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Shape Memory Rubber Bands & Supramolecular Ionic Copolymers

Brostowitz, Nicole R
http://rave.ohiolink.edu/etdc/view?acc_num=akron1418134490

Abstract Details

2014, Doctor of Philosophy, University of Akron, Polymer Engineering.
The primary focus of this dissertation is to understand the thermo-mechanical properties that govern shape memory in rubber blends. An ideal shape memory polymer (SMP) has a large entropic component that drives shape recovery with a distinct transition mechanism to control the recovery conditions. Polyisoprene rubber is highly elastic and shows shape memory behavior through strain induced crystallization above its glass transition temperature. However, this transition temperature is below 0°C and not suitable for most applications. Shape memory blends can tailor the transition temperature through selection of the switching phase. Most SMP blends require complicated synthesis routes or intensive compounding which would be inhibitive for production. A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Thermal, microscopic studies showed that stearic acid formed a percolated network of crystalline platelets within the natural rubber. Further investigation of the material interactions was carried out with a low molecular weight polyisoprene analog, squalene, and stearic acid gel. Tensile tests on the rubber band demonstrated the thermo-mechanical effect of swelling with stearic acid. Low hysteresis was observed under cyclic loading which indicated viability for the stearic acid swollen rubber band as an SMP. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acidand fixation below that point. Under manual, strain-controlled tensile deformation, the shape memory rubber bands exhibited fixity and recovery of 100% ± 10%. The recovery properties of the SMP were studied under various loading conditions and a model was fit to describe the potential recovery with relation to the fixation. An additional subject covered in this dissertation is supra-molecular ionic copolymers. Supramolecular interactions are non-covalent; e.g. hydrogen bonding, ionic interactions, van der Waals forces. Supramolecular interactions in polymers can be used to tailor the thermo-mechanical properties by controlling bond association and dissociation. Recent research has focused on hydrogen bonded systems due to established synthesis mechanisms. Reversibility of the supramolecular interactions can be triggered by environmental changes. Ionic interactions would provide greater bond strength and more control over operating conditions. Research has been limited on ionic copolymers due to complicated synthesis methods needed to include functionalization. Low molecular weight polymers were synthesized by atom transfer radical polymerization with post polymerization conversion to phosphonium end-groups. Both polystyrene and poly(methyl acrylate) were investigated with similar reaction conditions. Chromatography measured the molecular weight and indicated a low polydispersity consistent with controlled reactions. Copolymers were formed by interfacial mixing of the cationic polymers with multifunctional, anionic oligomers. Oligomers containing sulfonate groups were used to create linear or three-dimensional polymer networks. NMR and rheology was used to characterize the presence and effect of ionic groups when compared to the neat polymer.
Kevin Cavicchi, Dr. (Advisor)
Robert Weiss, Dr. (Advisor)
Avraam Isayev, Dr. (Committee Member)
Coleen Pugh, Dr. (Committee Member)
Chrys Wesdemiotis, Dr. (Committee Member)
163 p.
Polymers
shape memory, polymer, rubber, stearic acid

Recommended Citations

Citations

  • Brostowitz, N. R. (2014). Shape Memory Rubber Bands & Supramolecular Ionic Copolymers [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1418134490

    APA Style (7th edition)

  • Brostowitz, Nicole. Shape Memory Rubber Bands & Supramolecular Ionic Copolymers. 2014. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1418134490.

    MLA Style (8th edition)

  • Brostowitz, Nicole. "Shape Memory Rubber Bands & Supramolecular Ionic Copolymers." Doctoral dissertation, University of Akron, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1418134490

    Chicago Manual of Style (17th edition)

akron1418134490
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This open access ETD is published by University of Akron and OhioLINK.