Radical Polymerization Of Styrene Research Articles

Proton‐controlled nitroxide mediated radical polymerization of styrene

AbstractThe pyridyl alkoxyamine, which is composed of the 1‐phenylethyl radical and a pyridyl nitroxide fragments, displays protonation‐controlled CON bond homolysis. Its dissociation rate constant kd value is approximately halved at 100 °C in tert‐butyl benzene when it is protonated by one equivalent of trifluoroacetic acid. Moreover, the bulk polymerization of styrene at 125 °C is performed with a good control over the molecular weight and the dispersity when initiated with this alkoxyamine under its basic and acidic forms but the protonation has induced a strong decreased polymerization rate. In contrast, in the case of n‐butyl acrylate, the control over the polymerization is lost for the protonated pyridyl alkoxyamine because the pyridyl nitroxide is less thermally stable under its acidic form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Construction of phthalocyanine‐terminated polystyrene nanoarchitectures

Nanostructuring of phthalocyanine‐based materials is a powerful tool towards the preparation of new materials with outstanding properties. It has been previously shown that porphyrin‐functionalized and phthalocyanine‐functionalized polymers give rise to nanosized aggregates. With the goal in mind of searching new phthalocyanine‐containing polymeric materials that are able to self‐organize into stable supramolecular nanostructures, we have prepared unsymmetrically functionalized Zn(II) phthalocyanines that are able to behave as initiators in the atom transfer radical polymerization of styrene. Hybrid phthalocyanine–polystyrene materials of different tail lengths have been prepared, and their self‐organization behavior was studied by means of UV–Vis spectroscopy and transmission electron microscopy. Copyright © 2012 John Wiley & Sons, Ltd.

Preparation of main‐chain imidazolium‐functionalized amphiphilic block copolymers through combination of condensation polymerization and nitroxide‐mediated free radical polymerization and their micelle study

AbstractMain‐chain imidazolium‐functionalized amphiphilic block copolymers (PIL‐b‐PS) consisting of polyionic liquid (PIL) and polystyrene (PS) blocks have been first synthesized by condensation polymerization combined with nitroxide‐mediated free radical polymerization (NMP). The di‐functional imidazolium‐based ionic liquid (IL) having both hydroxyl and ester end groups was synthesized through Michael addition between imidazole and methylacrylate (MA) and further quaternization by 2‐chloroethanol. The HTEMPO (4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy) terminated polyionic liquid (HTEMPO‐PIL) as the hydrophilic block was prepared by condensation polymerization of di‐functional imidazolium IL and HTEMPO at a certain ratio. The hydrophobic PS block was synthesized by controlled radical polymerization of styrene using HTEMPO‐PIL through NMP, resulting PIL‐b‐PS block copolymers. The structure of block copolymers obtained has been characterized and verified by FTIR, 1H NMR, and size exclusion chromatography analyses. In addition, the morphology and size of the micelles formed by PIL‐b‐PS block copolymers in water were investigated by transmission electron microscopy and dynamic light scattering. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

New selenium‐based iniferter agent for living free radical polymerization of styrene under UV irradiation

AbstractP,P‐Diphenyl phosphinodiselenoic acid benzyl ester was synthesized and used as a mediator for the polymerization of styrene under UV–vis irradiation. Moderately controlled evidence was found: linear polymerization kinetics, linear evolution of molecular weight with monomer conversion, and relatively narrow molecular weight distribution (1.5–2.0). The structure of the obtained polymers was characterized using NMR and oxidative eliminaton. Based on polymerization results, an iniferter mechanism was proposed for the current polymerization system. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Preparation of Diamine‐β‐diketiminato Copper(II) Complexes and Their Application in the Reverse Atom‐Transfer Radical Polymerization of Styrene

AbstractCompound Et2NCH2CH2N=C(Me)CH=C(Me)NHCH2CH2NEt2 (HL), after conversion to the Li+ salt with use of MeLi, reacts with CuCl2 in toluene to yield CuClL (1). The compound adopts a four‐coordinate CuClN3 environment with a pendant amino arm. The same reaction with CuCl and[Cu(MeCN)4]BF4 leads to disproportionation with deposition of metallic copper. Crystals of compounds [CuL][CuCl2] (2) and [CuL]BF4 (3) were isolated in minor amounts from these reactions. The [CuL]+ ion in these compounds has a four‐coordinate CuN4 environment. Compound 2 was also obtained in good yields from the reaction between equivalent amounts of 1 and CuCl. Compound 1 was used to control the radical polymerization of styrene under ARGET ATRP conditions in the presence of glucose as reducing agent and bromoethylbenzene as initiator. The polymerization behavior indicates that the controlling ability of this system is negatively affected by its slow trapping rate and by the disproportionation of the CuL catalyst.

Polymerizable ionic liquids for the preparation of polystyrene/clay composites

AbstractPolymerizable ionic liquids (ILs) 1‐methyl‐3‐(4‐vinylbenzyl)imidazolium chloride, 1‐hexyl‐3‐(4‐vinylbenzyl)imidazolium chloride and 1‐dodecyl‐3‐(4‐vinylbenzyl)imidazolium chloride were prepared and used as new surfactants for the modification of montmorillonite (MMT). Functionalized MMTs were prepared by cationic exchange between sodium MMT and each of the ILs. Polystyrene (PS)/MMT composites were subsequently prepared by in situ intercalative free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in the PS matrix was achieved only for MMT functionalized with the 1‐dodecyl‐3‐(4‐vinylbenzyl)imidazolium‐based IL as revealed by X‐ray diffraction and electron microscopy. The exfoliated composites showed good transparency and higher decomposition temperature than virgin polymer matrix, particularly pronounced under air atmosphere (ΔTmax = 66 °C), data comparable to or even greater than those reported in the literature for exfoliated PS nanocomposites. Copyright © 2012 Society of Chemical Industry

Assessment of the influence of microwave irradiation on conventional and RAFT radical polymerization of styrene

Conventional and controlled/living radical polymerization of styrene under microwave irradiation has been investigated by carefully conducted experiments with regards to temperature and microwave power conditions. Comparison with the corresponding polymerizations using oil-bath heating has revealed no significant effect of microwave irradiation on the polymerization rate under conditions where it is ensured that the temperature of the polymerization mixture is the same regardless of heating mode. The rate enhancement often seen under microwave irradiation is, at least for the monomer styrene, most likely associated with an increase in temperature caused by the microwave irradiation. This study also exposes a number of experimental parameters that should be carefully considered in regards to control of temperature and power of the microwave reactor when conducting any chemical reaction under microwave irradiation.

Organic–inorganic hybrid tinphosphonate material with mesoscopic void spaces: an excellent catalyst for the radical polymerization of styrene

A new porous tinphosphonate HSnP-1 has been synthesized through the reaction of butylene-1,4-diphosphonic acid and SnCl4·5H2O under hydrothermal conditions at 453 K for 3 days in the absence of any structure directing agent. Powder X-ray diffraction, transmission and scanning electron microscopies (TEM and SEM), N2 sorption, solid state 13C CP MAS and 31P MAS NMR, UV-vis and FT IR spectroscopic tools are used to characterize the material. The crystallinity of HSnP-1 is sufficiently high under mildly acidic pH conditions and the crystal structure of the material has been indexed to the tetragonal phase with unit cell parameters a = b = 11.52 Å, c = 15.84 Å, α = β = γ = 90°. The surface area and the pore volume of the material were 338 m2 g−1 and 0.54 cc g−1, respectively. HSnP-1 showed outstanding catalytic activity in the radical polymerization of styrene at room temperature in the presence of aqueous H2O2 as an initiator under solvent-free conditions, whereas in the presence of aprotic solvent it facilitates partial oxidation of styrene to phenylacetaldehyde and acetophenone.

A comparison of verdazyl radicals modified at the 3-position as mediators in the living radical polymerisation of styrene and n-butyl acrylate

Four verdazyl radicals, with varying substituents at the 3-position, were synthesised and used to prepare unimolecular initiators for use in the stable free radical mediated living radical polymerisation of styrene and n-butyl acrylate. The addition of bulky substituents with differing electronic structures at the 3-position of the ring was investigated and the effects of these substituents on the properties of the verdazyl radical studied. The nature of the substituent was discovered to affect the rate and characteristics of polymerisation. The styrene and n-butyl acrylate homopolymers were chain extended to provide evidence of the verdazyl radical as the end group of the polymers.

Single molecule diffusion and its heterogeneity during the bulk radical polymerization of styrene and methyl methacrylate

The diffusion of perylene diimide dye molecules of clearly distinct size was observed during the thermally initiated polymerization of styrene and methyl methacrylate (MMA) at room temperature. A combination of fluorescence correlation spectroscopy and widefield fluorescence microscopy allowed us to cover the entire conversion range from free diffusion in the monomer solution to immobilization in the produced polymer glass. The evolution of diffusion coefficients differs significantly in both systems. The diffusion coefficient of both dyes decreases clearly more rapidly during the polymerization of MMA, i.e. at the same conversion, diffusion coefficients in the polymerizing MMA solution are clearly lower compared to the polymerizing styrene solution. Extrapolation of the diffusion of the dyes to the diffusion of polymer chains can explain the more pronounced Trommsdorff effect during the polymerization of MMA. In contrast to other methods, single molecule fluorescence microscopy allows for a direct visualization of heterogeneities in single molecule motion. Our measurements point to the fact that the reason for the distinct behaviour of both polymerization systems lies in structural heterogeneities evolving in the PMMA/MMA system already at rather low conversion. In contrast, during the polymerization of styrene, only minor heterogeneities were observed.

Synthesis of 9H-fluoren-9-yl benzodithioates and their application as reversible addition–fragmentation chain transfer agents in living radical polymerization of styrene

The reversible addition–fragmentation chain transfer (RAFT) polymerization is one of living radical polymerizations. In this study, four different 9H-fluoren-9-yl benzodithiolates (FBDTs) were synthesized, and used along with azobis(isobutyronitrile) (AIBN), a radical initiator, in polymerization of styrene (ST) at the molar ratio of 3:1. This new transfer agent exhibited the typical characteristic living free radical polymerization behaviors such as good control of molecule weight and narrow molecule weight distribution. It was concluded that the FBDTs can be used as the RAFT agents in free radical polymerization of vinyl monomers.

Synthesis and characterization of amphiphilic methoxypoly(ethylene glycol)-polystyrene diblock copolymer by ATRP and NMRP techniques

Amphiphilic block copolymers are used in a variety of applications, for example, as stabilizers for emulsions and dispersions or as compatibilizers in polymer blends. Amphiphilic diblock copolymer composed of methoxypoly(ethylene glycol) and polystyrene (MPEG-b-PS) was synthesized using atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP). In order to synthesize MPEG-b-PS diblock copolymer using ATRP, monofunctional MPEG macroinitiator (chloroacetylated MPEG [MPEG-Cl]) was prepared from monohydroxyfunctional poly(ethylene glycol) and initiated end group on the basis of chloroacetyl chloride. ATRP was carried out in bulk using MPEG-Cl as the macroinitiator, copper chloride (CuCl)/2,2′-bipyridine (bipy) as the catalyst ([MPEG-Cl]/[CuCl]/[bipy] = 1:1:3), and styrene as the monomer. For preparation of MPEG-b-PS by means of NMRP, firstly, 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-OH) was obtained by reduction of 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) with sodium ascorbat. Then, TEMPO-OH was coupled with chloroacetylated MPEG (MPEG-Cl) to yield the macroinitiator MPEG terminated with a TEMPO unit (MPEG-CO-TEMPO). At last, MPEG-CO-TEMPO was further used to prepare the diblock copolymer MPEG-b-PS by ‘living’ free radical polymerization of styrene. The products were purified and identified by Fourier transform infrared (FT-IR) spectroscopy, 1H nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC).

Activation–Deactivation Equilibrium of Atom Transfer Radical Polymerization of Styrene up to High Pressure

AbstractAtom transfer radical polymerization (ATRP) equilibrium constants, KATRP, are measured for copper‐mediated styrene polymerizations in acetonitrile solution using several different ligand and initiator systems. Application of high pressure increases the rate of an ATRP by enhancing both KATRP and the propagation rate coefficient. This favorable effect is not counterbalanced by an increase in dispersity. A comparison of the values of KATRP measured on monomer‐free model systems shows close agreement with values measured during styrene polymerization.

Probing the effects of π-π stacking on the controlled radical polymerization of styrene and fluorinated styrene

The addition of the π–π stacking agent octafluorotoluene (OFT) resulted in up to a 50% reduction in monomer conversion after 24 h for atom transfer radical polymerization (ATRP) reactions of styrene, when performed at 85 °C with 1 eq of OFT compared with styrene in the initial reaction mixture. Monitoring the progress showed that the ATRP of styrene in the presence of either OFT or hexafluorobenzene (HFB) maintained a linear relationship between monomer conversion and number average molecular weights, while showing a first order rate dependence on monomer. The effects of π–π stacking on the KATRP could be overcome by using adjusting the redox activity of the metal-ligand complex while maintaining reaction temperatures of 85 °C. Further experiments showed that nitroxide-mediated polymerizations of St were affected to an identical extent by the presence of the π–π stacking agent HFB. The ATRP of pentafluorostyrene (PFSt) in the presence of π–π stackers benzene or toluene showed an increase in monomer conversion compared with reactions in their absence, consistent with Mn π–π stacking increasing the stability of the active radical. Interactions between the π–π stacking agents OFT and HFB and the aromatic groups in the ATRP of St or PFSt were verified by 1H NMR analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Effects of dual initiators and catalytic additives on atom transfer radical polymerization of styrene

The effect of two initiators, so-called dual initiators system on atom radical transfer polymerization (ATRP), were studied with dimethyl-2,6-dibromohepanedioate (DMDBHD) and ethyl-2-bromoisobutyrate (EBIB). Cu(I)Br as catalyst and N,N,N′,N′,N′-pentamethyl-diethylenetriamine as ligand were employed for styrene ATRP. Interestingly, bimodal MWD were shown for the dual initiator system, and one of the peaks had higher molecular weight (MW) and the other had lower MW compared to a one-initiator system. The lower MW peak in bimodal peaks seemed to be mainly resulting from EBIB and the higher MW peak from DMDBHD. Furthermore, methylaluminoxane (MAO) was fed into the ATRP reaction to observe the effect of it on ATRP. As the MAO/CuBr molar ratio in feed increased from 0 to 1, the molecular weight and conversion increased without a notable change in PDI and curve shape of GPC. The conversion in the presence of MAO was also increased with the increase in MAO/CuBr molar ratio. The effect of Cp*TiCl3 on the ATRP was opposite to that of MAO. As the Cp*TiCl3/CuBr molar ratio increased from 0 to 1, the conversion of polymerization was down from 56 to 35%. Furthermore, the molecular weight was drastically decreased from 10,000 to 5,500, but their PDI did not show a significant change. These results can elucidated by the retarding effect of Cp*TiCl3 on the propagation of polymerization.

Well‐defined polymers containing 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane moiety: Synthesis, mechanism, and applications in catalysis

AbstractA series of well‐defined different chain lengths polymers, which contain the organometallic 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane core in the main chain, was obtained in one‐pot via a novel 1,3‐dichloro‐tetra‐n‐butyl‐distannoxane (complex A)/azobisisobutyronitrile (AIBN) initiating system used in reverse atom transfer radical polymerization of styrene in different concentrations. The introduction of organotin complex A was supported by 1H‐NMR, 13C–NMR, and the Inductive Coupled Plasma Emission Spectrometer analysis of the organotin‐containing polymer. Moreover, the mechanism of polymerization was investigated by changing the ratio of complex A to AIBN. It was concluded that the complex A not only acted as an important part of the initiator system but also introduced the functional organometallic group into the polymer chain. Additionally, the organotin‐containing polymer could be used as catalyst for esterification, and the reaction products' conversion could reach high up to 99% and does not decrease after four successive cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effect of the spacer length on binitroxide mediated radical polymerization of styrene

Series of binitroxides, (N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl)diaminoalkane), ·Cn· (n=0, 2, 3, 4 methylene groups), was used as mediators in the radical polymerization of styrene initiated with benzoyl peroxide (BPO). The length of the methylene spacer linking two 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radicals affected the polymerization process. For the mediators, ·C0·, ·C2· and ·C3·, elongation of the spacer decreases the conversion rate as well as the number average molecular weight (Mn), molecular weight distribution (MWD) and polydispersity index (PDI). For all these mediators, a bimodal MWD was confirmed. The use of N,N′-bis(4-(2,2,6,6-tetramethylpiperidin-1-yloxyl))diaminobutane, ·C4·, results in trimodal MWD with an additional polymer fraction with a high molecular weight originating from an uncontrolled process. In the initial stages of polymerization, electron spin resonance spectroscopy (ESR) showed that the combination reaction between ·C4· and growing polymer chain (P·) is much slower than that for the ·C0· controlling agent, thereby promoting the synthesis of long polymer chains. With the exception of the ·C0· mediator, the remaining biradicals did not exhibit spin-spin interactions between the TEMPO groups in the propagation of polymerization. Therefore, the spin-spin coupling between binitroxide ends does not appear to have a remarkable influence on the polymerization process. Open image in new window

Well‐defined polyoxazoline‐based alkoxyamines as efficient macroinitiators in nitroxide‐mediated radical polymerization of styrene

AbstractThe synthesis of two well‐defined 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide‐terminated poly(2‐methyl‐2‐oxazoline) with narrow dispersity (Mw/Mn = 1.1) has been achieved for the first time. The insertion of the alkoxyamine end groups at one or both ends of poly(2‐methyl‐2‐oxazoline) (PMEOX) chains has been successfully done using a method based on “terminating reagent method.” These macroinitiators have molecular weights ranging from 6.3 × 103 to 9.4 × 103 g mol−1. In contrast, attempt to introduce the alkoxyamine group at one end of PMEOX chain through the “initiator method” has furnished a mixture of alkoxyamine‐graft polyoxazolines because of rearrangement of alkoxyamine occurring during the synthesis of PMEOX. The macroinitiators obtained by terminating reagent method have been used successfully for polymerization of styrene by nitroxide‐mediated radical polymerization (NMP), which exhibited all the expected features of a controlled system. The control of NMP has been proved by a good agreement between theoretical and experimental molecular weights and by narrow dispersity (Mw/Mn < 1.2). Different types of well‐defined multiblock copolymers have been prepared: diblock copolymers poly[(2‐methyl‐2‐oxazoline)‐b‐(styrene)] (PMEOX‐b‐PS) and, for the first time, triblock copolymers poly[(styrene)‐b‐(2‐methyl‐2‐oxazoline)‐b‐(styrene)] (PS‐b‐PMEOX‐b‐PS). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Modeling Insights on the TEMPO Mediated Radical Polymerization of Styrene

Despite a great deal of research on nitroxide mediated radical polymerization (NMRP), its kinetic mechanism is not fully known yet. The focus of this work was to contribute further to the understanding of the kinetics of NMRP processes through refinements of a comprehensive mathematical model developed by our group for the bimolecular system. This work considered important secondary reactions that can occur during the NMRP process. It also analyzed important kinetic aspects via a sensitivity study on some key parameters of the system. It was observed that an irreversible reaction between the TEMPO controller and the chemical initiator is very important and must be considered in the NMRP mechanism, in order to be able to describe properly both conversion and average molecular weight data.

Atom transfer radical polymerization of styrene and methyl (meth)acrylates initiated with poly(dimethylsiloxane) macroinitiator: Synthesis and characterization of triblock copolymers

AbstractPoly(dimethylsiloxane)(PDMS)‐based triblock copolymers were successfully synthesized via atom transfer radical polymerization (ATRP) initiated with bis(bromoalkyl)‐terminated PDMS macroinitiator (Br‐PDMS‐Br). First, Br‐PDMS‐Br was prepared by reaction between the bis(hydroxyalkyl)‐terminated PDMS and 2‐bromo‐2‐methylpropionyl bromide. PSt‐b‐PDMS‐b‐PSt, PMMA‐b‐PDMS‐b‐PMMA and PMA‐b‐PDMS‐b‐PMA triblock copolymers were then synthesized via ATRP of styrene (St), methyl methacrylate (MMA) and methyl acrylate (MA), respectively, in the presence of Br‐PDMS‐Br as a macroinitiator and CuCl/PMDETA as a catalyst system at 80 oC. Triblock copolymers were characterized by FTIR, 1H‐NMR and GPC techniques. GPC results showed linear dependence of the number‐average molecular weight on the conversion as well as the narrow polydispersity indicies (PDI < 1.57) for the synthesized triblock copolymers which was lower than that of Br‐PDMS‐Br macroinitiator (PDI = 1.90), indicating the living/controlled characteristic of the reaction. Also, there was a very good agreement between the number‐average molecular weight calculated from 1HNMR spectra and that calculated theoretically. Results showed that resulting copolymers have two glass transition temperatures, indicating that triblock copolymers have microphase separated morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012