Structural studies of nanophase-separated poly(2-hydroxyethyl methacrylate)-l-polyisobutylene amphiphilic conetworks by solid-state NMR and small-angle x-ray scattering

Bicomponent nanophase-separated poly(2-hydroxyethyl methacrylate)-linked-polyisobutylene (PHEMA-l-PIB) amphiphilic conetworks were synthesized by radical copolymerization of methacrylate-telechelic polyisobutylene (MA-PIB-MA) and different amounts of 2-(trimethylsilyloxy)ethyl methacrylate (SEMA) followed by quantitative hydrolysis of the trimethylsilyl protecting groups. The PIB content of the resulting conetworks, determined by elemental analysis and solid-state H-1 NMR under fast magic angle spinning (MAS), varied between 17 and 63% w/w. Phase separation and morphology of these conetworks were investigated by DSC, small-angle X-ray scattering (SAXS), and for the first time by H-1 spin diffusion solid-state NMR. Two T-g values were observed by DSC in all samples. The observed T-g values were close to the literature values of both homopolymers (110 degreesC for PHEMA and -67 degreesC for PIB), indicating a strong phase-separated morphology in these conetworks. Parameters were optimized for the H-1 spin diffusion NMR experiments, and the measurements were carried out with six filtering cycles and a 10 mus delay between pulses at 90 degreesC. The NMR and SAXS measurements prove strong phase-separated morphology. The sizes of the hydrophilic (PHEMA) and hydrophobic (PIB) nanodomains were determined to be in the 5-15 nm range. The spin diffusion experiments also indicate strongly separated phases without a detectable interface with mixed components. The long period of our system seems to depend weakly on the volume fraction whereas the morphology of the nanophases depends on the volume fraction.