Synthesis,characterization, and property of amphiphilic fluorinated abc‐type triblock copolymers

Novel amphiphilic fluorinated ABC‐type triblock copolymers composed of hydrophilic poly(ethylene oxide) monomethyl ether (MeOPEO), hydrophobic polystyrene (PSt), and hydrophobic/lipophobic poly(perfluorohexylethyl acrylate) (PFHEA) were synthesized by atom transfer radical polymerization (ATRP) using N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA)/CuBr as a catalyst system. The bromide‐terminated diblock copolymers poly(ethylene oxide)‐block‐polystyrene (MeOPEO‐b‐PSt‐Br) were prepared by the ATRP of styrene initiated with the macroinitiator MeOPEO‐Br, which was obtained by the esterification of poly(ethylene oxide) monomethyl ether (MeOPEO) with 2‐bromoisobutyryl bromide. A fluorinated block of poly(perfluorohexylethyl acrylate) (PFHEA) was then introduced into the diblock copolymer by a second ATRP process to synthesize a novel ABC‐type triblock copolymer, poly(ethylene oxide)‐block‐polystyrene‐block‐poly(perfluorohexylethyl acrylate) (MeOPEO‐b‐PSt‐b‐PFHEA). These block copolymers were characterized by means of proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). Water contact angle measurements revealed that the polymeric coating of the triblock copolymer (MeOPEO‐b‐PSt‐b‐PFHEA) shows more hydrophobic than that of the corresponding diblock copolymer (MeOPEO‐b‐PSt). Bovine serum albumin (BSA) was used as a model protein to evaluate the protein adsorption property and the triblock copolymer coating posseses excellent protein‐resistant character prior to the corresponding diblock copolymer and polydimethylsiloxane. These amphiphilic fluoropolymers can expect to have potential applications for antifouling coatings and antifouling membranes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Direct synthesis of amphiphilic block copolymers, consisting of poly(methyl methacrylate) and poly(sodium styrene sulfonate) blocks through atom transfer radical polymerization

Amphiphilic block copolymers of methyl methacrylate (MMA) and sodium styrene sulfonate (SSNa) were successfully synthesized via direct atom transfer radical polymerization (ATRP) of SSNa. First, poly(sodium styrene sulfonate) (PSSNa) or poly(methyl methacrylate) (PMMA) macroinitiators were prepared using proper ATRP systems for each case. In some cases, functional initiators, which allow further reactions, were used. The macroinitiators were characterized and further used to synthesize PSSNa/PMMA block copolymers, by using proper solvent combinations, such as N,N-dimethylformamide/water or methanol/water at appropriate volume ratios, in order to ensure solubility of the synthesized amphiphilic copolymers. The molecular weight of the copolymers was determined by gel permeation chromatography, using water as eluent. By using a combination of analytical techniques like ¹H NMR, FTIR and thermogravimetry, the chemical structure and the actual copolymer composition were determined. Since, the block copolymers were soluble in water, forming hydrophilic/hydrophobic domains in aqueous solution, their micellization behavior was further studied by pyrene fluorescence probing.     

Synthesis and characterization of side‐chain liquid crystalline ABC triblock copolymers with p‐methoxyazobenzene moieties by atom transfer radical polymerization

A series of novel side‐chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine‐terminated diblock copolymer poly(ethylene oxide)‐block‐polystyrene (PEO‐PS‐Br) was prepared by the ATRP of styrene initiated with the macro‐initiator PEO‐Br, which was obtained from the esterification of PEO and 2‐bromo‐2‐methylpropionyl bromide. An azobenzene‐containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side‐chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)‐block‐polystyrene‐block‐poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PEO‐PS‐PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008     

Synthesis of a New Macroperoxy Initiator with Methyl Methacrylate and T-Butyl Peroxy Ester by Atom Transfer Radical Polymerization and Copolymerization with Conventional Vinyl Monomers

In this study, we present the synthesis of poly-MMA macroperoxy initiators obtained by the ATRP of MMA with bromo methyl benzyl t-butyl peroxy ester (t-BuBP) as an initiator, and CuX (X:Br or Cl)/2,2′-bipyridine (bpy) as a catalyst system at 0, 20, 30 and 40°C. The peroxygen groups do not decompose during the ATRP reaction, because low reaction temperatures used for the ATRP reaction are not enough to decompose them. The peroxygen groups of poly-PMMA macroperoxy initiators can lead them to react with a monomer by using appropriate reaction conditions to obtain the block or graft copolymers. For this purpose, poly-MMA macroperoxy initiators were used to synthesize poly(MMA-b-S) block copolymers with S and used for graft copolymerization of polybutadiene (PBd) and natural rubber (RSS-3) to obtain crosslinked poly(MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values of the crosslinked graft copolymers in CHCl₃ were calculated. The characterizations of the polymers were achieved by FT-IR, ¹H-NMR, GPC, DSC, SEM, and the fractional precipitation (γ) techniques. The reaction schemes were also performed using the HYPERCHEM 7.5 program. The mechanical properties of the products were investigated.     

Amphiphilic Seven-arm Star Triblock Copolymers with Diverse Morphologies in Aqueous Solution Induced by Crystallization and pH

Well-defined amphiphilic seven-arm star triblock copolymers containing hydrophobic crystalline poly(ε-caprolactone)(PCL) blocks, hydrophobic non-crystalline poly(tert-butyl acrylate)(PtBA) blocks and hydrophilic poly(ethylene glycol)(PEG) blocks were precisely synthesized by a combination of ring-opening polymerization(ROP), atom transfer radical polymerization(ATRP) and “click” reaction. Such star copolymers could self-assemble into “core-shell-corona” micelles and “multi-layer” vesicles depending on the fraction of each block. Meanwhile, the selective hydrolysis of middle PtBA blocks into the poly(acrylic acid)(PAA) blocks allowed the star block copolymers to further change their morphologies of aqueous aggregates in response to pH values.     

Synthesis of stimulus-responsive block copolymer gelators by atom transfer radical polymerisation

The synthesis of new stimulus-responsive block copolymer gelators using atom transfer radical polymerisation (ATRP) in either methanol or 2-propanol/water mixtures at 20 °C is described. Bifunctional and trifunctional initiators were used to prepare ABA triblock and I(BA)₃ three-arm star diblock copolymers, respectively, using a ‘one-pot’ ATRP protocol, in which the central block comprised poly(glycerol monomethacrylate) and the outer blocks comprised pH-responsive poly[2-(diethylamino)ethyl methacrylate] or poly[2-(diisopropylamino)ethyl methacrylate]. These copolymers dissolve molecularly in acidic solution but formed free-standing gels at around neutral pH on addition of base. Gel strength was judged by both tube inversion experiments and shear rheometry measurements and a comparison between the linear and star architectures was made.     

Synthesis of Poly(methyl methacrylate)-poly(poly(ethylene glycol) methacrylate)-polyisobutylene ABCBA Pentablock Copolymers by Combining Quasiliving Carbocationic and Atom Transfer Radical Polymerizations and Characterization Thereof

Novel, unique amphiphilic pentablock terpolymers consisting of the highly hydrophobic polyisobutylene (PIB) mid-segment attached to the hydrophilic combshaped poly(poly(ethylene glycol) methacrylate) (PPEGMA) polymacromonomer chains, which are coupled to poly(methyl methacrylate) (PMMA) outer segments were synthesized by the combination of quasiliving carbocationic polymerization and atom transfer radical polymerization (ATRP). First, a bifunctional PIB macroinitiator was prepared by quasiliving carbocationic polymerization and subsequent quantitative chain end derivatizations. Quasiliving ATRP of PEGMAs with different molecular weights (M_n = 188, 300 and 475 g/mol) led to triblock copolymers which were further reacted with MMA under ATRP conditions to obtain PMMA-PPEGMA-PIB-PPEGMA-PMMA ABCBA-type pentablock copolymers. It was found that slow initiation takes place between the PIB macroinitiator and PEGMA macromonomers with higher molecular weights via ATRP. ATRP of MMA with the resulting block copolymers composed of PIB and PPEGMA chain segments led to the desired block copolymers with high initiating efficiency. Investigations of the resulting pentablock copolymers by DSC, SAXS and phase mode AFM revealed that nanophase separation occurs in these new macromolecular structures with average domain distances of 11-14 nm, and local lamellar self-assembly takes place in the pentablocks with PPEGMA polymacromonomer segments of PEGMAs with M_n of 118 g/mol and 300 g/mol, while disordered nanophases are observed in the block copolymer with PEGMA having molecular weight of 475 g/mol. These new amphiphilic block copolymers composed of biocompatible chain segments can find applications in a variety of advanced fields.     

Synthesis and characterization of a new fluorinated macroinitiator and its diblock copolymer by AGET ATRP

A new fluorinated macroinitiator of poly 2,2,3,4,4,4-hexafluorobutyl methacrylate-Br (PHFMA-Br) was prepared via activator generated by electron transfer atom transfer radical polymerization (AGET ATRP), and then a series of fluorinated block copolymers with different fluorine content were successfully synthesized from the macroinitiator by the second step AGET ATRP. GPC, FTIR and ¹H NMR data obtained verified the synthesis. Contact angle measurement indicated that proper fluorine content could decrease the surface energy and increase the contact angle of the copolymer films. XPS characterization showed that the large difference in surface energy between the block and random copolymer film resulted from the difference of the fluorine content on the surface, although the fluorine content of the two copolymers in bulk was similar. The self-assembly behavior of the fluorinated block copolymer in selective solvents was evaluated by the TEM study, and the stable micelles with a core-shell structure were observed when the copolymer content was about 1 wt%.     

Synthesis of telechelics and block copolymers via “living” radical polymerization

Hydroxy‐telechelic poly(methyl methacrylate)s of molecular weights below 5000 were obtained by atom transfer radical polymerization (ATRP) of methyl methacrylate followed by end‐capping with allyl alcohol via atom transfer radical addition (ATRA). As initiators for the ATRP, monofunctional initiators with an additional hydroxy group in the molecule or bifunctional initiators were employed. The successful synthesis of the hydroxy‐telechelic PMMA was proved by determination of their molecular weight using MALDI‐TOF‐MS. The efficiency of the end‐capping reaction was determined by ¹H NMR spectroscopy using the allyl N‐(4‐tolyl)carbamate as end‐capping agent. Block copolymers comprising a poly(ethylene oxide) (PEO) block and a poly(methyl methacrylate) (PMMA) block were prepared by ATRP using a macroinitiator on the PEO basis. The dormant species of the macroinitiator consists of the phenyl chloroacetate moiety which shows a high rate of initiation. The successful synthesis of the poly(ethylene oxide)‐block‐poly(methyl methacrylate) was proved by ¹H NMR spectroscopy; the ratios of EO/MMA repeating units in the feed and the copolymer were nearly equal.     

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with ¹H and ¹³C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K_v for pyrene in the micelle and in aqueous solution was about 10⁵. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R_h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.     

ABA triblock copolymers from two mechanistic techniques: Polycondensation and atom transfer radical polymerization

ABA triblock copolymers were synthesized using two polymerization techniques, polycondensation, and atom transfer radical polymerization (ATRP). A telechelic polymer was synthesized via polycondensation, which was then functionalized into a difunctional ATRP initiator. Under ATRP conditions, outer blocks were polymerized to form the ABA triblock copolymer. Six types of samples were prepared based on a poly(ether ether ketone) or poly(arylene ether sulfone) center block with either poly(methyl methacrylate), poly(pentafluorostyrene), or poly(ionic liquid) outer blocks. As polycondensation results in polymers with broad molecular weight distribution (MWD), the center of these triblock copolymers are disperse, while the outside blocks have narrow MWD due to the control afforded from ATRP. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 228–238     

New Linear and Star‐Shaped Thermogelling Poly([R]‐3‐hydroxybutyrate) Copolymers

The synthesis of multi‐arm poly([R]‐3‐hydroxybutyrate) (PHB)‐based triblock copolymers (poly([R]‐3‐hydroxybutyrate)‐b‐poly(N‐isopropylacrylamide)‐b‐[[poly(methyl ether methacrylate)‐g‐poly(ethylene glycol)]‐co‐[poly(methacrylate)‐g‐poly(propylene glycol)]], PHB‐b‐PNIPAAM‐b‐(PPEGMEMA‐co‐PPPGMA), and their subsequent self‐assembly into thermo‐responsive hydrogels is described. Atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide (NIPAAM) followed by poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(propylene glycol) methacrylate (PPGMA) was achieved from bromoesterified multi‐arm PHB macroinitiators. The composition of the resulting copolymers was investigated by ¹H and ¹³C J‐MOD NMR spectroscopy as well as size‐exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The copolymers featuring different architectures and distinct hydrophilic/hydrophobic contents were found to self‐assemble into thermo‐responsive gels in aqueous solution. Rheological studies indicated that the linear one‐arm PHB‐based copolymer tend to form a micellar solution, whereas the two‐ and four‐arm PHB‐based copolymers afforded gels with enhanced mechanical properties and solid‐like behavior. These investigations are the first to correlate the gelation properties to the arm number of a PHB‐based copolymer. All copolymers revealed a double thermo‐responsive behavior due to the NIPAAM and PPGMA blocks, thus allowing first the copolymer self‐assembly at room temperature, and then the delivery of a drug at body temperature (37 °C). The non‐significant toxic response of the gels, as assessed by the cell viability of the CCD‐112CoN human fibroblast cell line with different concentrations of the triblock copolymers ranging from 0.03 to 1 mg mL^?1, suggest that these PHB‐based thermo‐responsive gels are promising candidate biomaterials for drug‐delivery applications.     

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     

三嵌段共聚物PS-PHB-PS的原子转移自由基聚合

为了克服聚β-羟基丁酸酯(PHB)的弱点, 得到性能良好的新材料, 本文利用原子转移自由基聚合方法, 以Br-PHB-Br为大分子引发剂, 苯乙烯为单体, 在CuBr/N,N,N′,N″,N″-五甲基–二乙基三胺(PMDETA)催化体系作用下合成了一种新的三嵌段共聚物聚苯乙烯-聚β-羟基丁酸酯-聚苯乙烯(PS-PHB-PS). 共聚物的链结构利用¹H NMR和¹³C NMR进行了表征, 分子量特性和链段组成利用凝胶渗透色谱(SEC)方法进行了测定. 聚合物的分子量随单体转化率的增加而线性增加, 分子量分布指数相对较窄. 这些特征都满足原子转移自由基活性聚合的理想要求. 所得到的共聚物PS-PHB-PS具有较好的生物相容性, 与PHB相比具有良好的耐热性.     

Preparation and characterization of biodegradable nanoparticles based on amphiphilic poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) triblock copolymer

Amphiphilic triblock copolymers of poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) (PHB-PEG-PHB) were directly synthesized by the ring-opening copolymerization of β-butyrolactone monomer using PEG as macroinitiator. Their structure, thermal properties and crystallization were investigated by ¹H NMR, differential scanning calorimetry (DSC) and X-ray diffraction. It was found that both PHB and PEG blocks were miscible. With the increase in the PHB block length, the triblock copolymers became amorphous because amorphous PHB block remarkably depressed the crystallization of the PEG block. Biodegradable nanoparticles with core-shell structure were prepared in aqueous solution from the amphiphilic triblock copolymers, and characterized by ¹H NMR, SEM and fluorescence. The hydrophobic PHB segments formed the central solid-like core, and stabilized by the hydrophilic PEG block. The nanoparticle size was close related to the initial concentrations of the nanoparticle dispersions and the compositions of the triblock copolymers. Moreover, the PHB-PEG-PHB nanoparticles also showed good drug loading properties, which suggested that they were very suitable as delivery vehicles for hydrophobic drugs.     

Diblock and triblock functional copolymers by controlled radical polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6‐tetramethylpiperidinyl‐1‐oxy). The polystyrene homopolymers served as initiators for the block copolymerization of phthalimide methylstyrene (PIMS) to synthesize polystyrene‐b‐poly(PIMS) diblock copolymers. Diblock copolymers with well defined structures as well as controlled and narrow molar mass distribution were obtained from the lower‐mass polystyrene homopolymers. The lower‐mass copolymers were found to be active as initiators in the synthesis of the polystyrene‐b‐poly(PIMS)‐b‐polystyrene triblock copolymers. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The diblock and triblock copolymers were modified using hydrazine as the reagent in order to obtain the corresponding functional amino block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1237–1244, 1999     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.     

Synthesis of well-defined ABC triblock copolymers with polypeptide segments by ATRP and click reactions

Well-defined ABC block copolymers consisting of poly(ethylene oxide) monomethylene ether (MPEO) as A block, poly(styrene) (PS) as B block and poly(γ-benzyl-l-glutamate) (PBLG) as C block were synthesized by the combination of atom transfer radical polymerization (ATRP) and click reactions. The bromine-terminated diblock copolymer poly(ethylene oxide) monomethylene ether-block-poly(styrene) (MPEO-PS-Br) was prepared by ATRP of styrene initiated with macro-initiator MPEO-Br, which was prepared from the esterification of MPEO and 2-bromoisobutyryl bromide, and converted into the azido-terminated diblock copolymer MPEO-PS-N₃ by simple nucleophilic substitutions in DMF in the presence of sodium azide. Propargyl-terminated PBLGs were synthesized by ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride in DMF at room temperature using propargyl amine as an initiator. ABC triblock copolymers MPEO-PS-PBLG with a wide range of number-average molecular weights from 1.55 to 3.75 × 10⁴ and a narrow polydispersity from 1.07 to 1.10 were synthesized via the click reaction of MPEO-PS-N₃ and the propargyl-terminated PBLG in the presence of CuBr and 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. The structures of these ABC block copolymers and corresponding precursors were characterized by NMR, IR and GPC. The results showed that click reaction was efficient. Therefore, a facile approach was offered to synthesize ABC triblock copolymers composed of crystallizable polymer MPEO, conventional vinylic polymer PS and rod-like α-helix polypeptide PBLG.     

ATRP of methyl methacrylate initiated with a bifunctional initiator bearing bromomethyl functional groups: Synthesis of the block and graft copolymers

This article reports the synthesis of the block and graft copolymers using peroxygen‐containing poly(methyl methacrylate) (poly‐MMA) as a macroinitiator that was prepared from the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in the presence of bis(4,4′‐bromomethyl benzoyl peroxide) (BBP). The effects of reaction temperatures on the ATRP system were studied in detail. Kinetic studies were carried out to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at 40 °C and free radical polymerization of styrene (S) at 80 °C. The plots of ln ([M_o]/[M_t]) versus reaction time are linear, corresponding to first‐order kinetics. Poly‐MMA initiators were used in the bulk polymerization of S to obtain poly (MMA‐b‐S) block copolymers. Poly‐MMA initiators containing undecomposed peroygen groups were used for the graft copolymerization of polybutadiene (PBd) and natural rubber (RSS‐3) to obtain crosslinked poly (MMA‐g‐PBd) and poly(MMA‐g‐RSS‐3) graft copolymers. Swelling ratio values (q_v) of the graft copolymers in CHCl₃ were calculated. The characterizations of the polymers were achieved by Fourier‐transform infrared spectroscopy (FTIR), ¹H‐nuclear magnetic resonance (¹H NMR), gel‐permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the fractional precipitation (γ) techniques. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1364–1373, 2010     

Synthesis,self-assembly,and pH-responsive drug release of PHMEMA-PEG-PHMEMA ABA triblock copolymers

Abstract

A series of tertiary amine containing PHMEMA-PEG-PHMEMA ABA triblock copolymers were synthesized by atom transfer radical polymerization (ATRP) using bromine-capped poly(ethylene glycol) (Br-PEG-Br) and 2-(hexamethyleneimino)ethyl methacrylate (HMEMA) as macro-initiator and monomers, respectively. The chemical structures and molecular weights of triblock copolymers were characterized by ¹H NMR and gel permeation chromatography (GPC). The self-assembly behaviors of copolymers in different pH conditions were studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Triblock copolymers self-assembled into micelles in water (pH 7.4) and the micelles disassembled at acidic pH (pH 5.0). Anticancer drug doxorubicin (DOX) was used as a drug model and physically encapsulated into polymeric micelles. The drug release of DOX-loaded polymeric micelles was pH-responsive; the drug-loaded micelles that had higher contents of tertiary amine in polymer pendant groups showed faster release speed. In addition, the drug-loaded micelles showed excellent inhibition efficacy against HeLa cells in vitro.