Comunicações científicas
SYNTHESIS OF POLYMER-BOUND CALIX[4]ARENES
Patrícia D. Barata, Alexandra I. Costa, Paulo A. Granja and José V. Prata
Secção de Química Orgânica, Departamento de Engenharia Química, Instituto Superior de Engenharia de Lisboa, R. Conselheiro Emídio Navarro, 1, 1949-014, Lisboa, Portugal E-mail: jvprata@deq.isel.pt
Publicado em: Livro de Resumos do 5º Encontro Nacional de Química Orgânica-1º Simpósio Luso-Japonês, Aveiro, Portugal, Julho de 2003.
Calixarenes are a versatile class of synthetic cyclic oligomers that possess intramolecular bow-shaped cavities capable of accommodate guest molecules or ions. Such host properties have been explored in several contexts, ranging from reaction catalysis to molecular recognition. In particular, the syntheses of polymeric materials incorporating calixarene units on the polymer backbone or the anchoring of appropriate functionalised calixarenes onto an insoluble or soluble polymeric matrix are recent developing areas of the chemistry of such compounds.
the substituents present in the lower rim permitted the development of two synthetic ways to the target polymers. One was the attachment, via hydroxyl group, of a trifunctionalised calix[4]arene derivative (2) to a Merrifield type resin and the other was the use of a tetrafunctionalised calix[4]arene (3) possessing one appropriated vinyl arm, apt to be used as a co-monomer in suspension polymerisations with styrene. The direct immobilisation of the unsubstituted tetrahydroxycalix[4]arene (1) onto the polymer support was also attempted despite of the predictable enhance degree of cross-linking introduced. Further synthetic elaboration on the polymers thus obtained allowed the preparation of several useful derivatives (7).
OR2 RO O R1O RO OOO 1: R1=R2= H 2: R1= Propyl or COPh; R2=H 3: R1= Propyl or COPh; R2=CH2PhCHCH2 3 P type resins 7: R=H, R=CH2CO2Et, R= CH2CO2H P P 3 P P P 3 Meth. 2) Suspension Polymerisation 4: R=H (method 1, from 1)
5: R= Propyl or COPh (Meth.1, from 2) 6: R= Propyl or COPh (Meth.2, from 3)
Acknowledgements. We thank Instituto Politécnico de Lisboa (Portugal) for partial financial support (project IPL/15/2001) and for a research fellowship to one of us (P.A.G.).
POTENTIAL ALTERNATIVES TO Cr VI-BASED PRE-TREATMENTS ON ALUMINIUM AND GALVANISED STEEL
A.C. Bastosa, R.G. Duartea, A. Cabralb, M.F. Montemora, A.M. Simõesa and M.G.S. Ferreirac*
aDepartment of Chemical Engineering, Instituto Superior Técnico, Lisboa, Portugal bDepartamento de Engenharia Química, ISEL, Lisboa, Portugal
cDepartment of Ceramics and Glass Engineering, University of Aveiro, Aveiro, Portugal
mgferreira@cv.ua.pt
Publicado em: Livro de Resumos do 54th Annual Meeting of the International Society of Electrochemistry, S. Pedro, Brasil, 31 Agosto a 5 de Setembro (2003).
Cr-VI based pre-treatments have been in use for long time on several materials, namely on aluminium alloys and galvanised steels. As it is known health and environmental problems make them a target of great criticism and forthcoming legislation could definitely ban them.
Different Cr-free alternatives have been reported, based on non-toxic or low toxicity chemicals, aiming to obtain processes that confer to the treated surfaces corrosion
indicating their pros and cons. Then the study focus on the use of organosilanes, zirconium and rare earth (Ce, La) salts, showing the role of the surface films obtained with these compounds on the corrosion resistance of the substrate. A comparison is made with chromate, where studies were also carried out. The techniques used were d.c. polarisation, electrochemical impedance spectroscopy (EIS), SEM, atomic force microscopy associated with Kelvin probe, SVET and Auger/XPS spectroscopy. On painted specimens salt spray was carried out.
The results allow discussing how certain species or films formed affect the rate of cathodic and anodic reactions, i.e., the mechanism involved in hindering corrosion.
Keywords: Cr-free pre-treatments, chromate conversion, aluminium, galvanised steel, Kelvin probe, SVET
1 mm Zinc (anode) Iron (cathode) scanned area -15 -1 5 -1 5 -1 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 15 15 3 0 45
anodic region
cathodic region
0a)
b)
SVET maps showing the current densities (µA.cm-2) of an iron-zinc galvanic couple
in contact with 0.1 NaCl solution (a) for 18 hours and (b) 20 min after addition of chromate to the previous solution. By the presence of chromate ions, not only the anodic area on zinc was suppressed, but mainly the cathodic area on iron. Thus, chromate seems to have also an important role in inhibiting the cathodic reaction. THE POTENTIAL OF SILANES AND RARE EARTH SALTS FOR CHROMATE REPLACEMENT ON ALUMINIUM ALLOYS AND GALVANIZED STEEL
M.G.S. Ferreiraa, R. Duarteb, A. Cabralc, M.F. Montemorb, A.M. Simõesb aDepartment of Ceramics and Glass Engineering, University of Aveiro, Aveiro, Portugal bDepartment of Chemical Engineering, Instituto Superior Técnico, Lisboa, Portugal cDepartment of Chemical Engineering, ISEL, Lisboa, Portugal
Publicado em: Livro de Resumos do EMCR’03 - 8th International Symposium on Electrochemical Methods in Corrosion Research, May 4-9, 2003, Ysermonde, Belgium
Cr-VI based pre-treatments have been in use for long time on several materials, namely on aluminum alloys and galvanized steels. As it is known health and environmental problems make them a target of great criticism and in the near future they could be definitely banned.
Different Cr-free alternatives have been reported, based on non-toxic or low toxicity chemicals, but none of them could be considered performing identically to chromates. Every treatment shows pros and cons when sets of key properties are considered. These include effectiveness for preventing corrosion and adhesion promotion for organic coatings, fatigue resistance, reliability and quality control.
In spite of the above a certain number of alternatives show high potential, if some improvements are carried out and the mechanisms involved are more deeply understood.
The present work focus on the use of silanes (BTESPT and APS) and rare earth (Ce, La) salts as chromate substitutes for Al 2024 aluminum alloy and galvanized steel. These compounds when applied by immersion and subsequent curing originate films that improve corrosion resistance and paint adherence to organic coatings. The films formed are characterized by Kelvin probe, SVRET, AFM, SEM and Auger/XPS. Corrosion resistance was assessed by electrochemical impedance spectroscopy, d.c. polarization and salt spray.
Comparison with the chromate conversion is also carried out, simultaneously with the discussion of the mechanisms involved in the different processes.
M.G.S. Ferreira, R. Duarte, A. Cabral, M.F. Montemor, A.M. Simões
aDepartment of Ceramics and Glass Engineering, University of Aveiro, Aveiro, Portugal bDepartment of Chemical Engineering, Instituto Superior Técnico, Lisboa, Portugal cDepartment of Chemical Engineering, ISEL, Lisboa, Portugal
Publicado em: Livro de Resumos do V LATINCORR 2003, 5º Congresso de Corrosion de la NACE Region Latinoamérica / 8º Congresso Iberoamericano de Corrosion e Proteccion, 20 a 24 de Outubro, Santiago, Chile (2003)
Cr-VI based pre-treatments have been in use for long time on several materials, namely on aluminum alloys and galvanized steels. As it is known health and environmental problems make them a target of great criticism and in the near future they could be definitely banned.Different Cr-free alternatives have been reported, based on non-toxic or low toxicity chemicals, but none of them could be considered performing identically to chromates. Every treatment shows pros and cons when sets of key properties are considered. These include effectiveness for preventing corrosion and adhesion promotion for organic coatings, fatigue resistance, reliability and quality control.In spite of the above a certain number of alternatives show high potential, if some improvements are carried out and the mechanisms involved are more deeply understood.The present work focus on the use of silanes (BTESPT and APS) and rare earth (Ce, La) salts as chromate substitutes for Al 2024 aluminum alloy and galvanized steel. These compounds when applied by immersion and subsequent curing originate films that improve corrosion resistance and paint adherence to organic coatings. The films formed are characterized by Kelvin probe, SVRET, AFM, SEM and Auger/XPS. Corrosion resistance was assessed by electrochemical impedance spectroscopy, d.c. polarization and salt spray. Comparison with the chromate conversion is also carried out, simultaneously with the discussion of the mechanisms involved in the different processes.
“ENGENHARIA” DE SUPERFÍCIES E INTERFACES DE DÍODOS DE POLÍMERO POR