Roshan T. A. Mayadunne

Living free radical polymerization with reversible addition - fragmentation chain transfer (the life of RAFT)

Free radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization) is discussed with a view to answering the following questions: (a) How living is RAFT polymerization? (b) What controls the activity of thiocarbonylthio compounds in RAFT polymeriza- tion? (c) How do rates of polymerization differ from those of conventional radical polymerization? (d) Can RAFT agents be used in emulsion polymerization? Retardation, observed when high concentra- tions of certain RAFT agents are used and in the early stages of emulsion polymerization, and how to overcome it by appropriate choice of reaction conditions, are considered in detail. Examples of the use of thiocarbonylthio RAFT agents in emulsion and miniemulsion polymerization are provided. # 2000 Society of Chemical Industry

A novel synthesis of functional dithioesters, dithiocarbamates, xanthates and trithiocarbonates

A novel synthesis of functional dithioesters, dithiocarbamates, xanthates and trithiocarbonates is described. Heating a bis(thiocarbonyl) disulfide with an azo-compound results in the formation of (thiocarbonyl)sulfanyl derivatives in moderate to high yield. The process is proposed as the method of choice for preparing tertiary (thiocarbonyl)sulfanyl compounds and is compatible with a wide range of functionalities (e.g. carboxy, hydroxy and nitrile).

Recent developments in biodegradable synthetic polymers.

This chapter reviews recent developments in biodegradable synthetic polymers focusing on tailoring polymer structures to meet material specification for emerging applications such as tissue engineered products and therapies. Major classes and new families of synthetic polymers are discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are summarized based on studies reported during the past 10-15 years. Polyesters and their copolymers, polyurethanes, polyphosphazenes, polyanhydrides, polycarbonates, polyesteramides and recently developed injectable polymer systems based on polypropylenefumarates, polyurethanes and acrylate/urethane systems are reviewed. Polyesters such as polyglycolides, polylactides and their copolymers still remain as the major class of synthetic biodegradable polymers with products in clinical use. Although various copolymerization methods have addressed needs of different applications, release of acidic degradation products, processing difficulties and limited range of mechanical properties remains as major disadvantages of this family of polymers. Injectable polymers based on urethane and urethane/acrylate have shown great promise in developing delivery systems for tissue engineered products and therapies.

Tailored polymer architectures by reversible addition-frasmentation chain transfer

Living radical polymerization methods that allow the preparation of polymers with predetermined molecular weight, narrow molecular weight distribution and tailored architecture (e.g. block, graft, stars) are offering a vast range of new and advanced materials. With applications ranging from surfactants, dispersants, coatings and adhesives, to microelectronics, membranes, drug delivery, and biomaterials they have the potential of revolutionizing a large part of the polymer industry.

Initiating free radical polymerization

The kinetics and mechanism of the initiation and reinitiation of free radical polymerization is reviewed. The importance of understanding the kinetics, specificity and efficiency of initiation and chain transfer when predicting polymerization kinetics and polymer composition is highlighted. These factors are particularly important when making low molecular weight polymers and in living or controlled polymerization processes. Examples of RAFT polymerization and catalytic chain transfer are provided.

Multiarm organic compounds for use as reversible chain-transfer agents in living radical polymerizations

Generic approaches to the synthesis of multi-thiocarbonyl thio compounds are described. A multi-hydroxy core was condensed with either α-bromophenyl acetic acid or 2-mercaptopropanoic acid in the presence of p-toluenesulfonic acid catalyst to afford the corresponding esters in quantitative yield. Treatment of the bromo esters with sodium methyl trithiocarbonate or the thiols with carbon disulfide, benzyl bromide and triethylamine then affords two series of trithiocarbonates. The process is exemplified by application to mono, di- or tri-pentaerythritol. These multi-thiocarbonyl thio compounds have application as chain-transfer agents in reversible addition fragmentation chain-transfer (RAFT) polymerization as precursors to star polymers.

Efficacy of antimicrobial polymer coatings in an animal model of bacterial infection associated with foreign body implants

OBJECTIVES To assess support discs, comprising polyethylene terephthalate (PET), coated with different polymer/levofloxacin combinations for antimicrobial activity in an animal model of infection, in order to explore the use of specific polymer coatings incorporating levofloxacin as a means of reducing device-related infections. METHODS Aliphatic polyester-polyurethanes containing different ratios of poly(lactic acid) diol and poly(caprolactone) diol were prepared, blended with levofloxacin and then used to coat support discs. The in vitro levofloxacin release profiles from these discs were measured in aqueous solution. Mice were surgically implanted with the coated discs placed subcutaneously and infection was initiated by injection of 10(6) cfu of Staphylococcus aureus into the subcutaneous pocket containing the implant. After 5, 10, 20 and 30 days, the discs were removed, and the number of bacteria adhering to the implant and the residual antimicrobial activity of the discs were determined. RESULTS In vitro, the release of levofloxacin from the coated discs occurred at a constant rate and then reached a plateau at different timepoints, depending on the polymer preparation used. In vivo, none of the discs coated with polymer blends containing levofloxacin was colonized by S. aureus, whereas 94% of the discs coated with polymer alone were infected. All discs coated with levofloxacin-blended polymers displayed residual antimicrobial activity for at least 20 days post-implantation. CONCLUSIONS Bioerodable polyester-polyurethane polymer coatings containing levofloxacin can prevent bacterial colonization of implants in an intra-operative model of device-related infections.