Valter Castelvetro

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.

Tailoring New Fluorinated Acrylic Copolymers as Protective Coatings for Marble

Abstract The protective performances of two new fluorinated acrylic copolymers (based on the monomers 1H,1H,2H,2H-perfluorodecyl methacrylate (XFDM) and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIM) are evaluated and compared with Paraloid B72, a commercial copolymer ethyl methacrylate/methyl acrylate (EM/MA) and its partially fluorinated homologous 2,2,2-trifluoroethyl methacrylate/MA (TFEM/MA). The polymeric materials have been tested on Candoglia marble, a very low open porosity stone (

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.

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.

Functionalized carbon nanotubes as a filler for dielectric elastomer composites with improved actuation performance

Among the broad class of electro-active polymers, dielectric elastomer actuators represent a rapidly growing technology for electromechanical transduction. In order to further develop this applied science, the high driving voltages currently needed must be reduced. For this purpose, one of the most widely considered approaches is based on making elastomeric composites with highly polarizable fillers in order to increase the dielectric constant while maintaining both low dielectric losses and high-mechanical compliance. In this work, multi-wall carbon nanotubes were first functionalized by grafting either acrylonitrile or diurethane monoacrylate oligomers, and then dispersed into a polyurethane matrix to make dielectric elastomer composites. The procedures for the chemical functionalization of carbon nanotubes and proper characterizations of the obtained products are provided in detail. The consequences of the use of chemically modified carbon nanotubes as a filler, in comparison to using unmodified ones, were studied in terms of dielectric, mechanical and electromechanical response. In particular, an increment of the dielectric constant was observed for all composites throughout the investigated frequency spectrum, but only in the cases of modified carbon nanotubes did the loss factor remain almost unchanged with respect to the simple matrix, indicating that conductive percolation paths did not arise in such systems. An effective improvement in the actuation strain was observed for samples loaded with functionalized carbon nanotubes. (Some figures may appear in colour only in the online journal)

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.

Evaluating Fluorinated Acrylic Latices as Textile Water and Oil Repellent Finishes

Three fluoropolymer latices, two of them commercially available and the third synthesized as a reference material, are applied by padding to wool, cotton, and polyester fabrics, and their performance is evaluated by means of technological standard test methods for water repellency, oil repellency, fabric hand, and mechanical properties. Surface modifications are further characterized by electron microscopy and less conventional techniques such as static and dynamic contact angle measurements, in order to assess the relevance of the surface composition and structure, at the microscopic level, for the observed properties of the fabric at the macroscopic level. The fluorinated coating does not significantly alter textile hand. Improved water and oil repellency, assessed by technological tests, generally correlate well to observed static and dynamic contact angle variations, although the latter are the result of a combination of contributions, including those deriving from composition and morphological heterogeneity of the surface exposed to wetting.

Photochemical stability of partially fluorinated acrylic protective coatings IV. Copolymers of 2,2,2-trifluoroethyl methacrylate and methyl α-trifluoromethyl acrylate with vinyl ethers

The photochemical stability of copolymers of 2,2,2-trifluoroethyl methacrylate with butyl vinyl ether (TFEMA/BVE) and of methyl α-trifluoromethyl acrylate with 2-ethylhexyl vinyl ether, has been investigated under artificial solar light irradiation. In both copolymers, as well as in a reference ethyl methacrylate/BVE copolymer, the photoageing behaviour is controlled by the reactivity of the corresponding ether component. The degradation occurs mainly in the tertiary positions of the ether units, followed either by formation of γ-lactones or by chain scissions. Only in the case of TFEMA/BVE does the fluorinated methyl of the side chain have an influence on the degradation pathways, i.e. a clear inhibition of cyclization.

Synthesis and electrooptical characterization of polysiloxanes containing indolyl groups acting as photoconductive substrates for photorefractive materials

Abstract Synthesis and electrooptical analysis of polysiloxane and poly-N-vinyl derivatives containing indolyl groups are reported. The indole group and some of its methyl derivatives have been taken into account in order to evaluate their behaviour, with respect to that of the widely employed carbazole group, when used as photoconductive centres attached to a polymer chain. The obtained data show that photoconductivity and traps formation mechanism can be inferred as functions of the physico-chemical parameters (electric dipole moment and ionization potential) of the different groups and polymers involved. To this end such parameters have been carefully computed for a series of pyrrole, indole and carbazole derivatives. The 2,3-dimethylindole derivative appears to be particularly promising due to its electrooptical behaviour in the red absorption region where measurements have been accomplished and are shown to be consistent with the theoretical predictions.