Francesco Ciardelli

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.

Comparative evaluation of fluorinated and unfluorinated acrylic copolymers as water repellent coating materials for stone

An investigation on the influence of side-chain fluorination on the performance of a series of acrylic-based copolymers as protective coating materials for stones has been carried out by comparing them with unfluorinated polymeric analogues. For this purpose, a series of copolymers of 1H,1H,2H,2H-perfluorodecyl methacrylate (XFDM) and 2,2,2 trifluoroethyl methacrylate (TFEM) with unfluorinated vinyl ether or acrylic comonomers have been synthesized, as well as their not fluorinated analogues, and applied to limestone and marble substrates. A silicone-type commercial product, widely employed in the protection of stones in buildings and other artifacts, has also been tested as a reference material. Their protection efficiencies were then comparatively evaluated in terms of surface properties, water permeability, and appearance. It is shown that the presence of fluorine always has, as expected, a positive influence on the protective action of the polymer, increasing the water repellency of the coated stone.

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.

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.

Photochemical stability of partially fluorinated acrylic protective coatings. I. Poly(2,2,2-trifluoroethyl methacrylate) and poly(1H, 1H, 2H, 2H-perfluorodecyl methacrylate-co-2-ethylhexyl methacrylate)s

Abstract The photochemical stability and photodegradation pathways of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) and copolymers of 1H,1H,2H,2H-perfluorodecyl methacrylate with 2-ethylhexyl methacrylate (XFDMA–EHMA) have been investigated under artificial solar light irradiation. The extent of degradation was assessed by weight loss and gel content determination, size exclusion chromatography and FTIR spectroscopy. PTFEMA exposed up to 2000 h showed only molecular changes due to a low extent of chain scission. The two XFDMA–EHMA copolymers underwent much more degradation, with extensive cross-linking, formation of low-molecular weight products, and oxidation reactions on the chains. The behaviour of the copolymers is controlled by the reactivity of the EHMA units, as was shown by comparison with results obtained on degradation of PEHMA homopolymer.

From homogeneous to supported metallocene catalysts

Abstract The mechanism of the monoalkene homogeneous polymerization with metallocene/methylalumoxane (MAO) system is reviewed with reference to structural and stereochemical control of the polymers as derived by the type of ligands around the transition metal (Zr and Ti). Major disadvantages of these homogeneous catalysts are the lack of morphology control and reactor fouling. Supported catalysts can allow to overcome these drawbacks and be utilized in cheaper bulk or gas-phase processes. Also they may permit the use of less MAO, while still offering facile control of polymer properties by ligand variation. Binding of well-defined transition metal complexes onto carefully prepared inorganic surfaces is certainly a very attractive approach to create new heterogeneous catalysts and to characterize highly reactive species. In this paper attention is on the use of alumina, silica and zeolites for supporting metallocenes of Ti and Zr. The amount of metallocene which can be attached to the surface of these supports is much lower than expected on the basis of simple physical absorption. This seems to indicate that attachment takes place at specific sites of the surface. In any case the amount of hydroxyl groups seems to play a determining role as shown by structural analysis and catalytic activity of olefin polymerization of the resulting heterogenized complexes. The formation of cationic species on the inorganic surface was proposed in a very analogous way as proposed in solution. Results concerning homo- and copolymerization of monoalkenes with different supported metallocene complexes are presented to discuss the effect of support nature and surface features.

Light-induced conformational changes in chiral polymers with photochromic side chains

Preparation de polymeres optiquement actifs avec un squelette hydrocarbure et peptide portant des groupes photoisomerisables azobenzene et stilbene dans les chaines laterales par copolymerisation et par modification chimique de polymeres preformes. Etude du comportement photochrome et de la conformation en solution par absorption UV, fluorescence et dichroisme circulaire

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.

Zeolite supported polymerization catalysts: Copolymerization of ethylene and α-olefins with metallocenes supported on HY zeolite

Abstract Copolymerization of ethylene with higher α -olefins, such as 4-methyl-1-pentene, 1-hexene, 1-octene and 1-dodecene, was carried out with both aspecific and isospecific bridged metallocene complexes, comparing the catalytic behaviour following metallocene supportation on methylalumoxane-pretreated HY zeolite (SiO 2 /Al 2 O 3 =5.7). A decrease in specific activity was generally observed after adsorption on zeolite of both non bridged and ansa -metallocene complexes, though molecular weights of the copolymers were found to be higher especially when employing α -olefins as polymerization solvents. On the other side, the incorporation of the α -olefin comonomer was reduced in the case of supported biscyclopentadienylzirconium dichloride, whereas similar contents of olefin units were incorporated in the copolymers prepared with soluble or supported ansa -zircono- or hafnocene. NMR analysis and DSC determined melting points of the produced copolymers are connected with a shape selectivity effect promoted by the support.

Structure control, coating properties and durability of fluorinated acrylic-based polymers

Fluorinated acrylates were employed for the synthesis of conventional, side-chain fluorinated, fully acrylic random copolymers, and of more unusual hybrid copolymers with vinyl ethers. The latter can feature alternating structure and peculiar material properties associated with fluorine or fluorinated groups substitution onto the polymer backbone. Improved efficacy and durability of the resulting coating, highly desirable for the consolidation and protection of highly valued works of art, was achieved through a systematic approach involving a detailed study of their photodegradation behavior, and extensive testing of protection efficacy upon application onto micro-and macroporous stone substrates of different chemical composition and morphology.