In this thesis, we explored the use of a renewable resource to produce more sustainable polymeric materials. Limonene, a monocyclic terpene existing in many essential oils extracted from citrus rinds, was the renewable monomer investigated. The d-limonene ((+)-limonene) isomer is a major component (~90%) of orange oils from orange juicing and peel processing. Having been used as a flavour and fragrance additive in cosmetics, foods and beverages, as well as a green solvent, limonene is of particular interest in polymerization, because it contains double bonds, which provide the bifunctionality necessary for polymerization. Limonene is also an allylic monomer (CH2=CH-CH2Y), which presents challenges in free-radical homopolymerization and thus, copolymerization was investigated herein to overcome this difficulty. 2-Ethylhexyl acrylate (EHA) and n-butyl methacrylate (BMA) were used in two separate projects, as comonomers with limonene. Using bulk free-radical copolymerization at 80℃, with benzoyl peroxide (BPO) as the initiator, high molecular weight (>100,000) EHA/limonene and BMA/limonene copolymers were produced. Reactivity ratios, important parameters used in the prediction of copolymer composition, were estimated and shown to accurately predict the copolymer composition of subsequent experiments. These can now be used for the application of appropriate semi-batch policies to further enhance limonene incorporation into the copolymers.

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<p> The Arrhenius equation for the ring opening isomerization of cyclopropylmethyl radicals (R•) to 3-buten-1-yl radicals (R•') for the 303-362 K temperature range was determined by thermolysis of cyclopropylmethyl [1-hydroxy-1-methylethyl] diazene in the presence of excess 1,1,3,3-tetra-methylisoindolin-2-yloxyl (Y•).</p> <p> Rate constants for coupling of R• with Y• were assumed to be proportional to diffusion controlled rate constants (kd) and rate constants (ki) for the isomerization were calculated from kd (corrected) and product ratios (RY/R'Y). The temperature dependence of ki, given by log(ki/s^-1) = (13.9 ± 0.4) - (7.6 ± 0.1)/θ, is significantly different from that determined by Ingold and co-workers by kinetic epr spectroscopy in the temperature range 128-153 K; log(ki/s^-1) = (11.34 ± 0.85) - (5.94 ± 0.57)/θ, where θ = 2.3 RT kcal mol^-1.</p> / Thesis / Master of Science (MSc)

<p> Aryl radical ring closures onto the azo functional group were investigated. A series of ortho-substituted aryl radicals (83a-f) have been generated by bromine abstraction from the corresponding 1-(orthobromophenyl)-1-methoxy-azoethanes (82a-f) by tributyltin radicals. The radicals generated underwent cyclization in the 5-endo sense, to ultimately afford the substituted indazoles (86a-f). There was also some evidence for cyclization to the other azo nitrogen (closure in the 4-exo sense) to form a 4-membered ring. The aryl radical also underwent hydrogen atom abstraction from tributyltin hydride in competition with cyclization. Since the rate constant for hydrogen atom abstraction from tributyltin hydride by aryl radicals is known, this makes it possible to estimate the rate constants for cyclization throughout the series.</p> / Thesis / Master of Science (MSc)

<p> The free radical polymerization of styrene in benzene using azo-bisisobutyronitrile as a catalyst has been studied both theoretically and experimentally. The molecular-weight distribution and conversion are predicted on the basis of a simplified kinetic mechanism, neglecting a number of minor side reactions. The steady-state assumption is investigated and is shown to be applicable in the case of styrene polymerization, a pseudo-steady-state being reached in less than one second. Using the steady-state approach a relatively simple kinetic model is obtained, suitable for computer simulation. The prime variables consist of the ordinary reaction conditions such as monomer concentration, solvent concentration, catalyst concentration, reaction temperature and reaction time.</p> <p> The polymerization was carried out isothermally in a stirred batch reactor from which samples were abstracted at various time intervals. Conversion was determined by precipitating the polymer with methanol, filtering, and weighing, and the molecular-weight distribution has been obtained by gel-permeation chromatography. A computer program was written to interpret the variation of refractive index with respect to the elution volume trace from the chromatograph, giving a readout of molecular chain length in monomer units versus weight fraction.</p> <p> The experimentally obtained conversion and distribution curves are compared with those obtained from the mathematical model. Except for bulk polymerization agreement between the two is good. Good agreement for conversion is obtained for all cases if the catalyst initiation efficiency is adjusted according to the monomer or solvent concentration. However, the same considerations do not give good agreement for molecular-weight distribution. Rather it appears that the rate constants instead of the catalyst efficiency are monomer or solvent concentration dependent, which would explain the discrepancies.</p> / Thesis / Master of Engineering (MEngr)

<p> Polymerization of styrene was carried out in continuous and batch reactors using azobisis obutyronitrile as initiator and benzene as solvent. Monomer conversion, molecular weight distribution (MWD) and viscosity were measured.</p> <p> Corrections to the conventional kinetic mechanism using results from the continuous reactor were determined. These corrections were applied to the batch reactor kinetic model and the conversion and MWD thus predicted were compared to experimental results. It was found that the corrections applied to the batch system were not adequate to give accurate predictions of conversion and MWD.</p> <p> A short computer study of the effect of oscillating monomer flow and temperature, as opposed to steady flow, on a transient continuous reactor was also carried out. It was found from this study that at low conversions oscillations in monomer flow will not affect the time average conversion and molecular weight. Oscillations in temperature caused an increase in time average conversion and a decrease in time average molecular weight as compared to results obtained when the reactor was operated at a steady temperature which was the average of the oscillating temperatures.</p> / Thesis / Master of Engineering (MEngr)

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Call number: LD2668 .T4 1984 G86 / Master of Science

"In situ polymerizing hydrogel systems play an important role in many tissue engineering applications. They have proven to be useful in biomedical applications that require conversion of liquid macromer solution to tissue compliant hydrogel under physiological conditions. A series of poly(ethylene glycol)-co-poly(lactate) diacrylate macromers were synthesized with variable PEG molecular weight and lactate content. The macromer compositions were confirmed by NMR spectroscopy and ion chromatography. These macromers were polymerized to form hydrogels by free radical polymerization using either redox or photochemical initiators. The current study focused on the optimization of polymerization conditions. Compressive modulus and residual acrylate analysis were used to evaluate polymerization efficiency. To characterize the network structure, the swelling ratio values were converted to the average molecular weight between crosslinks ( ) and mesh sizes (ξ) using Flory-Rehner theory. Current study suggested hydrophobic modification is desired to achieve high polymerization efficiency. Electrospinning is a developing technique to produce ultra fine fibrous structures from polymer solutions. Current research efforts have focused on understanding the effects of principal parameters such as molecular weight distribution (MWD) and polymer surfactant interactions on the morphology of the electrospun patterns. Fundamental understanding of the dilute solution rheology of the polydisperse polymer/solvent and polymer/solvent/surfactant systems was first established. Using viscometry, the on-set of entanglement concentrations could be obtained for various systems. Electrospinning was then carried out to evaluate the effects of polymer molecular weight, molecular weight distribution (MWD) and the polymer-surfactant interaction on the fiber formation and morphological features. The importance of increased chain entanglements due to high molecular weight component within the polydisperse system and the expansion of the coil dimension by binding the surfactant micelles have been recognized. The critical concentrations for incipient as well as stable fiber formation were determined. "