enamel,) and developed over a period of ten year time a niche and sizable market for the high performance polymer materials [40-44, 51-68]

The National Aeronautics and Space Administration (NASA)’s Langley Research Center was actively involved in polyimide R&D and developed various poly(amic acid)s thermoplastic formulations based on BTDA, and benzophenone group containing diamines These products were referred to as LARC-TPI polymers This technology was then made available for licensing to commercial enterprises worldwide

Contractors of US governments’ defense related projects were major customers for their uses in aerospace (Figure 3) and defense related applications [1-5, 23]

DuPont introduced a series of NR-150 formulation products as high temperature adhesives for high performance composites They were thermoplastic products used as binders, adhesives and coatings for structural composites They were designed for a broad range of aerospace applications, such as radome, jet engines, brake lining ablative heat shields, etc [43]

Monsanto developed and introduced SKYBOND brand of thermosetting polyimide for aerospace composite prepreg fabrication applications [4, 9]

Rhodia, Inc of New York, based on proprietary monomers, introduced thermosetting polyimide under the trade name of Nolimide-A 380 for extreme high temperature (>800°F, i.e., >426°C) adhesives intended for applications in the structural composites and construction of advanced supersonic transport and tactical fighter planes [71]

1975 - 1980

New players came in with other types of polyimides for aerospace and electrical applications Worldwide competition in R&D efforts expanded to a record level in the USA Major funding was provided by the US government for the R&D activities in novel polyimides for defense related hardware products and application development NASA-Lewis, NASA-Langley and Defense Advance Research Program of Agency of

US Govt (DARPA) were few of the leading collaborators [2-7, 9-10, 12-13, 23, 52]

1980 - 1985

The market expanded at an average rate of 10 to 13% per year Most of it was in electrical, aerospace, military aircraft and later in electronic applications R & D efforts and funding continued at a faster pace with an aim to develop new applications for microelectronic industries More new players came in with a wide variety of polyimides and photo-polyimide products and formulations DARPA funding increased further for the development of polyimides for advanced highly sophisticated military applications [3-5, 9, 12-13, 15, 20, 52, 72]

Figure-3: Application of high temperature, high performance polymers in aerospace application [23]

In 1980, Ciba-Geigy Corp introduced XU-218 polyimides having epoxy components

as encapsulants for pin-grid packages (PGP) containing electronic circuitry on silicon chip Subsequently this company introduced BMI chemistry based adhesive Matrimid series of products and Probimide a photosensitive polyimide formulation for photolithography in microelectronics application [3-5, 9, 13, 20, 73-75]

In 1981, Plastics Product Division of General Electric Corp (GE) introduced ULTEM 1000 , a melt processable thermoplastic polyetherimide resin (Tg 220°C)