W. G. Lloyd

Bio: W. G. Lloyd is an academic researcher from Dow Chemical Company. The author has contributed to research in topics: Diffusion (business) & Network topology. The author has an hindex of 3, co-authored 3 publications receiving 688 citations.

Network polymers. II. Experimental study of swelling

Abstract: The swelling behavior of vinyl-divinyl network polymers has been studied. Various monovinyl monomers (styrene, vinyltoluene, p-tert-butylstyrene, a series of n-alkyl methacrylates), divinyl monomers (divinylbenzene, ethylene dimethacrylate), and contacting solvents (ranging from n-alkanes to water) have been used. Attention is directed to the effects of introducing an initial good-solvent diluent at the time of polymerization. Results are interpreted in terms of changes of the free energies of solvent-Polymer mixing and network deformation. The relaxed volume of the network is shown to be closely related to the volume at which it is formed. The network modulus increases with increasing divinyl content and decreases sharply with increasing initial dilution. With high crosslinking and moderate initial dilution, an interesting special case arises: the volume of formation of the network, its relaxed volume, and its equilibrium swollen volume are all almost identical, and the swollen volume is essentially independent of polymer–solvent interaction. Networks prepared from monomers with large pendant groups exhibit a built-in dilution effect.

Network polymers. I. Theoretical remarks

Abstract: This paper consists of some general theoretical comments on the structure and swelling behavior of network polymers. The importance of network topology is emphasized. A hypothetical network consisting of “ghost” chains, which could pass freely through one another, would tend to shrink to submicroscopic size. This supercontraction would be prevented by either a volume exclusion effect or a restriction against cutting through (i.e., against alteration of network topology). In real networks, both of these restrictions are present. The swelling behavior of network polymers which were swollen at the time of network formation is discussed in terms of a crude molecular model.

Drug release kinetics and transport mechanisms of non-degradable and degradable polymeric delivery systems

Abstract: Importance of the field: The advancement in material design and engineering has led to the rapid development of new materials with increasing complexity and functions. Both non-degradable and degradable polymers have found wide applications in the controlled delivery field. Studies on drug release kinetics provide important information into the function of material systems. To elucidate the detailed transport mechanism and the structure-function relationship of a material system, it is critical to bridge the gap between the macroscopic data and the transport behavior at the molecular level.Areas covered in this review: The structure and function information of selected non-degradable and degradable polymers have been collected and summarized from literature published after the 1990s. The release kinetics of selected drug compounds from various material systems is discussed in case studies. Recent progress in the mathematical models based on different transport mechanisms is highlighted.What the reader wil...