HIGH TEMPERATURE SHAPE MEMORY POLYMERS & IONOMER MODIFIED ASPHALTS A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Ying Shi August, 2013 HIGH TEMPERATURE SHAPE MEMORY POLYMERS & IONOMER MODIFIED ASPHALTS Ying Shi Dissertation Accepted: Approved: ______________________ _______________________ Advisor Department Chair Dr. Robert A. Weiss Dr. Robert A. Weiss ______________________ _______________________ Committee Member Dean of the College Dr. Sadhan C. Jana Dr. Stephen Z. D. Cheng ______________________ _______________________ Committee Member Dean of the Graduate School Dr. Kevin Cavicchi Dr. George R. Newkome ______________________ _______________________ Committee Member Date Dr. Matthew Becker ______________________ Committee Member Dr. Yi Pang ii ABSTRACT This dissertation consists of two research subjects: High Temperature Shape Memory Polymers and Ionomer Modified Asphalts. Current development of thermally sensitive shape memory polymers (SMPs) has focused primarily on relatively low transition temperatures (Tc < 100°C) and elastomeric polymers, such as thermoplastic polyurethanes (TPU), crosslinked polyethylene, poly (ε-caprolactone), sulfonated EPDM and polynorbornene. Those materials are appropriate for applications such as biomedical and surgical materials, smart fabrics and heat shrinkable tubing. Materials used as aerospace or structural components often require higher modulus and switching temperatures for shape change and actuation. To the best of our knowledge, there have been no reports of thermoplastic SMPs with controllable switching temperatures above 100°C. There has been research on high temperature SMPs but based on thermoset polymer systems. High temperature thermoplastic shape memory polymers were developed from metal salts of sulfonated PEEK (M-SPEEK, M=Na+, Zn2+, Ba2+, Al3+, Zr4+) ionomer and composites of the M-SPEEK ionomers with a fatty acid salt. M- SPEEKs were prepared by neutralizing sulfonated PEEK acid to metal salts. The glass transition temperatures of M-SPEEK ionomers increased with increasing Coulomb energy of ion pairs and the ionomers were thermally stable to ~320°C. The M-SPEEK ionomers exhibited microphase separated morphologies and the average correlation length was determined by small angle X-ray scattering. Al-SPEEK and Zr-SPEEK showed crosslinked characteristics such as rubbery plateau above Tg and much reduced iii water uptake. The M-SPEEK ionomers exhibited reasonable shape memory behavior, in which the permanent network was provided by ionic nanodomains formed by the interaction of ionic groups and glass transition temperatures served as the switching temperatures. The relative poor shape efficiency of Na-SPEEK and Zn-SPEEK (80-90%) can be improved by blending M-SPEEK with a low molar mass crystalline compound NaOl. The composites were prepared from 70 wt% M-SPEEK (M = sodium or zinc) and 30 wt% sodium oleate (NaOl). Ionic nanodomains formed by the interactions of ionic groups provided a permanent physically crosslinked network and strong dipolar interactions between the ionomer and a dispersed phase of crystalline NaOl provided the temporary network. A temporary shape was achieved and fixed by deforming the material above the melting temperature (Tm) of NaOl and then cooling under stress to below Tm. The permanent shape was recovered by reheating the material above Tm without applying stress. Shape fixing efficiencies of 96% were achieved and shape recovery reached 100%. Triple shape memory behavior was also achieved for M- SPEEK/NaOl compounds using the glass transition of the ionomer and the melting point of the NaOl as two separate switching temperatures. Asphalt binders suffer from different kinds of distresses such as low temperature cracking, rutting and fatigue during “in life” service. In the regions with cold climate, thermal cracking of pavement occurs when low temperature shrinkage exceeds the ability of stress dissipation by the asphalt binders and leads to brittle fracture of the glassy pavement. The objective of the ionomer modified asphalt project is to improve the elasticity of the asphalt binder at low temperature in order to prevent the cracking. A iv performance grade 64-28 asphalt and partially neutralized copolymers of ethylene and methacrylic acid ionomer were mixed at four concentration levels (0-9 wt%) to yield ionomer modified asphalt blends. The thermal properties, morphology and viscoelastic behavior of ionomer modified asphalts were studied. The ionomer modified asphalt exhibited much better dispersion and smaller phase separation than did polyethylene modified asphalt. After establishing the linear viscoelastic range of response through strain sweep, frequency sweep tests at a temperature range of 30-80C were conducted to study the dynamic mechanic properties of the modified blends. The isothermal response curves were reduced to dynamic master curves of modulus and viscosity based on the time- temperature superposition principle. The effects of ionomer concentration and mixing time on the viscoelastic behavior were studied. The addition of ionomer improved the elasticity of the asphalt, but long times were needed to mix the ionomer into the asphalt and properties were very sensitive to mixing time. A series of SuperPave tests were conducted on both ionomer modified and neat asphalt, which simulating the real life temperature and traffic load condition. The performance grade of ionomer modified asphalt was transformed from 64-28 to 69.2-26.5. v ACKNOWLEDGEMENTS The completion of this dissertation took place with the help and encouragement of many people. Like they say, “it takes a village to raise a child”, I believe it took just as many people for my dissertation, and I owe thanks to them. I would like to express my deepest appreciation to my advisor Dr. Robert Weiss., who has the attitude and a substance of a genius. He is the best advisor I could ever ask for. Thank you for training to be a good scientist. I would like to thank Dr. Mitra Yoonessi for her support and guidance through the High T SMP project. Thank you for giving me the opportunity to explore other high T polymer project from OAI and thank you for your suggestions and assistance for job search. I also like to thank Dr. Montgomery T. Shaw and Dr. Richard Parnes at the University of Connecticut. Thank you for helping me understanding rheology and discussing my IMA project. I also like to give thanks to all members of my dissertation committee for their time and support: Dr. Kevin Cavicchi, Dr. Sadhan Jana, Dr. Matthew Becker, and Dr. Yi Pang, thank you. My group members and colleagues in the Polymer Engineering Department (Univ. Akron) and Institute of Materials Science (Univ. Conn.) have been a critical source of support and encouragement. I would like to thank my previous group member Dr. Jing vi Dong, Dr. Gerald Ling, Dr. Emmanuel Pitia, Dr. Xueyuan Wang, Dr. Hui Niu, and, Dr. Jinkun Hao for discussing my research problems. I also like to thank the current group members: Sahil Gupta, Longhe Zhang, Xing Lu, Zhiyang Zhao, and Murat Bakan. It was a great pleasure to work with you. Last but not the least I want to give much thanks to my mom, Lan Yang for her great support, and love. vii TABLE OF CONTENTS Page LIST OF TABLES .......................................................................................................... xivi LIST OF FIGURES .......................................................................................................... xv CHAPTER I. INTRODUCTION: HIGH TEMPERATURE SHAPE MEMORY POLYMERS .......... 1 1.1 Shape Memory Polymers.................................................................................. 1 1.2 Shape Memory Polymers versus Shape Memory Alloys ................................. 2 1.3 Thermal responsive shape memory polymers .................................................. 3 1.4 Research Objective ........................................................................................... 5 II. BACKGROUND AND LITERATURE REVIEW HIGH TEMPERATURE SHAPE MEMORY POLYMERS .................................................................................................... 6 2.1 Fundamental aspects of shape memory polymers ............................................ 6 2.1.1 Thermodynamic point of view ..................................................................... 7 2.1.2 Molecular mechanism of the shape memory effects .................................... 8 2.2 Classification of Shape Memory Polymers ................................................... 10 2.2.1 Physically cross-linked glassy networks .................................................... 10 2.2.2 Physically cross-linked semi-crystalline networks .................................... 13 2.2.3 Chemically cross-linked glassy networks .................................................. 15 2.2.4 Chemically cross-linked semi-crystalline networks .................................. 17 2.2.5 Other thermoplastic networks .................................................................... 18 2.3 Characterization Methods ............................................................................... 20 viii 2.3.1 Thermal properties characterization ........................................................... 20 2.3.2 Viscoelastic properties characterization ..................................................... 21 2.3.3 Morphology characterization .....................................................................