Reduction and hydroboration with borane and haloborane complexes of poly(propylene sulfide) grafted on crosslinked polystyrene

Preparation of borane and haloborane complexes of poly(propylene sulfide) grafted on crosslinked polystyrene was investigated. Graft polymer–borane was prepared by reaction of graft polymer with B₂H₆ and BH₃–THF. Graft polymer–haloborane was prepared by reaction with haloborane–tetrahydrofuran and by reaction of borane-bound graft polymer with halogen. Graft polymers with high borane (2.44 mmol/g) and haloborane (163 mmol/g) content were reached. The use of these graft polymers as polymeric reagents for reduction of carbonyl compounds and hydroboration was investigated. Aldehydes, ketones, carboxylic acids, and esters were reduced in high yields to the corresponding alcohols by borane-bound graft polymer. The graft polymer showed good chemoselectivity in competative reduction of cyclohexanone and other ketones and aldehydes, as well as in competative reduction of acetophenone and benzaldehyde. Reactivity of graft and homopolymer–borane was similar to that of borane–methyl sulfide. Hydroboration of alkenes with these graft polymers, followed by alkaline oxidation, led to the formation of the corresponding alcohols in high yields. Hydroboration was highly regioselective. Stability of the graft polymer–borane and recycling of that graft polymer were investigated. Cleavage of the poly(propylene sulfide) by the borane bound polymer took place to some extent. At 0°C no borane loss was found over a 5-week period. When recycled, 85% of the original borane content could be regenerated at the end of the fourth cycle.     

Grafted chain as spacer for an insoluble polymer ligand. II. Two-step polymerization using tetraethylthiuram disulfide as an initiator

In order to increase the percent grafting in the graft polymerization of chloromethylstyrene onto a crosslinked polystyrene bead with UV light irradiation, a two-step polymerization consisting of a suspension polymerization of styrene containing divinylbenzene using tetraethylthiuram disulfide as an initiator and then a subsequent graft polymerization of chloromethyl-styrene onto the crosslinked polystyrene bead was carried out. The percent grafting of up to 180% was obtained, the value being about twofold larger than that for the usual method using benzoyl peroxide as an initiator. The higher percent grafting was found to result from the higher grafting efficiency due to the preferential decomposition of diethyldithiocarbamate group in the crosslinked polystyrene bead with UV light irradiation. The chloromethyl group in the grafted chain was converted to aminomethyl group, and then to the iminodiacetic acid group, which was a ligand group. The adsorption behavior of Cu(II) by the ligand polymer and the catalytic activity of the complex in the decomposition of hydrogen peroxide were examined, and both properties were found to be improved by introducing grafted chain as spacer, especially markedly at a higher percent grafting.     

Selective plasma‐induced grafting of polystyrene onto polyolefin blends

Plasma pretreatment has been used to generate reactive radicals and oxygenated groups on polymer surfaces for graft polymerization. The polymer substrates studied were composed of a polypropylene–polyethylene (PP–PE) copolymer, which was predominantly PP, and also contained blended ethylene–propylene rubber (EPR) as either about 15 or about 60 mol %. A pure PP substrate was also studied for comparison. The grafted polymer was polystyrene (PS). Raman microspectroscopic 2‐dimensional mapping was used to elucidate the role of crystallinity and EPR in the plasma treatment and graft polymerization process. It was found that the plasma pretreatment favored the EPR component of the substrate and the graft yield was related to the EPR content. Crystallinity seemed to have a much less significant effect on the grafting reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1643–1652, 2003     

Encapsulation of fillers with grafted polymers for model composites

Glass beads were encapsulated by grafted polymers: polybutylacrylate and polystyrene. Grafting was performed by the polymerization initiated from the particle surface with preliminary adsorbed polyperoxide initiator. Grafting procedure and properties of grafted film were studied using model substrates: powders, plates, and wafers by wetting technique and SEM. Conditions of grafting affect the film structure. They are porous, and due to some sort of pores the wetting liquid is able to penetrate into covering and reach the substrate. Model epoxy composites were prepared with covered glass beads. The coverings allowed a decrease of adhesion between the matrix and bead surface to detect acoustic emission caused by the debonding process. The dependence of debonding stress from covering the structure and nature was studied. © 1996 John Wiley & Sons, Inc.     

Electro‐optical properties of polymer dispersed liquid crystal prepared by successively controlled living radical polymerization

Polymer dispersed liquid crystal (PDLC) films were obtained by successive controlled living radical polymerizations: starting polystyrene (M1) was obtained by reversible addition‐fragmentation polymerization (RAFT), M1 was converted to P‐chloromethylated polystyrene (M2) which was grafted with polystyrene branches by atom transfer radical polymerization (ATRP) to yield RAFT‐initiating graft polymer containing trithiocarbonate moieties in the backbone (M3, RAFT‐active grafted polystyrene), and then PDLC films were prepared by photo‐induced RAFT copolymerization of methyl acrylate with M3 in the presence of a nematic liquid crystal. The electro‐optical properties of the films were investigated for the purpose to apply them to optical devices. Experimental results showed that preferable properties could be acquired by controlling the amount of M3 and the liquid crystal E7 in the polymer matrix of PDLC films. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Graft polymers with macromonomers. I. Synthesis from methacrylate-terminated polystyrene

Pure graft polymers having uniform molecular weight polystyrene side chains were prepared by free radical copolymerization of methacrylate-terminated polystyrene macromonomers (MA-CROMER) with ethyl acrylate, butyl acrylate, or other suitable monomers. The MACROMER monomer was synthesized by living anionic polymerization under conditions that led to very narrow molecular weight distributions. Very effective end capping produced a material that was highly monofunctional. The graft copolymers were prepared by several techniques such as free radical solution polymerization, by aqueous suspension polymerization which produced beads, or by emulsion reactions which yielded stable latices. Polymerizations were reproducible. High conversion of the MACROMER monomer into pure graft polymers was achieved, and the product was contaminated with only a little homopolymer. The milled and molded phase-separated graft polymers had optical clarity and physical properties characteristic of polystyrene-reinforced triblock polymers. Compositions of 20-30% polystyrene were thermoplastic elastomers with good recovery. When polystyrene contents were increased, the graft products were strong, flexible thermoplastics with well defined yield strengths and increased permanent set. Copolymers of polystyrene macromers with acrylonitrile or vinyl chloride produced transparent polystyrene homopolymer-free graft polymer products having improved processing over polyacrylonitrile or poly(vinyl chloride) homopolymers.     

Chemical modification of polypropylene by nitroxide-mediated radical graft polymerization of styrene

Nitroxide-mediated free radical polymerization (LREP) was employed for the first time to prepare graft copolymer by having arylated polypropylene (Cl-PP) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PP carrying 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, maleic anhydride was grafted onto polypropylene by peroxide-catalyzed swell grafting method (PP-MAH). Next, PP-MAH reacted with ethanolamine to produce a hydroxyl group containing polypropylene (PP-OH) and the obtained PP-OH was treated with α-phenyl chloroacetyl chloride and converted to a chloroacetyl group containing polypropylene (PP-Cl). Finally, 1-hydroxyl-2,2,6,6-tetramethylpiperidine (TEMPO-OH) was synthesized by reducing TEMPO with sodium ascorbate and this functional nitroxyl compound was coupled with α-phenyl chloroacetylated polypropylene. The resulting macroinitiator (PP-TEMPO) for free radical polymerization was then heated in the presence of styrene for the formation of the graft copolymer. The prepared graft copolymer was characterized by Fourier transform infrared spectroscopy and ¹H NMR techniques. Glass transition temperature of grafted copolymer was investigated using thermogravimetric analysis and differential scanning calorimetric techniques. This approach using nitroxide-mediated macroinitiators is an effective method for the preparation of new materials.     

Surface modification of natural substrates by atom transfer radical polymerization

Surface modification of various solid polysaccharide substrates was conducted by grafting methyl acrylate (MA) and styrene via atom transfer radical polymerization (ATRP) to produce well‐defined polymer grafts. The hydroxyl groups on the surfaces of the substrates were reacted with 2‐bromoisobutyryl bromide followed by graft copolymerization under ATRP conditions. The studied substrates were filter paper, microcrystalline cellulose, Lyocell fibers, dialysis tubing, and chitosan films. The modified substrates were analyzed by FT‐IR, water contact angle measurements, TGA, and SEM. FT‐IR characterization of the grafted substrates showed significant differences between the different substrates in the amount of grafted polymer. Higher amounts of polymer seem to be possible to graft from native cellulose substrates than from regenerated cellulose substrates. To investigate whether the grafted polymers were “living” after a longer time period, a second layer of polystyrene was grafted from a filter paper modified with PMA one year ago. FT‐IR characterization of the filter paper showed a peak corresponding to styrene, indicating that a block copolymer had been formed on the surface. Graft copolymerization can be used to change and tailor the surface properties of the polysaccharide substrates. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4155–4162, 2006     

Effect of initiating groups introduced onto ultrafine silica on the molecular weight polystyrene grafted onto the surface

Summary The effect of initiating groups introduced onto silica surface on the molecular weight of grafted polystyrene chain was investigated. By the treatment of polystyrene-grafted silica with aqueous solution of alkali, surface grafted polystyrene was isolated from the surface. The molecular weight of polystyrene grafted onto the silica obtained from the radical graft polymerization initiated by peroxyester groups introduced onto the surface was found to be much larger than that from the cationic polymerization initiated by acylium perchlorate groups. The number of grafted polystyrene in the radical polymerization, however, was much less than that in the cationic polymerization. Furthermore, the effect of molecular weight of grafted polystyrene on the dispersibility of silica in tetrahydrofuran was examined.     

Chemical grafting of metallocene‐catalyzed functional polypropylene copolymer on glass substrates through surface modification

This work deals with surface modification of soda‐lime glass slides which, by itself, does not have hydroxyl groups at the surface. So, a glass surface pretreatment is needed, to create hydroxyl groups onto it, before carrying out the polypropylene (PP) grafting reaction. Different acid/base pretreatments were performed to develop an adequate concentration of superficial hydroxyl groups. Subsequently, a metallocenic polymerization (propylene‐α olefin graft reaction, catalyzed by EtInd₂ZrCl₂/methylaluminoxane), was carried out to provide graft‐PP chains chemically linked to the glass surface. The surface so modified can be further functionalized and tailored for different applications, including polymer composites. The pretreatment conditions that best preserved homogeneity and caused less damage to the glass surface resulted from a step of contact with dilute HF/NH₄F buffer, a washing step with distilled water, and a final exposure to KOH. After the propylene copolymerization was performed, part of the graft copolymer formed remained chemically bonded to the glass slide surface. The presence of grafted PP at the surface was confirmed by SEM, FTIR, and EDAX characterization, even after the physically adsorbed polymer was excluded by a severe solvent extraction treatment. From these results, the copolymerization of a hydroxy α‐olefin, grafted on a MAO‐pretreated glass slide, is foreseen as a possible way to graft polymers onto inorganic solids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Functionalization of crosslinked polystyrene resins: 2. Preparation of nucleophilic resins containing hydroxyl or thiol functionalities

Crosslinked polystyrene resins containing thiol or hydroxyl functionalities on a fraction of their aromatic rings were prepared by reaction of crosslinked polystyryllithium with elemental sulphur or oxygen followed by reduction of the resulting polymer. Similarly, resins containing hydroxymethyl or thiomethyl functional groups were prepared from chloromethylated polystyrene by displacement of chloride in procedures involving three phase systems and the use of a phase transfer catalyst. The degree of functionalization could be controlled easily and the sulphur containing polymers were free of disulphide bonds.     

Graft polymerization of N‐tert‐butylacrylamide onto polypropylene during melt extrusion and biocidal properties of its products

Functionalization of polypropylene (PP) by radical graft polymerization with N‐tert‐butylacrylamide (NTBA) was successfully conducted during melt extrusion, and the grafted products were employed as precursors of biocidal N‐halamine polymers. Graft polymerization conditions, including monomer and initiator concentrations, addition of a comonomer styrene (St), were studied. Fourier transformed spectroscopy (FTIR) results and nitrogen analysis confirmed the graft polymerization on PP backbone during the reactive extrusion. The results also indicated that increase in initiator concentration led to more PP chain scission and reduction in mixing torque or polymer chain length. As the monomer concentration rose, grafted monomer content in the products improved, revealing increased grafting copolymerization in the system. Addition of St as a comonomer adversely affected grafting of NTBA, but significantly prevented polymer chain scission. This may be due to lower tendency of NTBA for copolymerization. The halogenated products exhibited potent antimicrobial properties against Escherichia coli, and the antimicrobial properties were durable and regenerable. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Graft polymerization of acrylamide onto UV-irradiated films

Graft polymerization of acrylamide was attempted onto the surface of films preirradiated with UV radiation. The films employed are nylon 6, polypropylene, and ethylene–vinyl acetate copolymers. Following UV irradiation in air on films without photosensitizer, they were placed in monomer solution, degassed, and then heated to 50°C to effect the graft polymerization. After rigorous removal of homopolymers, polyacrylamide chains were found to be grafted in the surface region of the films to amounts up to several hundred micrograms per square centimeter of films. An ESCA study revealed the UV-irradiated but not yet grafted surfaces to be oxidized, and formation of peroxides was strongly suggested by the reaction of irradiated films with 1,1-diphenyl-2-picrylhydrazyl. It is likely that the initiator responsible for the graft polymerization is peroxides generated at and near the film surfaces upon UV irradiation. The grafted films became very slippery when contacted with water, in contrast with the films UV-irradiated but not yet grafted.     

Photografting of acrylic monomers on polystyrene support

Polystyrene xanthates, prepared through the reaction of chloromethylated polystyrene resins with potassium O-ethyl xanthate, have been used for the photografting of acrylic monomers. Monomers such as acrylamide, acrylic acid, methacrylic acid, and methyl methacrylate were grafted onto the xanthate polymers on irradiation with a 450 W medium-pressure mercury lamp (Hanovia). Among these monomers, the maximum graft efficiency was obtained for methyl methacrylate. The effect of cross-link density of the xanthate polymer on the percentage graft yield was also studied. Scanning electron microscopic studies have shown that appreciable grafting has taken place on the surface of the polymer in a uniform manner. © 1992 John Wiley & Sons, Inc.     

Free radical grafting of diethylmaleate on linear low-density polyethylenes

Grafting of preformed polymers is an important method for preparing polymers with functional groups. Lately, the use of extruders as polymerization reactors has increased considerably in industry. However, the knowledge of the total reaction process is still limited. Grafting of diethylmaleate on linear low-density polyethylenes (LLDPEs) was carried out in solution and in a corotating twin screw extruder. The effects of initiator and diethylmaleate concentrations, temperature, and reaction time on graft content and on crosslinking were investigated. The functionalization reaction was also conducted in the presence of an electron donor material to minimize the amount of crosslinked products in the extruder. The grafted products were characterized by means of FTIR and the thermal behavior of LLDPEs and that of its grafted products was determined.     

Cationic graft polymerization of polymers from carbon fiber initiated by acylium perchlorate groups introduced onto the surface

The cationic graft polymerization of several monomers initiated by acylium perchlorate groups introduced onto the carbon fiber surface was investigated to modify the surface. The introduction of acylium perchlorate groups was successfully achieved by the reaction of silver perchlorate with acyl chloride groups, which were introduced by the reaction of surface carboxyl groups with thionyl chloride. It was found that the cationic polymerization of styrene is initiated by acylium perchlorate groups on the carbon fiber. In the polymerization, polystyrene was grafted onto the carbon fiber surface through the propagation of polystyrene from the surface. Ungrafted polymer was also formed by the chain transfer reaction of growing polymer cation to the monomer. The acylium perchlorate groups have the ability to initiate cationic ring-opening polymerization of tetrahydrofuran (THF) and ε-caprolactone (CL), polyTHF and polyCL being grafted onto the carbon fiber surface, respectively. Polyacetals, such as poly(1,3-dioxolane) and polyoxymethylene, were able to graft onto the carbon fiber by cationic ring-opening polymerization of the corresponding monomers.     

Synthesis of polypropylene graft copolymers from a hydroxyl‐groups‐containing polypropylene precursor via atom‐transfer radical polymerization

Isotactic polypropylene graft copolymers, isotactic[polypropylene‐graft‐poly(methyl methacrylate)] (i‐PP‐g‐PMMA) and isotactic[polypropylene‐graft‐polystyrene] (i‐PP‐g‐PS), were prepared by atom‐transfer radical polymerization (ATRP) using a 2‐bromopropionic ester macro‐initiator from functional polypropylene‐containing hydroxyl groups. This kind of functionalized propylene can be obtained by copolymerization of propylene and borane monomer using isospecific MgCl₂‐supported TiCl₄ as catalyst. Both the graft density and the molecular weights of i‐PP‐based graft copolymers were controlled by changing the hydroxyl group contents of functionalized polypropylene and the amount of monomer used in the grafting reaction. The effect of i‐PP‐g‐PS graft copolymer on PP‐PS blends and that of i‐PP‐g‐PMMA graft copolymer on PP‐PMMA blends were studied by scanning electron microscopy. Copyright © 2006 Society of Chemical Industry     

Hg(II) removal with polyacrylamide grafted crosslinked poly(vinyl chloride) beads via surface‐initiated controlled/“living” radical polymerization

Polyacrylamide grafted crosslinked poly (vinyl chloride) beads (PAM‐PVC) were prepared by the surface‐initiated controlled/“living” radical polymerization (SI‐CLRP) methodology from the crosslinked poly(vinyl chloride) beads with surface modification with diethyldithiocarbamyl groups under UV irradiation. The macroiniferter, diethyldithiocarbamyl crosslinked poly(vinyl chloride) beads (DEDTC‐PVC) were prepared by the reaction of the surface C? Cl groups with sodium N,N‐diethyl dithiocarbamate. The “grafting from” polymerization exhibited some “living” polymerization characteristics and the percentage of grafting (PG%) increased linearly with polymerizing time and achieved 47.6% after 6 h UV irradiation. The beaded polymer with polyacrylamide surface was also characterized with Fourier transform infrared (FTIR) and scanning electron microscope (SEM). Its adsorption property for Hg(II) ion was also investigated preliminarily. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3385–3390, 2006     

Surface grafting of polymers onto aramid powder: graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface of aramid powder

The radical graft polymerization of vinyl monomers onto the surface of aramid powder, i.e., poly(p-phenylene terephthalamide) powder, initiated by azo groups introduced onto the surface was investigated. The introduction of azo groups onto the aramid surface was achieved by the reaction of surface acyl chloride groups, which were introduced by the treatment of aramid powder with adipoyl dichloride, with 2,2′-azobis[2-(2-imidazolyn-2-yl)propane] in the presence of pyridine: the amount of azo groups thus introduced onto the surface was determined to be 0.57 mmol/g by elemental analysis. It was found that the polymerizations of methyl methacrylate (MMA) and styrene were successfully initiated by the azo groups on the surface and that the corresponding polymers were grafted onto the surface. The percentage of surface grafting of polystyrene and poly(methyl methacrylate) (PMMA) increased up to 37.6 and 26.5%, respectively. Thermogravimetric analysis of polymer surface-grafted aramid powder confirmed that the grafting of polymers is limited on the surface. The polymerization rate was found to bear a first-order dependence on the concentration of aramid powder having azo groups. This suggests that in graft polymerization, unimolecular termination preferentially proceeds.     

Graft copolymers of starch and poly(2-hydroxy-3-methacryloyloxypropyltrimethyl-ammonium chloride). Preparation and testing as flocculating agents

The title monomer (I) has been graft polymerized onto whole wheat starch with both ceric ammonium nitrate and ferrous ammonium sulfate–hydrogen peroxide initiation. Three graft copolymers, which contained 4.5, 12.1, and 15.2% grafted poly(I), were characterized as to molecular weight of grafted branches and grafting frequency. Graft polymerization was proved by fractional precipitation. Graft copolymers were tested as flocculating agents for diatomaceous silica and nonmagnetic iron ore. The graft copolymers with 12.1 and 15.2% grafted poly(I) compared favorably in flocculating ability with a commercial high molecular weight cationic polyacrylamide.