Giacomo Ruggeri

Functionalization of montmorillonite by methyl methacrylate polymers containing side-chain ammonium cations

Non-extractable poly(methyl methacrylate) (PMMA)-montmorillonite adducts were prepared by two distinct processes: (a) In the first method, free-radical copolymerization of MMA with clay previously treated with 2-(N-methyl-N,N-diethylammonium iodide) ethyl acrylate (QD1) or 2-(N-butyl-N,N-diethylammonium bromide) ethyl acrylate (QD4) was performed. (b) The second method was based on the direct interaction of montmorillonite with various copolymers of MMA with QD1 or QD4. The structure of the adducts as determined by Fourier-transform infra-red spectroscopy, thermogravimetric analysis and X-ray diffraction was shown to consist of the insertion of MMA macromolecules between lamellar layers whose separation was consequently higher than in the polymer-free clay. The polymer was strongly fixed to the inorganic surfaces, probably due to cooperative formation of electrostatic bonding. The thermal stability of the organic polymers was substantially enhanced in the adducts.

Bis(benzoxazolyl)stilbene excimers as temperature and deformation sensors for biodegradable poly(1,4-butylene succinate) films

In this work, new and innovative polymeric film sensors based on excimer luminescence and responsive to both mechanical and temperature stress were obtained through the dispersion of moderate amounts (0.02–0.2 wt%) of the food-grade dye bis(benzoxazolyl)stilbene (BBS) into a thermoplastic aliphatic biodegradable polyester [poly(1,4-butylene succinate), PBS]. Emission from BBS excimers emerged with dye concentrations higher than 0.05 wt% conferring to the film a green luminescence (λexc. = 366 nm). On applying mechanical stress at rt, the PBS reorganization efficiently breaks the BBS arrangements leading to the prevalence of blue emission from the excited isolated chromophores. Moreover, the optical behaviour of PBS–BBS quenched blends was thermally affected in the range 50–80 °C, providing composite films characterized by a very sensitive temperature dependent luminescence response. The easy modulation of the luminescent properties of polyester films by varying the supramolecular organization of BBS dispersed molecules by thermal or mechanical perturbations suggests various applications in the field of smart and intelligent films from thermoplastic materials.

Mechanochromic polymer blends

Mechanochromic polymer blends, i.e.polymer blends characterised by optical responsiveness to mechanical stimuli, have evoked major interest and experienced significant progress in recent years. Various examples are reported of chromogenic materials composed of a functional dye covalently linked to the polymer chains or physically dispersed in the continuous macromolecular matrix, the latter appears to be a more sustainable route for the industrial scale-up of these materials. This feature article examines the properties and performances of various mechanochromic materials prepared by using different thermoplastic polymers with non-covalently incorporated aggregachromic dyes. More specifically, the general mechanism underlying the optical phenomenon is introduced and the different approaches used to obtain chromogenic materials are presented and discussed considering both dye features and polymer characteristics. The combination of the properties of the blend components can often result in drastic differences in the material chromogenic responsiveness. The article concludes commenting and discussing the application of these kind of polymer devices as a new type of advanced materials and the perspective thereof.

Some aspects of polypropylene functionalization by free radical reactions

Abstract Hydrocarbon/monomer combination products are detected by GC-MS in the reaction of 2-methylundecane with α-methylstyrene (MES) in the presence of peroxide initiators. On this basis, functionalization experiments of isotactic polypropylene (IPP) and of atactic polypropylene (APP) with MES, diethylfumarate and diethylamaleate have been carried out in solution and in bulk, in the presence of dicumylperoxide. The extent of functionalization, determined by i.r. spectroscopy, depends on the microstructure of the macromolecule being 0.5–1.0% by weight for IPP and 3.0–8.0% by weight for APP. In all functionalization experiments of IPP and APP, partial thermal degradation is observed but crosslinking is negligible.

Dielectric response analysis of a conducting polymer dominated by the hopping charge transport

The d.c. conductivity and the electric a.c. response from 100 Hz up to 40 MHz of poly(3n-decylpyrrole) were measured in the 80-330 K interval to characterize the charge transport behaviour of the system. The d.c. conductivity well fitted the variable range hopping model, and the loss factor, after having deducted the d.c. contribution, showed a relaxation peak when the conductivity versus frequency started to rise. The strength of this relaxation increased with temperature and became too large to be related to a dipolar relaxation; moreover, the temperature dependence of the loss peak frequency and d.c. conductivity coincided. The observed relaxation was attributed to the hopping charge transport, as further confirmed by the temperature behaviour of the relaxation strength and by the frequency dependence of the exponents of the power law which locally approximate the conductivity behaviour. As the activation energy of the d.c. conductivity differed from the frequency of the loss peak, the theoretical prediction concerning the selfsimilarity of the a.c. conductivity was roughly verified.

Polymer composites with smart optical properties

In this review we describe several examples concerning the attractive properties of smart polymer composites containing aggregachromic dyes of different nature and structure. The dye–polymer interphase interactions depend on the equilibrium between the aggregated and the isolated forms of chromophores dispersed within the polymer matrix. Such interactions are easily perturbed by external solicitations like mechanical or thermal stresses, which induce a clear and rapid change in the composite’s optical properties both in absorption and in emission. These new stimuli-responsive composite materials therefore appear promising for the development of smart and intelligent polymer devices for sensing and safety applications.

Optimization of an organic memristor as an adaptive memory element

The combination of memory and signal handling characteristics of a memristor makes it a promising candidate for adaptive bioinspired information processing systems. This poses stringent requirements on the basic device, such as stability and reproducibility over a large number of training/learning cycles, and a large anisotropy in the fundamental control material parameter, in our case the electrical conductivity. In this work we report results on the improved performance of electrochemically controlled polymeric memristors, where optimization of a conducting polymer (polyaniline) in the active channel and better environmental control of fabrication methods led to a large increase both in the absolute values of the conductivity in the partially oxydized state of polyaniline and of the on-off conductivity ratio. These improvements are crucial for the application of the organic memristor to adaptive complex signal handling networks.

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.

Synthesis and characterization of different poly(1‐vinylindole)s for photorefractive materials

The main goal of this research was to verify if some advantages could be obtained by the replacement of poly(1-vinylcarbazole), a component commonly employed for organic photorefractive materials, with various polymers containing side-chain heteroaromatic moieties. For this purpose, poly(1-vinylpyrrole), poly(1-vinylindole), and some methyl-substituted compounds of poly(1-vinylindole) were considered. The best conditions for both monomer synthesis and polymerization were found. A first possible advantage of the new polymeric substrates resided in the values of the glass-transition temperature, which, as expected, was constantly lower than that of poly(1-vinylcarbazole). This could lead to a material that requires the introduction of a lower quantity of plasticizer in the final photorefractive blend to display photorefractive behavior at room temperature. In addition, the verified higher electric dipole moments of the pyrrole and indole derivatives could improve the compatibility of the optically nonlinear component required in the system, typically an azo-molecule, by increasing its solubility inside the blend. All the synthesized vinyl monomers and polymers gave clear spectroscopic evidence of the formation of charge-transfer complexes with 2,4,7-trinitrofluorenylidenmalonitrile, an efficient sensitizer for photoconductivity.

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-%.