RADICAL POLYMERIZATION OF METHYL METHACRYLATE WITH DIPHENYL DISELENIDE UNDER THERMAL OR PHOTOIRRADIATIONAL CONDITIONS

Polymerization of methyl methacrylate (MMA) with diphenyl diselenide (DPDSE) in the presence of AIBN at 60°C was investigated. DPDSE was worked as a chain transfer agent (CTA). The chain transfer constant (C_tr) of DPDSE for MMA was estimated to be 1.43. On the other hand, DPDSE was functioned as a photoiniferter for the photopolymerization of MMA. In a limited range of conversion, both the polymer yield and number average of molecular weight ([Mbar]_n) increased with the reaction time, and the [Mbar]_n linearly increased with the yield. The terminal structure of poly(MMA) was investigated by the ⁷⁷Se NMR spectrum based on Methyl α-phenylseleno isobutylate (MSEPI) as model compound of the ω-chain end of poly(MMA). Further, photopolymerization of poly (MMA) containing phenylseleno group at ω-chain end as a polymeric photoiniferter with MMA effectively afforded a poly (MMA) having higher molecular weight.     

Electroactive methacrylate‐based triblock copolymer elastomer for actuator application

A series of ABA triblock copolymers of methyl methacrylate (MMA) and dodecyl methacrylate (DMA) [poly(MMA‐b‐DMA‐b‐MMA)] (PMDM) were synthesized by Ru‐based sequential living radical polymerization. For this, DMA was first polymerized from a difunctional initiator, ethane‐1,2‐diyl bis(2‐chloro‐2‐phenylacetate) with combination of RuCl₂(PPh₃)₃ catalyst and nBu₃N additive in toluene at 80 °C. As the conversion of DMA reached over about 90%, MMA was directly added into the reaction solution to give PMDM with controlled molecular weight (M_w/M_n ≤ 1.2). These triblock copolymers showed well‐organized morphologies such as body centered cubic, hexagonal cylinder, and lamella structures both in bulk and in thin film by self‐assembly phenomenon with different poly(methyl methacrylate) (PMMA) weight fractions. Obtained PMDMs with 20–40 wt % of the PMMA segments showed excellent electroactive actuation behaviors at relatively low voltages, which was much superior compared to conventional styrene‐ethylene‐butylene‐styrene triblock copolymer systems due to its higher polarity derived from the methacrylate backbone and lower modulus. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Glycoconjugated polymer: Synthesis and characterization of poly(vinyl saccharide)‐block‐polystyrene‐block‐poly(vinyl saccharide) as an amphiphilic ABA triblock copolymer

Styrene (St) was polymerized with α,α′‐bis(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyloxy)‐1,4‐diethylbenzene ( 1 ) as an initiator (bulk, [St]/] 1 ] = 570) at 120 °C for 5.0 h to obtain polystyrene having 2,2,6,6‐tetramethylpiperidiloxy moieties on both sides of the chain ends ( 2 ) with a number‐average molecular weight (M_n) of 14,300 and a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.14. 4‐Vinylbenzyl glucoside peracetate ( 3a ) was polymerized with 2 as a macromolecular initiator and dicumyl peroxide (DCP) as an accelerator in chlorobenzene at 120 °C. The polymerization with the [ 3a ]/[ 2 ]/[DCP] ratio of 30/1/1.2 for 5 h afforded a product in a yield of 73%; it was followed by purification with preparative size exclusion chromatography to provide the ABA triblock copolymer containing the pendant acetyl glucose on both sides of the chain ends ( 4a ; M_n = 21,000, M_w/M_n = 1.16). Similarly, the polymerization of 4‐vinylbenzyl maltohexaoside peracetate produced the ABA triblock copolymer containing the pendant acetyl maltohexaose on both side of the chain end ( 4b ; M_n = 31,800, M_w/M_n = 1.11). Polymers 4a and 4b were modified by deacetylation into amphiphilic ABA triblock copolymers containing the pendant glucose and maltohexaose as hydrophilic segment, 5a and 5b , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3978–3985, 2006     

Amphiphilic ABA triblock copolymer as surfactant in syntheses of microlatexes bearing cationic groups

Polystyrene microlatexes have been prepared by conventional emulsion polymerization with a novel amphiphilic water‐soluble ABA triblock copolymer, poly[2‐(dimethylamino)ethyl methacrylate]₁₅‐b‐poly(propylene oxide)₃₆‐b‐poly[2‐(dimethyl‐amino)ethyl methacrylate]₁₅ (PDMAEMA₁₅‐PPO₃₆‐PDMAEMA₁₅), as a polycationic emulsifier under acidic or neutral conditions. The ABA triblock copolymer was developed by oxyanion‐initiated polymerization in our laboratory. In this study, it acted well both as a polycationic polymeric surfactant to form block copolymeric micelles for emulsion polymerization and as a stabilizer to be anchored into the polystyrene microlatex or adsorbed onto its surface. The results obtained with various copolymer concentrations and different pH media showed that microlatex diameters decreased remarkably with increased concentration of this ABA triblock copolymeric emulsifier, but were not as much affected by the pH of media within the experimental range of 3.4–7.0. The observed difference of the particle sizes from transmission electron microscopy and dynamic light scattering measurements is discussed in terms of the effect of the absorbed surfactants and their electrical double layers. This difference has led to the formation of a cationic polyelectrolyte fringe on the surface of microspheres. The final microlatexes were characterized with respect to total conversion, particle diameter, and particle size distribution as well as colloidal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3734–3742, 2002     

Polymerizabilities of Several Polar Vinyl Monomers by Imidazole

Polymerizabilities of several polar vinyl monomers in the presence of imidazole (Im) have been studied in CDC1₃ and CD₃OD by NMR spectra. Acrylic acid formed a bimolecular adduct with Im as the initial adduct, while methacrylic acid was not obtained, On the other hand, methyl acrylate, methyl methacrylate (MMA), acrylamide (AAm), and acrylonitrile formed the initial adduct between Im and monomer, respectively. In these monomers, AAm and MMA gave each polymer in tetrahydrofuranat room temperature. The number-average molecular weight ([Mbar]_n) of AAm polymers was determined to be in the range of 1000 to 1500, and the [Mbar]_n of MMA polymers was found to be in the range of 2500 to 4500, The rate of polymerization R_p was expressed by the equations R_p = k[Im][AAm] and R_p = k[Im] [MMA]², respectively. The activation energy E_R was obtained by Arrheniuss's plots as E_R(AAm) = 9.6 kcal/mol and E_R(MMA) = 3.8 kcal/mol. These polymerization mechanisms are discussed on the basis of these results.     

Multiblock poly(4‐vinylpyridine) and its copolymer prepared with cyclic trithiocarbonate as a reversible addition–fragmentation transfer agent

The polymerization of 4‐vinylpyridine was conducted in the presence of a cyclic trithiocarbonate (4,7‐diphenyl‐[1,3]dithiepane‐2‐thione) as a reversible addition–fragmentation transfer (RAFT) polymerization agent, and a multiblock polymer with narrow‐polydispersity blocks was prepared. Two kinds of multiblock copolymers of styrene and 4‐vinylpyridine, that is, (ABA)_n multi‐triblock copolymers with polystyrene or poly(4‐vinylpyridine) as the outer blocks, were prepared with multiblock polystyrene or poly(4‐vinylpyridine) as a macro‐RAFT agent, respectively. GPC data for the original polymers and polymers cleaved by amine demonstrated the successful synthesis of amphiphilic multiblock copolymers of styrene and 4‐vinylpyridine via two‐step polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2617–2623, 2007     

Sequential synthesis of multiblock copolymers by atom transfer radical and cationic polymerization

ABCBA‐type pentablock copolymers of methyl methacrylate (MMA), styrene (S), and isobutylene (IB) were prepared by a three‐step synthesis, which included atom transfer radical polymerization (ATRP) and cationic polymerization: (1) poly(methyl methacrylate) (PMMA) with terminal chlorine atoms was prepared by ATRP initiated with an aromatic difunctional initiator bearing two trichloromethyl groups under CuCl/2,2′‐bipyridine catalysis; (2) PMMA with the same catalyst was used for ATRP of styrene, which produced a poly(S‐b‐MMA‐b‐S) triblock copolymer; and (3) IB was polymerized cationically in the presence of the aforementioned triblock copolymer and BCl₃, and this produced a poly(IB‐b‐S‐b‐MMA‐b‐S‐b‐IB) pentablock copolymer. The reaction temperature, varied from ?78 to ?25 °C, significantly affected the IB content in the product; the highest was obtained at ?25 °C. The formation of a pentablock copolymer with a narrow molecular weight distribution provided direct evidence of the presence of active chlorine at the ends of the poly(S‐b‐MMA‐b‐S) triblock copolymer, capable of the initiation of the cationic polymerization of IB in the presence of BCl₃. A differential scanning calorimetry trace of the pentablock copolymer (20.1 mol % IB) showed the glass‐transition temperatures of three segregated domains, that is, polyisobutylene (?87.4 °C), polystyrene (95.6 °C), and PMMA (103.7 °C) blocks. One glass‐transition temperature (104.5 °C) was observed for the aforementioned triblock copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6098–6108, 2004     

Phase behavior of SEBS triblock copolymer gels

Dynamic density functional theory calculations were performed for thermoplastic elastomer gels composed of an ABA triblock copolymer immersed in a B‐attractive solvent. The triblock copolymer model was parameterized for poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS), while the solvent model was parameterized for the hydrocarbon oil tetradecane. The effect of the solvent concentration and S‐EB interaction on the morphology was investigated, where complementary experimental data was used to validate results at χ_ABN ≈ 100. Agreement was observed at solvent volume fractions of 0.2, 0.4, and 0.6, which correspond to the cylindrical, spherical, and spherical phases, respectively. Qualitative agreement was observed for 0.8 volume fraction solvent, where a core‐shell spherical micelle morphology was found. For a 50/50 vol % mixture of polymer/solvent, the effect of solvent molecular weight on the morphology was considered, where a transition between micro and macrophase separation was predicted at a critical solvent molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1479–1491, 2011     

Chain center‐functionalized amphiphilic block polymers: Complementary hydrogen bond self‐assembly in aqueous solution

Hydrogen bonding self‐assemblies were formed in an aqueous medium from a pair of an amphiphilic ABA triblock copolymer and a hydrophobic homopolymer, both with a triple hydrogen bonding site that was complementary to each other and precisely placed at the main‐chain center: (PEGMA)_m–(MMA)_n– ADA –(MMA)_n–(PEGMA)_m and (MMA)_p– DAD –(MMA)_p ( A = hydrogen acceptor; D = hydrogen donor; PEGMA: PEG methacrylate; MMA: methyl methacrylate). The polymers were synthesized by the ruthenium‐catalyzed living radial polymerization with bifunctional initiators (Br– ADA –Br and Cl– DAD –Cl) aiming at pinpoint chain center functionalization to give a symmetric segmental sequence; ADA and DAD initiators were derived from 2,6‐diaminopyridine and thymine, respectively. On mixed equimolar in tetrahydrofuran (THF), both polymers spontaneously associated, and the apparently 1:1 assembly further grew into higher aggregate particles on subsequent addition of water. The aggregates in water/THF were relatively stable and uniform in size, which most likely stems from the intermolecular complementary hydrogen bond interaction at polymer chain centers. In sharp contrast, an equimolar mixture of ADA ‐block polymer and DAD ‐free poly(MMA) in water/THF resulted in larger and irregular particles, and thus short‐lived to eventually collapse. These results indicate that, however structurally marginal, precise pinpoint functionalization of macromolecular chains allows stable self‐assemblies via complementary hydrogen bond interaction even in aqueous media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4498–4504     

RAFT‐mediated emulsion polymerization of styrene using brush copolymer as surfactant macro‐RAFT agent: Effect of the brush copolymer sequence and chemical composition

The nonionic amphiphilic brush polymers such as poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] and poly[poly(ethylene oxide) methyl ether vinylphenyl‐b‐styrene‐b‐poly(ethylene oxide) methyl ether vinylphenyl] trithiocarbonate [P(mPEGV‐b‐St‐b‐mPEGV)‐TTC] with different monomer sequence and chemical composition are synthesized and their application as macro‐RAFT agent in the emulsion RAFT polymerization of styrene is explored. It is found that the monomer sequence in the brush polymers exerts great influence on the emulsion RAFT polymerization kinetics, and the fast polymerization with short induction period in the presence of P(mPEGV‐co‐St)‐TTC is demonstrated. Besides, the chemical composition in the brush polymer macro‐RAFT agent effect on the emulsion RAFT polymerization is investigated, and the macro‐RAFT agent with high percent of the hydrophobic PS segment leads to fast and well controlled polymerization. The growth of triblock copolymer colloids in the emulsion polymerization is checked, and it reveals that the colloidal morphology is ascribed to the hydrophobic PS block extension, and the P(mPEGV‐co‐St) block almost have no influence just on the size of the colloids. This may be the first example to study the monomer sequence and the chemical composition in the macro‐RAFT agent on emulsion RAFT polymerization, and will be useful to reveal the block copolymer particle growth. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The micellization of the diblock copolymer of ethylene oxide and styrene in benzene and the effect on the preparation of the star ABC triblock copolymer of ethylene oxide, styrene and methyl methacrylate

In the preparation of the ABC star triblock copolymer of ethylene oxide, styrene and methyl methacrylate (MMA), the photo-induced charge-transfer complex (CTC) was used to initiate the polymerization of the third monomer MMA. The CTC was composed of the diblock copolymer of poly(ethylene oxide) (PEO) and polystyrene (PS), PEO-b _i -PS, with an aromatic imino group at the conjunction point and benzophenone (BP). It was confirmed that the kinetic behavior of this macromolecular initiation system is nearly the same with a general small radical initiator: the polymerization rate R _p ∝ [PEO-b _i -PS]^0.48[BP]^0.45[MMA]^0.97. Moreover, if the molecular weight of the PEO block is fixed, R _p is independent of the molecular weight of the PS block.  By means of measurements of viscosity and fluorescence, it was found that the micelles of the diblock copolymer PEO-b _i -PS were formed in benzene. The aromatic imino groups were located on the boundary surfaces of the micelles and were fully exposed, and so the BP and MMA molecules easily approached them and affected the charge-transfer polymerization of MMA. Received: 18 August 1998 Accepted in revised form: 25 November 1998     

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

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

Living Cationic Polymerization of α-Methylstyrene. 2. Synthesis of Block and Random Copolymers with 2-Chloroethyl Vinyl Ether and End-Functionauzed Polymers†

Abstract

Both AB and BA block copolymers of α-methylstyrene (αMeSt) and 2-chloroethyl vinyl ether (CEVE) were synthesized by the sequential living cationic polymerization initiated with the HCl-CEVE adduct (1a)/SnBr₄ system in CH₂Cl₂ at -78°C. αMeSt-CEVE (AB) block copolymers with narrow molecular weight distributions ([Mbar]_w/[Mbar]_n ～ 1.15) were obtained when αMeSt was polymerized first, followed by addition of CEVE to the resulting αMeSt living polymer solution. The reverse order of monomer addition, from CEVE to αMeSt, also led to a BA-type block copolymer. In the polymerization of a mixture of the two monomers, almost random copolymers were obtained. Living polymerizations of αMeSt were also induced with functional initiating systems, HCl-functionalized vinyl ether adducts (1b-1d)/SnBr₄, to give end-function-alized poly(αMeSt)s with a methacrylate, an acetate, or a phthalimide terminal.     

Thermoresponsive diblock copolymer micellar macro‐RAFT agent‐mediated dispersion RAFT polymerization and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles

The micellar macro‐RAFT agent‐mediated dispersion polymerization of styrene in the methanol/water mixture is performed and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles is investigated. The thermoresponsive diblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] trithiocarbonate forms micelles in the polymerization solvent at the polymerization temperature and, therefore, the dispersion RAFT polymerization undergoes as similarly as seeded dispersion polymerization with accelerated polymerization rate. With the progress of the RAFT polymerization, the molecular weight of the synthesized triblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine]‐b‐polystyrene linearly increases with the monomer conversion, and the PDI values of the triblock copolymers are below 1.2. The dispersion RAFT polymerization affords the in situ synthesis of the triblock copolymer nanoparticles, and the mean diameter of the triblock copolymer nanoparticles increases with the polymerization degree of the polystyrene block. The triblock copolymer nanoparticles contain a central thermoresponsive poly [N‐(4‐vinylbenzyl)‐N,N‐diethylamine] block, and the soluble‐to‐insoluble ‐‐transition temperature is dependent on the methanol content in the methanol/water mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2155–2165     

Synthesis of star‐shaped copolymers with methyl methacrylate and n‐butyl methacrylate by metal‐catalyzed living radical polymerization: Block and random copolymer arms and microgel cores

Various star‐shaped copolymers of methyl methacrylate (MMA) and n‐butyl methacrylate (nBMA) were synthesized in one pot with RuCl₂(PPh₃)₃‐catalyzed living radical polymerization and subsequent polymer linking reactions with divinyl compounds. Sequential living radical polymerization of nBMA and MMA in that order and vice versa, followed by linking reactions of the living block copolymers with appropriate divinyl compounds, afforded star block copolymers consisting of AB‐ or BA‐type block copolymer arms with controlled lengths and comonomer compositions in high yields (≥90%). The lengths and compositions of each unit varied with the amount of each monomer feed. Star copolymers with random copolymer arms were prepared by the living radical random copolymerization of MMA and nBMA followed by linking reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 633–641, 2002; DOI 10.1002/pola.10145     

Well‐defined phosphonate‐functional copolymers through RAFT copolymerization of dimethyl‐p‐vinylbenzylphosphonate

Dibenzyltrithiocarbonate‐mediated RAFT polymerization of dimethyl‐p‐vinylbenzylphosphonate and its copolymerization with styrene are studied in order to access well‐defined statistical and block copolymers containing controlled amounts of dimethylphosphonate groups. NMR and SEC analysis of the (co)polymers confirm the controlled character of the polymerizations. ABA triblock copolymers are treated with TMSiBr/MeOH in order to transform the dimethylphosphonate groups into phosphonic acids while keeping the midchain trithiocarbonate group and triblock nature unaffected. Alternatively, the combination of trithiocarbonate aminolysis with TMSiBr/MeOH treatment of the same triblock copolymers leads to phosphonic acid‐functional diblock copolymer counterparts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2616‐2624     

Photoreversible Gelation of a Triblock Copolymer in an Ionic Liquid

The reversible micellization and sol–gel transition of block copolymer solutions in an ionic liquid (IL) triggered by a photostimulus is described. The ABA triblock copolymer employed, denoted P(AzoMA‐r‐NIPAm)‐b‐PEO‐b‐P(AzoMA‐r‐NIPAm)), has a B block composed of an IL‐soluble poly(ethylene oxide) (PEO). The A block consists of a random copolymer including thermosensitive N‐isopropylacrylamide (NIPAm) units and a methacrylate with an azobenzene chromophore in the side chain (AzoMA). A phototriggered reversible unimer‐to‐micelle transition of a dilute ABA triblock copolymer (1 wt %) was observed in an IL, 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim]PF₆), at an intermediate “bistable” temperature (50 °C). The system underwent a reversible sol–gel transition cycle at the bistable temperature (53 °C), with reversible association/fragmentation of the polymer network resulting from the phototriggered self‐assembly of the ABA triblock copolymer (20 wt %) in [C₄mim]PF₆.     

Curcumin,A Novel Natural Photoinitiator for the Copolymerization of Styrene and Methylmethacrylate

Curcumin (Cur), a natural colorant found in the roots of the Turmeric plant, has been reported for the first time as photoinitiator for the copolymerization of styrene (Sty) and methylmethacrylate (MMA). The kinetic data, inhibiting effect of benzoquinone and ESR studies indicate that the polymerization proceeds via a free radical mechanism. The system follows ideal kinetics (R_p α[Cur]^0.5[Sty]^0.97[MMA]¹). The reactivity ratios calculated by using the Finemann–Ross and Kelen‐Tudos models were r₁(MMA)=0.46 and r₂(Sty)=0.52. IR and NMR analysis confirmed the structure of the copolymer. NMR spectrum showing methoxy protons as three distinct groups of resonance between 2.2–3.75 δ and phenyl protons of styrene at 6.8–7.1 δ confirmed the random nature of the copolymer. The mechanism for formation of radicals and random copolymer of styrene and MMA [Sty‐co‐MMA] is also discussed.     

Synthesis of poly(n‐butyl acrylate) homopolymer and poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) triblock copolymer via AGET emulsion ATRP using a cationic surfactant

Cationic emulsions of triblock copolymer particles comprising a poly(n‐butyl acrylate) (PⁿBA) central block and polystyrene (PS) outer blocks were synthesized by activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP). Difunctional ATRP initiator, ethylene bis(2‐bromoisobutyrate) (EBBiB), was used as initiator to synthesize the ABA type poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) (PS‐PⁿBA‐PS) triblock copolymer. The effects of ligand and cationic surfactant on polymerizations were also discussed. Gel permeation chromatography (GPC) was used to characterize the molecular weight (M_n) and molecular weight distribution (MWD) of the resultant triblock copolymers. Particle size and particle size distribution of resulted latexes were characterized by dynamic light scattering (DLS). The resultant latexes showed good colloidal stability with average particle size around 100–300 nm in diameter. Glass transition temperature (T_g) of copolymers was studied by differential scanning calorimetry (DSC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 611–620     

Facile synthesis of dumbbell‐shaped dendritic‐linear‐dendritic triblock copolymer via reversible addition‐fragmentation chain transfer polymerization

We report the first instance of facile synthesis of dumbbell‐shaped dendritic‐linear‐dendritic triblock copolymer, [G‐3]‐PNIPAM‐[G‐3], consisting of third generation poly(benzyl ether) monodendrons ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM), via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The key step was the preparation of novel [G‐3]‐based RAFT agent, [G‐3]‐CH₂SCSSCH₂‐[G‐3] (1), from third‐generation dendritic poly(benzyl ether) bromide, [G‐3]‐CH₂Br. Due to the bulky nature of [G‐3]‐CH₂Br, its transformation into trithiocarbonate 1 cannot go to completion, a mixture containing ～80 mol % of 1 and 20 mol % [G‐3]‐CH₂Br was obtained. Dumbbell‐shaped [G‐3]‐PNIPAM₃₁₀‐[G‐3] triblock copolymer was then successfully obtained by the RAFT polymerization of N‐isopropylacylamide (NIPAM) using 1 as the mediating agent, and trace amount of unreacted [G‐3]‐CH₂Br was conveniently removed during purification by precipitating the polymer into diethyl ether. The dendritic‐linear‐dendritic triblock structure was further confirmed by aminolysis, and fully characterized by gel permeation chromatography (GPC) and ¹H‐NMR. The amphiphilic dumbbell‐shaped triblock copolymer contains a thermoresponsive PNIPAM middle block, in aqueous solution it self‐assembles into spherical nanoparticles with the core consisting of hydrophobic [G‐3] dendritic block and stabilized by the PNIPAM central block, forming loops surrounding the insoluble core. The micellar properties of [G‐3]‐PNIPAM₃₁₀‐[G‐3] were then fully characterized. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1432–1445, 2007