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     

Incorporation of metallic POSS,POSS copolymers,and new functionalized POSS compounds into commercial dental resins

An array of polyhedral oligomeric silsesquioxane (POSS) compounds, including metal, methacrylate, and amine functional POSS, and POSS copolymers were incorporated into aromatic and aliphatic dental resins. Heptaphenyl‐propylamine POSS and methacrylate derivatives were synthesized by corner‐capping and Michael addition reactions, respectively. The POSS compounds were tested for solubility in commercial resins at concentrations of 1, 5, 10, and 15 wt %, followed by UV polymerization of all soluble combinations. The POSS compounds generally increased modulus and had an unpredictable effect on T_g. The modulus of the aliphatic resin increased 83% by incorporation of 15 wt % aluminum‐phenyl POSS, while aromatic resins saw a maximum modulus improvement of 18% at 30°C and 72% at 160°C by incorporating 1 wt % of heptaphenyl‐methacrylate POSS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2856–2862, 2006     

Improvement of thermal ageing and transparency of methacrylate based poly(siloxane–silsesquioxane) for optoelectronic application

Trisilanolphenyl–polyhedral oligosilsesquioxane (trisilanolphenyl–POSS) structure is introduced into a polysiloxane network in an attempt to produce thermally stable material with improved transparency. A series of organic–inorganic resins comprised of diphenylsilanediol, 3‐methacryloxypropyl trimethoxysilane, and varying content of trisilanolphenyl–POSS were copolymerized through condensation followed by curing using phenyltris(hydrogendimethylsiloxy)silane as curing agent. Fourier transform infrared spectroscopy (FTIR), proton‐nuclear magnetic resonance spectroscopy (¹H‐NMR), and silicon‐nuclear magnetic resonance spectroscopy (²⁹Si‐NMR) were used to confirm the synthesized product. Excellent thermal stability, improved glass transition temperature (T_g), and lower coefficient of thermal expansion with the increasing POSS content were observed from thermomechanical analysis. Its extreme thermal degradation stability was attributable to the crosslinked network as well as the heavily substituted aromatic ring present in the system. Steric hindrance effect is noticeable beyond 5.66 mol % trisilanolphenyl–POSS content. Incorporation of POSS substituent in methacrylate‐based polysiloxane give excellent transparency and improved thermal discoloration resistance as deduced from UV/vis Spectrophotometer, making it a potential material to be used in optoelectronics. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45285.     

Dielectric properties of lithium‐perchlorate‐filled acrylonitrile–hexyl methacrylate copolymer films

A series of poly(acrylonitrile‐co‐hexyl methacrylate), PAN‐co‐PHMA, copolymers with various hexyl methacrylate (HMA) contents were synthesized by emulsion technique. The incorporation of HMA units into the copolymers was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy. Glass transition temperatures (T _g) and thermal decomposition temperatures of copolymers were determined by differential scanning calorimetry and thermogravimetric analysis. The T _g of copolymers were lowered monotonically by increasing HMA content, while thermal stabilities of copolymers were enhanced. The frequency dependence of dielectric properties of three different amounts of LiClO₄ salt doped copolymer films was investigated. The influence of molar fraction of HMA on dielectric constant and ac‐conductivity of copolymer films was examined. Samples with higher HMA contents showed better stability and conductivity, as a result of increase in free volume and the mobility of the dipoles. The ac conductivity of copolymers was also improved by increasing LiClO₄ salt which was due to the existence of more charge carriers. PAN(88)‐co‐PHMA(12) copolymer with 1.5 mol% of lithium salt exhibited ionic conductivity of the 7.8 × 10⁻⁴ S/cm at 298 K. POLYM. COMPOS., 38:1792–1799, 2017. © 2015 Society of Plastics Engineers     

Polyhedral oligomeric silsesquioxanes nanoreinforced methacrylate/epoxy hybrids

The aim of this study was to design novel binary and ternary copolymers based on methacrylate and/or epoxy monomers reinforced with 10 wt % mono‐/octafunctional polyhedral oligomeric silsesquioxanes (POSS) compounds bearing one or eight epoxy or methacrylate moieties. The experimental parameters such as temperature and time of reaction, comonomer ratio and the incorporation of various types of POSS that strongly influences the curing behavior, polymerization kinetics, glass transition temperature (T_g), thermostability and morphological structure of the obtained copolymers were investigated through DSC, FTIR, DMA, TGA, and SEM techniques. The obtained results evidenced that the complex kinetic mechanisms of curing reactions for the binary and ternary copolymers ± POSS influence the thermomechanical and morphological properties of the materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42912.     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Nanocomposites based on copolymers of fluorinated imide and polyhedral oligomeric silsesquioxane macromonomer: microstructure and morphology studies

Towards the development of copolymeric nanocomposites, N‐3(trifluoromethyl)phenyl‐7‐oxanorbornene‐5,6‐dicarboximide (TFI) monomer and a macromonomer of polyhedral oligomeric silsesquioxane (POSS) were synthesized. Ring‐opening metathesis polymerization to copolymerization of specified proportions of the two co‐monomers was carried out. All the monomers and polymers were characterized using Fourier transform IR analysis and ¹H and ²⁹Si NMR. Gel permeation chromatography shows that copolymeric nanocomposites have a lower average molar mass than a homopolymer of TFI (HTFI). TGA shows that the thermal stability of the copolymer is inversely proportional to the proportion of POSS units. DSC studies have demonstrated that the glass transition temperature (T_g) of a nanocomposite possessing 25 wt% POSS is at a higher temperature (180 °C) than that of HTFI (175 °C). Transmission electron microscopy and AFM images of copolymers are consistent with the self‐assembled spherical aggregation of POSS units, while X‐ray diffraction studies have confirmed the homogeneous dispersion of the same units within the nanocomposites. © 2012 Society of Chemical Industry     

DOPO‐Based Phosphorus‐Containing Methacrylic (Co)Polymers: Glass Transition Temperature Investigation

A two‐step synthetic procedure is designed for preparing new flame‐retardant methacrylic monomers containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as a substituent side group. DOPO and methacrylate moieties are linked by linear aliphatic hydrocarbon spacers (3 to 11 carbon atoms). Copolymerization with methyl methacrylate is carried out leading to copolymers containing between 2 and 10 wt% phosphorus. All homo‐ and copolymers exhibit a unique glass transition temperature (T_g ). A new group contribution for DOPO‐based substituent is extracted that leads to reasonable estimations of T_g s of other published polymers. The Fox equation provides a good estimation of T_g s for most copolymers and for physical blends of poly(methyl methacrylate) (PMMA) and DOPO. When using monomers having three and four carbon atoms in the hydrocarbon spacer, the T_g of copolymers remains close to that of PMMA over a wide range of composition.     

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

Poly(lauryl methacrylate)s with anthracene moieties in the side chain were converted with C₆₀‐fullerene and phenyl‐C₆₁‐butyric acid methyl ester (PCBM), resulting in new remendable (self‐healing) polymeric materials. The utilization of differently substituted anthracene monomers enabled the tuning of the reactivity and the resulting mechanical properties. Copolymers with different contents of the anthracene moieties were synthesized and characterized using size exclusion chromatography, ¹H nuclear magnetic resonance (NMR) spectroscopy as well as differential scanning calorimetry (DSC). ¹H NMR spectroscopic studies were utilized in order to investigate the reversibility of the Diels–Alder reaction between copolymers with C₆₀‐fullerene and PCBM, respectively, in solution. In order to investigate the conversion of the polymers with C₆₀‐fullerene and PCBM in bulk, additionally, DSC, nanoindentation, rheology, atomic force microscopy (AFM), 3D microscopy, simultaneous thermal analysis (STA) and FT‐Raman investigations were performed. The fullerene‐containing copolymers could be healed in a temperature range of 40–80 °C. Consequently, a new generation of low temperature remendable polymers could be established. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45916.     

Novel phenyl‐POSS/polyurethane aqueous dispersions and their hybrid coatings

A facile and rapid preparation of 3‐(2‐aminoethylamino)propylheptaphenylPOSS (AA‐POSS), a special phenyl‐POSS that contains two functional amino groups (Scheme 1), is demonstrated by the corner‐capping method. Then AA‐POSS forms a series of novel phenyl‐POSS/PU aqueous dispersions. The structure of AA‐POSS has been confirmed by ¹H, ¹³C, ²⁹Si NMR, and ESI‐MS. The POSS/PU hybrid films are studied by Fourier transform infrared spectrometer (FT‐IR), gel permeation chromatography (GPC), scanning electron microscope (SEM), X‐ray diffraction (XRD) spectra, differential scanning calorimetry (DSC) analysis, and thermal gravimetric analyzer (TGA). FT‐IR and GPC are conducted to validate the chemical structure of the hybrid PU. The properties of hybrid films display significant changes with notable increases in T_g, thermal properties, tensile strength, as well as surface hydrophobicity. These changes are attributed to the incorporation of novel POSS into PU. Moreover, these significant material property enhancements are achieved at low levels of POSS incorporation (only 4%). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1611–1620, 2013     

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     

Synthesis and characterization of poly[(1‐vinyl‐1,2,4‐triazole)‐co‐(monomer with carboxylic acid group(s))] and determination of monomer reactivity ratios: I. Acrylic acid

Copolymers of 1‐vinyl‐1,2,4‐triazole (VTAz) and acrylic acid (AA) having different mole ratios were synthesized using free radical‐initiated solution polymerization in dimethylformamide at 70 °C with α,α′‐azobisisobutyronitrile as initiator in nitrogen atmosphere. The compositions of the synthesized copolymers for a wide range of monomer feeds were determined using Fourier transform infrared (FTIR) spectroscopy through recorded absorption bands for VTAz (1510 cm^?1, C?N (triazole ring) stretching mode) and AA (1710 cm^?1, C?O stretching mode) units. The structures of the copolymers were characterized using FTIR and ¹H NMR spectroscopy. The copolymer compositions were also determined from ¹H NMR analysis following proton signals of carboxyl group at 11.8–12.5 ppm of AA and of triazole ring at 7.5–8.1 ppm of VTAz. Monomer reactivity ratios for the VTAz‐AA pair were estimated using linear methods, i.e. Fineman–Ross (FR) and Kelen–Tüdös (KT). From FTIR evaluation, monomer reactivity ratios were calculated as r₁ = 0.404 and r₂ = 1.496 using the FR method and r₁ = 0.418 and r₂ = 1.559 using the KT method. These values were found to be very close to those obtained from NMR evaluation. The two cases r₁r₂ < 1 and r₁ < r₂ indicated the random distribution of the monomers in the final copolymers and the presence of a greater amount of AA units in the copolymer than in the feed, respectively. The observed relatively high activity of complexed growing radical‐AA^? … VTAz was explained by the effect of complex formation between carbonyl groups and triazole fragments in chain growth reactions. Thermal behaviours of copolymers with various compositions were investigated using thermogravimetric and differential scanning calorimetric analyses. It was observed that thermal stabilities and glass transition temperatures of the copolymers increased resulting from complex formation between acid and triazole units. © 2012 Society of Chemical Industry     

Co‐(POSS#‐styrene) nanocomposites reduced the glass‐transition temperature,rubbery modulus,and melt viscosity of entangled polystyrene

The addition of polyhedral oligomeric silsesquioxane‐styrene copolymers, co(POSS#‐sty), to entangled polystyrene (PS) reduced (1) the glass‐transition temperature, T_g,blend, (2) the rubbery modulus, and (3) the melt viscosity. POSS#‐sty copolymers with # = 15, 25, and 45 wt% POSS were blended with PS. The blends were miscible and T_g,blend decreased with POSS#‐sty content. Strikingly, POSS#‐sty copolymers also reduced the melt viscosity, up to an order of magnitude reduction. The reductions of T_g,blend and melt viscosity were driven by the type of POSS#‐sty copolymer, POSS45‐sty producing the largest decrease of T_g,blend. Linear viscoelasticity and the time–temperature superposition (TTS) principle (using T_ref = T_g + 50 K to ensure iso‐frictional conditions) revealed that POSS#‐sty induced up to an order of magnitude reduction of the rubbery modulus G_e. The increase of free volume f_g promoted by POSS#‐sty induced the reduction of T_g,blend and G_e, as revealed by TTS analysis. The increase of free volume promoted by POSS#‐sty induced chain intercalation (TEM showed that POSS domains were smaller than the molecular mesh) and these are key factors for the chain disentanglement with the consequent rubbery modulus and melt viscosity reductions. The use of low‐molecular weight polystyrene alone will not produce increase of free volume and tube dilation. POLYM. ENG. SCI., 59:2377–2386, 2019. © 2019 Society of Plastics Engineers     

Characterization and CO2 sorption properties of poly[methacryloxypropylheptacyclopentyl‐T8‐silsesquioxane‐ co‐3‐methacryloxypropyltris(trimethylsiloxy)silane]

Poly[methacryloxypropylheptacyclopentyl‐T8‐silsesquioxane (MAPOSS)‐co‐3‐methacryloxypropyltris(trimethylsiloxy)silane (SiMA)] was synthesized through free radical polymerization. The physical and carbon dioxide (CO₂) sorption properties of the copolymer membranes were investigated in terms of the MAPOSS content. As the MAPOSS content increases, the membrane density increased, suggesting a decrease in the fractional free volume. In addition, the thermal stability was improved with increasing the MAPOSS content. These are because of the polyhedraloligomericilsesquioxane (POSS) units that restrict the high mobility of poly(SiMA) segments. The glass transition temperature, T_g of the copolymers was single T_g based on the differential scanning calorimetry, suggesting that the copolymers were random and not phase separation. Based on the CO₂ sorption measurement, the POSS units play a role in reducing Henry's dissolution by suppressing the mobility of the poly(SiMA) component, while POSS units increase the nonequilibrium excess free volume, which contributes to the Langmuir dissolution. Based on these results, the introduction of MAPOSS unit is one of the effective ways to improved the thermal stability and CO₂ sorption property due to the enhancement of the polymer rigidity. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and properties of fluorinated bis‐benzocyclobutene‐terminated arylene ether monomers

Four novel bis‐benzocyclobutene‐endcapped arylene ether monomers, 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane (BOPP3FE), 1,1′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1‐(3′,5′‐ditrifluoromethyl)phenyl‐2,2,2‐trifluoroethane(BOPP9FE), 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐1,1,1,3,3,3‐hexfluoropropane (BOP6FP), and 2,2′‐bis[4‐(4′‐benzocyclobutenyloxy)phenyl]‐propane (BOPP) were prepared and characterized. All the four monomers showed similar curing behaviors under N₂ (Differential scanning calorimetry: extrapolated onset and peak temperatures at 225–229°C and 261–263°C) and demonstrated low and steady melt viscosities between 110 and 200°C, indicating their good processability. After cure, the resulting BCB resins exhibited high T_g (232–282°C) and excellent thermal stability (T_5% > 433°C). The resins also showed good mechanical properties with the flexural strengths of 68–88 MPa and the flexural modulus of 2.52–3.15 GPa. Moreover, the resins also exhibited low dielectric constants (2.58–2.88), low dissipation factors (2.7 to 8.4 × 10?4) and low water absorptions in boiling water for 24 h (0.29–0.59%). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Copolymerization and thermal behavior of methyl methacrylate with N‐(phenyl/p‐tolyl) itaconimides

This study describes the synthesis, characterization, and thermal behavior of copolymers of methyl methacrylate (MMA) and N‐p‐tolyl itaconimide (PTI)/N‐phenyl itaconimide (I). Homopolymerization and copolymerization of N‐(phenyl/p‐tolyl) itaconimide with MMA was carried out by use of various mole fractions of N‐aryl itaconimide in the initial feed from 0.1 to 0.5, using azobisisobutyronitrile as an initiator and tetrahydrofuran as the solvent. The copolymer composition was determined by ¹H‐NMR spectroscopy using the proton resonance signals attributed to –OCH₃ of MMA (δ = 3.5–3.8 ppm) and the aromatic protons (δ = 7.0–7.5 ppm) of N‐aryl itaconimide. The reactivity ratios of the monomers were found to be r₁ (PTI) = 1.33 ± 0.05/r₂ (MMA) = 0.24 ± 0.03 and r₁ (I) = 1.465 ± 0.035/r₂ (MMA) = 0.385 ± 0.005. The molecular weight of the copolymers decreased with increasing mole fraction of N‐aryl itaconimide in the copolymers. Glass‐transition temperature (T_g) and thermal stability of PMMA increased with increasing amounts of itaconimides in the polymer backbone. A significant increase in the percentage char yield at 700°C was observed on incorporation of a low mole fraction of N‐aryl itaconimides. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1195–1202, 2003     

Study on thermal enhancement mechanism of POSS‐containing hybrid nanocomposites and relationship between thermal properties and their molecular structure

In this study, a series of poly(4‐acetoxystyrene) (PAS)‐octavinyl polyhedral oligomeric silsesquioxane (POSS) blends and the polystyrene (PS)‐octavinyl POSS blends were prepared by the solution‐blending method and characterized with Fourier transform infrared (FTIR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) techniques. The results show that the glass‐transition temperature (T_g) of the PAS‐POSS blends increases at a relatively low POSS content and then decreases at a relatively high POSS content. POSS can effectively improve the thermal stability of the PAS‐POSS blends at low POSS content, and T_g of PAS‐POSS blends decreases with the increase in POSS content at relatively high POSS content. However, the T_g of the PS‐POSS blends persistently decreases even at very low POSS content. T_g change mechanism was investigated in detail by XRD, TEM, and FTIR spectra. The influence mechanism of POSS content and dispersion in composites, and parent polymer structure on thermal properties of the blends was investigated in detail. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Curing behavior and properties of benzoxazine‐co‐self‐promoted phthalonitrile polymers

A new high‐performance copolymer was successfully obtained via concerted catalysis polymerization of mono‐functional benzoxazine (P‐a) and self‐promoted 4‐aminophenoxy phthalonitrile (4‐APN) monomers. The FTIR and DSC curves of the P‐a/4‐APN in different blend ratios suggested that the monomer blends can be completely cured without the addition of curing additive. The P‐a/4‐APN copolymers were cured at relatively lower curing temperatures and time. The TGA curves revealed that the P‐a/4‐APN copolymers have good thermal stability in terms of T₅, T₁₀, and char yield. A gradual increase in the glass transition temperature (T_g) values and decline were seen in the storage modulus as the loading of 4‐APN was increased from 10 to 30 wt % in the copolymer. The SEM analyses showed that copolymer's fracture surface is dendritic, showing the stress has been dispersed to a certain extent. The study revealed that the poly(P‐a/4‐APN) copolymer have much better thermal stabilities than the poly(P‐a), and the prepared copolymer can be used as a high‐performance thermosetting resin. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46578.     

Poly(vinyl pyrrolidone‐co‐octavinyl polyhedral oligomeric silsesquioxane) hybrid nanocomposites: Preparation,thermal properties,and Tg improvement mechanism

A series of poly(vinyl pyrrolidone‐co‐octavinyl polyhedral oligomeric silsesquioxanes) (PVP‐POSS) organic–inorganic hybrid nanocomposites containing different percentages of POSS were prepared via free radical polymerization and characterized by FTIR, high‐resolution ¹H‐NMR, solid‐state ²⁹Si‐NMR, GPC, DSC, and TGA. POSS contents in these nanocomposites can be effectively controlled by varying the POSS feed ratios which can be accurately quantified by FTIR curve calibration. On the basis of ²⁹Si‐NMR spectra, average numbers of reacted vinyl groups of each octavinyl‐POSS macromer are calculated to be 5–7, which depends on POSS feed ratios. Both GPC and DSC results indicate that these nanocomposites display network structure and the degree of crosslinking increases with the increase of the POSS content. The incorporation of POSS into PVP significantly improves their thermal properties (T_g and T_dec) primarily due to crosslinking structure and dipole–dipole interaction between POSS cores and PVP carbonyl groups. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Low‐κ nanocomposite films based on polyimides with grafted polyhedral oligomeric silsesquioxane

Nanocomposites of polyimides (PI) with covalently grafted polyhedral oligomeric silsesquioxane (R₇R′Si₈O₁₂ or POSS) units were prepared by thermally‐initiated free‐radical graft polymerization of methacrylcyclopentyl‐POSS (MA‐POSS) with the ozone‐pretreated poly[N,N′‐(1,4‐phenylene)‐3,3′,4,4′‐benzophenonetetra‐carboxylic amic acid] (PAA), followed by thermal imidization. The chemical composition and structure of the PI with grafted methacrylcyclopentyl‐POSS side chains (PI‐g‐PMA‐POSS copolymers) were characterized by nuclear magnetic resonance (NMR), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). The POSS molecules in each grafted PMA side chain of the amorphous PI films retained the nanoporous crystalline structure, and formed an aggregate of crystallites. The PI‐g‐PMA‐POSS nanocomposite films had both lower and tunable dielectric constants, in comparison with that of the pristine PI films. Dielectric constants (κ's) of about 3.0–2.2 were obtained. The present approach offers a convenient way for preparing low‐κ materials based on existing PI's. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006