Chapter 41
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 3, 2016 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch041
UV-Curing of Fluorinated Systems: Synthesis and Properties Roberta Bongiovanni, Giulio Malucelli, and Aldo Priola Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy
The study concerns the UV-curing of systems containing fluorinated products. New difunctional and monofunctional acrylic and methacrylic monomers bearing either a perfluoroalkyl chain or a perfluoropolyether structure were synthesized. The properties of the films obtained were investigated. By copolymerizing a small amount of the fluorinated acrylates with acrylic resins, while the bulk properties of the films were not changed, the surface properties were deeply modified and became highly hydrophobic. This behaviour was due to a selective enrichment of the fluorinated monomer at the film surface. The dependence of the surface properties on the monomer structure, on its concentration and on the type of substrate was studied.
© 2003
American Chemical Society In Photoinitiated Polymerization; Belfield, Kevin D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
499
500
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 3, 2016 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch041
Introduction Perfluorinated polymers show outstanding properties such as low surface tension, chemical inertness, thermal stability, together with a peculiar frictional, optical and electrical behavior (1-3). As the copolymerization of fluorinated with hydrogenated monomers improves the processability and reduces the cost of the products, several researches have focused on newfluorinatedcopolymers (4-8). Recently some authors showed that a small amount of the perfluoroalkylethylmethacrylate monomer introduced in the chain is enough to lower the surface tension (7). Others obtained good results from a series of methacrylates with oligohexafluoropropeneoxide side groups having different length (6). Due to the outstanding properties of fluorine derivatives described briefly above, the use offluorinatedmonomers in UV-curable systems seemed very promising topic to obtain films having particular characteristics (9), through a simple and fast polymerization technique (10,11). In this context we obtained interesting results curing new difunctional and monofunctional acrylic and methacrylic monomers bearing either a perfluoroalkyl chain or a perfluoropolyether structure (12-14). These products, when used as comonomers with hydrogenated acrylic systems, preferentially concentrate in the outermost layers of the films and strongly improve their hydrophobicity even when the amount of the fluorinated comonomer is very low (< 0.5% w/w). Pursuing this work we are performing a systematic investigation on fluorine-containing systems in order to get relationships between the structure of the fluorinated comonomer and the properties of the UV-cured films. In this paper we present the latest developments in this field and compare the behavior of different types of reactive comonomers in the modification of the surface properties of the cured films.
Materials and methods
Fluorinated monomers Two types of fluorinated derivatives have been investigated. Type A products are perfluoropolyether urethane methacrylates (PFEUMA) which can be mono or bifunctional. Their general structure is R -PFPE-Q where PFPE = - C F 0 - ( C F C F 0 ) - ( C F - 0 ) - , R = CH =C(CH )COO~CH -CH -NHCO-0-CH - and with ρ « q Q = - O C F C F or the R structure. H
2
H
2
2
2
3
2
3
p
2
2
q
2
2
H
In Photoinitiated Polymerization; Belfield, Kevin D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on February 3, 2016 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch041
501 The synthesis of bifunctional monomers is reported elsewhere (15). The monofunctional derivative was synthesized through a series of complex reactions, which gave rise to a mixture of alcohol, diol, and non-functionalized molecules (16). The mixture was subjected to a chromatographic separation, obtaining a middlefractionhaving OH functionality equal to 1.02, as reported in Ref.17. The fluorinated alcohol was reacted with isocyanatoethyl methacrylate (EIM). The full characterization of the final product is reported in (18). Type Β monomers are perfluorinated acrylates having general structure R - R - O C O - C H = C H where R = spacer group, i.e.-
