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The knowledge of the viscoelastic properties of molten polymers and the ability to predict their behavior under deformation is of prime interest to polymer scientists and industry. The discrete linear relaxation spectrum $ lbrack G sb{i}, lambda sb{i} rbrack$ is one of the important viscoelastic properties and it is widely used to characterize molten polymers. This spectrum is obtained from experimental values of the dynamic moduli $ lbrack G sp prime( omega), G sp{ prime prime}( omega) rbrack$. A linear regression method with and without regularization and a nonlinear regression method were compared for inferring a discrete spectrum from experimental data. Since experimental values are used, errors in the data will affect the reliability of the spectrum. Because of the limitations of the experimental apparatus, the moduli can only be determined over a certain frequency range. The values of the relaxation times ($ lambda sb{i}$) and the corresponding elastic moduli ($G sb{i}$) depend on the range of frequencies over which the storage and loss moduli ($G sp prime( omega$) and $G sp{ prime prime}( omega$)) are measured and the method used to calculate them. Also, experimental sources of errors such as uncertainty in the gap measurement, variation in the shape of the edge, residual stress due to the preparation of the sample, and temperature uncertainty will induce experimental errors in $G sp prime( omega)$ and $G sp{ prime prime}( omega)$. This work investigates the effect of time-scale truncation and experimental errors on the discrete relaxation spectrum.

A series of crystalline, substituted polyoxetanes were studied using X-ray fibre diffraction as the primary investigative tool. Three systems were probed, each presenting a unique facet of structure analyses. / The structure of poly(3,3-bis(hydroxymethyl)oxetane) using X-ray fibre diffraction was proposed. Modelling studies and FT-IR have been used to arrive at a probable conformation in which the backbone was found to be planar zigzag and the hydroxyls in the sidechain were extended. Few reflections were observed and it was not possible to grow lamellar single crystals for electron diffraction. / The preliminary structure of poly(3,3-bis(hydroxymethyl)oxetane) diacetate using X-ray fibre diffraction on films and fibres and electron diffraction on lamellar single crystals provided a tentative packing scheme based on the most intense equatorial reflections. CP/MAS $ sp{13}$C NMR indicates slight deviations in the environments for the acetate groups on the same residue. / X-ray fibre diffraction of atactic P(MHMO) resulted in a unit cell of comparable dimensions as in P(BHMO). The intensity and quality of the fibre patterns suggest identical structures. P(BHMO-co-MHMO) is a random copolymer in which the MHMO units are incorporated into the crystalline lattice of P(BHMO). One melting endotherm is observed for all compositions and decreases linearly with increasing content of MHMO. These data support a phenomenon known as isomorphism.

This thesis concentrates on three main areas of research in the field of poly(vinyl chloride), PVC: (1) microstructure determination and local chain motions of PVC in a plasticized system, (2) permeability of PVC and plasticized PVC to gases, and (3) computer modeling of the thermal degradation of PVC. / A quantitative carbon-13 NMR spectrum of PVC in 1,1,2,2-tetrachloroethane-d$ sb2$ (TCE-d$ sb2$) was recorded. Theoretical predictions using Bernoullian statistics permitted the reassignment of several resonances. Carbon-13 spin-lattice relaxation times and NOE values were measured as a function of temperature at two magnetic fields for PVC in two solvents, di-butyl phthalate (DBP) and TCE-d$ sb2$. The difference found in the simulation parameters, from the Dejean-Laupretre-Monnerie model, for PVC in the two solvents were rationalized by assuming a specific interaction between DBP and the CHCl group of PVC and to the relative solvent quality. / The permeability coefficients, P, of PVC films to oxygen were measured as a function of temperature and plasticizer type and concentration. The plasticizers used were di-(2-ethylhexyl) phthalate (DOP), tri-butyl phosphate (TBP), and a binary mixture of the two with a concentration of $ rm Phi sb{DOP}$ = 0.6). The effect of plasticizer type on the permeation coefficients of oxygen followed the trend: P(TBP) $>$ P($ rm Phi sb{DOP}$ = 0.6) $>$ P(DOP). Arrhenius plots of the permeability coefficients showed that the unplasticized and plasticized PVC films of low concentration of plasticizer ($ rm Phi sb{plas} < 0.2$) displayed a discrete change in the slope, in the vicinity of the glass transition temperature, that reflected changes in the activation energy for permeation. In addition, the permeation and diffusion coefficients of oxygen and hydrogen chloride gases in an unplasticized PVC film were measured as a function of temperature. The results suggest that the increase in segmental mobility of the polymer chains above the T$ rm sb{g}$ increases the diffusivity as well as the zone of activation for diffusion leading to the increase in segmental mobility of the polymer chains above the T$ rm sb{g}$ increases the diffusivity as well as the zone of activation for diffusion leading to the increase in both energy and entropy of activation. / A computer program has been written which simulates, according to Bernoullian statistics, the relative handedness of successive monomer units during polymerization and calculates the probabilities of configurational sequences before and after a specified degradation mechanism. At levels of degradation that are accessible to experimental verification by solution NMR ($<$2%), the changes in isotacticity that are predicted by these simulations are at (or under) the limits of experimental error. Furthermore, the simulations indicate that for the degradation to result in double bond lengths that correspond to experimentally determined values requires that the dehydrochlorination also include some atactic and syndiotactic sequences which, in turn, reduces the changes in P$ rm sb{mm}$. (Abstract shortened by UMI.)

Thermolysis of mixtures of linear low density polyethylene, LLDPE, and polystyrene, PS, was investigated. Mixtures having various polyethylene/polystyrene ratios were reacted in a stirred, batch reactor under a nitrogen atmosphere at moderate temperatures, ranging between 350 and 420$ sp circ$C. The major products collected included a volatile product, which was liquid at room temperature, and a wax-like residue. The liquid products were consistently found to contain over 90 percent styrene and toluene with the yield of styrene decreasing as the percentage of polyethylene in the mixture increased. Two fractions were identified in the residue: a high molecular weight polyethylene fraction and a lower molecular weight polystyrene fraction. A significant increase in the solubility of the residue in organic solvents at room temperature was observed as the polystyrene content was raised. The residue became completely soluble in chloroform at a 60/40 ratio of polyethylene/polystyrene. The effect of temperature on the degradation of a selected mixture was also investigated. At temperatures below 390$ sp circ$C, the volatile/residue ratio was independent of the reaction temperature. Above 390$ sp circ$C, the styrene and total liquid product yields increased with increasing temperature, while the yield of residue decreased.

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Twist grain boundaries, which are widely observed in block copolymer samples of lamellar phases, have been investigated through both direct numerical solution and multiple scale analysis of a coarse-grained mesoscopic model equation. We show that the twist boundary profile can be well described by a pair of Ginzburg-Landau equations (amplitude equations) characterizing the slow evolution of the lamellae. The stability of the grain boundary configuration has been examined, and our results show that the boundary width, albeit varying with twist angle, is of order epsilon-1/4 , with epsilon the measure of the distance to the order-disorder threshold. We also study the motion of twist grain boundaries subjected to slow transverse modulations of lamellae, and obtain both analytically and numerically the traveling velocity of the boundary as well as its dependence on modulation wavenumber.

The first part of this study concerns the examination of tetrahydrofuran ring-opening polymerization mediated by the palladium insertion polymerization catalysts, (bipy)Pd(CH3)(L)+ OTf- (L = NCCH3, PhN=C(H)Tol, tBuN=C(H)Tol, CH3 N=C(H)Tol). Mechanistic studies reveal a series of metal-based reactions prior to ring-opening, which can be utilized to control polymer molecular weights and end-groups. / The feasibility of combining this ring-opening reaction to insertion polymerization to generate new block co-polymers is subsequently investigated, and it forms the primary objective of the study. / The dual-functional palladium(II) complex (bipy)Pd(CH3)(NCCH 3)+OTf- is found to mediate a novel, single-step coupling of insertion and ring-opened monomers (CO, norbornene, THF) into new polymers. This coupling process follows an unusual route, involving enol lactone as an intermediate, and facilitated by weak Lewis acid. Similar coupling chemistry has been applied to the synthesis of polyTHF end-capped with a small polynorbornene fragment.