The Role of Amide Groups in Vinyl Monomers Containing Siloxane Groups for Highly Oxygen Permeable Hydrogels

Abstract

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.

Water structure and mobility in acrylamide copolymer glycohydrogels with galactose and siloxane pendant groups

“…(b)] whereas an increase in remaining residue is observed for p92DMA (18%) and p84DMA (11%). Yokota et al report similar behavior for acrylamide polymers containing methyl‐bis(trimethylsiloxy) pendant groups tested under nitrogen . They suggest the possible formation of a silicate structure at high temperatures resulting from recombination of cleaved silicone bonds, a behavior they first report observing during silicone degradation events in an Ar gas plasma .…”

“…Yokota et al report similar behavior for acrylamide polymers containing methyl‐bis(trimethylsiloxy) pendant groups tested under nitrogen . They suggest the possible formation of a silicate structure at high temperatures resulting from recombination of cleaved silicone bonds, a behavior they first report observing during silicone degradation events in an Ar gas plasma . For DMA copolymer hydrogels, greater phase separation and siloxane inhomogeneities, visually observed, may allow for the formation of a similar silicate structure.…”

“…Similar differences in comonomer inclusion have been reported in glycopolymers containing aromatic and NIPAM comonomers. Furthermore, the disparity between hydrophilic and siloxane‐containing vinyl monomers has been shown to impact compatibility; this can be mitigated by using an acrylamide monomer and additional amide groups . In our copolymer systems, adequate levels of ATris incorporation are achieved to allow comparison of properties as a function of composition.…”