We prepared octuply adenine (A)-functionalized polyhedral oligomeric silsesquioxane [(octakis­(vinylbenzyladenine-siloxy)­silsesquioxane, OBA-POSS] nanoparticles through the reaction of A with octakis­(benzyl chloride) POSS (OVBC-POSS), itself prepared through hydrosilylation of octakis­(dimethylsiloxy)­silsesquioxane (Q8M8 H) with vinyl benzyl chloride. We observed the self-assembly of lamellar structures from the complexation of a thymine (T)-functionalized polybenzoxazine (PA-T) with OBA-POSS, stabilized through complementary multiple hydrogen bonding interactions between the T groups of PA-T and the A groups of OBA-POSS. In addition, incorporating POSS presenting multiple, strong, complementary hydrogen bonding A units into the PA-T matrix significantly enhanced the thermal stability of this polymer, as evidenced using differential scanning calorimetry and thermogravimetric analysis.

Abstract:In this study we used anionic living polymerization to prepare two different homopolymers: a poly(methyl methacrylate) (PMMA) and a PMMA derivative presenting polyhedral oligomeric silsesquioxane (PMA-POSS) units as its side chains. We then employed differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) to investigate the miscibility and specific interactions of PMMA and PMA-POSS with three hydrogen bonding donor compounds: poly(vinyl phenol) (PVPh), phenolic resin, and bisphenol A (BPA). DSC revealed that all of the PVPh/PMMA, phenolic/PMMA, and BPA/PMMA blends exhibited a single glass transition temperature, characteristic of miscible systems; FTIR spectroscopic analyses revealed that such miscibility resulted from hydrogen bonding interactions between the C=O groups of PMMA and the OH groups of these three hydrogen bonding donor compounds. In contrast, all of the PVPh/PMA-POSS, phenolic/PMA-POSS, and BPA/PMA-POSS blends were immiscible: DSC revealed two OPEN ACCESSPolymers 2014, 6 927 glass transition temperatures arising from strong screening effects (FTIR spectroscopy) and high degrees of aggregation (WAXD) of the POSS nanoparticles. We propose that the value of the intramolecular screening effect (γ) should be very close to 1 for all PMA-POSS blend systems when POSS nanoparticles appear as the side chains of PMMA, such that the OH groups of the hydrogen bonding donor compounds cannot interact with the C=O groups of PMA-POSS.

P o l y( me t h y l m et h a c r y l a t e ) -b -poly-(methacryloyl polyhedral oligomeric silsesquioxane) (PMMA-b-PMAPOSS) block copolymers of various compositions were prepared through anionic living polymerization. We employed differential scanning calorimetry, Fourier transform infrared spectroscopy, small-angle X-ray scattering, transmission electron microscopy, and wide-angle X-ray diffraction to investigate the miscibility, specific interactions, and hierarchical self-assembly of PMMA-b-PMAPOSS block copolymers blended with a phenolic resin. We found that the added phenolic resin interacted preferentially with the PMMA blocks through hydrogen bonding between the OH groups of the former and the CO groups of the PMAPOSS. In other words, the OH groups of the phenolic resin did not interact with the CO groups of the PMAPOSS blocks, resulting in their immiscibility. Accordingly, this phenolic/PMMA-b-PMAPOSS blend behaved as a blend of homopolymer C and immiscible A-b-B diblock copolymer, where C is immiscible with B but interacts favorably with A; therefore, it displayed an order−order phase transition with increased phenolic resin content. Hierarchical self-assembly led to the formation of hexagonally packed cylindrical or lamellar nanostructures through microphase separation of the diblock copolymer segment, with POSS aggregates packing into a hexagonal lattice oriented perpendicular to the direction of the nanostructures.

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Certain strains of Bacillus sphaericus produce a highly toxic mosquito-larvicidal protein during sporulation which is active against vectors of dengue, encephalitis and malaria. This toxin is initially expressed as 51 and 42 kDa proteins and is converted to 43 and 39 kDa proteins, respectively, which form the active heterodimer complex. For a better understanding of the toxicity mechanism at the molecular level, the 51 kDa protein of the binary toxin of B. sphaericus strain 2297 was expressed as a glutathione-S-transferase fusion protein and puri®ed by af®nity chromatography. Protein crystals were grown from an amorphous precipitate in ®ve months using the hanging-drop vapor-diffusion method. The protein crystals were dissolved and were found to be composed of a proteolytically modi®ed 45.2 kDa derivative similar to the active form of this protein. The crystals form in space group P4 3 2 1 2 (or P4 1 2 1 2) and diffract to 2.6 A Ê , with unit-cell dimensions a = b = 133.48, c = 69.76 A Ê .