Block copolymers of acrylonitrile and poly(dimethylsiloxane)s

The chemical redox system of ceric ammonium nitrate(Ce⁴⁺) and poly(dimethylsiloxane)s (PDMS) with monohydroxy (MH), dihydroxy (DH), and diamine(DA) chain ends was used to polymerize acrylonitrile (AN) to produce monohydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (MH.PDMS‐b‐PAN), dihydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DH.PDMS‐b‐PAN), and α, ω‐diamine poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DA.PDMS‐b‐PAN) block copolymers. The concentration, reaction time, and the type of poly(dimethylsiloxane) affect the yield and the molecular weight of the copolymers. The ratio of AN/ceric salt/PDMS has remarkably affects the properties of formed copolymers. DH.PDMS‐b‐PAN copolymers were also prepared by electroinduced polymerization in the presence of catalytic amount of Ce⁴⁺ in a divided electrochemical cell where Ce³⁺ is readily oxidized into Ce⁴⁺ at the anode. The products were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, DSC, and their surface properties were investigated through contact‐angle measurements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characterization of the novel block copolymer poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine) by the combination of coordination and controlled free‐radical polymerizations

A novel block copolymer, poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine), was synthesized with a bifunctional initiator strategy. Poly(ε‐caprolactone) prepolymer with a 2,2,6,6‐tetramethylpiperidinyloxy (TEMPO) end group (PCL_T) was first obtained by coordination polymerization, which showed a controlled mechanism in the process. By means of ultraviolet spectroscopy and electron spin resonance spectroscopy, the TEMPO moiety was determined to be intact in the polymerization. The copolymers were then obtained by the controlled radical polymerization of 4‐vinyl pyridine in the presence of PCL_T. The desired block copolymers were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and NMR spectroscopy in detail. Also, the effects of the molecular weight and concentration of PCL_T on the copolymerization were investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2280–2285, 2004     

α‐cyclodextrin assisted self‐assembly of poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) in aqueous media

Poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) (PEG‐b‐PNIPAM) block copolymers were synthesized by atom transfer radical polymerization, and the α‐cyclodextrin (α‐CD) induced self‐assembly characteristics of the system were elucidated. Below the lower critical solution temperature (LCST) of PNIPAM, CD threaded onto the PEG segments and induced micellization to form rod‐shaped nanostructures comprising of a PEG/α‐CD condensed phase and a PNIPAM shell. Increasing the temperature of system above the LCST caused the PNIPAM segments to collapse, which resulted in the dethreading of the CD. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A novel approach for synthesis of poly(norbornene)‐co‐poly(styrene) block copolymers via metathesis polymerization and free‐radical polymerization

It is successfully realized that block copolymers are synthesized via metathesis polymerization followed by free‐radical polymerization. This method is performed using styrene (St) and norbornene, one block is synthesized using the Grubbs second generation catalyst in the presence of chain transfer agents, and the subsequent polymerization of St is initiated by azo compounds to complete the additional blocks in the copolymers. The use of free‐radical polymerization instead of controlled radical polymerization or ionic polymerization can be potentially superior for industrialization. As a result, the molecular weights of the block copolymers ranging from 10.4 to 54.3 kDa and polydispersity indices ranging from 1.30 to 1.91 are obtained. In principle, this new method can be potentially useful to prepare a broad range of block copolymers with cyclic olefin groups in the main chains, which may be used in some particular applications.     

Novel poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers through atom transfer radical polymerization

Poly(methyl methacrylate)‐block‐polyurethane‐block‐poly(methyl methacrylate) tri‐block copolymers have been synthesized successfully through atom transfer radical polymerization of methyl methacrylate using telechelic bromo‐terminated polyurethane/CuBr/N,N,N,N″,N″‐pentamethyldiethylenetriamine initiating system. As the time increases, the number‐average molecular weight increases linearly from 6400 to 37,000. This shows that the poly methyl methacrylate blocks were attached to polyurethane block. As the polymerization time increases, both conversion and molecular weight increased and the molecular weight increases linearly with increasing conversion. These results indicate that the formation of the tri‐block copolymers was through atom transfer radical polymerization mechanism. Proton nuclear magnetic resonance spectral results of the triblock copolymers show that the molar ratio between polyurethane and poly (methyl methacrylate) blocks is in the range of 1 : 16.3 to 1 : 449.4. Differential scanning calorimetry results show T_g of the soft segment at ?35°C and T_g of the hard segment at 75°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of poly(n‐butyl methacrylate)‐b‐polystyrene diblock copolymers by atom transfer radical emulsion polymerization

Poly(n‐butyl methacrylate) (PBMA)‐b‐polystyrene (PSt) diblock copolymers were synthesized by emulsion atom transfer radical polymerization (ATRP). PBMA macroinitiators that contained alkyl bromide end groups were obtained by the emulsion ATRP of n‐butyl methacrylate with BrCH₃CHCOOC₂H₅ as the initiator; these were used to initiate the ATRP of styrene (St). The latter procedure was carried out at 85°C with CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipyridine as the catalyst and polyoxyethylene(23) lauryl ether as the surfactant. With this technique, PBMA‐b‐PSt diblock copolymers were synthesized. The polymerization was nearly controlled; the ATRP of St from the macroinitiators showed linear increases in number‐average molecular weight with conversion. The block copolymers were characterized with IR spectroscopy, ¹H‐NMR, and differential scanning calorimetry. The effects of the molecular weight of the macroinitiators, macroinitiator concentration, catalyst concentration, surfactant concentration, and temperature on the polymerization were also investigated. Thermodynamic data and activation parameters for the ATRP are also reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2123–2129, 2005     

Chemo‐enzymatic synthesis of poly(2,2,2‐trichloroethyl 10‐hydroxydecanate)‐block‐polystyrene combining enzymatic self‐condensation polymerization and ATRP

Enzymatic polymerization in a non‐natural environment is of interest as an environmentally friendly methodology as an alternative to the use of conventional chemical organometallic catalysts. Chemo‐enzymatic synthesis of the AB‐type diblock copolymer poly(2,2,2‐trichloroethyl 10‐hydroxydecanate)‐block‐polystyrene (PHD‐b‐PSt) was carried out by combining enzymatic self‐condensation polymerization (eSCP) and atom‐transfer radical polymerization (ATRP). Biocatalyst Novozyme 435 was successful in catalyzing the eSCP of a novel ω‐hydroxyester, i.e. 2,2,2‐trichloroethyl 10‐hydroxydecanate. The resulting ? CCl₃‐terminated PHD initiated the ATRP of styrene, a ‘living’/controlled radical polymerization. The analysis of the hydrolysate from the copolymer proved the presence of a block copolymer structure. In addition, the well‐defined diblock copolymer PHD‐b‐PSt self‐assembled into nanoscale micelles in aqueous solution. The chemo‐enzymatic synthesis of diblock copolymer PHD‐b‐PSt was achieved by the combination of eSCP and ATRP. The structures and composition of the block copolymer were characterized by means of NMR, infrared and gel permeation chromatography measurements. Differential scanning calorimetry analysis showed that a microphase‐separation structure was formed in the copolymer, which was caused by the crystallization of the PHD segments. As investigated with atomic force microscopy and dynamic light scattering, these micelles had a mean diameter and a spherical shape. To our knowledge, this is the first example of a chemo‐enzymatic synthesis based on eSCP and ATRP. Copyright © 2007 Society of Chemical Industry     

Degradation and initiation polymerization mechanism of α‐methylstyrene‐containing macroinitiators

Copolymers obtained from radical copolymerization of α‐methylstyrene (AMS) and glycidyl methacrylate (GMA) behave as macroinitiators, when heated in the presence of a second monomer, giving rise to block copolymers. The relevant degradation and initiation polymerization mechanism of the macroinitiators were studied. Thermal depropagation of the macroinitiators generated monomers, identified by ¹H‐NMR, photoionization mass spectroscopy and FT‐IR. According to the results of structure analysis by GPC, ESR and NMR spectroscopy, the AMS‐GMA (head‐head) and AMS‐AMS (head‐head) bonds in the macroinitiators are easily scissored providing free radicals when the temperature is above 80°C. The radicals lead to subsequent polymerization of the second monomer, and thereby block copolymers are formed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Atom‐transfer radical polymerization of methyl methacrylate with α,α′‐dichloroxylene/CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine initiation system under microwave irradiation

The atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA), using α,α′‐dichloroxylene as initiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst was successfully carried out under microwave irradiation (MI). The polymerization of MMA under MI showed linear first‐order rate plots, a linear increase of the number‐average molecular weight with conversion, and low polydispersities, which indicated that the ATRP of MMA was controlled. Using the same experimental conditions, the apparent rate constant (k) under MI (k = 7.6 × 10^?4 s^?1) was higher than that under conventional heating (k = 5.3 × 10^?5 s^?1). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2189–2195, 2004     

Synthesis and characterization of novel lipid functionalized poly(ε‐caprolactone)s

A series of novel lipid functionalized poly(ε‐caprolactone)s (PCLs) were synthesized through ROP of ε‐caprolactone in the presence of threo‐9,10‐dihydroxyoctadecanoic acid, synthesized from oleic acid. PCLs with different molecular weights were obtained by controlling the molar ratio of the initiator to the monomer. DSC and XRD analysis indicate that the crystallinity of PCLs decreased when compared to unfunctionalized PCL. The enzymatic degradation study shows that for samples with lower lipid derivatives content, a higher enzymatic degradation rate was observed because the lipase enzymes attack the ester bonds of the polymer; increased lipid content therefore inhibits the action of the lipase enzymes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of poly(4‐diphenylaminostyrene)‐Poly(9‐vinylanthracene) binary block copolymer

Block copolymerization of plural types of monomers offers a new opportunity for the preparation of a variety of multifunctional polymers. Poly(4‐diphenylaminostyrene) (PDAS)‐poly(9‐vinylanthracene) (PVAN) binary block copolymer (PDAS‐PVAN) was synthesized by (living) anionic polymerization using the benzyllithium/N,N,N′,N′‐tetramethylethylenediamine system. The photoluminescence emission of PDAS‐PVAN was enhanced by the fluorescence resonance energy transfer from PDAS block to PVAN block in PDAS‐PVAN. The hole drift mobility of the copolymer was controllable by the amount of triphenylamino groups in the polymer chain. The optical and electrical properties of PDAS‐PVAN were adjustable through the polymer chain structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of diblock,triblock, and multiblock copolymers containing poly(3‐hydroxy butyrate) units

A poly[(R,S)‐3‐hydroxybutyrate] macroinitiator (PHB‐MI) was obtained through the condensation reaction of poly[(R,S)‐3‐hydroxybutyrate] (PHB) oligomers containing dihydroxyl end functionalities with 4,4′‐azobis(4‐cyanopentanoyl chloride). The PHB‐MI obtained in this way had hydroxyl groups at two end of the polymer chain and an internal azo group. The synthesis of ABA‐type PHB‐b‐PMMA block copolymers [where A is poly(methyl methacrylate) (PMMA) and B is PHB] via PHB‐MI was accomplished in two steps. First, multiblock active copolymers with azo groups (PMMA‐PHB‐MI) were prepared through the redox free‐radical polymerization of methyl methacrylate (MMA) with a PHB‐MI/Ce(IV) redox system in aqueous nitric acid at 40°C. Second, PMMA‐PHB‐MI was used in the thermal polymerization of MMA at 60°C to obtain PHB‐b‐PMMA. When styrene (S) was used instead of MMA in the second step, ABCBA‐type PMMA‐b‐PHB‐b‐PS multiblock copolymers [where C is polystyrene (PS)] were obtained. In addition, the direct thermal polymerization of the monomers (MMA or S) via PHB‐MI provided AB‐type diblocks copolymers with MMA and BCB‐type triblock copolymers with S. The macroinitiators and block copolymers were characterized with ultraviolet–visible spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, cryoscopic measurements, and thermogravimetric analysis. The increases in the intrinsic viscosity and fractional precipitation confirmed that a block copolymer had been obtained. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1789–1796, 2004     

Grafting of acrylic acid onto flax fibers using Mn(IV)‐citric acid redox system

When the flax fibers (machine tow) were treated with KMnO₄ solution, MnO₂ was deposited over‐all the fiber surface. The amount of MnO₂ deposited relied on the KMnO₄ concentration. Subjecting the flax‐containing MnO₂ to a solution consisting of monomer (acrylic acid, AA) and citric acid, CA (or any acid used in this work) resulted in formation of poly(AA)‐flax graft copolymer. Dependence of the polymer criteria, namely, the total percentage conversion (%TC) and the carboxyl content of the grafted flax fibers on various grafting parameters, viz., concentrations of the redox pair as well as AA, material‐to‐liquor ratio (M/R), duration and temperature of polymerization, kind of the acid and kind of the flax fibers pretreatment was studied systematically. The results indicated that the polymerizability of AA molecules, expressed as %TC (i.e., counting both grafting and homopolymerization) and thence the carboxyl content (i.e., evaluating the extent of AA grafting along the flax backbone) was optimized with the following conditions: [AA], 100% (based on weight of flax fibers, owf); [CA], 0.4 meq/1 g flax; [MnO₂], 0.4 meq/1 g flax; polymerization temperature, 40°C; polymerization time, 30 min; and the M/R, 1 : 50. A tentative mechanism for grafting of flax fibers with AA using MnO₂‐acid redox system was elucidated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3028–3036, 2006     

Maghnite‐H+ as a cationic catalyst in the synthesis of poly(1,3‐dioxolane) and α,ω‐methacryloyloxy‐poly(1,3‐dioxolane)

The polymerization of 1,3‐dioxolane catalyzed by Maghnite‐H^+; (Mag‐H⁺), a montmorillonite sheet silicate clay exchanged with protons, was investigated. The cationic ring‐opening polymerization of 1,3‐dioxolane was initiated by Mag‐H⁺ at different temperatures (20, 30, 50, and 70°C) in bulk and in a solvent (dichloromethane). The effects of the amount of Mag‐H⁺ and the temperature were studied. The polymerization rate and the average molecular weights increased with an increase in the temperature and the proportion of the catalyst. These results indicated the cationic nature of the polymerization and suggested that the polymerization was initiated by proton addition to the monomer from Mag‐H⁺. Moreover, we used a simple method, in one step in bulk and in solution at room temperature (20°C), to prepare a telechelic bismacromonomer: α,ω‐bisunsaturated poly(1,3‐dioxolane). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 78–82, 2006     

Amphiphilic diblock copolymers poly(2‐hydroxyethylmethacrylate)‐b‐(N‐phenylmaleimide) and poly(2‐hydroxyethylmethacrylate)‐b‐(styrene) using the macroinitiator poly(HEMA)‐Cl by ATRP: Preparation,characterization, and thermal properties

In recent years, much attention has been given to the development of specialty polymers from useful materials. In this context, amphiphilic block copolymers were prepared by atom transfer radical polymerization (ATRP) of N‐phenylmaleimide (N‐PhMI) or styrene using a poly(2‐hydroxyethylmethacrylate)‐Cl macroinitiator/CuBr/bipyridine initiating system. The macroinitiator P(HEMA)‐Cl was directly prepared in toluene by reverse ATRP using BPO/FeCl₃ 6 H₂O/PPh₃ as initiating system. The microstructure of the block copolymers were characterized using FTIR, ¹H‐NMR, ¹³C‐NMR spectroscopic techniques and scanning electron microscopy (SEM). The thermal behavior was studied by differential scanning calorimetry (DSC), and thermogravimetry (TG). The theoretical number average molecular weight (M_n,th) was calculated from the feed capacity. The microphotographs of the film's surfaces show that the film's top surfaces were generally smooth. The TDT of the block copolymer P(HEMA)₈₀‐b‐P(N‐PhMI)₂₀ and P(HEMA)₉₀‐b‐P(St)₁₀ of about 290°C was also lower than that found for the macroi′nitiator poly(HEMA)‐Cl. The block copolymers exhibited only one T_g before thermal decomposition, which could be attributed to the low molar content of the N‐PhMI or St blocks respectively. This result also indicates that the phase behavior of the copolymers is predominately determined by the HEMA block. The curves reveal that the polymers show phase transition behavior of amorphous polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atom transfer radical polymerization of styrene with 2‐(1‐bromoethyl)‐anthraquinone as an initiator

2‐(1‐Bromoethyl)‐anthraquinone (BEAQ) was successfully used as an initiator in the atom transfer radical polymerization of styrene with CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine as the catalyst at 110°C. The polymerizations were well controlled with a linear increase in the molecular weights (M_n's) of the polymers with monomer conversion and relatively low polydispersities (1.1 < weight‐average molecular weight (M_w)/M_n < 1.5) throughout the poly merizations. The resultant polystyrene thus possessed one chromophore moiety (2‐ethyl‐anthraquinone) at the α end and one bromine atom at the ω end, both from the initiator BEAQ. The intensity of UV absorptions of the resultant polymers decreased with increasing molecular weights of the polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2081–2085, 2006     

Application of a new unimolecular initiator in the synthesis of (α,ω) ketone functionalized polystyrene in nitroxide mediated polymerization

The ketone functionalized N‐alkoxyamine, a derivative of 4‐oxo‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (4‐oxo‐TEMPO) was synthesized and applied as an initiator in the nitroxide mediated polymerization of styrene in bulk at 120°C. In the presence of the prepared initiator: 1‐phenyl‐1‐(4‐oxo‐2,2,6,6‐tetramethylpiperidinoxy)propanone polymers with well‐defined molecular weight were obtained. By contrast, when an accelerator such as acetic anhydride (10%) was added to the system, lower control of polymerization was observed. Additionally, the functionality of polymers was evaluated on the basis of a quantitative investigation of UV–visible spectra of 2,4‐dinitrophenylhydrazone formed from the polymers and the synthesized initiator. The UV–vis spectra of the hydrazone derivatives obtained from polymers by means of 2,4‐dinitrophenylhydrazone made it possible to confirm that the polymers prepared in the presence of the ketone functionalized N‐alkoxyamine retain the ketone functionality on the polymer chain. The functionality for the obtained polymers exceeded 1 significantly. The obtained (α, ω) telechelic polymers are of great importance in the synthesis of new biohybrid materials such as bioconjugates with proteins or peptides as well as new polymer nanostructures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Different dispersion polymerization strategies influence the quality of fluorescent poly (St‐co‐GMA) microspheres

The polymerization strategy plays a vital role in the preparation of functional microspheres. In this work, fluorescent poly (styrene‐co‐glycidyl methacrylate) (PSt‐GMA) microspheres were synthesized via one‐stage and two‐stage dispersion polymerization with 4‐Bis(5‐phenyl‐1,3‐oxazol‐2‐yl)benzene (POPOP) as fluorescence agent. SEM and DLS were adopted to characterize the properties of prepared microspheres. The UV‐vis and fluorescence spectroscopy were used to analyze the mechanisms of two‐stage dispersion polymerization. The experimental results showed that the size distribution and fluorescence intensity of prepared microspheres could be improved by two‐stage dispersion polymerization compared to one‐stage dispersion polymerization. In addition, according to UV‐vis, the interactions between POPOP and Poly (N‐vinyl pyrrolidone) (PVP) as well as POPOP and Glycidyl methacrylate (GMA) could affect the particle size and its distribution. UV‐vis and fluorescence spectra implied that the POPOP existed outside of the particle's core via two‐stage strategy. The monomer conversion of styrene was similar at the beginning of reaction; however, the monomer conversion of styrene by two‐stage strategy was higher than that of by one‐stage strategy. In a word, two‐stage dispersion polymerization could prepare fluorescent microspheres with the monodispersion micrometer‐size and high quality. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41927.     

Synthesis of fluorescent methoxy poly(ethylene glycol)‐b‐Poly(ethyl cyanoacrylate)–2‐(N‐carbazolyl) ethyl methacrylate copolymer via living oxyanion‐initiated polymerization

The fluorescent amphiphilic block copolymer methoxy poly(ethylene glycol) (mPEG)‐b‐poly(ethyl cyanoacrylate) (PECA)–2‐(N‐carbazolyl) ethyl methacrylate (CzEMA) was synthesized via living oxyanion‐initiated polymerization. mPEG‐b‐PECA–CzEMA was characterized by gel permeation chromatography, ¹H‐NMR, and Fourier transform infrared spectroscopy. The results indicate that the polymerization was well controlled with a narrow molecular weight distribution. The mPEG‐b‐PECA–CzEMA nanoparticles prepared by nanoprecipitation techniques showed a narrow size distribution with an average diameter of less than 100 nm. The mPEG‐b‐PECA–CzEMA exhibited a strong carbazole fluorescence. Furthermore, it was found that the fluorescence intensity of mPEG‐b‐PECA–CzEMA was sensitive to a change in solvent. The results indicate that a subtle change in the state of the polymer micellar association may have altered the state of carbazole groups, which was responsible for the fluorescence emission. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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