Unusual behaviour in which the critical micelle concentration (CMC) values in water for a homologous series of the title amphiphiles increased with an increase in the number of carbons of the lipophilic alkyl chains was observed when these data were obtained by the common surface tension method using a Wilhelmy tensiometer.

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In order to improve the hydrophilicity of silicone-containing monomers, N-2-(N′,N′-dimethylcarbamoyl)ethyl-N-[3-tris(trimethylsiloxy)silylpropyl]acrylamide (SiDAAA) and N-2-(N′,N′-dimethylcarbamoyl)ethyl-N-{3-[methylbis(trimethylsiloxy)silyl]propyl}acrylamide (SiDAAA2) were designed. Although these two monomers had complicated side chain structures, these showed similar radical polymerizability (from 2.6 × 104 to 3.8 × 104 of Mn, and from 87 to 90% of conversion) as conventional silicone-containing monomer 3-tris(trimethylsiloxy)silylpropyl methacrylate (TRIS) due to the acrylamide backbone. Moreover, the additional amide group in those monomers contributed to improved miscibility during copolymerization with N-(hydroxyethyl)acrylamide (HEAA) and 2-hydroxyethyl methacrylate (HEMA), which was determined by light transmission observation at 88% transmittance using a SiDAAA/HEAA (50/50) hydrogel. In contrast, TRIS/HEAA was not miscible, and TRIS/HEMA (60/40) gave only 26% transmittance. The glass-transition temperatures of poly(SiDAAA) and poly(SiDAAA2) were 61 and 28 °C, which were much higher than that of poly(TRIS) at 0.8 °C. The oxygen permeability of the hydrogels varied with the copolymer composition, mainly due to the siloxanyl group contents. In particular, permeability coefficients of more than 100 Barrer (1 Barrer = 10−11 (cm3 O2) cm cm−2 s−1 mmHg−1) which is sufficient oxygen permeability for corneal safety in the case of contact lens applications, can be obtained at lower than 60% water content. The biocompatibility of these hydrogels is also discussed.