Divergent synthesis of dendrimer‐like macromolecules through a combination of atom transfer radical polymerization and click reaction

This article describes a divergent strategy to prepare dendrimer‐like macromolecules from vinyl monomers through a combination of atom transfer radical polymerization (ATRP) and click reaction. Firstly, star‐shaped polystyrene (PS) with three arms was prepared through ATRP of styrene starting from a three‐arm initiator. Next, the terminal bromides of the star‐shaped PS were substituted with azido groups. Afterwards, the azido‐terminated star‐shaped PS was reacted with propargyl 2,2‐bis((2′‐bromo‐2′‐methylpropanoyloxy)methyl)propionate (PBMP) via click reaction. Star‐shaped PS with six terminal bromide groups was afforded and served as the initiator for the polymerization of styrene to afford the second‐generation dendrimer‐like PS. Iterative process of the aforementioned sequence of reactions could allow the preparation of the third‐generation dendrimer‐like PS. When the second‐generation dendrimer‐like PS with 12 bromide groups used as an initiator for the polymerization of tert‐butyl acrylate, the third‐generation dendrimer‐like block copolymer with a PS core and a poly (tert‐butyl acrylate) (PtBA) corona was afforded. Subsequently PtBA segments were selectively hydrolyzed with hydrochloric acid, resulting an amphiphilic branched copolymer with inner dendritic PS and outer linear poly(acrylic acid) (PAA). Following the same polymerization procedures, the dendrimer‐like PS and PS‐block‐PtBA copolymers of second generation originating from six‐arm initiator were also synthesized. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3330–3341, 2007     

Preparation of star block copolymers with polystyrene‐block‐poly(ethylene oxide) as side chains on hyperbranched polyglycerol core by combination of ATRP with atom transfer nitroxide radical coupling reaction

The star block copolymers with polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as side chains and hyperbranched polyglycerol (HPG) as core were synthesized by combination of atom transfer radical polymerization (ATRP) with the “atom transfer nitroxide radical coupling” (“ATNRC”) reaction. The multiarm PS with bromide end groups originated from the HPG core (HPG‐g‐(PS‐Br)_n) was synthesized by ATRP first, and the heterofunctional PEO with α‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy group and ω‐hydroxyl group (TEMPO‐PEO) was prepared by anionic polymerization separately using 4‐hydroxyl‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (HTEMPO) as parents compound. Then ATNRC reaction was conducted between the TEMPO groups in PEO and bromide groups in HPG‐g‐(PS‐Br)_n in the presence of CuBr and pentamethyldiethylenetriamine (PMDETA). The obtained star block copolymers and intermediates were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, fourier transform‐infrared in detail. Those results showed that the efficiency of ATNRC in the preparation of multiarm star polymers was satisfactory (>90%) even if the density of coupling cites on HPG was high. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6754–6761, 2008     

Synthesis of sugar‐based macromolecules via sono‐ATRP in miniemulsion

Ultrasound‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is used for the first time for the preparation of complex macromolecular architectures by a facile two‐step synthetic route. Initially, esterification reaction of sucrose or lactulose with α‐bromoisobutyryl bromide (BriBBr) is conducted to receive multifunctional ATRP macroinitiators with 8 initiation sites, followed by polymerization of n‐butyl acrylate (BA) forming arms of the star‐like polymers. The brominated lactulose‐based molecule was examined as an ATRP initiator by determining the activation rate constant (k_a) of the catalytic process in the presence of a copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) catalyst in both organic solvent and for the first time in miniemulsion media, resulting in k_a = (1.03 ± 0.01) × 10⁴ M^?1 s^?1 and k_a = (1.16 ± 0.56) × 10³ M^?1 s^?1, respectively. Star‐like macromolecules with a sucrose or lactulose core and poly(n‐butyl acrylate) (PBA) arms were successfully received using different catalyst concentration. Linear kinetics and a well‐defined structure of synthesized polymers reflected by narrow molecular weight distribution (M_w/M_n = 1.46) indicated 105 ppm wt of catalyst loading as concentration to maintain controlled manner of polymerization process. ¹H NMR analysis confirms the formation of new sugar‐inspired star‐shaped polymers.     

Synthesis of inverse star block copolymer by combination of ATRP,ring opening polymerization,and “click chemistry”

The inverse star block copolymer, (poly(ε‐caprolactone)‐b‐polystyrene)₂‐core‐(poly(ε‐caprolactone)‐b‐polystyrene)₂, [(PCL‐PS)₂‐core‐(PCL‐PS)₂] has been successfully prepared by combination of atom transfer radical polymerization (ATRP), ring opening polymerization (ROP), and “Click Chemistry.” The synthesis includes the following five steps: (1) synthesis of a heterofunctional initiator with two ATRP initiating groups and two hydroxyl groups; (2) formation of (Br‐PS)₂‐core‐(OH)₂ via ATRP of styrene; (3) preparation of the (PCL‐PS)₂‐core‐(OH)₂ through “click” reaction of the α‐propargyl, ω‐acetyl terminated PCL with (N₃‐PS)₂‐core‐(OH)₂ which was prepared by transformation of the terminal bromine groups in (Br‐PS)₂‐core‐(OH)₂ into azide groups; (4) the ROP of CL using (PCL‐PS)₂‐core‐(OH)₂ as macroinitiator to form (PCL‐PS)₂‐core‐(PCL‐OH)₂; and (5) preparation of the (PCL‐PS)₂‐core‐(PCL‐PS)₂ through the ATRP of styrene using (PCL‐PS)₂‐core‐(PCL‐Br)₂ as macroinitiator which was prepared by reaction of the terminal hydroxyl groups at the end of the PCL chains with 2‐bromoisobutyryl bromide. The characterization data support structures of the inverse star block copolymer and the intermediates. The differential scanning calorimeter results and polarized optical microscope observation showed that the intricate structure of the inverse star block copolymer greatly restricted the movement of the PS segments and PCL segments, resulted in the increase of the glass transition temperature of PS segments and the decrease of crystallization ability of PCL segments. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7757–7772, 2008     

ABC‐type hetero‐arm star terpolymers through “Click” chemistry

Hetero‐arm star ABC‐type terpolymers, poly(methyl methacrylate)‐polystyrene‐poly(tert‐butyl acrylate) (PMMA‐PS‐PtBA) and PMMA‐PS‐poly(ethylene glycol) (PEG), were prepared by using “Click” chemistry strategy. For this, first, PMMA‐b‐PS with alkyne functional group at the junction point was obtained from successive atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMP) routes. Furthermore, PtBA obtained from ATRP of tBA and commercially available monohydroxyl PEG were efficiently converted to the azide end‐functionalized polymers. As a second step, the alkyne and azide functional polymers were reacted to give the hetero‐arm star polymers in the presence of CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine ( PMDETA) in DMF at room temperature for 24 h. The hetero‐arm star polymers were characterized by ¹H NMR, GPC, and DSC. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5699–5707, 2006     

Preparation of hydrophobic tannins‐inspired polymer materials via low‐ppm ATRP methods

The novel hydrophobic coating material was received for the first time by a two‐step synthetic route. Firstly, the 15‐functional brominated macroinitiator was prepared by the esterification methodology. Next step covers synthesis of star‐like polymers by poly(n‐butyl acrylate) (PBA) arms polymerization via three low‐ppm atom transfer radical polymerization (ATRP) approaches including application of copper and silver wire in SARA and ARGET ATRP, respectively, as driving forces in redox cycle of catalyst, and an external stimulus in the form of electric current (seATRP) as the third approach in copper(II) regeneration system. As expected, the electrochemically mediated technique allows synthesis of tannic acid‐inspired coating polymers in precisely controlled manner during the entire polymerization process, proved by linear first‐order kinetics plot in contrast to above‐mentioned methods, low dispersity (Ð = 1.18) of star‐shaped polymers, and high efficiency of initiation (? _i = 81%) determined after detaching of polymers side arms. Macromolecules received by all low‐ppm ATRP solutions were characterized by preserved chain‐end functionality (theoretical dead chain fraction; DCF_theo <1%). Adhesive and hydrophobic properties of received polymer materials were investigated by contact angles (θ) and free surface energy (FSE) calculations. Prepared polymer films besides excellent hydrophobic properties have great potential as a self‐healing solution.     

Synthesis of ABCD 4‐Miktoarm star‐shaped quarterpolymers by combination of the “click” chemistry with multiple polymerization mechanism

Well‐defined ABCD 4‐Miktoarm star‐shaped quarterpolymers of [poly(styrene)‐poly(tert‐butyl acrylate)‐poly(ethylene oxide)‐poly(isoprene)] [star(PS‐PtBA‐PEO‐PI)] were successfully synthesized by the combination of the “click” chemistry and multiple polymerization mechanism. First, the poly(styryl)lithium (PS^?Li⁺) and the poly(isoprene)lithium (PI^?Li⁺) were capped by ethoxyethyl glycidyl ether (EEGE) to form the PS and PI with both an active ω‐hydroxyl group and an ω′‐ethoxyethyl‐protected hydroxyl group, respectively. After these two hydroxyl groups were selectively modified to propargyl and 2‐bromoisobutyryl group for PS, the resulted PS was used as macroinitiator for ATRP of tBA monomer and the diblock copolymer PS‐b‐PtBA with a propargyl group at the junction point was achieved. Then, using the functionalized PI as macroinitiator for ROP of EO monomer and bromoethane as blocking agent, the diblock copolymer PI‐b‐PEO with a protected hydroxyl group at the conjunction point was synthesized. After the hydrolysis, the recovered hydroxyl group of PI‐b‐PEO was modified to bromoacetyl and then azide group successively. Finally, the “click” chemistry between them was proceeded smoothly. The obtained star‐shaped quarterpolymers and intermediates were characterized by ¹H NMR, FT‐IR, and SEC in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2154–2166, 2008     

Synthesis of well‐defined cyclodextrin‐core star polymers

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

Synthesis of amphiphilic A4B4 star‐shaped copolymers by mechanisms transformation combining with thiol‐ene reaction

Using core‐first strategy, the amphiphilic A₄B₄ star‐shaped copolymers [poly(ethylene oxide)]₄[poly(ε‐caprolactone)]₄ [(PEO)₄(PCL)₄], [poly(ethylene oxide)]₄[poly(styrene)]₄ [(PEO)₄(PS)₄], and [poly(ethylene oxide)]₄[poly(tert‐butyl acrylate)]₄ [(PEO)₄(PtBA)₄] were synthesized by mechanisms transformation combining with thiol‐ene reaction. First, using a designed multifunctional mikto‐initiator with four active hydroxyl groups and four allyl groups, the four‐armed star‐shaped polymers (PEO‐Ph)₄/(OH)₄ with four active hydroxyl groups at core position were obtained by sequential ring‐opening polymerization (ROP) of ethylene oxide monomers, capping reaction of living oxyanion with benzyl chloride, and transformation of allyl groups into hydroxyl groups by thiol‐ene reaction. Then, the A₄B₄ star‐shaped copolymers (PEO)₄(PS)₄ or (PEO)₄(PtBA)₄ were obtained by atom transfer radical polymerization (ATRP) of styrene or tert‐butyl acrylate (tBA) monomers from macroinitiator of (PEO‐Ph)₄/(Br)₄, which was obtained by esterification of (PEO‐Ph)₄/(OH)₄ with 2‐bromoisobutyryl bromide. The A₄B₄ star‐shaped copolymers (PEO)₄(PCL)₄ were also obtained by ROP of ε‐caprolactopne monomers from macroinitiator of (PEO‐Ph)₄/(OH)₄. The target copolymers and intermediates were characterized by size‐exclusion chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy, and nuclear magnetic resonance in detail. This synthetic route might be a versatile one to various A_nB_n (n ≥ 3) star‐shaped copolymers with defined structure and compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4572–4583     

Multiarm star block copolymers via Diels‐Alder click reaction

Two types of multiarm star block copolymers: (polystyrene)_m‐poly(divinylbenzene)‐poly(methyl methacrylate)_n, (PS)_m‐polyDVB‐(PMMA)_n and (polystyrene)_m‐poly(divinylbenzene)‐poly(tert‐butyl acrylate)_k, (PS)_m‐polyDVB‐(PtBA)_k were successfully prepared via a combination of cross‐linking and Diels–Alder click reactions based on “arm‐first” methodology. For this purpose, multiarm star polymer with anthracene functionality as reactive periphery groups was prepared by a cross‐linking reaction of divinyl benzene using α‐anthracene end functionalized polystyrene (PS‐Anth) as a macroinitiator. Thus, obtained multiarm star polymer was then reacted with furan protected maleimide‐end functionalized polymers: PMMA‐MI or PtBA‐MI at reflux temperature of toluene for 48 h resulting in the corresponding multiarm star block copolymers via Diels–Alder click reaction. The multiarm star and multiarm star block copolymers were characterized by using ¹H NMR, SEC, Viscotek triple detection SEC (TD‐SEC) and UV. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 178–187, 2009     

Multiarm star block and multiarm star mixed‐block copolymers via azide‐alkyne click reaction

The synthesis of multiarm star block (and mixed‐block) copolymers are efficiently prepared by using Cu(I) catalyzed azide‐alkyne click reaction and the arm‐first approach. α‐Silyl protected alkyne polystyrene (α‐silyl‐alkyne‐PS) was prepared by ATRP of styrene (St) and used as macroinitiator in a crosslinking reaction with divinyl benzene to successfully give multiarm star homopolymer with alkyne periphery. Linear azide end‐functionalized poly(ethylene glycol) (PEG‐N₃) and poly (tert‐butyl acrylate) (PtBA‐N₃) were simply clicked with the multiarm star polymer described earlier to form star block or mixed‐block copolymers in N,N‐dimethyl formamide at room temperature for 24 h. Obtained multiarm star block and mixed‐block copolymers were identified by using ¹H NMR, GPC, triple detection‐GPC, atomic force microscopy, and dynamic light scattering measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 99–108, 2010     

Synthesis of miktoarm star and miktoarm star block copolymers via a combination of atom transfer radical polymerization and stable free‐radical polymerization

A trifunctional initiator, 2‐phenyl‐2‐[(2,2,6,6‐tetramethyl)‐1‐piperidinyloxy] ethyl 2,2‐bis[methyl(2‐bromopropionato)] propionate, was synthesized and used for the synthesis of miktoarm star AB₂ and miktoarm star block AB₂C₂ copolymers via a combination of stable free‐radical polymerization (SFRP) and atom transfer radical polymerization (ATRP) in a two‐step or three‐step reaction sequence, respectively. In the first step, a polystyrene (PSt) macroinitiator with dual ω‐bromo functionality was obtained by SFRP of styrene (St) in bulk at 125 °C. Next, this PSt precursor was used as a macroinitiator for ATRP of tert‐butyl acrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C, affording miktoarm star (PSt)(PtBA)₂ [where PtBA is poly(tert‐butyl acrylate)]. In the third step, the obtained St(tBA)₂ macroinitiator with two terminal bromine groups was further polymerized with methyl methacrylate by ATRP, and this resulted in (PSt)(PtBA)₂(PMMA)₂‐type miktoarm star block copolymer [where PMMA is poly(methyl methacrylate)] with a controlled molecular weight and a moderate polydispersity (weight‐average molecular weight/number‐average molecular weight < 1.38). All polymers were characterized by gel permeation chromatography and ¹H NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2542–2548, 2003     

Poly(acrylate‐b‐styrene‐b‐isobutylene‐b‐styrene‐b‐acrylate) Block Copolymers via Carbocationic and Atom Transfer Radical Polymerizations

A series of polyacrylate‐polystyrene‐polyisobutylene‐polystyrene‐polyacrylate (X‐PS‐PIB‐PS‐X) pentablock terpolymers (X=poly(methyl acrylate) (PMA), poly(butyl acrylate) (PBA), or poly(methyl methacrylate) (PMMA)) was prepared from poly (styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymers (BCPs) using either a Cu(I)Cl/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. The PS‐PIB‐PS BCPs were prepared by quasiliving carbocationic polymerization of isobutylene using a difunctional initiator, followed by the sequential addition of styrene, and were used as macroinitiators for the atom transfer radical polymerization (ATRP) of methyl acrylate (MA), n‐butyl acrylate (BA), or methyl methacrylate (MMA). The ATRP of MA and BA proceeded in a controlled fashion using either a Cu(I)Cl/PMDETA or Cu(I)Cl/Me₆TREN catalyst system, as evidenced by a linear increase in molecular weight with conversion and low PDIs. The polymerization of MMA was less controlled. ¹H‐NMR spectroscopy was used to elucidate pentablock copolymer structure and composition. The thermal stabilities of the pentablock copolymers were slightly less than the PS‐PIB‐PS macroinitiators due to the presence of polyacrylate or polymethacrylate outer block segments. DSC analysis of the pentablock copolymers showed a plurality of glass transition temperatures, indicating a phase separated material.     

Functionalization of polymers prepared by ATRP using radical addition reactions

Low molecular weight linear poly(methyl acrylate), star and hyperbranched polymers were synthesized using atom transfer radical polymerization (ATRP) and end‐functionalized using radical addition reactions. By adding allyltri‐n‐butylstannane at the end of the polymerization of poly(methyl acrylate), the polymer was terminated by allyl groups. When at high conversions of the acrylate monomer, allyl alcohol or 1,2‐epoxy‐5‐hexene, monomers which are not polymerizable by ATRP, were added, alcohol and epoxy functionalities respectively were incorporated at the polymer chain end. Functionalization by radical addition reactions was demonstrated to be applicable to multi‐functional polymers such as hyperbranched and star polymers.     

Tripodal imidazole containing ligands for copper catalyzed ATRP

Tripodal imidazole containing ligands, bis((2‐pyridyl)methyl)(1‐methylimidazole‐2‐yl)methyl)amine (BPIA) and bis(1‐methylimidazole‐2‐yl)methyl)((2‐pyridyl)methyl)amine (BIPA), were synthesized and used for copper catalyzed atom transfer radical polymerization (ATRP) of n‐butyl acrylate (nBA). The molecular weights of poly(n‐butyl acrylate) (PnBA) catalyzed by CuBr/BPIA and CuBr/BIPA complexes increased linearly with nBA conversions and they were close to theoretical values with low polydispersities. ATRP equilibrium rate constant (K_ATRP) measurements showed that bothCuBr/BPIA and CuBr/BIPA complexes had high K_ATRP values, similar to that of CuBr/tri(2‐pyridylmethyl)amine (TPMA), which is one of the ATRP most active ligands. Activators regenerated by electron transfer (ARGET) ATRP of nBA with CuBr₂/BPIA and CuBr₂/BIPA complexes were also conducted and polymerization reached high nBA conversions, resulting in PnBA with low polydispersities. This suggests that the copper complexes with BPIA and BIPA were sufficiently stable and active to conduct ATRP when catalyst concentration was low. ARGET ATRP to form high molecular weight PnBA with CuBr₂/BPIA and CuBr₂/BIPA complexes was also successful. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2015–2024, 2008     

Synthesis and characterization of novel resorcinarene‐centered amphiphilic star‐block copolymers consisting of eight ABA triblock arms by combination of ROP,ATRP, and click chemistry

Novel amphiphilic eight‐arm star triblock copolymers, star poly(ε‐caprolactone)‐block‐poly(acrylic acid)‐block‐poly(ε‐caprolactone)s (SPCL‐PAA‐PCL) with resorcinarene as core moiety were prepared by combination of ROP, ATRP, and “click” reaction strategy. First, the hydroxyl end groups of the predefined eight‐arm SPCLs synthesized by ROP were converted to 2‐bromoesters which permitted ATRP of tert‐butyl acrylate (tBA) to form star diblock copolymers: SPCL‐PtBA. Next, the bromide end groups of SPCL‐PtBA were quantitatively converted to terminal azides by NaN₃, which were combined with presynthesized alkyne‐terminated poly(ε‐caprolactone) (A‐PCL) in the presence of Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine in DMF to give the star triblock copolymers: SPCL‐PtBA‐PCL. ¹H NMR, FTIR, and SEC analyses confirmed the expected star triblock architecture. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl acrylate) blocks gave the amphiphilic star triblock copolymers: SPCL‐PAA‐PCL. These amphiphilic star triblock copolymers could self‐assemble into spherical micelles in aqueous solution with the particle size ranging from 20 to 60 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2905–2916, 2009     

Dendrimer‐like miktoarm star terpolymers: A3‐(B‐C)3 via click reaction strategy

Two samples of dendrimer‐like miktoarm star terpolymers: (poly(tert‐butyl acrylate))₃‐(polystyrene‐poly(ε‐caprolactone))₃ (PtBA)₃‐(PS‐PCL)₃, and (PS)₃‐(PtBA‐poly(ethylene glycol)₃ were prepared using efficient Cu catalyzed Huisgen cycloaddition (click reaction). As a first step, azido‐terminated 3‐arm star polymers PtBA and PS as core (A) were synthesized by atom transfer radical polymerization (ATRP) of tBA and St, respectively, followed by the conversion of bromide end group to azide. Secondly, PS‐PCL and PtBA‐PEG block copolymers with alkyne group at the junction as peripheral arms (B‐C) were obtained via multiple living polymerization mechanisms such as nitroxide mediated radical polymerization (NMP) of St, ring opening polymerization (ROP) of ε‐CL, ATRP of tBA. Thus obtained core and peripheral arms were linked via click reaction to give target (A)₃‐(B‐C)₃ dendrimer‐like miktoarm star terpolymers. (PtBA)₃‐(PS‐PCL)₃ and (PS)₃‐(PEG‐PtBA)₃ have been characterized by GPC, DSC, AFM, and SAXS measurements. (PtBA)₃‐(PS‐PCL)₃ did not show any self‐organization with annealing due to the miscibility of the peripheral arm segments. In contrast, the micro‐phase separation of the peripheral arm segments in (PS)₃‐(PtBA‐PEG)₃ resulted in self‐organized phase‐separated morphology with a long period of ～ 13 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5916–5928, 2008     

Syntheses and characterization of 16‐arm star and star diblock copolymer and AB8 9‐miktoarm star copolymer via NMRP and ROP from dendritic multifunctional macroinitiators

A dendritic macroinitiator having 16 TEMPO‐based alkoxyamines, Star‐16 , was prepared by the reaction of a dendritic macroinitiator having eight TEMPO‐based alkoxyamines, [G‐3]‐OH , with 4,4′‐bis(chlorocarbonyl)biphenyl. The nitroxide‐mediated radical polymerization (NMRP) of styrene (St) from Star‐16 gave 16‐arm star polymers with PDI of 1.19–1.47, and NMPR of 4‐vinylpyridine from the 16‐arm star polymer gave 16‐arm star diblock copolymers with PDI of 1.30–1.43. The ring‐opening polymerization of ε‐caprolactone from [G‐3]‐OH and the subsequent NMRP of St gave AB₈ 9‐miktoarm star copolymers with PDI of 1.30–1.38. The benzyl ether linkages of the 16‐arm star polymers and the AB₈ 9‐miktoarm star copolymers were cleaved by treating with Me₃SiI, and the resultant poly(St) arms were investigated by size exclusion chromatography (SEC). The SEC results showed PDIs of 1.23–1.28 and 1.18–1.22 for the star polymers and miktoarm stars copolymers, respectively, showing that they have well‐controlled poly(St) arms. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1159–1169, 2007.     

Facile synthesis of AB2‐type miktoarm star polymers through the combination of atom transfer radical polymerization and ring‐opening polymerization

A novel miktofunctional initiator ( 1 ), 2‐hydroxyethyl 3‐[(2‐bromopropanoyl)oxy]‐2‐{[(2‐bromopropanoyl)oxy]methyl}‐2‐methyl‐propanoate, possessing one initiating site for ring‐opening polymerization (ROP) and two initiating sites for atom transfer radical polymerization (ATRP), was synthesized in a three‐step reaction sequence. This initiator was first used in the ROP of ?‐caprolactone, and this led to a corresponding polymer with secondary bromide end groups. The obtained poly(?‐caprolactone) (PCL) was then used as a macroinitiator for the ATRP of tert‐butyl acrylate or methyl methacrylate, and this resulted in AB₂‐type PCL–[poly(tert‐butyl acrylate)]₂ or PCL–[poly(methyl methacrylate)]₂ miktoarm star polymers with controlled molecular weights and low polydispersities (weight‐average molecular weight/number‐average molecular weight < 1.23) via the ROP–ATRP sequence. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2313–2320, 2004     

An efficient way to tune grafting density of well‐defined copolymers via an unusual Br‐containing acrylate monomer

A series of well‐defined amphiphilic graft copolymers, containing hydrophilic poly(acrylic acid) backbone and hydrophobic poly(butyl acrylate) side chains, were synthesized by sequential reversible addition fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) without any postpolymerization functionality modification followed by selective acidic hydrolysis of poly(tert‐butyl acrylate) backbone. tert‐Butyl 2‐((2‐bromopropanoyloxy)methyl)‐acrylate was first homopolymerized or copolymerized with tert‐butyl acrylate by RAFT in a controlled way to give ATRP‐initiation‐group‐containing homopolymers and copolymers with narrow molecular weight distributions (M_w/M_n < 1.20) and their reactivity ratios were determined by Fineman‐Ross and Kelen‐Tudos methods, respectively. The density of ATRP initiation group can be regulated by the feed ratio of the comonomers. Next, ATRP of butyl acrylate was directly initiated by these macroinitiators to synthesize well‐defined poly(tert‐butyl acrylate)‐g‐poly(butyl acrylate) graft copolymers with controlled grafting densities via the grafting‐from strategy. PtBA‐based backbone was selectively hydrolyzed in acidic environment without affecting PBA side chains to provide poly(acrylic acid)‐g‐poly(butyl acrylate) amphiphilic graft copolymers. Fluorescence probe technique was used to determine the critical micelle concentrations in aqueous media and micellar morphologies are found to be spheres visualized by TEM. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2622–2630, 2010