Aldo Priola

New fluorinated acrylic monomers for the surface modification of UV-curable systems

New fluorinated acrylates were synthesized and used as modifying additives for acrylic UV-curable systems. Their chemical structure is: CnF2n+1 R—OCO—CHCH2, where the linear perfluorinated chain contains from 4 to 10 carbon atoms, while R is a linear alkyl group containing or not a thioether group. Notwithstanding their very low concentration, the fluorinated monomers caused a dramatic change of the surface properties of the films, without changing their curing conditions and their bulk properties. X-ray photoelectron spectroscopy measurements showed that the monomers were able to concentrate selectively on the surfaces of the films, depending on their chemical structure and on the kind of substrate employed. The synthesis of the fluorinated monomers and the relationship between their chemical structure and the final surface properties of the UV-cured films will be discussed.

Cationic photopolymerization of vinyl ether systems: influence of the presence of hydrogen donor additives

Abstract Several alcohols (n-butanol, 2-propanol, 2-phenyl-2-propanol) and water were added to diethylene-glycol-divinyl-ether (DVE2) or triethylene-glycol-divinyl-ether (DVE3) in order to investigate their influence on the cationic photopolymerization in the presence of triarilsulfonium hexafluorophosfate as photoinitiator. Until 5% w/w concentration, the alcohols do not show any influence on the rate of polymerization, but they increase the final double bond conversion indicating a plasticization effect. Water causes a decrease of the rate of polymerization and an increase of the final double bond conversion. DSC and DMTA analyses show that the presence of the additives decreases the Tg of the UV-cured products. The results are interpreted on the basis of a chain transfer reaction involving -OH groups.

Perfluoropolyether structures as surface modifying agents of UV-curable systems

New functionalised macromers containing perfluoropolyether (PFPE) structures and methacrylic end groups were synthesised and used as modifying additives for acrylic UV-curable systems. Their chemical structure is Rh-Rf-Rh, where Rh= -CH 2 O-CONH-CH 2 CH 2 OCOC(CH 3 )=CH 2 and Rf=-CF 2 O-(CF 2 CF 2 O) p (CF 2 O) q -CF 2 - with p ≃ q. Notwithstanding their very low concentration, below 0.5 wt.-%, the fluorinated macromers cause a dramatic change of the surface properties of the films, without changing their curing conditions and their bulk properties. X-ray photoelectron spectroscopy (XPS) measurements showed that the macromers are able to concentrate selectively at the surfaces of the films, depending on their chemical structure and on the kind of substrate employed.

High resolution XPS investigation of photocured films containing perfluoropolyether acrylates

Abstract The paper reports an XPS investigation on films obtained by photopolymerising new perfluoropolyether methacrylates as pure products or added in low amounts to a typical UV-curable resin (Bisphenol A bis-ethylether diacrylate). The structure of the fluorinated monomers is Rf–Rh type, where Rh=–CH 2 O–CO–NH–CH 2 –CH 2 –OCOC(CH 3 ) CH 2 while Rf=CF 3 –CF 2 O–(CF 2 O) n (CF 2 –CF 2 O) m –CF 2 – for monomer 1 (PM 890, m / n =1.68), and Rf=Cl–CF 2 –CF(CF 3 )–O–(CF 2 CF(CF 3 )–O) 2 –CF 2 – for monomer 2 . Quantitative evaluation of the different atomic ratios was performed using take-off angles of 45 and 10° (very surface region) on both film sides, the one in contact with the glass substrate and the one exposed to air. The results obtained indicate strong fluorine enrichment on the air side of the films and a concentration gradient at the surface, while the glass side has a composition similar to the bulk.

Properties of polymeric films obtained from u.v. cured poly(ethylene glycol) diacrylates

Abstract The properties of u.v. cured poly(ethylene glycol) diacrylates (PEGDA) having MWs in the range 200–2000 and acrylic functionality near to two were evaluated. First, the properties of pure PEGDA oligomers, subjected to u.v. curing, were considered. Then, mixtures of different PEGDA oligomers with a typical epoxy acrylate resin were prepared and investigated. The double-bond conversion during the curing process was determined by FT i.r. analysis. D.s.c., t.m.a. and d.m.t.a. were used to evaluate the thermal and dynamic-mechanical behaviour of the networks obtained. As far as the pure PEGDA oligomers are concerned, the final double-bond conversion was always found to be complete, with the exception of the lowest MW oligomers. By using oligomers having MWs up to 1000, after the u.v. curing process, films having a completely amorphous structure were obtained. Oligomers having MWs higher than 1000 show, after curing, a partial PEG crystallinity. The T g values of amorphous films were found to decrease by increasing the MW of the oligomer, i.e. by decreasing the crosslinking density of the network. Good agreement with the Nielsen equation was observed. The equilibrium swelling values in water were found to increase by increasing the oligomer MW. The investigation of mixtures of PEGDA oligomers with a typical epoxy acrylate resin confirms the above reported results as far as the double-bond conversion, the thermal and the dynamic-mechanical behaviour are concerned. By changing the oligomer MW it is possible to change the properties of the u.v. cured films over a broad range.

High performance UV-cured coatings for wood protection

UV-curable systems based on the copolymerisation of a typical acrylic resin with a low amount of a fluorinated monomer (<1%, w/w) were used for the protection of wood panels. In the presence of the additives, the bulk properties and the adhesion of the acrylic films were unchanged, while a strong modification of the surface was obtained. The quality aspects and the chemical resistance of the coatings applied to the wood panels were also enhanced.

Poly(ϵ-caprolactone)-poly(fluoroalkylene oxide)-poly(ϵ-caprolactone) block copolymers. 2. Thermal and surface properties

Abstract The thermal and the surface properties of PCL–PFPE–PCL block copolymers having different PCL and PFPE block lengths were investigated by DSC, contact angles and XPS measurements. DSC analysis reveals for all the copolymers the presence of different amorphous phases; the phase located at low temperature was attributed to the fluorinated moiety. Tm values also demonstrated that PCL crystallizes from a pure phase. XPS measurements showed a strong surface enrichment in PFPE with respect to the bulk. Contact angle values showed a hydrophobic character of the film surface even if the trend was found not depending on the fluorine concentration as detected by XPS: this behavior may be explained by the presence of very flexible blocks, providing a highly dynamic surface. These structures can be potentially used as additives for the formation of polymers having ‘smart surfaces’ with selective adhesive properties.

Surface properties of methacrylic copolymers containing a perfluoropolyether structure

New copolymers obtained by free radical copolymerization of methylmethacrylate (MMA) with a methacrylic monomer containing a perfluoropolyether structure (PFEUMA) were prepared. The products showed an excellent surface activity evidencing hydrophobic and lipophobic properties; the water contact angle of the films was always very high (>105°). Angle-dependent XPS analyses showed that the fluorinated monomer preferentially concentrates at the air surface and a fluorine gradient normal to the surface is present. A surface reorganisation was observed by changing the interface. The wettability increased when the films were dipped in water; after complete drying, the surface regained its hydrophobicity.

Photopolymerization of poly(tetramethylene ether) glycol diacrylates and properties of the obtained networks

Abstract A series of poly(tetramethylene ether) glycol α,ω-diacrylates have been prepared from the corresponding hydroxy-terminated oligomers. The acrylation reaction, performed with acrylic acid in the presence of p -toluenesulfonic acid as a catalyst, allowed us to obtain oligomers with M n in the range 250–2000 and an acrylic functionality close to 2. The M n of the acrylated product was always lower than that of the starting oligomer, suggesting the occurrence of degradation reactions. These were attributed to an acidic hydrolytic attack on the oligomer chain. The oligomers were subjected to an ultra-violet light promoted curing process as thin films on glass substrates under N 2 atmosphere. Complete acrylic double-bond conversion was obtained in all cases, with the exception of the oligomer with the lowest molecular weight. The thermal and mechanical properties of the networks were investigated by means of differential scanning calorimetry, thermomechanical analysis and dynamic mechanical thermal analysis (d.m.t.a.). Amorphous and rubbery materials were obtained with the exception of those from the oligomers of the highest molecular weight, which showed partial crystallinity. By means of thermal analysis and d.m.t.a., T g values were measured and correlated to the molecular weights of the oligomers used. In particular, the T g values, as a function of the crosslinking density, agreed with those calculated by the Nielsen equation. Moreover, equilibrium swelling measurements in water were performed. The results obtained are discussed on the basis of Florys theory and interpreted in terms of the solubility parameters and the crosslinking densities of the networks.

Synthesis of poly(propylene-glycol-diacrylates) and properties of the photocured networks

A series of poly(propylene-glycol-diacrylates) (PPGDA) having molecular weights (MW) in the range 300–3,000 and an acrylic functionality near to two were synthesized by acrylation of the corresponding hydroxy-terminated oligomers with acrylic acid in the presence of p-toluensulphonic acid as a catalyst. The M¯n of the acrylated products was found slightly lower than that of the starting oligomers, indicating the occurrence of an acidic degradation reaction which does not influence the acrylic functionality. The acrylated oligomers were ultraviolet (UV) cured until a complete double bond disappearance was obtained: only in the presence of tripropylene-glycol-diacrylate (TPGDA) were small amounts of residual unsaturations revealed. Rubbery materials were usually obtained, with the exception of TPGDA. The properties of the cured PPGDA were investigated by means of differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical thermal analysis. The Tg values were found to decrease by increasing the MW of the used oligomers, that is, by increasing the length of the chain between the two acrylic double bonds. A good agreement with the Nielsen equation was found. Moreover, the equilibrium swelling values in water were measured; the obtained values were interpreted in terms of the solubility parameters of the oligomers and of the crosslinking density of the networks. Finally, some mixtures of PPGDA oligomers with a typical epoxy-acrylate resin were UV cured; their properties confirm the high flexibilizing effect of the PPGDA oligomers.