Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO₂) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO₂ also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO₂. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situ two-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO₂.

RAFT dispersion polymerisation of methyl methacrylate is performed in scCO₂ with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight.     

Synthesis and characterisation of advanced UHMWPE/silver nanocomposites for biomedical applications

A supercritical fluid (SCF) route for facile and homogeneous introduction of silver nanoparticles into polymer hosts is described. Our focus is on ultra-high molecular weight polyethylene (UHMWPE). We demonstrate that the metallic nanoparticles have a substantial effect upon the wear and tribochemical properties of the polymer substrate.     

2-Methyltetrahydrofuran (2-MeTHF) as a versatile green solvent for the synthesis of amphiphilic copolymers via ROP,FRP, and RAFT tandem polymerizations

2-methyltetrahydrofuran (2-MeTHF) is a readily available, inexpensive, neoteric, bio-based solvent. It has been adopted across a wide range of chemical processes including the batch manufacture of fine chemicals, enzymatic polycondensations and ring opening polymerizations. To reduce the environmental burden related to the synthesis of pharmaceutical-grade polymers based on lactide and caprolactone, we envisaged the use of 2-MeTHF. For the first time, we combined a series of metal-free and enzymatic ROPs with free radical and controlled RAFT polymerizations (carried out separately and in tandem) in 2-MeTHF, in order to easily tune the chemistry and the architecture of the final polymers. After a simple purification, the amphiphilic polymers were formulated into nanoparticles and tested for their cytocompatibility in three model cell lines, to assess their application as potential polymeric excipients for nanomedicines.     

Synthesis and activity of four (N,N‐dimethylamino)benzamide nonsteroidal anti‐inflammatory drugs based on thiazole and thiazoline

Four compounds derived from 2‐aminothiazole and 2‐amino‐2‐thiazoline were prepared by coupling the respective bases with the acid chlorides of either 3‐ or 4‐(N,N‐dimethylamino)benzoic acid. Products were identified using infrared spectroscopy, ¹H NMR spectroscopy and electrospray mass spectroscopy and in two cases by single‐crystal X‐ray diffraction. Of the four, N‐(thiazol‐2‐yl)‐3‐(N,N‐dimethylamino)‐benzamide (1), N‐(thiazolin‐2‐yl)‐4‐(N,N‐dimethylamino)benzamide (2), N‐(thiazolin‐2‐yl)‐3‐(N,N‐dimethylamino) benzamide (3) and N‐(thiazolin‐2‐yl)‐4‐(N,N‐dimethylamino)benzamide (4), the hydrochloride salts of compounds 3 and 4 showed anti‐inflammatory activity across a concentration range of 10^?2?5 × 10^?4 M while 3 (at a concentration of 10^?5 M) was found to have no adverse effect on myocardial function. The X‐ray crystal structure of 2 and the 1:1 adduct structure of 3 with 3‐(N,N‐dimethylamino)benzoic acid are reported.     

Sorption and Swelling of Poly(D,L-lactic acid) and Poly(lactic-co-glycolic acid) in Supercritical CO2

Summary: The equilibrium sorption and swelling behavior in supercritical CO₂ of poly(D,L-lactic acid) and poly(lactic-co-glycolic acid) has been studied at a temperature of 35 °C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. In terms of partial molar volume of CO₂ in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez-Lacombe equation of state, which is able to represent the actual behavior of the polymer-CO₂ systems with reasonable accuracy.     

Fabrication of polymer scaffolds for tissue engineering using surface selective laser sintering

A new approach to the fabrication of individual implants and scaffolds for tissue engineering—surface selective laser sintering (SSLS)—is proposed and realized. In contrast to the conventional selective laser sintering, the SSLS method makes it possible to sinter polymer microparticles and melt the near-surface layer rather than the microparticle as a whole. The effect of the laser radiation parameters and the structure and composition of the raw products on the structure and properties of the biomaterials sintered by the laser radiation is analyzed. This approach makes possible both the application of thermally unstable polymers (e.g., polylactides or polylactoglycolides) and the fabrication of scaffolds with incorporated bioactive proteins. The results obtained yield a regular physical basis for a new technology of the fabrication of various polymer scaffolds that represent important materials and elements of modern tissue engineering. The flexibility of the SSLS method is especially important at the stage of investigation of the cell and tissue responses needed for the optimization of the material for a specific application in tissue engineering.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.