The dielectric dispersion of poly(vinyl acetate) solutions was studied in an attempt to relate this behavior to the chemical nature of the material. The bridge method was employed in which capacitance measurement of solutions were made over a frequency range of 400 cycles to 500 kilocycles. The results of these experiments indicate that a vinyl type material possesses greater flexibility than cellulose derivatives in solution and, thus, the magnitude of capacitance changes over a frequency range is considerably reduced. Because of the very small changes in capacitance, reproducible results are difficult to obtain and definite conclusions as to the relation of dispersion to molecular weight are impossible. Dielectric dispersion studies were made on solutions of poly(vinyl acetate) in dioxane, ethylene chloride and acetone. / Master of Science

Carbon nanotubes (CNTs) were dispersed into polyvinyl acetate (PVAc ) adhesive cured by radio frequency (RF) to investigate their loading effects on PVAc adhesive curing time and lap shear bond strength performance. Main factors are CNT loading (0.08, 0.25 and 0.41%), RF curing time (15, 30, 45, 60 seconds), and clamping pressure (100, 160, and 240 psi). Experimental results indicated that CNT loading had significant effects on PVAc curing time and lap shear bond strength. Specifically, single lap shear joints bonded with 0.41% CNT loading adhesive had significantly higher lap shear bond strengths than one with PVAc only (0% CNT loading). The curing time of PVAc dispersed with a 41% CNT loading (15 seconds) was 30 seconds shorter than the one with a 0% CNT loading (45 seconds).

The purpose of this study was to improve the melt extrusion processability of polyvinyl acetate phthalate (PVAP) and investigate its use as a stabilizing polymer for supersaturated solutions of itraconazole (ITZ) in neutral pH aqueous media and in the solid-state during storage over time. Polyvinyl pyrrolidone vinyl acetate (PVPVA) was incorporated into PVAP as a carrier matrix with the aim of lowering the melt viscosity and increasing the plasticity of PVAP while maintaining its high glass transition temperature (Tg). Amorphous solid dispersions of ITZ (40% w/w) in a 30:70% w/w PVAP:PVPVA mixture were produced by melt extrusion. Solid-state analyses of the composition were performed using differential scanning calorimetry and X-ray diffraction. Dissolution analysis was conducted using a pH-change method. Solid-state analyses demonstrated that the extruded composition was entirely amorphous and ITZ was largely distributed in PVAP- and PVPVA-rich portions of the ternary dispersion. Dissolution analysis revealed that PVAP functioned to prolong the release of supersaturated levels of ITZ from the dispersion following an acidic-to-neutral pH transition. In the solid state, ITZ remained in its amorphous form throughout 6 months of storage. The results of this study suggest that substantial improvements in melt extrusion with PVAP can be achieved by incorporating PVPVA and that the PVAP-PVPVA polymer combination can stabilize amorphous ITZ. / Pharmaceutical Sciences

The work deals mainly with preparation protocol of nanocomposites. The task of this work is to study structural and procedural parameteres that control the dispersion of nanoparticles in polymer solution to be able to prepare desired spatial organization of nanoparticles. The work resolves the effect of various components such as polymer matrices, nanoparticles and solvent, in which matrices and nanoparticles are blended. Used components control final dispersion state of nanoparticles and it influences also properties of investigated materials such as glass transition temperature, stiffness and rheological properties.

No description available.

Les copolymères poly (acétate de vinyle-co-alcool vinylique), désignés par PVA, sont des tensioactifs macromoléculaires obtenus par hydrolyse partielle de poly (acétate de vinyle)(PVAc). Si les propriétés tensioactives des PVA ont pu être corrélées aux caractéristiques moléculaires il n'en est par de même en ce qui concerne les associats du type nanogels présents dans les solutions aqueuses. L'objectif de cette thèse était de caractériser les nanogels par des techniques telles que la diffusion dynamique de la lumière, la chromatographie d'exclusion stérique et la viscosimétrie. 9 PVA, de degrés d'hydrolyse de 73 à 88 mole% et de degrés de polymérisation de 650 à 2500 ont été étudiés. Il est apparu que les nanogels présent dans les PVA de DH =73 mole% et formés par interactions hydrophobe-hydrophobe entre séquences acétate ont des tailles entre 20-40 nm, avec des fractions volumiques de l'ordre de 20-30%. La désagrégation des nanogels par formation de complexes avec des tensioactifs anioniques du type SDS et SDBS a ensuite été démontrée. En faisant appel à la technique de fractionnement par « point de trouble » il est apparu que les chaînes les plus riches en acétate et en particulier celles ayant des longueurs des séquences acétate importantes complexent plus de SDS.Des « copolymères modèles » du type copolymères diblocs PVAc-b-PVOH comportant une séquence hydrophobe PVAc et une hydrophile PVOH ont pu être préparés par polymérisation RAFT, suivie par une réaction click. Une étude préliminaire de la micellisation de tels copolymères a permis de montrer la très grande analogie entre micelles de copolymères à blocs PVAc-b-PVOH et les nanogels de PVA examinés précédemment. / Poly (vinyl acetate-co-vinyl alcohol) copolymers, designated by PVA, are macromolecular surfactants obtained by partial hydrolysis of poly (vinyl acetate) (PVAc). If the surfactant properties of PVA have been correlated with molecular characteristics it is not the same for the colloidal aggregates in aqueous solutions so-called nanogels. The objective of this thesis was to characterize the nanogels using techniques such as dynamic light scattering, size exclusion chromatography and viscometry.9 PVA with degrees of hydrolysis between 73 and 88 mole% and polymerization degrees of 650 to 2500 were studied. It appeared that the nanogels, formed by hydrophobic-hydrophobic interactions between acetate sequences, are the size in the range of 20 to 40 nm with volume fractions between 20 and 30%. The disaggregation of nanogels by complex formation with anionic surfactants such as SDS and SDBS was further demonstrated. By using the "cloud point" fractionation technique it appeared that SDS is complexed by the sequences with high acetate content and in particular those with significant lengths of acetate sequences.As a model system diblock copolymers PVAc-b-PVOH containing a PVAc hydrophobie sequence and a PVOH hydrophilic sequence were prepared by RAFT polymerization, followed by a click reaction. A preliminary micellization study of these copolymers showed a very strong analogy between PVAc-b-PVOH block copolymer micelles and PVA nanogels discussed above.