Francesco Picchioni

Ionomeric membranes based on partially sulfonated poly(styrene): synthesis, proton conduction and methanol permeation

Homogeneuosly sulfonated poly(styrene) (SPS) was prepared with various concentration of sulfonic acid groups in the base polymer. Membranes cast from these materials were investigated in relation to proton conductivity and methanol permeability in the temperature range from 20°C to 60°C. It was found that both these properties increase as the polymer is increasingly sulfonated, with abrupt jumps occurring at a concentration of sulfonic acid groups of about 15 mol%. The most extensively sulfonated membrane exhibited conductivity equal to that of Nafion. As a consequence, this membrane material is potentially an appealing alternative to the very expensive Nafion, for a number of electrochemical applications. For the membrane with the highest degree of sulfonation we measured a methanol permeability about 70% smaller than for Nafion. This characteristic is especially desirable in applications related to the direct methanol fuel cell (DMFC).

Grafting of diethyl maleate and maleic anhydride onto styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS)

In this paper a study of the bulk functionalization of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) with diethyl maleate (DEM) or maleic anhydride (MAH) and dicumyl peroxide (DCP) as initiator in a Brabender mixer is described. The determination of the functionalization degree (FD) by NMR analysis indicates that the FD values depend on the feed composition and in particular on the DEM/DCP ratio. All obtained products were fractionated by solvent extraction and characterized by IR, NMR and GPC. The results obtained show that the functionalization takes place with a very large preference at the aliphatic carbons of the polyolefin block. Moreover occurrence of degradation and chain extension reactions gives a functionalized product with a MWD larger than 1. Acetone extraction allows the isolation of styrene rich oligomers, thus the high MW functionalized polymer has a lower content of aromatic units than original SEBS. The results are described with reference to reaction mechanism previously reported in case of the functionalization under similar conditions of polymonoalkenes.

Controlled Functionalization of Olefin/styrene Copolymers through Free Radical Processes

The functionalization of styrene-b-(ethylene-co-1-butene)-b-styrene triblock copolymer (SEBS) and styrene-co-butadiene (SBR) random copolymer by free radical processes is presented. SEBS was functionalized in the melt with diethyl maleate (DEM) and dicumyl peroxide (DCP) as initiator. The functionalization degree (FD) ranges from 0.1 to 1.6% mol and depends on the feed composition and in particular on the DEM/DCP ratio. Such functionalization takes place with a very large preference at the aliphatic carbons of the polyolefin block. The functionalization of SBR was performed by radical addition in solution of two functional thiols (thioglicolic acid and its aliphatic ester), in the presence of free radical initiators. The addition occurs at the vinyl double bonds of the 1-2 butadiene units with high selectivity. FD can be tuned in the range 1-10mol%. These data are rationalized in the frame of the general reaction mechanism of free radical polymerization. A general reaction scheme is proposed which allows the design of proper conditions for favoring functionalization versus degradation and crosslinking depending on the nature of molecules and macromolecules involved.

Blends of syndiotactic polystyrene with SEBS triblock copolymers

Blending of styrene-b-(ethylene-co-1-butene)-b-styrene (SEBS) triblock copolymers with syndiotactic polystyrene (PSsyn) has been performed in a Brabender mixer above the higher glass transition temperature of the triblock copolymer but below the PSsyn melting point. The large excess of the triblock copolymer over the homopolymer as well as the significant amount of plasticized amorphous PSsyn phase allowed the easy processing under the used temperature conditions with good interface compatibility. The consequent interfacial adhesion between the amorphous PS phase and the unmelted PSsyn crystallites affects both the final morphology of the blend as well as its dynamic behavior. Indeed, such solid particles act as reinforcing point of the overall blend structure, as evidenced by scanning electron microscopy. Moreover, they contribute to a Tg increase in the order of 20 °C with respect to pure SEBS and to an appreciable conservation of mechanical properties at temperatures higher than the Tg of the PS blocks of SEBS. The mechanical and thermal behavior of the synthesized blends has been studied and tentatively correlated to the molecular weight ratio between PSsyn and the PS blocks of SEBS.

Solid-State Modification of Polypropylene (PP): Grafting of Styrene on Atactic PP

Grafting of unsaturated vinyl monomers onto polypropylene (PP) is a convenient route to develop new polymeric materials with synergistic properties. Particular attention must be paid to the formation of graft copolymer relative to the formation of homopolymer, since the final properties are dependent both on the dispersion of the new polymer into the iPP matrix, which is controlled by the degree of grafting, as well as on the chemical nature of the in-situ formed polymer chains. In the present work the grafting reaction of styrene on atactic PP (aPP), considered as good model system for the more studied solid-state modification of isotactic PP (iPP), has been investigated in the presence of two different radical initiators in order to get a first insight into the grafting reactions onto PP. Several grafting reactions were carried out by changing the chemical compositions of the starting polymerization mixture, whose homogeneity was accurately investigated by Raman spectroscopy. Infrared-spectroscopy (FT-IR) was used for qualitative and quantitative characterization of the reaction product. A quantitative separation procedure, based on the concept of selective solvent extraction, has been established which enables the determination of the grafting efficiency (Φ) as well as the exact chemical composition of the final product. Finally, all products were characterized by means of Differential Scanning Calorimetry (DSC) in order to study their thermal behaviour.

A novel method of preparing metallic Janus silica particles using supercritical carbon dioxide

In this study, we demonstrate a novel fabrication method to prepare metallic Janus silica particles by embedding nanosized silica particles on a spherical polystyrene (PS) substrate in supercritical carbon dioxide (sc CO2), followed by labelling with gold nanoparticles on the exposed part of the silica colloids. To this end, three main types of Janus particles displaying two distinct surfaces are produced by recovering silica from the polystyrene template. Embedment of particles into the PS template in sc CO2 allows for precise control of the degree of embedding of particles and subsequent modification of the partially exposed particle surface. The embedding degree, as well as the final Janus balance, can be varied over a wide range through control of pressure, temperature, or treatment time of sc CO2. Hierarchical PS-silica composites and embedment are evaluated by scanning electron microscopy (SEM). Partial surface modification with gold nanoparticles is investigated by transmission electron microscopy (TEM). With this method various functionalized Janus particles with tuneable properties can be prepared by adjusting various surface modifiers and polymer substrates in the future.

Blends of Syndiotactic Polystyrene with SBS Triblock Copolymers

Blending of polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymers with syndiotactic polystyrene (PSsyn) has been performed in a Brabender mixer above the glass transition temperature of the triblock copolymer but below the melting point of PSsyn. The presence of a large excess of amorphous SBS (at least 70 wt.-%) as well as of the amorphous PSsyn phase (about 60 wt.-%, also above its Tg) allowed the easy mixing of the components. In contrast, the presence of unmelted PSsyn crystallites affects both the final morphology of the blend as well as its dynamic behavior. Indeed, according to the dynamic thermomechanical analysis (DMTA) data it is possible to suggest that such solid particles act to reinforce the overall blend structure (as in composite materials filled with inorganic solid particles). Similar behavior is also observed for the SBS copolymer alone below the Tg of the styrene blocks, Tg (PS). This conclusion is supported by both the compatibility of the blends, and the thermal and dynamic thermomechanical behavior at T > Tg (PS) as investigated by means of Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and DMTA. The results obtained are tentatively compared with those of similar blends obtained from toluene solution.

Formation and Compatibilizing Effect of the Grafted Copolymer in the Reactive Blending of 2-Diethylsuccinate Containing Polyolefins With Poly-ε-caprolactam (Nylon-6)

The intermolecular reaction and its role in determining the partial compatibility between diethylsuccinate containing linear low-density polyethylene or ethylene propylene copolymer and poly-e-caprolactam (PA6) has been investigated in the melt using a Brabender mixer. The reaction product has been submitted to selective solvent extraction with formic acid and n-heptane; the characterization of the two extracted fractions and the insoluble residue has demonstrated the formation of a polyolefin-nylon (PO-PA6) grafted copolymer. The formation of grafted copolymer has an evident effect on the compatibilization of the two original polymers, indeed the differential scanning calorimetry analysis shows a remarkable decrease of temperature and enthalpy of PA6 crystallization. Moreover scanning electron microscopy micrographs show clear evidence of size reduction of PA6 domains associated with improved interface interactions.

The effect of hydrophilic and hydrophobic block length on the rheology of amphiphilic diblock Polystyrene-b-Poly(sodium methacrylate) copolymers prepared by ATRP

Following our previous investigation on the effect of molecular architecture on the rheology of Polystyrene-b-Poly(sodium methacrylate) copolymers (PS-b-PMAA), we consider here diblock PS-b-PMAA copolymers characterized by a different length of either the hydrophilic or the hydrophobic block. Various copolymers characterized by different PS or PMAA block length have been prepared by ATRP (kinetics is also discussed) and studied from the point of view of their rheological behaviour in water. To the best of our knowledge, this is the first systematic investigation concerning the effect of block length on the rheology of diblock polyelectrolytes. We found that the hydrophobic block length has small influence on the rheology. Surprisingly, the polymers with shortest PMAA blocks yield the strongest gels at high concentration. A simple model based on the classical theories of self-assembly and percolation of amphiphilic polymers has been here developed in order to explain the observed data.

Insights in starch acetylation in sub- and supercritical CO2.

An in-depth study on the acetylation of starch with acetic anhydride (Ac(2)O) and sodium acetate (NaOAc) as the catalyst in pressurized carbon dioxide (scCO(2)) in a broad pressure range (8-25MPa) and a temperature of 90°C is provided. Highest degrees of substitution (DS) of 0.29 (1h reaction time) and 0.62 (24h reaction time) were found near the critical point of the mixture (15MPa). The phase behavior of the system CO(2), starch and acetic anhydride (Ac(2)O) was studied in a high pressure view cell. The critical points were a clear function of the temperature and increased from the range of 9.4-10MPa to 14.5-14.8MPa when going from 50 to 90°C (Ac(2)O mole fraction at the critical point in the range of 0.08-0.09). Acetylation experiments with a range of starch particles sizes showed a clear relation between the DS and the particle size.