Polyimide/polyoxometalate copolymer thin films: synthesis,thermal and dielectric properties

A mono‐lancunary keggin‐type decatungstosilicate (SiW₁₁) polyoxometalate (POM) modified by γ‐aminopropyltriethoxysilane (KH550) was incorporated into polyimide (PI) through copolymerization. Nuclear magnetic resonance (NMR), fourier transition infrared spectroscopy (FTIR), and wide angle X‐ray diffraction (WAXD) were used to characterize the structure and composition of the polyoxometalate–organosilane hybrid (SiW₁₁KH550) and PI/SiW₁₁KH550 copolymers. The differential scanning calorimetry (DSC) studies indicate that the glass transition temperature (T_g) of PI/SiW₁₁KH550 copolymers increases from 330°C (for neat PI) to 409°C (for the copolymer sample with 10 wt% of SiW₁₁KH550). Dielectric measurement showed that both the dielectric constant and the dielectric loss for the copolymer thin films decreased with the increase in SiW₁₁KH550 content, and the dielectric constant and dielectric loss values decreased to 2.1 and 3.54 × 10^?3, respectively, for the copolymer sample with 10 wt% of SiW₁₁KH550. The incorporation of SiW₁₁KH550 into polymer matrices is a promising approach to prepare PI films with a low dielectric constant and low dielectric loss. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Ethylene/Norbornene Copolymerization with iPr(Cp)(Flu)ZrCl2 Catalyst: Effect of MAO Cocatalyst and 3rd Monomer

The copolymerization of ethylene and norbornene (N) was carried out with iPr(Cp)(Flu)ZrCl₂ catalyst and modified methylaluminoxane (MMAO) cocatalyst. The catalytic activity was dependent on the structure of MMAO, i.e., MMAO-4 exhibited higher catalyst activity than MMAO-3A containing more i-butyl groups. The glass transition temperature (T_g) and the composition of the produced copolymer were not affected by MMAO type. With styrene derivatives as 3^rd monomer, T_g of copolymer increased while the catalytic activity decreased. With the addition of 3^rd monomer, not only the content of 3^rd monomer but also the content of N increased.     

Copolymerization of N-Vinylcarbazole with 2-Dimethylaminoethyl Methacrylate

The thermal copolymerization of N-vinylcarbazole (VCz) with 2-dimethylaminoethyl methacrylate (DMAEM) initiated by α,α′-azobisisobutyronitrile (AIBN) in solution in tetrahydrofuran at 60°C has been studied. Different compositions of copolymer were prepared and characterized by UV, IR, and ¹H-NMR spectroscopy, viscosity measurements, and thermal studies. The estimation of the composition of VCz and DMAEM in the copolymer was carried out by UV spectroscopy. The reactivity ratio of VCz (r ₁) and DMAEM (r ₂) was determined by the methods of Mayo and Lewis, Kelen and Tüdös, and Tidwell and Mortimer.     

Free Radical Copolymerization of N‐(4‐Carboxyphenyl)maleimide with Hydropropyl Methacrylate

Abstract

The free radical copolymerization of N‐(4‐carboxyphenyl)maleimide (CPMI) (M₁) with hydropropyl methacrylate (HPMA) (M₂) was carried out with 2,2′‐azobis(isobutyronitrile) (AIBN) as an initiator in ethyl acetate at 75°C. The composition of copolymer prepared at low conversion was determined by elemental analysis. The monomer reactivity ratios were found to be r ₁?=?0.31 and r ₂?=?1.11 as determined by the YBR equation. The number‐average molecular weight and polydispersity were determined by gel permeation chromatography (GPC). Furthermore, the solvent effect on this copolymerization system was also investigated. The resulting copolymer was characterized by FTIR and ¹H‐NMR spectroscopy. The thermal stability of copolymers was determined by thermogravimetric analysis (TGA). It was found that the copolymer shows step‐by‐step degradation, the initial decomposition temperature (T _i), and final decomposition temperature (T _f) increased with increasing the component of CPMI in copolymer.     

RING OPENING COPOLYMERIZATION OF SUCCINIC ANHYDRIDE-ETHYLENE OXIDE BY Al(Ⅲ) ORGANOMETALLIC CATALYSTS

Ring opening copolymerization of succinic anhydride (SA) with ethylene oxide (EO)was successfully carried out by using a series of aluminum-based catalyst in 1,4-dioxane at62±2℃. The results showed that in-situ AlR_3-H_2O (R=ethyl, iso-butyl) catalysts gavehigher molecular weight (M_w～10~4), while Al(OR)_3 catalysts gave the higher alternatingcopolymer structure with slightly lower molecular weight. The in-situ AlR_3-H_2O systemshave been evaluated in more detail for the reaction which showed the optimum H_2O/Almolar ratio to be 0.5. The copolymers with different composition (F_(SA)/F_(EO)= 36/64to 45/55 mol/mol) were synthesized by using different monomer feed ratio. The melt-ing point (T_m), glass transition temperature (T_g) and enthalpy of fusion (ΔH_f) of thesecopolymers are depended on the copolymer composition and in the range of 87～102℃,-12～-18℃, and 37～66J/g, respectively. The second heating scan of DSC also in-dicated that the higher alternating copolymer was more easily recrystallized. The onsetdecomposition temperature was more than 300℃ under nitrogen and influenced by thecopolymer composition.     

Block copolymerization of methylmethacrylate via ATRP method using a macroinitiator produced by ring opening polymerization: Characterization,dielectric properties,and a kinetic investigation

Poly(2-(3-methyl-3-phenylcyclobutyloxirane-co-?-caprolactone) [P(PCBO-co-?-CL)] was synthesized by ring opening polymerization (ROP) of 2-(3-methyl-3-phenylcyclobutyloxirane and ?-caprolactone (?-CL) using benzyl alcohol as the initiator and Sn(Oc)₂ as the catalyst. To produce a macroinitiator from copolymer with hydroxyl end group was carried out reaction of acylation with choloroacetyl chloride. The molecular structures of copolymers were confirmed by FT-IR, ¹H-NMR spectroscopies and gel permeation chromatography (GPC). A kinetic series of methyl methacrylate (MMA) via ATRP method were studied in the presence of this macroinitiator and using CuBr/2,2′-bipyridine (bpy) as catalyst at 110°C. The kinetic study showed that the polymerization proceeded in a controlled way up to high conversions and the number-average molecular weight (M_n) increased depending on time. The thermal properties of copolymers were evaluated by TGA and DSC measurements. The temperature and frequency dependence of dielectric constant (?) and dielectric loss factor (?″) of P[(PCBO-co-?-CL)-b-PMMA] and that of doped with different concentration of EuCl₃ were investigated between the frequency of 100–2000 Hz and temperature range (300–430 K). Also, the ac conductivity has been measured to see the effect of frequency and temperature.     

Low temperature splinting activity and catalytic behavior of nano Ag doped sulphamicacid bridged diblock copolymer

A novel silver nanoparticle doped diblock copolymer was synthesized by a 3‐step process via bulk polymerization process under nitrogen atmosphere. The above prepared polymer is characterized by FTIR spectroscopy, fluorescence emission spectroscopy, circular dichroism (CD), HRTEM, and FESEM. The sulphamicacid end capped poly(ε‐caprolactone) (P1) system exhibited higher tensile strength than the sulphamicacid bridged diblock copolymer (P2) and nano Ag doped sulphamicacid bridged diblock copolymer (P3) systems. The splinting activity of the diblock copolymers was tested and confirmed the low temperature splinting activity of the diblock copolymer. The Ag nanoparticle catalyzed catalytic reduction of p‐nitrophenol (NiP) was tested, and the apparent rate constant (k_app) was determined as 7.36 × 10⁻³ sec⁻¹. The thermal studies were carried out by DSC and TGA methods. The TGA study declared that the P1 system has higher degradation temperature than the P2 and P3 systems. The P1 system has higher melting temperature (T_m) (75.5°C) than the P2 and P3 systems. The CD study indicated that the conformation of sulphamicacid was not changed even after the formation of nano Ag doped sulphamicacid bridged diblock copolymer.     

Molecular dynamics of poly(ATRIF) homopolymer and poly(AN-co-ATRIF) copolymer investigated by dielectric relaxation spectroscopy

Aiming to develop new dielectric polymers containing CN and F groups with strong dipole moments, a novel copolymer of acrylonitrile (AN) and 2,2,2-trifluoroethyl acrylate (ATRIF) was synthesized in acetonitrile by free radical process as well as the respective homopolymer (poly(ATRIF)). The copolymer’s composition and microstructure were analyzed by FTIR, ¹H and ¹³C NMR spectroscopy and SEC. The molar incorporation of AN determined in the copolymer by NMR was 58 mol%. Thermogravimetric analysis of poly(AN-co-ATRIF) copolymer showed good thermal stability comparatively to the fluorinated homopolymer.Both copolymer, poly(AN-co-ATRIF), and homopolymer, poly(ATRIF), were dielectrically characterized over a frequency range from 10⁻¹ to 10⁶ Hz, and in a temperature range from 223 to 393 K. The dominating relaxation process detected in both materials is the α-relaxation, associated with the dynamic glass transition. A VFTH temperature dependence of the relaxation times (τ) was found for both materials, as characteristic of cooperative processes, from which the respective glass transition temperatures (T_g(τ = 100 s)) were estimated, which differ ∼40 K, the one of the copolymer being higher (307 K) in accordance to the calorimetric analysis. This effect was attributed to a higher stiffness of the backbone in the copolymer originated by the inclusion of the acrylonitrile groups. Both relaxation functions have the same breath of relaxation times allowing constructing a single master curve, indicating similar non-exponential character. A less fragile behavior was found for the copolymer. This was rationalized in a more straightforward way by the free volume approach instead from a correlation between fragility and intermolecular coupling. It was found that in the copolymer the free volume increases at a lower rate with the temperature increase. It was inferred from the VFTH temperature dependence of the dc conductivity and low values of the decoupling index that ion motion is significantly influenced by the dynamics of the α-process.     

Synthesis,Characterization, and Reactivity Ratios of Phenyl Methacrylate-N-vinyl-2-pyrrolidone Copolymers

Free radical solution copolymerization of phenyl methacrylate and N-vinyl-2-pyrrolidone was carried out using benzoyl peroxide in 2-butanone solution at 70°C. The composition of the copolymer was determined using ¹H-NMR spectra by comparing the intensities of aromatic protons to that of total protons. The results were used to calculaie the copolymerization reactivity ratios by both the Fineman-Ross (F-R) and Kelen-Tüdös (K-T) methods. The reactivity ratios are r ₁ = 4.49 ± 1.27 and r ₂ = 0.05 ± 0.09 as determined by the K-T method. These values are in good agreement with those determined by the F-R method. The FT-infrared and ¹³C-NMR spectra of the copolymer are discussed.     

Living Carbocationic Copolymerizations. V. Synthesis of Isobutylene/p-Methylstyrene Copolymers with the Constant Copolymer Composition Technique in the Leidenfrost Reactor

Abstract

Living copolymerization of the isobutylene (IB)-p-methylstyrene (pMeSt) monomer pair in combination with the constant copolymer composition (CCC) technique produces high molecular weight ( M _n ≈ 100,000 g·mol^?1) and narrow molecular weight distribution ( M _w/ M _n ≈ 1.45) compositionally uniform IB/pMeSt copolymer molecules in the industrially important IB/pMeSt = 97–99/3–1 mol% composition range. Syntheses were carried out with TiCl₄ coinitiator in n-butyl chloride homogeneous solution at ?85°C by the use of the Leidenfrost reactor (i.e., by direct cooling of the charge with liquid nitrogen). In order to carry out the CCC technique it was necessary to obtain reliable copolymerization reactivity ratios. These investigations led to r_IB = 0.5 ± 0.1 and r _pMeSt = 10 ± 4. The attainment of CCC and living copolymerization conditions has been quantitatively demonstrated by dedicated diagnostic plots. Specifically, the attainment of CCC conditions was proven by the analysis of composite rate plots (comonomers input and corresponding copolymer formed versus time) and composition plots (comonomer composition in feed and copolymer formed versus weight of copolymer formed, W _p), and living copolymerization was proven by linearly ascending number-average molecular weight of copolymer ( M _n) versus W _p plots starting at the origin.     

N‐Vinylpyrrolidone and Ethoxyethyl Methacrylate Copolymer: Synthesis,Characterization and Reactivity Ratios

Free radical copolymerization of N‐vinyl‐2‐pyrrolidone with 2‐ethoxyethyl methacrylates was carried out with 2,2′‐azobisisobutyronotrile as an initiator in 1,4‐dioxane. The resulting copolymer was characterized by FTIR, H¹‐NMR and C¹³‐NMR spectroscopic techniques thermal properties of copolymer were determined by DSC and TGA. The reactivity ratios of the monomers were computed by the Fineman‐Rose (F‐R), Kelen‐Tudos (K‐T) and extended Kelen‐Tudos (EK‐T) method at lower conversion, using the data obtained from both FTIR and elemental analysis studies; the results are in good agreement with each other. The average reactivity ratio, Alfrey‐Price Q and e values were found to be r ₁=0.769, r ₂=0.266 and Q ₁=0.0859, e ₁=0.4508, respectively for NVP/EOEMA copolymer. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on obtained reactivity ratio. The number average molecular weight and polydispersity were determined by GPC.     

Synthesis of gradient copolymers with simultaneously tailor‐made chain composition distribution and glass transition temperature by semibatch ATRP: From modeling to application

Recent studies have demonstrated that gradient copolymers exhibit unique thermal properties. Although these properties can be determined by copolymer composition, other factors such as chain and sequence lengths and their distributions can also influence them. Accordingly, the synthesis of gradient copolymers requires simultaneously tailor‐made chain structure and thermal properties. In this work, we carried out a systematic study on the preparation of poly(methyl methacrylate‐grad‐2‐hydroxyethyl methacrylate) [poly(MMA‐grad‐HEMA)] with synchronously tailor‐made chain composition distribution and glass transition temperature (T_g) through semibatch atom transfer radical polymerization. First, a comprehensive model for simultaneously predicting gradient copolymer microstructure and T_g was presented using the concept of pseudo‐kinetic rate coefficients and Johnston equation. The model was validated by comparing simulation results with the classical reference data. Furthermore, the model was used to guide the experimental synthesis of the poly(MMA‐grad‐HEMA) gradient copolymers potentially as excellent damping material. The thermal properties of these gradient copolymer samples were evaluated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel synthesis of biodegradable amphiphilic linear and star block copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol)

Biodegradable, amphiphilic, diblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol) (PCL‐b‐PEG), triblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol)‐block‐poly(ε‐caprolactone) (PCL‐b‐PEG‐b‐PCL), and star shaped copolymers were synthesized by ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) or star poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. For the same PCL chain length, the materials obtained in the case of linear copolymers are viscous whereas in the case of star copolymer solid materials are obtained with low T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3975–3985, 2007     

Synthesis and characterization of conducting copolymer of (<Emphasis Type="Italic">N</Emphasis><Superscript>1</Superscript>,<Emphasis Type="Italic">N</Emphasis><Superscript>3</Superscript>-bis(thiophene-3-ylmethylene)benzene-1,3-diamine-co-3,4-ethylenedioxythiophene)

Electrochemical copolymerization of N ¹,N ³-bis(thiophene-3-ylmethylene)benzene-1,3-diamine (TMBA) with 3,4-ethylenedioxythiophene (EDOT) was carried out in a CH₃CN/LiClO₄ (0.1 M) solvent-electrolyte via potentiodynamic electrolysis. Chemical structure of the monomer was determined by nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FTIR) spectroscopy. The resulting copolymer was characterized by cyclic voltammetry (CV), FTIR, scanning electron microscopy (SEM), and thermogravimetry analyses (TGA). Conductivity measurements of the copolymer and PEDOT (poly(3,4-ethylenedioxythiophene)) were carried out by the four-probe technique.     

Study of synthesis and properties of tetrafluoroethylene–propylene copolymers

Bulk copolymerization of tetrafluoroethylene (TFE) with propylene (P) initiated by tert-butyl peroxybenzoate (TBPB) in the temperature interval 323–363 K, monomer pressure from 2 to 9 MPa, and TFE and P molar ratio from 20/80 to 90/10 was carried out. The effect of these reaction conditions on the yield, molecular weight, and polymer composition of the copolymer synthesized was studied. Rubber-like alternating copolymers in a wide range of monomer compositions of TFE and P (from 40 to 80 mol %) were obtained. The reaction proceeds in a stationary state without an induction period. Monomolecular chain transfer reaction (C_p = 5 × 10^?4) to propylene takes place. The relative reactivity ratio of P and TFE (0.15 and 0.01, respectively) and apparent activation energy E_α = 75.8 kJ/mol of the reaction were determined.     

New copolymers of a tautomerizable β‐ketonitrile monomer: Synthesis,characterization and solution tautomerism

The monomer 2‐methyl‐3‐oxo‐5‐phenyl‐4‐pentenonitrile (MOP) was prepared by reaction of ethyl cinnamate and propionitrile in alkaline mixture. This monomer exhibits three possible tautomeric forms. The tautomeric equilibria of MOP and its copolymers with styrene in different solvents were analyzed by ¹H NMR spectroscopy. The bulk and solution radical copolymerization initiated with azobisisobutyronitrile was carried out at 60 °C. The products were characterized by ¹H NMR, ¹³C NMR, HSQC NMR, HMBC NMR, and FTIR spectroscopies. The weight‐average molecular weight and polydispersity index were analyzed with size exclusion chromatography. The monomer reactivity ratios were obtained with the Fineman‐Ross method, obtaining a value of r₁r₂ = 0.286. MOP copolymer composition as well as the nature of the solvent significantly affected the tautomeric equilibrium. Regression analysis of the copolymer composition with solvatochromic parameters showed a good linear correlation, as quantitatively expressed by means of the linear solvation energy relationship using the empirical set of Kamlet‐Taft solvent parameters. This behavior could be attributed to polymer–polymer or polymer‐solvent interactions prevalent in solvents of different polarity, which are responsible for changes in macromolecular chain conformations, as confirmed by FTIR and viscometric studies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Comprehensive 2D NMR analysis: Acrylonitrile/ethyl methacrylate copolymers synthesized by ATRP at ambient temperature

Copolymerization of acrylonitrile and ethyl methacrylate using atom transfer radical polymerization (ATRP) at ambient temperature was carried out under optimized reaction conditions using 2‐bromopropionitrile as initiator and CuBr/2,2′‐bipyridine as the catalyst system. The copolymer composition, obtained from ¹H NMR spectra, were used to determine the monomer reactivity ratios (r_A = 0.68 and r_E = 1.75) involved in ATRP. Two‐dimensional NMR (heteronuclear single quantum correlation and total correlated spectroscopy) experiments were employed to resolve the highly overlapping and complex ¹H and ¹³C{¹H} NMR spectra of copolymers. The complete spectral assignments of the quaternary carbons viz. carbonyl and nitrile carbons were done with the help of heteronuclear multiple bond correlation spectra. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2955–2971, 2006     

Prediction dielectric constant of different ternary liquid mixtures at various temperatures and compositions using artificial neural networks

Artificial neural networks (ANNs) were successfully developed for the modeling and prediction dielectric constant of different ternary liquid mixtures at various temperatures (?10°C?≤?t?≤?80°C) and over the complete composition range (0?≤?x ₁,?x ₂,?x ₃?≤?1). A three-layered feed forward ANN with architecture 7-16-1 was generated using seven parameters as inputs and its output is dielectric constant of media. It was found that properly selected and trained neural network could fairly represent the dependence of dielectric constant of different ternary liquid mixtures on temperature and composition. For the evaluation of the predictive power of the generated ANN, an optimized network was applied for predicting the dielectric constant in the prediction set, which were not used in the modeling procedure. Squared correlation coefficient (R ²) and root mean square error for prediction set are 0.9997 and 0.2060, respectively. The mean percent deviation (MPD) for the property in the prediction set is 0.8892%. The results show nonlinear dependence of dielectric constant of ternary mixed solvent systems on temperature and composition is significant.     

Characterization of ethylene/propylene copolymers by means of a GPC-4D technique

Copolymer composition and comonomer distribution are important magnitudes in polymer material that have a big effect on different kind of properties and consequently there are several ways to study.In this work several ethylene/propylene copolymers synthesized with two different metallocene catalysts and a Ziegler–Natta catalyst and covering a wide composition range were studied. Characterization was carried out by nuclear magnetic resonance (¹³C NMR) and by gel permeation chromatography with 4 detectors (GPC-4D): refractive index, viscosity, multi-angle light scattering and infrared detectors.Different behaviour in the comonomer distribution along the molecular weight was obtained for metallocene and for ZN copolymers as expected due to the differences between these catalytic systems. Nevertheless, Ziegler–Natta copolymers present more homogeneous comonomer distribution due to the synthesis method. Study of conformation of chains in solution was improved by defining the scaling law of R_g against the number of repeat units because it avoids the effect of the repetitive unit size. Both metallocene copolymer sets show similar dependence of q value with the copolymer composition, however Ziegler–Natta copolymers show different behaviour with q values independent on copolymer composition. This different behaviour has been related with the effects of the heterogeneity of the ethylene distribution and of the molecular weight of the samples.