Synthesis of chiral micelles and nanoparticles from amino acid based monomers using RAFT polymerization

Homopolymers of ^tbutyl acrylate (P^tBuA) and a monosubstituted acrylamide (PAM) having an amino acid moiety in the side chain, N‐acryloyl‐(L )‐phenylalanine methyl ester 1 , have been synthesized by Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization. Diblock copolymers of these homopolymers were also synthesized by chain extending P^tBuA with monomer 1 and after modification, using simple acid deprotection chemistries of the acrylate block to afford a poly (acrylic acid) block, an optically active amphiphilic diblock copolymer was isolated. The optically active amphiphilic diblock copolymers, which contain chiral amino acid moieties within the hydrophobic segment, were then self‐assembled to afford spherical micelles which were subsequently crosslinked throughout the shell layer to afford robust chiral nanoparticles. The hydrodynamic diameters (D_h) of the block copolymer micelles and nanoparticles were measured by dynamic light scattering (DLS) and the dimensions of the nanoparticles were determined using tapping‐mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3690–3702, 2008     

The synthesis and self‐assembly of ABA amphiphilic block copolymers containing styrene and oligo(ethylene glycol) methyl ether methacrylate in dilute aqueous solutions: Elevated cloud point temperatures for thermoresponsive micelles

A series of ABA amphiphilic triblock copolymers possessing polystyrene (PS) central hydrophobic blocks, one group with “short” PS blocks (DP = 54–86) and one with “long” PS blocks (DP = 183–204) were synthesized by atom transfer radical polymerization. The outer hydrophilic blocks were various lengths of poly(oligoethylene glycol methyl ether) methacrylate, a comb‐like polymer. The critical aggregation concentrations were recorded for certain block copolymer samples and were found to be in the range circa 10⁻⁹ mol L⁻¹ for short PS blocks and circa 10⁻¹² mol L⁻¹ for long PS blocks. Dilute aqueous solutions were analyzed by transmission electron microscopy (TEM) and demonstrated that the short PS block copolymers formed spherical micelles and the long PS block copolymers formed predominantly spherical micelles with smaller proportions of cylindrical and Y‐branched cylindrical micelles. Dynamic light scattering analysis results agreed with the TEM observations demonstrating variations in micelle size with PS and POEGMA chain length: the hydrodynamic diameters (D_H) of the shorter PS block copolymer micelles increased with increasing POEGMA block lengths while maintaining similar PS micellar core diameters (D_C); in contrast the values of D_H and D_C for the longer PS block copolymer micelles decreased. Surface‐pressure isotherms were recorded for two of the samples and these indicated close packing of a short PS block copolymer at the air–water interface. The aggregate solutions were demonstrated to be stable over a 38‐day period with no change in aggregate size or noticeable precipitation. The cloud point temperatures of certain block copolymer aggregate solutions were measured and found to be in the range 76–93 °C; significantly these were ∼11 °C higher in temperature than those of POEGMA homopolymer samples with similar chain lengths. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7739–7756, 2008     

Mechanical properties of block copolymer vesicle and micelle modified epoxies

Block copolymers with and without reactive functionalities can improve fracture resistance in brittle epoxies even when added in relatively small amounts (<5 wt %). At certain compositions, amphiphilic block copolymers spontaneously self‐assemble into vesicles, spherical micelles, or wormlike micelles in thermoset resins, and these morphologies are retained with the full curing of the resins. The addition of such block copolymers leaves the glass‐transition temperature of these blends relatively unchanged, whereas the fracture resistance increases up to a factor of 3.5 for the vesicle‐modified blends. For epoxies modified with block copolymers self‐assembled into a spherical geometry (vesicles or spherical micelles), the fracture resistance scales with the ratio of the interparticle distance to the average vesicle (or spherical micelle) diameter (D_i/D_p) and increases as this quantity is reduced. Greater adhesion between the vesicle and epoxy resin improves the fracture resistance only at higher values of D_i/D_p, at which the materials are more brittle. Debonding and subsequent matrix plastic deformation are identified as the toughening mechanisms in these blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2444–2456, 2003     

Synthesis,micelle formation,and bulk properties of poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐polyhedral oligomeric silsesquioxane amphiphilic hybrid copolymers

The synthesis, micelle formation, and bulk properties of semifluorinated amphiphilic poly(ethylene glycol)‐b‐poly(pentafluorostyrene)‐g‐cubic polyhedral oligomeric silsesquioxane (PEG‐b‐PPFS‐g‐POSS) hybrid copolymers is reported. The synthesis of amphiphilic PEG‐b‐PPFS block copolymers are achieved using atom transfer radical polymerization (ATRP) at 100 °C in trifluorotoluene using modified poly(ethylene glycol) as a macroinitiator. Subsequently, a proportion of the reactive para‐F functionality on the pentafluorostyrene units was replaced with aminopropylisobutyl POSS through aromatic nucleophilic substitution reactions. The products were fully characterized by ¹H‐NMR and GPC. The products, PEG‐b‐PPFS and PEG‐b‐PPFS‐g‐POSS, were subsequently self‐assembled in aqueous solutions to form micellar structures. The critical micelle concentrations (cmc) were estimated using two different techniques: fluorescence spectroscopy and dynamic light scattering (DLS). The cmc was found to decrease concomitantly with the number of POSS particles grafted per copolymer chain. The hydrodynamic particle sizes (R_h) of the micelles, calculated from DLS data, increase as the number of POSS molecules grafted per copolymer chain increases. For example, R_h increased from ～60 nm for PEG‐b‐PPFS to ～80 nm for PEG‐b‐PPFS‐g‐POSS25 (25 is the average number of POSS particles grafted copolymer chain). Static light scattering (SLS) data confirm that the formation of larger micelles by higher POSS containing copolymers results from higher aggregation numbers (N_agg), caused by increased hydrophobicity. The R_g/R_h values, where R_g is the radius of gyration calculated from SLS data, are consistent with a spherical particle model having a core‐shell structure. Thermal characterization by differential scanning calorimetry (DSC) reveals that the grafted POSS acts as a plasticizer; the glass transition temperature (T_g) of the PPFS block in the copolymer decreases significantly with increasing POSS content. Finally, the rhombohedral crystal structure of POSS in PEG‐b‐PPFS‐g‐POSS was verified by wide angle X‐ray diffraction measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 152–163, 2010     

Using the reversible addition–fragmentation chain transfer process to synthesize core‐crosslinked micelles

Poly(2‐hydroxyethyl acrylate)–poly(n‐butyl acrylate) block copolymers were synthesized with the reversible addition–fragmentation chain transfer (RAFT) process. The block copolymers were synthesized successfully with either poly(2‐hydroxyethyl acrylate) or poly(n‐butyl acrylate) macro‐RAFT agents. The resulting block copolymers had narrow molecular weight distributions (polydispersity index = 1.3–1.4). Copolymer self‐aggregation in water yielded micelles, with the hydrodynamic diameter (D_h) values of the aggregates dependent on the length of both blocks according to D_h ～ N_BA^1.17N_HEA^0.57, where N_BA is the number of repeating units of n‐butyl acrylate and N_HEA is the number of repeating units of 2‐hydroxyethyl acrylate. The micelles were subsequently stabilized via chain extension of the block copolymer with a crosslinking agent. The successful chain extension in a micellar system was confirmed by an increase in the molecular weight, which was detected with membrane osmometry. The crosslinked particles showed noticeably different aggregation behavior in diverse solvent systems. The uncrosslinked micelles formed by the block copolymer (N_HEA = 260, N_BA = 75) displayed a definite critical micelle concentration at 5.4 × 10^?4 g L^?1 in aqueous solutions. However, upon crosslinking, the critical micelle concentration transition became obscure. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2177–2194, 2006     

Morphological switching of unimolecular micelles of ternary graft copolymers in different solvents

A series of ternary graft copolymers with poly(3‐azido‐2‐hydroxypropyl methacrylate) (P(GMA‐N₃)) as the main chain, end‐functionalized poly(ethylene glycol) methyl ether (MPEG), poly(t‐butyl acrylate) (PtBA), and poly(2‐cinnamoyloxyethyl methacrylate) (PCEMA) as the side‐chains, was synthesized via the combination of atom transfer radical polymerization (ATRP) and click chemistry. The formation of well‐defined ternary graft copolymers was confirmed by both size exclusion chromatography (SEC) and ¹H NMR spectroscopy The loose and worm‐like morphology of the ternary graft copolymer in a common solvent (N,N‐dimethylformamide) for both the backbone and the grafts was directly visualized via atomic force microscopy (AFM). The average height, width, and length of these solvated macromolecules were about 1.5, 17, and 45 nm, respectively. The ternary graft copolymers underwent self‐assembly in different selective solvents (dichloromethane, methanol, and water) and thus yielded unimolecular micelles (UMs) with different morphologies. The morphological transitions in response to variations in the selective solvents was investigated by AFM as well as/or transmission electron microscopy (TEM). Experimental results showed that the micellar morphology of the ternary graft copolymer changed from a pearl‐necklace to a worm‐like structure and then to a spherical structure when the selective solvent was respectively changed from CH₂Cl₂ to CH₃OH and then to H₂O. SEC characterization revealed that the compact globules formed in H₂O with PCEMA/PtBA as the hydrophobic core arose due to intramolecular folding. Thus, multicompartment UMs were generated. The volume ratio of the multicompartment UMs formed in H₂O was in close agreement with their molecular weight ratio. The hydrodynamic diameters (D_h) of the acquired multicompartment UMs and their polydispersity indices were characterized by dynamic light scattering. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1021–1030     

Concentration controlled multilevel self‐assembly of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) block copolymers investigated by AFM

Concentration dependent morphology of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) copolymer aggregates in aqueous system was investigated by atomic force microscopy (AFM). The AFM results show that, at a low concentration, 4 × 10^?5 g/mL, spherical micelles occur, and unmicellized molecules are not distributed homogeneously in the copolymer aqueous solution. Unequal outspread clusters composed of wormlike aggregates are formed at a moderate copolymer concentration, 4 × 10^?4 g/mL, those wormlike aggregates are orderly packed in the clusters. At a high concentration of 0.05 g/mL, the copolymer aqueous system is indeed a gel at room temperature, outspread clusters of wormlike aggregates join together to forma network structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1412–1418, 2008     

Self-assembly of amphiphilic ABC star triblock copolymers and their blends with AB diblock copolymers in solution: self-consistent field theory simulations

The self-assembled morphologies of amphiphilic ABC star triblock copolymers consisting of hydrophilic A blocks and hydrophobic B and C blocks and the blends with their counterpart linear AB diblock copolymers in solution are investigated by 2D real-space implementation of self-consistent field theory (SCFT) simulation. The star triblock copolymers self-assemble in solution to form various micellar structures from hamburger, to segmented wormlike, to toroidal segmented micelles, and finally to vesicles with simultaneously increasing hydrophobic lengths of blocks B and C. When the length of hydrophobic blocks B and C is asymmetric, specific bead-on-string worm micelles are found. Particularly, when the star ABC triblock copolymer is in a strong segregation regime and both B and C blocks are strongly hydrophobic, quite long segmented wormlike micelles are obtained, which had not been found in previously investigated diblock and linear ABC triblock copolymers solution. Additionally, raspberry micelles with beads dispersed on the core also occur in the strong segregation regime of bulk star ABC triblock copolymers. Furthermore, the aggregate morphology of ABC star triblock copolymers is strongly influenced by the addition of linear AB diblock copolymers. The most significant feature is that the long segmented worms will become shorter, to form hamburger micelles with the addition of AB diblock copolymers. These simulations are in good agreement with the experimental findings by Lodge's group.     

Amphiphilic block and statistical copolymers with pendant glucose residues: Controlled synthesis by living cationic polymerization and the effect of copolymer architecture on their properties

Amphiphilic block and statistical copolymers of vinyl ethers (VEs) with pendant glucose residues were synthesized by the living cationic polymerization of isobutyl VE (IBVE) and a VE carrying 1,2:5,6‐di‐O‐isopropylidene‐D ‐glucose (IpGlcVE), followed by deprotection. The block copolymer was prepared by a two‐stage sequential block copolymerization, whereas the statistical copolymer was obtained by the copolymerization of a mixture of the two monomers. The monomer reactivity ratios estimated with the statistical copolymerization were r₁ (IBVE) = 1.65 and r₂ (IpGlcVE) = 1.15. The obtained statistical copolymers were nearly uniform with the comonomer composition along the main chain. Both the block and statistical copolymers had narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ∼ 1.1). Gel permeation chromatography, static light scattering, and spin–lattice relaxation time measurements in a selective solvent revealed that the block copolymer formed multimolecular micelles, possibly with a hydrophobic poly(IBVE) core and a glucose‐carrying poly(VE) shell, whereas the statistical copolymer with nearly the same molecular weight and segment composition was molecularly dispersed in solution. The surface properties of the solvent‐cast films of the block and statistical copolymer were also investigated with the contact‐angle measurement. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 459–467, 2001     

Synthesis of maltopentaose‐conjugated surface‐active styrenic monomers and their micellar homopolymerization in water

Maltopentaose (Mal₅)‐conjugated surface‐active styrenic monomers 1a , 1b , and 1c are described, which contain hydrophobic spacers, such as C1, C5, and C7 alkylene chains, respectively. The glycomonomers 1a‐c were synthesized by the direct β‐N‐glycosyl reaction of styrene derivatives with aminoalkyl groups 4a‐c onto Mal₅ in dry methanol, followed by the N‐acetylation with acetic anhydride. The self‐assembling properties for the aqueous solutions of 1a‐c were characterized by surface tension measurements and light scattering experiments, providing the physicochemical parameters for the formed 1a‐c micelles including the critical micelle concentration, apparent hydrodynamic radius (R_h,app), and weight average aggregation number (N_agg). The transmission electron microscope observations revealed the most important result in this study that 1a produced loose spherical micelles with the number average diameter (d_n) of 26 nm, while both 1b and 1c formed worm‐like micelles with the polymerizable core and the Mal₅ shell, whose number average contour lengths (l_ns) were 130 nm and 68 nm, respectively. The radical homopolymerizations of 1a‐c in water provided a substantial result in this study that 1b and 1c , that is, the glycomonomers forming the worm‐like micelles, showed a very high homopolymerizability in water. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1671–1679     

Synthesis of core‐crosslinked carbosilane block copolymer micelles and their thermal transformation to silicon‐based ceramics nanoparticles

Carbosilane fine particles were synthesized by core‐crosslinking of carbosilane block copolymer micelles and they were pyrolytically transformed into silica nanoparticles. The carbosilane block copolymer, poly(1‐(3‐butenyl)‐1‐methylsilacyclobutane)‐block‐polystyrene, (polyBMSB‐b‐polySt), [(m, n) = (31, 16), (54, 30), and (75, 28)], was synthesized by anionic polymerization of BMSB and St, where m and n represent polymerization degrees of BMSB and St segments, respectively. The block copolymer formed micelles in N,N‐dimethylformamide (DMF). The hydrodynamic diameters (D_h) of the micelles evaluated by dynamic light scattering ranged from 40 to 158 nm depending on the copolymer molecular weight. The core of the micelle was cross‐linked by Pt‐catalyzed hydrosilation with 1,2‐bis(dimethylsilylethane). The D_h of the core‐cross‐linked micelles in THF ranged from 56 to 164 nm. These precursor particles were pyrolyzed at 850 °C under N₂ to give ceramic nanoparticles. The diameters of the spherical ceramic particles estimated by AFM ranged from 25 to 60 nm. X‐ray fluorescence analysis of the ceramic products revealed that it consisted of mainly SiO₂ rather than SiC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3778–3787, 2005     

The pH induced vesicle to micelle morphology transition of a THP‐protected polymer

A diblock copolymer consisting of tetrahydropyranyl acrylate (THPA) as a pH‐deprotectable block, and a permanently hydrophobic block, methyl acrylate, was synthesized by RAFT polymerization using a quaternary amine functionalized, hydrophilic, RAFT chain transfer agent. The polymer self‐assembled in water to form vesicles with D_h = 130 nm, as determined by DLS and cryogenic transmission electron microscopy. Acid catalyzed deprotection of the THPA units to yield acrylic acid resulted in a vesicle to micelle morphology transition, as evidenced by the decrease in hydrodynamic diameter to D_h = 19 nm and the observation of micelles by dry state transmission electron microscopy. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3026–3031     

Preparation of poly(aryleneethynylene)–type copolymers containing flexible linking methylene units. Optical properties of the copolymers suggesting occurrence of energy transfer between π–conjugated local units

Palladium–catalyzed polycondensation between 2,5–diiodo–3–hexylthiophene I–Th(Hex)–I with mixtures of p–diethynylbenzene HCC—Ph—CCH and α,ω–diethynylalkane HCC(CH₂)_lCCH (l = 3 or 8) gives poly(aryleneethynylene) PAE–type copolymers [CC(CH₂)_lCC—Th(Hex)]_m[CC—Ph—CC—Th(Hex)]_n containing the methylene unit. The copolymers have a molecular weight (M_n) of about 1.2 × 10⁴ as determined by GPC (polystyrene standard) and are considered to possess essentially a random sequences in view of the —CC(CH₂)_lCC— and —CC—Ph—CC— units as judged from their UV–visible spectra. By the incorporation of the (CH₂)_l unit, the λ_max position of the corresponding PAE homopolymer [CC—Ph—CC—Th(Hex)]_n is shifted to a shorter wavelength. However, the copolymers give rise to a photoluminescence PL peak essentially agreeing with a PL peak of the homopolymer, suggesting occurrence of energy transfer in the copolymer. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2201–2207, 1998     

Supramolecular complexes of poly(3‐Hexylthiophene)‐block (and random)‐poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] copolymers with perylene bisimide

Block and random copolymers of poly(3‐hexylthiophene) and poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] with side‐chain carboxylic functionality ((P3HT‐b‐P3COOH) and (P3HT‐r‐P3COOH) were developed by Grignard Metathesis (GRIM) polymerization. The carboxylic functionality was introduced in the side chain via the oxazoline route. Both the block and random polythiophene copolymers were complexed with pyridine functionalized perylene bisimide to obtain supramolecular block and random polymer complexes. The complex formation in both systems was confirmed by ¹H NMR, WXRD and SAXS studies. An expansion of d spacing upon complex formation was observed in both the block and random copolymer, which could be traced by WXRD. Hole and electron mobilities measured for the supramolecular complexes indicated values which were higher by an order of magnitude for the supramolecular block complex (μ_h ≈ 2.9 × 10⁻⁴ cm²/Vs; μ_e ≈ 3.1 × 10⁻⁶ cm²/Vs) as compared to the random (μ_h ≈ 1.4 × 10⁻⁵ cm²/Vs; μ_e ≈ 4.7 × 10⁻⁷ cm²/Vs) copolymer. These results are indicative of the higher degree of disorder prevailing in the films of random copolymer system compared to the block copolymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1574–1583     

Construction of temperature responsive hybrid crosslinked self‐assemblies based on PEG‐b‐P(MMA‐co‐MPMA)‐b‐PNIPAAm triblock copolymer: ATRP synthesis and thermoinduced association behavior

A novel amphiphilic thermosensitive poly(ethylene glycol)₄₅‐b‐poly(methyl methacrylate₄₆‐co‐3‐(trimethoxysilyl)propyl methacrylate)₂‐b‐poly(N‐isopropylacrylamide)₄₂₉ (PEG₄₅‐b‐P(MMA₄₆‐co‐MPMA₂)‐b‐PNIPAAm₄₂₉) triblock copolymer was synthesized via consecutive atom transfer radical polymerization techniques. The thermoinduced association behavior of the resulting triblock copolymers in aqueous medium was further investigated in detail by ¹H NMR, transmission electron microscopy, and dynamic light scattering. The results showed that at the temperature (25 °C) below the LCST, PEG₄₅‐b‐P(MMA₄₆‐co‐MPMA₂)‐b‐PNIPAAm₄₂₉ triblock copolymers self‐assembled into the core crosslinked micelles with the hydrophobic P(MMA‐co‐MPMA) block constructing a dense core, protected by the mixed soluble PEG and PNIPAAm chains acting as a hydrophilic shell simultaneously. With an increase in temperature, the resulting core‐shell micelles converted into a new type of micelles with the hydrophilic PEG chains stretching out from the hydrophobic core through the collapsed PNIPAAm shell. On the other hand, at the temperature (40 °C) above the LCST, such triblock copolymers formed the crosslinked vesicles with the hydrophobic PNIPAAm and P(MMA‐co‐MPMA) blocks constructing a membrane core and the soluble PEG chains building the hydrophilic lumen and the shell. On further decreasing the temperature, the resulting vesicles underwent transformation from the shrunken to the expanded status, leading to the formation of swollen vesicles with enlarged size. This study is believed to present the first formation of two types of hybrid crosslinked self‐assemblies by thermoinduced regulation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Electric field manipulation of charged copolymer worm micelles

Manipulation of diblock copolymer worm micelles by external electric fields is visualized by fluorescence microscopy in dilute, aqueous solution. Hydrodynamic coupling of the poly(acrylic acid)-(1,4)-polybutadiene (PAA-PBD) worm motion to the electric field and the effective stiffening of the worms in an oscillating electric field are demonstrated. A brief discussion on using this technique to estimate the rheological properties of wormlike micelles is presented.     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

Flexibility transitions and looped adsorption of wormlike chains

When deposited from a solution onto a surface, superpolymeric chains display revealing transitions in their apparent stiffness. With simulated chains in adsorption, we varied the backbone rigidity and measured the chain persistence length (l_Pads). As the three‐dimensional persistence length (l_P3) increases toward the contour length, a transition can be seen from l_Pads = l_P2 (i.e., the two‐dimensional persistence length) to l_Pads = l_P3. Looped conformations decrease in frequency with a distinct nonlinear dependence. Finally, comparisons with experiments on polymeric worm micelles and purified neurofilaments demonstrate a simple new method for assessing the flexibility of these novel superpolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 280–286, 2005     

Synthesis of amphiphilic block copolymers bearing stable nitroxyl radicals

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG‐b‐PTAm and a triblock copolymer MPEG‐b‐PLA‐b‐PTAm, which can self‐assemble into micelles with nitroxyl radicals‐containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010