1‐Hexene Polymerization over Supported Titanium–Magnesium Catalyst: The Effect of Composition of the Catalytic System and Polymerization Conditions on Temperature Dependence of the Polymerization Rate

The effect of temperature on the rate of 1‐hexene polymerization over supported titanium–magnesium catalyst of composition TiCl₄/D₁/MgCl₂ + AlR₃/D₂ (D₁ is dibutyl phthalate, D₂ is propyltrimethoxysilane, and AlR₃ is an organoaluminum cocatalyst) is studied. The unusual data that the polymer rate decreases when temperature is increased from 30 to 70 °C are obtained. The 1‐hexene polymerization rate and the pattern of changes in polymerization rate with temperature depend on a combination of factors such as cocatalyst (AlEt₃ or Al(i‐Bu)₃) and presence/absence of hydrogen and an external donor in the reaction mixture. These factors differ in their effects on catalytic activity at different polymerization temperatures, so the temperature coefficient (E_eff) values calculated using the Arrhenius dependence of the polymerization rate on polymerization temperature vary greatly. The “normal” Arrhenius plot where polymerization rate increases with temperature is observed only for polymerization with the Al(i‐Bu)₃ cocatalyst in the presence of hydrogen and without an external donor. Formation of high‐molecular‐weight polyhexene at low polymerization temperatures results in catalyst particle fragmentation, which may additionally contribute to the increase in polymerization rate as polymerization temperature is reduced.     

Higher α‐olefin polymerizations catalyzed by rac‐Me2Si(1‐C5H2‐2‐CH3‐4‐tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

Polymerizations of higher α‐olefins, 1‐pentene, 1‐hexene, 1‐octene, and 1‐decene were carried out at 30 °C in toluene by using highly isospecific rac‐Me₂Si(1‐C₅H₂‐2‐CH₃‐4‐^t Bu)₂Zr(NMe₂)₂ (rac‐1) compound in the presence of Al(iBu)₃/[CPh₃][B(C₆F₅)₄] as a cocatalyst formulation. Both the bulkiness of monomer and the lateral size of polymer influenced the activity of polymerization. The larger lateral of polymer chain opens the π‐ligand of active site wide and favors the insertion of monomer, while the large size of monomer inserts itself into polymer chain more difficultly due to the steric hindrance. Highly isotactic poly(α‐olefin)s of high molecular weight (MW) were produced. The MW decreased from polypropylene to poly(1‐hexene), and then increased from poly(1‐hexene) to poly(1‐decene). The isotacticity (as [mm] triad) of the polymer decreased with the increased lateral size in the order: poly(1‐pentene) > poly(1‐hexene) > poly(1‐octene) > poly(1‐decene). The similar dependence of the lateral size on the melting point of polymer was recorded by differential scanning calorimetry (DSC). ¹H NMR analysis showed that vinylidene group resulting from β‐H elimination and saturated methyl groups resulting from chain transfer to cocatalyst are the main end groups of polymer chain. The vinylidene and internal double bonds are also identified by Raman spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1687–1697, 2000     

A highly active neodymium chloride isopropanol complex/modified methylaluminoxane catalyst for preparing polyisoprene with high cis-1,4 stereospecificity and narrow molecular weight distribution

<正>Neodymium chloride isopropanol complex(NdCl_3·3~iPrOH) activated by modified methylaluminoxane(MMAO) was examined in isoprene polymerization in hexane,with regards to Nd compounds,aluminum(Al) compounds,[Al]/[Nd] ratio,polymerization temperature and time.NdCl_3-3~iPrOH exhibited high activity producing polymers featuring high cis-1,4 stereospecificity(96%),very high molecular weight(M_n1.0×10~6) and fairly narrow molecular weight distribution (MWD,M_w/M_n2.0) simultaneously.In comparison,neodymium isopropoxide also showed high activity providing polymers with narrow MWD(M_w/M_n = 2.07),but somewhat low cis-1,4 content(ca.92%),while neodymium chloride had no activity under present polymerization conditions.The Al compounds affected the polymer yield in the order of Al(i-Bu)_3MMAOAl(i-Bu)_2H.MMAO as cocatalyst afforded polyisoprene with high M_n over 1.0×10~6,whereas as stronger chain transfer agent than MMAO,Al(i-Bu)_3 and Al(i-Bu)_2H yielded polymers with low M_n(1.0×10~5-8.0×10~5). NdCl_3·3~iPrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low[Al]/[Nd]ratio of 30,and the produced polymer remained high cis-1,4 content of 95.8%along with high M_n over 1.0×10~6 even at elevated temperatures up to 70℃.The polymerization rate is of the first order with respect to the concentration of isoprene.The mechanism of active species formation was discussed preliminarily.     

Polymerization of n-Octylallene with Rare Earth Catalyst Composed of Ln(P204)3/Al(i-Bu)3

Polymerization of n‐octylallene was successfully carried out using a conventional binary rare earth catalytic system composed of rare earth tris(2‐ethylhexylphosphonate) (Ln(P₂₀₄)₃) and tri‐isobutyl aluminum (Al(i‐Bu)₃) for the first time. The effects of catalyst, solvent, reaction time and temperature on the polymerization of n‐octylallene were studied. The resulting poly(n‐octylallene) has weight‐average molecular weight of 11000, molecular weight distribution of 1.4 and 96% yield under the moderate reaction conditions: [Al]/[Y] =50 (molar ratio), [n‐octylallene]/[Y] =100 (molar ratio), polymerized at 80°C for 20 h in bulk. The poly(n‐octylallene) obtained consisted of 1,2‐ and 2,3‐polymerized units, and was characterized by FT‐IR, ¹H NMR and GPC. Further investigation shows that the polymerization of n‐octylallene has some living polymerization characteristics, preparing the polymer with controlled molecular weight and narrower molecular weight distribution.     

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

The effect of AlR3 on propylene polymerization by rac‐(EBI)Zr(NMe2)2/AlR3/[CPh3][B(C6F5)4] catalyst

Ansa‐zirconocene diamide complex rac‐(EBI)Zr(NMe₂)₂ [rac‐1, EBI = ethylene‐1,2‐bis(1‐indenyl)] reacted with AlR₃ (R = Me, Et, iBu) or Al(iBu₂)H and then with [CPh₃][B(C₆F₅)₄] (2) in toluene in order to perform propylene polymerization by cationic alkylzirconium species, which are in situ generated during polymerization. Through the sequential NMR‐scale reactions of rac‐1 with AlR₃ or Al(iBu₂)H and then with 2, rac‐1 was demonstrated to be transformed to the active alkyzirconium cations via alkylated intermediates of rac‐1. The cationic species generated by using AlMe₃, AlEt₃, and Al(iBu₂)H as alkylating reagents tend to become heterodinuclear complex; however, those by using bulky Al(iBu)₃ become base‐free [rac‐(EBI)Zr(iBu)]⁺ cations. The activity of propylene polymerization by rac‐1/AlR₃/2 catalyst was deeply influenced by various parameters such as the amount and the type of AlR₃, metallocene concentration, [Al]/[2] ratio, and polymerization temperature. Generally the catalytic systems using bulky alkylaluminum like Al(iBu)₃ and Al(iBu)₂H show higher activity but lower stereoregularity than those using less bulky AlMe₃ and AlEt₃. The alkylating reagent Al(iBu)₃ is not a transfer agent as good as AlMe₃ or AlEt₃. The polymerization activities show maximum around [Al]/[2] ratio of 1.0 and increase monotonously with polymerization temperature. The overall activation energy of both rac‐1/Al(iBu)₃/2 and rac‐1/Al(iBu)₂H catalysts is 6.0 kcal/mol. As the polymerization temperature increases, the stereoregularity of the resulting polymer decreases markedly, which is demonstrated by the decrease of [mmmm] pentad value and by the increase of the amount of polymer soluble in low boiling solvent. The physical properties of polymers produced in this study were investigated by using ¹³C‐NMR, differential scanning calorimetry (DSC), viscometry, and gel permeation chromatography (GPC). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1523–1539, 1999     

Regulation of Molecular Weight Characteristics and Microtacticity of Polyhexene Produced over Highly Active Supported Titanium–Magnesium Catalysts

The data on the effect of polymerization temperature of 1‐hexene within the 30–70 °C range in the presence of a highly active supported titanium–magnesium catalyst on molecular weight characteristics and microtacticity of polyhexene, with cocatalyst composition being additionally varied (AlEt₃ or Al(i‐Bu)₃), in the absence and presence of an external stereoregulating electron‐donating compound and hydrogen, are reported. Polymerization conditions, making it possible to specifically regulate molecular weight and molecular weight distribution of polyhexene over a broad range ((M_w = 7 × 10⁴–2.2 × 10⁶ g mol⁻¹; M_w/M_n = 3.7–33) and regulate isotacticity of polyhexene (content of mmmm pentads from 56% to 96%), while retaining high catalyst activity, are determined.     

Preparation of thermoresponsive polymers bearing amino acid diamide derivatives via RAFT polymerization

We report here the synthesis of well‐defined homopolymer bearing amino acid diamide, poly(N‐acryloyl‐L ‐valine N′‐methylamide), via reversible addition fragmentation chain transfer (RAFT) polymerization using alkynyl‐functionalized 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl‐propionic acid propargyl alcohol ester as chain transfer agent (CTA) and 2,2′‐azobis(isobutyronitrile) as initiator. The effects of a variety of parameters, such as temperature and solvent, on RAFT polymerization were examined to determine the optimal control of the polymerization. The controlled nature of RAFT polymerization was evidenced by the controllable molecular weight and low‐molecular‐weight polydispersity index (M_w/M_n) of resulting homopolymers and further demonstrated to have retained end‐group functionality by the fact of the successful formation of block copolymers from further RAFT polymerization by using the resultant polymer as macro‐CTA, as well as from “click” chemistry. Thermoresponsive property of the prepared polymer was evaluated in terms of the lower critical solution temperature in aqueous solution by measuring the transmittance variation at 500 nm from UV/vis spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3573–3586, 2010     

Effects of external donors and hydrogen concentration on oligomer formation and chain end distribution in propylene polymerization with Ziegler‐Natta catalysts

The effect of type and concentration of external donor and hydrogen concentration on oligomer formation and chain end distribution were studied. Bulk polymerization of propylene was carried out with two different Ziegler‐Natta catalysts at 70 °C, one a novel self‐supported catalyst (A) and the other a conventional MgCl₂‐supported catalyst (B) with triethyl aluminum as cocatalyst. The external donors used were dicyclopentyl dimethoxy silane (DCP) and cyclohexylmethyl dimethoxy silane (CHM). The oligomer amount was shown to be strongly dependent on the molecular weight of the polymer. Catalyst A gave approximately 50 % lower oligomer content than catalyst B due to narrower molecular weight distribution in case of catalyst A. More n‐Bu‐terminated chain ends were found for catalyst A indicating more frequent 2,1 insertions. Catalyst A also gave more vinylidene‐terminated oligomers, suggesting that chain transfer to monomer, responsible for the vinylidene chain ends, was a more important chain termination mechanism for this catalyst, especially at low hydrogen concentration. Low site selectivity, due to low external donor concentration or use of a weak external donor (CHM), was also found to increase formation of vinylidene‐terminated oligomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 351–358, 2010     

Polymerization via Insertion of Ethylene into Al−C bond under Mild Conditions: Mechanistic Studies on the Promotion Exerted by a Catalytic Amount of Cationic Gadolinium Metallocene

The cationic gadolinium metallocene [(C₅Me₅)₂Gd][B(C₆F₅)₄], when combined with an excess amount of Al(ⁱBu)₃, efficiently produces polyethylene at 80 °C under 0.8 MPa pressure of ethylene. After quenching, the resulting polyethylene has ethyl group at one end and isobutyl group at the other terminal. Because no Gd-alkyl species appears to be involved, a mechanism with conventional coordinative chain transfer polymerization (CCTP) is not feasible. Density functional theory (DFT) analyses indicate a novel mechanism in which the cationic Gd plays a crucial role by coordinating ethylene and assists the insertion of the coordinated ethylene into Al−C bond.     

Synthesis and characterization of novel aliphatic polycarbonates

A new six‐membered cyclic carbonate monomer, 5‐benzyloxy‐trimethylene carbonate, was synthesized from 2‐benzyloxy‐1,3‐propanediol, and the corresponding polycarbonate, poly(5‐benzyloxy‐trimethylene carbonate) (PBTMC), was further synthesized by ring‐opening polymerization in bulk at 150 °C using aluminum isobutoxide [Al(OⁱBu)₃], aluminum isopropoxide, or stannous octanoate as an initiator. The results showed that a higher molecular weight polycarbonate could be obtained in the case of Al(OⁱBu)_3. The protecting benzyl group was removed subsequently by catalytic hydrogenation to give a polycarbonate containing a pendant hydroxyl group (PHTMC). The polycarbonates obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR,¹³C NMR, gel permeation chromatography, and DSC. NMR results of PBTMC offered no evidence for decarboxylation occurring during the propagation. The pendant hydroxyl group in PHTMC resulted in an enhancement of the hydrophilicity of the polycarbonate. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 70–75, 2002     

Novel neodymium (III) isopropoxide‐methylaluminoxane catalyst for isoprene polymerization

A novel catalyst composed of neodymium (III) isopropoxide [Nd(OiPr)₃] and methylaluminoxane (MAO) was examined in isoprene polymerization. The Nd(OiPr)₃‐MAO catalyst proved to be highly effective in heptane even at low [Al]/[Nd] ratios (ca. 30) to give polyisoprene that possessed high cis‐1,4 stereoregularity (> ca. 90%), a high number‐average molecular weight (M_n ～10⁵), and relatively narrow molecular weight distributions (M_w/M_n = 1.9–2.8). The catalyst activity increased with an increasing [Al]/[Nd] ratio from 10 to 80 as well as temperature of aging and polymerization from 0 to 60 °C. The polymerization proceeded in the first order with respect to the monomer concentration. Aliphatic solvents (heptane and cyclohexane) achieved a higher yield and M_n of polymer than toluene as a solvent. The M_w/M_n ratio remained around 2.0, and the gel permeation chromatographic curve was always unimodal, indicating that this system is homogeneous and involves a single active site. The microstructure of polyisoprene was determined by IR, ¹H NMR, and ¹³C NMR. The cis‐1,4 contents of the final polymers stayed in the range of 90–92%, regardless of reaction conditions, indicating the high stability of stereospecificity of the catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1838–1844, 2002     

Reversible Addition Fragmentation Chain Transfer Polymerization of Isobutyl Methacrylate

Abstract

The reversible addition fragmentation chain transfer (RAFT) bulk polymerization of isobutyl methacrylate (i‐BMA) has been studied using 2‐cyanoprop‐2‐yl dithionaphthalate (CPDN) as RAFT agent in the presence of 2,2′‐azobisisobutyronitrile (AIBN). The results of polymerizations of i‐BMA show that i‐BMA can polymerize in a controlled way by RAFT polymerization using CPDN as RAFT agent; i.e., the polymerization rate is first order with respect to monomer concentration, molecular weight increases linearly with monomer conversion, and polydispersities are relatively low (PDI?<?1.2). The structure of the polymer was characterized by ¹H‐NMR. A chain‐extension experiment of the resulting polymer was successfully carried out. The influences of [i‐BMA]₀/[CPDN]₀/[AIBN]₀ molar ratio and reaction temperature were investigated.     

Controlled radical polymerization of N‐vinylcaprolactam mediated by xanthate or dithiocarbamate

Controlled radical polymerization of N‐vinylcaprolactam (NVCL) via reversible addition‐fragmentation chain transfer (RAFT) polymerization or macromolecular design via the interchange of xanthate (MADIX) was described, employing 2‐diphenylthiocarbamoylsulfanyl‐2‐methyl‐propionic acid (CTA1), ((O‐ethylxanthyl)methyl)benzene (CTA2) and (1‐(O‐ethylxanthyl)ethyl)benzene (CTA3) as chain transfer agents (CTA). It was found that all the CTAs led to controlled radical polymerization of NVCL, with the molecular weight increased along with the conversion of monomer and a relatively narrow molecular weight distribution could be obtained, as determined with matrix‐assisted laser desorption and ionization time‐of‐flight (MALDI‐TOF) and gel permeation chromatography (GPC), the polydispersity indices, as determined by MALDI‐TOF, were typically on the order of 1.24, but the polymerization did not proceed in a strictly living manner. The chain transfer ability of these CTAs was in the following order: CTA1 ≈ CTA2 < CTA3. MALTI‐TOF measurement showed that the major population of polymer retained the chain‐end functional group, but minor population deactivated by radical coupling. In preparation of the block copolymer of NVCL and vinyl acetate (VAc) by sequential polymerization, the sequence of monomer addition was important. Using VAc as the first monomer could lead to a block copolymer presenting a unimodal GPC trace and a narrow PDI index, and if NVCL was used as the first monomer, the polymerization was less well controlled. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3756–3765, 2008     

Kinetics of the styrene emulsion polymerization using n‐dodecyl mercaptan as chain‐transfer agent

The kinetics of the styrene emulsion polymerization using n‐dodecyl mercaptan as chain‐transfer agent was studied. It was found that the chain‐transfer agent (CTA) had no effect on polymerization rate but substantially affected the molecular weight distribution (MWD). The efficiency of the CTA in reducing the MWD was lowered by the mass‐transfer limitations. The process variables affecting CTA mass transfer were investigated. A mathematical model for the process was developed. The outputs of the model include monomer conversion, particle diameter, number of polymer particles, and number‐average and weight‐average molecular weights. The model was validated by fitting the experimental data. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4490–4505, 2000     

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     

Controlled polymerization of methacrylates at ambient temperature using trithiocarbonate chain transfer agents via SET‐RAFT–cyclohexyl methacrylate: A model study

Controlled radical polymerization of cyclohexyl methacrylate (CHMA), at ambient temperature, using various chain transfer agents (CTAs) is successfully demonstrated via single electron transfer‐radical addition fragmentation chain transfer (SET‐RAFT). Well‐controlled polymerization with narrow molecular weight distribution (M_w/M_n) < 1.25 was achieved. The polymerization rate followed first‐order kinetics with respect to monomer conversion, and the molecular weight of the polymer increased linearly up to high conversion. A novel, fluorescein‐based initiator, a novel fluorescent CTA and two other CTAs comprising of butane thiol trithiocarbonate with cyano (CTA 1) and carboxylic acid (CTA 3) as the end group were synthesized and characterized. The polymerization is observed to be uncontrolled under SET and less controlled under atom transfer radical polymerization (ATRP) condition. CTA 2 and 3 produces better control in propagation compared with CTA 1, which may be attributed to the presence of R group that undergoes ready fragmentation to radicals, at ambient temperature. The poly(cyclohexyl methacrylate) [P(CHMA)] prepared through ATRP have higher fluorescence intensity compared with those from SET‐RAFT, which may be attributed to the quenching of fluorescence by the trithiocarbonate and the long hydrocarbon chain. It is observed that block copolymers P(CHMA‐b‐t‐BMA) produced from P(CHMA) macroinitiators synthesized via SET‐RAFT result in lower polydispersity index in comparison with those synthesized via ATRP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Facile one‐pot/one‐step technique for preparation of side‐chain functionalized polymers: Combination of SET‐RAFT polymerization of azide vinyl monomer and click chemistry

An azido‐containing functional monomer, 11‐azido‐undecanoyl methacrylate, was successfully polymerized via ambient temperature single electron transfer initiation and propagation through the reversible addition–fragmentation chain transfer (SET‐RAFT) method. The polymerization behavior possessed the characteristics of “living”/controlled radical polymerization. The kinetic plot was first order, and the molecular weight of the polymer increased linearly with the monomer conversion while keeping the relatively narrow molecular weight distribution (M_w/M_n ≤ 1.22). The complete retention of azido group of the resulting polymer was confirmed by ¹H NMR and FTIR analysis. Retention of chain functionality was confirmed by chain extension with methyl methacrylate to yield a diblock copolymer. Furthermore, the side‐chain functionalized polymer could be prepared by one‐pot/one‐step technique, which is combination of SET‐RAFT and “click chemistry” methods. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

MAO‐free polymerization of propylene by rac‐ Me2Si(1‐C5H2‐2‐Me‐4‐tBu)2Zr(NMe2)2 compound

Ansa‐zirconocene diamide complex rac‐Me₂Si(CMB)₂Zr(NMe₂)₂ (rac‐1, CMB = 1‐C₅H₂‐2‐Me‐4‐^tBu) reacts with AlR₃ (R = Me, Et, i‐Bu) and then with [CPh₃]⁺[B(C₆F₅)₄]⁻ (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NMR‐scale reactions of rac‐1 with various amount of AlMe₃ and 2, rac‐1 transforms first to rac‐Me₂Si(CMB)₂Zr(Me)(NMe₂) (rac‐3) and rac‐Me₂Si(CMB)₂ZrMe₂ (rac‐4) by the reaction with AlMe₃, and then to [rac‐Me₂Si(CMB)₂ZrMe]⁺ (5⁺) cation by the reaction of the resulting mixtures with 2. The activities of propylene polymerizations by rac‐1/Al(i‐Bu)₃/2 system are dependent on the type and concentration of AlR₃, resulting in the order of activity: rac‐1/Al(i‐Bu)₃/2 > rac‐1/AlEt₃/2 > rac‐1/MAO ≫ rac‐1/AlMe₃/2 system. The bulkier isobutyl substituents make inactive catalytic species sterically unfavorable and give rise to more separated ion pairs so that the monomers can easily access to the active sites. The dependence of the maximum rate (R_{p, max}) on polymerization temperature (T_p) obtained by rac‐1/Al(i‐Bu)₃/2 system follows Arrhenius relation, and the overall activation energy corresponds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i‐Bu)₃ concentration. The analysis of regiochemical errors of iPP shows that the chain transfer to Al(i‐Bu)₃ is a minor chain termination. The 1,3‐addition of propylene monomer is the main source of regiochemical sequence and the [mr] sequence is negligible, as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac‐1/Al(i‐Bu)₃/2 system keeps high activity over a wide range of [Al(i‐Bu)₃]/[Zr] ratio between 32 and 3,260. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1071–1082, 1999     

Reversible addition‐fragmentation chain transfer polymerization of methacrylates containing hole‐ or electron‐transporting groups

The controlled/living radical polymerization of 2‐(N‐carbazolyl)ethyl methacrylate (CzEMA) and 4‐(5‐(4‐tert‐butylphenyl‐1,3,4‐oxadiazol‐2‐yl)phenyl) methacrylate (t‐Bu‐OxaMA) via reversible addition‐fragmentation chain transfer polymerization has been studied. Functional polymers with hole‐ or electron‐transfer ability were synthesized with cumyl dithiobenzoate as a chain transfer agent (CTA) and AIBN as an initiator in a benzene solution. Good control of the polymerization was confirmed by the linear increase in the molecular weight (MW) with the conversion. The dependence of MW and polydispersity index (PDI) of the resulting polymers on the molar ratio of monomer to CTA, monomer concentration, and molar ratio of CTA to initiator has also been investigated. The MW and PDI of the resulting polymers were well controlled as being revealed by GPC measurements. The resulting polymers were further characterized by NMR, UV‐vis spectroscopy, and cyclic voltammetry. The polymers functionalized with carbazole group or 1,3,4‐oxadiazole group exhibited good thermal stability, with an onset decomposition temperature of about 305 and 323 °C, respectively, as determined by thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 242–252, 2007