Photooxidative Stability of Copolymers Containing Hexafluoroisopropyl Groups

摘要

Fluorinated polymers are widely employed for their unique properties of high chemical and weather resistance, and for their surface characteristics which cause excellent oil and water repellency. Such properties are fundamental for applications as protective surface coatings, but it is necessary at the same time that the polymers display good film forming capability and adhesion to the substrates. Furthermore, specific cases like those involving the protection of valuable stone buildings and monuments, require the coatings have reversibility, vapour permeability and optical transparency. A convenient way for achieving such multifunctional behaviour is to design polymer structures where different types of properly selected functional groups might be introduced in a controlled form. By conventional free-radical processes fluorinated acrylic and methacrylic monomers can be copolymerised with, e.g. unfluorinated ones, obtaining structures with random distributions of the fluorinated groups, where solubility in suitable solvents, glass transition temperatures, film forming and adhesion capability, are modulated through selection of the type and content of the different monomers. Superior control of the macromolecular structure may be achieved when acrylic/methacrylic monomers with fluorine substitution either in the main chain or in the ester groups are copolymerised with vinyl ethers. The latter monomers are incapable of polymerising under free radical conditions but, thanks to the high electron density on their double bond, they can form charge transfer complexes with the fluorinated monomers yielding copolymers where, according to the monomer compositions and to the distance of fluorine from the acrylic double bond, the vinyl ether distribution vary between isolated units, to quasi-alternating, to fully-alternating. We have undertaken a systematic study concerning synthesis, structure, surface properties and reactivity characteristics of copolymers based on 1,1,1,3,3,3-hexafluoroisopropyl methacrylate (HFIMA) and 1,1,1,3,3,3-hexafluoroisopropyl α-fluoroacrylate (HFIFA) with vinyl and propenyl ethers. The particular configuration of the fluorinated ester group makes HFIMA and HFIFA particularly attractive for design of high water-repellent polymers. The presence of the α-F atom in HFIFA is expected to improve the chemical stability of the main chain, and eventually modify its surface properties. Introduction of vinyl ether type monomers allows to modulate the fluorine content, and therefore solubility, glass transition tepmperature, and other properties useful for coating applications.