Thermoresponsive core-shell-corona micelles of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene

Core-shell-corona micelles with a thermoresponsive shell self-assembled by triblock copolymer of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene (PEG₄₅-b-PNIPAM₁₆₈-b-PS₄₆) are studied by ¹H NMR, light scattering and atomic force microscopy. The thermoresponsive triblock copolymer, which has a relatively short hydrophobic PS block, can disperse in water at room temperature to form core-shell-corona micelles with the hydrophobic PS block as core, the thermoresponsive PNIPAM block as shell and the hydrophilic PEG block as corona. At temperature above lower critical solution temperature (LCST) of the PNIPAM block, the PNIPAM chains gradually collapse on the PS core to shrink the size and change the structure of the resultant core-shell-corona micelles with temperature increasing. It is found that there possibly exists an interface between the PNIPAM shell and PEG corona of the core-shell-corona micelles at temperature above LCST of the PNIPAM block.     

Amphiphilic cylindrical brushes with poly(acrylic acid) core and poly(n-butyl acrylate) shell and narrow length distribution

Core-shell cylindrical polymer brushes with poly(t-butyl acrylate)-b-poly(n-butyl acrylate) (PtBA-b-PnBA) diblock copolymer side chains were synthesized via ‘grafting from’ technique using atom transfer radical polymerization (ATRP). The formation of well-defined brushes was confirmed by GPC and ¹H NMR. Multi-angle light scattering (MALS) measurements on brushes with 240 arms show that the radius of gyration scales with the degree of polymerization of the side chains with an exponent of 0.57±0.05. The hydrolysis of the PtBA block of the side chains resulted amphiphilic cylindrical core-shell nanoparticles. In order to obtain a narrow length distribution of the brushes, the backbone, poly(2-hydroxyethyl methacrylate), was synthesized by anionic polymerization in addition to ATRP. The characteristic core-shell cylindrical structure of the brush was directly visualized on mica by scanning force microscopy (SFM). Brushes with 1500 block copolymer side chains and a length distribution of l_w/l_n=1.04 at a total length l_n=179 nm were obtained. By choosing the proper solvent in the dip-coating process on mica, the core and the shell can be visualized independently by SFM.     

Synthesis of PLLA‐PEOMA comb‐block‐comb type molecular brushes based on AGET ATRP and ring‐opening polymerization

BACKGROUND: Molecular brushes are types of macromolecules with densely grafted side chains on a linear backbone. The synthesis of macromolecular brushes has stimulated much interest due to their great potential in applications in various fields. Poly(L ‐lactide)–poly(ethylene glycol) methyl ether methacrylate (PLLA‐PEOMA) comb‐block‐comb molecular brushes with controlled molecular weights and narrow molecular weight distributions were successfully synthesized based on a combination of activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) and ring‐opening polymerization. The synthetic route is a combination of the ‘grafting through’ method for AGET ATRP of the PEOMA comb block and the ‘grafting from’ method for the synthesis of the PLLA comb block. Poly(2‐hydroxyethyl methacrylate) (PHEMA) was synthesized by ATRP, and PLLA side chains and PEOMA side chains were grown from the backbones and the terminal sites of PHEMA, respectively. RESULTS: The number‐average degrees of polymerization of PLLA chains and poly[poly(ethylene glycol) methyl ether methacrylate] (PPEOMA) comb blocks were determined using ¹H NMR spectroscopy, and the apparent molecular weights and molecular weight distributions of the brush molecules were measured using gel permeation chromatography. The crystallization of the components in the comb‐block‐comb copolymers was also investigated. The crystallization of PLLA side chains is influenced by PLLA chain length and the content of PPEOMA in the molecular brushes. The comb‐block‐comb copolymer composed of hydrophobic PLLA and hydrophilic PEOMA can self‐assemble into a micellar structure in aqueous solution. CONCLUSION: A combination of AGET ATRP and ring‐opening polymerization is an efficient method to prepare well‐defined comb‐block‐comb molecular brushes. The physical properties of the molecular brushes are closely related to their structures. Copyright © 2009 Society of Chemical Industry     

Structural effect of a series of block copolymers consisting of poly(N-isopropylacrylamide) and poly(N-hydroxyethylacrylamide) on thermoresponsive behavior

Well-defined diblock and triblock copolymers consisting of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-hydroxyethylacrylamide) (PHEAA) were prepared using the atom transfer radical polymerization (ATRP) method. The number-average molecular weight and fraction of each segment were precisely controllable by adjusting the monomer/initiator ratio in feed. The lower critical solution temperature (LCST) of a series of block copolymers with different compositions was examined using a turbidimetry analysis. The copolymers with a relatively lower molar fraction of HEAA units in the polymer chain exhibited phase transition phenomenon, in which the LCST depended on the fraction in the copolymer. On the other hand, the LCST disappeared for the copolymers with higher HEAA unit molar fractions. The ¹H NMR measurement clarified that the disappearance of the LCST was attributed to the formation of the water-soluble micelle. Furthermore, the thermoresponsive property of the series of block copolymers was elucidated on the basis of the structural effect of the copolymer, which includes the order and length of the block segments.     

Shell-core-corona aggregates formed from poly(styrene)-poly(4-vinylpyridine) block copolymer induced by added homopolymer via interpolymer hydrogen-bonding

The solution behavior of poly(styrene)-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer with added poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) homopolymer in DMF is studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). It is found that coaggregation takes place when mixing PS-b-P4VP block copolymer and POAA homopolymer in DMF due to the strong interpolymer hydrogen-bonding between POAA chains and P4VP blocks. The coaggregation is a diffusion-controlled process and the complexation-induced aggregates are very stable. NMR measurements demonstrate that the resultant aggregates are much more swollen compared with typical amphiphilic block copolymer core-shell micelles. DLS measurements with Eu³⁺ as a probe combined with TEM observation, are employed to study the structure of the aggregates. Results reveal that the formed aggregates are core-shell spheres with the P4VP/POAA complexes as core and the PS blocks as shell when the weight ratio of POAA to PS-b-P4VP is lower. However, a core-shell-corona structure forms with a thin layer of POAA chains adsorbed on the initial core-shell aggregates with increasing weight content of POAA to 60%. Finally, possible mechanisms of the structural transitions are proposed.     

Synthesis, characterization and self-assembly behavior in water as fluorescent sensors of cationic water-soluble conjugated polyfluorene-b-poly(N-isopropylacrylamide) diblock copolymers

A series of well-defined novel water-soluble diblock copolymers containing conjugated amino-terminal polyfluorene (PF) block and coil-like poly(N-isopropylacrylamide) (PNIPAM) have been successfully synthesized through atom transfer radical polymerization (ATRP) initiated by a 2-bromoisobutyrate end-capped PF macroinitiator using CuCl/HMTETA (1,1,4,7,10,10-hexamethyltriethylenetetramine) as the catalyst. The first-order kinetic plots indicate the presence of a constant number of active species during the polymerization. The molecular weight and molecular weight distribution can be well controlled, implying synthesis of well-defined block structures of the copolymers. The chemical structures of block copolymers have been characterized by ¹H NMR, UV-vis, and photoluminescence (PL) spectra. PF aggregates are formed in water with the increase of temperature for the conjugated-ionic diblock copolymer synthesized, as confirmed by dynamic light scattering (DLS). The formation of excimers within the PF aggregates results in improved Förster resonance energy transfer (FRET) efficiencies.     

Fabrication of thermo-responsive hydrogels from star-shaped copolymer with a biocompatible β-cyclodextrin core

A thermally reversible hydrogel composed of a three-arm star copolymer with a specific host β-cyclodextrin (β-CD) center has been developed. The synthesis of this star copolymer initiates with β-CD core, from which sequential polymerization of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) block and a hydrophilic poly(N,N-dimethylacrylamide) (PDMA) block as asymmetric arms (named β-CD-g-(PNIPAM-b-PDMA)₃) is performed via RAFT protocol. Below the lower critical solution temperature (LCST) of PNIPAM segment, the polymer is of good water-solubility and exhibits a sol state. Upon thermal stimulus, free-standing hydrogels can be formed rapidly at sufficiently high concentrations. By comparing the sol–gel transition of the star polymer with that of its linear counterpart without this feature, we concluded that the special star-shape topology and the thermal-collapsed PNIPAM chains were responsible for this gelation behavior. The rheology measurements indicate the mechanical properties of the polymer hydrogels and the thermal reversibility of the sol–gel transition. Using Rhodamine B as a molecule to model a typical drug, we realize the favorable encapsulation and releasing process from the hydrogel, demonstrating that this star polymer has the potential to function as an injectable hydrogel for drug delivery and gene transport.     

Synthesis and characterization of four- and six-arm star-shaped poly(ε-caprolactone)-b-poly(N-vinylcaprolactam): Micellar and core degradation studies

Star-shaped copolymers with four and six poly(ε-caprolactone)-block-poly(N-vinylcaprolactam) (S(PCL-b-PNVCL)) arms were successfully synthesized by combining ring opening polymerization (ROP) of ε-caprolactone (CL) and reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylcaprolactam (NVCL). The resulting star copolymers were characterized using ¹H NMR, GPC and UV–vis. The numbers of arms in the star-shaped PCL-b-PNVCL block copolymers were demonstrated using degradation studies under acidic conditions, and the individual PNVCL chains were characterized by GPC and ¹H NMR. In aqueous solution, star-shaped PCL-b-PNVCL block copolymers self-assembled into large aggregates or micelles with sizes varying from 54 to 300 nm, depending on the molecular weight of the copolymer and the relative lengths of the hydrophobic and hydrophilic segments. Micelles were characterized by atomic force microscopy (AFM), dynamic light scattering (DLS) and scanning electron microscopy (SEM).     

Optically active thermosensitive amphiphilic polymer brushes based on helical polyacetylene: preparation through “click” onto grafting method and self-assembly

Optically active, thermosensitive, and amphiphilic polymer brushes, which consist of helical poly(N-propargylamide) main chains and thermosensitive poly(N-isopropylacrylamide) (PNIPAm) side chains, were prepared via a novel methodology combining catalytic polymerization, atom transfer radical polymerization (ATRP), and click chemistry. Helical poly(N-propargylamide) bearing α-bromoisobutyryl pendent groups was synthesized via catalytic polymerization, followed by substituting the –Br moieties with azido groups. Then, alkynyl terminated PNIPAm formed via ATRP was successfully grafted onto the azido functionalized helical polymer backbones via click chemistry, providing the expected polymer brushes. GPC, FT-IR, and ¹H-NMR measurements indicated the successful synthesis of the novel amphiphilic polymer brushes. UV–vis and CD spectra evidently demonstrated the helical structures of the polymer backbones and the considerable optical activity of the final brushes. The polymer brushes self-assembled in aqueous solution forming core/shell structured nanoparticles, which were comprised of optically active cores (helical polyacetylenes) and thermosensitive shells (PNIPAm).     

Doubly thermo-responsive brush-linear diblock copolymers and formation of core-shell-corona micelles

Doubly thermo-responsive brush-linear diblock copolymer of poly[poly(ethylene glycol) methyl ether vinylphenyl]-block-poly(N-isopropylacrylamide) (PmPEGV-b-PNIPAM) is prepared by RAFT polymerization. The obtained brush-linear diblock copolymer exhibits two lower critical solution temperatures (LCSTs) corresponding to the linear poly(N-isopropylacrylamide) (PNIPAM) block and the brush poly[poly(ethylene glycol) methyl ether vinylphenyl] (PmPEGV) block in water. This brush-linear diblock copolymer undergoes a two-step temperature sensitive micellization. At temperature above the first LCST, the brush-linear diblock copolymer self-assembles into core-corona micelles with the dehydrated PNIPAM block forming the core and the solvated brush PmPEGV block forming the corona. When temperature increases above the second LCST, the polystyrene backbone in the brush PmPEGV block collapses onto the dehydrated PNIPAM core to form core-shell-corona micelles, in which the dehydrated PNIPAM block forms the core, the collapsed polystyrene backbone in the brush PmPEGV block forms the shell and the solvated poly(ethylene glycol) side-chains forms the corona. The effect of the length of the PNIPAM block and the length of the poly(ethylene glycol) side-chains on the thermo-responsive micellization and the size of core-shell-corona micelles is investigated.     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Double-responsive core-shell-corona micelles from self-assembly of diblock copolymer of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide)

Self-assembly of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM], which was obtained from part hydrolysis of PtBA-b-PNIPAM synthesized by sequential atom transfer radical polymerization (ATRP) was studied. Thermo- and pH-responsive core-shell-corona (CSC) micelles with different structures were formed from (PtBA-co-PAA)-b-PNIPAM in aqueous solution. At pH 5.8 and 25 °C, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PtBA segments as the core, hydrophilic PAA/PNIPAM segments as the mixed shell. Increasing temperatures, core-shell micelles converted into CSC micelles with PtBA as the core, collapsed PNIPAM as the shell and soluble PAA as the corona. Moreover, decreasing pH at 25 °C, PAA chains collapsed onto the core resulting in CSC micelles with PtBA as the core, PAA as the shell and PNIPAM as the corona.     

Synthesis and micellization of thermo- and pH-responsive block copolymer of poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine)

A novel double-hydrophilic block copolymer poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP) with low polydispersity which could respond to both temperature and pH stimuli in aqueous solution was synthesized by atom transfer radical polymerization. Micellization of the copolymer in aqueous solution was characterized by dynamic and static laser scattering, ¹H NMR and transmission electron microscopy. In aqueous solution, the copolymer existed as unimer at pH 2.8 at 25 °C. When the temperature was raised to 50 °C at pH 2.8, the copolymer associated into spherical core-shell micelles with the PNIPAM block forming the core and the P4VP block forming the shell. On the other hand, when pH was increased from 2.8 to 6.5 at 25 °C, the copolymer associated into spherical core-shell micelles with the core formed by the P4VP block and the shell formed by the PNIPAM block. The process was reversible. The critical aggregation temperature of the block copolymer is 36 °C, and the critical aggregation pH value is 4.7.     

Dispersing multi-walled carbon nanotubes with water-soluble block copolymers and their use as supports for metal nanoparticles

Oxidized multi-walled carbon nanotubes (MWCNTs) were dispersed in aqueous and organic solvents by non-covalent modification with a double-hydrophilic block copolymer, poly(ethylene oxide)-b-poly [2-(N,N-dimethylamino)ethyl methacrylate] (PEO-b-PDMA). The PDMA segments were anchored onto the surface of the oxidized MWCNTs through multi-site zwitterionic interactions between the amino and the carboxyl groups while the PEO segments formed corona to promote the solubility of MWCNTs in different solvents. FT-IR and ¹H NMR spectroscopy gave structural information on the resulting composite, supporting the successful modification. Thermal gravimetric analysis showed that the grafting yield could reach 26%. UV/vis and transmission electron microscopy provided direct evidence for the individual dispersion. The resulting modified MWCNTs could find broad spectrum of applications. As an example, Au and Pt nanoparticles were attached on the sidewall of the modified MWCNTs by using the amino groups of PDMA segments.     

Controllable synthesis of poly(N-vinylpyrrolidone) and its block copolymers by atom transfer radical polymerization

At room temperature atom transfer radical polymerization (ATRP) of N-vinylpyrrolidone (NVP) was carried out using 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclo-tetradecane (Me₆Cyclam) as ligand in 1,4-dioxane/isopropanol mixture. Methyl 2-chloropropionate (MCP) and copper(I) chloride were used as initiator and catalyst, respectively. The polymerization of NVP via ATRP could be mediated by the addition of CuCl₂. The resultant poly(N-vinylpyrrolidone) (PNVP) has high conversion of up to 65% in 3 h, a controlled molecular weight close to the theoretical values and narrow molecular weight distribution between 1.2 and 1.3. The living nature of the ATRP for NVP was confirmed by the experiments of PNVP chain extension. With PNVP-Cl as macroinitiator and N-methacryloyl-N′-(α-naphthyl)thiourea (MANTU) as a hydrophobic monomer, novel fluorescent amphiphilic copolymers poly(N-vinylpyrrolidone)-b-poly(N-methacryloyl-N′-(α-naphthyl)thiourea) (PNVP-b-PMANTU) were synthesized by ATRP. PNVP-b-PMANTU copolymers were characterized by ¹H NMR, GPC-MALLS and fluorescence measurements. The results revealed that PNVP-b-PMANTU presented a blocky architecture.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Synthesis of poly(styrene-co-acrylonitrile) copolymer brushes on silica nanoparticles through surface-initiated polymerization

In the present investigation, silica nanoparticles have been coated with poly(styrene-co-acrylonitrile) (SAN) copolymer brushes synthesized via surface-initiated atom transfer radical polymerization (ATRP). In the initial step, silica nanoparticles were functionalized with triethoxysilane-based ATR initiator, 6-(2-bromo-2-methyl) propionyloxy hexyl triethoxysilane. Successful formation of the covalent linkages between ATRP initiator and silica nanoparticles is further corroborated using thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The surface initiated ATRP of the styrene and the acrylonitrile mediated by a copper complex was carried out using the initiator fixed silica nanoparticles in the presence of a sacrificial (free) initiator. The polymerization is preceded in a living manner in all examined cases, producing nanoparticles coated with well-defined poly(styrene-co-acrylonitrile) (SAN) brushes with molecular weight in the range of 12–22 kDa. SAN-grafted silica nanoparticles were characterized using TGA which showed significant weight loss in the temperature range of 340–420 °C confirming the formation of the polymer brushes on the surface with graft densities in the range of 0.109–0.190 chains/nm². Successful formation of the SAN copolymer brushes are further characterized by FTIR and proton nuclear magnetic resonance spectroscopy techniques. Differential scanning calorimetric studies revealed that the SAN copolymer grafted onto silica nanoparticles exhibits higher glass transition temperatures than free SAN copolymers. Transmission electron microscopy and dynamic light scattering studies revealed that the SAN copolymer-grafted silica nanoparticles showed relatively fine dispersion in organic solvents such as tetrahydrofuran, when compared to bare silica nanoparticles.     

Formation and properties of multivariant assemblies of surface-tethered diblock and triblock copolymers

We present methodologies for fabricating block copolymer assemblies grafted onto flat solid substrates, where each block of the copolymer possesses a systematic and gradual variation of molecular weight as a function of the position on the substrate. We demonstrate the utility of this technique on two case studies. In the first project, we generate surface-tethered poly[(2-hydroxyethyl methacrylate)-b-(methyl methacrylate)] (PHEMA-b-PMMA) diblock copolymer brushes and study systematically morphological transitions associated with collapsing either the top PMMA or the bottom PHEMA block while keeping the other block solvated. Scanning force microscopy studies of systems having the top block collapsed reveal the presence of either flat (F), or micellar (M) or bicontinuous (BC) morphologies, whose locus in the phase diagram agrees with theoretical predictions and results of computer simulations. The second case study demonstrates the extension of the deposition method to the case of surface-anchored triblock copolymer brushes. Specifically, we present results pertaining to the formation of poly[(2-hydroxyethyl methacrylate)-b-(methyl methacrylate)-b-(dimethylaminoethyl methacrylate)] brushes with independent variation of all three block lengths.     

Complex micelles with a responsive shell for controlling of enzymatic degradation

Complex polymeric micelles with a PLA core and a mixed PEG/PNIPAM shell were prepared by self-assembly of two block copolymers: poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(N-isopropylacrylamide)-b-poly(lactic acid) (PNIPAM-b-PLA). Using ¹H NMR spectroscopy and dynamic light scattering, the micellization and the enzymatic degradation status were characterized. At 25 °C, the PNIPAM block is hydrophilic and the PLA core is prone to the enzymatic degradation, resulting in the disassembly of the micelles. While increasing the temperature to 45 °C, the PNIPAM collapsed onto the PLA core, protecting the PLA core from the attack by the enzyme, and the micelles exhibit a resistance to the enzymatic degradation. Furthermore, the enzymatic degradation rate of the micelles can also be tuned by changing the ratio of PEG to PNIPAM. With increasing content of PNIPAM, the conformation of the collapsed PNIPAM changes from patchy domains to a continuous and dense layer, and the enzyme accessibility to the PLA core is changed.     

Synthesis,characterization, and application of novel amphiphilic poly(D‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐ poly(D‐gluconamidoethyl methacrylate) triblock copolymers

Novel amphiphilic ABA‐type poly(D ‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐poly(D ‐gluconamidoethyl methacrylate) (PGAMA‐b‐PU‐b‐PGAMA) tri‐block copolymers were successfully synthesized via the combination of the step‐growth and copper‐catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO‐PU‐OH) was synthesized by the step‐growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA‐b‐PU‐b‐PGAMA block copolymers were synthesized via copper‐catalyzed ATRP of GAMA in N, N‐dimethyl formamide at 20°C in the presence of 2, 2′‐bipyridyl using Br‐PU‐Br as macroinitiator and characterized by ¹H‐NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by ¹H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo‐gravimetric analysis, and differential scanning calorimetric study. Spherical Ag‐nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri‐block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013