Hasan A. Al-Muallem

Polystyrene with dendritic branching by convergent living anionic polymerization. II. Approach using vinylbenzyl chloride

Vinylbenzyl chloride (VBC) has been used as a coupling agent in Convergent Living Anionic Polymerization to produce polymers with dendritic branching. The slow addition of a stoichiometric amount of VBC to living polystyrene chains allows the coupling to proceed through macromonomer formation followed by vinyl addition. Changing the reaction conditions produced two types of structures. Star-shaped polymers with a hyperbranched core were made by the continuous slow addition of VBC alone, and chain-extended hyperbranched structures with varied molecular weight between branch points were produced by the slow addition of VBC mixed with different amounts of styrene monomer. The extent of growth of the two different types of structures ranged from 2.4 to 2.6 generations for the case of VBC added alone, corresponding to an average of 5.3 to 6.1 arms attached to the hyperbranched core, and from 3.2 to 4.2 generations for polymers produced from the addition of VBC mixed with styrene. Relatively low polydispersities were obtained for all samples. The highly branched nature of the polymers was reflected in the low intrinsic viscosity relative to linear polystyrene and in the dependence of glass-transition temperature on the molecular weight relative to the number of end groups.

Synthesis and solution properties of a new pH-responsive polymer containing amino acid residues

Abstract The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was cyclopolymerized in water using ammonium persulfate as an initiator to afford a cationic polyelectrolyte which on acidic hydrolysis of the pendant ester groups gave the corresponding cationic acid salt (CAS). The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB). The solution properties of the APE having two basic functionalities were investigated in detail by potentiometric and viscometric techniques. Basicity constants of the amine as well as the carboxylate groups in APE are ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; as the degree of protonation (α) of the whole macromolecule increases, the protonation of the amine nitrogens and carboxylate groups becomes increasingly more difficult and easier, respectively. While the APE, PB and CAS were found to be soluble in salt-free water, the corresponding PB and CAS of the SO2 copolymers of the amine salt 1 were found to be insoluble in water.

Synthesis and solution properties of a new ionic polymer and its behavior in aqueous two-phase polymer systems

Abstract The amine salt, N , N -diallyl- N -carboethoxymethylammonium chloride was copolymerized in dimethyl sulfoxide using ammonium persulfate or azo-bis-isobutyronitrile (AIBN) to afford the cationic polyelectrolyte (CPE) having five-membered cyclic structure on the polymeric backbone. The CPE on acidic (HCl) hydrolysis of the pendent ester groups gave the corresponding cationic acid salt (CAS) having the equivalent of chloride salt of N , N -diallylammonio ethanoic acid as monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB) [having the monomeric unit equivalent of sodium N , N -diallylaminoethanoate and N , N -diallylammonioethanoate] by treatment with two and one equivalent of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson–Hasselbalch equation; the protonation of the APE becomes more and more difficult as the degree of protonation ( α ) of the whole macromolecule increases. The composition and phase diagram of the aqueous two-phase systems of APE and poly(ethyelene glycol) (PEG) has been studied for the first time for this class of ionic polymers. The CAS and PB were found to be virtually insoluble in water.

Synthesis of hybrid dendritic-linear block copolymers with dendritic initiators prepared by convergent living anionic polymerization

Hybrid dendritic-linear block copolymers were made in one-pot by convergent living anionic polymerization. Dendritic polystyrene macroinitiators were synthesized by slowly adding a mixture of either vinylbenzyl chloride (VBC) or 4-(chlorodimethylsilyl)styrene (CDMSS) and styrene (1 : 10 molar ratio of coupling agent to styrene) to a solution of living polystyryllithium. The addition was ceased prior to the addition of a stoichiometric amount of coupling agent to retain a living chain end. To the living dendritically branched polystyrene was then added either styrene or isoprene to polymerize a linear block from the dendritic polystyrene. The resulting copolymers were characterized by gel permeation chromatography coupled with multiangle laser light scattering (GPC-MALLS), which clearly demonstrated the formation of diblock copolymers. The diblock copolymers were further characterized by 1H NMR, which showed the presence of the two blocks in the case of dendritic polystyrene-block-linear polyisoprene. The measurement of intrinsic viscosity showed that the dilute solution properties of the block copolymers are greatly influenced by the dendritic portion.

1,3-Dipolar cycloaddition reactions of a heterocyclic nitrone

Abstract A study of the regio- and stereo-chemical behaviour of the 1,3-dipolar cycloaddition of a series of alkenes with 5,6-dihydro-1,4-oxazine 4-oxide (1) has been carried out. Stereoselectivity in these cycloadditions has been explained in terms of steric factors and secondary orbital interactions. The ratio of the trans and cis conformers of the cycloaddition products has been determined. The nitrone (1) was found to be more reactive than its carbocyclic counterparts.

Nitrone cycloaddition : peracid oxidation of perhydro-1,2-oxazolo[3,2-c][1,4]oxazines

Abstract Regiochemistry of peracid induced ring opening of perhydro-1,2-oxazolo[3,2-c][1,4]oxazines ( 2 ) and ( 6 ) in aprotic solvent is dictated by orientation of lone pair of electrons on nitrogen. In contrast to the case with the corresponding hexahydro-2H-isoxazolo[2,3-a]pyridines ( 17 ), the oxidation of ( 2 ) gives mainly an equilibrium mixture of aldonitrone ( 3 ) and its hydroxylamine tautomer ( 4 ) which undergo stereoselective cycloaddition with styrene and methyl methacrylate. The X-ray diffraction study reveals the 6-5 ring system in ( 2 ) to be cis fused.

A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Abstract Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH2=CH–CH2)2NH+CH(CO2H)(CH2)2CO2H Cl−] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. −[−CH2(C4H6)NH+{CH(CO2H)(CH2)2CO2H Cl−}CH2−]−n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±−) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO4 from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.

Apparent kinetics of nonisothermal high temperature oxidative degradation of ethylene homopolymers: effects of residual catalyst surface chemistry and structure

The effects of two supported residual catalysts—one Ziegler-Natta and another metallocene—on the nonisothermal thermooxidative degradation of the resulting ethylene homopolymers were investigated using TGA experiments and kinetic modeling. The rigorous constitutive kinetic model (developed in this study), unlike the analytical Horowitz and Metzger model, fitted very well to the entire TGA curve, without distribution of activation energy Ea, for n (overall degradation order) = 1 for both polymers. Neither n nor Ea varied as a function of fractional weight loss of the polymer. Hence, the proposed unified molecular level concept of surface chemistry and structure of the residual catalysts held all through the degradation process. The above feature of n and Ea also indicates the suitability of the model formulation and the effectiveness of the parameter-estimation algorithm. Random polymer chain scission, with the cleavage of the −C−C− and the −O−O− (hydroperoxide) bonds, prevailed. The types of residual catalyst surface chemistry and structure varied the bond cleavage process. The metallocene Zr residual catalyst caused more thermooxidative degradation in MetCat HomoPE than what the Ti one did in Z-N HomoPE. The rigorous constitutive model-predicted apparent kinetic energy Ea, and frequency factor Z also support this finding. The proposed degradation mechanism suggests that the Zr residual catalyst more (i) decreased the activation energy required to decompose the −C−C− and the −O−O− bonds, and (ii) eliminated β-hydrogen (by the carbonyl functionalities) from the polymer chains. These findings were attributed to the differences in surface chemistry and structure of the residual catalysts. Therefore, the current study presents a rigorous constitutive kinetic model that duly illustrates the influence of the characteristic surface chemistry and structure of the residual catalysts on the high temperature oxidative degradation of polyethylenes.

Synthesis and application of polyzwitterionic and polyampholytic maleic acid-alt-(diallylamino)propylphosphonates

Ammonium persulfate-initiated alternate copolymerization of maleic acid with phosphonic acid monomer [(CH2CH–CH2)2NH+(CH2)3PO3H2Cl−] (I) and phosphonate ester monomer [(CH2CH–CH2)2NH+(CH2)3PO3Et2Cl−] (II) gave polyzwitterion (PZ): poly[(I–HCl)-alt-maleic acid] III and polyampholyte (PA): poly[(II)-alt-maleic acid] IV, respectively. PA IV, upon ester hydrolysis, gave PZ III. The pH-induced changes of backbone charges in tetraprotic III (with respect to each repeating unit) and diprotic IV were examined by viscosity measurements. PA IV exhibited antipolyelectrolyte character in the presence of neutral salt NaCl. Several protonation constants K of the CO2− and trivalent nitrogen in III and IV have been determined. The performance evaluation as a potential antiscalant in reverse osmosis (RO) plants was examined. III containing acid motifs of –PO3H2 at a concentration of 15 ppm demonstrated remarkable efficiency of ≈100% in inhibition of CaSO4 scale from its supersaturated solution for several days at 40 °C, while precipitation occurred within 10 min in the presence of 20 ppm of IV containing ester motifs of –PO3Et2.

Rice husk supported catalysts for degradation of chlorobenzenes in capillary microreactor

Chlorinated organic pollutants are persistent, toxic, and ubiquitously distributed environmental contaminants. These compounds are highly bioaccumulative and adversely affect the ozone layer in the atmosphere. As such, their widespread usage is a major cause of environmental and health concern. Therefore, it is important to detoxify such compounds by environment friendly methods. In this work, rice husk supported platinum (RHA-Pt) and titanium (RHA-Ti) catalysts were used, for the first time, to investigate the detoxification of chlorobenzenes in a glass capillary microreactor. High potential (in kV range) was applied to a reaction mixture containing buffer solution in the presence of catalyst. Due to high potential, hydroxyl and hydrogen radicals were produced, and the reaction was monitored by gas chromatography-mass spectrometry. The main advantage of this capillary reactor is the in situ generation of hydrogen for the detoxification of chlorobenzene. Various experimental conditions influencing detoxification were optimized. Reaction performance of capillary microreactor was compared with conventional catalysis. Only 20 min is sufficient to completely detoxify chlorobenzene in capillary microreactor compared to 24 h reaction time in conventional catalytic method. The capillary microreactor is simple, easy to use, and suitable for the detoxification of a wide range of chlorinated organic pollutants.