A degradable,porous, emulsion‐templated polyacrylate

A polyHIPE is a highly porous, emulsion‐templated polymer synthesized by polymerizing a monomer and a crosslinking comonomer in the continuous phase of a high‐internal phase emulsion (HIPE). The synthesis of degradable polyHIPE could be of interest for biomedical applications such as tissue engineering scaffolds. In this research, a poly(ε‐caprolactone) (PCL) oligomer with terminal vinyl groups was used as the crosslinking comonomer for a polyHIPE based on t‐butyl acrylate (tBA). The porous structure, properties, water absorption, and hydrolytic degradation of the polyHIPE were investigated. The polyHIPE containing 50 wt % PCL exhibited very large voids, 1 to 3 mm in diameter that resulted from the destabilization of the HIPE on addition of PCL, making the polyHIPE more suitable for tissue engineering applications. The relatively flexible PCL enhanced segmental mobility, yielding two glass transition temperatures and a significant reduction in modulus. When exposed to a 3 M aqueous solution of NaOH, the t‐butyl groups underwent hydrolysis and the PCL underwent degradation, rapidly leading to the complete disintegration of the macromolecular structure. The tBA‐based polyHIPE containing 50 wt % PCL exhibited enhanced cell adhesion, penetration, and growth indicating that it is a suitable candidate for further research and development. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Nanocomposites through copolymerization of a polyhedral oligomeric silsesquioxane and methyl methacrylate

The mechanical properties and thermal stability of polymers can be enhanced through the formation of nanocomposites. Nanocomposites consisting of hybrid copolymers of methacrylcyclohexyl polyhedral oligomeric silsesquioxane (POSS‐1) and methyl methacrylate (MMA) with up to 92 wt % (51 mol %) POSS‐1 and with superior thermal properties were synthesized using solution polymerization. The POSS‐1 contents of the copolymers were similar to or slightly higher than those in the feeds, the polydispersity indices were relatively low, and the degree of polymerization decreased with increasing POSS‐1 content. POSS‐1 enhanced the thermal stability, increasing the degradation temperature, reducing the mass loss, and preventing PMMA‐like degradation from propagating along the chain. The mass loss was reduced in a high POSS‐1 content copolymer since the polymerization of POSS‐1 with itself reduced sublimation. Exposure to 450 °C produced cyclohexyl‐POSS‐like remnants in the POSS‐1 monomer and in all the copolymers. The degradation of these remnants, for the copolymers and for the POSS‐1 monomer, yielded 75% SiO₂ and an oxidized carbonaceous residue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4264–4275, 2007     

Polymerization and nanocomposites properties of multifunctional methylmethacrylate POSS

Thermally induced polymerization of multifunctional methylmethacrylate POSS (MMA‐POSS) was studied in this work for preparation of polymer/POSS nanocomposites. The polymerization of MMA‐POSS could be promoted with benzoyl peroxide (BPO). Self‐assembly of POSS into a layer‐by‐layer structure in the MMA‐POSS polymer (TP‐MMA‐POSS) is observed with a transmission electron microscopy. An ultra‐low‐k value of about 1.85 is measured with TP‐MMA‐POSS. In addition, polyimide‐POSS nanocomposites are also prepared. These nanocomposites demonstrate good homogeneity and enhanced mechanical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5157–5166, 2008     

Preparation of remarkably tough polyHIPE materials via polymerization of oil‐in‐water HIPEs involving 1‐vinyl‐5‐aminotetrazole

Interconnected microcellular polymeric monoliths having unexpected high mechanical strength have been prepared using the high internal phase emulsion (HIPE) methodology. Oil‐in water concentrated emulsions of aqueous 1‐vinyl‐5‐amino [1,2,3,4]tetrazole (1‐VAT) mixed with a low molar ratio (7%) of N,N′‐methylenebisacrylamide as crosslinking agent were prepared using dodecane as dispersed phase and a mixture of hydrophilic surfactants. “Reverse” polyHIPE materials were obtained after radical copolymerization, solvent extraction, and drying. Their morphology, chemical composition, and physicochemical behavior are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2942–2947, 2010     

Properties of epoxy networks derived from the reaction of diglycidyl ether of bisphenol A with polyhedral oligomeric silsesquioxanes bearing OH‐functionalized organic substituents

A polyhedral oligomeric silsesquioxane (POSS), consisting mainly of a mixture of octahedra, nonahedra, and decahedra with bulky and flexible organic substituents, with three secondary hydroxyls per organic group, was used to modify epoxy networks produced by the homopolymerization of diglycidyl ether of bisphenol A in the presence of benzyldimethylamine. Several physical, thermal, and mechanical properties of the cured materials containing 0, 10, 30, and 50 wt % POSS were determined. The addition of POSS increased the elastic modulus and the yield stress measured in uniaxial compression tests, mainly because of the increase in the cohesive energy density produced by hydrogen bonding through the hydroxyl groups. A constant yield stress/elastic modulus ratio equal to 0.03 was observed for different POSS concentrations and test temperatures. The glass‐transition temperature decreased with POSS addition because of the flexibility of organic branches present in the POSS structure and the decrease in the crosslink density (determined from the rubbery modulus). Although a combination of a reduction in the glass‐transition temperature (plasticization) with an increase in the glassy modulus (antiplasticization) is a well‐known phenomenon, what is original is that in this case it was not the result of the suppression (or reduction in intensity) of subglass relaxations but was produced by an increase in the cohesive energy density. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1451–1461, 2003     

Nanoindentation,nanoscratch, and nanotensile testing of poly(vinylidene fluoride)‐polyhedral oligomeric silsesquioxane nanocomposites

Nanocomposites composed of a poly(vinylidene fluoride) (PVDF) matrix and 0, 3, 5, and 8 wt % fluoropropyl polyhedral oligomeric silsesquioxane (FP‐POSS) were prepared by using the solvent evaporation method. The morphology and the crystalline phase of the nanocomposites were investigated by digital microscopy, scanning probe microscopy, X‐ray diffractometer, and Fourier transform infrared spectroscopy. FP‐POSS acted as nucleating agent in PVDF matrix. A small content of FP‐POSS resulted in an incomplete nucleation of PVDF and generated bigger spherical particles, whereas higher contents led to a complete nucleation and formed more separate and less‐crosslinked particles. Nanoindentation, nanoscratch, and nanotensile tests were carried out to study the influence of different contents of FP‐POSS on the key static and dynamic mechanical properties of different systems. The nanocomposite with 3 wt % FP‐POSS was found to possess enhanced elastic properties and hardness. However, with the increase of the FP‐POSS content, the elastic modulus and hardness were found to decrease, and the improvement on stiffness was negative at contents of 5 and 8 wt %. Compared with neat PVDF, the scratch resistance of the PVDF/FP‐POSS nanocomposites was decreased due to a rougher surface derived from the bigger spherulites. Nanotensile testing results showed both the stiffness and toughness of PVDF‐FP_3% were enhanced and further additions of FP‐POSS brought dramatic enhancements in toughness while associated with a decline in stiffness. Dynamical mechanical properties indicated the viscosity of the nanocomposites increased with the increasing FP‐POSS contents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis,morphology, and properties of hydroxyl terminated‐POSS/polyimide low‐k nanocomposite films

Polyhedral oligomeric silsequioxane (POSS), having eight hydroxyl groups for the preparation of nanocomposites with polyimide (PI) was synthesized by the direct hydrosilylation of allyl alcohol with octasilsesquioxane (Q₈M₈^H) with platinum divinyltetramethyl disiloxane Pt(dvs) as a catalyst. The structure of allyl alcohol terminated‐POSS (POSS‐OH) was confirmed by FTIR, NMR, and XRD. A high performance, low‐k PI nanocomposite from pyromellitic dianhydride (PMDA)‐4,4'‐oxydianiline (ODA) polyamic acid cured with POSS‐OH was also successfully synthesized. The incorporation of POSS‐OH into PI matrix reduced dielectric constant of PI without loosing mechanical properties. Furthermore, the effects of POSS‐OH on the morphology and properties of the PI/POSS‐OH nanocomposites were investigated using UV–vis, FTIR, XRD, SEM, AFM, transmission electron microscope (TEM), TGA, and contact angle. The homogeneous dispersion of POSS particles was confirmed by SEM, AFM, and TEM. The nanoindentation showed that the modulus increased upon increasing the concentration of POSS‐OH in PI, whereas the hardness did not increase very much with respect to loading of POSS, due to soft‐interphase around POSS molecules in the resulting nanocomposites. Overall results demonstrated the nanometer‐level integration of the polymer and POSS‐OH. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5887–5896, 2008     

Ethylene polymerization and copolymerization with a polar monomer using an α‐iminocarboxamide nickel complex activated by trimethylaluminum

An α‐iminocarboxamide nickel complex was activated by trimethylaluminum (TMA) and used in the polymerization of ethylene and its copolymerization with 10‐undecen‐1‐ol. The best activity was observed upon activation with 9 equiv of TMA at a temperature of 26 °C. NMR spectroscopic studies did not show 10‐undecen‐1‐ol incorporation. However, FTIR analyses suggest the incorporation of a very small amount of comonomer, which affects the glass transition temperature, the degree of branching, and the mechanical properties of the materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 54–59, 2008     

Porous polyurethanes synthesized within high internal phase emulsions

PolyHIPE are highly porous, emulsion‐templated polymers typically synthesized via free‐radical polymerization within a water‐in‐oil (W/O) high internal phase emulsion (HIPE) whose dispersed, aqueous phase occupies more than 74% of the volume. The synthesis of a polyHIPE containing biodegradable polymers is not straightforward because the presence of both an organic phase and an aqueous phase within the HIPE limits the type of polymerization reactions that can be used. This article describes the synthesis of polyHIPE containing biodegradable poly(ε‐caprolactone) (PCL) groups through the step‐growth reaction of a diisocyanate with a flexible PCL triol to form a crosslinked polyurethane. The reaction of the diisocyanate with the water in the HIPE produced urea groups and large bubbles from the generation of CO₂. The polymer walls between these bubbles consisted of a porous, emulsion‐templated structure. Polymerization with an excess of diisocyanate produced a significant enhancement in the amounts of urea and CO₂. The reduction in the flexible PCL content and the enhancement in the rigid urea content produced an increase in wall modulus that was over 20‐fold. The ability to synthesize polyHIPE through such step‐growth reactions is an important advance in the adaptation of polyHIPE for such applications as tissue engineering. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5806–5814, 2009     

Synthesis and characterization of novel PDMS nanocomposites using POSS derivatives as cross‐linking filler

We report the synthesis and characterization of novel elastomeric nanocomposites containing polyhedral oligomeric silsesquioxanes (POSS) as both the cross‐linker and filler within a polydimethylsiloxane (PDMS) polymer matrix. These polymer composites were prepared through the reaction of octasilane‐POSS (OS‐POSS) with vinyl‐terminated PDMS chains using hydrosilylation chemistry. In addition, larger super‐POSS cross‐linkers, consisting of two pendant hepta(isobutyl)POSS molecules attached to a central octasilane‐POSS core, were also used in the fabrication of the PDMS composites. The chemical incorporation of these POSS cross‐linkers into the PDMS network was verified by solid‐state ¹H magic angle spinning NMR. Based on dynamic mechanical analysis, the PDMS nanocomposites prepared with the octafunctional OS‐POSS cross‐linker exhibited enhanced mechanical properties relative to polymer systems prepared with the tetrafunctional TDSS cross‐linker at equivalent loading levels. The observed improvements in mechanical properties can be attributed to the increased dimensionality of the POSS cross‐linker. The PDMS elastomers synthesized from the larger super‐POSS molecule showed improved mechanical properties relative to both the TDSS and OS‐POSS composites due to the increased volume‐fraction of POSS filler in the polymer matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2589–2596, 2009     

Polymerized pickering HIPEs: Effects of synthesis parameters on porous structure

A polyHIPE is a highly porous polymer synthesized from monomers within the external phase of a high internal phase emulsion (HIPE). The large amount of difficult to remove surfactant needed for HIPE stabilization can affect the properties of the resulting polymer. A Pickering emulsion is a surfactant‐free emulsion stabilized by solid particles that preferentially migrate to the interface. In this article, the synthesis of crosslinked polyacrylate polyHIPEs based on Pickering HIPEs stabilized using silane‐modified silica nanoparticles is described and the effects of the synthesis parameters on the porous structure are discussed. The silane chemistry, silane content, and nanoparticle content had significant effects on the size of the polyhedral, relatively closed‐cell polyHIPE voids that resulted from aqueous‐phase initiation. Increasing the mixing intensity reduced the wall thickness and produced a more open‐cell structure. The locus of initiation had a significant effect on polyHIPE morphology. Organic‐phase initiation yielded larger, more spherical voids from the more extensive coalescence before the structure could be “locked‐in” at the gel point. Most significantly, the nanoparticles were located within the polymer walls rather than at the interface, as might be expected. The void walls were shown to be an assembly of nanoparticle agglomerate shells that become embedded within the polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1516–1525, 2010     

Ethylene/POSS copolymerization behavior of postmetallocene catalysts and copolymer characteristics

Copolymerization of ethylene with iso‐butyl substituted monoalkenyl(siloxy)‐ or monoalkenylsilsesquioxane (POSS) comonomers over bis(phenoxy‐imine) and salen‐type titanium and zirconium catalysts was studied. It was found that the polyreaction performance was significantly depended by the kind of the catalyst and by the structure and concentration of POSS in the feed. The POSS comonomer was efficiently incorporated into the polymer chain at up to 0.2 mol %. The differences in the copolymer compositions as the functions of the catalyst kind and the POSS comonomer were observed, including the varied number‐average sequence length of ethylene and unsaturated end groups, as determined by ¹H NMR and FT‐IR. The presence of POSS comonomers affected also the melting and crystallization behavior of the copolymers, as evidenced by DSC, because of influence on the polymer chain arrangement. The POSS units could act as the nucleating agents. Moreover, the crystal and structural parameters of ethylene/POSS copolymers were evaluated on the basis of X‐ray results, and the limited self‐aggregation of POSS incorporated into the polymer chain, the small number and size of POSS aggregates, and the increased crystallinity degree of copolymers were demonstrated. The ethylene/POSS copolymers produced by postmetallocenes offered also high thermal stability and interesting morphological properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3918–3934     

Organic–inorganic hybrid hydrogels involving poly(N‐isopropylacrylamide) and polyhedral oligomeric silsesquioxane: Preparation and rapid thermoresponsive properties

3‐Acryloxypropylhepta(3,3,3‐trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS) was synthesized and used as a modifier to improve the thermal response rates of poly(N‐isopropylacrylamide) (PNIPAM) hydrogel. The radical copolymerization among N‐isopropylacrylamide (NIPAM), the POSS macromer and N,N′‐methylenebisacrylamide was performed to prepare the POSS‐containing PNIPAM cross‐linked networks. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) showed that the POSS‐containing PNIPAM networks displayed the enhanced glass transition temperatures (T_g's) and improved thermal stability when compared with plain PNIPAM network. The POSS‐containing PNIPAM hydrogels exhibited temperature‐responsive behavior as the plain PNIPAM hydrogels. It is noted that with the moderate contents of POSS, the POSS‐containing PNIPAM hydrogels displayed much faster response rates in terms of swelling, deswelling, and re‐swelling experiments than plain PNIPAM hydrogel. The improved thermoresponsive properties of hydrogels have been interpreted on the basis of the formation of the specific microphase‐separated morphology in the hydrogels, that is, the POSS structural units in the hybrid hydrogels were self‐assembled into the highly hydrophobic nanodomains, which behave as the microporogens and promote the contact of PNIPAM chains and water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 504–516, 2009     

Preparation of polyHIPE via CuAAC “click” chemistry and its application as a highly efficient adsorbent of Cu(II) ions

A hydrophilic emulsion‐templated porous polymer (polyHIPE) is synthesized by CuAAC “click” chemistry. Herein, a 4,4′‐diazidostilbene‐2,2′‐disulfonic acid disodium salt‐4H₂O (DAS) and tripropargylamine in the mixture of water and N,N‐dimethylformamide solution is used as external phase of the high internal phase emulsion template, and paraffin liquid is involved as the internal phase. The resulting polyHIPE has a well‐defined interconnected pore structure, which could be tailored by changing preparation parameters, such as reagent content, internal phase volume fraction, and surfactant concentration. Thermal analysis shows that the polyHIPE is stable under 180 °C. Owing to the presence of a large number of sodium sulfonate groups from the reagent DAS and the triazoles groups produced in the reaction, the polyHIPE is proved to be a highly efficient adsorbent of heavy metal ion (i.e., up to 52 mg/g for Cu(II) ions) in water. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2129–2135     

Synthesis of semitelechelic POSS‐polymethacrylate hybrids by thiol‐mediated controlled radical polymerization with unusual thermal behaviors

We have developed an efficient and versatile method for the synthesis of polyhedral oligomeric silsesquioxanes (POSS)‐polymethacrylate hybrids, such as POSS‐poly(methyl methacrylate) (POSS‐PMMA), POSS‐poly(ethyl methacrylate) (POSS‐PEMA), and POSS‐poly(benzyl methacrylate) (POSS‐PBzMA) of controllable molecular weights and low polydispersities by thiol‐mediated radical polymerization at elevated temperature (100 °C). By tuning the reactant concentrations and degree of polymerization of the grafted polymethacrylate chains, POSS content in these hybrid materials could be varied. MALDI‐TOF‐MS analysis of the hybrid molecule shows that the nanoscale POSS moiety is connected to the end of polymethacrylate chain through the sulfur atom bridge. These hybrid materials were further characterized using various techniques such as FTIR, XRD, NMR, TGA, and DSC. In all synthesized hybrids, the incorporation of POSS moiety at the end of polymethacrylate chain resulted in the decrease of glass transition temperature (T_g) compared to that of neat polymethacrylates of comparable molecular weights. Surprisingly, POSS‐PMMA hybrids only with relatively high POSS content (～ 10 and 16 wt %) showed physical aging behavior as reveled by DSC study. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1111–1123, 2008     

Aliphatic Polyester/polyhedral Oligomeric Silsesquioxanes Hybrid Networks via Copper‐free 1,3‐dipolar Cycloaddition Click Reaction

In this study, we describe the preparation and characterization of a new class of thermoset hybrid networks containing aliphatic polyester and polyhedral oligomeric silsesquioxanes (POSS). The copper‐free 1,3‐dipolar cycloaddition click reaction of internal alkyne functionalized aliphatic polyester and multifunctional azido POSS with different concentrations led to highly crosslinked thermoset networks. The click reactions performed under ambient conditions (i.e., in tetrahydrofuran at room temperature for 1 day) in the absence of any catalyst. The chemical composition of hybrid networks and homogenous distribution of POSS molecules were confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy with energy dispersive spectroscopy. The swelling ratios of hybrid networks were commonly decreased by increasing POSS‐N₃ content and by changing polar solvents to apolar solvents. Thermogravimetric analysis results demonstrated that the thermal stability of hybrid networks increased with higher POSS feeding ratio. Tensile tests were applied to evaluate the mechanical properties of hybrid networks. Compared to neat aliphatic polyester, the mechanical properties of hybrid networks significantly improved. For instance, the tensile strength were enhanced from 5 MPa to 19 MPa by increasing the concentration of azido functionalized POSS from 10 to 40. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2222–2227     

Preparation,characterization, and properties of novel biodegradable aliphatic–aromatic copolyester nanohybrids with polyhedral oligomeric silsesquioxanes moieties

Biodegradable aliphatic–aromatic copolyester nanohybrids, with polyhedral oligomeric silsesquioxane (POSS) moieties tethered between poly(lactic acid) (PLA) and poly(butylene terephthalate) segments, is designed and prepared. First, (bis(2‐hydroxyethyl) dipropionate POSS, BH‐POSS) is synthesized under mild conditions, then in situ polycondensation is carried out in the presence of terephthalic acid, PLA oligomer, 1,4‐butanediol, and BH‐POSS. 1 H‐NMR and Fourier transfer infrared spectroscopy confirm that Michael addition reaction of amino‐POSS and hydroxyethyl acrylate takes place efficiently and forms BH‐POSS in high yield at room temperature. Owing to similar functional groups, BH‐POSS could be easily incorporated into the macromolecular chains and obtain final copolyester nanohybrids. Moreover, X‐ray diffractometry and transmission electron microscopy observations demonstrate that POSS moieties occur self‐assembly behaviors and form nanoaggregates with the diameter of 50–100 nm. The thermal stability and mechanical properties of the copolyester nanohybrids containing BH‐POSS are substantially improved. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Kinetics of ethylene polymerization reactions with chromium oxide catalysts

Principal kinetic data are presented for ethylene homopolymerization and ethylene/1‐hexene copolymerization reactions with two types of chromium oxide catalyst. The reaction rate of the homopolymerization reaction is first order with respect to ethylene concentration (both for gas‐phase and slurry reactions); its effective activation energy is 10.2 kcal/mol (42.8 kJ/mol). The r₁ value for ethylene/1‐hexene copolymerization reactions with the catalysts is ～30, which places these catalysts in terms of efficiency of α‐olefin copolymerization with ethylene between metallocene catalysts (r₁ ～ 20) and Ti‐based Ziegler‐Natta catalysts (r₁ in the 80–120 range). GPC, DSC, and Crystaf data for ethylene/1‐hexene copolymers of different compositions produced with the catalysts show that the reaction products have broad molecular weight and compositional distributions. A combination of kinetic data and structural data for the copolymers provided detailed information about the frequency of chain transfer reactions for several types of active centers present in the catalysts, their copolymerization efficiency, and stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5315–5329, 2008     

Crystallization behavior and morphological development of isotactic polypropylene blended with nanostructured polyhedral oligomeric silsesquioxane molecules

The thermal properties and morphological development of isothermally crystallized isotactic polypropylene (iPP) blended with nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules at very small loading of POSS were studied with differential scanning calorimeter (DSC), thermal gravimetric analysis, dynamic mechanical analysis, polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). The result of DSC indicated that the crystallization rate of iPP increases with the increase in POSS contents during crystallization; moreover, the melting temperature of iPP/POSS nanocomposites slightly decreases, while the heat of fusion increases with the addition of POSS molecules at melting and remelting traces. The storage modulus and thermal stability, respectively, remarkably decrease, while the glass transition temperature of isothermally crystallized iPP/POSS nanocomposites increases slightly with the increase in POSS contents. The morphologies results of WAXD and POM show that the POSS molecules form about 35 nm sized nanocrystals and aggregate to form thread‐like and network structure morphologies, respectively, in the molten state even when the POSS content is very small. These results, therefore, suggest that the interaction force between the POSS molecules should be larger than the force between POSS molecules and iPP matrix; however, those interactions depend on the chain length of functionalized substituents on the POSS cage. Therefore, the POSS molecules aggregate forming nanocrystals and act as an effective nucleating agent for iPP and influence the thermal properties of iPP/POSS nanocomposites due to the shorter chain length of functionalized substituents, methyl, on the POSS cage. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2122–2134, 2006     

Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008