Initiated Polymerization Of Styrene Research Articles

Photooxidative Generation of Dodecaborate-Based Weakly Coordinating Anions.

Redox-active proanions of the type B12(OCH2Ar)12 [Ar = C6F5 (1), 4-CF3C6H4 (2), 3,5-(CF3)2C6H3 (3)] are introduced in the context of an experimental and computational study of the visible-light-initiated polymerization of a family of styrenes. Neutral, air-stable proanions 1-3 were found to initiate styrene polymerization through single-electron oxidation under blue-light irradiation, resulting in polymers with number-average molecular weights (Mn) ranging from ∼6 to 100 kDa. Shorter polymer products were observed in the majority of experiments, except in the case of monomers containing 4-X (X = F, Cl, Br) substituents on the styrene monomer when polymerized in the presence of 1 in CH2Cl2. Only under these specific conditions are longer polymers (>100 kDa) observed, strongly supporting the formulation that reaction conditions significantly modulate the degree of ion pairing between the dodecaborate anion and cationic chain end. This also suggests that 1-3 behave as weakly coordinating anions (WCA) upon one-electron reduction because no incorporation of the cluster-based photoinitiators is observed in the polymeric products analyzed. Overall, this work is a conceptual realization of a single reagent that can serve as a strong photooxidant, subsequently forming a WCA.

Initiation Mechanisms of Styrene with Methyl Ethyl Ketone Peroxide-Cobalt System

Unsaturated polyester resins (UPR) cured with styrene has been widely used in the various industrial fields. Methyl ethyl ketone peroxides (MEKP)-cobalt(II) system is the most common initiator for the curing of UPR. However, its initiation mechanisms currently remain elusive. In this study, the monomeric MEKP (MEKP-1) was firstly separated out from the commercial MEKP products, and then the radical initiation mechanisms of MEKP-1 catalyzed by cobalt isooctoate in the presence and absence of styrene were comparatively investigated by a combination of nitroxide radical trapping technique and HPLC-ESI/MS (high performance liquid chromatography-electrospray ionization/mass spectrometry). The amount of trapped products originated from methyl radical, ethyl radical and hydroxyl radical was significantly larger than that of trapped products from other radicals. These results indicated that methyl, ethyl and hydroxyl radicals were the dominant intermediate radicals formed in the initiation process of MEKP-cobalt(II) system, which would serve as the primary source to initiate styrene polymerization.

Kinetics of nanocomposite formation by thermal polymerization of styrene in the polyvinylidene fluoride matrix

The kinetics of polystyrene (PS) accumulation in polyvinylidene fluoride (PVDF) films as a result of the thermal polymerization of styrene sorbed from a styrene-toluene-divinylbenzene solution at 90°C was studied. After accumulation of ∼65 wt % PS in the sample, the thermal polymerization rate increased by approximately an order of magnitude. This was explained by an increase in the volume of the nanosized PS phase saturated with the monomer from the surrounding solution. The thermal polymerization of styrene in the PVDF matrix proceeded in the formed nanoreactors at a constant monomer concentration in them. The rate of thermal polymerization of styrene in the PVDF film was an order of magnitude higher than that in the surrounding solution. The initiation of styrene polymerization at the interface between PVDF and monomer-saturated PS nanoinclusions was assumed to be heterogeneous.

QM/MM Studies on Scandium-Catalyzed Syndiospecific Copolymerization of Styrene and Ethylene

The copolymerization of styrene and ethylene by the cationic half-sandwich scandium alkyl species (η5-C5Me5)Sc(CH2SiMe3) has been computationally investigated by using the quantum mechanics/molecular mechanics (QM/MM) method. It has been found that the initiation of styrene polymerization both kinetically and energetically prefers 2,1-insertion (secondary insertion, free-energy barrier of 12.6 kcal/mol, and exergonic by 19.1 kcal/mol) to 1,2-insertion (primary insertion, free-energy barrier of 19.0 kcal/mol, and exergonic by 8.9 kcal/mol). This is in contrast to a titanocene-based catalyst system, in which the initiation of styrene polymerization was computationally found to prefer 1,2-insertion, while the subsequent styrene insertion (polymerization) proceeds in a 2,1-insertion pattern. In the current Sc-based catalyst system, although the insertion of styrene into the metal–alkyl bond of the active species is kinetically slower than that of ethylene, the formation of a styrene π-complex is more favorable than that of an ethylene complex. Also, the insertion of styrene into an ethylene-preinserted species is more energetically favorable than continuous ethylene insertion into the ethylene-preinserted species. These thermodynamic factors could add to a better understanding of styrene–ethylene copolymerization. The thermodynamic preference for the insertion of styrene rather than that of ethylene into the active species with an ethylene end group was not reported for group 4 catalyst systems. It is also found that the syndiospecific selectivity is inherently determined by the substituent of the ancillary ligand η5-C5Me5.

Multihydroxyl-Functional Polystyrenes in Continuous Flow

We describe the synthesis of end-functionalized polystyrenes by living anionic polymerization in a microstructured reactor via termination by acetal-protected functional epoxides. Initiation of styrene polymerization by alkyllithium takes place in a micromixing device with efficient heat and mass transfer properties. A newly developed continuous polymerization−termination sequence enabled quantitative functionalization of the living carbanions by nucleophilic displacement with different, specifically designed glycidyl ethers (ethoxy ethyl glycidyl ether (EEGE), 1,2-isopropylidene glyceryl glycidyl ether (IGG), and trans-2-phenyl-1,3-dioxane glycidyl ether (PDGE)). Upon acidic hydrolysis the end-capped polystyrenes release multiple hydroxyl groups (2−3) at the chain end. Temperature and flow rates have been varied to control molecular weights and to optimize the reaction conditions for maximum polymerization and termination efficiency. The polymers were analyzed in detail using NMR spectroscopy, size exclusion chromatography (SEC), and MALDI-ToF-MS. Molecular weights of the samples prepared ranged between 1800 and 9000 g/mol. For all of the novel termination agents full termination was confirmed by MALDI-ToF MS. The approach presented is applicable for a large variety of monomers that are polymerizable by carbanionic polymerization.

Computational Fluid Dynamics Study of a Styrene Polymerization Reactor

AbstractThe computational fluid dynamics (CFD) approach was adopted to simulate benzoyl peroxide (BPO)‐initiated styrene polymerization in a laboratory‐scale continuous stirred‐tank reactor (CSTR). The CFD results revealed the effects of non‐homogeneity and the short‐circuiting of the unreacted styrene and initiator on the reactor performance. The study also investigated the effects of the impeller speed and the residence time on the conversion and the flow behavior of the system. The CFD simulation showed that intense mixing remained confined to a small region near the impeller. With increasing impeller speed, it was found that the perfectly mixed region near the impeller expanded, thus reducing non‐homogeneity. Different contours were generated and exhibited the effect of the mixing parameters on the propagation rate and styrene conversion. The monomer and initiator conversions predicted with the CFD model were compared to those obtained with a CSTR model. The CFD model accounts for the non‐ideality behavior of the polymerization reactor, and hence conversion predictions are more realistic.

Cellulose Nanocrystals Grafted with Polystyrene Chains through Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP)

This paper reports the synthesis of cellulose nanocrystals grafted by polystyrene chains via surface-initiated ATRP. Naturally occurring cellulose was first hydrolyzed to obtain cellulose nanocrystals. Their surface was then chemically modified using 2-bromoisobutyryl bromide to introduce initiating sites for ATRP. A varying extent of surface modification was achieved by changing reaction conditions. Further initiation of styrene polymerization from these modified nanocrystals with a CuBr/PMDETA (N,N,N',N',N''-pentamethyldiethylenetriamine) catalytic system and in the presence of a sacrificial initiator produced polysaccharide nanocrystals grafted by polystyrene chains. A range of nanocrystals-g-polystyrene with different graft lengths (theoretical polymerization degree = 27-171) was synthesized through this method and characterized by elemental analysis, XPS, FT-IR, TEM, and contact angle measurements. We are thus able to produce cellulose nanoparticles with varying grafting densities (by altering extent of initiator surface modification) and varying polymer brush length (through polymerization control). The nanocrystals-g-polystyrene (NC-g-PS) particles were tested for their capacity to absorb 1,2,4-trichlorobenzene from water. The results obtained show that they can absorb the equivalent of 50% of their weight in pollutant compared to 30 wt % adsorption for nonmodified nanocrystals, while also displaying faster absorption kinetics.

Ca‐Mediated Styrene Polymerization: Tacticity Control by Ligand Design

AbstractNew heteroleptic benzylcalcium complexes with modified fluorenyl ligands were prepared which include a complex with a chelating dimethylamino substituent, [9‐(2‐Me2N‐ethyl)fluorenyl][2‐Me2N‐α‐Me3Si‐benzyl]Ca (4), and a series of complexes with bulky substituents like tBu‐, Ph(Me)2C‐, Me(Ph)2C‐ and Me(4‐tBuC6H4)2C‐ in the 2‐ and 7‐positions of the fluorenyl ligand (complexes 5 through 9, respectively). Crystal structures of 4, [(2,7‐tBu‐9‐Me3Si‐fluorenyl)(2‐Me2N‐benzyl)Ca]2 (5) and [2,7‐Ph(Me)2C‐9‐Me3Si‐fluorenyl][2‐Me2N‐α‐Me3Si‐benzyl]Ca·THF (6) show that modification of the fluorenyl ligand hardly affects the coordination mode of the benzylic ligand. Also, in solution all compounds are of heteroleptic nature and it was shown that fluorenyl modifications hardly affect the barriers for inversion at the chiral benzylic carbon atom [18.7(2)–19.2(2) kcal/mol]. Complex 4 does not initiate styrene polymerization, which underscores the importance of a free coordination site at calcium. Complexes 5–9 initiate styrene polymerization, and the syndiotacticity of the obtained polymers increases with the bulkiness of the substituents on the fluorenyl ligands. Syndiotacticities up to r = 95 % (rr = 90 %) were obtained.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Organocobalt chelates as initiators of emulsion polymerization of styrene

The kinetics of decomposition of organocobalt chelates in the pH range of 2.2–7.0 has been studied. It has been shown that the rate constant of decomposition of the octyl chelate complex at 20°C changes from ∼3 × 10−3 to ∼6 × 10−6 s−1 in the above pH range. The rate constants of decomposition of complexes with ethyl, octyl, and cetyl ligands, as estimated at 20°C and pH 8.3, are 1.69 × 10−4, 1.39 × 10−4, and 2.42 × 10−5 s−1, respectively. As evidenced by emission spectrometry measurements, ∼100% of organocobalt chelates with ethyl and isopropyl ligands occur in the aqueous phase, while organocobalt chelates with octyl and cetyl ligands are partitioned between monomer and aqueous phases. The rates of initiation of the emulsion polymerization of styrene have been measured by the inhibited polymerization procedure. It has been demonstrated that among three tested compounds (diphenyl picryl hydrazyl, hydroquinone, and benzoquinone), benzoquinone has been found to be a suitable inhibitor for the polymerization under study. The rates of initiation of styrene polymerization at 30°C for organocobalts with ethyl, octyl, and cyclohexyl ligands are 1.0 × 10−7, 1.04 × 10−7, and 3.7 × 10−6 mol/(l s), respectively. The rate constant of decomposition of the organocobalt complex with the octyl ligand at 30°C is 2.28 × 10−5 s−1, and the efficiency of initiation with this complex is 0.95.

Synthesis of poly(vinyl acetate)‐b‐polystyrene and poly(vinyl alcohol)‐b‐polystyrene copolymers by cobalt‐mediated radical polymerization

AbstractWell‐defined poly(vinyl acetate) macroinitiators, with the chains thus end‐capped by a cobalt complex, were synthesized by cobalt‐mediated radical polymerization and used to initiate styrene polymerization at 30 °C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)‐b‐polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)‐b‐polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)‐b‐polystyrene copolymers self‐associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 81–89, 2007

Structural features and initiating properties of the hexaadduct of polystyryllithium and fullerene C60 in tetrahydrofuran and their role in synthesis of heteroarm star-like polymers

Structural transformations of the hexaadduct of polystyryllithium and fullerene C60 in the course of interaction with a proton donor or 1,1-diphenylethylene and at initiation of styrene polymerization were studied, and their role in the formation of heteroarm star-like polymers with C60 center of branching and arms of polystyrene and poly-2-vinylpyridine was elucidated.

Atom transfer radical polymerization of styrene initiated by 2-(4-chloromethyl-phenyl)-benzoxazole with high activity and fluorescent property

Functionalized polystyrene (PSt) was synthesized utilizing atom transfer radical polymerization (ATRP), which was conducted by using 2-(4-chloromethyl-phenyl)-benzoxazole (CMPB) as initiator, CuCl/PMDETA as catalyst, and cyclohexanone as solvent. The mechanism of ATRP was proved by characterizing the structure of PSt via 1H NMR and preparing of PSt-b-PMMA block copolymer. The polymerization showed first order with respect to monomer concentration and relatively narrow polydispersity (Mw/Mn range from 1.30 to 1.50). Factors such as different reaction temperatures, mole ratio of monomer to initiator and so on, which can affect the ATRP system, were discussed in the paper. Moreover, CMPB showed high activity and could initiate styrene polymerization even at ambient temperature. The optical property of initiator was well preserved in the obtained PSt, and the end-functionalized PSt exhibited strong fluorescent emission at 351nm.

Diethyl ketone triperoxide: thermal decomposition reaction in chlorobenzene solution and its application as initiator of polymerization

AbstractThe kinetics of the thermal decomposition reaction of diethyl ketone triperoxide (3,3,6,6,9,9‐hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane, DEKT) in chlorobenzene solution were studied in the temperature range 99.0–148.0°C and at initial concentrations of (1.65–4.97) × 10−2 M. The thermolysis of DEKT follows a first‐order kinetic law up to at least ca 80% triperoxide conversion. The activation parameter values for the initial O—O bond rupture in chlorobenzene (ΔH‡=134.6±1.7 kJ mol−1; ΔS‡ = 4.2 ± 3.8 J mol−1 K−1) and the reaction products observed support a stepwise reaction mechanism which includes as a first step the unimolecular homolytic cleavage of one peroxidic bond of the DEKT molecule giving rise to a biradical as intermediate. Additionally, the results obtained were compared with those obtained in toluene, toluene–styrene (50%, v/v) and chlorobenzene–styrene (50%, v/v) solution, showing that the decomposition reaction is strongly solvent dependant. Further, the biradical intermediate obtained in all cases was used to initiate styrene polymerization. It was demonstrated that DEKT can effectively act as initiator in styrene polymerization and its performance is similar to that presented by a multifunctional initiator giving rise to high molecular weight polystyrene at a high reaction rate. Copyright © 2004 John Wiley & Sons, Ltd.

Numerical investigation of kinetics of free‐radical polymerization on spinning disk reactor

AbstractSpinning disk reactor (SDR) technology has been demonstrated to achieve significant enhancements in free radical polymerization rates. The effect on the rate may be attributed to the unique hydrodynamic environment experienced by the reacting polymer films. The rotating surface of a SDR promotes extension of the polymer chains, which may prevent the propagating chains from terminating through bimolecular reactions. In this article, a numerical simulation is performed to investigate how reduced rates of termination would affect time conversion behavior of free radical initiated styrene polymerization. Comparisons have been made between model predictions and SDR experimental results. The closeness between predicted and experimental results yields strong evidence that the hydrodynamic regime created on the surface of a SDR can lead to reduced rates of bimolecular termination. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 693–699, 2003

Homo‐ and copolymerization of styrene using combined diphenylzinc‐additive initiator systems

AbstractCombined systems including diphenylzinc, Ph2Zn, a metallocene, and methylaluminoxane, MAO, have been employed to initiate styrene polymerization and the copolymerization of styrene with p‐alkylsubstituted styrenes and α‐olefins. Both polymerization and copolymerization processes depend on the nature of the metallocene included in the initiator system, the presence of Ph2Zn, the temperature, and the solvent used. S/1‐alkene copolymers were obtained when the initiator systems included a zirconocene, but not when a titanocene participated.

Elaboration of corona functionalized regular unimolecular hyperbranched polystyrene nanoparticles

Functional arborescent graft polystyrenes prepared by the graft-on-graft technique, involving the iterative grafting of end functional polymer chains onto reactive polymer backbones were synthesized. The zero-generation comb polymers and then the first generation hyperbranched structures were obtained by the coupling reaction of living α-acetal polystyryllithium onto linear or comb chains of poly(chloroethyl vinyl ether) (PCEVE) of controlled DP n and structure. Both the PS grafts and the PCEVE reactive backbones were synthesized individually by living polymerization techniques. Initiation of styrene polymerization from acetal functionalized lithium derivatives yield the co-functionalization of all external polystyrene branches. Derivatization of these acetal branch termini allowed the generation of aldehyde, hydroxyl and carboxyl groups as well as the introduction of functional organic molecules at the periphery of the nanoparticles.

Oligomeric benzoin photoinitiators

AbstractNovel oligomeric photoinitiators were synthesised by reacting benzoin with isophorone diisocyanate‐terminated oligomers of dihydroxy‐terminated depolymerization products of polyethylene terephthalate (PET). PET was depolymerized by ethylene glycol (EG), hexylene glycol (HG), polyethylene glycol 10 000 (PEG), and α, ω‐dihydroxy poly(dimethyl siloxane)s (PDMS). Oligomeric photoinitiators were used as free radical initiators for polymerization of styrene and acrylonitrile. Formation of block copolymers was illustrated by several characterisation methods such as FTIR, 1H‐NMR, DSC, and GPC. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 500–508, 2002

New neutral Ni(II)- and Pd(II)-based initiators for polymerization of styrene

Neutral nickel and palladium σ-acetylide complexes [Ni(CCPh) 2(PBu 3) 2] and [Pd(CCPh) 2(PBu 3) 2] are novel initiators for the polymerization of styrene in CHCl 3 over a range of polymerization temperature from 40 to 60 °C. Between them, the nickel catalyst exhibited much higher activity than the palladium catalyst. The polystyrene obtained with Ni(II) initiator was a syndio-rich atactic polymer and its weight-average molecular weight reached 279 000. The mechanism of the polymerization was discussed and a radical mechanism was proposed.

Polymerization and copolymerization of styrene by Ph2Zn-metallocene-MAO initiator systems.

Combined systems including diphenylzinc, Ph2Zn, a metallocene, and methylaluminoxane, MAO, have been employed to initiate styrene polymerization. These initiator systems have been also used to initiate the copolymerization of styrene with p-alkylsubstituted styrenes and with α-olefins. Both polymerization and copolymerization processes depend on the nature of the metallocene included in the initiator system, the presence of Ph2Zn, the temperature and the solvent used. Titanocenes produced syndiotactic polystyrene, s-PS, while zirconocenes gave atactic polystyrene, a-PS, with a certain content, less the 20% of s-PS. For copolymerizations the conversion to polymer was also influenced by the comonomer nature and its molar proportion in the initial feed, as well as the sort of metallocene, titanocene or zirconocene included.

The soluble and insoluble product of diphenylzinc-water systems as initiator in styrene polymerization

The solution resulting from reaction between Ph2Zn and H2O in benzene was used by itself and separated in soluble and insoluble fractions to initiate styrene polymerization. The soluble fraction produced the largest polymer conversion while the insoluble was reponsible of the highest molecular weights. Resulting polystyrenes were atactic but up to 80–85% syndiotactic triads were detected by 1H-NMR analysis. Polystyrene obtained using benzene as solvent showed a low crystalline content while the polymer obtained using dichloromethane did not produce any crystalline fraction.