Robust POSS-PEG networks. Nanostructure, viscoelasticity and shape memory behavior

Polyhedral oligomeric silsesquioxane (POSS) is a nanostructured soft material that tremendously influences the properties of polymers. This paper delineates the preparation of polyurethane–POSS hybrid materials by physical blending and in-situ polymerization, and studies their properties. In the physical blending method, a polyurethane (BDO–PU) was prepared by using polycaprolactone diol (PCL-diol) as a soft segment, 4,4 $$^\prime $$ -methylenebis(phenyl isocyanate) (MDI) as a diisocyanate and 1,4-butanediol (BDO) as a chain extender. The PU–POSS hybrid material (BDO–PU/POSS) was then prepared by the dispersion of POSS (octahydroxy POSS) molecules in the synthesized BDO–PU matrix by the solution mixing method. In the in-situ polymerization method, POSS–PU and POSS–BDO–PU hybrid materials were prepared using POSS and the combination of POSS and BDO as a crosslinker or a chain extender. The formation of PU and PU–POSS hybrid materials was confirmed by Fourier transform infrared and differential scanning calorimetry analyses. The introduction of octahydroxy POSS molecules into the PU matrix resulted in a reduction of glass transition temperature ( $$T_{\mathrm {g}})$$ . However, POSS–PU hybrid materials prepared by the in-situ polymerization method had significantly less $$T_{\mathrm {g}}$$ compared to the hybrid materials prepared by the solution or physical blending method. The incorporation of POSS molecules by using the in-situ polymerization process resulted in an increase in the surface hydrophobicity (water contact angle, WCA $$=$$ 125 $$^{\circ }$$ ) compared to the same prepared by using the solution blending process (WCA $$=$$ 106 $$^{\circ }$$ ). Moreover, the WCA values of all hybrid materials (WCA $$=$$ 106–125 $$^{\circ }$$ ) are much higher than those of the pristine BDO–PU (WCA $$=$$ 84 $$^{\circ }$$ ). The higher WCA value of the hybrid materials is due to the combined effect of the hydrophobic nature of POSS molecules as well as the increased surface roughness, as evidenced by the AFM 3D images. The hybrid materials prepared by the in-situ polymerization method exhibited improved mechanical and thermal properties compared to those prepared by the solution blending method.

Helical polymers present some interesting and distinctive properties, and one of the most distinguished applications of them is the chiral recognition and resolution of enantiomers. In this work, star-shaped hybrid helical poly (phenyl isocyanide) (PPI) with polyhedral oligomeric silsesquioxanes (POSS) as the core was designed and synthesized by "grafting to" strategy. The homoarm star-shaped hybrid POSS-(PPI)8 was first obtained by the click reaction between azide-modified POSS (POSS-(N3 )8 ) and alkynyl-modified PPI (PPI-Alkynyl). The hybrid POSS-(PPI)8 was with predominated left-handed helical conformation and exhibited excellent ability in the enantioselective crystallization of racemic compounds. In the meantime, heteroarm star-shaped hybrid (PEG)4 -POSS-(PPI)4 was prepared by the click reaction of POSS-(N3 )8 with PPI-Alkynyl and alkynyl-modified poly (ethylene glycol) (PEG-Alkynyl). The hybrid (PEG)4 -POSS-(PPI)4 was amphiphilic, and it could self-assemble to form spherical micelles in aqueous solutions.

Crystallization studies at quiescent and shear states in isotactic polypropylene (iPP) containing nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules were performed with in situ small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC was used to characterize the quiescent crystallization behavior. It was observed that the addition of POSS molecules increased the crystallization rate of iPP under both isothermal and nonisothermal conditions, which suggests that POSS crystals act as nucleating agents. Furthermore, the crystallization rate was significantly reduced at a POSS concentration of 30 wt %, which suggests a retarded growth mechanism due to the molecular dispersion of POSS in the matrix. In situ SAXS was used to study the behavior of shear‐induced crystallization at temperatures of 140, 145, and 150 °C in samples with POSS concentrations of 10, 20, and 30 wt %. The SAXS patterns showed scattering maxima along the shear direction, which corresponded to a lamellar structure developed perpendicularly to the flow direction. The crystallization half‐time was calculated from the total scattered intensity of the SAXS image. The oriented fraction, defined as the fraction of scattered intensity from the oriented component to the total scattered intensity, was also calculated. The addition of POSS significantly increased the crystallization rate during shear compared with the rate for the neat polymer without POSS. We postulate that although POSS crystals have a limited role in shear‐induced crystallization, molecularly dispersed POSS molecules behave as weak crosslinkers in polymer melts and increase the relaxation time of iPP chains after shear. Therefore, the overall orientation of the polymer chains is improved and a faster crystallization rate is obtained with the addition of POSS. Moreover, higher POSS concentrations resulted in faster crystallization rates during shear. The addition of POSS decreased the average long‐period value of crystallized iPP after shear, which indicates that iPP nuclei are probably initiated in large numbers near molecularly dispersed POSS molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2727–2739, 2001

Transparent cellulose/polyhedral oligomeric silsesquioxane nanocomposites with enhanced UV-shielding properties

Sorbitol-type nucleating agents can be used to aid dispersion of polyhedral oligomeric silsesquioxane (POSS) molecules in isotactic polypropylene (iPP) and to promote self-assembly of POSS molecules into nanoparticles. In this paper, the interactions between a sorbitol-type nucleating agent and POSS molecules were investigated using polarized optical microscopy and rotational rheometry. Dibenzylidene sorbitol (DBS), a nucleating agent of iPP, was used in conjunction with two non-reactive POSS—trisilanolphenyl-POSS (ph-TPOSS) and octaisobutyl-POSS (bu-MPOSS). DBS formed three-dimensional fibrillar networks in iPP upon cooling from a homogeneous state. These fibrillar networks were characterized as gels using oscillatory shear rheometry. Trisilanolphenyl-POSS was incompatible with iPP but offered strong hydrogen bonding possibility with DBS; bu-MPOSS, on the other hand, was compatible with iPP but did not produce significant interactions with DBS. It was found that as low as 0.5 wt % of ph-TPOSS molecules in a ternary compound with 0.7 wt % DBS subdued fibrillar network formation by DBS and altered the rheological properties of the compounds. No such effect was seen in compounds of bu-MPOSS, although viscosity showed strong reduction. The storage modulus vs loss modulus data provided much better indication of changes of morphology in iPP/POSS and iPP/DBS/POSS compounds than loss tangent vs oscillatory frequency plots.

Polymer membrane based gas transport and pervaporation processes are fast growing areas in separation technology and have received wide attention as areas of ‘clean technology’. Mechanically stable novel polyhedral oligomeric silsesquioxane (POSS) embedded poly(vinyl alcohol) (PVA)/poly(ethylene oxide) (PEO) blend membranes were prepared by solution blending followed by casting. The addition of carboxymethyl cellulose enhanced the interfacial activities of the PVA and PEO blends. The peripheral organic substituent on POSS plays a key role in achieving compatibility with polymers whereas the rigid Si–O–Si core of POSS imparts high mechanical strength. Compared to PVA membrane, poly(ethylene glycol) and octa(tetramethylammonium) functionalized POSS embedded PVA/PEO membranes exhibit 680% and 580% enhancement in Young's modulus as well as 130% and 140% improvement in tensile strength respectively. The Einstein, Kerner and Frankel–Acrivos models were applied to compare the experimental and theoretical Young's modulus of PVA‐PEO/POSS membranes. The presence of an ethylene oxide tail on POSS as well as PEO in the blend membrane enhances the CO 2 affinity of the membrane. The presence of a hydrophilic functional group on the POSS improves the hydrophilicity of the membrane and produces more binding sites for water molecules in the membrane during the pervaporation separation of a tetrahydrofuran–water azeotropic mixture. The transport properties of the membrane are further elucidated by means of free volume defect analysis carried out by positron annihilation lifetime spectroscopy and coincidence Doppler broadening spectroscopy. © 2019 Society of Chemical Industry

Polymer-protein interactions are crucial for determining the activity of both polymer and protein for many bio-related applications. Poly(ethylene glycol) (PEG) as a well-known antifouling material is often coated on surfaces to form highly solvated brushes, which exhibit excellent protein-repellent properties. However, unlike surface-induced antifouling effects, little is known about the intrinsic PEG-protein interactions in aqueous solution, which is an important yet neglected problem. Here, we investigate the interactions between PEG and proteins in aqueous solution using fluorescence spectroscopy, atomic force microscopy (AFM), and nuclear magnetic resonance (NMR). Two important characteristics, molecular weight of PEG and mass ratio of PEG : protein, are examined to determine the effect of each on PEG-protein interactions as well as binding characteristics between PEG and proteins. In contrast to too long and too short PEG chains, collective results have shown that PEG with optimal molecular weight (MW) is more capable of interacting with proteins, which induces the conformational change of proteins through more stable binding sites and stronger interactions with long chain PEG. Enhanced PEG-protein interactions are likely due to the change of hydrophilicity to amphiphilicity of PEG with increasing MWPEG. In contrast to almost none or weak interactions of PEG surfaces with proteins, this work provides new evidence to demonstrate the existence of interactions between PEG and proteins in aqueous solution, which is important not only for better understanding of the structure-activity relationship of PEG both in solution and on surfaces, but also for the rational design of new PEG-based materials for specific applications.

We investigated the self-assembled structures and photoresponsive and crystallization behaviors of supramolecules composed of 4-methoxy-4′-hydroxyazobenzene (Azo) molecules and polyethylene glycol (PEG) that were formed through hydrogen-bonding interactions. The Azo/PEG complexes exhibited the characteristics of photoresponse and crystallization, which originated from Azo and PEG, respectively. When Azo/PEG complexes were dissolved in solvents, hydrogen-bonding interaction hindered the rotation and inversion of mesogens, causing a reduction in the photoisomerization rate compared with the photoisomerization rate of the neat Azo. The confinement of Azo/PEG complexes in thin films further resulted in a substantial decrease in the photoisomerization rate but an increase in the amounts of H-aggregated and J-aggregated mesogens. Regarding PEG crystallization, ultraviolet irradiation of Azo/PEG complexes increased the quantity of high-polarity cis isomers, which improved the compatibility between mesogens and PEG, subsequently increasing the crystallization temperature of PEG. Moreover, the complexation of Azo and PEG induced microphase separation, forming a lamellar morphology. Within the Azo-rich microphases, mesogens aggregated to form tilted monosmectic layers. By contrast, PEG crystallization within the PEG-rich microphases was hard confined, indicating that the domain size of the lamellar morphology was unchanged during PEG crystallization.

Hydrolytic degradation of POSS–PEG–lactide hybrid hydrogels

A coarse-grained model has been developed for simulating the self-assembly of nonyl-tethered polyhedral oligomeric silsesquioxane (POSS) nanoparticles in solution. A mapping scheme for groups of atoms in the atomistic molecule onto beads in the coarse-grained model was established. The coarse-grained force field consists of solvent-mediated effective interaction potentials that were derived via a structural-based coarse-graining numerical iteration scheme. The force field was obtained from initial guesses that were refined through two different iteration algorithms. The coarse-graining scheme was validated by comparing the aggregation of POSS molecules observed in simulations of the coarse-grained model to that observed in all-atom simulations containing explicit solvent. At 300 K the effective coarse-grained potentials obtained from different initial guesses are comparable to each other. At 400 K the differences between the force fields obtained from different initial guesses, although small, are noticeable. The use of a different iteration algorithm employing identical initial guesses resulted in the same overall effective potentials for bare cube corner bead sites. In both the coarse-grained and all-atom simulations, small aggregates of POSS molecules were observed with similar local packings of the silsesquioxane cages and tether conformations. The coarse-grained model afforded a savings in computing time of roughly two orders of magnitude. Further comparisons were made between the coarse-grained monotethered POSS model developed here and a minimal model developed in earlier work. The results suggest that the interactions between POSS cages are long ranged and are captured by the coarse-grained model developed here. The minimal model is suitable for capturing the local intermolecular packing of POSS cubes at short separation distances.

The purpose of the present study was to investigate the effect of polyethylene glycol (PEG) molecular weights (6000, 12000 and 20000) as solid dispersion (SD) carriers on the dissolution behavior of simvastatin. SDs with various drug : carrier ratios were prepared by solvent method and evaluated for dissolution rate. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy and solubility studies were also performed on the optimum SD formulation. Samples prepared with all three types of PEG showed improved drug dissolution compared to intact drug and corresponding physical mixtures. Meanwhile, the best result was obtained by PEG 12000 with drug : carrier ratio of 1:7 which showed a 3-fold increase in dissolution rate compared to the intact drug. Based on DSC and XRD, no crystalline change occurred during the sample preparation. Solubility studies revealed that increasing the PEG molecular weight resulted in higher phase solubility of drug. In addition, saturated solubility of the optimum SD was significantly higher than that of intact drug and the related physical mixture (24.83, 8.74 and 8.88 μg/mL, respectively) that could be due to the decreased particle size and aggregation. The results confirmed the influence of PEG molecular weight on drug dissolution rate from solid dispersion systems.

Sequential and selective shape memory by remote electrical control

Polyhedral oligomeric silsesquioxane (POSS) is an important building block for constructing organic-inorganic hybrid molecules or polymers. In this work, we report amphiphilic, incompletely condensed POSSs (IC-POSSs) possessing various substituents on the seven silicon atoms and two kinds of poly(ethylene glycol)s (PEGs) with different chain lengths. The IC-POSS cores possessed comparable thermal stability to that of the completely condensed POSS (CC-POSS) analogs, despite their open cage structure. The amphiphilic IC-POSSs formed micelles of different sizes and had polydispersity indices (PDIs) that were dependent on the substituents and the PEG chain length. Additionally, the lower critical solution temperatures (LCSTs) were observed for amphiphilic IC-POSSs possessing shorter PEG chains, while aqueous solutions of those with longer PEG chains showed high transmittance even at 80 °C. Amphiphilic incompletely condensed polyhedral oligomeric silsesquioxanes possessing various substituents and poly(ethylene glycol)s of different chain lengths have been developed. It has been elucidated that their self-association behaviors in water are dependent on the substituents and chain lengths of poly(ethylene glycol)s. Precise molecular design, excellent thermal stability, and good dispersibility have been realized at once.

Allergy evaluation of messenger RNA vaccine reactions is crucial, with a specific role for polyethylene glycol testing

Superhydrophobic porous surface fabricated via phase separation between polyhedral oligomeric silsesquioxane-based block copolymer and polyethylene glycol