Controlled/living radical polymerization in aqueous dispersed systems

Sustainable polymerizations in recoverable microemulsions

Free radical and atom-transfer radical polymerizations were conducted in monomer/ionic liquid microemulsions. After the polymerization and isolation of the resultant polymers, the mixture of the catalyst and ionic liquids (surfactant and continuous phase) can be recovered and reused, thereby dramatically improving the environmental sustainability of such chemical processing. The addition of monomer to recovered ionic liquid mixtures regenerates transparent, stable microemulsions that are ready for the next polymerization cycle upon addition of initiator. The method combines the advantages of IL recycling and microemulsion polymerization and minimizes environmental disposable effects from surfactants and heavy metal ions.

Drug delivery systems: Advanced technologies potentially applicable in personalized treatments

Advanced drug delivery systems (DDS) present indubitable benefits for drug administration. Over the past three decades, new approaches have been suggested for the development of novel carriers for drug delivery. In this review, we describe general concepts and emerging research in this field based on multidisciplinary approaches aimed at creating personalized treatment for a broad range of highly prevalent diseases (e.g., cancer and diabetes). This review is composed of two parts. The first part provides an overview on currently available drug delivery technologies including a brief history on the development of these systems and some of the research strategies applied. The second part provides information about the most advanced drug delivery devices using stimuli-responsive polymers. Their synthesis using controlled-living radical polymerization strategy is described. In a near future it is predictable the appearance of new effective tailor-made DDS, resulting from knowledge of different interdisciplinary sciences, in a perspective of creating personalized medical solutions.

Nitroxide-Mediated Radical Polymerization in Nanoreactors: Can Dilution or Increased Nitroxide Concentration Provide Benefits Similar to Compartmentalization?

Compartmentalization of a nitroxide-mediated radical polymerization system can lead to improved levels of both control and livingness, but at the cost of a reduced polymerization rate. Improved control is a result of the confined space effect on deactivation, whereas improved livingness stems from the segregation effect on bimolecular termination. Modelling and simulations have been carried out for the systems styrene/2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and styrene/2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxy (TIPNO) using the respective nitroxide-based polystyrene macroinitaitors (alkoxyamines) at 125°C to elucidate whether similar benefits can be obtained in the corresponding bulk polymerizations by merely diluting the systems or by addition of extra free nitroxide. The results have shown that neither approach leads to simultaneous improvement in control and livingness relative to the corresponding bulk systems, thus accentuating the merits of compartmentalization in nanoreactors.

Synthesis of Core - Shell Nanoparticles with Polystyrene Core and PEO Corona from Core-Crosslinked Micelles by the RAFT Process

Core–shell nanoparticles have been synthesized by core crosslinking of micelles. The underlying block copolymer, poly(oligo(ethylene glycol methyl ether methacrylate))-block-polystyrene (POEGMA-b-PS), was synthesized successfully by the reversible addition–fragmentation chain transfer (RAFT) process, using POEGMA as a macro-RAFT agent. The block copolymers were self-assembled into micelles in aqueous media and the resulting micelles and the RAFT endgroup, located in the core of the micelle, were used for the subsequent crosslinking step using a crosslinker, divinyl benzene (DVB). The rate of the crosslinking reaction was found to be slow with less than 20% conversion being achieved after 72 h. Nevertheless, crosslinked micelles were obtained and only a small fraction of free block copolymers remained. Cytotoxicity tests confirmed the biocompatibility of the prepared core-crosslinked micelles. In addition the crosslinked micelles were taken up by L929 cells without causing any signs of cell damage.

Control of molecular weight of polystyrene using the reverse iodine transfer polymerization (RITP)-emulsion technique

The RITP-emulsion polymerization of styrene in the presence of molecular iodine has been successfully performed using potassium persulfate (KPS) as an initiator and 1-hexadecanesulfonate as an emulsifier under argon atmosphere at 80°C for 7 hrs in the absence of light. The effects of the iodine concentration, molar ratio between KPS and iodine, and solid contents on the molecular weight of polystyrene (PS) were studied. As the iodine concentration increased from 0.05 to 0.504 mmol under the fixed [KPS]/[I(2)] ratio at 4.5, the weight-average molecular weight of PS substantially decreased from 126,120 to 35,690 g/mol, the conversion increased from 85.0% to 95.2%, and the weight-average particle diameter decreased from 159 to 103 nm. In addition, as the ratio of [KPS]/[I(2)] increased from 0.5 to 6.0 at the fixed [I(2)] of 0.504 mmol, the weight-average molecular weight of PS decreased from 72,170 to 30,640 g/mol with high conversion between 81.7% and 96.5%. Moreover, when the styrene solid content increased from 10 to 40 wt.% at the fixed [KPS]/[I(2)] ratio of 4.5, the weight-average molecular weight of PS varied between 33,500 and 37,200 g/mol, the conversion varied between 94.9% and 89.7% and the weight-average diameter varied from 122 to 205 nm. Thus, the control of molecular weight of PS less than 100,000g/mol with high conversion (95%) and particle stability of up to 40 wt.% solid content were easily achieved through the usage of iodine with suitable ratio of [KPS]/[I(2)] in the RITP-emulsion polymerization technique, which is of great industrial importance.

Atom transfer radical polymerization in aqueous dispersed media

During the last decade, atom transfer radical polymerization (ATRP) received significant attention due to its exceptional capability of synthesizing polymers with pre-determined molecular weight, well-defined molecular architectures and various functionalities. It is economically and environmentally attractive to adopt ATRP to aqueous dispersed media, although the process is challenging. This review summarizes recent developments of conducting ATRP in aqueous dispersed media. The issues related to retaining “controlled/living” character as well as colloidal stability during the polymerization have to be considered. Better understanding the ATRP mechanism and development of new initiation techniques, such as activators generated by electron transfer (AGET) significantly facilitated ATRP in aqueous systems. This review covers the most important progress of ATRP in dispersed media from 1998 to 2009, including miniemulsion, microemulsion, emulsion, suspension and dispersed polymerization.