Low-temperature polymerization of methyl methacrylate emulsion gels through surfactant catalysis

Synthesis of Polymers with Narrow Molecular Mass Distribution through Interface-Initiated Room-Temperature Polymerization in Emulsion Gels

Homopolymers of n-butyl acrylate, methyl methacrylate, styrene, and their random copolymers were prepared via interface-initiated polymerization of emulsion gels at 20 °C. The polymerization was conducted in a free radical polymerization manner without inert gas protection. Compared with the polymers synthesized at 60 °C, the polymerization of emulsion gels at 20 °C produced homo- and copolymers with a higher molecular mass and a narrower molecular mass distribution. The polydispersity indices for the polymers synthesized at 20 °C were found to be between 1.12 and 1.37. The glass transition temperatures for the as-synthesized butyl acrylate copolymers agree well with the prediction from the Gordon-Taylor equation. Interface-initiated room-temperature polymerization is a robust, energy-saving polymerization technique for synthesizing polymers with a narrow molecular mass distribution.

Low Temperature, In Situ Polymerization of Vinyl Acetate in Silica Containing Emulsion Gels

Vinyl acetate (VAc) was polymerized to about 90% conversion in 9 h at 40°C from the colloidal microstructure of the VAc/fumed silica/cetyltrimethylammonium bromide (CTAB) system. The glass transition ( $T_g$ ) of poly(vinyl acetate) (PVAc) polymerized in these emulsion gels with silica was higher ( $T_g={41}^{°}\text{C}$ ) than those of PVAc made from bulk polymerization at 60°C ( $T_g={31}^{°}\text{C}$ ) and the weight average molar mass ( $M_w$ ) was also larger ( $M_w$ about 300 kg/mol) than those from bulk polymerization ( $M_w=125\text{kg}/\text{mol}$ ). Increased $M_w$ , $T_g$ , and lowered processing temperature for these composites could facilitate new applications for PVAc.

Basic Principles of Emulsion Templating and Its Use as an Emerging Manufacturing Method of Tissue Engineering Scaffolds

Tissue engineering (TE) aims to regenerate critical size defects, which cannot heal naturally, by using highly porous matrices called TE scaffolds made of biocompatible and biodegradable materials. There are various manufacturing techniques commonly used to fabricate TE scaffolds. However, in most cases, they do not provide materials with a highly interconnected pore design. Thus, emulsion templating is a promising and convenient route for the fabrication of matrices with up to 99% porosity and high interconnectivity. These matrices have been used for various application areas for decades. Although this polymer structuring technique is older than TE itself, the use of polymerised internal phase emulsions (PolyHIPEs) in TE is relatively new compared to other scaffold manufacturing techniques. It is likely because it requires a multidisciplinary background including materials science, chemistry and TE although producing emulsion templated scaffolds is practically simple. To date, a number of excellent reviews on emulsion templating have been published by the pioneers in this field in order to explain the chemistry behind this technique and potential areas of use of the emulsion templated structures. This particular review focusses on the key points of how emulsion templated scaffolds can be fabricated for different TE applications. Accordingly, we first explain the basics of emulsion templating and characteristics of PolyHIPE scaffolds. Then, we discuss the role of each ingredient in the emulsion and the impact of the compositional changes and process conditions on the characteristics of PolyHIPEs. Afterward, current fabrication methods of biocompatible PolyHIPE scaffolds and polymerisation routes are detailed, and the functionalisation strategies that can be used to improve the biological activity of PolyHIPE scaffolds are discussed. Finally, the applications of PolyHIPEs on soft and hard TE as well as in vitro models and drug delivery in the literature are summarised.

Cationic surfactant blocks radical-inhibiting sites on silica

Surfactant-catalyzed room-temperature radical polymerization of methyl methacrylate (MMA) was conducted in the presence of fumed silica nanoparticles and water. Three types of surfactants, cationic (CTAB), nonionic (Triton X-100) or anionic (SDS), were used to catalyze the decomposition of the initiator, 2,2'-azobisisobutyronitrile (AIBN). The surfactant-catalyzed decomposition rate constant for AIBN at room temperature was found to be independent of the surfactant type. However, the rates of polymerization of the MMA emulsion gels at room temperature were found to depend on the types of surfactant with: cationic>nonionic>anionic. An inhibition period was observed for the polymerizations with nonionic and anionic surfactants. The radical-inhibition was likely due to the reactions between the radicals and the silanol groups on fumed silica. This inhibition can be reduced by using cationic surfactants to block these surface silanols.

Modulation of bactericidal action in polymer nanocomposites: light-tuned Ag+ release from electrospun PMMA fibers

Silver rate release from electrospun PMMA fibers tuned by combination of silver ions and silver nanoparticles produced by UV irradiation.