Octafunctional Polyhedral Oligomeric Silsesquioxane Research Articles

Novel Organic/Inorganic Hybrid Star Polymer Surface-Crosslinked with Polyhedral Oligomeric Silsesquioxane

Novel organic/inorganic hybrid star polymer was prepared dually crosslinked within inner-core via divinylbenzene (DVB) and outer-surface via octafunctional polyhedral oligomeric silsesquioxane (POSS). Core cross-linked star polymers bearing dialkynyl-terminated polystyrene arms, (dialkynyl-PS)n-CCL, were synthesized at first by the atom transfer radical polymerization (ATRP) of DVB using α,α-dialkynyl-terminated PS macroinitiator, followed by the subsequent fractionation. Under high dilution conditions, (dialkynyl-PS)n-CCL was subjected to surface cross-linking with octa(3-azidopropyl) polyhedral oligomeric silsesquioxane, POSS-(N3)8, via click reaction, affording POSS-functionalized hybrid polymer doubly cross-linked within core and surface regions, SCL-(PS)n-CCL. FT-IR, 1H NMR, GPC, and elemental analysis results revealed that on average, the obtained hybrid polymer possesses a cross-linked PDVB inner core, ∼14 linear PS arms (the Mw per arm of 5.1 kDa), and ∼4-5 POSS moieties at outer surface. Differential scanning calorimetry (DSC) thermograms and thermogravimetric analysis (TGA) revealed that after surface cross-linking the thermal stability of SCL-(PS)n-CCL is considerably improved. This work provides a proof-of-concept example for the preparation of dually cross-linked hybrid star polymer, which represents a novel category of organic/inorganic composite materials with unique chain architectures.

Hyperbranched polyhedral oligomeric silsesquioxane (HB‐POSS) nanomaterials for high transmission and radiation‐resistant space and solar applications

ABSTRACTHyperbranched polycarbosiloxanes and polysiloxanes with octafunctional polyhedral oligomeric silsesquioxane (POSS) branchpoints and curable alkoxysilane or silanol end‐groups were formulated with linear polysiloxanes to fabricate transparent and robust nanostructured POSS‐containing materials for use in a range of high performance space and solar applications. The effect of methyl vs. phenyl content, architecture and linear polysiloxane mass on transmission, thermal, physical, and proton, electron and UV radiation resistance properties was determined, and the physical properties of the nanomaterials were tailored to produce adhesives, or rigid or flexible coatings as desired. The methyl formulations showed superior electron resistance relative to a commercial space control material and to a POSS‐free HB polymer control material, even when directly exposed to radiation in coating form, whereas the phenyl formulations were shown to have inferior electron and UV resistance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3849–3861, 2013

Hyperbranched Polycarbosiloxanes and Polysiloxanes with Octafunctional Polyhedral Oligomeric Silsesquioxane (POSS) Branch Points

Three series of hyperbranched polycarbosiloxanes (HB-PCSOX) and polysiloxanes (HB-PSOX) were prepared from octafunctional polyhedral oligomeric silsesquioxane (POSS) monomers and various difunctional silanes by bimolecular nonlinear A8-B2 polymerization (BMNLP) and characterized by IR, 1H NMR, 29Si NMR, SEC, DSC, and for refractive index. Series 1 was prepared from T8vinyl8 and disilane monomers, and series 2 was prepared from T8(OSiMe2H)8 and divinylsilane monomers (where T denotes an SiO3 unit), both via platinum-catalyzed hydrosilylation polymerization. Series 3 was prepared from T8(OSiMe2OH)8 and dichlorosilane monomers via hydrolysis–condensation polymerization. Structure–property relationships were determined as methyl vs phenyl content was varied. These HB POSS polymers were then functionalized with curable alkoxysilane end groups and formulated with linear polysiloxanes to fabricate transparent and robust nanostructured POSS-containing coatings for use in a range of high-performance space and solar applications.

Temperature and pH dual-responsive behavior of polyhedral oligomeric silsesquioxane-based star-block copolymer with poly(acrylic acid-block-N-isopropylacrylamide) as arms

Poly(acrylic acid-block-N-isopropylacrylamide) (PAAc-b-PNIPAm)-tethered octafunctional polyhedral oligomeric silsesquioxane (POSS) were synthesized via POSS-initialized atom transfer radical polymerization. When very short PAAc blocks are placed between the POSS core and PNIPAm short chains, the critical temperature (T c) of POSS-PAAc-b-PNIPAm determined by cloud point measurements varies in a wide temperature range with pH, and its T c is even lower than that of POSS-PNIPAm with similar chain length at pH = 5.0, indicating a synergic effect between high local chain density and intramolecular interaction between PAAc and PNIPAm. When the PAAc blocks are relatively long, the pH response of POSS-PAAc-b-PNIPAm diminishes owing to the reduced local PNIPAm chain density.

Thermal Behavior of Caged Silsesquioxane (POSS) Studied by Molecular Dynamics Simulations

In order to simulate the thermal behavior of one of the most useful inorganic–organic hybrid materials, octa-functional polyhedral oligomeric silsesquioxane (POSS), molecular dynamics (MD) simulations of crystals of POSSs having methyl, i-butyl, and cyclopentyl substituents were performed using the universal force field. The crystal structures obtained by the MD calculations were in good agreement with those reported based on experimental results. On the basis of their molecular expansion behaviors, the lattice lengths were also evaluated, from which the expansion of each lattice length as a function of temperature was found to be dependent upon the substituents.

Dimethacrylic/epoxy interpenetrating polymer networks including octafunctional POSS

This investigation presents the synthesis of simultaneous interpenetrating polymer networks based on dimethacrylic/epoxy resins with or without polyhedral oligomeric silsesquioxane (POSS) via in situ polymerization. The curing behavior was studied using differential scanning calorimetry (DSC). The influence of the organic groups from the POSS cages on the curing kinetics of the IPNs was also studied by FT-IR spectrometry. The homogeneous phase structure of the cured IPN was proved by DMA tests. Additionally the integrity of the IPN was also demonstrated by thermal decomposition which occurs in one single step.

Material Properties and Reliability of Anisotropic Conductive Films (ACFs) Modified by POSS for Chip-on-Glass Assembly

This paper describes the effect of polyhedral oligomeric silsesquioxane (POSS) in anisotropic conductive films (ACFs) composition on the material properties and reliability of ACF interconnections for chip-on-glass (COG) applications. Series of POSS modified ACFs containing 0wt%, 2wt%, 4wt%, 6wt% and 8wt% contents of octa-methacrylated POSS were formulated and characterized. The POSS added in the formulations favorably affected on the materials properties of ACFs by lowering coefficient of thermal expansion (CTE) and increasing modulus (E′). In addition, an increase in the POSS contents led to higher curing density and, as a result, thermo-mechanical properties of ACFs were improved. But, the adhesion strength of ACF materials was decreased with the POSS content, due to higher modulus originated from octa-functional POSS. The reliability performances of COG assemblies using POSS modified ACFs were also investigated. In conclusion, the materials properties and module reliability of COG assemblies were improved with increasing POSS content in ACFs.

Stable Dispersions of Hybrid Nanoparticles Induced by Stereocomplexation between Enantiomeric Poly(lactide) Star Polymers

We report the formation and characterization of stable dispersions of hybrid nanoparticles in solution formed via stereocomplexation of enantiomeric poly(lactide) hybrid star polymers. The hybrid starlike polymers, having polyhedral oligomeric silsesquioxane (POSS) nanocages as the core and either poly(L-lactide) (PLLA) or poly(D-lactide) (PDLA) as the arms, are synthesized via ring-opening polymerization of lactide using octafunctional POSS as the macroinitiator. In the solid state, differential scanning calorimetry and wide-angle X-ray scattering measurements confirmed the formation of the stereocomplex in the mixture of POSS-star-PLLA and POSS-star-PDLA (50:50, wt %). In a solution of the same mixture in tetrahydrofuran (THF), sterocomplexation leads to formation of hybrid nanaoparticles. Detailed accounts of the nanoparticle formation and influence of aging and concentration have been presented. It was observed that at low concentration the stereocomplexed nanaoparticles remain stable over 45 days and are not sensitive to dilution, suggesting the formation of a stable hybrid nanoparticle dispersion in solution. In contrast, the aggregates of the individual POSS-star-PLLA or POSS-star-PDLA in THF, formed via weak solvophobic interactions, tended to disintegrate into smaller aggregates on dilution. Exploiting the PLLA-PDLA stereocomplexation with an appropriate molecular design can be a versatile route to develop stable organic/inorganic hybrid nanoparticle dispersions.

Organic-inorganic hybrid nanocomposites of poly(sodium 4-styrenesulfonate) and octafunctional polyhedral oligomeric silsesquioxane (POSS)

The hybrid nanocomposites of poly(sodium 4-styrenesulfonate) (PSS) and octafunctional polyhedral oligomeric silsesquioxane (POSS) (Cube-aminopropyl) were prepared using Cube-aminopropyl as a cross-linker at various weight ratios. Ionic interactions between PSS and Cube-aminopropyl played a critical role in the formation of new hybrid gels with Cube-aminopropyl. The nanocomposites obtained were insoluble in organic or aqueous solvents. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the hybrid gels were comprised of three-dimensional network structures derived from Cube-aminopropyl as a cross-linker.

Computational exploration of polymer nanocomposite mechanical property modification via cross-linking topology

Molecular dynamics simulations have been performed in order to study the effects of nanoscale filler cross-linking topologies and loading levels on the mechanical properties of a model elastomeric nanocomposite. The model system considered here is constructed from octafunctional polyhedral oligomeric silsesquioxane (POSS) dispersed in a poly(dimethylsiloxane) (PDMS) matrix. Shear moduli, G, have been computed for pure and for filled and unfilled PDMS as a function of cross-linking density, POSS fill loading level, and polymer network topology. The results reported here show that G increases as the cross-linking (covalent bonds formed between the POSS and the PDMS network) density increases. Further, G is found to have a strong dependence on cross-linking topology. The increase in shear modulus, G, for POSS filled PDMS is significantly higher than that for unfilled PDMS cross-linked with standard molecular species, suggesting an enhanced reinforcement mechanism for POSS. In contrast, in blended systems (POSS/PDMS mixture with no cross-linking) G was not observed to significantly increase with POSS loading. Finally, we find intriguing differences in the structural arrangement of bond strains between the cross-linked and the blended systems. In the unfilled PDMS the distribution of highly strained bonds appears to be random, while in the POSS filled system, the strained bonds form a netlike distribution that spans the network. Such a distribution may form a structural network "holding" the composite together and resulting in increases in G compared to an unfilled, cross-linked system. These results are of importance for engineering of new POSS-based multifunctional materials with tailor-made mechanical properties.

Simulated Assembly of Nanostructured Organic/Inorganic Networks

We perform lattice Monte Carlo simulations to study nanostructured networks formed by linking organically functionalized inorganic nanoscale building blocks. We develop a minimal lattice model of an octafunctional nanoscale building block (NBB) by representing the inorganic core with a rigid cube and the organic linkers with “bead-spring” chains. Using this model, we explore the effect of linker length on network properties including porosity, spatial distribution of NBBs, and extent of cross-linking during assembly. We compare our results with recent experimental data on networks of octafunctional polyhedral oligomeric silsesquioxane (POSS) cubes.