Phosphate glasses are used in a variety of technological applications, from hosts for solid state lasers to materials for medical treatments. In general, phosphate glasses have lower glass transition temperatures than silicate glasses, due in part to the generally lower number of bridging oxygens between the phosphate tetrahedra that make up the glass structure. The relatively poor chemical durability of phosphate glass often limits potential applications, although certain phosphate systems (viz., the iron phosphates) are so chemically stable that they can be used as inert hosts for radioactive and hazardous wastes. The structure and properties of phosphate glasses will be reviewed, as will be our recent studies of the interactions between phosphate glasses and aqueous environments. Richard Brow is a Curators’ Professor in the Materials Science & Engineering Department at Missouri S&T (formerly the University of Missouri-Rolla), where his research interests include the structure and properties of inorganic glasses. Prior to his arrival at Missouri S&T in 1998, he was a principal member of the technical staff at Sandia National Labs in Albuquerque, NM. He has over 175 publications and holds eleven US patents, the latter principally for sealing glasses for a variety of electronic and optoelectronic applications.

We use stochastic Monte Carlo computer simulation following the bond fluctuation model to study the effects of (i) grafting density (σ) of surface-anchored initiators and solvent quality and (ii) the effect of simultaneous bulk- and surface-initiated reaction on controlled radical polymerization from flat impenetrable substrates under good and poor solvent conditions. Our model includes a mechanism for activation/deactivation of the chains and neglects termination and/or chain transfer reactions; the system is thus “truly living”. We find that under these conditions, surface-initiated polymerizations at low σ resemble those in the bulk. In contrast, at high initiator σ these surface-initiated polymerizations result in gradients of the free monomer and chain-end concentrations, which lead to an uneven growth of the chains and ultimately yield polymers with broad molecular weight distributions. Poor solvent conditions exacerbate this problem by collapsing the chains and in some cases forming chain aggregates, which further restrict the access of free monomers by the active polymer chain-ends and contribute to their uneven growth and ultimately broader length distributions relative to good solvent conditions. While at low σ the molecular weight distributions can be described by the conventional Schulz-Zimm distribution function, at high grafting densities this approach fails to describe accurately the dispersity in chain lengths. For simultaneous surface- and bulk-initiated polymerization the molecular weights and molecular weight distributions of both classes of polymers depend on the grafting density of the surface-bound polymers and the fraction of polymers on the surface (η) relative to that in bulk. In general, polymer grafts on the surface possess lower molecular weight and higher polydispersity index compared to their bulk counterparts. The differences between the molecular weight of the two populations of polymers decreases with decreasing σ and increasing η. Our work provides evidence that the common practice of using the molecular weight of bulk-initiated polymers in estimating σ of polymeric anchors on flat substrates is not generally valid.