Consecutive Atom Transfer Radical Polymerization Research Articles

Well-Defined pH-Responsive Self-Assembled Block Copolymers for the Effective Codelivery of Doxorubicin and Antisense Oligonucleotide to Breast Cancer Cells.

The worldwide steady increase in the number of cancer patients motivates the development of innovative drug delivery systems for combination therapy as an effective clinical modality for cancer treatment. Here, we explored a design concept based on poly(ethylene glycol)-b-poly(2-(dimethylamino)ethyl methacrylate)-b-poly(2-hydroxyethyl methacrylate-formylbenzoic acid) [PEG-b-PDMAEMA-b-P(HEMA-FBA)] for the dual delivery of doxorubicin (DOX) and GTI2040 (an antisense oligonucleotide for ribonucleotide reductase inhibition) to MCF-7 breast cancer cells. PEG-b-PDMAEMA-b-PHEMA, the precursor copolymer, was prepared through chain extensions from a PEG-based macroinitiator via two consecutive atom transfer radical polymerization (ATRP) steps. Then, it was modified at the PHEMA block with 4-formylbenzoic acid (FBA) to install reactive aldehyde moieties. A pH-responsive polymer-drug conjugate (PDC) was obtained by conjugating DOX to the polymer structure via acid-labile imine linkages, and subsequently self-assembled in an aqueous solution to form DOX-loaded self-assembled nanoparticles (DOX-SAN) with a positively charged shell. DOX-SAN condensed readily with negatively charged GTI2040 to form GTI2040/DOX-SAN nanocomplexes. Gel-retardation assay confirmed the affinity between GTI2040 and DOX-SAN. The GTI2040/DOX-SAN nanocomplex at N/P ratio of 30 exhibited a volume-average hydrodynamic size of 136.4 nm and a zeta potential of 21.0 mV. The pH-sensitivity of DOX-SAN was confirmed by the DOX release study based on the significant cumulative DOX release at pH 5.5 relative to pH 7.4. Cellular uptake study demonstrated favorable accumulation of GTI2040/DOX-SAN inside MCF-7 cells compared with free GTI2040/DOX. In vitro cytotoxicity study indicated higher therapeutic efficacy of GTI2040/DOX-SAN relative to DOX-SAN alone because of the downregulation of the R2 protein of ribonucleotide reductase. These outcomes suggest that the self-assembled pH-responsive triblock copolymer is a promising platform for combination therapy, which may be more effective in combating cancer than individual therapies.

Precise Synthesis of PS-PLA Janus Star-Like Copolymer.

In this work, an efficient strategy is designed for the precise synthesis of novel Janus star-like copolymer (polystyrene)8 -b-(poly(l-lactide))8 , (PLLA)8 -b-(PS)8 , consisting of two types of chemically distinct polymer arms, PS and PLLA, in an asymmetric structure. During the synthesis, PLLA hemisphere carrying protected hydroxyl groups at the focal point was first synthesized via a combined reactions of esterification, light-induced "Click" chemistry, and ring opening polymerization (ROP) using a specially designed dendron as initiator. After removing the protecting moiety, the terminal hydroxyl groups on the dendron segment is increased fourfold and further modified into bromopropionate-based macroinitiator through a two-step end group transformation reaction, followed by atom transfer radical polymerization (ATRP) of styrene to obtain the desired (PLLA)8 -b-(PS)8 Janus star-like copolymer. The versatility and efficiency of the designed synthetic strategy are demonstrated by the well-defined molecular characteristics and high yields of the targeted product. In addition to the controlled degradation behavior of the PLLA segments, the remaining bromide groups located at the distal end of PS arms could allow for further fabrication of diverse building blocks through consecutive ATRP of various monomers. This work signifies the first time for facile and precise synthesis of Janus star-like copolymer with unique biphasic structure and function control.

PH-Responsive Tumor-Targetable Theranostic Nanovectors Based on Core Crosslinked (CCL) Micelles with Fluorescence and Magnetic Resonance (MR) Dual Imaging Modalities and Drug Delivery Performance.

The development of novel theranostic nanovectors is of particular interest in treating formidable diseases (e.g., cancers). Herein, we report a new tumor-targetable theranostic agent based on core crosslinked (CCL) micelles, possessing tumor targetable moieties and fluorescence and magnetic resonance (MR) dual imaging modalities. An azide-terminated diblock copolymer, N3-POEGMA-b-P(DPA-co-GMA), was synthesized via consecutive atom transfer radical polymerization (ATRP), where OEGMA, DPA, and GMA are oligo(ethylene glycol)methyl ether methacrylate, 2-(diisopropylamino)ethyl methacrylate, and glycidyl methacrylate, respectively. The resulting diblock copolymer was further functionalized with DOTA(Gd) (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakisacetic acid) or benzaldehyde moieties via copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) chemistry, resulting in the formation of DOTA(Gd)-POEGMA-b-P(DPA-co-GMA) and benzaldehyde-POEGMA-b-P(DPA-co-GMA) copolymers. The resultant block copolymers co-assembled into mixed micelles at neutral pH in the presence of tetrakis[4-(2-mercaptoethoxy)phenyl]ethylene (TPE-4SH), which underwent spontaneous crosslinking reactions with GMA residues embedded within the micellar cores, simultaneously switching on TPE fluorescence due to the restriction of intramolecular rotation. Moreover, camptothecin (CPT) was encapsulated into the crosslinked cores at neutral pH, and tumor-targeting pH low insertion peptide (pHLIP, sequence: AEQNPIYWARYADWLFTTPLLLLDLALLVDADEGTCG) moieties were attached to the coronas through the Schiff base chemistry, yielding a theranostic nanovector with fluorescence and MR dual imaging modalities and tumor-targeting capability. The nanovectors can be efficiently taken up by A549 cells, as monitored by TPE fluorescence. After internalization, intracellular acidic pH triggered the release of loaded CPT, killing cancer cells in a selective manner. On the other hand, the nanovectors labeled with DOTA(Gd) contrast agents exhibited increased relaxivity (r1 = 16.97 mM−1·s−1) compared to alkynyl-DOTA(Gd) small molecule precursor (r1 = 3.16 mM−1·s−1). Moreover, in vivo MRI (magnetic resonance imaging) measurements revealed CCL micelles with pHLIP peptides exhibiting better tumor accumulation and MR imaging performance as well.

Synthesis of β-cyclodextrin-Based Star Block Copolymers with Thermo-Responsive Behavior

Star polymers are one example of three-dimensional macromolecules containing several arms with similar molecular weight connected to a central core. Due to their compact structure and their enhanced segment density in comparison to linear polymers of the same molecular weight, they have attracted significant attention during recent years. The preparation of block-arm star copolymers with a permanently hydrophilic block and an “environmentally” sensitive block, which can change its nature from hydrophilic to hydrophobic, leads to nanometer-sized responsive materials with unique properties. These polymers are able to undergo a conformational change or phase transition as a reply to an external stimulus resulting in the formation of core–shell nanoparticles, which further tend to aggregate. Star-shaped copolymers with different cores were synthesized via atom transfer radical polymerization (ATRP). The core-first method chosen as synthetic strategy allows good control over the polymer architecture. First of all the multifunctional initiators were prepared by esterification reaction of the hydroxyl groups with 2-chloropropionyl chloride. Using β-cyclodextrin as core molecules, which possess a well-defined number of functional groups up to 21, allows defining the number of arms per star polymer. In order to prepare stimuli-responsive multi-arm copolymers, containing a stimuli-responsive (poly(N-isopropylacrylamide) (PNIPAAm)) and a non-responsive block (poly(N,N-dimethylacrylamide) (PDMAAm)), consecutive ATRP was carried out. The polymers were characterized intensively using NMR spectroscopy and size exclusion chromatography (SEC), whereas the temperature-depending aggregation behavior in aqueous solution was determined via turbidimetry and differential scanning calorimetry (DSC).

Synthesis, characterization and bulk properties of well-defined poly(hexafluorobutyl methacrylate)-block-poly(glycidyl methacrylate) via consecutive ATRP

A well-defined fluorine-containing copolymer with pendant epoxy groups, poly(2,2,3,4,4,4-hexafluorobutyl methacrylate-block-glycidyl methacrylate) (PHFBMA-b-PGMA), was prepared by sequential atom transfer radical polymerization (ATRP). The amphiphilic copolymer PHFBMA-b-PGMA(OH) with pendant hydroxyl groups was obtained after ring-opening reaction of the epoxy groups from PGMA. The macroinitiator agent PHFBMA-Br and its copolymers were proved to be successfully synthesized by characterization of FTIR, 1H NMR and gel permeation chromatography (GPC). The chain growth experiment demonstrated that a linear first-order relationship was fitted under the conditions. In addition, the fluorinated copolymers with functional groups in the side chain could keep the contact angle and the advantages of fluoropolymers while improving the hydrophilic property. Meanwhile, TGA testing showed that the copolymers had better thermal stability than its homopolymer. TEM observation indicated that microspheres were embedded in the stable micelles when the final copolymer concentration of aqueous solution was 1wt%.

PH-responsive destabilization and facile bioconjugation of new hydroxyl-terminated block copolymer micelles

New hydroxyl-terminated amphiphilic block copolymers (HO-ABPs) having pendant t-butyl groups for pH-responsiveness and terminal OH groups for bioconjugation are reported. These HO-ABPs consist of hydrophilic poly(oligo(ethylene oxide) monomethyl ether methacrylate) and hydrophobic poly(t-butyl methacrylate) blocks and were synthesized by a consecutive atom transfer radical polymerization in the presence of an OH-terminated bromine initiator. Aqueous self-assembly of HO-ABPs resulted in colloidally stable micellar aggregates being capable of encapsulating hydrophobic guest molecules. They were nontoxic to cells and destabilized in response to low pH. A facile bioconjugation of HO-ABP micelles for active targeting is demonstrated by conjugation with biotin (vitamin H) and competitive assay exhibiting >93% ABP chains conjugated with biotin in each micelle. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

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

AbstractA 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

Highly Sensitive Detection of Protein Toxins by Surface Plasmon Resonance with Biotinylation-Based Inline Atom Transfer Radical Polymerization Amplification

Ultrasensitive detection of proteins is of great importance to proteomics studies. We report here a method to enhance detection sensitivity in surface plasmon resonance (SPR) spectroscopy by coupling a polymerization initiator to a biospecific interaction and inducing inline atom transfer radical polymerization (ATRP) for amplifying SPR response. Bacterial cholera toxin (CT) is chosen as the model protein that has been covalently immobilized on the surface for demonstrating the principle. The specific recognition is achieved by use of biotinylated anti-CT, which allows initiators with a biotin tag to be fixed at the protein binding site through a neutravidin bridge and triggers the localized growth of polymer brushes of poly(hydroxyl-ethyl methacrylate) (PHEMA) via an ATRP mechanism. To further enhance the signal, a second ATRP reaction is conducted that takes advantage of the hydroxyl groups of PHEMA brushes from the first step to form hyperbranched polymers onto the sensing surface. The two consecutive ATRP steps significantly improve SPR detection, allowing low amounts of CT that yield no direct measurement to be quantified with large signals. The resulting polymer film has been characterized by optical and atomic force microscopy. Ascorbic acid (AA) is employed as deoxygen reagent in the catalyst mixture that effectively suppresses oxygen interference, shortening the reaction time and making it possible for applying this ATRP approach to flow injection based SPR detection. A calibration curve of PHEMA amplification for CT detection based on surface coverage has been obtained that displays a correlation in a range from 8.23 x 10(-15) to 3.61 x 10(-12) mol/cm(2) with a limit of detection of 6.27 x 10(-15) mol/cm(2). The versatile biotin-neutravidin interaction used here should allow adaptation of ATRP enhancement to many other systems that include DNA, RNA, peptides, and carbohydrates, opening new avenues for ultrasensitive analysis of biomolecules with flow-injection assay and SPR spectroscopy.

Order-order transition induced by mesophase formation in a novel type of diblock copolymers based on poly(isobutyl methacrylate) and poly[2,5-di(isopropyloxycarbonyl)styrene

Novel diblock copolymers based on poly(isobutyl methacrylate) (PiBMA) and poly[2,5-di(isopropyloxycarbonyl)styrene] (PiPCS) were designed and prepared via consecutive atom transfer radical polymerization. They had relatively low molecular weight distributions and tunable molecular weights. The molecular characterization of the copolymers was performed with proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The phase structures and transitions were investigated by differential scanning calorimetry, small- and wide-angle X-ray scattering, and polarized optical microscopy experiments. A PiPCS block with a polymerization degree higher than 168, exhibited a stable hexagonal columnar liquid crystalline (Colh LC) phase, regardless of the length of PiBMA block. The PiPCS block underwent a coil-to-rod conformational change when it transformed into Colh LC phase. For the PiBMA-b-PiPCS diblock copolymer, this conformational transition resulted in a topological change from a coil-coil to a rod-coil type structure. With increasing PiPCS fraction, the block copolymers' microphase separated structure changed from an undetermined phase, to a lamellar phase, to a PiBMA columnar phase in the coil-coil system. The original microphase separated structure observed with coil PiPCS block could evolve into a lamellar morphology, with a significantly increased long period when PiPCS transformed into Colh LC phase. Thereafter it served as a rod in the block copolymers studied. This microphase separated structure transition was triggered by the coil-to-rod (isotropic-to-LC) transition and was irreversible due to the fact that the LC phase of PiPCS block remained at higher temperatures until decomposition.

Encapsulation of nanomaterials within intermediary layer cross-linked micelles using a photo-cross-linking agent

A new method for encapsulating nanomaterials within intermediary layer cross-linked (ILCL) polymeric micelles using a bifunctional photo-cross-linking agent was developed. For ILCL polymeric micelles, an amphiphilic triblock copolymer of poly(ethylene glycol)-b-poly(2-hydroxyethyl methacrylate)-b-poly(methyl methacrylate) (PEGPHEMA-PMMA) was synthesized via consecutive atom transfer radical polymerization (ATRP). Di(4-hydroxyl benzophenone) dodecanedioate (BPD) was used as a bifunctional photo-cross-linking agent. The PMMA-tethered Au nanoparticles and BPD, or pyrene and BPD were encapsulated in the PEG-PHEMA-PMMA micelles, and their intermediary layers were photo-cross-linked by UV irradiation for 1 h. The HEMA units donated labile hydrogens to the excited-state benzophenone groups in BPD, and they were subsequently cross-linked by BPD through radicalradical combination. The spherical structures of the PEG-PHEMA-PMMA micelles containing the Au nanoparticles or pyrene were unaffected by the photo-cross-linking process.

Pentablock copolymers of poly(ethylene glycol), poly((2-dimethyl amino)ethyl methacrylate) and poly(2-hydroxyethyl methacrylate) from consecutive atom transfer radical polymerizations for non-viral gene delivery

Well-defined pentablock copolymers (PBPs) of P(HEMA)- b-P(DMAEMA)- b-PEG- b-P(DMAEMA)- b-P(HEMA) (in which PEG = poly(ethylene glycol), P(DMAEMA) = poly((2-dimethyl amino)ethyl methacrylate), and P(HEMA) = poly(2-hydroxyethyl methacrylate)), with different block lengths of P(DMAEMA), for non-viral gene delivery were prepared via consecutive atom transfer radical polymerizations (ATRPs) from the same di-2-bromoisobutyryl-terminated PEG (Br–PEG–Br) center block. The PBPs demonstrate good ability to condense plasmid DNA (pDNA) into 100–160 nm size nanoparticles with positive zeta potentials of 25–35 mV at PBPs/pDNA weight ratios of 5–25. The PBPs exhibit very low in vitro cytotoxicity and excellent gene transfection efficiency in HEK293 and COS7 cells. In particular, the transfection efficiencies of all the PBPs in HEK293 cells are comparable to, or higher than those of polyethylenimine (PEI, 25 kDa) at most weight ratios. The ability of the copolymers to condense plasmid DNA and the transfection efficiency of the resulting complexes are dependent on the chain length of P(DMAEMA) blocks. In addition to reducing the cytotoxicity and increasing the stability of the plasmid complexes, the PEG center block and the short P(HEMA) end blocks also help to enhance the gene transfection efficiency. Thus, the approach to well-defined block copolymers via ATRP provides a versatile means for tailoring the structure of non-viral gene vectors to meet the requirements of low cytotoxicity, good stability and high transfection capability for gene therapy applications.

Synthesis of Amphiphilic ABCBA‐Type Pentablock Copolymer from Consecutive ATRPs and Self‐Assembly in Aqueous Solution

AbstractSummary: A novel amphiphilic ABCBA‐type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2‐dimethylaminoethyl methacrylate)‐block‐poly(2,2,2‐trifluoroethyl methacrylate)‐block‐poly(ε‐caprolactone)‐block‐poly(2,2,2‐ trifluoroethyl methacrylate)‐block‐poly(2‐dimethylaminoethyl methacrylate) (PDMAEMA‐ b‐PTFEMA‐b‐PCL‐b‐PTFEMA‐b‐PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and 1H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self‐assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.

Synthesis of ABC-type miktoarm star polymers by “click” chemistry, ATRP and ROP

ABC-type miktoarm star polymers, poly(ethylene oxide)-block-polystyrene-block-poly ( ε-caprolactone)s (PEO- b-PS- b-PCL) were synthesized via combination of “click” chemistry, atom-transfer radical polymerization (ATRP) and ring opening polymerization (ROP). Azide ended PEO arms, PEO–N 3, and a trifunctional molecule, propargyl 2-hydroxylmethyl-2-(α-bromoisobutyraloxymethyl)-propionate (PHBP), were prepared first, respectively. A “click” reaction of PEO–N 3 and PHBP generated a PEO macroinitiator, PEO–(Br)(OH) with two functionalities, one is hydroxyl group and the other is α-bromoisobutyraloxyl group. Consecutive ATRP of styrene (St) and ROP of ε-caprolactone ( ε-CL) from the PEO macroinitiator produced the PEO- b-PS- b-PCL miktoarm stars. All the structures of the polymers were determined.

PH- and temperature-responsive hydrogels from crosslinked triblock copolymers prepared via consecutive atom transfer radical polymerizations

Well-defined poly((2-dimethyl amino)ethyl methacrylate- co-2-hydroxyethyl methacrylate)- b-poly( N-isopropylacrylamide)- b-poly((2-dimethyl amino)ethyl methacrylate- co-2-hydroxyethyl methacrylate), or P(DMAEMA- co-HEMA)- b-P(NIPAAm)- b-P(DMAEMA- co-HEMA), triblock copolymers were synthesized by consecutive atom transfer radical polymerizations (ATRPs), using ethylene glycol di-2-bromoisobutyrate (Br–EG–Br) as the starting ATRP initiator. The hydroxyl groups of the incorporated HEMA units were used as crosslinking sites for the preparation of smart hydrogels. The so-prepared hydrogels exhibited both temperature- and pH-sensitive behavior derived, respectively, and independently, from the P(NIPAAm) blocks and P(DMAEMA) units, in the crosslinked matrices. The hydrogels exhibited a lower critical solution temperature (LCST) of 31–32 °C in aqueous media of pH 1–7, not unlike that of the P(NIPAAm) homopolymer. The swelling ratios and swelling/deswelling kinetics of the hydrogels depended strongly on pH and temperature of the medium. The copolymers were characterized by gel-permeation chromatography, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and 1H nuclear magnetic resonance ( 1H NMR) spectroscopy. The resultant stimuli-responsive hydrogels were characterized by differential scanning calorimetry (DSC). These stimuli-responsive hydrogels will have potential applications in biomedical areas, such as tissue engineering and drug delivery.

Brush-Type Amphiphilic Diblock Copolymers from “Living”/Controlled Radical Polymerizations and Their Aggregation Behavior

Two brush-type amphiphilic diblock copolymers, poly(poly(ethylene glycol)methyl ether methacrylate-block-polystyrene) (P(PEGMA)-b-PS) and poly(glycidyl methacrylate)-block-poly(poly(ethylene glycol)methyl ether methacrylate) (P(GMA)-b-P(PEGMA)) were synthesized, respectively, via consecutive atom-transfer radical polymerizations (ATRPs) and reversible addition-fragmentation chain-transfer (RAFT) polymerizations. The diblock copolymers were characterized by gel permeation chromatography (GPC), (1)H nuclear magnetic resonance (NMR) spectroscopy, and FT-IR spectroscopy. The aggregation behavior of the two amphiphilic diblock copolymers in water was also studied. Scanning electron and transmission electron microscopic images revealed that spherical micelles (40-80 nm in diameter) from self-assembly of the P(PEGMA)-b-PS copolymers and wormlike micelles (60-120 nm in length and 20-30 nm in diameter) from self-assembly of the P(GMA)-b-P(PEGMA) copolymers were prevalent. The spherical P(PEGMA)-b-PS micelles could self-assemble gradually into giant aggregates of several micrometers in diameter.

Three-Dimensionally Ordered Porous Membranes Prepared via Self-Assembly and Reverse Micelle Formation from Well-Defined Amphiphilic Block Copolymers

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(tert-butyl acrylate) (PtBA), or PFS-b-PtBA copolymers, were synthesized via consecutive atom transfer radical polymerizations (ATRPs). Amphiphilic block copolymers of PFS and poly(acrylic acid) (PFS-b-PAAC copolymers) were prepared via hydrolysis of the corresponding PFS-b-PtBA copolymers. The chemical structure and composition of the PFS-b-PtBA and PFS-b-PAAC block copolymers were studied by nuclear magnetic resonance (NMR) spectroscopy, themogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The amphiphilic PFS-b-PAAC copolymers were cast into porous membranes by phase inversion in aqueous media. The surface and cross-sectional morphology of the PFS-b-PAAC membranes were studied by scanning electron microscopy (SEM). Membranes with well-defined pores of sizes in the micrometer range were obtained as a result of inverse micelle formation. The pH of the aqueous media for phase inversion and the PAAC content in the PFS-b-PAAC copolymers could be used to adjust the pore size of the membranes.

Tadpole-Shaped Amphiphilic Block−Graft Copolymers Prepared via Consecutive Atom Transfer Radical Polymerizations

Tadpole-shaped (or rod−coil) block−graft copolymers, consisting of a pentafluorostyrene polymer (PFS) block and a glycidyl methyacrylate polymer (PGMA) block with grafted poly(tert-butyl acrylate) (PtBA) side chains, or PFS-b-(PGMA-g-PtBA) copolymers, were synthesized by consecutive atom transfer radical polymerizations (ATRP's). The process involved (i) synthesis of PFS via ATRP, (ii) synthesis of well-defined PFS-b-PGMA via ATRP, (iii) coupling of the bromoacid initiators with the glycidyl methacrylate units in the PGMA block to generate the PFS-b-PGMA macroinitiators, and (iv) ATRP-mediated graft copolymerization with tert-butyl acrylate to generate the PFS-b-(PGMA-g-PtBA) copolymer. Hydrolysis of the PtBA side chains in the block−graft copolymer into the acrylic acid polymer (PAAC) side chains gave rise to an amphiphilic PFS-b-(PGMA-g-PAAC) macromolecule with a brush-shaped hydrophilic head (rod) and a hydrophobic tail (coil). The copolymers were characterized by composition analysis, gel permeation chromatography (GPC), thermogravimetric analyses (TGA), nuclear magnetic resonance (NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The macromolecular architecture of the copolymer was suggested by atomic force microscopy (AFM) images and micelle formation.

Star Polymers with Alternating Arms from Miktofunctional μ-Initiators Using Consecutive Atom Transfer Radical Polymerization and Ring-Opening Polymerization

The synthesis of unique miktofunctional μ-initiators, combining initiator sites for both controlled ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) arranged in an alternating fashion, is described. This initiator was used to prepare miktoarm star block copolymers in a core-out approach utilizing consecutive ATRP and ROP processes. NMR and GPC studies on the block copolymers comprising poly(methyl methacrylate) (PMMA) and poly(caprolactone) (PCL) confirm the versatility of this approach which is independent of the order of polymerization. Furthermore, amphiphilic alternating arm block copolymers containing poly(caprolactone) and poly(acrylic acid) blocks were also prepared by this method.