Elisa Passaglia

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.

New fluorinated acrylic polymers for improving weatherability of building stone materials

Acrylic polymers are widely used for their suitability to be shaped in different molecular structures. However, while very appropriate for many applications, these materials are characterized by a limited outdoor stability. In order to improve this last characteristic while maintaining the simple and flexible synthetic route, a study was performed based on the preparation of fluorinated polymers from acrylic monomers where several H-atoms in different positions were replaced with F-atoms. The structure design was aimed to optimize (e.g. minimize) the fluorine content of the final material while obtaining improved chemical and photochemical stability, good filmability and limited permeability to condensed water. The preparation of polymers of methacrylates derived from partially fluorinated alcohol by free radical mechanism is described. The fluorine content and distribution in the macromolecules is modulated by selecting different monomers and by copolymerization with nonfluorinated acrylates or vinylethers. The selection of the comonomers and their relative content in the polymer allows to control the glass transition temperature and the filmability as well as the protection efficiency of the coating. Polymers derived from more complex monomers such as α-trifluoromethyl-methylacrylate are also described. The suitability of these new materials for protective coating of stones is tested by evaluating their stability to different chemical and physical agents and their selective permeability to water vapour vs. condensed water.

Functionalization of SBR copolymer by free radical addition of thiols

The reaction of the random styrene/butadiene copolymer (SBR) with two functional thiols (thioglycolic acid and its aliphatic ester) in the presence of free radical initiators is described. The reaction leads to addition of the thiol group to the vinyl double bonds of the 1,2-butadiene units of the copolymer with high selectivity. As a consequence the resulting macromolecules contain covalently bonded carboxylic or carboxylate groups. The influence of the reaction conditions on the relative probability of the addition reaction with respect to crosslinking, degradation and chain transfer reactions is discussed. The degree of functionalization (FD) can be modulated in the range from 1 to 10 mol-%.

Nanocomposites Based on Thermoplastic Polymers and Functional Nanofiller for Sensor Applications

Thermoplastic polymers like polyolefins, polyesters, polyamide, and styrene polymers are the most representative commodity plastics thanks to their cost-efficient manufacturing processes, excellent thermomechanical properties and their good environmental compatibility, including easy recycling. In the last few decades much effort has been devoted worldwide to extend the applications of such materials by conferring on them new properties through mixing and blending with different additives. In this latter context, nanocomposites have recently offered new exciting possibilities. This review discusses the successful use of nanostructured dispersed substrates in designing new stimuli-responsive nanocomposites; in particular, it provides an updated description of the synthetic routes to prepare nanostructured systems having the typical properties of thermoplastic polymers (continuous matrix), but showing enhanced optical, conductive, and thermal features dependent on the dispersion topology. The controlled nanodispersion of functional labeled clays, noble metal nanoparticles and carbon nanotubes is here evidenced to play a key role in producing hybrid thermoplastic materials that have been used in the design of devices, such as NLO devices, chemiresistors, temperature and deformation sensors.

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.

Homopolymerization of Methyl Methacrylate by Novel Ziegler-Natta-Type Catalysts Based on Bis(chelate)-nickel(II) Complexes and Methylaluminoxane

Novel catalytic systems based on bis-(chelate)nicke(II) precursors, such as bis (α-nitroacetophenonate)nickel(II) [Ni(naph) 2 ] and bis(2,6-diisopropyl―benzenesalicyladiminate)nickel(II) [Ni(dipbs) 2 ], and methylaluminoxane (MAO)= as the cocatalyst were employed for the polymerization of methyl methacrylate (NMA). Reaction paramethers were examined. Under proper conditions, the Ni(dipbs) 2 /MAo system allowed to obtain poly(MMA) with a very high productivity (TOF up to 70 000 h-1) and a remarkable syndiospecificity degree (rr > 80%) at room temperature without addition of an ancillary Lewis base.

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.

Homo‐ and copolymers of hexafluoroisopropyl methacrylate and α‐fluoroacrylate with alkyl vinyl ethers: Microstructure and thermal properties

A study is reported, dealing with the microstructure and thermal behavior of the homopolymers of 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIM) and 1,1,1,3,3,3-hexafluoroisopropyl α-fluoroacrylate (HFIFA), as well as of their copolymers with various vinyl ethers. The aim of this work was a better understanding of the role that fluorine content and distribution—first in the monomer and then along the ensuring macromolecular chain—play in determining the polymerizability of the selected vinyl monomers, and the final properties of the polymeric material. Primary (n-butyl, isobutyl, 2-ethylhexyl), secondary (cyclohexyl), and tertiary (tert-butyl) vinyl ethers were employed as the comonomers. A general tendency towards comonomer alternation was observed upon radical initiated copolymerization with HFIFA. On the other hand, the relatively more electron-rich HFIM did not usually yield strictly alternating sequences, unless the bulky tert-butyl vinyl ether was employed. The incorporation of electron-rich vinyl ether monomers within a partially fluorinated polymeric chain by simple radical initiated process was considered particularly interesting in view of the possible application of these materials as water-repellent protective coatings. In this case, the fluorinated units should provide the low energy surface (water repellency) and, possibly, photo- and thermostability, whereas the vinyl ether counits should grant improved adhesion and adequate film-forming properties.

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.