Synthesis and comparative biodegradability studies of three poly(alkylene succinate)s

Poly(alkylene succinates) were synthesized from succinic acid and aliphatic diols with 2 to 4 methylene groups by melt polycondensation. DSC, ¹H NMR, WAXD and molecular weight measurements were used to characterise the polymers. Biodegradability studies of polyesters with the same average molecular weight, included enzymatic hydrolysis for several days using Rhizopus delemar lipase at pH 7.2 and 30 °C. DSC traces of biodegraded polyesters revealed that hydrolysis affected mainly the amorphous material. For all polyesters an increase in glass transition, melting point and heat of fusion was recorded. In the first days of enzymatic hydrolysis, fast rates of mass loss were observed accompanied by a rapid reduction of intrinsic viscosity and molecular weight, thus indicating a mixed endo- and exo-type hydrolysis mechanism. Afterwards, it turned to an exo-type mechanism, taking place in the crystalline phase, since after 15-25 days of enzymatic hydrolysis molecular weight was stabilized, while mass loss kept on decreasing though in a slower rate. End-group analysis revealed that carboxyl and hydroxyl groups increased due to ester bonds' scission. The biodegradation rates of the polymers decreased following the order PPSu > PESu ≥ PBSu and it was attributed to the lower crystallinity of PPSu compared to other polyesters, rather than to differences in chemical structure. Finally, a simple theoretical kinetic model was developed and Michaelis-Menten parameters were estimated.     

The ionic liquid ethyltri-n-butylphosphonium tosylate as solvent for the acid-catalysed hetero-Michael reaction

A new and convenient method for the acid-catalysed Michael addition reactions of alcohols, thiols and amines to methyl vinyl ketone has been developed using the ionic liquid ethyltri-n-butylphosphonium tosylate. The reaction conditions are mild and obviate the need for toxic and expensive Lewis acid catalysts, offering advantages over more commonly used systems.     

The theta temperature of star polymers

We use equations derived from the blob theory to calculate the blob size and the theta temperature of star polymers. In contrast to the case of linear polymers these two parameters are calculated to depend on molecular mass for star polymers. For a given star polymer the theta temperature can be lower or higher than that of the corresponding linear polymer depending on the number and length of its branches. The results are compared with the blob model of Daoud and Cotton for star polymers. Experimental results obtained in the course of this study confirm our calculations.     

Soluble carbon nanotubes

Carbon nanotubes have attracted great interdisciplinary interest because of their unique structure and properties. However, carbon-nanotube research is challenged by several problems, such as: i) mass production of material, ii) control of length, diameter, and chirality, and iii) manipulation for use in diverse technological fields. Issues regarding the synthesis and purification as well as the functionalization and solubilization of carbon nanotubes are relevant topics in this rapidly growing field. In this paper, covalent and noncovalent approaches to functionalized and solubilized nanotubes are examined in detail, with particular emphasis on the change of properties that accompany the chemical modification.     

Highly fluorescent streptavidin-coated CdSe nanoparticles: preparation in water, characterization, and micropatterning

CdSe quantum dots (QDs) with a high fluorescence quantum yield of 25% and a narrow size distribution were synthesized in a single step in water using glutathione as a stabilizing molecule. The exceptional optical properties enabled for the first time the detection of in-water-prepared single quantum dots at room temperature. For application as fluorescent bioanalytical probes, the QDs were coated with streptavidin. These QDs self-assemble with high contrast on micropatterned biotin while preserving their optical properties and their capability to bind in addition biotinylated molecules, a prerequisite for the development of novel supramolecular structures and bioassays.     

On the nature of the bonding in 1:1 adducts of O2

A survey of the potential energy surface for a 1:1 copper dioxygen complex, (C(3)N(2)H(5))CuO(2), reveals two distinct states in the valence region, a singlet ((1)A(1)) and a triplet ((3)B(1)). The former spans a continuum from Cu(III)-O(2)(2-) to Cu(I)-O(2)((1)Delta(g)), while the latter spans Cu(II)-O(2)(1-) to Cu(I)-O(2)((3)Sigma(g)(-)). The point at which the potential energy curves for the two states cross marks an abrupt discontinuity in electron distribution, where the system shifts from dominant Cu(III)-O(2)(2-) character to Cu(II)-O(2)(1-). On this basis, we argue that there is no continuum between Cu(III)-peroxide and Cu(II)-superoxide: the two are represented by distinct states that differ both in symmetry and multiplicity.     

New way of presenting the universal calibration of gel permeation chromatography to include macromolecules with very high segment density

The universal calibration of gel permeation chromatography presents deviations when star‐shaped polymers are used, especially when they present high segment density. Polymers presenting high segment density also have higher values of Flory's parameter Φ than the corresponding flexible, linear polymers. This deviation disappears if we express the hydrodynamic volume of the polymers with the quantity [η]M/Φ (where [η] is the intrinsic viscosity and M is the molecular mass) instead of the commonly used quantity [η]M. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2388–2391, 2005     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.