Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references. Also available via World Wide Web.

The work elucidates the novel physical and thermal properties of thin and ultra-thin films of crosslinked polymer and organized microstructures with a special emphasis on surface and interfacial effects and the structure-property relationships. Two major crosslinked polymer coatings have been thoroughly investigated: polymer microstructures fabricated by multi-laser interference lithography (IL), and plasma polymer coatings. We unveiled intriguing thermal properties of plasma polymer films originating from their physical state and exploiting the same for the design of ultrasensitve chemical sensors. A novel paradigm of surface coatings, single and bi-component periodic, porous crosslinked polymeric structures, has been introduced and thoroughly studied. Surface, interfacial, and mechanical properties of these novel class crosslinked polymer coatings clearly demonstrate the enormous potential of the IL microstructures as organized multicomponent polymer systems. When subjected to external or internal stresses the periodic porous structures can exhibit a sudden and dramatic pattern transformation resulting in remarkable change in the photonic, phononic and mechanical properties of these structures. Furthermore, the confinement of these instabilities to localized regions results in complex hierarchical structures. The two polymer coatings (plasma polymers and IL microstructures) with complementary attributes (such as periodic structure, vertical stratification, residual internal stresses, and high surface and interface tunability) enabled us to understand and design novel multifunctional polymer coatings.

The compound 2,6-anthracenedicarboxylic acid is used as a comonomer for the synthesis of poly(ethylene terephthalate). The resulting copolymers are characterized and further functionalized by Diels-Alder grafting or crosslinking through the anthracenate unit. Diels-Alder reaction is used to graft small molecules and oligomers endcapped with maleimide as dienophiles on to poly(ethylene terephthalate-co-2,6-anthracenedicarboxylate),PET-co-A. Maleimide-capped poly(ethylene glycol) is grafted onto PET-co-A to improved its hydrophilicity. 2,6-Anthracenedicarboxylic acid is also incorporated into the known liquid crystalline polymer, LCP, poly(4-oxybenzoate-co-1,4-phenylene isophthalate), HIQ40. The resulting copolymer, poly(4-oxybenzoate-co-1,4-phenylene isophthalate-co-2,6-phenylene anthracenate), HIQ40-co-A, shows LCP behavior. These HIQ40-co-A copolymers are grafted with maleimide end-capped monomers and polymers andcrosslinked with bismaleimides through a Diels-Alder mechanism.

Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Tsukruk, Vladimir; Committee Member: Gall, Ken; Committee Member: Griffin, Anselm; Committee Member: Jang, Seung Soon; Committee Member: Thio, Yonathan. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The removal of higher hydrocarbons from natural gas streams is an important separation that has been identified as a growth area for polymer membranes. An ideal membrane material for this separation would be more permeable to higher hydrocarbons (i.e., C3+ compounds) than to CH₄. This allows the CH₄ rich permeate to be retained at or near feed pressure, thus minimizing the requirement for repressurization followingmembrane separation. A polymer which demonstrates the ability to separate vapor from gases with high efficiency is poly [1-(trimethylsilyl)-1-propyne] (PTMSP). PTMSP is a stiff chain, high free volume glassy polymer well known for its very high gas permeability and outstanding vapor/gas selectivity. However, PTMSP is soluble in many organic compounds, leading to potential dissolution of the membrane in process streams where its separation properties are of greatest interest. PTMSP also undergoes significant physical aging, which is the gradual relaxation of non-equilibrium excess free volume in glassy polymers. Crosslinking PTMSP with bis(azide)s was undertaken in an attempt to increase the solvent resistance and physical stability of the polymer. A fundamental investigation into crosslinking PTMSP with a bis(azide) crosslinker was the focus of this thesis. Pure gas transport measurements were conducted with N₂, O₂, CH₄, C₂H6, C₃H₈, and n-C₄H₁₀ over temperatures raging from -20°C to 35°C and pressures ranging from 0 to 20 atm. Mixed gas permeation experiments were conducted using a 98 mol % CH₄, and 2 mol % n-C₄H₁₀ mixture. The mixed gas permeation experiments were conducted at temperatures ranging from -20°C to 35°C, and pressures ranging from 4 to 18 atm. Inorganic nanoparticles such as fumed silica (FS) were added to uncrosslinked and crosslinked PTMSP, and the effects of their addition on the transport properties were investigated. Crosslinking PTMSP with bis(azide)s increases its solvent resistance, and crosslinked films are insoluble in common PTMSP solvents such as toluene. At all temperatures, the initial pure and mixed gas permeabilities of crosslinked PTMSP films are less than those of uncrosslinked PTMSP. This decrease in permeability is consistent with the fractional free volume (FFV) decrease that accompanies crosslinking. Pure gas solubility coefficients are relatively unaffected by the crosslinking process, so the decrease in permeability is caused by decreases in diffusivity. The addition of FS nanoparticles increases the initial pure and mixed gas permeabilities of uncrosslinked and crosslinked PTMSP. The pure gas permeabilities and solubilities of all PTMSP films increase when the temperature decreases, while the diffusivities decrease. The rates of change in pure gas transport properties with temperature is similar for all films, so the temperature dependence of pure gas transport properties of PTMSP is unaffected by the addition of crosslinks or FS. The aging of uncrosslinked and crosslinked PTMSP films was investigated by monitoring N₂, O₂ and CH₄ permeabilities and FFV over time. The FFV and permeabilities of crosslinked films decreased over time, so crosslinking did not arrest the physical aging of PTMSP, as has been previously reported, and these differences in aging observations are likely to be a consequence of differences in post film casting thermaltreatments. The addition of 10 wt % polysiloxysilsesquioxanes (POSS) nanoparticles decreases the permeabilities of uncrosslinked and crosslinked PTMSP by approximately 70 %, and the permeability and FFV values of the resulting nanocomposite films were stable over the course of 200 days. In all PTMSP films, the mixed gas permeabilities of n-C₄H₁₀ increase with decreasing temperature, while the mixed gas CH₄ permeabilities decrease with decreasing temperature. As a result, the mixed gas n-C₄H₁₀/CH₄ permeability selectivities increase with decreasing temperatures. The addition of crosslinks and FS nanoparticles to PTMSP decreases the mixed gas n-C₄H₁₀/CH₄ permeability selectivities, and changes in the free volume characteristics of PTMSP caused by crosslinking and FS nanoparticles are thought to reduce the blocking of CH₄ permeation by n-C₄H₁₀. / text

Thesis (Ph. D.)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Karl I. Jacob; Committee Member: Anselm C. Griffin; Committee Member: C. P. Wong; Committee Member: Rina Tannenbaum; Committee Member: William J. Koros; Committee Member: Yonathan S. Thio.

Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.

Mixed matrix nanocomposite membranes composed of a crosslinkable polyimide matrix and high-silica molecular sieve particles were developed for purifying natural gas. It was shown that ideal mixed matrix effects were not possible without sieve surface modification. A previously developed Grignard procedure was utilized to deposit magnesium hydroxide nanostructures on the sieve surface in order to enhance polymer adhesion. Analyses of Grignard-treated sieves pointed to the formation of non-selective voids within the surface deposited layer. These voids were suspected to lead to lower-than-expected membrane performance. In order to improve membrane transport, a reactive sizing procedure was developed to fill these voids with polyimide-miscible material. In a serendipitous discovery, as-received sieves--when treated with this reactive sizing procedure--resulted in nearly identical membrane performance as reactive-sized, Grignard-treated sieves. This observation lead to the speculation of a non-ideal transport mechanism in mixed matrix membranes.

Natural gas is one of the fastest growing primary energy sources in the world today. The increasing world demand for energy requires increased production of high quality natural gas. For the natural gas to be fed into the mainline gas transportation system, it must meet the pipe-line quality standards. Natural gas produced at the wellhead is usually "sub-quality" and contains various impurities such as CO2, H2S, and higher hydrocarbons, which must be removed to meet specifications. Carbon dioxide is usually the most abundant impurity in natural gas feeds and high CO2 partial pressures in the feed can lead to plasticization, which causes loss of some methane product and may ultimately render the membrane ineffective. Moreover, the presence of highly sorbing higher hydrocarbons in the feed can further reduce membrane performance. Covalent crosslinking has been shown to increase plasticization resistance in dense films by suppressing the degree of swelling and segmental chain mobility in the polymer, thereby preserving the selectivity of the membrane. This research focuses on extending the dense film success to asymmetric hollow fibers. In this work, the effect of high pressure CO2 (up to 400 psia CO2 partial pressure) on CO2/CH4 mixed gas separation performance was investigated on defect-free the hollow fiber membrane at different degrees of crosslinking. All the crosslinked fibers were shown to exhibit good resistance to selectivity losses from CO2 induced plasticization, significantly more than the uncrosslinked fibers. Robust resistance of the hollow fiber membranes in the presence of toluene (a highly sorbing contaminant) was also demonstrated as the membranes showed no plasticization. Antiplasticization was found to occur in the presence of toluene feeds with the crosslinkable fibers used in this work.

Our research focuses on re-using a waste a material, cross-linked polyethylene abbreviated XLPE, which is a widely used coating for wires. XLPE is strong and has excellent thermal properties due to its chemical structure - what leads to the significance of recycling this valuable polymer. Properties of XLPE include good resistance to heat, resistance to chemical corrosion, and high impact strength. A wire is usually composed of a metal core conductor and polymeric coating layers. One creates a new coating, including little pieces of recycled XLPE in the lower layer adjacent to the wire, and virgin XLPE only in the upper layer. Industries are often wasting materials which might be useful. Mostly, some returned or excess products could be recycled to create a new type of product or enable the original use. This method helps cleaning the waste, lowers the costs, and enhances the income of the manufacturing company. With the changing of the thickness of the outer layer, the roughness changes significantly. Moreover, different processing methods result in surfaces that look differently.