Graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate) by chain transfer reaction

To obtain highly branched graft copolymers, styrene (St) was grafted onto poly(vinyl p-nitrobenzoate) (PVNB) as a trunk polymer through the chain transfer reaction of growing polystyrene (PSt) radicals to the pendent aromatic nitro groups on the trunk polymer. The number of PSt branches increased with St concentration at constant concentrations of PVNB and azobisisobutyronitrile (AIBN) as an initiator, and decreased with AIBN concentration at constant PVNB and St concentrations. The maximum number of branches attained was 43 (P_n of PVNB was 970), which corresponds to 23 monomer units of PVNB per PSt branch. It is confirmed from the results of infrared spectroscopy that the addition of the growing polystyrene radicals occurs not at the benzene rings but at the nitro groups on the benzene rings. Polymerization of St was also carried out in the presence of isopropyl p-nitrobenzoate (IPNB) as a model compound of PVNB. IPNB was found to retard the polymerization of styrene more strongly than PVNB. The chain transfer constant of the polystyrene radicals to IPNB was more than twice as large as that to PVNB.     

Graft copolymerization of styrene onto cellulose acetate p-nitrobenzoate by chain transfer reaction

Styrene was grafted onto cellulose acetate p-nitrobenzoate (CANB) by chain transfer reaction of growing polymer radicals to the pendant nitro groups of CANB. A copolymer with a branch for every 17.2 nitro groups was obtained. This result indicates that the pendant aromatic nitro group is more effective in obtaining a graft copolymer by radical mechanism than pendant double bond on the trunk polymer previously reported, where graft copolymers with a branch for several hundred of double bonds are produced.     

Graft frequency of graft copolymers by chain transfer of growing polymer radicals to trunk polymers containing nitro groups

The relationship between the chain transfer constant, extent of monomer conversion, and number of branches was derived for the graft copolymerization through chain transfer of growing polymer radicals to the pendent aromatic nitro groups on the trunk polymer. The equation derived enables us to predict the number of branches for a given monomer trunk polymer. The relationship obtained is compared with the experimental data previously reported for the graft copolymerization of styrene onto poly(vinyl p-nitrobenzoate). The value of α′, the ratio of nitro groups with branches to those which are attacked by polystyrene radicals, is less than unity except for the graft copolymers obtained with high initiator concentrations and at early stages of the reaction. This lowering of α′ is attributed to the steric hindrance of branches already formed on the trunk polymer which prevents the attack of polystyrene radicals on the nitro groups and side reactions, such as reaction of the nitroso groups formed as an intermediate with styrene.     

Graft copolymerization of styrene onto poly(p-nitrophenyl acrylate) by chain transfer reaction

Styrene (St) was polymerized in the presence of poly(p-nitrophenyl acrylate) (PNPA) with azobisisobutyronitrile as an initiator to prepare graft copolymers through the chain transfer reaction of growing polystyrene (PSt) radicals to the aromatic nitro groups on PNPA. The maximum number of branches attained was 16.4 (P _n of PNPA was 1780), which corresponds to 108 monomer units per PSt branch. This is far less than the value of 43, previously obtained for poly(vinyl p-nitrobenzoate) as a trunk polymer. Therefore, several model compounds for trunk polymers were prepared, and the chain transfer constants of PSt radicals to these model compounds were determined. As a result of the Hammett plot, it is concluded that higher electron attracting property of the substituents increases the reactivity of nitro groups to the growing PSt radicals, resulting in more highly branched graft copolymers.     

Modeling of “living” free‐radical polymerization processes. I. Batch,semibatch, and continuous tank reactors

A comprehensive mathematical model is developed for “living” free‐radical polymerization carried out in tank reactors and provides a tool for the study of process development and design issues. The model is validated using experimental data for nitroxide‐mediated styrene polymerization and atom transfer radical copolymerization of styrene and n‐butyl acrylate. Simulations show that the presence of reversible capping reactions between growing and dormant polymer chains should boost initiation efficiency when using free nitroxide in conjunction with conventional initiator and also increase the effectiveness of thermal initiation. A study shows the effects of the value of the capping equilibrium constant and capping reaction rate constants for both nitroxide‐mediated styrene polymerization (using alkoxyamine as polymer chain seeds) and atom transfer radical polymerization of n‐butyl acrylate (using methyl 2‐bromopropionate as chain extension seeds). Also the effect of introducing additional conventional initiator into atom transfer radical polymerization of n‐butyl acrylate is studied. It is found that the characteristics of long chain growth are determined by the fast exchange of radicals between growing and dormant polymer chains. Polymerization results in batch, semibatch, and a series of continuous tank reactors are analyzed. The simulations also show that a semibatch reactor is most flexible for the preparation of polymers with controlled architecture. For continuous tank reactors, the residence time distribution has a significant effect on the development of chain architecture. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1630–1662, 2002     

Further discussion on the estimation of primary polymer chain length of vinyl-type network polymers based on the thermal decomposition of azo crosslinks

2,2′-Azobis[N-(2-propenyl)-2-methylpropionamide] (APMPA) having two carbon-carbon double bonds and an azo group was copolymerized with vinyl benzoate (VBz) at 60 °C, providing an azo groups containing VBz/APMPA prepolymer or crosslinked polymer which acts as a soluble or insoluble polymeric azo initiator, respectively. The gelation in VBz/APMPA (90/10 mol/mol) copolymerization was discussed briefly in order to reveal the characteristic polymerization behavior of APMPA as a novel crosslinker. Then, the resulting poly(VBz-co-APMPA)s as prepolymers or crosslinked polymers were thermally decomposed at elevated temperatures in the presence of lauryl mercaptan (LM) as a chain transfer agent; thus, the polymeric radicals generated through the cleavage of azo crosslinks would undergo the chain transfer reaction with LM to give primary polymer chains. This will provide a new approach to estimate the primary polymer chain length of vinyl-type network polymers by cutting all crosslinks in the network at the gel point as defined for the derivation of Stockmayer's equation.     

ESR study of reactions of cellulose initiated by the ceric ion method

The ESR spectra of microcrystalline cellulose and purified cotton cellulose reacted with ceric ammonium nitrate in nitric acid were determined. The effects of the concentration of ceric ion, atmosphere, temperature, and graft copolymerization with acrylonitrile on the rates of formation and decay of radicals in the cellulose molecule were determined under both static and dynamic conditions. Under static conditions, after the desired conditions of reaction, the samples were frozen at –100 or –160°C., and then the concentration of free radicals was determined. Under dynamic conditions ceric ion solution was continuously flowed through the celluloses while these determinations were being made at 25°C. In the presence of oxygen the rate of decay of free radicals was decreased. On initiation of copolymerization reactions with acrylonitrile, there was an increase in radical concentration, then a decrease. Apparently, during graft copolymerization the radical site initially on the cellulose molecule was retained on the end of the growing polymer chain. Then additional ceric ion coordinated with the hydroxyl groups of the cellulose, leading to the formation of additional radical sites. An Arrhenius interpretation of the effect of temperature on the formation of these additional radical sites gave apparent activation energies for radical formation on cotton cellulose as 34 kcal./mole and on microcrystalline cellulose as 29 kcal./mole.     

Synthesis of graft copolymers from a linear polyolefin through a combination of coordination polymerization and atom transfer radical polymerization

This article reports on a facile route for the preparation of methyl acrylate and methyl methacrylate graft copolymers via a combination of catalytic olefin copolymerization and atom transfer radical polymerization (ATRP). The chemistry first involved a transforming process from ethylene/allylbenzene copolymers to a polyolefin multifunctional macroinitiator with pendant sulfonyl chloride groups. The key to the success of the graft copolymerization was ascribed to a fast exchange rate between the dormant species and active radical species by optimization of the various experimental parameters. Polyolefin‐g‐poly(methyl methacrylate) and polyolefin‐g‐poly(methyl acrylate) graft copolymers with controlled architecture and various graft lengths were, thus, successfully prepared under dilute ATRP conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Star graft copolymer via grafting‐onto strategy using a comb!ination of reversible addition–fragmentation chain transfer arm‐first technique and aldehyde–aminooxy click reaction

A facile synthetic pathway to a multi‐arm star graft polymer has been developed via a grafting‐onto strategy using a combination of a reversible addition–fragmentation chain transfer (RAFT) arm‐first technique and aldehyde–aminooxy click reaction. A star backbone bearing aldehyde groups was prepared by the RAFT copolymerization of acrolein (Ac), an existing commercial aldehyde‐bearing monomer, with styrene (St), followed by crosslinking of the resultant poly(St‐co‐Ac) macro‐RAFT agent using divinylbenzene. The aldehyde groups on the star backbone were then used as clickable sites to attach poly(ethylene glycol) (PEG) side chains via the click reaction between the aldehyde groups and aminooxy‐terminated PEG, leading to a structurally well‐defined star graft copolymer with arms consisting of poly(St‐co‐Ac) as backbone and PEG as side chains. Crystalline morphology and self‐assembly in water of the obtained star graft copolymer were also investigated. Opportunities are open for the star graft copolymer to form either multimolecular micelles or unimolecular micelles via control of the number of grafted PEG side chains. © 2013 Society of Chemical Industry     

Contribution to the mechanism of the thiuram vulcanization. I. Polymerization of styrene in the presence of tetramethylthiuram disulfide and natural rubber

The influence of the concentration of tetramethylthiuram disulfide (TMTD) on grafting of natural rubber by styrene at 80°, 95°, 115°, and 130°C and constant molar ratio of rubber and styrene was studied. It was found that the dependence R_p = f([TMTD]^½) at all followed temperatures goes through a maximum and that TMTD substantially decreases the amount of bound rubber in the graft copolymer. The analysis of the kinetic data and the results of separation of polymer mixtures showed the significant role in the process of the termination reactions of the growing polymer and the rubber radicals with the RS radicals. The derived kinetic relation is in good agreement with the experimental, results and allows calculation of the transfer rate constants of RS radical on rubber.     

Preparation of polymers with pendant quinonoid groups and their photocrosslinking with visible light irradiation

Photosensitive polymers with pendant quinonoid groups were prepared by the reaction of p-(benzoquinon-2-ylthio) acetic acid (QTAA) or p-(p-benzoquinon-2-ylthio)benzoic acid (QTBA) with hydroxyethyl methacrylate-methyl methacrylate copolymer. The polymers showed a strong π-π^* absorption band at around 410 nm and were efficiently crosslinked by visible light irradiation. Somewhat higher photosensitivity of QTAA-bound polymer compared with that of QTBA-bound polymer suggested some contribution of intramolecular hydrogen abstraction of QTAA to the photocrosslinking.     

Graft copolymerization of methoxypoly(ethylene glycohol) methacrylate onto polyacrylonitrile and evaluation of nonthrombogenicity of the copolymer

Methoxypoly(ethylene glycohol) methacrylate was grafted onto polyacrylonitrile in dimethylsulfoxide solution via thioamide formation, where ammonium peroxydisulfate was used as an initiator. Optimum conditions for the graft copolymerization, such as degree of thioamidation of the trunk polymer, feeding concentration of the acrylate and the trunk polymer, and temperature were examined. Also the rate of graft polymerization was found to be proportional to concentrations of the acrylate and the trunk polymer. An increase of the degree of the grafting increased water content of the graft copolymer and decreased interfacial free energy between the copolymer and water. In vivo tests showed that the graft copolymer obtained was highly nonthrombogenic.     

Addition of thionucleophiles to nitrocinnamates: approach toward synthesis of (alkyl/aryl)thio-amino acids

The addition of alkyl or aryl thiols to α-nitro or β-nitrocinnamate in the presence of base provided Michael addition products. In the case of β-nitro compounds reaction occurred via the formation of anti-Michael adducts. Selective nitro reduction of α-nitroadducts gives access to β-thio-α-amino acid derivatives.     

Novel flexible network polymers consisting of oligomeric primary polymer chains originated in the mechanistic discussion of multiallyl crosslinking polymerization

Summary It is well known that allyl monomers polymerize only with difficulty and yield polymers having low molecular weights, i.e., oligomers. Inevitably, free-radical multiallyl crosslinking polymerization provides network polymers consisting of oligomeric primary polymer chains, i.e., having abundant dangling chains. This led to the development of novel flexible network polymers such as amphiphilic network polymers (I) consisting of short primary polymer chains and long crosslink units with opposite polarities, simultaneous interpenetrating networks (II) consisting of both polyurethane (PU) and polymethacrylate (PM) networks with oligomeric primary polymer chains, and network polymers (III) consisting of centipede-type primary polymer chains. Thus, the solution copolymerizations of benzyl methacrylate with tricosaethylene glycol dimethacrylate in the presence of lauryl mercaptan yielded I consisting of nonpolar, short primary polymer chains and polar, long crosslink units. The opposite type of I was prepared by the copolymerization of 2-hydroxyethyl methacrylate, a polar monomer having a hydroxyl group, with heneicosapropylene glycol dimethacrylate, a nonpolar monomer having a poly(oxypropylene) unit. The equimolar polyaddition crosslinking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol, leading to PU networks, and the free-radical crosslinking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate in the presence of CBr₄, leading to PM networks, were progressed simultaneously, providing II formed via the topological crosslink between PU and PM network structures. The post-copolymerizations of oligomeric allyl methacrylate/alkyl methacrylate precopolymers, having different amounts of pendant allyl groups and different molecular weights, with allyl benzoate/vinyl benzoate monomer mixtures were conducted to give III.     

Controlled radical copolymerization of vinyl acetate and dibutyl maleate by iodine transfer radical polymerization

Iodine transfer radical homo‐ and copolymerization of vinyl acetate (VAc) with dibutyl maleate (DBM) were carried out in the presence of ethyl iodoacetate (EtIAc) and 2,2′‐azobis(isobutyronitrile) (AIBN) as chain transfer agent and initiator, respectively, at 60 °C. Molecular weight and its distribution and (co)polymer structure (i.e. copolymer composition and chain end groups) were analysed using gel permeation chromatography and ¹H NMR spectroscopy, respectively. Homo‐ and copolymerization reactions proceed via a controlled characteristic with predetermined molecular weight and relatively narrow molecular weight distribution. The presence of DBM in the reaction mixture decreases the consumption rate of EtIAc as well as the polymerization rate. This is attributed to the effect of DBM on the transfer constant to the EtIAc and probably on the iodine exchange rate constant between the growing chains. The effect of the concentration of AIBN, EtIAc and overall monomers on the conversion, molecular weight and its distribution was studied. Simultaneously high conversion and molecular weight with a relatively narrow molecular weight distribution can be achieved only when equimolar and intermediate concentration of EtIAc and AIBN is used in the reaction mixture. End‐group analysis by ¹H NMR reveals that iodinated VAc end groups in the (co)polymer chains are unstable, resulting in aldehyde end groups. Thermogravimetric analysis shows that the thermal stability of the VAc‐based polymer increases on incorporating DBM units into the copolymer chains. © 2013 Society of Chemical Industry     

Phase‐transfer‐agent‐aided polymerization and graft copolymerization of acrylamide

The use of phase‐transfer catalysts, with water‐insoluble initiators, for polymerization and graft copolymerization reactions was explored. The polymerization of a water‐soluble vinyl monomer, acrylamide (AAm), and the graft copolymerization of AAm onto a water‐insoluble polymer backbone, isotactic polypropylene (IPP), with a water‐insoluble initiator, benzoyl peroxide (BPO), and a phase‐transfer catalyst, tetrabutyl ammonium bromide (Bu₄N⁺Br^?), were carried out in a water/xylene binary solvent system. The conversion percentage of AAm into polyacrylamide (PAAm) and the percentage of grafting of AAm onto IPP were determined as functions of various reaction parameters, such as the BPO, AAm, and phase‐transfer‐catalyst concentrations, the amounts of water and xylene in the water/xylene mixture, the time, and the temperature. The graft copolymer, IPP‐g‐PAAm, was characterized with IR spectroscopy and thermogravimetric analysis. By a comparison of the results of the phase‐transfer‐catalyzed graft copolymerization of AAm onto IPP and the preirradiation method, it was observed that the optimum reaction conditions were milder for the phase‐transfer‐catalyst‐aided graft copolymerization. Milder reaction conditions, including the temperature, the time of reaction, and a moderate initiator (BPO), in comparison with high‐energy γ‐rays, led to better quality products, and the reaction proceeded smoothly with high productivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2364–2375, 2004     

Ionic graft copolymerization. VI. Graft copolymerization of β-propiolactone and N-vinylcarbazole onto trunk polymer containing carboxylic acid,sulfonic acid,and their salts

It was pointed out in previous papers that both cationic and anionic polymerization might be involved simultaneously in grafting onto trunk polymers containing ? COOH or ? SO₃Na. The graft copolymerization of β-Propiolactone (βPL)–N-vinylcarbazole (NVCZ) onto styrene-divinylbenzene copolymers containing carboxylic acid, sulfonic acid, and their salts was carried out in order to distinguish between the polymers produced by anionic and cationic mechanisms. The polymer obtained by the polymerization of βPL–NVCZ with BF₃·OEt₂, a typical cationic catalyst, consisted mainly of NVCZ units, but the polymer obtained with BuLi, a typical anionic catalyst, consisted mainly of βPL units. In the graft copolymerization of NVCZ–βPL onto trunk polymer containing ? COOH, the NVCZ contents of the branch polymer and the tolueneinsoluble fraction were estimated to be ca. 50 mole-%; therefore these polymers were produced by both cationic and anionic mechanisms. In the case of graft copolymerization onto the trunk polymer containing SO₃Na, it was found that both cationic and anionic polymerization also occurred simultaneously.     

Aminolysis reaction of poly(N-4-methylphenylitaconimide) and its graft copolymerization

Polyitaconimide and copolymers of itaconimide were transformed to macromolecules having diamido pendent groups via an aminolysis reaction. The polymers obtained were cast into films, which were then graft copolymerized with acrylamide (AAM) using ceric ion as an initiator. Radical homopolymerization and copolymerization of N-4-methylphenylitaconimide with methyl acrylate or ethyl acrylate were carried out at 60°C in benzene; high molecular weight polymer and copolymers (M?_n = 10⁴–10⁵) were obtained. The resulting polymer and copolymers were reacted with n-butylamine in order to produce polymers possessing a pendent 4-tolylcarbamoyl group (4-CH₃C₆H₄NHCO-), which can significantly promote the acrylamide (AAM) graft copolymerization initiated with ceric ion. Transparent films of the polymers were graft copolymerized with AAM in the presence of ceric ion at 45°C. The formation of graft polymers was verified by water absorption percentage, XPS and SEM.     

Ionic graft copolymerization. VII. Ionic graft copolymerization of β-propiolactone onto the trunk polymers containing pyridine,amide, sulfonyl chloride,and carboxylic acid anhydride groups

The graft copolymerization of β-propiolactone (βPL) onto the various trunk polymers containing polar substituents such as pyridine, amide, sulfonyl chloride, and carboxylic acid anhydride groups was carried out. In the grafting onto the basic trunk polymer containing 4-vinylpyriding units, two kinds of grafting mechanism are supposed. In the case of rigorously dried trunk polymer, the polymerization is initiated by betaine and proceeds with higher grafting efficiency. Another is initiated by pyridinium hydroxide and proceeds with lower grafting efficiency. Another is initiated by pyridinium hydroxide and proceeds with lower grafting efficiency in the presence of some amount of water. With acidic trunk polymer containing sulfonyl chloride groups, no graft copolymer was produced. The grafting efficiency of βPL onto the amphoteric trunk polymer containing acrylamide units was found to be between those of basic and acidic trunk polymer. In addition, the grafting by means of ionic copolymerization of βPL with maleic anhydride units contained in trunk polymer proceeded with very high grafting efficiency.     

Dispersion copolymerization of polyoxyethylene macromonomer and styrene. Part 3. Molecular characterization of polystyrene-graft-polyoxyethylene copolymers

Graft copolymers (polystyrene-graft-polyoxyethylene) (PS-graft-PEO) were prepared by the dispersion copolymerization of methacryloyl-terminated polyoxyethylene macromonomer and styrene initiated by an oil-soluble initiator (dibenzoyl peroxide, DBP). The apparent molecular weights of graft copolymers measured by size exclusion chromatography in tetrahydrofuran were found to be proportional to the -0·8th power of DBP concentration. This reaction order supports the termination of growing radicals by a first order radical loss process. The molecular weight distribution estimated from the size exclusion chromatography (SEC) data was found to decrease slightly with DBP concentration and to drop rapidly with macromonomer concentration. This was attributed to chain transfer events and to the increase of particle number: the higher the particle number the lower the monomer concentration in the particles. The bulkiness of the macromonomer molecules and the high segment density around the propagating reaction loci hinder the incorporation of macromonomer molecules into a copolymer growing chain. ©1997 SCI