The ligand effect in Ti‐mediated living radical styrene polymerizations initiated by epoxide radical ring opening. 1. Alkoxide and bisketonate Ti complexes

Bisketonate and alkoxide Ti(III) complexes derived from Zn reduction of Ti(IV) precursors were evaluated as catalysts for the living radical polymerization (LRP) of styrene initiated by Ti‐catalyzed epoxide radical ring opening and mediated by reversible termination with Ti(III). No polymerization occurred with tris(2,2,6, 6‐tetramethyl‐3,5‐heptanedionato)titanium (III), whereas dichlorobis(2,2,6,6‐tetramethyl‐3,5‐heptanedionato)titanium (IV) affords only a free radical polymerization. Preliminary living features were displayed by (ⁱPrO)₂TiCl₂. Investigations of the effect of epoxide/Ti/Zn ratios, temperature, and nature of the epoxide demonstrated that (ⁱPrO)₃TiCl provides a linear dependence of M_n on conversion over a wide range of conditions with an optimum for [Sty]/[epoxide group]/[Ti]/[Zn] = 50/1/2/4 at 90 °C. However, the polydispersity could not be reduced below 1.4–1.5, with an initiator efficiency of 0.15. These results were rationalized in terms of a combination of decreased Ti oxophilicity and ligand exchange. The lowered oxophilicity decreases the initiation rate and broadens M_w/M_n. The fast alkoxide exchange promotes a weak dependence of the polymerization on reaction conditions and generates macromolecular Ti species with reduced ability to mediate LRP. Thus, while monofunctional epoxides provide homogeneous polymerizations and narrower M_w/M_n, difunctional initiators may lead to gel formation at high conversion. Nonetheless, all polymerizations were light gray to colorless and afforded white polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6028–6038, 2005     

Titanium‐mediated living radical styrene polymerizations. VI. Cp2TiCl‐catalyzed initiation by epoxide radical ring opening: Effect of the reducing agents,temperature, and titanium/epoxide and titanium/zinc ratios

The effects of the reducing agent, temperature, and epoxide/Ti and Ti/Zn ratios were investigated for the Cp₂TiCl‐catalyzed living radical polymerization of styrene initiated by epoxide radical ring opening. No reduction of bis(cyclopentadienyl)titanium dichloride occurred with Cu, Devarda's alloy, Ni, Ce, Cr, Sn, Mo, and ascorbic acid, whereas Al, lithium nitride, Mn, Sm, and Fe led to free‐radical or poorly controlled polymerizations. The best results were obtained with Zn alloy, powder, or nanoparticles. Nano‐Zn provided the lowest polydispersity index values, highest initiator efficiency (IE), and fastest reaction rate while maintaining a well‐defined living polymerization. Progressively lower polydispersity was obtained with an increasing excess of Zn with an optimum at Cp₂TiCl/Zn = 1/2. This was rationalized through the heterogeneous nature of Zn and its possible involvement in the reversible termination step. The polymerization was insensitive to light or dark conditions, and a linear dependence of M_n on the conversion was observed at all temperatures in the 60–130 °C range with an optimum at 70–90 °C. A stoichiometric 1/2 epoxide/Ti ratio provided low polydispersity (weight‐average molecular weight/number‐average molecular weight < 1.2) and high IE, whereas increasing the epoxide/Ti ratio to 1/3 maintained a low polydispersity index but decreased the IE. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2156–2165, 2006     

Titanium‐mediated living radical styrene polymerizations. V. Cp2TiCl‐catalyzed initiation by epoxide radical ring opening: Effect of solvents and additives

The effects of solvents, additives, ligands, and solvent in situ drying agents as well as catalyst and initiator concentrations have been investigated in the Cp₂TiCl‐catalyzed radical polymerization of styrene initiated by epoxide radical ring opening. On the basis of the solubilization of Cp₂Ti(III)Cl and the polydispersity of the resulting polymer, the solvents rank as follows: dioxane ≥ tetrahydrofuran > diethylene glycol dimethyl ether > methoxybenzene > diphenyl ether ≥ bulk > toluene ? pyridine > dimethylformamide > 1‐methyl‐2‐pyrrolidinone > dimethylacetamide > ethylene carbonate, acetonitrile, and trioxane. Alkoxide additives such as aluminum triisopropoxide and titanium(IV) isopropoxide are involved in alkoxide ligand exchange with the epoxide‐derived titanium alkoxide and lead to broad molecular weight distributions, whereas similarly to strongly coordinating solvents, ligands such as bipyridyl block the titanium active site and prevent the polymerization. By contrast, softer ligands such as triphenylphosphine improve the polymerization in less polar solvents such as toluene. Although mixed hydrides such as lithium tri‐tert‐butoxyaluminum hydride, sodium borohydride, and lithium aluminum hydride react with bis(cyclopentadienyl)titanium dichloride to form mixed titanium hydride species ineffective in polymerization control, simple hydrides such as lithium hydride, sodium hydride, and especially calcium hydride are particularly effective as in situ trace water scavengers in this polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2015–2026, 2006     

Simultaneous control of the stereospecificity and molecular weight in the ruthenium‐catalyzed living radical polymerization of methyl and 2‐hydroxyethyl methacrylates and sequential synthesis of stereoblock polymers

The stereospecific living radical polymerizations of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) were achieved with a combination of ruthenium‐catalyzed living radical and solvent‐mediated stereospecific radical polymerizations. Among a series of ruthenium complexes [RuCl₂(PPh₃)₃, Ru(Ind)Cl(PPh₃)₂, and RuCp*Cl(PPh₃)₂], Cp*–ruthenium afforded poly(methyl methacrylate) with highly controlled molecular weights [weight‐average molecular weight/number‐average molecular weight (M_w/M_n) = 1.08] and high syndiotacticity (r = 88%) in a fluoroalcohol such as (CF₃)₂C(Ph)OH at 0 °C. On the other hand, a hydroxy‐functionalized monomer, HEMA, was polymerized with RuCp*Cl(PPh₃)₂ in N,N‐dimethylformamide and N,N‐dimethylacetamide (DMA) to give syndiotactic polymers (r = 87–88%) with controlled molecular weights (M_w/M_n = 1.12–1.16). This was the first example of the syndiospecific living radical polymerization of HEMA. A fluoroalcohol [(CF₃)₂C(Ph)OH], which induced the syndiospecific radical polymerization of MMA, reduced the syndiospecificity in the HEMA polymerization to result in more or less atactic polymers (mm/mr/rr = 7.2/40.9/51.9%) with controlled molecular weights in the presence of RuCp*Cl(PPh₃)₂ at 80 °C. A successive living radical polymerization of HEMA in two solvents, first DMA followed by (CF₃)₂C(Ph)OH, resulted in stereoblock poly(2‐hydroxyethyl methacrylate) with syndiotactic–atactic segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3609–3615, 2006     

Polymerization of vinyl chloride with half‐titanocene/methylaluminoxane catalysts

The polymerization of vinyl chloride (VC) with half‐titanocene /methylaluminoxane (MAO) catalysts is investigated. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst (Cp* = η⁵‐pentamethylcyclopentadienyl) afforded high‐molecular‐weight poly(vinyl chloride) (PVC) in good yields, although the polymerization proceeded at a slow rate. With the Cp*TiCl₃/MAO catalyst, the polymer was also obtained, but the polymer yield was lower than that with the Cp*Ti(OCH₃)₃/MAO catalyst. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was influenced by the MAO/Ti mole ratio and reaction temperature, and the optimum was observed at the MAO/Ti mole ratio of about 10. The optimum reaction temperature of VC with the Cp*Ti(OCH₃)₃/MAO catalyst was around 20 °C. The stereoregularity of PVC obtained with the Cp*Ti(OCH₃)₃/MAO catalyst was different from that obtained with azobisisobutyronitrile, but highly stereoregular PVC could not be synthesized. From the elemental analyses, the ¹H and ¹³C NMR spectra of the polymers, and the analysis of the reduction product from PVC to polyethylene, the polymer obtained with Cp*Ti(OCH₃)₃/MAO catalyst consisted of only regular head‐to‐tail units without any anomalous structure, whereas the Cp*TiCl₃/MAO catalyst gave the PVC‐bearing anomalous units. The polymerization of VC with the Cp*Ti(OCH₃)₃/MAO catalyst did not inhibit even in the presence of radical inhibitors such as 2,2,6,6,‐tetrametylpiperidine‐1‐oxyl, indicating that the polymerization of VC did not proceed via a radical mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 248–256, 2003     

In situ‐generated Ru(III)‐mediated ATRP from the polymeric Ru(III) complex in the absence of activator generation agents

Past research has examined the atom transfer radical polymerization (ATRP) with high oxidation state metal complexes and without the need for any additives such as reducing agent or free radical initiator. To extend this research, half‐metallocene ruthenium(III) (Ru(III)) catalysts were used for the polymerization of methyl methacrylate (MMA) for the first time. These catalysts were generated in situ simply by mixing phosphorus‐containing ligand and pentamethylcyclopentadienyl (Cp*) Ru(III) polymer ((Cp*RuCl₂)_n). The complexes in their higher oxidation state such as Cp*RuCl₂(PPh₃) were air‐stable, highly active, and removable catalysts for the ATRPs of MMA with both precision control of molecular weight and narrow polydispersity index. The addition of ppm amount of metal catalyst contributed to the formation of very well‐defined homopolymers and copolymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Sterically Less‐Hindered Half‐Titanocene(IV) Phenoxides: Ancillary‐Ligand Effect on Mono‐, Bis‐, and Tris(2‐Alkyl‐/arylphenoxy) Titanium(IV) Chloride Complexes

A series of mono‐, bis‐, and tris(phenoxy)–titanium(IV) chlorides of the type [Cp*Ti(2‐R? PhO)_nCl_3?n] (n=1–3; Cp*=pentamethylcyclopentadienyl) was prepared, in which R=Me, iPr, tBu, and Ph. The formation of each mono‐, bis‐, and tris(2‐alkyl‐/arylphenoxy) series was authenticated by structural studies on representative examples of the phenyl series including [Cp*Ti(2‐Ph? PhO)Cl₂] ( 1 PhCl2 ), [Cp*Ti(2‐Ph? PhO)₂Cl] ( 2 PhCl ), and [Cp*Ti(2‐Ph? PhO)₃] ( 3 Ph ). The metal‐coordination geometry of each compound is best described as pseudotetrahedral with the Cp* ring and the 2‐Ph? PhO and chloride ligands occupying three leg positions in a piano‐stool geometry. The mean Ti? O distances, observed with an increasing number of 2‐Ph? PhO groups, are 1.784(3), 1.802(4), and 1.799(3) Å for 1 PhCl2 , 2 PhCl , and 3 Ph , respectively. All four alkyl/aryl series with Me, iPr, tBu, and Ph substituents were tested for ethylene homopolymerization after activation with Ph₃C⁺[B(C₆F₅)₄]^? and modified methyaluminoxane (7% aluminum in isopar E; mMAO‐7) at 140 °C. The phenyl series showed much higher catalytic activity, which ranged from 43.2 and 65.4 kg (mmol of Ti?h)^?1, than the Me, iPr, and tBu series (19.2 and 36.6 kg (mmol of Ti?h)^?1). Among the phenyl series, the bis(phenoxide) complex of 2 PhCl showed the highest activity of 65.4 kg (mmol of Ti?h)^?1. Therefore, the catalyst precursors of the phenyl series were examined by treating them with a variety of alkylating reagents, such as trimethylaluminum (TMA), triisobutylaluminum (TIBA), and methylaluminoxane (MAO). In all cases, 2 PhCl produced the most catalytically active alkylated species, [Cp*Ti(2‐Ph? PhO)MeCl]. This enhancement was further supported by DFT calculations based on the simplified model with TMA.     

The syndiospecific polymerization of styrene in the presence of fluorine‐containing half‐sandwich metallocenes

The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η⁵‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η⁵‐octahydrofluorenyl titanium tristrifluoro‐acetate, η⁵‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η⁵‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)₃ > [Cp*Ti(OCOCF₃)₂]₂O ≈ Cp*TiCl₃, and for octahydrofluorenyl compounds, [656]Ti(OMe)₃ > [656]Ti(OCOC₆F₅)₃ > [656]Ti(OCH₃)₂(OCOCF₃) > [656]Ti (OCOCF₃)₃. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000     

Heterochain model for simultaneous long‐chain branching and crosslinking. II. Application to free‐radical polymerization

The matrix formula developed in the context of hetrochain theory, M?_w = M?_wp + WF ( I ? M )^?1 S , was applied to describe the molecular weight development during free‐radical homopolymerization. All of the required probabilistic parameters are expressed in terms of the kinetic‐rate constants and various concentrations. In free‐radical polymerization, the primary chains are formed consecutively, and the number of heterochain types, N, is extrapolated to infinity. Practically, such extrapolation can be conducted on the basis of the calculated values for only three different N values with sufficient accuracy. This matrix formula is valid regardless of the chemical and reactor systems used, as long as the primary chain‐connection statistics is considered Markovian. The gel point can be determined simply by solving an equation det( I ? M ) = 0. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2791–2800, 2004     

Iron‐catalyzed living radical polymerization of acrylates: Iodide‐based initiating systems and block and random copolymerizations

A half‐metallocene iron iodide complex [Fe(Cp)I(CO)₂] induced living radical polymerization of methyl acrylate (MA) in conjunction with an iodide initiator [(CH₃)₂C(CO₂Et)I, 1 ] and Al(Oi‐Pr)₃ to give polymers of controlled molecular weights and narrow molecular weight distributions (MWDs) (M_w/M_n < 1.2). With the use of chloride and bromide initiators, the MWDs were broader, whereas the molecular weights were similarly controlled. Other acrylates such as n‐butyl acrylate (nBA) and tert‐butyl acrylate (tBA) can be polymerized with 1 /Fe(Cp)I(CO)₂ in the presence of Ti(Oi‐Pr)₄ and Al(Oi‐Pr)₃, respectively, to give living polymers. The 1 /Fe(Cp)I(CO)₂ initiating system is applicable for the synthesis of block and random copolymers of acrylates (MA, nBA, and tBA) and styrene of controlled molecular weights and narrow MWDs (M_w/M_n = 1.2–1.3). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2033–2043, 2002     

Weak Ligand‐Field Effect from Ancillary Ligands on Enhancing Single‐Ion Magnet Performance

A series of bis‐pentamethylcyclopentadienyl‐supported Dy complexes containing different ancillary ligands were synthesized and characterized. Magnetic studies showed that 1 Dy [Cp*₂DyCl(THF)], 1 Dy’ [Cp*₂DyCl₂K(THF)]_n, 2 Dy [Cp*₂DyBr(THF)], 3 Dy [Cp*₂DyI(THF)] and 4 Dy [Cp*₂DyTp] (Tp=hydrotris(1‐pyrazolyl)borate) were single‐ion magnets (SIMs). The 1D dysprosium chain 1 Dy’ exhibited a hysteresis at up to 5 K. Furthermore, 3 Dy featured the highest energy barrier (419 cm^?1) among the complexes. The effects of ancillary ligands on single‐ion magnetic properties were studied by experimental, ab initio calculations and electrostatic analysis methods in detail. These results demonstrated that the QTM rate was strongly dependent on the ancillary ligands and that a weak equatorial ligand field could be beneficial for constructing Dy‐SIMs.     

Dicarbonyl pentaphenylcyclopentadienyl iron complex for living radical polymerization: Smooth generation of real active catalysts collaborating with phosphine ligand

We achieved metal‐catalyzed living radical polymerization (LRP) through “unique” catalyst transformation of iron (Fe) complex in situ. A dicarbonyl iron complex bearing a pentaphenylcyclopentadiene [(Cp^Ph)Fe(CO)₂Br: Cp^Ph = η‐C₅Ph₅] is too stable itself to catalyze LRP of methyl methacrylate (MMA) in conjunction with a bromide initiator [H‐(MMA)₂‐Br]. However, an addition of catalytic amount of triphenylphosphine (PPh₃) for the system led to a smooth consumption of MMA giving “controlled” polymers with narrow molecular weight distributions (～90% conversion within 24 h; M_w/M_n = 1.2). FTIR and ³¹P NMR analyses of the complex in the model reaction with H‐(MMA)₂‐Br and PPh₃ demonstrated that the two carbonyl ligands were irreversibly eliminated and instead the added phosphine was ligated to give some phosphorous complexes. The ligand exchange was characteristic to the Cp^Ph complex: the exchange was much smoother than other cyclopentadiene‐based complexes [i.e., CpFe(CO)₂Br: Cp = C₅H₅; Cp*Fe(CO)₂Br, Cp* = C₅Me₅]. The smooth transformation via the ligand exchange would certainly contribute to the controllability at the earlier stage in the polymerization as well as at the latter. The catalytic activity was enough high, as demonstrated by the successful monomer addition experiment and precise control even for higher molecular weight polymer (M_w/M_n < 1.2 under 1000‐mer condition). Such an in situ transformation from a stable complex would be advantageous to practical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Atom transfer radical polymerization of functional monomers employing Cu‐based catalysts at low concentration: Polymerization of glycidyl methacrylate

Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of an epoxide‐containing monomer, glycidyl methacrylate (GMA), was successfully carried out using low concentration of catalyst (ca. 105 ppm) at 60 °C in anisole. The copper complex of tris(2‐pyridylmethyl)amine was used as the catalyst, diethyl 2‐bromo‐2‐methylmalonate as the initiator, and 2,2′‐azobisisobutyronitrile as the reducing agent. When moderate degrees of polymerization were targeted (up to 200), special purification of the monomer, other than removal of the polymerization inhibitor, was not required to achieve good control. To synthesize well‐defined polymers with higher degrees of polymerization (600), it was essential to use very pure monomer, and polymers of molecular weights exceeding 50,000 g mol^?1 and M_w/M_n = 1.10 were prepared. The developed procedures were used to chain‐extend bromine‐terminated poly(methyl methacrylate) macroinitiator prepared by activators regenerated by electron transfer (ARGET) ATRP. The Sn^II‐mediated ARGET ATRP technique was not suitable for the polymerization of GMA and resulted in polymers with multimodal molecular weight distributions. This was due to the occurrence of epoxide ring‐opening reactions, catalyzed by Sn^II and Sn^IV. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chain transfer to solvent in the radical polymerization of N‐isopropylacrylamide

Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, C_tr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (M_n) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

Cp2TiCl‐catalyzed living radical polymerization of styrene initiated from peroxides

The effects of the reaction conditions and nature of the initiator were investigated in the Cp₂Ti(III)Cl‐catalyzed living radical polymerization of styrene initiated by benzoyl peroxide (BPO), tert‐butyl peroxide (TBPO), tert‐butyl peroxybenzoate (TBPOB), dicumyl peroxide (CPO), and tert‐butylperoxy 2‐ethylhexyl carbonate (TBPOEHC). The reversible termination of the growing chains with Cp₂Ti(III)Cl affords a linear dependence of molecular weight on conversion over a wide range of temperatures (60–120 °C) with an optimum in polydispersity (M_w/M_n < 1.2) for St/BPO/Cp₂TiCl₂/Zn = 100/1/3/6 at 60–90 °C. The similarity of the kinetic parameters from polymerizations initiated by peroxides with vastly different half‐life times (t = 1 h, t = 543 h) and the minimum peroxide/Ti = 1/2 ratio required for a living process indicate that initiation occurs primarily by the redox reaction of the peroxide with Cp₂Ti(III)Cl rather than peroxide thermal decomposition. This is consistent with one Ti equivalent consumed in the redox initiation and the second one utilized in the reversible termination of the growing chains. Qualitatively, based on the livingness of the process, these initiators ranked as BPO > TBPOB ～ TBPO > CPO > TBPOEHC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1106–1116, 2006     

Radical heterogeneous polymerization behavior of N‐methyl‐α‐fluoroacrylamide in benzene

The polymerization of N‐methyl‐α‐fluoroacrylamide (NMFAm) initiated with dimethyl 2,2′‐azobisisobutyrate (MAIB) in benzene was studied kinetically and with electron spin resonance. The polymerization proceeded heterogeneously with the highly efficient formation of long‐lived poly(NMFAm) radicals. The overall activation energy of the polymerization was 111 kJ/mol. The polymerization rate (R_p) at 50 °C is given by R_p = k[MAIB]^0.75±0.05 [NMFAm]^0.44±0.05. The concentration of the long‐lived polymer radical increased linearly with time. The formation rate (R_p?) of the long‐lived polymer radical at 50 °C is expressed by R_p? = k[MAIB]^1.0±0.1 [NMFAm]^0±0.1. The overall activation energy of the long‐lived radical formation was 128 kJ/mol, which agreed with the energy of initiation (129 kJ/mol), which was separately estimated. A comparison of R_p? with the initiation rate led to the conclusion that 1‐methoxycarbonyl‐1‐methylethyl radicals (primary radicals from MAIB), escaping from the solvent cage, were quantitatively converted into the long‐lived poly(NMFAm) radicals. Thus, this polymerization involves completely unimolecular termination due to polymer radical occlusion. ¹H NMR‐determined tacticities of resulting poly(NMFAm) were estimated to be rr = 0.34, mr = 0.48, and mm = 0.18. The copolymerization of NMFAm(M₁) and St(M₂) with MAIB at 50 °C in benzene gave monomer reactivity ratios of r₁ = 0.61 and r₂ = 1.79. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2196–2205, 2001     

Synthesis and characterization of high molecular weight atactic polybutene‐1 with a monotitanocene/methylaluminoxane catalyst system

A novel catalyst precursor, the monotitanocene (η⁵‐pentamethylcyclopentadienyl) titanium tricinnamyloxide [Cp*Ti(OCH₂? CH?CHC₆H₅)₃], was synthesized and employed for butene‐1 polymerization in the presence of methylaluminoxane. The effects of the polymerization conditions on the catalytic activity, molecular weight, stereoregularity, and regioregularity of the polymer so obtained were investigated in detail. The results show that the monotitanocene is desirable for the production of atactic polybutene‐1 coupled with good yields under typical polymerization conditions, high molecular weight (weight‐average molecular weight = 5.3–9.6 × 10⁵), and stereoirregularity with the Bernoullian factor B equal to 0.95, which indicates that chain‐end control is predominant. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4068–4073, 2001     

Synthesis and characterization of well‐defined ABC‐type triblock copolymers via atom transfer radical polymerization and stable free‐radical polymerization

An asymmetric difunctional initiator 2‐phenyl‐2‐[(2,2,6,6 tetramethylpiperidino)oxy] ethyl 2‐bromo propanoate ( 1 ) was used for the synthesis of ABC‐type methyl methacrylate (MMA)‐tert‐butylacrylate (tBA)‐styrene (St) triblock copolymers via a combination of atom transfer radical polymerization (ATRP) and stable free‐radical polymerization (SFRP). The ATRP‐ATRP‐SFRP or SFRP‐ATRP‐ATRP route led to ABC‐type triblock copolymers with controlled molecular weight and moderate polydispersity (M_w/M_n < 1.35). The block copolymers were characterized by gel permeation chromatography and ¹H NMR. The retaining chain‐end functionality and the applying halide exchange afforded high blocking efficiency as well as maintained control over entire routes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2025–2032, 2002     

Proton‐controlled nitroxide mediated radical polymerization of styrene

The 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 k_d 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