Reactive blending of bioaffine polyesters through free-radical processes initiated by organic peroxides

Reactive polymer blending of poly(β-hydroxybutyrate) (PHB) and its valerate copolymers (PHBV) are reported, following two different methodologies, namely polymerization of rubber inclusions in the preformed matrix or reactive melt blending of preformed polymers. As second phase, poly(butyl acrylate) (PBA) and polycaprolactone (PCL) are used. The results of spectroscopic, thermal, mechanical and morphological analysis indicate the existence of chemical interactions between the blend components. Such interactions are also responsible of a drastic change in the morphology.     

Dynamic-mechanical behaviour in the molten state of iPP/HOCP blends

Dynamic-mechanical data at various temperatures and for different blend compositions are presented for the system iPP/HOCP. The data, in all cases corresponding to the molten state, are relevant not only in view of the processing but especially because they allow some considerations on the blend structure. The data, looked at in different ways (namely the complex viscosity as a function both of frequency and temperature and in the form of Cole-Cole plots), seem to indicate that the system is always in a single phase. This appears somehow in contrast to some microscopic observations recently reported in literature: the discrepancy may be, however, also due to changes in the miscibility due to the applied stress.     

Chain transfer by radical addition-fragmentation mechanisms: Synthesis of macromonomers and end-functional oligomers

Appropriately substituted allylic sulfides, sulfones, bromides, phosphonates, stannanes and peroxides, vinyl ethers and thionocarbonyl compounds are effective chain transfer agents in free radical polymerizations. These compounds function by a radical addition-fragmentation mechanism by which fragments derived from the chain transfer agents are installed at both ends of polymer chains. This provides a convenient method for preparing both mono- and di-end functional oligomers and polymers. Allylic peroxides fragment to give epoxy end groups while the other allylic compounds give rise to macromonomers by introducing terminal double bonds.     

Interactions of halophenols with aqueous micellar systems

The interaction of a series of halophenols with sodium dodecyl sulphate and hexadecyltrimethylammonium bromide micelles was studied by different techniques (high-performance liquid chromatography, apparent acidity constant, spectral shift). The contributions of the halogens to the free energy of transfer from water to micelles are calculted. Correlations between the free energy of transfer for water/micellar solutions and for the classical octanol/water system are good. The application of micellar systems in chromatography and acid-base titrations is verified.     

Some Remarks on Group Bundles and <Emphasis Type="Italic">C</Emphasis>* Dynamical Systems

We introduce the notion of fibred action of a group bundle on a C(X)-algebra. By using such a notion, a characterization in terms of induced C*-bundles is given for C*-dynamical systems such that the relative commutant of the fixed-point C*-algebra is minimal (i.e., it is generated by the centre of the given C*-algebra and the centre of the fixed-point C*-algebra). A class of examples in the setting of the Cuntz algebra is given, and connections with superselection structures with nontrivial centre are discussed. The author was partially supported by the European Network “Quantum Spaces - Noncommutative Geometry” HPRN-CT-2002-00280.     

Substituent effects on the chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane in the presence of disulfides and thiols

The chain‐transfer behavior of 7‐methylene‐2‐methyl‐1,5‐dithiacyclooctane was investigated in the presence of four chain‐transfer agents: thiophenol (PhSH), thiobenzoic acid (BzSH), diphenyl disulfide (PhSSPh), and dibenzoyl disulfide (BzSSBz). The chain‐transfer constants for these compounds at 60 °C were 0.38 (PhSH), 0.76 (BzSH), 0.24 (PhSSPh), and 0.05 (BzSSBz). The variations in the thiol chain‐transfer constants could be explained in terms of the stability of the resulting radicals. The chain transfer to the disulfides, however, appeared to be determined by the electronic character of the disulfide bond, and this suggests that the transfer took place via an addition–fragmentation mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4421–4425, 2002     

Purification and stability of glutaryl-7-ACA acylase from pseudomonas sp.

The enzyme glutaryl-7-ACA acylase fromPseudomonas sp. NCIMB 40474, produced by a recombinantEscherichia coli host, was purified to homogeneity. The enzyme is a tetramer composed of two couples of asymmetric dimers, each of them constituted of two subunits of mol wt 18 and 52 kDa, respectively. It was found that glutaric acid, one of the products of the substrate hydrolysis, is an effective acylase inhibitor. Between pH 6.0 and pH 10.0, the enzymatic activity is almost constant, but below pH 6.0 it progressively declines. The acylase activity decreased sharply as a function of guanidine HC1 concentration. The loss is significant even at concentrations of denaturant lower than those causing unfolding, as suggested by UV spectroscopy and fluorescence emission studies. In these conditions (low denaturant concentration and low pH) the inactivation of the enzyme is caused by the tetramer dissociation into dimers. The lability of the quaternary structure of the enzyme is a key feature that must be taken into account for the improvement of the catalyst stability.     

On the possibility of an unusual extension of the minimax theorem

Summary A natural extension of the minimax theorem for cooperative games is considered.This work was prepared at the Econometric Research Program of Princeton University and it has been partially supported by the Office of Naval Research under contract No. 1958 (16).     

Properties of solution-grown crystals of fractions of isotactic polypropylene with different degrees of stereoregularity

Solution-grown crystals of fractions of isotactic polypropylene (IPP) with different degrees of stereoregularity have been obtained by isothermal crystallization from α-chloronaphthalene, using a self-seeding technique. Electron micrographs of samples, crystallized under the same undercooling, show that, with decreasing fraction of isotactic pentads, the perfect rectangular shape of the single crystal is lost and the presence of more complex morphologies is increasingly observed. The equilibrium dissolution temperature T_d of IPP fractions, from polymers prepared with a titanium based catalyst, decreases linearly with decreasing percentage of isotactic pentads. An extrapolated value of 171°C is obtained for the equilibrium dissolution temperature of a crystal of IPP with 100% isotactic pentads, i.e., an IPP crystal free of configurational defects. The melting temperature T′_m and the apparent enthalpy of fusion ΔH of crystallized and annealed crystal aggregates have been determined by differential calorimetry. The equilibrium melting temperature T_m also depends greatly upon the isotactic pentad concentration. For 100% concentration the extrapolated value of T_m is 181°C. T_m decreases about 1°C per 1% decrease in the isotactic pentad population. The observed equilibrium melting and dissolution temperature depression does not follow the predictions of the Flory equation for copolymer crystallization. In fact, the effect of decreasing probability of isotactic sequence propagation is to depress T_d and T_m much more rapidly. The apparent enthalpy of fusion of both solution-grown crystals and melt-recrystallized samples decreases with an increase in the number of configurational impurities along the chain. For the most stereoregular fraction the average length of isotactic stereoblocks has been compared with the lamellar thickness of solution-grown lath-shaped single crystals.