Influence of chemical structure on the values of free surface energy of the coatings made
of poly(urethane-siloxane) copolymers
Polimery 2008, No 11/12, 808
Segmental poly(urethane-siloxane) (PUR-PDMS) copolymers were prepared by two-stage (prepolymer) method. In the first stage a polyaddition of 4,4'-diphenylmethane diisocyanate (MDI, rigid segments) with poly(oxytetramethylene) glycol (PTMG, soft segments) was carried in mass. In the following batches PTMG was replaced - in the wide range of amount - with α,ω-di(hydroxyethyleneoxypropylene) poly(dimethylsiloxane) (PDMS, soft segments) (Table 1). At the next stage the chain of prepared isocyanate prepolymer was extended with 1,4-butanediol (BD, soft segment). In this way a series of PUR-PDMS copolymers, differing in chemical structure (confirmed by IR analysis, Fig. 1-3) but containing the same part of soft segments (63 wt. %) and of increasing hydrophobicity, was synthesized. An interpretation of IR spectra has been done applying the intensities of selected bands for quantitative evaluation of copolymers' compositions and to characterize the polarity of the structures obtained, using specially defined structural parameter αp (Table 3-5). The values of surface free energy (SEP) and its components were determined, using van Oss-Chauhury-Good's model, on the basis of contact angle (Θ) measurements for three standard liquids (Table 2). It was found that introduction of PDMS segments to the linear chain of PUR polymer caused decrease in SEP and the main role played the polar component (Table 6).
Key words: segmental polyurethanes, poly(urethane-siloxane) copolymers, chemical structure, IR spectra, surface free energy, van Oss-Chauhury-Good's model, structure polarity, hydrophobicity
P. Król, Ł. Byczyński
Influence of chemical structure on the values of free surface energy of the coatings made of poly(urethane-siloxane) copolymers