Viscometric Analysis of Miscibility and Interactions for Binary,Ternary Polycarbonate/Brominated Polystyrene + Chloroform Systems at Different Temperatures

Viscosities of ternary systems consist of polycarbonate (PC)/brominated polystyrene (PBrS) in chloroform and their corresponding binary systems were measured at different temperatures (20, 25, and 30°C). All the measurements were carried out at the concentration ranges of 0.1–0.6 g·dL^?1. The mass ratio of PC to PBrS was selected as 75:25, 50:50, and 25:75 in the ternary solutions. Two empirical expressions of Huggins and Kraemer equations with three-parameters were used for reproducing of the experimental viscosity data. The fitting parameters were obtained for the corresponding temperatures. The miscibility criteria on the basis of the sign of Δ[η]_m based on the difference between experimental and ideal values of [η]_m, was calculated by applying the Garcia et al., theoretical equation. The effect of temperature on the viscosity data was also studied. The results from this method were correlated with the miscibility data obtained for the same system by differential scanning calorimeter (DSC) findings.     

Polystyrene/decahydronaphthalene/propane phase equilibria and polymer conformation properties from intrinsic viscosities

The influence of dissolved propane (up to 31.2 wt %) on the phase equilibria of 5 wt % polystyrene (PS) dissolved in 66/34 wt % trans/cis‐decahydronaphthalene (DHN) was measured over the temperature range of 323–423 K. A suitable temperature, pressure, and propane composition operating space was defined to measure intrinsic viscosities of a single fluid phase. Intrinsic viscosities of PS in cosolvent mixtures of propane and trans/cis‐DHN were measured between 323 and 423 K and between 70 and 208 bar. The addition of propane to the isomeric mixture of DHN resulted in a decreased solvent quality for PS, causing a contraction of the PS coil. The most dramatic decrease in solvent quality with the addition of propane occurred at 323 K and 70 bar with approximately a 36% reduction in the viscometric radius with the addition of 45 mol % propane to DHN. At 423 K, the solvent quality was less sensitive to the addition of propane and only a 13% reduction in the viscometric radius was observed at 70 bar and 45 mol % propane in DHN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Application of AM SURE™ resin to solid-phase peptide synthesis

A core-shell structure was found in AM SURE™ resin, in which most amino groups were located at the skin layer. The AM SURE™ resin revealed better synthetic efficiency, compared to the noncore-shell type resin in the synthesis of the fragment 65-74 of acyl carrier protein, the fragment 27-35 of HIV (human immunodeficiency virus) fusion inhibitor (T-20) and the Jung-Redemann 10-mer.     

Anomalies of Glass Transition: Manifestation in fullerene core polystyrene stars

Segmental dynamics around T_g in the 4- and 6-arm fullerene (C₆₀) core star-like polystyrenes with different preset arm lengths was studied by DSC as compared to that in the linear PS and PS/C₆₀ blend. The anomalies in glass transition behavior were found for the stars including both suppression and facilitation of segmental motion, and pronounced dynamic heterogeneity within a transition range. The results are interpreted in terms of breakdown of intermolecular cooperativity of segmental motions and PS-C₆₀ interactions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Cold crystallization behavior of polyamide 6 in PS‐g‐PA6 graft copolymers

TEM micrographs show that the PA grafts of PS‐g‐PA6 graft copolymers, which are obtained directly by extracting homo‐PA6 out from the homo‐PA6/PS‐g‐PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50–60 nm. This article reports on a unique crystallization behavior of the PA6 grafts in PS‐g‐PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 65–73, 2010     

Stereospecific styrene polymerization and ethylene–styrene copolymerization with titanocenes containing a pendant amine donor

A series of monocyclopentadienyl titanium complexes containing a pendant amine donor on a Cp group ( A = CpTiCl₃, B = Cp^NTiCl₃, C = Cp^NTiCl₂TEMPO, for Cp = C₅H₅, Cp^N = C₅H₄CH₂CH₂N(CH₃)₂, and TEMPO = 2,2,6,6‐tetramethylpiperidine‐N‐oxyl) are investigated for styrene homopolymerization and ethylene–styrene (ES) copolymerization. When activated by methylaluminoxane at 70 °C, complexes with the amine group ( B and C ) are active for styrene homopolymerization and afford syndiotactic polystyrene (sPS). The copolymerizations of ethylene and styrene with B and C yield high‐molecular weight ES copolymer, whereas complex A yields mixtures of sPS and polyethylene, revealing the critical role that the pendant amine has on the polymerization behavior of the complexes. Fractionation, NMR, and DSC analyses of the ES copolymers generated from B and C suggest that they contain sPS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1579–1585, 2010     

A facile strategy to modify TiO2 nanoparticles via surface‐initiated ATRP of styrene

A core‐shell hybrid nanocomposites, possessing a hard core of nano titanium dioxide (n‐TiO₂) and a soft shell of brushlike polystyrene (PS), were successfully prepared by surface‐initiated atom transfer radical polymerization (ATRP) at 90 °C in anisole solution using CuBr/PMDETA as the catalyst, in the presence of sacrificial initiator. FTIR, ¹H NMR, XPS, TEM, SEM, TGA, and DSC were used to determine the chemical structure, morphology, thermal properties, and the grafted PS quantities of the resulting products. TEM images of the samples provided direct evidence for the formation of a core‐shell structure. The thermal stabilities of the grafted polymers were dramatically elevated relative to that of pristine PS according to TGA results. DSC results demonstrated that the TiO₂‐PS nanocomposites exhibited higher glass transition temperature (T_g) compared with pristine PS. The molecular weights of the free polymers formed by sacrificial initiator, which were similar to that of surface‐attached polymers were measured by GPC instrument which showed that the molecular weights of PS were well controlled with a relatively narrow polydispersity index (PDI < 1.2). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1782–1790, 2010     

Phosphorus ligands for iron(III)‐mediated ATRP of styrene via generation of activators by monomer addition

Styrene polymerization via generation of activators by monomer addition (GAMA) for atom transfer radical polymerization (ATRP) has been examined extensively with bulk FeX₃ and FeX₂ at 110 °C in conjunction with various phosphorus‐bearing ligands. It was found that GAMA possesses advantages over normal ATRP. Most importantly, narrower polydispersity index (PDI) values were observed from the styrene polymerizations with Fe(III) over those with Fe(II). Every instance of 2‐(diphenylphosphino)‐N,N′‐dimethyl‐[1,1′‐biphenyl]‐2‐amine and 2‐(diphenylphosphino) pyridine with the Fe(III) system were controlled excellently without addition of any radical initiator or reducing agent additives. Initiator type was found to exert a significant factor to influence on the controllability of polymerization. The initiation of 1‐phenylethyl chloride and methyl‐2‐chloropropionate gave rise to formation of polymers with narrow PDI (1.05–1.20), whereas those from 1‐phenylethyl bromide increased to 1.35. The GAMA of bulk styrene exhibited the best performance in terms of both rate and controllability compared with toluene and anisole. Both formation of block copolymer from the macroinitiator and efficient perturbation of polymerization with 2,2,6,6‐tetramethylpiperidine 1‐oxyl provided firm evidence to support the living and radical characteristics for the GAMA of styrene. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 144–151, 2010     

Investigation of clay modifier effects on the structure and rheology of supercritical carbon dioxide‐processed polymer nanocomposites

Superior property enhancements in polymer–clay nanocomposites can be achieved if one can significantly enhance the nanoclay dispersion and polymer–clay interactions. Recent studies have shown that nanoclays can be dispersed in polymers using supercritical carbon dioxide (scCO₂). However, there is need for a better understanding of how changing the clay modifier affects the clay dispersability by scCO₂ and the resultant nanocomposite rheology. To address this, the polystyrene (PS)/clay nanocomposites with “weak” interaction (Cloisite 93A clay) and “strong” interaction (Cloisite 15A clay) have been prepared using the supercritical CO₂ method in the presence of a co‐solvent. Transmission electron microscopy images and small‐angle X‐ray diffraction illustrate that composites using 15A and 93A clays show similar magnitude of reduction in the average tactoid size, and dispersion upon processing with scCO₂. When PS and the clays are coprocessed in scCO₂, the “dispersion” of clays appears to be independent of modifier or polymer–clay interaction. However, the low‐frequency storage modulus in the scCO₂‐processed 15A nanocomposites is two orders of magnitude higher than that of 93A nanocomposites. It is postulated that below percolation (solution blended composites), the strength of polymer–clay interaction is not a significant contributor to rheological enhancement. In the scCO₂‐processed nanocomposites the enhanced dispersion passes the percolation threshold and the interactions dictate the reinforcement potential of the clay–polymer–clay network. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 823–831, 2010     

Reversible coordinative chain transfer polymerization of styrene by rare earth borohydrides,chlorides/dialkylmagnesium systems

The ability of various rare earth borohydride and chloride complexes/n‐butylethylmagnesium systems to operate styrene chain transfer polymerization in mild conditions has been assessed. Thirteen precatalysts have been considered: the rare earth trisborohydrides Ln(BH₄)₃(THF)_x (x = 3, Ln = Nd (1), La (2), Sm (3), x = 2, Ln = Y (4), Sc (5)), the rare earth chlorides LnCl₃(THF)_x (x = 3, Ln = Nd (6), La (7), Sm (8), Y (9), x = 2, Ln = Sc (10)), the mixed La(BH₄)₂Cl(THF)_2.6 (11) and the half‐lanthanidocenes Cp*Ln(BH₄)₂(THF)₂ (Ln = Nd (12), La (13)). Six systems were found to be active precatalysts for the polymerization of styrene. 1 , 2 , and 11 led to an efficient transmetalation of the growing polystyrene chain with the simultaneous occurrence of βH elimination, whereas 7 , 12 , and 13 led to catalyzed chain growth behavior. It is noteworthy that the catalyzed chain growth obtained with 12 and 13 occurs with significant stereoselectivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 802–814, 2010