Step-growth Polymerization Reactions Research Articles

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Volatilization of Toxic α,β-Unsaturated Aldehydes Compounds During Activated Sludge Treatment of Polyester Manufacturing Industry Wastewater

Polyester manufacturing wastewater consists of water formed as a coproduct of step-growth polymerization reactions, typically performed between diols and dicarboxylic acids. Due to the solubility of the reactants and byproducts of polymerization, the wastewater is typically heavily contaminated and can possess considerable toxicity that can strongly inhibit biological wastewater treatment processes. However, very little has been published on the treatment of wastewater produced during polyester manufacture. We have demonstrated that the toxicity of the wastewater is largely attributable to volatile organic compounds (VOCs). Gas chromatography and mass spectrometry analysis of the wastewater revealed highly toxic and mutagenic α,β-unsaturated aldehydes (acrolein congeners) as major components of the VOCs present. Activated sludge treatment was performed under two aeration regimes, coarse bubble sparging and passive aeration through the surface layer, to access their effect on biodegradation/volatilization. After 24 h of incubation in the presence of 10% polyester plant wastewater, coarse bubble sparging resulted in 88% reduction in chemical oxygen demand compared to 45% with passive aeration, both largely attributable to VOC volatilization. The polyester wastewater demonstrated high toxicity as indicated by a net decline in volatile suspended solids under both culture conditions, consistent with previous toxicity assays. Results indicate that significant VOC volatilization would occur during activated sludge treatment of polyester manufacturing wastewater containing the identified acrolein congeners. To prevent toxic VOCs exposure to plant workers and improve biodegradability, we recommend polyester wastewater containing α,β-unsaturated aldehydes be pretreated by air stripping to remove VOCs and incineration of the stripped VOCs before activated sludge treatment.

Polycondensation of new optically active diacid with diisocyanates in the presence of tetrabutylammonium bromide as a green media under microwave heating

Ionic liquids ( IL)s have been recognized as ‘green’ alternatives to the organic solvents in a range of synthesis, catalysis and electrochemistry due to their unique chemical and physical properties. In this investigation, (2S)-5-(3-phenyl-2-phthalimidylpropanoylamino)isophthalic acid was prepared in three steps. The step-growth polymerization reaction of this novel diacid with various aromatic and aliphatic diisocyanates such as 4,4′-methylene bis(4-phenylisocyanate) ( 8a), toluylene-2,4-diisocyanate ( 8b), hexamethylene diisocyanate ( 8c) and isophorone diisocyanate ( 8d) were carried out in the presence of tetrabutylammonium bromide (TBAB) as a molten ionic liquid under microwave irradiation conditions and was compared with polymerization in traditional solvent like N-methyl-2-pyrrolidone (NMP). This process is safe and green since toxic and volatile organic solvent such as NMP was eliminated. The resulting new polymers were obtained in good yields with inherent viscosities ranging between 0.25 and 0.46 dL g −1 and were characterized with FT-IR, 1H-NMR, elemental and thermogravimetric analysis techniques.

An Approach to Modulate Degradation and Mesenchymal Stem Cell Behavior in Poly(ethylene glycol) Networks

A simple, sequential approach for creation of hydrolytically degradable poly(ethylene glycol) (PEG) hydrogels has been developed and characterized. The chemistry involves an initial step growth polymerization reaction between PEG-diacrylate and dithiothreitol (DTT) to form acrylate-terminated (-PEG-DTT-)n PEG chains, followed by photocross-linking to form a hydrogel network. Varying the extent of step growth polymerization prior to photocross-linking allowed for control over the equilibrium swelling ratio, degradation, and erosion of PEG hydrogels. Hydrogel degradability had a significant effect on behavior of human mesenchymal stem cells (hMSCs) encapsulated within PEG hydrogels, both in the presence and absence of an RGDSP cell adhesion ligand. In particular, enhanced network degradability resulted in enhanced hMSC viability and spreading during in vitro culture. Comparison of degradable and nondegradable hydrogels with similar physical properties (e.g., equilibrium swelling ratio) demonstrated that hMSC viability and spreading were dependent on network degradability. This study demonstrates that hydrolytically degradable PEG hydrogels can be formed via a sequential step growth polymerization and photocross-linking process and the resulting materials may serve as promising matrices for 3-dimensional stem cell culture and tissue engineering applications.

Influence of polymerization procedure on polymer topology and other structural properties in highly branched polymers obtained by A2 + B3 approach

Computational studies were carried out to investigate the influence of polymerization procedure on the topology and various macromolecular characteristics of the highly branched polymers formed by the reaction of A2 and B3 type monomers through step-growth polymerization reactions. The influence of three different polymerization procedures on the properties of the polymers formed was investigated, namely, (i) slow addition of A2 over B3, (ii) slow addition of B3 over A2, and (iii) mixed A2+B3. Topology, degree of branching, number and weight average molecular weights, and polydispersity index of the polymers were determined using Monte Carlo simulations, assuming different levels of cyclization ratios during the reactions. Interestingly model polymers obtained by the slow addition of B3 over A2 produced much higher degree of branching or truly hyperbranched polymers, when compared with the other two methods, which mainly resulted in linear growth with slight branching.

Molten Salt as a Green Reaction Medium: Synthesis of Polyureas Containing 4-phenylurazole Moiety in the Main Chain in the Presence of Tetrabutylammonium bromide as an Ionic Liquid

AbstractIonic Liquids (IL)s have been generating increased interest over the last decade. ILs were initially introduced as an alternative green reaction media because of their unique chemical and physical properties of nonvolatility, nonflammability, thermal stability, and controlled miscibility. The step-growth polymerization reactions of 4-phenylurazole (PHU) with various diisocyanates such as hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), and toluylene-2,4-diisocyanate (TDI) were performed in the presence of tetrabutylammonium bromide (TBAB) as a reaction medium with or without dibutyltin dilurate (DBTDL) as a catalyst. The polymerization reaction gave similar results in the presence or absence of DBTDL, indicating that, the catalyst is not needed in this process. The resulting polyureas showed high yields and moderate inherent viscosities in a range of 0.23-0.29 dL/g in N,N-dimethylformamide (DMF) at 25 °C and they are soluble in most polar aprotic organic solvents. This method was compared with the polymerization reaction in conventional solvent such as, N,N-dimethylacetamide (DMAc). In the case of using TBAB, higher yields and inherent viscosities were obtained. All of the above polymers were characterized by FT-IR and thermogravimetric analysis (TGA).

Conjugated Polyelectrolyte-Grafted Silica Microspheres

A direct method for preparation of conjugated polymer-grafted silica particles is reported. Silica particles (0.3 and 5 mum diameter) are treated with a 3-(trimethoxysilyl)propylamine derivative that is functionalized with an aryl iodide unit. A solution step-growth polymerization reaction is performed in solution that contains a dispersion of the aryl iodide-functionalized particles. The reaction is a Pd(0)-catalyzed (Sonogashira) A-B-type polymerization of an oligo(ethylene glycol)-fuctionalized diiodobenzene and a bis(propyloxy)sulfonate-substituted diethynylbenzene. The overall process affords silica particles that feature a surface graft layer of an anionic poly(phenylene ethynylene)-type conjugated polyelectrolyte. The particle surface modification process was monitored by infrared (FTIR) spectroscopy, and the polymer-grafted silica particles were characterized by thermogravimetric analysis, scanning and transmission electron microscopy, confocal fluorescence microscopy, and absorption and fluorescence spectroscopy. The conjugated polyelectrolyte-grafted silica particles are highly fluorescent, and a Stern-Volmer quenching study of the particles' fluorescence with electron-transfer- and energy-transfer-type quenchers shows that the quenching response depends on the type of quenching mechanism.

Synthesis of a Catechol-Based Poly(ether ether ketone) (“o-PEEK”) by Classical Step-Growth Polymerization and by Entropically Driven Ring-Opening Polymerization of Macrocyclic Oligomers

An amorphous, catechol-based analogue of PEEK (“o-PEEK”) has been prepared by a classical step-growth polymerization reaction between catechol and 4,4‘-difluorobenzophenone and shown to be readily soluble in a range of organic solvents. Copolymers with p-PEEK have been investigated, including an amorphous 50:50 composition and a semicrystalline though still organic-soluble material comprising 70% p-PEEK. o-PEEK has also been obtained by entropy-driven ring-opening polymerization of the macrocyclic oligomers (MCO's) formed by cyclo-condensation of catechol with 4,4‘-difluorobenzophenone under pseudo-high-dilution conditions. The principal products of this latter reaction were the cyclic dimer 3a (20 wt %), cyclic trimer 3b (16%) cyclic tetramer 3c (14%), cyclic pentamer 3d (13%) and cyclic hexamer 3e (12%). Macrocycles 3a−c were isolated as pure compounds by gradient column chromatography, and the structures of the cyclic dimer 3a and cyclic tetramer 3c were analyzed by single-crystal X-ray diffraction. A ...

Synthesis of Photoactive Polyureas Derived from 4-(4-Dimethylaminophenyl)-1,2,4-triazolidine-3,5-dione and Diisocyanates

4-(4-Dimethylaminophenyl)-1,2,4-triazolidine-3,5-dione (DAPTD) was prepared from 4-dimethylaminobenzoic acid in five steps. The reaction of monomer DAPTD with n-isopropylisocyanate was performed at room temperature in N,N-dimethylacetamide (DMAc) solution and the resulting bis-urea derivative was obtained in high yield and was finally used as a model compound for polymerization reaction. The step-growth polymerization reactions of monomer with hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI) and toluene-2,4-diisocyanate (TDI) were performed in DMAc solution in the presence of pyridine, triethylamine or dibutyltin dilurate as catalysts. Some physical properties and structural characterization of these novel polyureas are reported. Fluorimetric studies of the model compound as well as polymers were performed.

Diisocyanate route as a convenient method for the preparation of novel optically active poly(amide–imide)s based on N-trimellitylimido- S-valine

A new class of optically active poly(amide–imide)s based on an α-amino acid was synthesized via direct polycondensation reaction of different diisocyanates with a chiral diacid monomer. The step-growth polymerization reactions of N-trimellitylimido- S-valine (TISV) ( 1) with 4,4′-methylene-bis(4-phenylisocyanate) (MDI) ( 2) was performed under microwave irradiation, as well as solution polymerization under graduate heating and reflux conditions. The optimized polymerization conditions for each method were performed with tolylene-2,4-diisocyanate (TDI) ( 3), hexamethylene diisocyanate (HDI) ( 4), and isophorone diisocyanate (IPDI) ( 5) to produce optically active poly(amide–imide)s via diisocyanate route. The resulting polymers have inherent viscosities in the range of 0.02–1.10 dL/g. Decomposition temperatures for 5% weight loss ( T 5) occurred above 300 °C (by TGA) in nitrogen atmospheres. These polymers are optically active, thermally stable and soluble in amide-type solvents. Some structural characterization and physical properties of this new optically active poly(amide–imide)s are reported.

Design and characterization of nanoporous polymeric materials via reactive encapsulation of a chemically inert solvent

Nanoporous polymeric materials are used as polyelectrolytes in fuel cells, separation membranes, sensors and actuators, templates for nanoparticle synthesis, and electroactive material in biomedical applications. Design of nanoporous polymeric materials for such applications entails controlling permeability by tailoring the pore size and pore chemistry. A novel method of synthesizing nanoporous polymeric materials is employed in this work. This technique involves the synthesis of nanoporous polymeric materials by reactive encapsulation of an inert solvent using a step-growth cross-linking polymerization reaction carried out until completion without micro/macroscopic phase separation. Key structural features of the porous materials synthesized in this way were investigated by scanning electron microscopy (SEM) after extraction and supercritical drying using carbon dioxide. Micrographs of the materials synthesized using the reactive encapsulation technique showed that materials with pore sizes less than 100 nm are obtained. Micrographs also showed that the reactive encapsulation technique can be employed to synthesize nanoporous polymeric materials of desired porosity and pore size by changing the solvent content.

Nanoporous thermosets via Reactive Encapsulation of a Chemically Inert Solvent versus Free Radically Polymerized and Phase Separating Systems

ABSTRACTNanoporous thermosets are used as polyelectrolytes in fuel cells, separation membranes, and sensors and actuators, etc. Design of nanoporous thermosets for such applications entails controlling permeability by tailoring the pore size and pore chemistry. Usually free radically polymerizing and simultaneously phase separating systems are used to synthesize porous thermosets. A novel method of synthesizing nanoporous polymeric materials is employed in this work. This technique involves the synthesis of nanoporous thermosets by reactive encapsulation of an inert solvent using step-growth crosslinking polymerization reaction carried out until completion without phase separation into macroscopic phases. Key structural features of the porous materials synthesized by the reactive encapsulation technique were investigated by Scanning Electron Microscopy (SEM) after extraction and supercritical drying using carbon dioxide. Micrographs of the materials synthesized using the reactive encapsulation technique showed that the porous materials of pore size less than 100nm are obtained. Micrographs also showed that the reactive encapsulation technique can be employed to synthesize nanoporous polymeric materials of desired porosity and pore size by changing the solvent content. In addition, porous thermosets were also synthesized using free radical chemistry and phase separating system. The differences in the porous morphology of both these systems were enunciated using SEM micrographs.

Synthesis and characterization of new polyureas derived from 4‐(4′‐Methoxyphenyl)urazole

Abstract4‐(4′‐Methoxyphenyl)urazole (MPU) was prepared from 4‐methoxybenzoic acid in five steps. The reaction of monomer MPU with n‐isopropylisocyanate was performed at room temperature in N,N‐dimethylformamide solution, and the resulting bis‐urea derivative was obtained in high yield and was finally used as a model for polymerization reaction. The step‐growth polymerization reactions of monomer MPU with hexamethylene diioscyanate, isophorone diioscyanate, and toluene‐2,4‐diioscyanate were performed in N,N‐dimethylacetamide solution in the presence of pyridine as a catalyst. The resulting novel polyureas have an inherent viscosity (ηinh) in a range of 0.07–0.21 dL/g in DMF and sulfuric acid at 25°C. These polyureas were characterized by IR, 1H‐NMR, elemental analysis, and TGA. Some physical properties and structural characterization of these novel polyureas are reported. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1141–1146, 2002

Synthesis of ether‐linked bisoxazolines and their use in step‐growth polymerization reactions with phenolics

AbstractSix new ether‐linked bisoxazolines have been synthesized via reaction of p‐hydroxyphenyl‐2‐oxazoline with dihalides. These bisoxazolines may be used as chain extenders or crosslinkers for resins, monomers or polymers containing various acidic groups, including phenolics, via step‐growth (1 : 1) reactions. As an illustration, a phenol‐formaldehyde polycondensate (Alnovol) and an enzyme oligomerized bisphenol A resin, as well as poly (p‐hydroxystyrene), was chain extended and crosslinked to produce thermosets with high glass transition temperatures. The new bisoxazolines were also polymerized with diphenol compounds, such as diphone D and bisphenol P to generate linear or branched oligomers and polymers. Differential scanning calorimetry was used to evaluate the potential for polymerization and crosslinking reactions. Preliminary results showed that the new, ether‐linked bisoxazolines have potential for formulating high performance thermosets. Copyright © 2002 John Wiley & Sons, Ltd.

A quantum mechanical study of the bonding of a silyl ester to hydrated alumina

The bonding of methyltrimethoxysilane (MTMS), a model for alkoxysilane primers and adhesion promoters, to a hydrated alumina cluster has been studied with density functional theory. The most probable site for formation of an aluminosiloxane bond is at a surface hydroxyl defect site, such as might exist at a step dislocation on a hydrated alumina surface rather than the more symmetric tuck-in site with pseudo-C 3v symmetry on the (0 0 0 1) surface. The energetics of the step-growth polymerization reaction of MTMS has also been studied, and it is concluded that the oligomerization/polymerization reaction, which consumes water and releases methanol, is practically athermal. Thus, the polymerization reaction is primarily driven by entropic factors. At low coverage, chemisorbed alkoxysilanes will most likely be unevenly distributed as determined by the irregularity of the surface defects and as influenced by the relative humidity at the time of application. At high coverage, well-aged alkoxysilanes on metal or semi-metal oxide surfaces are probably best represented as polymerized (thermoset) resins that are chemically bonded to the substrate at most, if not all, accessible hydroxyl sites.

An Alternate Synthetic Approach for Soluble Nonlinear Optical Polyimides

Three functionalized second-order nonlinear optical polyimides were synthesized by the step growth polymerization reaction between a chromophore-containing dianhydride and three different diamine compounds. This alternate approach (i.e., incorporating a nonlinear chromophore into a dianhydride monomer) may avoid troublesome syntheses of the chromophore-containing diamine and can provide easy preparation of the polyimides with various chromophores. The number-average molecular weights (Mn) of final polymers determined by GPC ranged between 10 000 and 16 800 (Mw/Mn = 1.59−2.28). No melting was detected and they showed relatively low glass-transition temperatures ranging from 161 to 181 °C. They are readily soluble in aprotic polar solvents such as tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidinone, and so forth. High optical quality films were prepared by spin casting from a 10 wt % cyclohexanone or N-methylpyrrolidinone solution. The second harmonic generation (SHG) coefficients, d33, of the polymers were determined to be 24−37 pm/V (d33(∞) = 7−10 pm/V) at a fundamental wavelength of 1064 nm. All of the poled polymer samples showed outstanding orientational stability up to 125 °C without any measurable decay of the SHG signal. In particular, the polyimide with a 4,4‘-(hexafluoroisopropylidene)dianiline unit (PI-2-DANS) showed the best dynamical thermal stability of the poling-induced dipole alignment up to ca. 170 °C.

Exactly alternating silarylene–siloxane polymers. I. The synthesis and stability of bis(1,1-tetramethylene-3-phenylureido)dimethylsilane

Ureidosilanes have been found to be active monomers for the preparation of siloxane polymers by step-growth polymerization reactions at low temperatures. For this purpose, very high monomer purities are required, and the present investigation was concerned with the purity and stability of bis(1,1-tetramethylene-3-phenylureido)dimethylsilane prepared from the diaminosilane and phenyl isocyanate. Preparation of the monomer by this reaction at −20°C gave directly a product of very high purity suitable for the preparation of very high molecular weight polymers. Pseudo-first-order rate constants were obtained on the hydrolysis of the monomer during synthesis and storage.

Synthesis of perfluoroalkylether oxadiazole elastomers

A method for the simultaneous chain extension and crosslinking of perfluoroalkylethers which yields a thermally stable perfluoroalkylether oxadiazole elastomer crosslinked by trifunctional perfluoroalkylether-1,3,5-triazine is reported. In the preparation, hydroxylamine crystals prepared from hydroxylamine hydrochloride to which sodium butoxide had been added is mixed with perfluoroalkylether dinitrile to obtain the monomer, as the nitrile is converted to amidoxime. Monomers are heated at 140 to 200 C to form poly(perfluoroalkylether oxadiazole) with a 1,2,4-oxadiazole structure by a step-growth polymerization reaction. Simultaneous chain extension and crosslinking are observed to occur when the purified monomer is heated directly and when the remaining nitrile in the monomer is allowed to react with excess ammonia to form the corresponding amidine, which is then heated. Weight loss studies show the thermal stability of the perfluoroalkylether elastomer to be generally better than fluorosilicone or polyester elastomers, especially in air, indicating its potential usefulness for high-performance elastomeric applications.