Preparation and characterization of star ABC triblock copolymer of ethylene oxide,styrene and methyl methacrylate

A universally significant method,which combines the anionic polymerization with photoinduced charge transfer polymerization,for preparation of soluble star ABC triblock copolymer of ethylene oxide,styrene and methyl methacrylate,was described.The poly(ethylene oxide) (PEO) block was formed by initiation of phenoxy an-ions using p-aminophenol protected by Schiff's base as the parent compound Then the charge transfer system composed of PEO chains with deprotected-amino end groups and benzophenone initiated the polymerization of styrene and methyl metnacrylate sequentially under UV irradiation.The formed star triblock copolymer of styrene,ethylene oxide and methyl methacrylate could be purified by thin-layer chromatography (TLC) and characterized by IR,1H NMR,GPC (gel permeation chromatogrphy) and PGC (pyrolysis gas chromatography).     

Investigation of microstructure of the acrylonitrile‐styrene copolymers by 2‐D NMR spectroscopy

Acrylonitrile‐Styrene (A/S) copolymers were prepared by photopolymerization using uranyl nitrate ion as initiator. The copolymer compositions were determined by elemental analysis, and comonomer reactivity ratios were determined by nonlinear least squares error in variables method (EVM). The complete spectral assignment of the ¹³C and ¹H‐NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and by the two dimensional ¹³C‐¹H Heteronuclear Single Quantum Correlation (HSQC) and TOCSY experiments. The methylene and methine carbon resonance show both stereochemical and compositional sensitivity. The 2‐D Total Correlated Spectroscopy (TOCSY) experiment was used to ascertain the various geminal coupling between the methylene protons. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 721–727, 1999     

Poly(acrylonitrile‐co‐methyl methacrylate‐co‐methyl acrylate): Synthesis and stereosequence distribution analysis by 2D NMR

Terpolymers of acrylonitrile (A), methyl methacrylate (B), and methyl acrylate (M) were synthesized under optimized atom transfer radical polymerization conditions using 2‐bromopropionitrile as an initiator and CuBr/dinonyl bipyridine as a catalyst. Variation of the feed composition led to terpolymers with different compositions. Composition of synthesized terpolymers were calculated from quantitative ¹³C{¹H} NMR spectra. Number average molecular weight and polydispersity index were determined by gel permeation chromatography. The overlapping and broad signals of the terpolymers were assigned completely to various compositional and configurational sequences by correlation of one‐dimensional ¹H, ¹³C{¹H}, and distortionless enhancement by polarization transfer and two‐dimensional heteronuclear single quantum coherence (HSQC) and total correlation spectroscopy (TOCSY). 2D HSQC NMR study shows one to one correlation between carbon and proton signals, while 2D TOCSY spectra were used to confirm 1, 2 bond geminal couplings between nonequivalent protons of same methylene group. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 25–37, 2009     

Molecular weight-dependence of free volume in polystyrene studied by positron annihilation measurements

Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o-Ps) lifetime (τ₃) and intensity (I₃) were measured from 5°C to T_g + 30°C for each sample. From these data, the free volume hole size, 〈v_f(τ₃)〉, and fractional free volume h_ps=CI₃〈v_f(τ₃)〉 were calculated. The temperature dependences of τ₃, 〈v_f(τ₃)〉 and h_ps show a discrete change in slope at an effective glass transition temperature, T_g,ps, which is measurably below the conventional bulk T_g. This suggests that τ₃ is sensitive to large holes which retain their liquid-like mobility in the glassy state. Good agreement was found for T > h_g,ps between h_ps and the theoretical free volume fraction h_th deduced from experimental P-V-T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below T_g,ps, deviations between h_ps and h_th are observed, h_ps falling increasingly below h_th as temperature decreases. Whereas h_ps and h_th depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha-Somcynsky h-function in the melt, gives improved agreement with h_ps in the glassy state. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of linear ABC triblock copolymer of ethylene oxide,methyl methacrylate,and styrene

A well‐defined linear ABC triblock copolymer of ethylene oxide (EO), methyl methacrylate (MMA), and styrene (St) was prepared by sequential living anionic and photo‐induced charge transfer polymerization (CTP) using p‐aminophenol as parent compound. In the first step, the diblock copolymer of PEO‐b‐PMMA with a protected aniline end group at PEO end was prepared by initiating of phenoxo‐anion the polymerization of EO and MMA successively, then the diblock copolymer of PEO‐b‐PMMA via deprotection of aniline at PEO end constituted a binary initiation system with benzophenone (BP) by charge transfer complex mechanism to initiate the polymerization of St under UV‐irradiation. The GPC and NMR measurements support that in copolymerization, either in the first or second step, neither homopolymer nor side reactions, such as chain transfer or chain termination, was found. The effect of the concentration of PEO_a‐b‐PMMA and St, and the polarity of solvent on the polymerization rate (R_p) of CTP is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 825–833, 1999     

Study of free volume in high-vinyl polybutadiene/cis-polyisoprene blends using positron annihilation spectroscopy

High-Vinyl Polybutadiene (HVBD)/cis-Polyisoprene (CPI) blends were characterized by Differential Scanning Calorimetry (DSC) and Positron Annihilation Lifetime Spectroscopy (PALS). A single DSC glass transition temperature T_g is observed, whose composition dependence strongly deviates from additivity, and shows an apparent cusp when the weight fraction of HVBD ≈ 0.75. The free-volume hole size, V_h, and the scaled fractional free volume, h_ps/C, = I₃V_h were determined by PALS from the orthopositronium (o-Ps) intensities, I₃, and lifetimes, τ₃, over a temperature range encompassing T_g and the temperature at which “positronium bubble” formation occurs. In the glass, V_h and h_ps/C are smaller for CPI than for HVBD, but the thermal expansion coefficient for hole volume, α_f, is larger in the melt for CPI than for HVBD; thus, an iso-hole volume temperature occurs in these blends at T_iso ≈ −34°C. Above and below T_iso, V_h and h_ps/C each show a negative departure from additivity. A quantitative interpretation of the cusp in the composition dependence of T_g can be obtained, via a modified analysis of Kovacs, using free-volume quantities from PALS, with the ratio of scaling constants C_CPI/C_HVBD as an adjustable parameter. At high temperatures, the positron bubble size is smaller in CPI than in HVBD. This agrees with the observation that the thermal expansivity of hole volume, and, hence the internal pressure are larger in the equilibrium melt of CPI. The effect of e⁺-irradiation on the o-Ps intensity was investigated. I₃ decreases more rapidly in the melt as T → T_g, and then more slowly in the glass, suggesting that the effect is due to trapping of radical or ionic species which inhibit o-Ps formation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 861–871, 1998     

A positron annihilation study on the microstructure of cyanate ester resin toughened by carboxyl‐terminated butadiene‐acrylonitrile rubber system

The toughness of cyanate ester (CE) resin matrix improves significantly with the addition of carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN). The curing behavior of the system was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The results show that carboxyl groups on the CTBN chain have a slight activation effect on the CE curing reaction at the beginning of the curing process. Phase separation was found to be the main toughening mechanism for CE/CTBN composites. The existence of macro‐size pores induced by the decomposition of a small amount of the low weight molecular part of CTBN might be another toughening mechanism. It is confirmed that positron annihilation lifetime spectroscopy (PALS) is still valid in such a system where macropores filled with gas molecules exist. When a high weight percentage of CTBN (>8%) was added to CE, free‐positron annihilation was found to be the dominant annihilation process in the macropores. For CTBN weight percentage higher than 8%, the contribution of ortho‐positronium (o‐Ps) annihilation in the macropores to τ₃ and I₃ was found to be insignificant. It is effective to use PALS as a probe of free‐volume properties in such systems by determining the changes in the τ₃ and I₃ of the composite. The compatibility and interfacial adhesion of the composites can be estimated from the changes in the free‐volume properties of the composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of alkali post‐treatment on the particle morphology of soap‐free poly(methyl methacrylate‐ethyl acrylate‐acrylic acid) latices

Poly(methyl methacrylate‐ethyl acrylate‐acrylic acid) P(MMA‐EA‐AA) latices with narrow particle size distribution and “clean” particle surface were first synthesized by batch soap‐free emulsion polymerization, and the latex particles with anomalous morphology were obtained by alkali post‐treatment. Effects of treatment temperature and time, initial pH value, as well as 2‐butanone amount, on the morphology of latex particles were investigated. Results showed that anomalous structure of the dried latex particles could be easily identified using transmission electron microscopy (TEM) observation under the conditions of temperature >60°C, initial pH > 10.5 and 4.0–7.0 ml of 2‐butanone used. The higher the pH value is, the earlier the anomalous structure will occur. The volume expansion (ΔV) of the particle increased with the increase in treatment temperature and 2‐butanone amount. However, with the increase of initial pH value and treatment time, ΔV increased first and then decreased, and different maximum of ΔV values were observed based on different conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Free‐volume change during the volume phase transition of polyacrylamide gel studied by positron annihilation: Solvent‐composition dependence

Changes in the free‐volume parameters of polyacrylamide (PAAm) gels during the volume phase transition (VPT) were studied with the positron annihilation lifetime technique. The VPT was induced through the variation of the solvent composition in a mixture of acetone and water. The PAAm gels containing 0 and 4 mol % carboxyl groups in their polymer chains were adapted to compare the effect of the presence of ionic groups on the microscopic environment. The change of the free‐volume property is discussed on a nanoscopic scale, with attention paid to the interactions between the polymer chains and the solvent molecules. It is proven that the variations of the free‐volume parameters correlate significantly with the VPT phenomenon. The results of the free volume for both gels are well‐explained when an interaction parameter, ε_g, is assumed. The interpretation suggests that the state of the interactions among the components (the polymer chain, acetone, and water molecules) plays an important role in the change of the free volume of PAAm gels during the VPT. An increase of the dispersion of the free‐volume size near the VPT point was observed for the ionized PAAm gel. The broadened size distribution of the free volume of the ionized PAAm gel around the VPT point lay between those of pure water and the corresponding mixed solvent, suggesting that a local minimum of the average free‐volume size at the VPT point is caused by the increase of a specific interaction, hydrogen bonding. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 922–933, 2000     

Free‐volume change in volume phase transition of polyacrylamide gel as studied by positron annihilation: Salt dependence

Variation of free‐volume parameters—average radius size, number concentration, and size distribution—of a polyacrylamide (PAAm) gel containing 4 mol % carboxylate anions is studied during a volume phase transition (VPT) caused by a change of sodium chloride (NaCl) concentration. A positron annihilation lifetime technique is used for the determination of the free‐volume characteristics. The measurement is performed in an acetone–water 3 : 2 (v/v) [0.27 : 0.73 (mol/mol)] mixed solvent at 20°C, and the free‐volume parameters deduced from the analysis of a positron annihilation curve are utilized. An average free‐volume size of the swollen PAAm gel, ∼ 0.32 nm in radius, almost agrees with that of the mixed solvent for a corresponding salt concentration, while the size of the collapsed gel, which is ∼ 0.28 nm in radius, is smaller than that of the mixed solvent. The results for the collapsed gel indicate that the hydrogen bond plays a significant role in the nanoscopic environment. The radius of the free‐volume of the swollen PAAm gel seems to be influenced by the composition between acetone and water. An inhomogeneity of the nanoscopic structure inside the PAAm gels is discussed in terms of a dispersion of a size distribution of the free‐volume. It is concluded that a change of the nanoscopic environment of the PAAm gel during the VPT can be monitored through the free‐volume parameters obtained by the positron annihilation lifetime technique. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2634–2641, 1999     

Effect of modified graphene and microwave irradiation on the mechanical and thermal properties of poly(styrene‐co‐methyl methacrylate)/graphene nanocomposites

The effect of modified graphene (MG) and microwave irradiation on the interaction between graphene (G) and poly(styrene‐co‐methyl meth acrylate) [P(S‐co‐MMA)] polymer matrix has been studied in this article. Modification of graphene was performed using nitric acid. P(S‐co‐MMA) polymer was blended via melt blending with pristine and MG. The resultant nanocomposites were irradiated under microwave at three different time intervals (5, 10, and 20 min). Compared to pristine graphene, MG showed improved interaction with P(S‐co‐MMA) polymer (P) after melt mixing and microwave irradiation. The mechanism of improved dispersion and interaction of modified graphene with P(S‐co‐MMA) polymer matrix during melt mixing and microwave irradiation is due to the presence of oxygen functionalities on the surface of MG as confirmed from Fourier transform infrared spectroscopy. The formation of defects on modified graphene and free radicals on P(S‐co‐MMA) polymer chains after irradiation as explained by Raman spectroscopy and X‐Ray diffraction studies. The nanocomposites with 0.1 wt% G and MG have shown a 26% and 38% increase in storage modulus. After irradiation (10 min), the storage modulus further improved to 11.9% and 27.6% of nanocomposites. The glass transition temperature of nanocomposites also improved considerably after melt mixing and microwave irradiation (but only for polymer MG nanocomposite). However, at higher irradiation time (20 min), degradation of polymer nanocomposites occurred. State of creation of crosslink network after 10 min of irradiation and degradation after 20 min of irradiation of nanocomposites was confirmed from SEM studies. Copyright © 2014 John Wiley & Sons, Ltd.     

Copolymerization with depropagation: A study of α‐methyl styrene/methyl methacrylate in bulk at elevated temperatures

Previously published material on the α‐methyl styrene/methyl methacrylate (α‐MS/MMA) copolymer system at temperatures above the ceiling temperature of α‐MS has focused on low‐conversion results. Several attempts have been made to estimate copolymer reactivity ratios from experimental data, but in most cases errors are present in the determination of copolymer composition variables. In this article, the results of rigorous parameter estimations, as applied to two sets of equations developed independently by P. Wittmer (Adv Chem 1971, 99, 140–174) and H. Kruger, J. Bauer, and J. Rubner (Makromol Chem 1987, 188, 2163–2175), are discussed. Experimental data for the copolymer system at low conversions, as well as over the full conversion range, are presented, covering a temperature range of 60–140 °C. A comparison of the data trends with traditional copolymer systems indicates that the reversibility of both MMA and α‐MS must be considered when composition, polymerization rate, or molecular weight equations are being developed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1981–1990, 2000     

Stereochemical and compositional assignment of acrylonitrile/methyl methacrylate copolymers by DEPT and inverse HECTOR NMR spectroscopy

The acrylonitrile/methyl methacrylate copolymers of different monomer concentration were prepared by photo polymerization using uranyl ion as initiator. The carbon 13 and proton spectra of these copolymers are overlapping and complex. The complete spectral assignment of the ¹³C- and ¹H-NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and two dimensional ¹³C–¹H Heteronuclear Single Quantum Correlation (HSQC) experiments. The methylene, methine and the methyl carbon resonances show both stereochemical (triad level) and compositional (dyad, triad, tetrad, pentad and hexad level) sensitivity. 2D Double Quantum Filtered Correlated Spectroscopy (DQFCOSY) experiment was used to ascertain the various geminal couplings between the methylene protons. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1081–1092, 1998     

Probing the microstructure of Nafion-117 using positron annihilation spectroscopy

We report a new result on positron annihilation studies in acid- and cation-neutralized (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, UO₂²⁺, Ni²⁺) Nafion membranes using positron lifetime and Doppler-broadened annihilation radiation (DBAR) measurements. The free-volume structure is characterized using a simple quantum mechanical model of positronium (Ps) in a spherical well. Our studies indicate that formation and expansion of clusters is always associated with a change in free-volume structure resulting in smaller free-volume holes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 771–776, 1997     

Effect of thermal history on the free volume properties of semi‐crystalline poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) membranes by positron annihilation lifetime spectroscopy

Free volume properties of a series of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) membranes, which were produced by various nonisothermal crystallization processes (rapid‐, step‐, and slow‐cooling processes), were investigated using positron annihilation lifetime (PAL) spectroscopy over a temperature range of 25–90 °C. From the annihilation lifetime parameters, the temperature dependence of free volume size, amount, size distribution, and fractional free volume and thermal expansion properties of free volume were discussed. A model which assumed that amorphous phase was subdivided into mobile and rigid amorphous fractions (MAF and RAF) in the semicrystalline polymer was considered to interpret the temperature dependence of those free volume properties. Morphological observation of the semicrystalline polymer by small‐angle X‐ray scattering (SAXS) indicated that the rapid‐cooled (cold‐crystallized) membranes showed a much thinner thickness of the repeating lamellar/amorphous layers and most likely higher amount of RAF, which restrained the chain motion, than the step‐ and slow‐cooled (melt‐crystallized) membranes. The difference of free volume properties among various PHBV membranes was created according to the crystalline structure of the polymer from different thermal history. The polymer crystallized with slower cooling rate induced higher crystallinity and resulted in less free volume amount and lower fractional free volume. In addition, the thermal expansion coefficients of free volume size were affected by the crystallization rate of PHBV polymer. Larger distribution of the free volume size of melt‐crystallized membranes was observed as a result of the bimodal distribution of the lamellar periodicity and less amount of RAF than that of the cold‐crystallized membranes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 855–865, 2009     

Effect of CO2 exposure on free volumes in polystyrene studied by positron annihilation spectroscopy

Free‐volume properties, size and distribution, in amorphous polystyrene exposed to CO₂ gases have been measured as a function of pressure to 800 psi (5.5 MPa), of time, and of temperature using positron annihilation lifetime spectroscopy. The free volume increases significantly and its distribution broadens as a function of pressure. The free volume relaxes as a function of time with a characteristic time of 15 h, and 5.7 h for 400, and 800 psi, respectively, after depressurizing under vacuum. A portion of free volume created by CO₂ exposure remains permanently in the polymer after CO₂ exposure. The glass transition temperature decreases significantly as a function of CO₂ pressure from the free‐volume data and is compared with the differential scanning calorimeter results. The observed free‐volume variations as a function of pressure, time, and temperature are discussed in terms of hole expansion, creation, free‐volume relaxation, plasticization, and hole filling in amorphous polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 388–405, 2008