Polymerization of methyl methacrylate by 2‐pyrrolidinone and n‐dodecyl mercaptan

The bulk polymerization of methyl methacrylate initiated with 2‐pyrrolidinone and n‐dodecyl mercaptan (R‐SH) has been explored. This polymerization system showed “living” characteristics; for example, the molecular weight of the resulting polymers increased with reaction time by gel permeation chromatographic analysis. Also, the polymer was characterized by Fourier transform infrared spectroscopy, ¹H NMR, and ¹³C NMR techniques. The polymer end with the iniferter structures was found. By the initial‐rate method, the polymerization rate depended on [2‐pyrrolidinone]^1.0 and [R‐SH]⁰. Combining the structure analysis and the polymerization‐rate expression, a possible mechanism was proposed. n‐Dodecyl mercaptan served dual roles—as a catalyst at low conversion and as a chain‐transfer agent at high conversion. Finally, the thermal properties were studied, and the glass‐transition temperature and thermal‐degradation temperature were, respectively, 25 and 80–100 °C higher than that of the azobisisobutyronitrile system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3692–3702, 2002     

Synthesis and characterization of unsymmetrical benzonitrile‐containing polyimides: Viscosity‐lowering effect and dielectric properties

A new unsymmetrical diamine, 2‐(3‐aminophenoxy)‐6‐(4‐aminophenoxy)benzonitrile (3,4‐APBN), is synthesized via two consecutive S_NAr reactions and the temperature‐dependent reactivity of the fluorides in 2,6‐difluorobenzonitrile, whose first S_NAr reaction occurs at 70 °C and second, at 100 °C, allowing timing control of reaction sequence and circumventing the transetherification side reaction. Thus, a series of polyimides (PIs) is prepared from the polymerization of 3,4‐APBN with five common dianhydrides (6FDA, DSDA, OPDA, BTDA, and PMDA). For comparison, a second series is also prepared from two symmetrical diamines ([2,6‐bis(3‐aminophenoxy)benzonitrile (3,3‐APBN) and 2,6‐bis(4‐aminophenoxy)benzonitrile (4,4‐APBN)] and 6FDA or PMDA. The processability of the poly(amic acids) (PAAs), for the first series is greatly improved since their solution viscosities are much lower than PAAs based on symmetrical diamines. Besides having high glass‐transition temperatures (249–332 °C), and thermal stability [5% weight loss in the range of 505–542 °C (air) and 512–546 °C (nitrogen)], these PIs form tough, transparent and flexible films that have a tensile‐strength range of 82.1–121.3 MPa, elongations‐at‐break of 5.33–9.81%, and tensile moduli of 2.11–2.97 GPa. Their film dielectric constants are 3.08–3.62 at 10 kHz, moderately higher than that (2.92) of analogous PI (CP2) without nitrile groups. Overall, we found that the reduction of structural symmetry in repeat units can improve the polymer processibility as well as increasing their dielectric constants. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4998–5011     

Thiol‐functionalized 1,3‐benzoxazine: Preparation and its use as a precursor for highly polymerizable benzoxazine monomers bearing sulfide moiety

We describe a new strategy for preparation of benzoxazine monomers based on in situ preparation of a thiol‐functionalized benzoxazine and successive chemical modification of the thiol moiety. The thiol‐functionalized benzoxazine can be prepared from its precursor bearing two benzoxazine moieties linked by disulfide bond. Reductive cleavage of the disulfide bond of the precursor with using triphenylphosphine as a reducing agent allows successful preparation of the thiol‐functionalized benzoxazine. By performing this reduction process in the presence of epoxides and acrylates, the formation of the thiol moiety and its successive reaction with those electrophiles proceed efficiently to give the corresponding benzoxazines with sulfide moieties. The benzoxazine monomers thus prepared exhibit much higher polymerization ability than those without sulfide moiety. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1448–1457     

Synthesis and characterization of new segmented polyurethanes with side‐chain,liquid‐crystalline chain extenders

Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and ¹H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004     

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

A new chiral half‐titanocene complex, [CpTiCl₂(O‐(S)?2‐Bu)], is synthesized and characterized by ¹H and ¹³C NMR spectroscopy. This complex is employed for the coordination polymerization of n‐butyl and n‐hexyl‐ isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left‐handed helix is produced, due to the chiral (S)?2‐butoxy group, which is bound to the polymer chain end. The polymerization of 3‐(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2‐Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half‐titanocene complex. However, a statistical copolymer of 2‐ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2141–2151     

New polysaccharide-g-polyacrylonitrile copolymers: synthesis and thermal characterization

Various natural and modified polysaccharides (i.e. arabic gum, tragacanth gum, xanthan gum, sodium alginate, chitosan, sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose) were modified using ceric-initiated graft polymerization of acrylonitrile under inert atmosphere. Grafting was confirmed using spectral (FT-IR) proofs. The grafting parameters were determined by conventional methods. Thermal characteristics of the homopolymer-free copolymers were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) under nitrogen atmosphere. The major thermal transitions as well as the activation energy of the major decomposition stages were investigated. The polyacrylonitrile (PAN)-grafted polysaccharides were recognized to be thermally stable more than the corresponding non-grafted substrates, although they begin to decompose at relatively lower temperatures than the non-grafted counterparts. Copyright © 2003 John Wiley & Sons, Ltd.     

High-temperature chiral nematic phase in naphthalene and cholesterol derivative liquid crystal: characterisation and dielectric relaxation study

In this article, we report the synthesis of the naphthalene and cholesterol derivative 2-(cholesterol-n-decanoate)-6-(heptyloxy benzoate) naphthalene (2CD6HBN) liquid crystal (LC) having chiral nematic (N*) mesophase. The synthesised mesophase has been characterised using polarising optical microscopy (POM) and differential scanning calorimetric (DSC) study. The presence of the rigid and less polarisable cores causes a higher N*-Iso transition temperature. The relaxation phenomenon of the present LC sample was analysed by the dielectric relaxation spectroscopic study. The dielectric properties, electrical conductivity and the relaxation time were observed as a function of the temperature. The relaxation time follows the first-order exponential decay–type equation. The properties of the LC sample have also been correlated with the structure of the compound.     

Polyaniline doped by a new class of dopants,benzoic acid and substituted benzoic acid: synthesis and characterization

This work reports on a new class of dopants, benzoic acid and substituted benzoic acids such as 2‐hydroxybenzoic acid, 2‐chlorobenzoic acid, 4‐nitrobenzoic acid, 2‐methoxybenzoic acid, 3‐methylbenzoic acid, 4‐methylbenzoic acid, 3‐aminobenzoic acid and 4‐aminobenzoic acid, for polyaniline. Benzoic acids can be used to dope polyaniline by mixing benzoic acid (or a substituted benzoic acid) with polyaniline in the common solvent 1‐methyl‐2‐pyrrolidone. Properties of benzoic acid doped polyaniline salts are studied using Fourier transform infra‐red, X‐ray diffraction spectroscopy, scanning electron microscopy, thermogravimetric analysis and conductivity measurements. The conductivity of polyaniline‐benzoic acid salt was found to be high (10⁻² S/cm) when compared to polyaniline‐substituted benzoic acid salts (10⁻³–10⁻⁵ S/cm). Copyright © 2005 John Wiley & Sons, Ltd.     

Molecular design,synthesis, and nonlinear optical properties of novel T‐type polyimides with exceptionally high thermal stability of the second harmonic generation

2,5‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐4′‐nitrostilbene dianhydride was prepared and reacted with 1,4‐phenylenediamine, 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide, and 4,4′‐(hexafluoroisopropylidene)dianiline to yield unprecedented novel T‐type polyimides ( 4 – 7 ) containing 2,5‐dioxynitrostilbenyl groups as nonlinear optical chromophores, which constituted parts of the polymer backbones. 4 – 7 were soluble in polar solvents such as acetone and N,N‐dimethylformamide. They showed thermal stability up to 300 °C in thermogravimetric analysis thermograms; the glass‐transition temperatures obtained from differential scanning calorimetry thermograms were around 153 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064‐cm^?1 fundamental wavelength were around 4.35 × 10^?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 45 °C higher than the glass‐transition temperature, and there was no SHG decay below 200 °C because of the partial main‐chain character of the polymer structure, which was acceptable for nonlinear optical device applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3189–3199, 2004     

Promoting effect of thiophenols on the ring‐opening polymerization of 1,3‐benzoxazine

Thiophenol and p‐nitrothiophenol were evaluated as promoters for the ring opening polymerization of benzoxazine. The ring‐opening polymerization of p‐cresol type monofunctional N‐phenyl benzoxazine 1a with 10 mol % of thiophenols proceeded at 150 °C, leading to the high conversion of 1a more than 95% within 5 h, whereas the polymerization of 1a without thiophenols did not proceed under the same conditions. The promotion effect of the thiophenols on curing of bisphenol‐A type N‐phenyl benzoxazine 1b was also investigated. In the differential scanning calorimetric (DSC) analysis of the polymerization of 1b at 150 °C without using any promoters, an exothermic peak attributable to the ring‐opening reaction of benzoxazine was observed after 8 h. In contrast, in the DSC analysis of the polymerization of 1b with addition 20 mol % of p‐nitrothiophenol, an exothermic peak was observed within 2 h, to clarify the significant promoting effect of p‐nitrothiophenol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2523–2527     

Synthesis,characterization and evaluation of new fluorene‐based dimethacrylates for formulating dental composites

This study focused on the preparation and evaluation of several new fluorene‐based dimethacrylates, as possible intermediates to formulate improved dental composites. As the first step towards modification of the composite formulation, the new monomers and unfilled resin matrix were prepared. The formulated and visible light‐cured materials were found to be more hydrophobic, along with having higher wet (water saturated) glass transition temperatures (T_g) than the commonly used matrix resins based on 2,2‐bis(4(2‐hydroxy‐3‐methacryloxy‐propyloxy))‐phenylpropane (Bis GMA). In addition, the new matrix resins exhibited greater compressive strength, along with greater resistant to creep and fracture. Finally, the results suggested a correlation may exist between creep and the homologous temperature (T/T_g) of the light‐cured neat resins, where the T/T_g may be used to compare the mechanical properties of different materials at various temperature. Copyright © 1999 John Wiley & Sons, Ltd.     

Novel Approach to Oligomers and Polymers Containing Neutral and Cationic Iron Moieties Within and Pendent to Their Backbones

Polymers containing neutral and cationic iron moieties within and pendent to their backbones were prepared. The redox properties of the neutral and cationic iron centers were examined using cyclic voltammetry. Photolysis of the organometallic polymers led to decoordination of the cationic cyclopentadienyliron moieties from the polymer backbones. Glass transition temperatures of the resulting ferrocene‐based polymers were lower than those of the mixed neutral/cationic polymers.     

Synthesis,thermal, and rheological properties of poly(trimethylene terephthalate)/BaSO4 nanocomposites

A novel method was developed for fabricating poly(trimethylene terephthalate) (PTT)/BaSO₄ nanocomposites using in situ polymerization. A nano‐BaSO₄ suspension was prepared by reacting H₂SO₄ with Ba(OH)₂ in 1,3‐propanediol (PDO). The mean size of original nano‐BaSO₄ is 15–23 nm. PTT matrix was synthesized by condensation polymerization of bis(3‐hydroxypropyl terephthalate) after the completion of transesterification of dimethyl terephthalate (DMT) with PDO. It was found that the addition of BaSO₄ had little influence on the synthesis of PTT. The properties of nanocomposites with a wide range of BaSO₄ fraction were systematically studied. The morphologies of the composites were investigated by transmission electron microscopy (TEM), which showed that agglomerate structures did not form until BaSO₄ content higher than 8 wt%. The thermal properties of the nanocomposites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC results revealed that the triple endothermic melting phenomenon is only observed for the nanocomposites which contained 4 wt% BaSO₄, other samples exhibit double endothermic melting. These results indicated that nano‐BaSO₄ could induce a microcrystal to form more perfect morphology and restrain the formation of much thicker lamellar crystallinity, that is, nano‐BaSO₄ could induce the formation of more uniform crystallinity. Besides, the crystallization ability of the composites was greatly improved by loading nano‐BaSO₄. The TGA results suggested that nano‐BaSO₄ slightly increased the maximum‐decomposing‐rate temperature 1 (T_max1), but markedly increased the maximum‐decomposing‐rate temperature 2 (T_max2). Furthermore, the steady‐state shear behavior of samples was investigated by a parallel‐plate rheometer. The storage modulus (G') and loss modulus (G”) curves shifted to higher modulus upon addition of 2–16 wt% of nano‐BaSO₄. All of the samples investigated exhibited the expected shear‐thinning behavior. Proper contents of nano‐BaSO₄ would decrease the shear viscosity of nanocomposites, whereas superfluous amounts would greatly increase the viscosity of nanocomposites and the composites which loaded 8 wt% nano‐BaSO₄ revealed an equivalent shear viscosity compared to pure PTT. Copyright © 2008 John Wiley & Sons, Ltd.     

Physicochemical characterization of α‐chitin, β‐chitin,and γ‐chitin separated from natural resources

We isolated α‐chitin, β‐chitin, and γ‐chitin from natural resources by a chemical method to investigate the crystalline structure of chitin. Its characteristics were identified with Fourier transform infrared (FTIR) and solid‐state cross‐polarization/magic‐angle‐spinning (CP–MAS) ¹³C NMR spectrophotometers. The average molecular weights of α‐chitin, β‐chitin, and γ‐chitin, calculated with the relative viscosity, were about 701, 612, and 524 kDa, respectively. In the FTIR spectra, α‐chitin, β‐chitin, and γ‐chitin showed a doublet, a singlet, and a semidoublet at the amide I band, respectively. The solid‐state CP–MAS ¹³C NMR spectra revealed that α‐chitin was sharply resolved around 73 and 75 ppm and that β‐chitin had a singlet around 74 ppm. For γ‐chitin, two signals appeared around 73 and 75 ppm. From the X‐ray diffraction results, α‐chitin was observed to have four crystalline reflections at 9.6, 19.6, 21.1, and 23.7 by the crystalline structure. Also, β‐chitin was observed to have two crystalline reflections at 9.1 and 20.3 by the crystalline structure. γ‐Chitin, having an antiparallel and parallel structure, was similar in its X‐ray diffraction patterns to α‐chitin. The exothermic peaks of α‐chitin, β‐chitin, and γ‐chitin appeared at 330, 230, and 310, respectively. The thermal decomposition activation energies of α‐chitin, β‐chitin, and γ‐chitin, calculated by thermogravimetric analysis, were 60.56, 58.16, and 59.26 kJ mol^?1, respectively. With the Arrhenius law, ln β was plotted against the reciprocal of the maximum decomposition temperature as a straight line; there was a large slope for large activation energies and a small slope for small activation energies. α‐Chitin with high activation energies was very temperature‐sensitive; β‐Chitin with low activation energies was relatively temperature‐insensitive. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3423–3432, 2004     

Interactions between metal chlorides and poly(vinyl pyrrolidone) in concentrated solutionsand solid‐state films

The rheological behavior of poly(vinyl pyrrolidone) (PVP)/N,N‐dimethylformamide (DMF) solutions containing metal chlorides (LiCl, CaCl₂, and CoCl₂) were investigated, and the results showed that the nature of the metal ions and their concentration had an obvious effect on the steady‐state rheological behavior of PVP–DMF solutions with different molecular weights. The apparent viscosity of the PVP–DMF solutions increased with an increasing metal‐ion concentration, and the viscosity increment was dependent on the metal‐ion variety_. For a CaCl₂‐containing PVP–DMF solution, for example, the critical shear rate at the onset of shear thinning became smaller with increasing CaCl₂ concentration. It was believed that multiple interactions among metal ions, carbonyl groups of PVP, and amide groups in DMF determined the solution properties of these complex fluids; therefore, ¹³C NMR spectroscopy was used to detect the interactions in systems of PVP–CaCl₂–DMF and PVP–LiCl–DMF solutions. NMR data showed that there were obvious interactions between the metal ions and the carbonyl groups of the PVP segments in the DMF solutions. Furthermore, IR spectra of the PVP/metal chloride composites demonstrated that the interaction between the metal ions and carbonyl groups in the PVP unit occurred and that the PVP chain underwent conformational variations with the metal‐ion concentration. DSC results indicated that the glass transition temperatures of the PVP/metal chloride composites increased with the addition of metal ions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1589–1598, 2007     

Synthesis and properties of novel Y‐type nonlinear optical polyimides with high thermal stability of second harmonic generation

2,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐1‐(2,2‐dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide and 4,4′‐(hexafluoroisopropylidene)dianiline to yield novel Y‐type polyimides 5‐7 containing 2,4‐dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5‐7 are soluble in polar solvents such as dimethylsulfoxide and N,N‐dimethylformamide. Polymers 5‐7 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with T_g values obtained from differential scanning calorimetry thermograms in the range 179–194 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films at the 1064 nm fundamental wavelength were around 5.56 × 10^?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 °C higher than the glass‐transition temperature there was no SHG decay below 215 °C because of the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3078–3087, 2008     

Synthesis and characterization of fully aliphatic polyimides from an aliphatic dianhydride with piperazine spacer for enhanced solubility,transparency, and low dielectric constant

A new series of fully aliphatic polyimide (API) based on a novel aliphatic dianhydride monomer‐2,2′‐(1,4‐piperazinediyl)‐disuccinic anhydride (PDA), in which two units of succinic anhydride have been connected by an aliphatic heterocyclic piperazine spacer that possesses aminomethylene (‐NCH₂) moiety in the aliphatic/alicylic backbone capable of inducing charge transfer (CT) interactions in the polyimide network, was successfully synthesized. The APIs were soluble in common polar organic solvents. The polyimide films of PDA with alicyclic diamines were almost colorless. T₁₀ (temperature of 10% weight loss) of APIs were ranged from 299–418 °C and T_g of API3‐API6 were in the temperature range of 170 to 237 °C. The light‐colored polyimide films of API3‐API6 possessed good mechanical properties with tensile strength of 54–72 Mpa, tensile modulus of 1.6–2.3 Gpa and elongation at break of 4–9%. The polyimide films of API3‐API6 were highly flexible and free‐standing which is quite rare in fully APIs. The dielectric constant of one of the synthesized API (API4) was as low as 2.14. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2316–2328