A series of reactive poly(aryl ether ketone) oligomers of controlled molecular weight, based on substituted hydroquinones and 4,4$\sp\prime$-difluorobenzophenone, have been synthesized and incorporated into commercial high performance epoxy-amine resin systems. The thermal and spectroscopic characteristics of the oligomers as a function of chemical structure and molecular weight have been evaluated. The oligomers are initially miscible in the epoxy-amine mixtures but are observed to phase separate during the curing process. Two phases, a thermoplastic-rich phase and a thermoset-rich phase have been identified. Four distinct morphologies; a thermoset-rich continuous phase with thermoplastic-rich inclusions, a thermoplastic-rich and thermoset-rich mixed continuous phase, a thermoplastic-rich continuous phase with thermoset-rich inclusions, and a single phase system have been observed. The morphology/property/processing relationship has been studied as a function of oligomer loading level, oligomer chemical structure, oligomer molecular weight, and curing temperature. The final thermal and mechanical properties were shown to be dependent on the phase separated morphology. Resins with thermoplastic-like toughness and thermoset-like processing characteristics have been attained when a thermoplastic-rich continuous phase is achieved. Composite and adhesive characteristics have also been measured. The synthesis and characterization of novel thermotropic liquid crystalline poly(aryl ether ketone)s is also presented. A series of copolymers based on a 4,4$\sp\prime$-biphenol mesogen and a crystal disrupting substituted hydroquinone have been synthesized. Copolymers containing between 50% and 75% biphenol were found to possess liquid crystalline characteristics. These materials are believed to be the first thermotropic liquid crystalline poly(aryl ether ketone)s reported to date.

Diblock-Copolymer Melts at patterned surfaces are investigated. Above the order-disorder transition (ODT) of the bulk, density-functional theory is used to calculate the density profile at the surface. Below the ODT self-consistent field theory (SCFT) is employed to extract numerically possible density variations across a thin film. The orientation of the diblocks and lamellar morphology at the surface depends on the ratio of natural lamellar bulk period to surface period [special characters omitted]. The diblocks can be either perpendicular or parallel to the surface, inducing parallel or perpendicular lamellar morphology. Individual polyelectrolytes and their counterions are studied with SCFT. Scaling behavior and density distribution are numerically calculated and compared to known results. Although the scaling roughly agrees with expected results, the density distribution and the end-to-end vector distribution do not. Apparently, fluctuations significantly contribute to angular averaged SCFT of an individual polymer. Dilute polymer solutions under shear are investigated with renormalization group theory of the Gaussian model and with Brownian dynamics simulations of the bead-rod model. The material functions derived from the first model using coupled Langevin equations agree qualitatively with the ones derived from the diffusion equation of the same model. They exhibit shear thickening for high shear rates due to the unrestricted extensibility of the chain. The excluded volume interaction is responsible for shear thinning at intermediate shear rates. The simulations yield shear thinning behavior for all shear rates, independent of the presence or absence of excluded volume or hydrodynamic interactions. A good agreement with experiments is obtained for the relative extension with increasing shear rate. In theta-solutions an unexpected shrinkage of the chain is observed for high shear rates.

Computational quantum chemistry was used as a tool to predict needed thermochemistry and kinetics for two classes of problems: formation and destruction of NOx pollutants and development of new fire-resistant polymers. Of the latter, polycarbodiimides and polyhydroxyamides (PHA's) were studied. Different methods were used: HF/6-31 G(d), BAC-MP4 (bond-additivity corrections to UMP4 energies and HF vibrational frequencies), PM3 semi-empirical, and combinations. On the NOx problem, work focused on using theory to generate improved kinetics in H2/O2/NOx combustion. The results were a set of thermochemical data and highpressure-limit kinetics for NOx formation and destruction. Hartree-Fock structures and frequencies and fourth-order Moeller-Plesset energies were used for reactions of H/N/O-species involving H1N1O1 , N1O2, N2O1, H1N 2O1, and N2O2 surfaces, including NH + NO ↔ N2O + H, N2O + O ↔ NO + NO, N + OH ↔ NO + H, N + O2 ↔ NO + O, and N + NO ↔ N2 + O. Thermochemical results were discussed in the form of potential energy surfaces. In general, BAC-MP4 heats of formation compared consistently well to literature data. The results generated from this work allowed evaluation of pressure-dependent kinetics and, ultimately, a refined group of reactions for the NOx mechanism. Strengths of particular bonds and bonding combinations in polycarbodiimides were calculated. Work focused on effects of R groups, chain size and stereoregularity on bond dissociation energies (BDE). Specifically, five polycarbodiimide systems were studied: (1) R=R′=H, (2) R=R′ =CH3, (3) R=R′=CH2CH 3, (4) R=CH(CH3)(Phenyl), R′=H, and (5) R=CH(CH3)(phenyl), R′=CH 3. Methyl- and ethyl-substituted polycarbodiimides decreased the bond strength of the central C-N bond. Ligands on the amine (backbone) nitrogen weakened its chain C-N bond dramatically. However, a lower barrier reaction has also been identified. Results imply rapid, concerted unzipping of this polymer, a result consistent with experiment. For the polyhydroxyamide (PHA) system, a model cyclization reaction of PHA to polybenzoxazole (PBO) was evaluated. PHA cyclization to PBO has been studied experimentally, but a detailed theoretical reaction surface has never been evaluated. Moreover, a plausible mechanism by which PHA arrives at PBO had not been previously determined. The calculated overall heat of reaction was thermoneutral, and decomposition was determined to occur at 212°C, compared to the 215°C experimental value. The hydrogen-transfer reaction and a four-center concerted transition-state reaction were found to be the limiting steps.

The steric nature of the new topology created by the starburst polymer has been studied by $\sp{13}$C and $\sp2$H dynamic nuclear magnetic resonance (NMR) relaxation measurements. For two series of poly(amidoamines), PAMAM, (one OH terminated, the other NH$\sb2$ terminated), $\sp{13}$C correlation times ($\tau$) of the terminal carbons were found to be almost independent of the number of end groups; $\tau$ varied from 1.0 $\times$ 10$\sp{-11}$ to 6.3 $\times$ 10$\sp{-11}$, and no evidence of dense-packing of the end groups was observed. The $\tau$'s of the methylene carbons on the interior of the dendrimers were found to increase with molecular weight, indicative of a progressive increase in local monomer density within the polymer. No significant differences in relaxation parameters of the internal carbons were observed for the NH$\sb2$ terminated PAMAM compared to the OH terminated analogues, in either D$\sb2$O or DMSO-d$\sb6$. Thus, the results reflect topological effects, and are not due to specific solvent or end group behavior. Larger relaxation times were observed for both series when measured in D$\sb2$O. While the differences in polymer behavior in the two solvents indicate that the polymer chains are more flexible in D$\sb2$O than in DMSO-d$\sb6$, intrinsic viscosities were determined to be comparable in the two solvents (0.04-0.10 dl/g). The difference in the NMR behavior is thus attributed to strong H-bonding between the polymer and DMSO, resulting in an increase in the hydrodynamic volume of the mobile unit. The relaxation behavior of the terminal carbon, in D$\sb2$O, differed upon changing the end group. The terminal carbon of the OH terminated PAMAM was observed to be less mobile than the corresponding carbon atom in the NH$\sb2$ terminated PAMAM. $\sp2$H NMR relaxation measurements were used in a more extensive study of the mobility of amine terminated PAMAM chains as a function of molecular weight and positions. The $\tau$'s were found to increase with molecular weight, irrespective of the location of the labelling. In the last generation the $\tau$'s were found to increase as the number of termini increases from 3($\tau$ = 1.7 $\times$ 10$\sp{-12}$s) to 384 ($\tau$ = 2.2 $\times$ 10$\sp{-11}$s), and were smaller than the $\tau$'s observed when the polymers were labelled at interior positions. No significant difference in relaxation parameters was observed when the label was located in the interior repeat units, irrespective of chain length following deuteration. No evidence of radial gradients was observed.

Thesis (M.S.)--Marquette University, 2009. / Rajendra Rathore, Mark Steinmetz, James Gardinier, Advisors.

Thesis (M.Sc.)--Victoria University of Wellington, 2009. / Includes bibliographical references.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study is to further investigate the effect of using six different light source types with different light output intensities on the parameters of a mathematical model that predicts the DOC in VLDC’s. In this equation: D = Dp In(E0/Ec), D is the depth of cure in millimeters, E is the curing energy in J/cm2, Ec is the critical curing energy for the composite to reach a gel layer, and Dp is a characteristic coefficient. Three LED and three halogen dental curing units with different light output intensities were used to cure three shades (B1, A3, D3) of a hybrid resin composite. The exposure duration was at the intervals of 10, 20, 30, and 40 seconds for each sample setting. ISO scraping technique was performed to measure the depth of cure of each sample. Regression analysis was used to assess the fit of the proposed mathematical model D = Dp In(E0/Ec) to the experimental data obtained in this study. 72 For all the shade-light combinations; A3, B1, and D3 had significantly different regression lines (P < 0.05) with significantly higher Dp and Ec for B1 than A3 and D3. The only exceptions were for the Ec values between B1 and D3 in Allegro, Astralis 5, and Visilux 2 groups; and the Ec between A3 and B1 in Allegro group. The Dp and Ec parameters didn’t show significant differences between A3 and D3 shades in all the groups. Also, most of the significant differences for Dp values occurred in the B1 shade-light combinations; however, none of the D3 shade-light combinations showed significant differences for Dp. Several factors play combined influential effects on the kinetics of polymerization and depth of cure in VLDC’s. The shade has a more dominant effect on both parameters Dp and Ec than the curing light type or source output intensity. As we cure lighter shades “B1,” the effect of using different lights with different output intensities on the two parameters Dp and Ec will be greater and more significant than for darker shades “A3 or D3.” The clinical significance drawn from this study is that clinicians should recognize that using curing lights w/ increased output intensities doesn’t absolutely increase the DOC of VLDC’s especially with the darker shades.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study was 1) To determine the impact of eliminating or delaying the photo-activation procedure on the polymerization contraction stress (PCS)and degree of conversion (DC) of a dual-cured resin luting agent, and 2) To determine the amount of delay in photo-initiation of the dual-cured resin cements that can achieve a reduced PCS value with the highest possible DC. The amount of PCS and DC of a dual-cured resin luting agent was determined using a tensometer and ATR spectroscopic technique, respectively. Photo-activation delay in seven tested groups was 0 min, 2 min, 4 min, 6 min, 8 min, 10 min and no photoactivation. Five samples for each group were tested. There were two hypotheses for this study: 1) A significant decrease in the amount of PCS associated with delayed photo-activation, and 2) A significant increase in DC associated with delayed photo-activation.The PCS of the chemical-cure luting agent had significantly lower value than all of the light-cure groups. For the light-cure groups, those with a 4-min delay had higher PCS than those with delays of 0 min, 2 min, 6 min, 8 min, and 10 min. The zero (0)-min and 2-min delay had higher PCS than the 6-min, 8-min, and 10-min delay; and the 6-min delay had higher PCS than the 8-min and 10-min delay. The PCS decreased 0.086 MPa per minute of delay. The DC of the chemical-cure luting agent had significantly lower value than the 2-min, 4-min, 6-min, 8-min, and 10-min delaylight cure. For the light-cure groups, 0-min delay had a lower DC than the 2-min, 4-min, 6-min, 8-min, and 10-min delay; 2-min delay had lower DC than 4-min, 6-min, 8-min, and 10-min delay. The 4-min and 6-min delay had lower DC than the 8-min and 10-min delay; and the 8-min delay had a lower degree of conversion by peak area than the 10- minute delay. The DC increased 0.021 per minute of delay. Extending the stress relief period of the dual-cured luting agents by delaying light activation has a significant impact on PCS and DC values. There was significant decrease in PCS with the delayed light curing of the resin luting agent. Significant increase in DC was noticed when light activation was delayed in the dual-cured resin luting agents.

Indiana University-Purdue University Indianapolis (IUPUI) / Purpose: Dental sealant forms a physical barrier to prevent pit and fissure caries; therefore, the retention rate becomes a main factor of the sealant’s effectiveness. Electrospun nylon-6/N6 nanofibers have shown good mechanical properties, such as high tensile strength and fracture toughness. Chitosan/CH has received significant attention due to properties such as antibacterial activity. The purpose of this study was to synthesize and evaluate the effect of incorporating N6 and CH electrospun nanofibers on the physical-mechanical and antibacterial properties of an experimental resin-based sealant. Methods and Materials: Nanofiber synthesis: N6 pellets were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol at a concentration of 10wt%. Practical-grade chitosan was dissolved in trifluoroacetic acid and dichloromethane (60:40 TFA/DCM) at 7 wt%. Electrospinning parameters were optimized in order to fabricate defect-free N6 and chitosan nanofiber mats. Morphological and chemical characterizations were performed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively after vacuum drying the mats for 48 h. The average fiber diameter was determined from SEM images by measuring the diameter of 120 fibers using ImageJ software. Experimental Sealant: N6 and CH electrospun mats (3×3cm2) were immersed into a resin mixture of BIS-GMA/TEGDMA. Once no bubbles were seen, the resin-modified N6 and CH mats were put on a glass plate, light-cured (“TRIAD 2000”) for 2 min and then submitted to a cryomilling process to obtain a fine micron-sized powder. Three different filler levels (1 wt%, 2.5 wt%, 5 wt%) were used to prepare the N6 and CH incorporated resin-based sealants. Additionally, a commercially available resin-based sealant and the experimental resin mixture (unfilled) were used as controls. Three-point flexural testing, Vickers microhardness testing, and agar diffusion testing were performed on the experimental sealants and the commercial sealant. Data were analyzed by one-way ANOVA and Fisher's Protected Least Significant Differences Pair-wise comparisons between groups (5%). Results: The average fiber diameter for N6 was found to be 503±304 nm and 595±411 nm for CH. No significant difference was found between fiber diameter (p = 0.0601). FTIR confirmed the characteristic peaks for N6 ((CO-NH and [-(CH2)5-].) and CH (N-H and C2F3O2-). CH-5% group had significantly higher (p = 0.0000) FS (115.3±4.5 MPa) than all other groups. CH-1% and CH-2.5% groups had significantly higher FS than the control (unfilled) (p = 0.0016 and p = 0.0033 respectively); Helioseal Clear (p = 0.0000), and nylon groups. N6-5% had significantly higher flexural strength than Helioseal Clear (p = 0.0013) and N6-2.5% (p = 0.0250). CH-1% had significantly higher hardness values than all other groups, and CH-5% (p = 0.0414) had significantly higher values than N6-2.5%. No antibacterial inhibition was seen in any of the tested groups. Conclusions: CH and N6 nanofibers were successfully prepared via electrospinning and used to modify the experimental resin-based dental sealants. The overall results indicated that CH-containing sealants presented the highest flexural strength and hardness; however, none of the CH groups displayed antimicrobial properties. Further investigation is needed to enhance the physico-mechanical properties of the experimental resin-based sealants using nylon-6 and CH.