POSS related polymer nanocomposites

This review describes the syntheses of polyhedral oligomeric silsesquioxane (T₈-POSS) compounds, the miscibility of POSS derivatives and polymers, the preparation of both multifunctional and monofunctional monomers and polymers containing POSS including styryl-POSS, methacrylate-POSS, norbornyl-POSS, vinyl-POSS, epoxy-POSS, phenolic-POSS, benzoxazine-POSS, amine-POSS, and hydroxyl-POSS. The thermal, dynamic mechanical, electrical, and surface properties of POSS-related polymeric nanocomposites prepared from both monofunctional and multifunctional POSS monomers are discussed. In addition, we describe the applications of several high-performance POSS nanocomposites in such systems as light emitting diodes, liquid crystals, photo-resist materials, low-dielectric constant materials, self-assembled block copolymers, and nanoparticles.     

有机-无机杂化纳米结构体——多面体低聚硅倍半氧烷研究进展

多面体低聚硅倍半氧烷是基于化学键合作用形成的分子内杂化体系,其改性后的材料是一类具有广泛潜在应用价值的新型有机-无机杂化材料。介绍了多面体低聚硅倍半氧烷单体的结构、性能、单体及其衍生物的合成,以及其改性聚合物材料在航空、航天、生物、电子等高科技领域内的应用前景。针对国内的研究现状,指出低聚硅倍半氧烷-聚合物杂化体系研究所存在的问题。     

Hybrid networks based on epoxidized camelina oil

Lately, renewable resources received great attention in the macromolecular compounds area, regarding the design of the monomers and polymers with different applications. In this study the capacity of several modified vegetable oil-based monomers to build competitive hybrid networks was investigate, taking into account thermal and mechanical behavior of the designed materials. In order to synthesize such competitive nanocomposites, the selected renewable raw material, camelina oil, was employed due to the non-toxicity and biodegradability behavior. General properties of epoxidized camelina oil-based materials were improved by loading of different types of organic-inorganic hybrid compounds – polyhedral oligomeric silsesquioxane (POSS) bearing one (POSS1Ep) or eight (POSS8Ep) epoxy rings on the cages. In order to identify the chemical changes occurring after the thermal curing reactions, FT-IR spectrometry was employed. The new synthesized nanocomposites based on epoxidized camelina oil (ECO) were characterized by dynamic mechanical analyze and thermogravimetric analyze. The morphology of the ECO-based materials was investigate by scanning electron microscopy and supplementary information regarding the presence of the POSS compounds were establish by energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. The smooth materials without any separation phase indicates a well dispersion of the Si–O–Si cages within the organic matrix and the incorporation of this hybrid compounds into the ECO network demonstrates to be a well strategy to improve the thermal and mechanical properties, simultaneously.     

Formation of nanostructured epoxy networks containing polyhedral oligomeric silsesquioxane (POSS) blocks

Nanostructured epoxy networks, based on DGEBA and poly(oxypropylene)diamine (Jeffamine D), containing nano-sized inorganic blocks, polyhedral oligomeric silsesquioxanes (POSS), were investigated. The POSS were incorporated in the network as crosslinks or as pendant units by using octa- or monoepoxy-POSS monomers, respectively, as well as diepoxides with pendant POSS. The authors focused on investigating the relationship between the network formation process and the final product properties. The reactivity of the epoxy-functional POSS monomers, the hybrid systems' time of gelation, the gel fractions and the phase structure of the networks were determined using ¹H or ¹³C NMR spectroscopy, chemorheology experiments, sol-gel analysis and transmission electron microscopy (TEM).All the POSS epoxides tested show a reduced reactivity if compared to their respective model compounds due to sterical crowding in the neighborhood of their functional groups and due to reduced epoxy group mobility. The incorporation of pendant POSS into networks of the type DGEBA-Jeffamine D-monoepoxy-POSS hence took place only in the late reaction stage. Together with the high tendency of these POSS to aggregation, the kinetics favors the formation of small nano-phase-separated POSS domains, which act as physical crosslinks due to their covalent bonds to the organic matrix. At POSS loadings higher than 70%, topological constraint by POSS leads to a strongly reduced elastic chain mobility, thus additionally strongly reinforcing the networks. The network build-up and gelation of the octaepoxy-POSS-Jeffamine D system were slow compared to the reference DGEBA-Jeffamine D network due to a low octaepoxy-POSS reactivity and due to its strong tendency to cyclization reactions with primary amines. The topology of the amino groups is shown to be very important. In contrast to monoepoxy-POSS, the octaepoxy-POSS becomes dispersed as oligomeric junctions (purely chemical crosslinks) of the network in the cured product. The octaepoxide's reinforcing effect is small and is given only by its high functionality and not by its inorganic nature. The functionality effect is reduced by the mentioned cyclizations.     

Preparation and properties of ethylene/POSS copolymer with rac‐Et(Ind)2ZrCl2 catalyst

The various monovinyl‐functional polyhedral oligomeric silsesquioxane (POSS) monomers had been copolymerized with ethylene (E) using rac‐Et(Ind)₂ZrCl₂ and a modified methylaluminoxane (MMAO) cocatalyst. The unreacted POSS monomer could be removed completely by washing the copolymerization product with n‐hexane. And the copolymers were characterized with ¹H NMR, TEM, DSC, TGA, and GPC to know the composition, thermal properties, molecular weight and its distribution, respectively. According to ¹H NMR data, the monomer reactivity ratios of various POSS monomers were calculated by the Fineman‐Ross and Kelen‐Tudos methods. Thermogravimetric analysis of E/POSS copolymers exhibited an improved thermal stability with a higher degradation temperature and char yields, demonstrating that the inclusion of inorganic POSS nanoparticles made the organic polymer matrix more thermally robust. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of styrene/styryl–polyhedral oligomeric silsesquioxane hybrid copolymers

BACKGROUND: Organic–inorganic nanocomposites were prepared by copolymerization of various monomers and polyhedral oligomeric silsesquioxane (POSS) derivatives. Preliminary results showed that styrene/styryl–POSS copolymers could be obtained using CpTiCl₃ catalyst. In the work reported here, the copolymerization of styrene and styryl‐substituted POSS was studied in detail for a more effective catalyst, Cp*TiCl₃. RESULTS: The glass transition temperature (T_g) of the copolymers prepared increased with increasing POSS content. The degradation temperature (T_d) of the copolymers was 60 °C higher than that of syndiotactic polystyrene under nitrogen. Although the thermal properties were improved by incorporation of POSS, the catalytic activity decreased with POSS content. The racemic triad and syndiotactic index of the copolymers decreased with increasing POSS content. Gel permeation chromatograms of the copolymers exhibited multimodal distribution due to the presence of multi‐active centres, which were formed by interaction of Ti with the POSS siloxane linkage. CONCLUSION: With the incorporation of POSS, the thermal properties of polystyrene were improved. The styrene/styryl–POSS copolymers are formed through the various active sites arising from the interactions of Ti with POSS. Copyright © 2008 Society of Chemical Industry     

Synthesis, characterization, and properties of chain terminated polyhedral oligomeric silsesquioxane-functionalized perfluorocyclobutyl aryl ether copolymers

A new class of perfluorocyclobutyl (PFCB) polymers covalently functionalized with polyhedral oligomeric silsesquioxane (POSS) is presented. Three discreetly functionalized POSS monomers possessing thermally reactive trifluorovinyl aryl ether (TFVE) were prepared in good yields. The POSS TFVE monomers were prepared by initial corner-capping of cyclopentyl (-C₅H₉), iso-butyl (-CH₂CH(CH₃)₂), or trifluoropropyl (-CH₂CH₂CF₃) functionalized POSS trisilanols with acetoxyethyltrichlorosilane followed by sequential acid-catalyzed deprotection and coupling with 4-(trifluorovinyloxy)benzoic acid. TFVE-functionalized POSS monomers were thermally polymerized with 4,4′-bis(4-trifluorovinyloxy)biphenyl or 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomers via a condensate-free, [2 + 2] step-growth polymerization. The polymerization afforded solution processable PFCB polymers with POSS macromer installed on the polymer chain ends. POSS monomers and their corresponding copolymers were characterized by ¹H, ¹³C, ¹⁹F, and ²⁹Si NMR, GPC, ATR-FTIR, and elemental combustion analysis. GPC trace analysis showed agreeable number-average molecular weight for various weight percent of cyclopentyl or iso-butyl and trifluoropropyl chain terminated POSS PFCB copolymers. DSC analysis showed the introduction of increasing POSS weight percent in the endcapped PFCB copolymers lowers the glass transition temperatures as high as 31 °C. On the other hand, the trifluoropropyl POSS endcapped PFCB polymer glass transition temperature was unaffected when copolymerized with the more fluorinated 2,2-bis(4-trifluorovinyloxybiphenyl)-1,1,1,3,3,3-hexafluoropropane monomer. TGA analysis of POSS PFCB copolymers showed step-wise decomposition of copolymers resulting from the initial degradation of the POSS cages at 297-355 °C in nitrogen and air which was confirmed by pyrolysis coupled with GC-MS. This initial weight loss was proportional to the weight percent of POSS incorporated into the polymer. The balance of decomposition was observed at 450-563 °C in nitrogen and air which is higher than the PFCB homopolymers in most cases. Polymer surface characterization was performed on spin cast transparent, flexible films. These composite films exhibited good POSS dispersion within the matrix PFCB polymer as was shown by TEM analysis.     

Synthesis and characterization of polybenzoxazine networks nanocomposites containing multifunctional polyhedral oligomeric silsesquioxane (POSS)

A new class of polybenzoxazine/POSS nanocomposites with network structure is prepared by reacting multifunctional benzoxazine POSS (MBZ-POSS) with benzoxazine monomers (Pa and Ba) at various compositional ratios. Octafunctional cubic silsesquioxane (MBZ-POSS) is used as a curing agent, which is synthesized from eight organic benzoxazine tethers through hydrosilylation of vinyl-terminated benzoxazine monomer (VP-a) with octakis(dimethylsiloxy)silsesquioxane () using a platinum complex catalyst (Pt-dvs). Incorporation of the silsesquioxane core into polybenzoxazine matrix could significantly hinder the mobility of polymer chains and enhance the thermal stability of these hybrid materials. For these nanocomposites, increasing the POSS content in the hybrids is expected to improve its thermal properties with respect to the neat polybenzoxazine. The morphology feature is useful to explain the thermal property changes (T_g and T_d) and AFM images show that the presence of POSS aggregation in larger scales occurs at higher POSS contents. The reason of the heterogeneous phase separation may be from the less compatibility of the inorganic silsesquioxane core with organic benzoxazine species and the homopolymerization of MBZ-POSS. In the course of the formation of the polybenzoxazine/POSS hybrids, POSS particles were separated from the polybenzoxazine rich region, leading to POSS rich domains in the range of 50-1000 nm.     

Poly(ethylene terephthalate)/clay nanocomposites with trisilanolphenyl polyhedral oligomeric silsesquioxane as dispersant: simultaneously enhanced reinforcing and stabilizing effects

This paper presents a new approach for the preparation of poly(ethylene terephthalate) (PET)/clay nanocomposites using surfactant‐free clay (sodium montmorillonite, Na‐MMT) with trisilanolphenyl polyhedral oligomeric silsesquioxane (Tsp‐POSS) as dispersant. The dispersion of clay in the PET/Na‐MMT/Tsp‐POSS nanocomposites is enhanced over that in PET/Na‐MMT by using a very small amount of Tsp‐POSS, which acts as functional spacer to keep clay platelets apart and pull monomers in, and, at the same time, acts as a PET chain extender. As a result, thermomechanical properties and thermo‐oxidative stability of PET/Na‐MMT/Tsp‐POSS are improved simultaneously compared with those of PET/organoclay nanocomposites. © 2013 Society of Chemical Industry     

Multilayered confinement of iPP/TPOSS and nylon 6/APOSS blends

A series of isotactic polypropylene and nylon 6 blends with silsesquioxane (POSS) additives were produced, then layered to nanometer thicknesses to test the effects of confinement upon polymer property modification. POSS is shown to be a poor filler, lacking solubility and favorable interaction with the polymer matrices. It was initially hypothesized that under extreme confinement and orientation, such as in melt-spun fibers, or confined within 2D nanoscale layers, that POSS would undergo forced-assembly into elongated, rebar-like reinforcement structures, or even act as crosslinking molecules for the polymer chains. The current results, however, show POSS existing as large, phase separated aggregates, in order to minimize interactions with the polymer matrix; the aggregates behave as debonded hard particles upon tensile deformation. POSS has been previously shown to enhance the properties of polymer matrices in which the POSS molecules have been grafted to, or copolymerized within the chain, but this is not the case for these POSS blends. In comparison to results from the iPP/DBS/TPOSS system, in which POSS is unable to directly interact with the polymer matrix, and the nylon 6/APOSS system, in which POSS can potentially form hydrogen bonds with the polymer matrix, the results are similar and reveal that POSS blends are largely incompatible with the polymer matrix. Small improvements in blend properties can be made via functionalization of the POSS cage, in order to enhance interactions, but these improvements are quite limited.