Yu-Der Lee

Properties of thermoplastic polyurethane elastomers containing liquid crystalline chain extender (I) synthesis and properties of hard segments

Abstract Polyurethanes prepared from 1,6-diisocyanate hexane (HDI) and 2,4-tolylene diisocyanate (2,4-TDI) with liquid crystalline chain extender 4,4′-bis( n -hydroxyalkyloxy)biphenyl ( n -PBP, n = 2, 3, 6) were reported. Characterizations of monomers and polymers were performed by infrared spectroscopy (IR), 1 H-NMR, solid-state C 13 -NMR, and elemental analysis. The phase transition behaviors of polyurethanes were investigated by Global TSC, DSC, and polarized microscopy (POM). Our results showed that monomers 4,4′-bis(n-hydroxyalkyloxy) biphenyl exhibit smectic type mesophase. It was observed that the longer the spacer length of polyurethanes, the higher the chain mobility, the larger DOD (degree of disorder) value and the lower the relaxation time. Also the phase transition temperature of polyurethanes decreases with increasing spacer length. DSC measurements and texture observations indicated that H2, H3, H6 and T6 exist in both mesophase and crystal phase. Quantitative analysis of temperature dependence hydrogen bonding revealed that hydrogen bonded content ( X b ) of the Cue5fb group for all samples decreased with increasing temperature. For the H series, both X b and ΔH decrease with increasing spacer length of the mesogenic diol.

A real-time study of the phase-separation process during polymerization of rubber-modified epoxy

Abstract The phase-separation process of a rubber-modified epoxy system during curing was described in terms of a nucleation-growth mechanism. It was derived from morphological observations that spherical domains were developed during polymerization in a continuous matrix. The morphological changes were recorded in real time by means of optical microscopy. We have applied a model to predict the amount and radius of the dispersed phase that segregated during a thermosetting polymerization. The model was based on the Flory-Huggins equation for the thermodynamic description as well as constitutive equations for the nucleation and growth rates. Using this model, we could semi-quantitatively interpret and describe the phase-separation process of the second phase from a curing mixture. During the initial polymerization period, the mixture remained homogeneous; at a certain reaction extent a thermodynamically stable rubber-rich phase with critical particle size rc or larger grew spontaneously. The build-up of molecular weight in the matrix during polymerization resulted in the changing of the two-phase morphology and the fixation of the spherical domain structure. Nucleation was the controlling factor of the phase-separation process. We concluded that the nucleation and growth of spherical second phase was expected to be directly related to the interfacial tension, increase of molecular weight, thermodynamic properties and composition gradient.

Studies of alkali soluble resin as a surfactant in emulsion polymerization

In this work, alkali soluble resin (ASR) was evaluated as a surfactant in emulsion polymerization of methyl methacrylate (MMA), styrene (SM), and butylacrylate (BA). A decrease in reaction rate was observed with ASR as the surfactant in the MMA system but not in the SM system. Kinetic analysis indicated that ASR retards the reaction rate and reduces the average number of radicals per latex particle in the MMA system. Experimental results also showed that the reaction rate of BA was slow and that the BA latex was unstable with ASR as the surfactant. A grafting reaction was observed in the presence of ASR via gel permeation chromatography (GPC) measurements. The transmission electron micrograph was employed to observe the morphology of latex as well. It depicted that the particles were surrounded by ASR to stabilize the latex particle.

Surfactant characteristics of random block polyelectrolyte polyester emulsifier (SMTAPE) in aqueous solution and on polystyrene latex particles

Abstract The surfactant characteristics of novel random block polyelectrolyte polyester emulsifiers, SMTAPE, were investigated by analyzing the surface tension of a variety of SMTAPE with different molecular weights and different hydrophilicities in aqueous solution, and also by studying the change of surface tension of polystyrene (PS) latex with increasing SMTAPE emulsifier concentration. The SMTAPE emulsifier was found to lower the surface tension of water by about 15xa0mN/m at the CMC. All of the investigated SMTAPE emulsifiers show two CMC break points, which were attributed to their broad molecular weight distribution. A Langmuir type adsorption isotherm was observed in this system. The surface area occupied by an SMTAPE molecule on a PS latex particle at 25°C was found to be 187xa0A2 at saturation. The conformation of SMATAPE emulsifier molecule adsorbed on a PS latex particle is thought to be a hydrophobic segment “trains” anchored to the polymer surface.

Structural effects of a novel polymeric emulsifier – SSIPM modified tetracarboxylic acid terminated polyester on the emulsion polymerization of butyl methacrylate

Abstract A novel polymeric emulsifier, SMTAPE, was prepared by end-capping sulfopolyester polyol with TMA in this study. This polymeric emulsifier is applied for BMA emulsion polymerization. Also investigated herein is how SMTAPE’s chemical structures, e.g. SSIPM contents and molecular weights, influence the behavior of emulsion polymerization and subsequent PBMA lattices. Experimental results indicate that SMTAPE emulsifiers with a shorter average hydrophobic length stabilize the PBMA latex by the depletion mechanism. Although possessing good mechanical stability, using those emulsifiers has a higher coagulum during the synthesis stage. However, the SMTAPE emulsifiers with a longer average hydrophobic length anchor strongly on the PBMA latex particles and stabilize them by an electrostatic force with a negligible amount of steric stabilization. Although possessing better synthesis stability, using these emulsifiers has a poor mechanical stability. In addition, according to these experimental results, formation of the subsequent PBMA latex is attributed to a coagulation process of particle precursors, micellar particles as well as existing PBMA latex particles.