Chain Transfer Polymerization Of Styrene Research Articles

Surfactant-free nanoencapsulation using reactive oligomers obtained by reversible addition fragmentation chain transfer polymerization of styrene and maleic anhydride

Reactive oligomers of styrene–maleic anhydride having controlled architecture were prepared using reversible addition fragmentation chain transfer (RAFT) polymerization. The co-oligomers were characterized by FTIR, Raman, NMR and GPC. The arrangement of co-monomers (i.e. the architecture) in the co-oligomeric RAFT agents could be controlled by changing the molar feed ratio of styrene to maleic anhydride in the range of 1–5.25 under controlled polymerization conditions. Non-alternating (homopolymer) blocks of styrene could be suppressed even at high mole ratios > 1 and the resultant co-oligomeric RAFT agents consisting of mainly alternating (SMS) and semi-alternating (SSM) sequences of styrene and maleic anhydride were obtained. These macro RAFT agents behaved as efficient reactive surfactants and their self-aggregation behavior was greatly influenced by their architecture. These could be successfully used for surfactant-free nanoencapsulation of active hydrophobic materials, such as n-octadecane, indicating their suitability for various applications.

Tadpole-shaped magnetic block copolymer: Self-assembly induced increase of magnetic susceptibility

Self-assembly induced increase of magnetic susceptibility for the tadpole-shaped block copolymer based on paramagnetic FeCl4 pyridinium was reported in this work. The tadpole-shaped block copolymer was prepared by sequential reversible addition-fragmentation chain transfer polymerization of styrene (St) and 4-vinylpyridine (4VP) at the presence of chain transfer agent-modified polyhedral oligomeric silsesquioxanes (POSS). The corresponding magnetic block copolymer (POSS-PSt-b-QP4VP(FeCl4)) was obtained by quternization of 4VP and complexation with FeCl3. The prepared block copolymer was paramagnetic with magnetic susceptibility of 15.4 × 10−6 emu g−1, as investigated by superconducting quantum interference device. Surprisingly, the magnetic susceptibility of the block copolymer was almost doubled (27.5 × 10−6 emu g−1) after self-assembly in thin film. Since the composition of the block copolymer is unchanged, the increase of the susceptibility should be generated by the self-assembly, which makes the magnetic FeCl4− more ordered. And, self-assembly will be an efficient and convenient method in improving magnetic properties of such polymers.

Reversible addition fragmentation chain transfer polymerization of styrene from the edge of graphene oxide nanolayers

A graphene oxide modifier containing chain transfer agent moieties (CR) was synthesized by an esterification reaction between 1,4-butanediol and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid. CR moieties were grafted at the edge of GO in low and high graft densities to yield GCRL and GCRH respectively. Then, GCRL and GCRH were used in grafting from reversible addition fragmentation chain transfer polymerization of styrene. Grafting of CR moieties was approved by Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy, and Raman spectroscopy. Expansion of graphene oxide interlayer by oxidation and functionalization processes was evaluated by X-ray diffraction. Conversion values of styrene monomer were obtained from gas chromatography. Molecular weight and PDI values of attached polystyrene chains were studied by size exclusion chromatography. Thermogravimetric analysis was also used to investigate the degradation temperatures, char contents, and graft contents. The attached modifier content in GCRH and GCRL is estimated to be 7.6 and 4.0% respectively. Scanning electron and transmission electron microscopies show that flat and smooth layers of graphite are wrinkled during the oxidation and then turned to opaque layers as a consequence of polymer grafting.

Polystyrene-attached graphene nanolayers by reversible addition-fragmentation chain transfer polymerization: a grafting from epoxy groups with various densities

Graphene oxide was chemically functionalized with a modifier synthesized from coupling reaction of ethylenediamine and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid in low and high graft densities. Then, the modified graphenes were used in grafting from reversible addition-fragmentation chain transfer polymerization of styrene. Successful synthesis and grafting of modifier was approved by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy (FTIR). Also, FTIR, X-ray photo electron spectroscopy, and Raman spectroscopy were used to confirm the successful grafting of modifier moieties. Molecular weight and polydispersity index of attached polystyrene chains were studied by size exclusion chromatography. Thermogravimetric analysis was used to investigate the degradation temperatures, char contents, and graft ratios. Weight ratio of modifier in modified graphenes is calculated to be 4.93 × 10−2 and 12.23 × 10−2 for low and high graft densities. Also, molar ratio of modifier is 121.22 and 300.71 μmol/g respectively. Scanning electron and transmission electron microscopies show that graphite layers with flat surface were wrinkled during the oxidation process and also polystyrene-grafted graphenes are observed as opaque layers.

Scandium-Catalyzed Syndiospecific Chain-Transfer Polymerization of Styrene Using Anisoles as a Chain Transfer Agent

The polymerization of styrene in the presence of various anisole derivatives has been examined by using the half-sandwich scandium diaminobenzyl complex (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 with borate [Ph3C][B(C6F5)4]. The syndiospecific chain transfer polymerization of styrene proceeded efficiently via the ortho-C–H bond activation of anisoles, affording the corresponding end-ortho-anisyl-functionalized syndiotactic polystyrenes. The molecular weight of the resulting polymers could be controlled in a wide range by changing the styrene/anisole feeding ratio. Propenyl and halogen (F, Cl, Br, and I) substituents on the anisole compounds are compatible with the present catalyst system, thus enabling easy introduction of unsaturated C═C double bond or halogen moieties together with the anisole functionality to the chain end of syndiotactic polystyrene.

β‐Diketiminate‐supported magnesium alkyl: synthesis, structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η2‐HC[C(Me)NMes]2} (2) (Mes = mesityl, 2,4,6‐Me3C6H2), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH4)2(THF)2 (1) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1, 2 and Al(i‐Bu)3 leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.

In Situ Reversible Addition–Fragmentation Chain Transfer Polymerization of Styrene in the Presence of MCM‐41 Nanoparticles: Comparing “Grafting from” and “Grafting through” Approaches

ABSTRACTThe preparation of polystyrene/MCM‐41 nanocomposites was carried out by “grafting from” and “grafting through” approaches and in the presence of unmodified MCM‐41, using reversible addition–fragmentation chain transfer (RAFT) polymerization. The MCM‐41 was modified by attaching S‐dodecyl‐S′‐(α,α′‐dimethyl‐α′′‐acetic acid)trithiocarbonate (DDMAT) as the RAFT agent and methacrylate group using 3‐methacryloxypropyldimethylchlorosilane. The kinetics of styrene RAFT polymerization by different approaches was compared with the model polymerization mediated by free DDMAT. The quantity of the grafted chain grown from the surface and inside of the pores of MCM‐41 and free polymer chains in bulk was determined by thermogravimetric analysis. The molecular weight of the produced polymer chains increased linearly with the monomer conversion for three methods. The gel permeation chromatography showed that the molecular weight of grafted and free polymer chains in the “grafting from” approach is higher than other methods, and molecular weight distributions were relatively narrower whereas the rate of polymerization for “grafting from” was higher. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2013, 32, 21372; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21372

One-Step Synthesis of Cross-Linked Block Polymer Precursor to a Nanoporous Thermoset.

Using a simultaneous block polymerization/in situ cross-linking from a heterofunctional initiator approach, we produced a nanostructured and cross-linked block polymer in a single step from a ternary mixture of monomers and used it as a precursor for a cross-linked nanoporous material. Using 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol as a heterofunctional initiator, simultaneous ring-opening transesterification polymerization of d,l-lactide in the presence of tin 2-ethylhexanoate as a catalyst and reversible addition-fragmentation chain transfer polymerization of styrene at 120 °C produced a polylactide-b-polystyrene (PLA-b-PS) block polymer. Incorporation of divinylbenzene in the polymerization mixture allowed in situ cross-linking during the simultaneous block polymerization to result in the cross-linked block polymer precursor in one step. This material was converted into cross-linked nanoporous polymer by etching PLA in a basic solution.

Surface‐Initiated Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization of Styrene from Laponite Clay Surfaces

AbstractSurface‐initiated reversible addition fragmentation chain transfer polymerisation of styrene was conducted from the surface of Laponite clay particles. A new cationic chain transfer agent, 2‐(2‐(butylthio‐carbonothioylthio)propanoyloxy)‐N,N,N‐trimethylethanaminium iodide was synthesised and attached to the clay surface from which polymerisation was initiated. A free RAFT agent, ethyl 2‐(butylthiocarbonothioylthio)propanoate was added in solution to control the polymerisation of free polymer. The grafted and free polymer were then analysed by SEC to get insight into the polymerisation. The thermal stability of the polymer/clay nanocomposites and grafted clay particles was investigated by TGA.

Preparation of a Novel Dispersant for Carbon Black Dispersing and Fixing

The branched poly (styrene-alt-maleic anhydride) (BPSMA) was synthesized by chain transfer polymerization of styrene (St) and maleic anhydride (MA) using (4-vinylphenyl)methanethiol (VPMT) as a chain transfer agent and benzoyl peroxide (BPO) as an initiator. Fourier transforms infrared (FTIR) spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) BPSMA confirmed that the copolymer with the branched structure. BPSMA exhibited high dispersing efficiency for CB particles, and prepared CB dispersion showed excellent stability to centrifugal forces and treatment temperature. In addition, BPSMA can also greatly improve the prubbing and washing fastness of the cotton fabrics when cotton fabrics was printed using this dispersion.

Syndio‐ and Isoselective Coordinative Chain Transfer Polymerization of Styrene Promoted by ansa‐Lanthanidocene/ Dialkylmagnesium Systems

AbstractCombinations of the discrete neutral allyl ansa‐lanthanidocenes {Me2C(Cp)(Flu)}Nd[1,3‐ (SiMe3)2C3H3] and rac‐{Me2C(Ind)2}Y[1,3‐ (SiMe3)2C3H3] with di(n‐butyl)magnesium constitute efficient binary catalytic systems for the stereocontrolled coordinative chain transfer polymerization of styrene, yielding near‐perfect syndio‐ and isospecific polystyrenes, respectively, with high activities and productivities. By adjusting the amount of di(n‐butyl)magnesium, up to 200 polymer chains can be generated per lanthabide center, and good control of the molecular weight features enables the tailoring of low to medium molecular weight polymers.

Reversible coordinative chain transfer polymerization of styrene by rare earth borohydrides, chlorides/dialkylmagnesium systems

AbstractThe ability of various rare earth borohydride and chloride complexes/n‐butylethylmagnesium systems to operate styrene chain transfer polymerization in mild conditions has been assessed. Thirteen precatalysts have been considered: the rare earth trisborohydrides Ln(BH4)3(THF)x (x = 3, Ln = Nd (1), La (2), Sm (3), x = 2, Ln = Y (4), Sc (5)), the rare earth chlorides LnCl3(THF)x (x = 3, Ln = Nd (6), La (7), Sm (8), Y (9), x = 2, Ln = Sc (10)), the mixed La(BH4)2Cl(THF)2.6 (11) and the half‐lanthanidocenes Cp*Ln(BH4)2(THF)2 (Ln = Nd (12), La (13)). Six systems were found to be active precatalysts for the polymerization of styrene. 1, 2, and 11 led to an efficient transmetalation of the growing polystyrene chain with the simultaneous occurrence of βH elimination, whereas 7, 12, and 13 led to catalyzed chain growth behavior. It is noteworthy that the catalyzed chain growth obtained with 12 and 13 occurs with significant stereoselectivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 802–814, 2010

Reversible addition–fragmentation chain transfer polymerization of styrene using a novel thiophene dithioester as the reversible addition–fragmentation chain transfer agent

AbstractBenzyl thiophene‐2‐carbodithioate and 2‐methyl‐2‐(4‐methylcyclohex‐3‐enyl)propyl thiophene‐2‐carbodithioatewere synthesized. The reversible addition–fragmentation chain transfer polymerizations of styrene with benzyl thiophene‐2‐carbodithioate and 2‐methyl‐2‐(4‐methylcyclohex‐3‐enyl)propyl thiophene‐2‐carbodithioate as chain‐transfer agents and with 2,2′‐azobisisobutyronitrile as an initiator were carried out. The polymerization kinetics were investigated. An ab initio calculation method was used to explore the differences between benzyl thiophene‐2‐carbodithioate and benzyl benzodithioate. The structure of the obtained polymers was characterized with 1H‐NMR. Chain‐extension experiments of the obtained polymer with styrene were carried out. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Reversible addition–fragmentation chain transfer polymerization of styrene under microwave irradiation

AbstractReversible addition–fragmentation chain transfer (RAFT) polymerizations of styrene under microwave irradiation (MI), with or without azobisisobutyronitrile, were successfully carried out in bulk at 72 and 98 °C, respectively. The results showed that the polymerizations had living/controlled features, and there was a significant enhancement of the polymerization rates under MI in comparison with conventional heating (CH) under the same conditions. The polymer structures were characterized with 1H and 13C NMR. The results showed the same structure for both polymers obtained by MI and CH. Successful chain‐extension experimentation further demonstrated the livingness of the RAFT polymerization carried out under MI. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6810‐6816, 2006

Kinetic model of reversible addition fragmentation chain transfer polymerization of styrene in seeded emulsion

AbstractA detailed model describing the kinetics of living polymerization mediated by reversible addition‐fragmentation chain transfer (RAFT) in seeded emulsion polymerization is developed. The model consists of a set of population balance equations of the different radical species in the aqueous phase and in the particle phase (accounting for radical segregation) as well as for the dormant species in the particle phase. The entire population of radicals was divided into several distinguished species, based on their length and their chain end group. The model results are helpful in understanding inhibition and retardation phenomena that are typical for RAFT emulsion polymerizations. While inhibition is due to the radical loss in form of the RAFT leaving group, retardation is mostly caused by a small amount of short dormant chains in the particle phase, leading to a slight increase of radical loss via RAFT exchange with radicals entering a particle. The model results are compared to a series of experiments, using cumyl dithiobenzoate as a RAFT agent in polymerizations of styrene. The agreement between experimental and model results is good and, notably, the only parameters considered adjustable were the RAFT exchange rate coefficients. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6114–6135, 2006

Reversible addition–fragmentation chain transfer polymerization of styrene with benzoimidazole dithiocarbamate as a reversible addition–fragmentation chain transfer agent

AbstractTwo novel dithiocarbamates [2‐Y‐benzoimidazole‐1‐carbodithioic acid benzyl esters: Y = methyl (1b) or phenyl (1c)] were synthesized and successfully used in the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene in bulk with thermal initiation. The effects of the temperatures and concentration ratios of the styrene and RAFT agents on the polymerization were investigated. The results showed that the polymerization of styrene could be well controlled in the presence of 1b or 1c. The linear relationships between ln([M]0/[M]) and the polymerization time (where [M]0 is the initial monomer concentration and [M] is the monomer concentration) indicated that the polymerizations were first‐order reactions with respect to the monomer concentration. The molecular weights increased linearly with the monomer conversion and were close to the theoretical values. The molecular weight distributions [weight‐average molecular weight/number‐average molecular weight (Mw/Mn)] were very narrow from 5.3% conversion up to 94% conversion (Mw/Mn < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006

Influence of the chemical structure of dithiocarbamates with different N‐groups on the reversible addition–fragmentation chain transfer polymerization of styrene

AbstractPolymerizations of styrene with azobisisobutyronitrile initiation or thermal initiation have been performed in the presence of dithiocarbamates with different N‐groups, that is, benzyl 4,5‐diphenyl‐1H‐imidazole‐1‐carbodithioate (2a), benzyl 1H‐1,2,4‐triazole‐1‐carbodithioate (2b), benzyl indole‐1‐carbodithioate (2c), benzyl 2‐phenyl‐indole‐1‐carbodithioate (2d), benzyl phenothiazine‐10‐carbodithioate (2e), benzyl 9H‐carbazole‐9‐carbodithioate (2f), and benzyl dibenzo[b,f]azepine‐5‐carbodithioate (2g). The results show that the structure of the N‐group of dithiocarbamates has significant effects on the activity of dithiocarbamates for the polymerization of styrene. 2a, 2b, 2c, 2d, and 2f are effective reversible addition–fragmentation chain transfer (RAFT) agents for the RAFT polymerization of styrene, and the polymerizations have good living characteristics. However, in the cases of 2e and 2g, the obtained polymers have uncontrolled molecular weights and broad molecular weight distributions. The polymerization rate is markedly influenced by the conjugation structure of the N‐group of the dithiocarbamate, and the polymerization rate of 2b is greater than that of 2a. For 2b, the rate of polymerization seems independent of the RAFT agent concentration. However, a significant retardation in the rate of polymerization can be observed in the case of 2c. 2d is more effective than 2c, and the substitution group of phenyl on this dithiocarbamate has obvious effects on the effectiveness of the controlled polymerization of styrene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4849–4856, 2005

Reversible addition–fragmentation chain transfer polymerization of styrene initiated by tetraethylthiuram disulfide

The RAFT polymerization of styrene in bulk was carried out using tetraethylthiuram disulfide (TETD) as an initiator and 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as a chain transfer agent at different temperatures. The results of the polymerization showed that TETD could initiate the RAFT polymerization of styrene in the living way. The kinetics of the polymerization showed first order. The molecular weights of the polymers increased linearly with conversions and were close to the theoretical values ( M n,th). The polydispersities of the polymers remained relatively narrow (<1.3). The structure of the polymer was characterized by 1H NMR. The result showed that there were moieties of CPDN and TETD attained at the end of the polymer. Using these double functional end capped polymers, the chain-extension experiments were successfully carried out not only in the conventional RAFT polymerization way, but also under UV irradiation.

Beyond Inhibition: A 1H NMR Investigation of the Early Kinetics of RAFT-Mediated Polymerization with the Same Initiating and Leaving Groups

In situ 1H nuclear magnetic resonance (NMR) spectroscopy has been used to directly investigate the processes that occur during the early stages (typically the first few monomer addition steps) of an AIBN-initiated reversible addition−fragmentation chain transfer polymerization of styrene in the presence of the RAFT agent cyanoisopropyl dithiobenzoate at 70 and 84 °C. The change in concentration of important dithiobenzoate species as a function of time has been investigated. It was found that the reaction was extremely selective during the period of consumption of the initial RAFT agent (defined as the initialization period), with almost no production of RAFT-capped chains of degree of polymerization greater than unity until all of the cyanoisopropyl dithiobenzoate was converted to its single monomer adduct. The rate-determining step for this process was found to be the addition (propagation) of the cyanoisopropyl radicals to styrene. During the period where the initial RAFT agent was consumed, fragmentati...

Cobalt(II)-Mediated Catalytic Chain Transfer Polymerization of Styrene: Estimating Individual Rate Coefficients via Kinetic Modeling

The individual rate coefficients for hydrogen abstraction (ktr), cobalt−carbon bond formation (kdeac), and cobalt−carbon bond homolysis (kac) have been determined for the cobaloxime-mediated chain transfer polymerization of styrene at 60 °C using kinetic simulations in combination with experimental data. Values of 2.7 × 106 L mol-1 s-1, 4.8 × 104 L mol-1 s-1, and 8.7 × 10-4 s-1 for ktr, kdeac, and kac, respectively, were found to adequately describe reactions associated with the catalytic chain transfer process with the overall model reproducing experimental observations such as molecular weight evolution with time and the initiator concentration dependency of the apparent chain transfer constant. The effect of photohomolysis of the Co−C bond, leading to an increased free catalyst concentration in the presence of strong UV radiation or a decreased free catalyst concentration under darkened conditions, was modeled by simply varying the value for kac.