Diffusion Mechanism of As‐spun Polyacrylonitrile Fiber in a Dimethyl Sulfoxide‐Water Coagulation Bath

In this paper, the diffusion mechanism of as‐spun PAN fiber was investigated in dimethyl sulfoxide‐water by determining the dynamic compositions of the fibers and the diffusion coefficients of solvent and nonsolvent during coagulation. The diffusion process could be divided into two stages. Results showed that the first stage of the diffusion process was the most important during the whole process, which was fundamental to further study on the formation mechanism. Also, compared with wet spinning, the dry‐jet wet spinning method had the advantage of mild coagulating at a high jet‐stretch. At high concentrations, the diffusion coefficients increased and the ratio of solvent diffusion coefficient to nonsolvent diffusion coefficient decreased; an increasing temperature resulted in the increase of both diffusion coefficients with a decrease in their ratios. To some extent, for the PAN‐DMSO‐water system, the more the ratios D_s*/D_n* tended to 1, the more the cross‐section shapes of as‐spun PAN fiber tended to be circular.     

Quaterpolymerization of Ethylene,Propylene, Dicyclopentadiene,and Methylcyclopentadienyl-5-endo-norborn-2-enyl-methane

Abstract

The quaterpolymerization of methylcyclopentadienyl-5-endo-norborn-2-enyl-methane with ethylene, propylene, and either endo- or exo-dicyclopentadiene was studied by using the catalyst system VAcac₃-Et₂AlCl. The influence of catalyst and polyenes concentrations, catalyst modifiers, and other polymerization parameters on the general properties of quaterpolymers was investigated. The polymers obtained showed a random distribution of the comonomeric units and the ability to covulcanize with 1,4-cis-polyisoprene.     

Trityl Salt-Initiated Cationic Polymerization of 1,2-Cyclohexene Oxide: Structural Analyses of the Products

The polymerization of 1,2-cyclohexene oxide was carried out at 0°C in dichloroethane with triphenylmethyl hexafluoroarsenate as the initiator. A typical reaction product (PCHO-1) was analyzed by infrared and nuclear magnetic resonance spectroscopy as well as by gel-permeation chromatography, x-ray diffraction, and differential scanning calorimetry (DSC). The x-ray and DSC data show that PCHO-1 is an amorphous substance. The results of the NMR analyses show that the propagation step in the trityl salt-initiated polymerization obeys Bernoullian statistics with a P_m value of 0.38.     

Synthesis and Polymerization of Spiro Oxyphosphoranes

Novel methods of synthesis of spiro acyloxyphosphoranes are described emphasizing the significance of the first isolated instance of these new species. Then, the no-catalyst alternating copolymerizations of the combinations of cyclic phosphorus(III) compounds (serving as nucleophilic monomer, M_N) with acrylic acid derivatives and with α-keto acids (electrophilic monomer, M_E) are mentioned. These copolymerizations proceed without added initiator. Spiro oxyphosphoranes play an important role in the copolymerization scheme in the equilibrium with the ⁺M_N - M_E ^? zwitterion, the key intermediate of the copolymerization. Finally, new reactions of spiro acyloxyphosphoranes with nucleophiles, alcoholysis and aminolysis polymerizations are presented.     

Synthesis of Main‐Chain Liquid‐Crystalline Polyesters Containing Diphenyl Mesogens by Chemo‐Enzymatic Route †

Main‐chain thermotropic liquid‐crystalline polyesters containing rigid biphenyl mesogens and flexible spacers were synthesized by chemo‐enzymatic route. The enzyme‐catalyzed polymerization showed high regio‐ and chemo‐ selectivity, and is environmentally friendly. The resulting polyesters were characterized with ¹H‐NMR, ¹³C‐NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and polarized light optical microscopy (POM).     

Thermal Properties of Copoly(L‐lactic acid/glycolic acid) by Direct Melt Polycondensation

Poly(L‐lactic acid‐co‐glycolic acid) (PLGA) was prepared from hydroxy‐acids with melt polymerization. In this way, the copoly(L‐LA/GA) (PLGA) was synthesized directly using a binary catalyst (tin chloride dihydrate/p‐toluenesulfonic acid). The thermal properties of PLGA were studied by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The results show that the melting point of PLGA decreases with increasing mole fraction of GA units in the copolymer. In addition, the melting point of polymer also decreases with increasing degree of racemization of the polymer.     

Microwave‐assisted Chemical Reactions

Microwave (MW) radiation has been used in chemical analysis and chemical synthesis. MW heating under controlled conditions offers distinct advantages over conventional heating. The reactions are carried out in environmentally clean and safe solvents and in many cases, reactions can be carried out under solvent‐free conditions. This method of synthesis has grown rapidly and found its use in various sectors. This paper reviews some of the reactions that have been accelerated with higher yields under MW irradiation. The application of MW‐assisted synthesis in the medicinal and pharmaceutical industries will be emphasized.     

Copolymerization of N‐tert‐Butylacrylamide with Ethylene Glycol Dimethacrylate

N‐tert‐butylacrylamide (NtBA) was copolymerized with ethylene glycol dimethacrylate (EDMA) in butanone solution over a wide composition and conversion range, using dibenzoyl peroxide (Bz₂O₂) as a free‐radical initiator. The copolymer composition was determined from the nitrogen content. Using only low conversion (≤20%) collected for the copolymerization reactions, monomer reactivity ratios were estimated using the Kelen‐Tüdos graphical method and were found to be r₁=0.26 (NtBA) and r₂=7.05 (EDMA). In order to get a better insight into the mechanism of nanoporous copolymers of NtBA with EDMA preparation by thermal degradation of copolymers of N‐acryl‐N,N′‐di‐tert‐butylurea (A‐DitBuU) with EDMA, nonporous copolymers (model compound), of the same chemical structure and composition, were prepared by performing copolymerization of NtBA with EDMA up to the high conversion of 97–100%. Thermal behavior of nanoporous and nonporous copolymers of NtBA with EDMA was studied.     

Binary and Ternary Copper(II) Complexes with NIPAAm/IA Copolymers and Aminoacids: Interpretation of UV‐Visible Spectra and Cyclic Voltammograms

The complex formations of homopolymers and copolymers of poly(N‐isopropyl acrylamide) (PNIPAAm), polyacrylamide (PAAm) and poly(itaconic acid) (PIA) with Cu(II) ions in aqueous solutions were studied by using UV‐visible spectra in the region of 200–1100 nm and cyclic voltammograms between ?0.800 V and 0.600 V. According to the optical and electrochemical spectra of the polymer‐ and copolymer‐Cu(II) complexes and their ternary complexes with alanine, i.e., absorptions and the shifts in the wavelength of the maximum absorptions, currents and potentials of the peaks in the pH range of 3–12, the intensities of anodic and cathodic peak currents of polymers containing IA groups decrease with increasing pH and they show maximum absorptions at lower wavelengths than do the homopolymers used in this work. The peak point of the visible band shifts from 800 to 650 nm, with increasing pH, while the intensity of the third anodic peak observed after pH=4 increases in the case of both Ala‐Cu(II) and its ternary solution with P(NIPAAm‐co‐IA, 9.8 mol%). Both the pH‐dependent shifts of maximum absorptions and the appearence of the third anodic peaks as the pH raised were interpreted as a presence of tetracoordinated Cu(II) complexes in the solution and on the electrode surface, involving combined carboxyl, amide and amine interaction.     

Studies on Synthesis and Characterization of Charge Transfer Polymerization of Styrene and Alkyl Methacrylates

Abstract

Copolymers involving styrene and homologues of alkyl methacrylates (viz., methyl, ethyl, and butyl methacrylates) were synthesized at 60°C by employing a mixture of n‐butylamine and carbontetrachloride as charge transfer (CT) initiators in dimethyl sulphoxide medium. The CT complex was characterized by UV spectroscopy while the respective copolymers were characterized by employing infrared (IR) and ¹H NMR spectroscopy. The copolymer compositions were determined by using ¹H NMR spectroscopy and the reactivity ratios were computed by Fineman–Ross (F–R) and Kelen–Tudos (K–T) methods. The reactivity ratios of Sty‐MMA and Sty‐EMA copolymers indicate that higher level of styrene is incorporated in the copolymer. On the other hand the Sty‐BMA system exhibits different behavior. The higher value of r ₂ is obtained denoting that BMA is more active than styrene and hence, more BMA is present in the copolymer chain. In Sty‐MMA and Sty‐BMA systems, the product of r ₁ and r ₂ is greater than 1, representing the formation of high degree of random copolymers. However, in the case of Sty‐EMA, the product of r ₁ and r ₂ is less than 1 indicating the formation of alternating copolymer.