Broja M. Mandal

Poly-2,3- and 2,7-Bicyclo[2.2.1]hept-2-enes: Preparation and Structures of Polynorbornenes

Abstract The polymerization of norbornene in the presence of either radical catalysts having a short half-life at the polymerization temperature or ethylaluminum dichloride yields a saturated polymer having a rearranged structure with 2,7 linkages. Polymerization in the presence of either Pd(C6H5CN)2Cl2 or Ziegler-Natta catalysts containing TiCI4 and A1R3 or R2 A1C1 yields a saturated polymer with 2,3 linkages.

Blends of HCl-doped polyaniline nanoparticles and poly(vinyl chloride) with extremely low percolation threshold : a morphology study

Abstract Blends of hydrochloric acid-doped polyaniline (PANI·HCl) nanoparticles and poly(vinyl chloride) (PVC) have been prepared by redispersing sedimented colloidal particles of PANI in tetrahydrofuran solutions of PVC using ultrasound and casting the film from the dispersion. The blends have the characteristics of extremely low percolation threshold at a volume fraction of PANI of 4.02 × 10 −4 . The morphology of the blends as revealed by transmission electron microscopy (TEM) of the blend films directly cast on TEM grids is discussed. Above the percolation threshold the dispersed PANI·HCl phase shows a globular network morphology in contrast to the fibrillar network morphology observed earlier for PANI·HCl-poly(vinyl alcohol) blends prepared by the present method.

Dispersion polymerization of acrylamide: Part II. 2,2′-Azobisisobutyronitrile initiator

Dispersion polymerization of acrylamide in tert-butyl alcohol (TBA)-water media (TBA ⩾ 50 vol %) using poly(vinyl methyl ether) (PVME) as the stabilizer and 2,2′-azobisisobutyronitrile (AIBN) as the initiator at 50°C has been studied. The conversion-time curve shows autoacceleration taking place from the very early stage of the reaction (measured from 4% conversion level). Molecular weight increases with conversion indicating that the gel effect is operative. This suggests that a major part (if not the whole) of the polymerization occurs in the particle phase. The effects of the concentrations of the stabilizer, the initiator, the monomer, and the solvent composition on particle size have been explained on the basis of particle phase polymerization. The feeding of the particles by the monomer presumably occurs through the solvent channels of the swollen particles. The swelling data of polyacrylamide films in various TBA-water mixtures are given. The similarity and differences between the AIBN and ammonium persulfate (APS) initiated systems (published earlier by us) have been discussed. In general, particles are more polydisperse and bigger in the former case than in the latter.

Analogue calorimetry of polymer blends: poly(styrene-co-acrylonitrile) and poly(phenyl acrylate) or poly(vinyl benzoate)

Abstract Unlike poly(phenyl acrylate) (PPA), its isomer poly(vinyl benzoate) (PVBZ) is immiscible with poly(styrene- co -acrylonitrile) (SAN). The difference in miscibility behaviour of PPA and PVBZ towards SAN is also reflected in the heats of mixing ( ΔH m ) of the low-molecular-weight analogues of the respective blend components at compositions corresponding to o SAN = 0.92 in the blend. It turns out that propionitrile, the hydrogenated monomer of polyacrylonitrile (PAN), is very unsuitable as an analogue of the latter. In contrast, acetonitrile, having a solubility parameter closer to PAN, is a fairly acceptable analogue of PAN as far as miscibility of the latter with PPA is concerned in the PAN-rich region, o PAN > 0.7.

Miscibility and phase diagrams of poly(phenyl acrylate) and poly(styrene-co-acrylonitrile) blends

Abstract The miscibility of blends of poly(phenyl acrylate) (PPA) and poly(styrene-co-acrylonitrile) (SAN) of different copolymer compositions has been studied by a film clarity test, Tg and cloud-point (Tp) studies. It was revealed that the miscibility of solvent-cast blends varies greatly from solvent to solvent. Careful annealing of solvent-cast blends below the cloud temperature and above the Tg removed the solvent effect on the lower AN content side of the miscibility window. On the higher AN content side of the miscibility window the solvent effect could not be removed by annealing at the highest permissible temperature ( p ⋍ 220° C ). The phase diagrams of the blends were determined. The miscibility window at various temperatures has been constructed. It ranges between 11.5 and 32 wt% AN at 200°C. The various binary polymer segment interaction parameters have been evaluated using the composition of the miscibility window and the mean-field model.

Interpenetrating polymer network composites of polypyrrole and poly(vinyl acetate)

Abstract Interpenetrating polymer network (IPN) composites of polypyrrole (PPy) and poly(vinyl acetate) (PVAc) were prepared by dipping FeCl 3 impregnated PVAc films into solutions of pyrrole in water. PVAc becomes colored due to partial dehydroacetylation and also insoluble due to FeCl 3 treatment. These properties do not change on leaching out FeCl 3 from the films. However, differential scanning calorimetry shows that the T g of PVAc remains unchanged in the FeCl 3 treated films indicating that the dehydroacetylation did not proceed to significant extent. The FeCl 3 impregnated films however swell rapidly with simultaneous leaching of FeCl 3 when they are immersed in water. The extent of swelling decreases with decrease in temperature. Considerable swelling occurs even below the T g of the polymer. PPy forms inside the swollen films when the impregnated films are dipped into aqueous solutions of pyrrole instead of water. The DSC studies of the composite films reveal that the T g of PVAc is increased to higher temperatures with increased incorporation of PPy indicating that there may be some mixing between PPy and PVAc. The percolation threshold for electrical conductivity occurs between 3.5 to 5 wt.% of PPy in the composites. The threshold values are found to be insensitive to the degree of swelling of the FeCl 3 impregnated films. The low values of f p have been attributed to fractal growth of PPy phase in the water channels of the swollen films. This view is supported by the SEM images of the cryofracture surface of the composites which reveal the formation of PPy particles in the channels formed by water during swelling of the films. The effects of O 2 , moisture and temperature on the conductivity of the films have also been studied. The present method is not universally applicable. Thus, with PMMA or polycarbonate used as the matrix polymers FeCl 3 goes quickly into solution in water without swelling of the films and no composite is formed.

Thermodynamic characterization of binary polymer blends by inverse gas chromatography

Abstract The gas chromatographic method of characterization of polymer blends with regard to the state of binary polymer mixtures, origin of miscibility in miscible blends, evaluation of the noncombinatorial free energy parameters χ23′ and χ23*′ for miscible blends, and structural information of microphase-separated copolymer systems, etc. are reviewed with discussions of some selected polymer-polymer systems. A brief discussion of the principle and practice of GC with a polymer stationary phase, of the evaluation of χ and χ*, of sources of error and accuracy of the method, and of column support materials and support loading is also presented. Preliminary results of an inverse gas chromatography study of the newly reported miscible polymer pair poly(vinyl propionate) and poly(ethyl acrylate) are presented.

Dispersion polymerization of pyrrole using ethylhydroxy‐ethylcellulose as a stabilizer

Oxidative polymerization of pyrrole has been studied using FeCl3 or (NH4)2S2O8 (APS) as oxidant, ethylhydroxyethylcellulose (EHEC) as a steric stabilizer and water or aqueous ethanol as the dispersion medium. Transmission electron micrographic images of the particles from the as-prepared dialysed dispersions in aqueous ethanol show small as well as large particles (about a decade larger) when FeCl3 is used as the oxidant but only large particles when APS is used as the oxidant. Small particles are not found when the dispersions are prepared in water, irrespective of the oxidant used. The particle size decreases with an increase in molecular weight of the stabilizer for the same stabilizer concentration. The minimum amount of stabilizer required to support dispersion polymerization decreases upon increasing the alcohol content of the medium.

END-GROUP STUDIES USING DYE TECHNIQUES

Abstract The end group in a macromolecule is a birth and death record stamped on the molecule itself. Generally the end group differs in composition from the main chain and constitutes a minute fraction of the macromolecule. Its quantitative determination demands ultra sensitive methods and the results are highly significant from the viewpoint of both theoretical and practical interests. The theoretical interests include: 1. Knowledge of the transient free-radical intermediates participating in the initiation reaction in radical polymerization vis -i-vis the chemistry of free radicals. 2. Determination of the rate of initiation from the extent of in corporation of initiator fragment and rate of polymerization [1]. 3. Knowledge of the mode of termination reaction. 4. Determination of degree of polymerization (DP) when the mode of termination is known. 5. Elucidation of the chain-transfer process and the determination of the chain-transfer constant.

Novel polyaniline dispersions using poly(vinyl methyl ether) stabilizer

Abstract Oxidative dispersion polymerization of aniline using poly(vinyl methyl ether) (PVME) dispersant in water or aqueous alcohol media yields dispersions of submicronic conducting polyaniline (PANI) particles which have rice grain morphology. The conductivity of the particles in pressed pellet form ranged between 0.03–5 S cm−1 depending on the synthesis condition. Dispersion polymerization is best effected in aqueous alcohol (50–70% v/v alcohol). Using 50% ethanol as the polymerization medium dispersions containing 5 wt% PANI were prepared.