Christine J. T. Landry

In situ polymerization of tetraethoxysilane in poly (methyl methacrylate) : morphology and dynamic mechanical properties

Abstract Dynamic mechanical spectroscopy and transmission electron microscopy were utilized to investigate the properties of composites resulting from the formation of a cross-linked inorganic network via the polymerization of tetraethoxysilane (TEOS) in situ in a poly(methyl methacrylate) (PMMA) binder. The results show that the morphology and physical properties obtained are governed by sample preparation and by the catalyst used to polymerize the TEOS; major differences are obtained when the polymerization of TEOS is performed in different pH regimes. The morphologies which develop are consistent with the known differences in gel structures obtained during the polymerization of TEOS in acidic or basic media. When TEOS is reacted under acidic conditions at elevated temperatures, small ( A ) SiO2 domains which are well dispersed in the PMMA matrix result, producing a composite material with a high plateau modulus above the Tg of PMMA which extends to at least 250°C. The time-temperature-transformation concept, proposed by Gillham for thermosetting organic polymers, is employed to explain some of these results.

In situ polymerization of tetraethoxysilane in polymers: chemical nature of the interactions

Abstract The formation of molecular composites by the in situ polymerization of tetraethoxysilane in various organic polymers has been studied. The results show that highly homogeneous, transparent composites can be formed for polymers such as poly (methyl methacrylate), poly (vinyl acetate), poly (vinyl pyrrolidone), and poly (N,N-dimethylacrylamide). These composites have improved mechanical properties and increased solvent resistance. Strong interactions between the SiO2 networks and these polymers were observed, and the data suggest hydrogen bonding between residual hydroxyls on the SiO2 and carbonyl groups on the polymer chains as the major source of these interactions.

Miscibility and mechanical properties of a ternary polymer blend: polystyrene/polycarbonate/tetramethyl polycarbonate

Abstract The phase behaviour and morphology of a ternary blend, consisting of polystyrene (PS), bisphenol A polycarbonate (PC) and tetramethyl bisphenol A polycarbonate (TMPC), are investigated by thermal and mechanical analysis and by transmission electron microscopy. It is shown that the TMPC, which is miscible with each of the other components of the blend, does not solubilize the two immiscible polymers, PS and PC. Two glass transitions are observed for most of the blend compositions. Single phases are obtained only at very high TMPC content. The interaction parameters for the three binary blends were obtained from the literature and utilized to calculate the spinodal for the ternary blend. The theoretical calculation agrees well with the experimental data. It is shown that the relative molecular weights of the polymers have a considerable effect on the phase diagram of the ternary blend.

Physical aging of blends of cellulose acetate polymers with dyes and plasticizers

Abstract A systematic study of physical aging in polymers that have been plasticized by the addition of dyes and polymeric plasticizers is undertaken using the heat capacity as the structural probe. The dyes are actually dye sets and are mixtures of various dyes with slight structural differences, each with a different glass transition temperature (Tg). The polymeric plasticizers are low molecular weight polyesters that have low values of Tg. From experimental results and their analysis, it is shown that aging occurs under ambient temperature conditions most rapidly for the polymer–dye samples that have their Tg value at 20°C above ambient temperature. The results for these thermorheologically complex blends also indicate that, although the incorporation of the polymeric plasticizers substantially reduces the Tg of the blend, the distribution of relaxation times is broadened. Kinetics of aging for the blends are determined using the Tool–Narayanaswamy model for structural relaxation. The fictive temperatures were calculated as a function of annealing temperatures and annealing times in order to assess the effects of storage upon the practical performance of these blends.

On the Effect of Organic Substitution of Silicon Alkoxides in Poly(Vinyl Acetate) Organic-Inorganic Composites

Abstract Organic-inorganic composites (OICs) were prepared via the in-situ polymerization of an organically (phenyl) substituted trialkoxysilane, phenyltriethoxysilane (PhTEOS), in the presence of poly(vinyl acetate) (PVAc). The mechanical reinforcement above T g previously observed in OICs of unfunctionalized organic polymers such as PVAc with acid catalyzed in-situ polymerized tetraalkoxysilane was not observed when the tetraalkoxysilane was replaced with PhTEOS. Although both systems are optically transparent and both exhibit a high degree of hydrogen bonding between the carbonyl of PVAc and the residual hydroxyls of the silicate, the polymerization of the alkoxide is different. The tetra-functional alkoxide polymerizes to form a load-supporting silicate network, leading to a high plateau in the tensile modulus above T g, whereas the trifunctional alkoxide reacts to form primarily low molecular weight oligomers. These increase the T g of the PVAc but do not provide mechanical reinforcement.

Solid State NMR Studies of Polymer Interfaces

The interface and interfacial regions in multiphase systems arc of prime importance because they have a direct impact on the physical, mechanical, and chemical properties of the material such as fracture response, impact strength, adhesion, and gas or small molecule permeability. Interfaces are important not just in polymer blends and composites hut also in laminates. multilayer coatings, rubber-toughened materials and semicrystalline polymers. The characterization of the structure and dynamics of interfaces offers numerous challenges. In terms of structure, molecular composition and the distribution of chain ends at the interface are of interest. Questions of dynamics include the kinetics of interface formation during melt processing, melt bonding, solution coating, or latex coalescence. At the molecular level these kinetic processes depend on the dynamics of chain interdiffusion, and physical entanglement dynamics.

Polystyrene-Poly(Vinylphenol) Copolymers as Compatibilizers for Organic-Inorganic Composites

Random, graft, and block copolymers of polystyrene (PS) and poly(4-vinylphenol) (PVPh), and PVPh homopolymer are shown to act as compatibilizers for incompatible organic-inorganic composite materials. The VPh component reacts, or interacts strongly with the polymerizing inorganic (titanium or zirconium) alkoxide. The organic components studied were PS, poly(vinyl methyl ether), and poly(styrene-co-acrylonitrile). The use of such compatibilizers provides a means of combining in situ polymerized inorganic oxides and hydrophobic polymers. This is seen as a reduction in the size of the dispersed inorganic phase and results in improved optical and mechanical properties.