Orietta Monticelli

POSS-based hybrids by melt/reactive blending

Organic–inorganic polyhedral oligomeric silsesquioxane (POSS)–polymer hybrids have gained a wide research interest in the last decade, thanks to the great versatility of POSS synthesis and availability of different chemical structures, aimed at modifications of physical/chemical properties of polymers or at delivering new functional properties. Traditionally, in situ copolymerisation of POSS to produce hybrid organic–inorganic polymers with pendent POSS groups has been used both for thermoplastics and thermosets. In recent years, attention has been also given to the possibility of preparing POSS–polymer systems by melt blending techniques, taking advantage of (i) miscibility of POSS into polymers thanks to physical interactions or (ii) chemical reaction between POSS and the polymer. These two methods, usually referred to respectively as melt blending and reactive blending, represent very appealing, inexpensive and environmentally friendly processes for industrial development of POSS technology. This paper reviews the present state of the art on both melt blending and reactive blending of POSS into thermoplastic polymers, discussing present achievements and limitations from both methods.

Stimuli Responsive Hydrogels Prepared by Frontal Polymerization

Frontal polymerization was used as an alternative method for the easy and fast preparation of polymer hydrogels prepared from N-isopropylacrylamide (NIPAAm) and N-vinylcaprolactam (VCL), the latter being less toxic and less expensive than NIPAAm. All samples were characterized in terms of their swelling behavior, and their thermal properties were investigated by DSC. It was found that VCL influences both pore size and shape distribution. Moreover, also the swelling ratio of the materials is dependent on the monomer ratio. Eventually, by a comparison with analogous samples prepared by the classical polymerization technique, it was found that the two methods give rise to hydrogels characterized by very diverse swelling capability; furthermore, swelling reversibility was also found to be different when temperature is allowed to cyclically vary between values that are below and above the lower critical solution temperature. In particular, samples prepared by frontal polymerization are characterized by lower swelling ratio and larger swelling recovery capability.

Deposition of amino-functionalized polyhedral oligomeric silsesquioxanes on graphene oxide sheets immobilized onto an amino-silane modified silicon surface

The reaction between amino-functionalized polyhedral oligomeric silsesquioxanes (POSS-NH2) and graphene oxide (GO) sheets was used to graft POSS-NH2 onto a GO layer immobilized onto a layer of (3-aminopropyl)triethoxysilane, self-assembled onto Si substrate. The chemical composition and surface morphology as well as the surface properties of the prepared films were investigated by means of Fourier transform infrared spectroscopy, water contact angle measurements and field emission electron microscopy. Tribological measurements performed with a nanoindenter showed that such hydrophobic trilayer film exhibited a reduced friction coefficient suitable for applications in lubricant coatings.

Hyperbranched Aramids by the A2 + B3 versus AB2 Approach: Influence of the Reaction Conditions on Structural Development

Hyperbranched aromatic polyamides (pPDT) from A2 (p-phenylene diamine)+ B3 (trimesic acid) reactants have been prepared using direct polycondensation in solution. The influence of various polymerization parameters on the polymer structure development and the sol content, as well as on gel formation, has been thoroughly investigated. Prior to the attainment of the gel point, whose occurrence is linked quite strongly to the reaction conditions, the resultant hyperbranched polymers are fully soluble even at room temperature, not only in concentrated H2SO4, but also in aprotic polar solvents (DMF, NMP, DMAc, DMSO). At 80°C, under typical experimental conditions, gel formation starts just under 120 min. At a higher temperature (115°C), the attainment of crosslinking reactions is accelerated (gel point occurs at about 20 min). Both the presence of added salt (LiCl) to the reaction medium at 80°C and the use of highly purified reagents promotes earlier gel occurrence. By increasing the molar ratio of primary amino to carboxyl groups from two-thirds to one, the network formation is delayed. A molar ratio of 1/2 leads to the formation of oligomers only. Both the polymer structure development and the degree of branching of pPDT have been evaluated by NMR spectroscopy as functions of reaction conditions. As compared to pPDT, polymers prepared from the homologous AB2 monomer show similar intrinsic viscosity and glass transition temperature, but higher molecular weights and distinct differences in the relative ratio of the various structural units. The lyotropic and thermotropic behaviour of both polymers has been found.

PLA/POSS Nanofibers: A Novel System for the Immobilization of Metal Nanoparticles

In this work, a novel catalytic system is developed, consisting of palladium nanoclusters homogenously dispersed on the surface of nanostructured polymer nanofibers based on poly(L-lactic acid) (PLLA) and polyhedral oligomeric silsesquioxanes (POSS). Indeed, PLLA nanofibers containing amino-functionalized silsesquioxane molecules (POSS-NH2), potentially capable of interacting with the metal precursor, are prepared by means of electrospinning. Conversely to the polymer matrix, which does not show any tendency to retain the metal precursor, the submicrometric dispersion of POSS-NH2 in the PLLA nanofibers, as demonstrated by SEM-EDS analysis, turns out to promote the formation of metal nanoclusters. TEM measurements show a uniform distribution of Pd nanoparticles, characterized by an average dimension of ca. 4 nm, along the fibers. The prepared system proves a relevant catalytic activity toward the hydrogenation of stilbene under heterogeneous conditions. Moreover, as demonstrated by XPS measurements, the support is capable of retaining the catalyst during the hydrogenation reaction, thus preventing its leaching.

On the development of a facile approach based on the use of ionic liquids: preparation of PLLA (sc-PLA)/high surface area nano-graphite systems

In this work, a novel method to prepare composite systems based on polylactide (PLA) and high surface area nano-graphite (HSAG) has been developed, consisting of the application of ionic liquids (ILs) as dispersing/exfoliating agents for nanofillers. Indeed, the proposed approach is easy as well as with a low environmental impact, involving neither the use of co-solvents nor the preliminary oxidation of graphite. As a preparatory screening, systems based on either poly(L-lactide) (PLLA), or an equimolar mixture of poly(L-lactide) (PLLA) and poly(D-lactide) PDLA, and ionic liquids are prepared by melt-blending the polymer matrices with different kinds and amounts of imidazolium-type ILs. Among the tested ILs, 1-butyl-3-methylimidazoliumhexa-fluorophosphate ([bmim][PF6]) shows the highest solubility and the lowest tendency to decompose the polymer matrix during the processing. DSC and TGA measurements highlight that the above IL induces a slightly plasticizing effect on PLLA, with a limited decrease – of about 20 °C for the sample with the highest amount of [bmim][PF6] – of the onset degradation temperature. As evidenced by FE-SEM measurements, the chosen IL features a high sonication-assisted capability of dispersing/exfoliating the nano-graphite, thus allowing obtaining a system containing 2% by mass of the nanofiller, organized in aggregates with an average dimension of 300 nm and composed of few layers. Conversely to the direct insertion of the HSAG into the polymer matrix (which produces micrometer-sized aggregates) when the previously-prepared [bmim][PF6]/HSAG system is incorporated, a submicrometric dispersion of the nano-graphite is obtained. The presence of the finely dispersed nanofiller has a nucleating effect on PLLA crystallization, significantly increasing the crystal nucleation density. Moreover, it is of utmost relevance that, in the case of the stereocomplex-PLA-based systems, the HSAG promotes the exclusive formation of stereocomplex crystals over homo-crystals.

POSS vapor phase grafting: a novel method to modify polymer films

In this paper, a novel method for the preparation of surface modified polymer films is proposed, by the vaporization of polyhedral oligomeric silsesquioxanes (POSS) and reaction on the polymer surface. This method was successfully applied to the grafting of an amino-functionalized POSS (POSS-NH2) on poly(styrene-co-maleic anhydride) (PSMA), showing efficient grafting to produce a POSS-rich polymer layer on the vapor-treated surface. The thickness of this layer was found to be controlled by diffusion of POSS, allowing tailoring of the grafted layer thickness with the treatment time. The processing temperature window was found to be defined by the following conditions: (i) high enough to allow significant POSS volatilization, (ii) high enough to allow sufficient polymer chain mobility to react with POSS and (iii) low enough to avoid specimens deformation by polymer flow during the treatment.

On a novel catalytic system based on electrospun nanofibers and M-POSS.

We report on a novel catalytic system based on electrospun polymer nanofibers, which were modified with a metal-containing polyhedral oligomeric silsesquioxanes (M-POSS). In particular, a titanium-based POSS, characterized by an amino group as reactive side, was contacted with poly(styrene-co-maleic anhydride) (PSMA) nanofibers, which were dispersed in a solvent capable of solubilizing the above metal silsesquioxane. FTIR measurements evidenced the occurrence of the reaction between the MA group of PSMA and the amino group of POSS molecule. The catalytic activity of the PSMA/Ti-POSS-NH(2) system was proved in the degradation of sulforhodamine B under UV light. The presence of metal center, directly attached to the nanofiber surface, renders the system catalytically active.

Synthesis, Characterization and Properties of a Hyperbranched Aromatic Polyamide: Poly(ABZAIA)

Full Paper: A hyperbranched aromatic polyamide has been prepared by direct polycondensation of 5-(4-aminobenzoylamino)isophthalic acid (ABZAIA), using the modified Higashi’ s method. The resultant polymer is soluble in aprotic polar solvents such as DMF, DMAc, NMP, and DMSO. Intrinsic viscosities of poly(ABZAIA) samples, measured in sulfuric acid at 258C, are in the range between 0.2 and 0.3 dL N g ‐1 . Glass transition temperature (Tg) is placed around 1508C and onset temperature of thermal decomposition at about 2758C. Full molecular weight distribution, evaluated by a SEC apparatus equipped with three different detectors, gives M — w values in the range between 55 000 and 300 000 g N mol ‐1 , with a polydispersity index, M — w/M — n, relatively large and generally around 3 ‐4. Poly(ABZAIA), synthesized in suitable experimental conditions, shows rather low values of Mark-Houwink a constant. Together with [g] data, these a values are consistent with a hyperbranched, close-to-globular shape of our polymer. Highly concentrated polymer solutions (A 40 wt.-%) in NMP show shear birefringence under polarized light. The specific surface area of the powdered material, calculated by nitrogen adsorption/desorption isotherm, is ca. 40 m 2 N g ‐1 .

Fast‐activated anionic polymerization of ε‐caprolactam in suspension, 1. Role of the continuous phase on characteristics and properties of powdered PA6

The fast-activated anionic polymerization of e- caprolactam has been performed in suspension in order not only to efficiently dissipate the heat of polymerization, but also to directly synthesize powdered polyamide 6. The continuous phase of the system is composed of polyisobutene oils: five fractions, different in their molecular weights and viscosities, have been used and thoroughly studied in terms of their influence on polymerization yield, as well as on polyamide 6 chemical and physical properties, and on shape and size of the polymer particles. The above characterizations have been performed on samples synthesized varying the weight ratio between the suspending medium and the droplets made of monomer, initiator (sodium caprolactamate) and ultra-fast activator (cyclohexyl carbamoyl caprolactam).