Synthesis of emulsion styrene butadiene rubber by reversible addition–fragmentation chain transfer polymerization and its properties

Emulsion polymerization is generally used to synthesize styrene butadiene rubber (SBR), and the molecular weight of this rubber can be easily increased. However, the broad molecular weight distribution (MWD) of SBR increases energy loss and adversely affects the dynamic viscoelastic properties. To overcome this disadvantage, reversible addition–fragmentation chain transfer (RAFT) polymerization, which is a type of living polymerization, is applied to emulsion polymerization for preparing RAFT emulsion SBR (ESBR). The molecular weight and microstructure of RAFT ESBR are compared to those of commercially available ESBR 1502 by gel permeation chromatography and proton nuclear magnetic resonance spectroscopy. The aforementioned two polymers are used to prepare unfilled ESBR compounds, which are compared in terms of key physical properties (abrasion resistance, mechanical properties, and dynamic viscoelastic properties). It is confirmed that various physical properties of RAFT ESBR are improved due to its narrow MWD. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47069.     

Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition–fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide

Reversible addition–fragmentation chain transfer (RAFT) polymerization was used to control the grafting of 2,2,2-trifluoroethyl methacrylate (TFEMA) with ramie fibers in supercritical carbon dioxide (scCO₂). The hydroxyl groups of the ramie fibers were converted to 2-dithiobenzoyl isobutyrate as the RAFT chain transfer agent (cellulose-CTA). Then, the subsequent grafting with TFEMA was mediated by RAFT polymerization in the presence of 2-(ethoxycarbonyl)prop-2-yl dithiobenzoate (ECPDB) as the free RAFT chain transfer agent (free CTA). The modified ramie fibers were highly hydrophobic with water contact angles of up to 149°. Size exclusion chromatography showed narrow polydispersity (PDI = 1.28) of the grafted poly(TFEMA) chains. This grafting polymerization process is a novel and environmentally friendly approach for the preparation of functional grafted copolymers utilizing ramie fiber biomass.     

Using dilatometry in the reversible addition fragmentation transfer polymerization of N-(S)-(−)-α-methylbenzyl methacryloylamine

Optically active polymers were prepared using reversible addition-fragmentation chain transfer polymerization (RAFT) of N-(S)-α-methylbenzylmethacryloylamine (N-(S)-α-MBMA), a functional optically active monomer. RAFT polymerizations were carried out at 70 °C in ethanol using AIBN as a thermal initiator and benzyl or (1-phenyl)ethyl dithiobenzoate (BDB and PEDB, respectively) as the RAFT agents. The kinetic study was performed by dilatometry. Plots of conversion vs time indicated that the polymerizations followed first order kinetics. ¹H NMR, IR, and UV–vis spectrophotometric studies confirmed the presence of thiocarbonylthio moieties (−SCS-) in the polymer chains. The molecular weight distributions (MWDs) were moderately narrow with polydispersity indices between 1.3 and 1.6, which indicated that the control of the reaction was not completely achievement using BDB or PEDB as RAFT agents. The optical activity [α]_D²⁵ measurements of synthesized polymers by RAFT did not show a noticeably linear increase dependence with respect to molecular weight, as was previously reported for another controlled free radical polymerization (CRP) system.     

ω-Iodinated poly(dimethylsiloxane) as a chain transfer agent in iodine transfer radical polymerization of vinyl acetate and dibutyl maleate: synthesis and structural characterization

Iodine transfer radical homo- (ITP) and copolymerization (ITCP) of vinyl acetate (VAc) with dibutyl maleate (DBM) initiated by 2,2?-azobis(isobutyronitrile) (AIBN) were performed in bulk at 80 °C in the presence of ω-iodo- terminated poly(dimethylsiloxane) (PDMS-I) as a macro-chain transfer agent (macro-CTA). ¹H-NMR and gel permeation chromatography (GPC) results confirmed formation of the PDMS-b-PVAc diblock copolymer. Moreover, the results of ¹H-NMR showed that the iodo-terminated chain ends are unstable and decompose to the aldehyde moieties. On the other hand, different behaviour was observed in the ITCP of the VAc and DBM. ¹H-NMR and GPC results showed that presence of DBM in the reaction medium leads to degradation of the C-I bond of the PDMS-I, resulting in the generation of HI. In fact, PDMS-I acts as in situ generator of the CTA in the presence of DBM via reaction between the generated HI and VAc. In other words, it was found that P(VAc-co-DBM) copolymer chains are synthesised by ITP mechanism in the presence of in situ generated 1-iodoethyl acetate as a CTA. Therefore, a mixture of PDMS and P(VAc-co-DBM) chains was obtained.     

Synthesis of core–shell-type styrene acrylic latexes with low NMA content and their application in pigment printing pastes

In this paper, novel core–shell polymers comprising styrene (St) and butyl acrylate (BA) in both core and shell layers of the polymer particles have been synthesized and employed in pigment printing pastes which were applied on 100% cotton and 65% cotton/35% polyester (PET) fabrics. The aim was to reduce the NMA content and the formation of free formaldehyde from pigment printing pastes by employing newly synthesized core-/shell-type polymers. After five washing cycles, the synthesized core-/shell-type polymer including 1% NMA in the core and 1% NMA in the shell with T _g values +30°C and ?20°C, respectively, with lowest total NMA content (1.03%) yielded the best result and showed closest ΔE values to the commercially available polymer including 4% NMA. Dry and wet rubbing fastness results showed no significant changes in the absence of NMA when compared with NMA containing samples. The penetration degree of the pigment pastes of the corresponding polymers was relatively higher on 100% cotton fabric for both red- and blue-colored pigments. A negligible decrease in color strength has been observed for all polymers when colored in red.     

Study of macroinitiator efficiency and microstructure–thermal properties in the atom transfer radical polymerization of methyl methacrylate

The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with poly vinylacetate macroinitiator (PVAc-CCl₃) and CuCl/PMDETA as catalyst was successfully carried out in bulk and solution. The apparent propagation rate constant () and concentration of active species ([P°]) were higher in the bulk. In solution they increased with polarity of solvent. Two different molecular weights of macroinitiators were used in ATRP of MMA. The linear relation of Ln[M]₀/[M] versus time was only confirmed for the low molecular weight macroinitiator. The ratio of was calculated in the bulk reaction with the low molecular weight macroinitiator, this ratio was 1.77 × 10¹⁴ M⁻¹ s⁻¹ for larger macroinitiator in solution. The MWD of block copolymers were sharper with lower molecular weight macroinitiator in the solution, but it appeared broader in the bulk polymerization. Our results indicated that smaller molecular weight macroinitiator was more efficient and formed a block copolymer with lower PDI. Thermal analysis and microstructure of the block copolymers are investigated by ¹H NMR, FT-IR, TGA and DSC. The chain tacticity of the MMA units is found not to be sensitive to the kinetic of the reactions with two different molecular weights of macroinitiator. DSC measurement shows two different transitions at 39 and 108 °C assigned to PVAc and PMMA blocks. The TGA profile shows a three-step degradation. The initial small weight loss that occurs around 220 °C and two large weight loss around 238 and 310 °C are attributed to dechlorination step and decomposition of the PMMA and PVAc blocks.     

Synthesis of new chiral phosphine–phosphites and diphosphites and their application in asymmetric hydroformylation

A new chiral phosphine–phosphite and two strictly related diphosphites have been synthesised and tested in the asymmetric hydroformylation of styrene. The catalytic efficiency of the phosphine–phosphite appears distinctly higher than that of the two diphosphites; in particular, it furnishes 2-phenylpropanal with very high regioselectivity and enantioselectivity up to 40%.     

Synthesis and characterization of new soluble multisite phase transfer catalysts and their catalysis in free radical polymerization of methyl methacrylate aided by ultrasound—A kinetic study

Four different soluble phase transfer catalysts (PTCs) containing single, di, tri, and tetra active sites have been prepared and proved by FT-IR, ¹H NMR, ¹³C NMR, mass, elemental analysis, and conductivity measurement. The presence of the number of active sites in each catalyst was also been confirmed by determining their rate of polymerization of methyl methacrylate (MMA) using potassium peroxydisulfate (PDS) as a water soluble initiator in biphase medium. The comparative study reveals that the R_p of MMA determined in the presence of PTC combined with ultrasound has shown twofold enhancement in the activity than PTC alone. The observed order of activity was found to be of single-site < di-site < tri-site < tetra-site. Further, the thorough kinetic study of free radical polymerization of MMA has been investigated using superior tetra site viz., HBTAMPDTC and by varying the experimental parameters such as [MMA], [K₂S₂O₈], [MPTC], and the temperature. Based on the observed kinetic results and activation parameters, a suitable mechanism was proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Controlled/“living” atom transfer radical polymerization of styrene in the synthesis of amphiphilic diblock copolymers from a poly(ethylene glycol) macroinitiator

Summary   Atom transfer radical polymerization (ATRP) of styrene was initiated by a poly(ethylene glycol) macroinitiator prepared by quantitative esterification of MPEG2000 with 2-chloropropionyl chloride. The polymerization carried out at 130°C catalyzed by addition of cuprous chloride and 2,2'-bipyridine has been found to comply to the criteria for a “living” polymerization, since a linear

Surface modification of magnesium hydroxide and its application in flame-retardant oil-extended styrene–ethylene–butadiene–styrene/polypropylene composites

Magnesium hydroxide (MH) was modified with triethoxysilane and polymethyl–vinyl silicone rubber and used to prepare flame-retardant oil-extended styrene–ethylene–butadiene–styrene (O-SEBS)–polypropylene (PP) composites. The water contact angle of modified magnesium hydroxide (MMH) reached 141°; this indicated that MMH possessed excellent hydrophobic properties. The samples (1.6 mm) passed the UL-94 V-0 rating during vertical burning tests when the loading amount of MH or MMH was 70 wt %. This indicated the modification did not decrease the flame-retardant properties of MH. The tensile strength and elongation at break values of the MMH–O-SEBS–PP composites increased by 20.4 and 88.9%, respectively, compared with those of the MH–O-SEBS–PP composites. The modification of MH enhanced the interfacial compatibility between the flame retardant and the matrix; thus, the mechanical performance was enhanced. Moreover, MMH was scarcely extracted after water treatment for 168 h at 70 °C. As a result, the mechanical properties and flame retardancy of the MMH–O-SEBS–PP composites were well maintained after the water treatment. The modification of the MH endowed the O-SEBS–PP composites with an excellent compatibility and water-resistant performance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47129.     

Synthesis of imidazole-based NHC–Au(I) complexes and their application in non-enzymatic glucose sensing

In this study, imidazole-based NHC–Au(I) complexes were prepared. Geometrically optimized structures and molecular orbital energy diagrams were computed using density functional theory. Cyclic voltammetry and amperometric methods were used to evaluate the catalytic activity of the NHC–Au(I)-modified electrodes toward glucose oxidation. The mechanism of electrocatalytic oxidation at NHC–Au(I)-modified electrodes is explained on the basis of the oxidation and reduction potentials in the presence of glucose. Applicability of NHC–Au(I)-modified electrode was extended to determine the glucose level in the blood serum and the precision of the method was found to be satisfactory. The non-enzymatic sensor exhibited excellent reproducibility, repeatability, antifouling, and anti-interference characteristics.     

Synthesis and characterization of new Mg–O–F system and its application as catalytic support

The Mg–O–F system (MgF₂–MgO) with different contents of MgF₂ (100–0%) and MgO is tested as support of iridium catalysts in the hydrogenation of toluene as a function of the MgF₂/MgO ratio. Mg–O–F samples have been prepared by the reaction of magnesium carbonate with hydrofluoric acid. The MgF₂–MgO supports, after calcination at 500 °C, are classified as mesoporous of surface area (34–135 m²·g^− 1) depending on the amount of MgO introduced. The Ir/Mg–O–F catalysts have been tested in the hydrogenation of toluene. The highest activity, expressed as TOF, min^− 1, was obtained for the catalyst supported on Mg–O–F containing 75 mol%MgF₂.     

Synthesis and characterization of polybenzimidazole–nanodiamond hybrids via in situ polymerization method

Poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI) was polymerized in poly(phosphoric acid) (PPA) with the presence of the pristine nanodiamonds (NDs) (0.2–5 wt %) to fabricate NDs-g-OPBI/OPBI nanocomposites via Friedel–Crafts (F-C) reaction. The OPBI chains were successfully attached to the NDs through F-C reaction between carboxylic acid from OPBI and NDs, which was proved by nuclear magnetic resonance, X-ray photoelectron, and X-ray diffraction. NDs-g-OPBI/OPBI nanocomposites show more homogeneous dispersion than the physical blending containing pristine NDs and OPBI matrix, as showed through scanning electronic microscopy images. The mechanical properties, including Young's modulus, yield strength, and tensile strength are all improved by the introduction of NDs (<1 wt %) without loss of ductility, which overcomes the brittleness brought by the addition of inorganic reinforced agent in traditional composites. Dynamic mechanical analysis results showed that the modulus of the ND-g-OPBI/OPBI nanocomposites was significantly higher than OPBI matrix, and the NDs-g-OPBI/OPBI nanocomposites displayed more pronounced improvement than the physical blending, which could be ascribed to the homogeneous dispersion of NDs particles and the covalent bonding between NDs and OPBI via F-C reaction. Thermogravimetric analysis indicated that all the OPBI nanocomposites containing NDs displayed the improved thermal stability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of chiral benzene-based tetraoxazolines and their application in asymmetric Friedel–Crafts alkylation of indole derivatives with nitroalkenes

A series of new chiral benzene-based tetraoxazoline ligands were prepared in good yields through the reaction of 1,2,4,5-benzenetetracarboxylic acid and chiral β-amino alcohols by continuous removal of water, and the asymmetric Friedel–Crafts alkylation of indole derivatives with nitroalkenes was tested using the chiral catalysts, which were generated in situ by refluxing the above ligands and anhydrous zinc chloride in solvent. In most case, good yields (up to 99%) and excellent enantioselectivities (up to 98% ee) were obtained.     

Synthesis of yellow pyridonylazo colorants and their application in dye–pigment hybrid colour filters for liquid crystal display

Nine yellow azo dyes were designed and synthesised by using different diazo components and pyridonyl coupling components for application in dye–pigment hybrid colour filters for liquid crystal displays. The synthesised dyes were characterised by proton nuclear magnetic resonance and elemental analysis. The thermal stability was examined by thermogravimetric analysis, and solubility was estimated in industrial solvents such as N-methyl-2-pyrrolidone and propylene glycol methyl ether acetate. The dyes, which exhibited suitable physical properties for use in a dye–pigment hybrid colour filter, were fabricated into colour filters, and their optical properties were measured.     

Synthesis and characterization of composites based on polyaniline and styrene–divinylbenzene copolymer using benzoyl peroxide as oxidant agent

This work presents a method to prepare composites based on polyaniline (Pani) and styrene–divinylbenzene copolymers (SD) by in situ polymerization of aniline using benzoyl peroxide as oxidant agent. The composites were obtained from copolymers with two degrees of porosities which have higher and lower surface areas. Emeraldine Pani was prepared using hydrochloric acid as dopant. One cycle or four cycles of aniline polymerization were performed. The copolymers and their respective composites characterizations were performed by infrared spectroscopy, thermogravimetric analysis, physical nitrogen adsorption–desorption measurements, morphology analysis, elemental analysis and determination of Brönsted acid sites. The Pani was distributed overall porous SD copolymer producing composites with high surface area. Then, they were evaluated as catalysts for esterification reaction of a fat acid. It was found that that composites prepared with four cycles of in situ polymerization presented best catalytic activity than one cycle composites.     

Synthesis of cobalt complexes and their evaluation as an adhesion promoter in a rubber–steel wire system

Cobalt adhesion promoters are considered as one of the most important ingredients in the tyre industry for adhesion between the rubber compound and the brass plated steel cord for manufacturing of steel-belted radial tyres. Most of the commercially available cobalt compounds are either higher fatty acid salts, or cobaltchelate complexes, e.g., cobalt octate, naphthenate, stearate and cobalt-boron complexes. Among all the available cobalt salts, cobalt-boron complexes are the most popular ones and bond well. Considering the availability, economics and performance of the different cobalt salts, an attempt has been made in this study to synthesise different cobalt-chelate complexes and to make a comparative evaluation. In some of the cases the cobalt complexes developed showed better adhesion properties as compared to the control compound.     

Preparation of conducting composite particles of styrene–methyl acrylate copolymer as the core and graphite-incorporated polypyrrole as the shell by surfactant-free mini emulsion polymerization

A series of nearly monodispersed poly(styrene–methyl acrylate) (SMA) copolymer latex particles were coated with polypyrrole having different graphite contents. The composite particles were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The d.c. conductivity and the electrochemical behaviour of the particles were studied by using a standard four-probe method and a cyclic voltameter respectively. The dependence of electrical conductivity of the composites on the concentration of graphite in the polypyrrole shell, the methyl acrylate content in SMA copolymer and the temperature was also investigated. The electrical conductivity of the samples can be tuned by varying the graphite content in the polypyrrole shell phase. The d.c. conductivity decreases with increasing methyl acrylate content in the core particles. Electrochemical study (at a scan rate of 50 mV s⁻¹) reveals that the particles are sufficiently stable under redox potential and should find potential applications in various optoelectronic devices.