Kinetics of atom transfer radical polymerization of crosslinkable terpolymer P(MMA‐BA‐HEMA)

A crosslinkable terpolymer P(MMA‐BA‐HEMA) was prepared by atom transfer radical copolymerization of 2‐hydroxyethyl methacrylate, methyl methacrylate and butyl acrylate. The structure of the terpolymer was characterized by ¹H NMR and gel permeation chromatography. The effects on the polymerization of ligand, initiator, solvent, CuCl₂ added in the initial stage and reaction temperature were investigated. The optimal reaction conditions were ethyl 2‐bromopropionate as initiator, CuCl/PMDETA as catalyst, cyclohexanone as solvent, catalyst/ligand = 1:1.5, [M]₀:[I]₀ = 200:1 and temperature 70 °C. The reaction followed first‐order kinetics with respect to monomer concentration, indicating the best control over the polymerization process, a constant concentration of the propagating radical during the polymerization, efficient control over M_n of the polymer and low polydispersity (M_w/M_n < 1.3). © 2013 Society of Chemical Industry     

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

Two 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 (M_w/M_n)] were very narrow from 5.3% conversion up to 94% conversion (M_w/M_n < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006     

Assessment of kinetics of photoinduced Fe‐based atom transfer radical polymerization under conditions using modeling approach

Kinetic insight into photoinduced Fe‐based atom transfer radical polymerization (ATRP) involving monomer‐mediated photoreduction was performed by modeling approach for the first time. Preliminary numerical analysis of number‐average molar mass (M_n) derivation in this specific system was given. Simulation results provided a full picture of reactant concentration and reaction rate throughout the entire polymerization. Methyl 2,3‐dibromoisobutyrate (MibBr₂) generated from methyl methacrylate (MMA)‐mediated photoreduction as the leading factor for the deviation of M_n from theoretical value was confirmed by reaction contributions in α‐bromophenylacetate (EBPA) containing system. Reasonable predictions were made with respect to the polymerizations under a variety of initial conditions. Results show that increasing light intensity will shorten transition period and increase steady state polymerization rate; decreasing catalyst loading will cause the decrease in polymerization rate and M_n deviation; varying initiation activity will slightly increase the time to attain steady state of dispersity (M_w/M_n) evolution and enormously change the fraction of reaction contributions; increasing targeted chain length will extend transition period, decrease steady state polymerization rate, increase M_n deviation degree with same reaction contributions, and decrease the time to attain the steady state of M_w/M_n. The numerical analysis presented in this work clearly demonstrates the unique ability of our modeling approach in describing the kinetics of photoinduced Fe‐based ATRP of MMA. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Methylaluminoxane‐activated neodymium chloride tributylphosphate catalyst for isoprene polymerization

The polymerization of isoprene was examined by using a novel binary catalyst system composed of neodymium chloride tributylphosphate (NdCl₃·3TBP) and methylaluminoxane (MAO). The NdCl₃·3TBP/MAO catalyst worked effectively in a low MAO level ([Al]/[Nd] = 50) to afford polymers with high molecular weight (M_n ～10⁵), narrow molecular weight distribution (M_w/M_n = 1.4–1.6), and high cis‐1,4 stereoregularity (> 96%). The catalytic activity increased with an increasing [Al]/[Nd] ratio from 30 to 100 and polymerization temperature from 0 to 50°C, while the M_n of polymer decreased. The presence of free TBP resulted in low polymer yield. Polymerization solvent remarkably affected the polymerization behaviors; the polymerizations in aliphatic solvents (cyclohexane and hexane) gave polymer in higher yield than that in toluene. The M_w/M_n ratio of the producing polymer remained around 1.5 and the gel permeation chromatographic curve was always unimodal, indicating the presence of a single active site in the polymerization system. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40153.     

Photoinduced controlled/“living” polymerization of methyl methacrylate with flavone as photoinitiator

Photochemically mediated controlled/“living” polymerization of methyl methacrylate (MMA) triggered by flavone was studied. The polymerization was performed in ethanol at ambient temperature with CuBr₂/Tris(2‐dimethylaminoethyl)amine (Me₆TREN) as complex catalyst and ethyl 2‐bromoisobutyrate (EBiB) as initiator. The molar mass of poly(methyl methacrylate) (PMMA) was obtained and exhibited relatively narrow molecular weight distribution (M_w/M_n) which was characterized by gel permeation chromatography (GPC). Chain extension further indicated that the living nature was maintained in the photopolymerization system. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43845.     

Photo‐Induced atom transfer radical polymerization with nanosized α‐Fe2O3 as photoinitiator

Photo‐induced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was achieved in poly(ethylene glycol)‐400 with nanosized α‐Fe₂O₃ as photoinitiator. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in conjunction with ethyl 2‐bromoisobutyrate (EBiB) as ATRP initiator and FeCl₃·6H₂O/Triphenylphosphine (PPh₃) as complex catalyst. The photo‐induced polymerization of MMA proceeded in a controlled/living fashion. The polymerization followed first‐order kinetics. The obtained PMMA had moderately controlled number‐average molecular weights in accordance with the theoretical number‐average molecular weights, as well as narrow molecular weight distributions (M_w/M_n). In addition, the polymerization could be well controlled by periodic light‐on–off processes. The resulting PMMA was characterized by ¹H nuclear magnetic resonance and gel permeation chromatography. The brominated PMMA was used further as macroinitiator in the chain‐extension with MMA to verify the living nature of photo‐induced ATRP of MMA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42389.     

RATRP of MMA in AIBN/FeC1<Subscript>3</Subscript>/PPh<Subscript>3</Subscript> initiation system under microwave irradiation

Summary Reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) under microwave irradiation (MI), using azobisisobutyronitrile (AIBN) /FeC1₃/triphenylphosphine (PPh₃) as the initiating system, was successfully carried out in N, N-dimethylformamide (DMF) at 69°C. Plots of In ([MI₀/[M]) vs. time and molecular weight evolution vs. conversion showed a linear dependence. A polymer for reaching 82% conversion, with molecular weight (M_n) 34,000 and polydispersity index (PDI) 1.37, was obtained under MI (90U') with the ratio of [MMA]₀/[AIBN]₀/[FeCl₃]₀/[PPh₃]₀ = 1600/2/4/8 in only 60 min; while 840 min was required under conventional heating (CH) process for reaching 82 % conversion (M_n = 48,000 and PDI = 1.31) at identical polymerization conditions, indicating a significant enhancement of the polymerization rates and apparent initiator efficiencies under MI. Received: 2 September 2002/Revised version: 3 October 2002/Accepted: 10 December 2002 Correspondence to Xiulin Zhu     

Activators regenerated by electron transfer in ATRP of methyl methacrylate with alcohol as reducing agent in the presence of a base

Poly(methyl methacrylate) (PMMA) was synthesized via activators regenerated by electron transfer (ARGET) in atom transfer radical polymerization (ATRP) (ARGET ATRP) of methyl methacrylate in N,N-dimethylformamide and using ethyl 2-bromoisobutyrate as initiator, CuCl₂ as catalyst, N,N,N′,N′-tetramethylethylene-diamine as ligand and ethanol as a reducing agent. The polymerization temperature was kept at 70 °C. A well-defined PMMA with predetermined molecular weight and narrow molecular weight distribution was obtained. A linear relationship between ln([M]₀/[M]) and polymerization time was found to show the living and controllable radical polymerization. The molecular weights of the obtained polymers increased linearly with monomer conversion and the data are in good agreement with the theoretical values with narrow molecular weight distribution (M _w/M _n). That is to say, alcohols were found to be a kind of highly efficient agents in the presence of Na₂CO₃ in this system. The effects of temperature, different types of alcohols and the amount of n-propanol on the polymerization were investigated. With increasing temperature (changed from 70 to 90 °C) and the amount of n-propanol (changed from 500:1:1:2:1:2 to 500:1:1:2:10:2), the conversion increased from 15.6 to 34.7 % and from 8.6 to 26.8 %, respectively. However, the value of M _w/M _n became broader when the molar ratio of [MMA]₀/[EBiB]₀/[CuCl₂]₀/[TMEDA]₀/[n-propanol]₀/[Na₂CO₃]₀ was 500:1:1:2:1:2, indicating that the amount of n-propanol played an important role in ARGET ATRP of MMA. The activation energy was calculated to be 51.96 kJ/mol. The different types of alcohol were demonstrated to be an efficient reducing agent in this system except for tert-butyl alcohol. The “living” feature of the obtained polymer was further verified by a chain extension experiment. The obtained polymer was characterized by ¹H NMR and GPC.     

Synthesis of PMMA‐PTHF‐PMMA and PMMA‐PTHF‐PST linear and star block copolymers

Combination of cationic, redox free radical, and thermal free radical polymerizations was performed to obtain linear and star polytetramethylene oxide (poly‐THF)‐polymethyl methacrylate (PMMA)/polystyrene (PSt) multiblock copolymers. Cationic polymerization of THF was initiated by the mixture of AgSbF₆ and bis(4,4′ bromo‐methyl benzoyl) peroxide (BBP) or bis (3,5,3′,5′ dibromomethyl benzoyl) peroxide (BDBP) at 20°C to obtain linear and star poly‐THF initiators with M_w varying from 7,500 to 59,000 Da. Poly‐THF samples with hydroxyl ends were used in the methyl methacrylate (MMA) polymerization in the presence of Ce(IV) salt at 40°C to obtain poly(THF‐b‐MMA) block copolymers containing the peroxide group in the middle. Poly(MMA‐b‐THF) linear and star block copolymers having the peroxide group in the chain were used in the polymerization of methyl methacrylate (MMA) and styrene (St) at 80°C to obtain PMMA‐b‐PTHF‐b‐PMMA and PMMA‐b‐PTHF‐b‐PSt linear and star multiblock copolymers. Polymers obtained were characterizated by GPC, FT‐IR, DSC, TGA, ¹H‐NMR, and ¹³C‐NMR techniques and the fractional precipitation method. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 219–226, 2004     

Graft copolymers and high‐molecular‐weight star‐like polymers by atom transfer radical polymerization

Grafting of tert‐butyl acrylate (tBuA), methyl methacrylate (MMA), and styrene (St) monomers (M) by Cu(I)‐mediated ATRP from polystyrene (PSt) macroinitiator (M_n = 5620, polydispersity index, PDI = 1.12), containing initiating 2‐bromopropionyloxy groups (I) (bound to 34% of aromatic cores; 11 groups per backbone), was performed using conditions suitable for the respective homopolymerizations. The preparation of PSt‐g‐PtBuA in bulk using an initial molar ratio [M]₀/[I]₀ = 140 had a controlled character up to M_n = (132–148) × 10³ (PDI = 1.08–1.16). With MMA and St and using the same [M]₀/[I]₀, preliminary experiments were made; the higher the monomer conversion, the broader was the distribution of molecular weight of the products. Graft copolymerizations of all these monomers at [M]₀/[I]₀ = 840 or 1680 were successfully conducted up to high conversions. Low‐polydispersity copolymers, with very long side chains, in fact star‐like copolymers, were obtained mainly by tuning the deactivator amount in the reaction mixture. (PSt‐g‐PtBuA, DP_n,sc (DP of side chain) = 665, PDI = 1.24; PSt‐g‐PMMA, DP_n,sc = 670, PDI = 1.43; PSt‐g‐PSt, DP_n,sc = 324, PDI = 1.11). Total suppression of intermolecular coupling was achieved here. However, the low concentrations of initiator required long reaction times, leading sometimes to formation of a small amount (～5%) of low‐molecular‐weight polymer fraction. This concomitant process is discussed, and some measures for its prevention are proposed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3662–3672, 2006     

Synthesis of star polymethyl acrylate by SET-LRP at ambient temperature

The star-shaped polymethyl acrylate (PMA) was synthesized by single electron transfer living radical polymerization (SET-LRP) at 30 °C in dimethyl sulfoxide, using 2,2-dibromomethyl-1,3-dibromopropane as the multifunctional initiator, Cu⁰ powder and tris-(2-dimethylamino ethyl)amine (Me₆-TREN) as catalyst. The structure of polymer was analyzed by ¹H NMR, and the results showed that the star-shaped PMA had perfect chain ends (–Br) retention. In addition, the polymerization proceeded smoothly and the time dependence of ln([M]₀/[M]) was linear, which could indicate a first order propagation rate with respect to both radicals and monomer concentration, the polymerization was the living polymerization. The M _n and M _w/M _n of polymer were being measured by Gel Permeation Chromatography. The k _p^app = 0.0367 h⁻¹ and the conversion was 36.3% at 16 h, meanwhile the M _n^GPC of the polymer was 13,300 and the M _w/M _n was 1.40.     

Tripodal “click” ligands for copper‐catalyzed ATRP

A series of tris(R‐methyltriazolylmethyl)amines [R = C₆H₅ ( 1 ), 4‐FC₆H₄ ( 2 ), 4‐MeOC₆H₄ ( 3 ), Fc ( 4 )] were prepared and used as ligands for catalytic ATRP of methyl methacrylate (MMA). Despite a lower activity, the CuBr/ 4 catalyst promoted relatively well controlled polymerization compared to CuBr/ 1 , as evidenced by narrower polydispersity indices. Meanwhile, no polymerization activity was observed with CuBr/ 2 and CuBr/ 3 under the catalytic conditions investigated. The CV measurements of CuBr₂ complexes supported 1 and 4 in DMSO showed E_1/2 values of –0.206 and –0.224 V, respectively, confirming the more electron‐rich nature of CuBr/ 4 . Although both CuBr/ 1 and CuBr/ 4 catalysts were only partially soluble in several organic solvents used, kinetic studies revealed a pseudo first order linear plot of ln[M]₀/[M]_t versus time. Addition of CuBr₂ into the polymerization systems led to a decrease in polymer polydispersities and the observed rate constants (k_obs). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Photo-induced atom transfer radical polymerization of MMA with chlorophll A as photoinitiator

In this work, photoinduced free radical polymerization of methyl methacrylate (MMA) was performed at ambient temperature in dimethyl sulfoxide with chlorophll A as a photosensitizer. Well controlled polymerization of MMA was achieved. The linear first order plot of ln([M]₀/[M]) vs time was observed. Well-defined polymethyl methacrylates (PMMA) with narrow molecular weight distribution (M_w/M_n) were prepared. It indicated that the polymerization was controllable. The chain-end fidelity was demonstrated by ¹H NMR spectra. Chain extension experiments demonstrated the living feature of polymerization. The initiation and moderation of polymerization were manipulated by the periodic light on-off experiments.     

A kinetic study on polymerization of methyl methacrylate with di‐t‐butyl perfumarate

Di‐t‐butyl perfumarate (DBPF) was found to induce the radical polymerizations of various vinyl monomers at 60°C in benzene, although the initiation activity was considerably lower than those of dimethyl 2,2′‐azobisisobutyrate and benzoyl peroxide. The polymerizations with DBPF showed a tendency of dead‐end polymerization. The polymerization of methyl methacrylate (MMA) with DBPF was kinetically studied in chlorobenzene. The initial polymerization rate (R_p) was given by R_p = k [DBPF]^0.5 [MMA]^1.1. The overall activation energy of the polymerization was 47 kJ/mol, a very low value. Use of this value and activation energies of propagation and termination for MMA gave an unexpectedly low activation energy (65 kJ/mol) to the decomposition of DBPF, a t‐butyl perester, in the polymerization system. An ESR study on the polymerization of di‐2‐ethylhexyl itaconate with DBPF revealed that the observed dead‐end tendency comes from the consumption of DBPF. These results suggest that the initiator efficiency of DBPF is considerably low in the present polymerization systems. Some solvent effect was observed on the polymerization of MMA with DBPF. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 218–224, 2000     

Nitroxide‐mediated synthesis of styrenic‐based segmented and tapered block copolymers using poly(lactide)‐functionalized TEMPO macromediators

Poly(styrene)‐poly(lactide) (PS‐PLA), poly (tert‐butyl styrene)‐poly(lactide) (PtBuS‐PLA) diblocks, and poly(tert‐butyl styrene)‐poly(styrene)‐poly(lactide) (PtBuS‐PS‐PLA) segmented and tapered triblocks of controlled segment lengths were synthesized using nitroxide‐mediated controlled radical polymerization. Well‐defined PLA‐functionalized macromediators derived from hydroxyl terminated TEMPO (PLA_T) of various molecular weights mediated polymerizations of the styrenic monomers in bulk and in dimethylformamide (DMF) solution at 120–130°C. PS‐PLA and PtBuS‐PLA diblocks were characterized by narrow molecular weight distributions (polydispersity index (M_w/M_n) < 1.3) when using the PLA_T mediator with the lowest number average molecular weight M_n= 6.1 kg/mol while broader molecular weight distributions were exhibited (M_w/M_n = 1.47‐1.65) when using higher molecular weight mediators (M_n = 7.4 kg/mol and 11.3 kg/mol). Segmented PtBuS‐PS‐PLA triblocks were initiated cleanly from PtBuS‐PLA diblocks although polymerizations were very rapid with PS segments ～ 5–10 kg/mol added within 3–10 min of polymerization at 130°C in 50 wt % DMF solution. Tapering from the PtBuS to the PS segment in semibatch mode at a lower temperature of 120°C and in 50 wt % DMF solution was effective in incorporating a short random segment of PtBuS‐ran‐PS while maintaining a relatively narrow monomodal molecular weight distribution (M_w/M_n ≈ 1.5). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Synthesis of well‐defined polystyrene by radical polymerization using 1,1,2,2‐tetraphenyl‐1,2‐ethanediol/feCl3/PPh3 initiation system

Well‐defined polystyrenes with an α‐hydrogen atom and an ω‐chlorine atom end groups and narrow polydispersity (M_n = 2500–4200, M_w/M_n = 1.29–1.48) have been synthesized by a free radical polymerization process using a 1,1,2,2‐tetraphenyl‐1,2‐ethanediol (TPED)/FeCl₃/PPh₃ initiation system. The end groups were monitored by ¹H nuclear magnetic resonance spectroscopy. When the polymerization of styrenes in bulk carried out at 120°C and the ratio of [St]₀ : [TPED]₀ : [FeCl₃]₀ : [PPh₃]₀ was 200 : 1 : 4 : 12, the polymerization exhibited some living/controlled radical polymerization characteristics. The polymerization mechanism was proposed proceeding via a reverse atom transfer radical polymerization (ATRP). Because the polymers obtained were end‐functionalized by chlorine atoms, they were used as macroinitiators to proceed chain extension polymerization in the presence of CuCl/2,2′‐bipyridine catalyst system via a conventional ATRP process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1607–1613, 2000     

The effect of initiator‐to‐monomer ratio on the properties of the polybutadiene‐ol synthesized by free radical solution polymerization of 1,3‐butadiene

Polybutadiene‐ol was synthesized by solution radical polymerization of 1,3‐butadiene in the presence of hydrogen peroxide as initiator and 2‐propanol as solvent. The ratio of initiator to monomer molar concentration, [I₀]/[M₀], was varied while temperature, reaction time and the type and amount of solvent were kept constant. The effects on the M_n; M_w; M_v; PDI, OH‐number and functionality of the synthesized polyols were studied. By taking several samples during a polymerization batch and analyzing them, the time of reaction was chosen as 100 min, after which the PDI changed dramatically. M_n decreased exponentially with increasing [I₀]/[M₀] according to the relationship M_n = 565.55 ([I₀]/[M₀])^?0.7553. The decrease observed in M_w gradually levelled off with increasing [I₀]/[M₀] and molecular weight distribution broadened at larger values of [I₀]/[M₀]. The OH‐number increases with [I₀]/[M₀]. In addition to the number‐average molecular weight, functionality is dependent on the number of hydroxyl‐terminated chain radicals in the reaction medium. Copyright © 2003 Society of Chemical Industry     

Preparation of poly(styrene‐b‐2‐hydroxyethyl acrylate) block copolymer using reverse iodine transfer polymerization

Reverse iodine transfer polymerizations (RITP) of 2‐h‐ydroxyethyl acrylate (HEA) were performed in N,N‐dimethylformamide at 75°C using AIBN as initiator. Poly(2‐hydroxyethyl acrylate) (PHEA) with M_n = 3300 g mol^?1 and M_w/M_n <1.5 were obtained. Homopolymerization of styrene in RITP was also carried out under similar conditions using toluene as solvent. The resulting iodo‐polystyrene (PS‐I) with (M_{n, SEC} = 607 g mol^?1, polydispersity index (PDI) = 1.31) was used as a macroinitiator for the synthesis of amphiphilic block copolymers based on HEA with controlled well‐defined structure. Poly(styrene‐b‐2‐hydroxyethyl acrylate) (PS‐b‐PHEA) with M_n = 13,000 g mol^?1 and polydispersity index (M_w/M_n) = 1.4 was obtained, copolymer composition was characterized using ¹H‐NMR and FTIR, whereas SEC and gradient HPLC were used to confirm the formation of block copolymer and the living character of polymer chains. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Copper‐based reverse ATRP process for the controlled radical polymerization of methyl methacrylate

A series of copper‐based reverse atom transfer radical polymerizations (ATRP) were carried out for methyl methacrylate (MMA) at same conditions (in xylene, at 80°C) using N,N,N′,N′‐teramethylethylendiamine (TMEDA), N,N,N′,N′,N′‐pentamethyldiethylentriamine (PMDETA), 2‐2′‐bipyridine, and 4,4′‐Di(5‐nonyl)‐2,2′‐bipyridine as ligand, respectively. 2,2′‐azobis(isobutyronitrile) (AIBN) was used as initiator. In CuBr₂/bpy system, the polymerization is uncontrolled, because of the poor solubility of CuBr₂/bpy complex in organic phase. But in other three systems, the polymerizations represent controlled. Especially in CuBr₂/dNbpy system, the number‐average molecular weight increases linearly with monomer conversion from 4280 up to 14,700. During the whole polymerization, the polydispersities are quite low (in the range 1.07–1.10). The different results obtained from the four systems are due to the differences of ligands. From the point of molecular structure of ligands, it is very important to analyze deeply the two relations between (1) ligand and complex and (2) complex and polymerization. The different results obtained were discussed based on the steric effect and valence bond theory. The results can help us deep to understand the mechanism of ATRP. The presence of the bromine atoms as end groups of the poly(methyl methacrylate) (PMMA) obtained was determined by ¹H‐NMR spectroscopy. PMMA obtained could be used as macroinitiator to process chain‐extension reaction or block copolymerization reaction via a conventional ATRP process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of star‐shaped poly(ϵ‐caprolactone) by samarium‐based tetrafunctional initiator and its dilute‐solution properties

An in situ–generated tetrafunctional samarium enolate from the reduction of 1,1,1,1‐tetra(2‐bromoisobutyryloxymethyl)methane with divalent samarium complexes [Sm(PPh₂)₂ and SmI₂] in tetrahydrofuran has proven to initiate the ring‐opening polymerization of ?‐caprolactone (CL) giving star‐shaped aliphatic polyesters. The polymerization proceeded with quantitative conversions at room temperature in 2 h and exhibited good controllability of the molecular weight of polymer. The resulting four‐armed poly(?‐caprolactone) (PCL) was fractionated, and the dilute‐solution properties of the fractions were studied in tetrahydrofuran and toluene at 30°C. The Mark–Houwink relations for these solvents were [η] = 2.73 × 10^?2M_w^0.74 and [η] = 1.97 × 10^?2M_w^0.75, respectively. In addition, the unperturbed dimensions of the star‐shaped PCL systems were also evaluated, and a significant solvent effect was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 175–182, 2006