Copper Catalyzed ATRP of Methyl Methacrylate Using Aliphatic α-Bromo Ketone Initiator

The atom transfer radical polymerization (ATRP) of MMA was examined using 3-bromo-3-methyl-butanone-2 (MBB) as an initiator in the presence of CuBr as catalyst and 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine (BPIEP) as a tridentate N-donor ligand. The effect of various other N-donor ligands including a bisoxazoline ligand, namely, 2,6-bis(4,4-dimethyl-2-oxazolin-2-yl) pyridine (dmPYBOX) was studied in ATRP and reverse ATRP of MMA. The ATRP of MMA in toluene at 90 °C using MBB as initiator was relatively slow in the case of bidentate and faster in the case of tridentate N-donor ligands. The apparent rate constant, k_app, with MBB as initiator and BPIEP as ligand in toluene (50%, v/v) at 90 °C was found to be 7.15 × 10⁻⁵ s⁻¹. In addition, reverse ATRP of MMA in diphenylether at 70 °C using BPIEP/CuBr₂ as catalyst system was very effective in reducing the reaction time from several hours to 24 h for polymerization of MMA.     

Atom Transfer Radical Polymerization of Methyl Methacrylate with α,α,α′,α′‐Tetrachloroxylene as an Initiator

The homogeneous ATRP of methyl methacrylate (MMA) using α,α,α′,α′‐tetrachloroxylene (TCX)/CuCl/N,N,N′,N″,N″–pentamethyldiethylenetriamine (PMDETA) as the initiating system has been successfully carried out. The kinetic plots showed first order relationship vs. monomer concentration. Well‐controlled polymerizations with low polydispersities (M_w/M_n=1.15?1.25) polymers have been achieved. The molecular weights increased linearly with monomer conversions and were close to the theoretical values, indicating high initiation efficiency. The polymerization rate increased significantly with an increase of TCX concentration. The rate of polymerization was about 0.6 orders with respect to the concentration of initiator. The polymerization rate increased significantly with an increase of CuCl concentration. The dependence of ln k_p ^app on ln ([CuCl]₀) indicated a 0.91 order. The apparent activation energy was calculated ΔE_app ^≠=43.3 KJ/mol, and the enthalpy of the equilibrium, ΔH_eq ⁰, was estimated to be 21.1 KJ/mol. The structure of obtained PMMA was analyzed by means of ¹H NMR spectroscopy. The result proved that the TCX acted as a bifunctional initiator for ATRP of MMA.     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

Polymerization of methyl acrylate mediated by copper(0)/Me6‐TREN in hydrophobic media enhanced by phenols; Single electron transfer‐living radical polymerization

Phenol has been used as an additive to enhance the rate of SET‐LRP in toluene at ambient temperature. A direct relationship between reaction time and amount of phenol added has been found with the optimum amount being ～ 20 equiv. of phenol with respect to initiator. Polymerization of methyl acrylate (MA) has been carried out in the presence of varying amounts of phenol and the rate of polymerization depends on the concentration of phenol relative to initiator. With a 20‐fold excess 93% conversion is observed after 218 min (PDI = 1.06, M_n = 11,500 g mol^?1) when compared with 80% conversion with a 5‐fold excess (PDI = 1.21, M_n = 5310 g mol^?1). When nonsterically hindered phenols are employed in a 20 molar excess with respect to the initiator the polymerizations have good linear first‐order kinetics and give polymers with PDI between 1.06 and 1.16. When a highly hindered phenol is employed there is a significant induction period prior to polymerization taking place which is similar to when using no phenol. Less hindered phenols accelerated the polymerization when compared with polymerizations with no added phenol. Increasing steric hindrance at the ? OH prevents this coordination which indicates that the role of phenol is different with either copper(0) or copper(I). Aliphatic and aromatic esters and amides were used successfully as initiators giving polymers with M_n close to that predicted at ～ 10,000 g mol^?1 and PDI typically less than 1.10. An induction period is observed in most cases which can be removed by a pre‐equilibrium step before the addition of monomer. This results in excellent first‐order kinetics being observed in the polymerization of MA in toluene solution (50 vol %). Here Cu(0) (powder)/Me₆‐TREN with 20 equiv. of phenol and all of the reactants, except the monomer, were added to the reaction flask and stirred for 45 min at 25 °C. The structure of the polymer is shown by MALDI TOF MS to contain bromide chain ends derived from the alkyl bromide initiator. The retention of this end group is consistent with living radical polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7376–7385, 2008     

Titanium complexes of dialkanolamine ligands as initiators for living ring‐opening polymerization of ε‐caprolactone

The titanium complexes with one ( 1a , 1b , 1c ) and two ( 2a , 2b ) dialkanolamine ligands were used as initiators in the ring‐opening polymerization (ROP) of ε‐caprolactone. Titanocanes 1a and 1b initiated living ROP of ε‐caprolactone affording polymers whose number‐average molecular weights (M_n) increased in direct proportion to monomer conversion (M_n ≤ 30,000 g mol^?1) in agreement with calculated values, and were inversely proportional to initiator concentration, while the molecular weight distribution stayed narrow throughout the polymerization (M_w/M_n ≤ 1.2 up to 80% monomer conversion). ¹H‐NMR and MALDI‐TOF‐MS studies of the obtained poly(ε‐caprolactone)s revealed the presence of an isopropoxy group originated from the initiator at the polymer termini, indicating that the polymerization takes place exclusively at the Ti–OⁱPr bond of the catalyst. The higher molecular weight polymers (M_n ≤ 70,000 g mol^?1) with reasonable MWD (M_w/M_n ≤ 1.6) were synthesized by living ROP of ε‐caprolactone using spirobititanocanes ( 2a , 2b ) and titanocane 1c as initiators. The latter catalysts, according MALDI‐TOF‐MS data, afford poly(ε‐caprolactone)s with almost equal content of α,ω‐dihydroxyl‐ and α‐hydroxyl‐ω(carboxylic acid)‐terminated chains arising due to monomer insertion into “Ti–O” bond of dialkanolamine ligand and from initiation via traces of water, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1230–1240, 2010     

Visible‐light induced RAFT polymerization of styrenic monomers with aromatic aldehydes as organophotoredox catalysts

A photoinduced electron transfer‐reversible addition‐fragmentation chain transfer (PET‐RAFT) polymerization of p‐methylstyrene (p‐MS) and styrene (St) with 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid as the chain transfer agent (CTA) and aromatic aldehydes, including 4‐cyanobenzaldehyde (PC1), 2,4‐dimethoxy benzaldehyde, and 4‐methoxy benzaldehyde, as organic photocatalysts has been demonstrated via irradiation with 23 W compact fluorescent lamps. The kinetics of the polymerizations shows first order with respect to monomer conversions. Linear evolution of the M_n of the produced polymers with the monomer conversion is observed. Meanwhile, the as‐prepared polymers are of relatively narrow polydispersity (PDI = M_w/M_n). For instance, the polymerization of p‐MS shows living polymerization features using PC1 within a range of solvents. Especially, the M_n of PpMS increased from about 2100 to 12,700 g/mol with the monomer conversion from 8% to 52% in tetrahydrofuran. The controlled polymerization of St is also observed under optimal reaction conditions. However, the M_n discrepancy between the experimental readings and theoretical calculations is greater at the monomer conversions greater than 40% and the PDI increased gradually over the monomer conversion. This is probably because that CTA is strongly sensitive to the light irradiation with wave range around its characteristic absorption wavelength, leading to significant decomposition of CTA moieties during the RAFT polymerization. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2072–2079     

Polymerization kinetics of rac‐lactide initiated with alcohol/stannous octoate using in situ attenuated total reflectance‐fourier transform infrared spectroscopy: An initiator study

rac‐Lactide polymerization kinetics in THF at 72 °C were monitored in real‐time using mid‐infrared ATR‐FTIR spectroscopy, with diamond composite insertion probe and light conduit technology. Monomer concentration as a function of time was acquired using the 1240 cm^?1 resonance associated with the ? CO? O? C? stretch. Polymerizations were initiated with either n‐propanol (PrOH), ethylene glycol (EG), trimethylol propane (TMP), or pentaerythritol (PENTA) with the coinitiator stannous octoate (Sn(Oct)₂). Polymerizations were found to be reversible at high monomer conversions, with a residual monomer concentration at 72 °C (345 K) of 0.081 M. The polymerizations were internally first‐order with respect to monomer, indicating a constant concentration of propagating centers. For a typical reaction with [rac‐LA]₀ = 1.0 M, [PENTA]₀ = 1.3 × 10^?2 M, and [Sn(Oct)₂] = 2.5 × 10^?2 M, the first‐order rate constant, k_app was measured as 1.8 × 10^?4 s^?1. First‐order rate constants were determined to be independent of polymer architecture (i.e., initiator functionality) and proportional to [Sn(Oct)₂] for [Sn(Oct)₂]₀/[ROH]₀ ? 1, where [ROH]₀ represents the initial concentration of initiating hydroxyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 797–803, 2009     

Atom transfer radical polymerization of N‐vinyl carbazole: Optimization to characterization

The homopolymerization of N‐vinylcarbazole was performed with atom transfer radical polymerization (ATRP) with Cu(I)/Cu(II)/2,2′‐bipyridine (bpy) as the catalyst system at 90 °C in toluene. N‐2‐Bromoethyl carbazole was used as the initiator, and the optimized ratio of Cu(I) to Cu(II) was found to be 1/0.3. The resulting homopolymer, poly(N‐vinylcarbazole) (PVK), was formed after a monomer conversion of 76% in 20 h. The molecular weight as well as the polydispersity index (PDI) showed a linear relation with the conversion, which showed control over the polymerization. A semilogarithmic plot of the monomer conversion with time was linear, indicating the presence of constant active species throughout the polymerization. The initiator efficiency and the effect of the variation of the initiator concentration on the polymerization were studied. The effects of the addition of CuBr₂, the variation of the catalyst concentration with respect to the initiator, and CuX (X = Br or Cl) on the kinetics of homopolymerization were determined. With Cu(0)/CuBr₂/bpy as the catalyst, faster polymerization was observed. For a chain‐extension experiments, PVK (number‐average molecular weight = 1900; PDI = 1.24) was used as a macroinitiator for the ATRP of methyl methacrylate, and this resulted in the formation of a block copolymer that gave a monomodal curve in gel permeation chromatography. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1745–1757, 2006     

Kinetic study on the living/controlled cationic polymerization of p‐methoxystyrene coinitiated by tris(pentafluorophenyl)borane

A kinetic study of the living cationic polymerization of p‐methoxystyrene using 1‐(4‐methoxyphenyl)ethanol ( 1 )/B(C₆F₅)₃ initiating system in a mixture of CH₃CN with CH₂Cl₂ 1:1 (v/v) at room temperature was carried out utilizing a wide variety of conditions. The polymerization proceeded in a living fashion even in the presence of a large amount of water ([H₂O]/[B(C₆F₅)₃] ratio up to 20) to afford polymers whose M_n increased in direct proportion to monomer conversion with fairly narrow MWDs (M_w/M_n ≤ 1.3). The investigation revealed that the rate of polymerization was first‐order in B(C₆F₅)₃ concentration, while a negative order in H₂O concentration close to ?2 was obtained. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decreased concentration in free Lewis acid, the true coinitiator of polymerization. A mechanistic scheme to explain the kinetic behavior of living p‐methoxystyrene polymerization is proposed, which has been validated by PREDICI simulation on multiple‐data curves obtained by ¹H NMR in situ polymerization experiment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6928–6939, 2008     

AGET ATRP of water‐soluble PEGMA: Fast living radical polymerization mediated by iron catalyst

In this work, living radical polymerizations of a water‐soluble monomer poly(ethylene glycol) monomethyl ether methacylate (PEGMA) in bulk with low‐toxic iron catalyst system, including iron chloride hexahydrate and triphenylphosphine, were carried out successfully. Effect of reaction temperature and catalyst concentration on the polymerization of PEGMA was investigated. The polymerization kinetics showed the features of “living”/controlled radical polymerization. For example, M_n,GPC values of the resultant polymers increased linearly with monomer conversion. A faster polymerization of PEGMA could be obtained in the presence of a reducing agent Fe(0) wire or ascorbic acid. In the case of Fe(0) wire as the reducing agent, a monomer conversion of 80% was obtained in 80 min of reaction time at 90 °C, yielding a water‐soluble poly(PEGMA) with M_n = 65,500 g mol^?1 and M_w/M_n = 1.39. The features of “living”/controlled radical polymerization of PEGMA were verified by analysis of chain‐end and chain‐extension experiments. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effects of hydration and hydrophilicity on Na‐Clay‐supported aqueous‐phase catalysis for atom transfer radical polymerization

Hydrated sodium montmorillonite (Na‐clay) has been used as a catalyst support for the heterogeneous atom transfer radical polymerization of benzyl methacrylate in the presence of various concentrations of water, reducing agent, and CuBr₂ in anisole at ambient temperature. The polymerization was promoted via reduction of Cu^II to Cu^I through the addition of sodium ascorbate (NaAsc) as a reducing agent in aqueous solution. The polymerizaton proceeded in a controlled manner and produced poly(benzyl methacylate) with moderately narrow molecular weight distribution (MWD) when performed under optimum conditions of hydration (10 wt % ≤ H₂O/Na‐clay ≤ 21 wt %) and reducing agent (0.15 ≤ [NaAsc]/[I] ≤ 0.23). The polymerization was uncontrolled if hydration and NaAsc exceed above their optimum range of concentrations. Apparent rate of the polymerization (k_app) increased in the presence of decane–anisole (1/3, v/v) mixture solvent. Selective adsorption of decane at the interfaces of the hydrated clay was attributed for the rate enhancement due to increased polymer and hydrophobic interface interaction. The polymerization progressed in a controlled manner as confirmed by the first‐order time‐conversion plot, linear increase in molecular weights, and moderately narrow MWDs over conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Optimized water‐based ATRP of an anionic monomer: Comprehension and properties characterization

The effect of pH and the ligand nature over the atom transfer radical polymerization (ATRP) of the anionic monomer sodium 2‐acrylamido‐2‐methylpropanesulfonate (AMPSNa) was investigated in aqueous medium by using ω‐halogenated poly(ethylene oxide) and CuBr, as macroinitiator and catalyst, respectively. The stability of both catalytic complexes and macroinitiator was investigated in function of pH, that is, fixed between 7.5 and 12. UV‐VIS spectroscopy confirmed a good catalytic complex stability in the studied conditions. Hydrolysis of the macroinitiator ester group at pH higher than 7.5 was detected by ¹H NMR and GPC, yielding ill‐defined polymer samples when ATRP is performed in alkaline conditions. 2,2′‐Bipyridyl (Bpy), 1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA), and tris(2‐methylaminoethyl)amine (Me₆‐TREN)‐based complexes were compared at the optimal pH (pH 7.5). When polymerization was carried out in the presence of CuBr · 2Me₆‐TREN complex block copolymers with narrow molecular weight distribution (1.1 ≤ M _W/M _n ≤ 1.3), and good agreement between theoretical and experimental molar masses was obtained. Moreover, increasing the PAMPSNa polymerization degrees (n) did not affect the control over the polymerization. Preliminary characterization of the diblock copolymers behavior in aqueous medium revealed a strong polyelectrolyte effect independently of n. Interestingly, occurrence of interactions between the PEO and PAMPSNa‐blocks was also evidenced by differential scanning calorimetry and thermogravimetric analyses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1108–1119, 2009     

Synthesis of azobenzene‐containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene‐containing amphiphilic diblock copolymers

The well‐defined azobenzene‐containing homopolymers, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)} (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. The first‐order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs ≤ 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly{6‐(4‐phenylazophenoxy)hexyl methacrylate (AHMA)}‐b‐poly{2‐(dimethylamino)ethyl methacrylate (DMAEMA)} (PAHMA‐b‐PDMAEMA), was prepared with the obtained PAHMA as the macro‐RAFT agent. The structures and properties of the polymers were characterized by ¹H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl₃) solution (PAHMA₂₃‐b‐PDMAEMA₉₇ (4 × 10^?5 M, M_n(GPC) = 18,400 g/mol, PDI = 1.48) and PAHMA₂₈‐b‐PDMAEMA₁₁₇ (6 × 10^?5 M, M_n(GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA‐b‐PDMAEMA in CHCl₃ was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self‐assembled micelles composed of azobenzene‐containing amphiphilic diblock copolymers, (PAHMA‐b‐QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N‐dimethyl formamide (DMF)/H₂O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5652–5662, 2008     

Aqueous MADIX/RAFT polymerization of diallyldimethylammonium chloride: Extension to the synthesis of poly(DADMAC)‐based double hydrophilic block copolymers

Macromolecular design by interchange of xanthates/reversible addition fragmentation chain transfer polymerization (MADIX/RAFT) of diallyldimethylammonium chloride (DADMAC) using the hydrophobic O‐ethyl‐S‐(1‐methoxycarbonyl) ethyl dithiocarbonate MADIX/RAFT mediating agent, Rhodixan A1, was investigated. Attempts to obtain an efficient control of DADMAC polymerization in a water/ethanol mixture failed because of significant chain transfer to ethanol. The use of a water‐soluble Rhodixan A1‐terminated acrylamide oligomer as the MADIX/RAFT agent enabled the controlled polymerization of DADMAC in water at 50 °C using the cationic azo initiator V‐50. An excellent agreement was found between experimental and theoretical M_n values throughout polymerization and over a broad range of initial concentration of xanthate. Polydispersity indexes (PDIs) at the end of the polymerization were abnormally high for a process showing a linear increase of M_n with monomer conversion (1.8 < PDI < 2.0). This feature was explained by the measurement of a high transfer constant to xanthate (C_x = 18.8 ± 1.6) but a low interchange transfer constant (C_ex = 1.5). Nevertheless, poly(acrylamide)–poly(DADMAC) double hydrophilic block copolymers (DHBCs) of controlled M_n and composition could be successfully synthesized for the first time. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Single electron transfer‐living radical polymerization of methyl methacrylate in fluoroalcohol: Dual control over molecular weight and tacticity

The Cu(0)‐mediated single electron transfer‐living radical polymerization (SET‐LRP) of methyl methacrylate (MMA) using ethyl 2‐bromoisobutyrate (EBiB) as an initiator with Cu(0)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine as a catalyst system in 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) was studied. The polymerization showed some living features: the measured number‐average molecular weight (M_n,GPC) increased with monomer conversion and produced polymers with relatively low polydispersities. The increase of HFIP concentration improved the controllability over the polymerization with increased initiation efficiency and lowered polydispersity values. ¹H NMR, MALDI‐TOF‐MS spectra, and chain extension reaction confirmed that the resultant polymer was end‐capped by EBiB species, and the polymer can be reactivated for chain extension. In contrast, in the cases of dimethyl sulfoxide or N,N‐dimethylformamide as reaction solvent, the polymerizations were uncontrolled. The different effects of the solvents on the polymerization indicated that the mechanism of SET‐LRP differed from that of atom transfer radical polymerization. Moreover, HFIP also facilitated the polymerization with control over stereoregularity of the polymers. Higher concentration of HFIP and lower reaction temperature produced higher syndiotactic ratio. The syndiotactic ratio can be reached to about 0.77 at 1/1.5 (v/v) of MMA/HFIP at ?18 °C. In conclusion, using HFIP as SET‐LRP solvent, the dual control over the molecular weight and tacticity of PMMA was realized. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6316–6327, 2009     

Atom transfer radical polymerization of styrene using the novel initiator ethyl 2‐N,N‐(diethylamino)dithiocarbamoyl‐butyrate

The atom transfer radical polymerizations (ATRPs) of styrene initiated by a novel initiator, ethyl 2‐N,N‐(diethylamino)dithiocarbamoyl‐butyrate (EDDCB), in both bulk and solution were successfully carried out in the presence of copper(I) bromide (CuBr) and N,N,N′,N″,N″‐pentamethyldiethylenetriamine at 115 °C. The polymerization rate was first‐order with respect to the monomer concentration, and the molecular weights of the obtained polymers increased linearly with the monomer conversions with very narrow molecular weight distributions (as low as 1.17) up to higher conversions in both bulk and solution. The polymerization rate was influenced by various solvents in different degrees in the order of cyclohexanone > dimethylformamide > toluene. The molecular weight distributions of the produced polymers in cyclohexanone were higher than those in dimethylformamide and toluene. The results of ¹H NMR analysis and chain extension confirmed that well‐defined polystyrene bearing a photo‐labile N,N‐(diethylamino)dithiocarbamoyl group was obtained via ATRP of styrene with EDDCB as an initiator. The polymerization mechanism for this novel initiation system is a common ATRP process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 32–41, 2006     

2‐[(Diphenylphosphino)methyl]pyridine as ligand for iron‐based atom transfer radical polymerization

2‐[(Diphenylphosphino)methyl]pyridine (DPPMP) was successfully used as a bidentate ligand in the iron‐mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with various initiators and solvents. The effect of the catalytic system on ATRP was studied systematically. Most of the polymerizations with DPPMP ligand were well controlled with a linear increase in the number‐average molecular weights (M_n) versus conversion and relatively low molecular weight distributions (M_w/M_n = 1.10–1.3) being observed throughout the reactions, and the measured molecular weights matched the predicted values. Initially added iron(III) bromide improved the controllability of the polymerization reactions in terms of molecular weight control. The ratio of ligand to metal influenced the controllability of ATRP system, and the optimum ratio was found to be 2:1. It was shown that ATRP of MMA with FeX₂/DPPMP catalytic system (X = Cl, Br) initiated by 2‐bromopropionitrile (BPN) was controlled more effectively in toluene than in polar solvents. The rate of polymerization increased with increasing the polymerization temperature and the apparent activation energy was calculated to be 56.7 KJ mol^?1. In addition, reverse ATRP of MMA was able to be successfully carried out using AIBN in toluene at 80 °C. Polymerization of styrene (St) was found to be controlled well by using the PEBr/FeBr₂/DPPMP system in DMF at 110 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2922–2935, 2008     

SET‐LRP of acrylonitrile in ionic liquids without any ligand

Use of ionic liquids as reaction media was investigated in the design of an environmentally friendly single electron transfer‐living radical polymerization (SET‐LRP) for acrylonitrile (AN) without any ligand by using Fe(0) wire as catalyst and 2‐bromopropionitrile as initiator. 1‐Methylimidazolium acetate ([mim][AT]), 1‐methylimidazolium propionate ([mim][PT]), and 1‐methylimidazolium valerate ([mim][VT]) were applied in this study. First‐order kinetics of polymerization with respect to the monomer concentration, linear increase of the molecular weight, and narrow polydispersity with monomer conversion showed the controlled/living radical polymerization characters. The sequence of the apparent polymerization rate constant of SET‐LRP of AN was k_app ([mim][AT]) > k_app ([mim][PT]) > k_app ([mim][VT]). The living feature of the polymerization was also confirmed by chain extensions of polyacrylonitrile with methyl methacrylate. All three ionic liquids were recycled and reused and had no obvious effect on the controlled/living nature of SET‐LRP of AN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of well‐defined cyclodextrin‐core star polymers

The synthesis of 21‐arm methyl methacrylate (MMA) and styrene star polymers is reported. The copper (I)‐mediated living radical polymerization of MMA was carried out with a cyclodextrin‐core‐based initiator with 21 independent discrete initiation sites: heptakis[2,3,6‐tri‐O‐(2‐bromo‐2‐methylpropionyl]‐β‐cyclodextrin. Living polymerization occurred, providing well‐defined 21‐arm star polymers with predicted molecular weights calculated from the initiator concentration and the consumed monomer as well as low polydispersities [e.g., poly(methyl methacrylate) (PMMA), number‐average molecular weight (M_n) = 55,700, polydispersity index (PDI) = 1.07; M_n = 118,000, PDI = 1.06; polystyrene, M_n = 37,100, PDI = 1.15]. Functional methacrylate monomers containing poly(ethylene glycol), a glucose residue, and a tert‐amine group in the side chain were also polymerized in a similar fashion, leading to hydrophilic star polymers, again with good control over the molecular weight and polydispersity (M_n = 15,000, PDI = 1.03; M_n = 36,500, PDI = 1.14; and M_n = 139,000, PDI = 1.09, respectively). When styrene was used as the monomer, it was difficult to obtain well‐defined polystyrene stars at high molecular weights. This was due to the increased occurrence of side reactions such as star–star coupling and thermal (spontaneous) polymerization; however, low‐polydispersity polymers were achieved at relatively low conversions. Furthermore, a star block copolymer consisting of PMMA and poly(butyl methacrylate) was successfully synthesized with a star PMMA as a macroinitiator (M_n = 104,000, PDI = 1.05). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2206–2214, 2001     

RAFT Polymerization of Styrene in the Presence of 2‐Nonyl‐benzoimidazole‐1‐carbodithioic Acid Benzyl Ester

A novel dithiocarbamate, 2‐nonyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1a ), was synthesized and successfully used in RAFT polymerization of styrene in bulk with thermal initiation. The effect of molar ratio of styrene to RAFT agent on the polymerization was investigated. The linear relationship between ln([M]₀/[M]) and polymerization time indicated that the polymerization was first‐order with respect to monomer concentration. The molecular weights increased linearly with monomer conversion and were close to corresponding theoretical values. The molecular weight distributions (M _w /M _n ) kept very narrow (M _w /M _n <1.1) at a wide range of conversions of 14.2% to 73.3%. The obtained polymer had a strong ultraviolet absorption at 329 nm, which indicated that the 1a moiety remained at the end of polymer chain.