Pentablock Copolymers Research Articles

Injectable self-assembled block copolymers for sustained gene and drug co-delivery: An in vitro study

A temperature-responsive pentablock copolymer (PB) was designed to deliver DNA and provide prolonged gene expression by forming a thermogelling release depot after subcutaneous or intratumoral injection. A synthetic barrier gel was developed based on poly(ethylene glycol) diacrylate to enable the released vectors to instantly and continuously transfect cultured cells. The aim of this setup was to provide a simple and controlled in vitro system to mimic tumor matrix to optimize the release system and to study the influence of the continuous and sustained release of the polyplexes on the in vitro transfection. The porosity of the barrier gel was adjusted by addition and removal of Pluronic F127 (PL), and the properties of the gel were characterized by visual inspection and scanning electron microscopy (SEM). Concentrated PB-based vector was administered to the barrier gel and allowed to be released to the buffer. We found that most of feed vector could be released from the barrier gel without unpacking the polymer–DNA complexes. Based on the specific construction of the PB-based vectors, an anti-cancer drug paclitaxel (PTX) was further loaded into the same vector designed for DNA delivery, thus formulating a gene and drug co-delivery system. This system was tested for sustained delivery to human ovarian carcinoma cells SKOV3 using the barrier gel in vitro as a tumor mimic. Transfection efficiency was found to be significantly enhanced by co-delivering PTX, while PTX also showed its effect as an anti-cancer drug to induce cell death. Yet both of the two effects of PTX shown in SKOV3 cells turned out to be dramatically weaker in ARPE-19 cells, a human non-cancerous cell line, which might be related to the nature of the vector itself. Instant release of vectors showed the ability to maintain transfection up to the fourth day, making the gene expression stable at least for the first 5 days. Further study is still needed to improve the duration of effective release.

Synthesis and self-assembly of double-hydrophilic pentablock copolymer with pH and temperature responses via sequential atom transfer radical polymerization

ABCBA pentablock double-hydrophilic copolymer of poly(diethylene glycol monomethyl ether methacrylate)- block-poly(2-( N,N-dimethylamino)ethyl methacrylate)- block-poly(ethylene glycol)- block-poly(2-( N,N-dimethylamino)ethyl methacrylate)- block-poly(diethylene glycol monomethyl ether methacrylate) (PMEO 2MA- b-PDMAEMA- b-PEG- b-PDMAEMA- b-PMEO 2MA) was synthesized by sequential atom transfer radical polymerization (ATRP). The copolymer is hydrophilic at low temperature and pH values (at temperatures lower than 26 °C and acidic pH values), and became amphiphilic when pH and (or) temperature changed. Investigation shows that the copolymer can self-assembly into micelles with various structures under the conditions of temperature higher than 26 °C or basic solutions. The self-assembly behavior and multi-responsive properties of the copolymer in water were investigated by DLS and TEM. The self-assembly behavior of the copolymer can be adjusted by the alteration of pH values or temperature. Therefore, the copolymer will have the potential applications in biomedical field.

Synthesis and characterization of BAB and CBABC tri- and PentaBlock copolymers via atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) technique was applied successfully for the synthesis of poly(n-butyl methacrylate-b-styrene-b-n-butyl methacrylate) (PBMA-b-PS-b-PBMA), (BAB) and poly(methyl methacrylate-b-n-butyl methacrylate-b-styrene-b-n-butyl methacrylate-b-methyl methacrylate) (PMMA-b-PBMAb- PS-b-PBMA-b-PMMA), (CBABC) linear tri- and pentablock copolymers, respectively, in solution for the first time. Difunctional polystyrene macroinitiator that contains a bromide end-group was prepared by ATRP of styrene with dimethyl-2,6-dibromoheptanedioate (DMDBHD). The formation of block copolymers was confirmed by gel permeation chromatography (GPC), nuclear magnetic resonance (1H NMR) spectroscopy, and differential scanning calorimetry (DSC). Good agreement was observed between the theoretical and experimental molecular weights. The molecular weight distribution (MWD) was narrow and did not change much with the progress of the reaction. A linear increase in the number average molecular weight (M n ) with conversion was observed indicating that the polymerizations followed a ‘living’/controlled process. Both BAB and CBABC block copolymers showed core-shell type flower-like micellar structures when toluene is used as a selective solvent for A block (polystyrene). Open image in new window

PH‐Sensitive Pentablock Copolymer Nanocapsules as Nontoxic and Efficient Gene Carriers

A biodegradable amphiphilic pentablock copolymer PAE-PCL-PEG-PCL-PAE with a pH-sensitive unit was synthesized for use as a nontoxic, biodegradable carrier for gene delivery by forming nanocapsules entrapping nucleic acid drugs. The PAE block can interact with plasmid DNA to form polyelectrolyte complexes in an acidic environment. At physiological pH, the PAE blocks are deprotonated and form an insoluble skin, resulting in the formation of nanocapsules that encapsulate plasmid DNA. The surface charges of the nanocapsules became almost neutral at pH = 7.4, and their size ranged from 210 to 280 nm. The nanocapsule maintained most of its transfection efficiency even in the presence of serum. These nanocapsules are therefore potential carriers for systemic gene therapy.

Novel linear fluoro-silicon-containing pentablock copolymers: synthesis and their properties as coating materials

A series of linear fluorosilicone pentablock copolymers consisting of poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA) and poly(dodecafluoroheptyl methacrylate) (PDFHM), named as PDMS-b-(PMMA-b-PDFHM)2, have been synthesized by ATRP and their thermal properties, self-assembly behavior in different solutions and surface features of films have been systematically investigated. TGA measurements reflect that the thermal stability of PDMS-b-(PMMA-b-PDFHM)2 is enhanced by the middle-block PDMS. TEM observation and DLS analysis reveal that PDMS-b-(PMMA-b-PDFHM)2 is able to self-assemble into unimers in both chloroform and dioxane solutions, and spherical micelles with a core–corona structure in chloroform, oblate spheroidal micelles with a multilayer core–corona structure in dioxane. The diameters of micelles in the dioxane solution are larger, while the concentrations of unimers in the chloroform solution are higher. SCA, QCM-D and XPS measurements have confirmed that the unimers play a dominant role in governing the surface properties of PDMS-b-(PMMA-b-PDFHM)2 films. In the case of PDMS-b-(PMMA-b-PDFHM)2 with a PMMA/PDMS weight ratio of 10 : 1 and 20%wt of DFHM content, the film cast from chloroform solution has a lower surface free energy of 16.8 mN m−1, lower adsorbed amounts of 8.6 × 104 ng cm−2 for water and 6.6 × 104 ng cm−2 for hexadecane, and higher surface stability. Such excellent thermal and surface properties demonstrate that this novel pentablock copolymer PDMS-b-(PMMA-b-PDFHM)2 is a promising candidate as a coating material.

Characterization of temperature-induced association in aqueous solutions of charged ABCBA-type pentablock tercopolymers

In this work, two novel linear ABCBA pentablock tercopolymers, which are composed of an anionic poly(4-styrenesulfonic acid sodium) (PSSS) block on both ends and two thermosensitive poly(N-isopropylacrylamide) (PNIPAAM) blocks that are separated by a hydrophilic poly(ethylene glycol) (PEG) block have been synthesized via a simple “one-pot” ATRP procedure. The two studied samples have the following compositions: (P(SSS)12-b-P(NIPAAM)63-b-P(EG)34-b-P(NIPAAM)63-b-P(SSS)12 (C34) and P(SSS)14-b-P(NIPAAM)65-b-P(EG)77-b-P(NIPAAM)65-b-P(SSS)14 (C77). The main difference between the copolymers is the length of the hydrophilic block, which plays a crucial role for the physical properties of the copolymers in aqueous solution. A solution of the C34 sample becomes turbid at elevated temperatures and compact interchain complexes are formed with a behavior that is reminiscent of a suspension of particles. A solution of C77 becomes turbid at intermediate temperatures but it is transformed to a transparent solution at high temperatures. Depending on the polymer concentration, this pentablock copolymer forms a fragmented or interconnected network at elevated temperatures. At sufficiently high polymer concentration, the viscosity measurements indicate that a reversible hydrogel is formed. The interchain complexes or networks are readily broken up under the influence of shear flow. The results from the small angle neutron scattering experiments reveal significant structural differences between the pentablock copolymers at different temperatures.

Sensing Polymer/DNA Polyplex Dissociation Using Quantum Dot Fluorophores

We characterized the dissociation of polymer/DNA polyplexes designed for gene delivery using water-soluble quantum dots (QDs). A pH-responsive pentablock copolymer was designed to form stable complexes with plasmid DNA via tertiary amine segments. Dissociation of the polyplex was induced using chloroquine where the efficiency of this process was sensed through changes in QD fluorescence. We found that increasing concentrations of pentablock copolymer and DNA led to quenching of QD fluorescence, while chloroquine alone had no measurable effect. The mechanism of quenching was elucidated by modeling the process as the combination of static and dynamic quenching from the pentablock copolymer and DNA, as well as self-quenching due the bridging of QDs. Tertiary amine homopolymers were also used to study the effect of chain length on quenching. Overall, these QDs were found to be highly effective at monitoring the dissociation of pentablock copolymer/DNA polyplexes in vitro and may have potential for studying the release of DNA within cells.

Synthesis and Thermal Properties of Novel Biodegradable ABCBA Pentablock Copolymers from Poly (Ethylene glycol), L-Lactide and p-Dioxanone

In this work, new biodegradable ABCBA type pentablock copolymers with different mole ratio of L -lactide and PPDO-b-PEG-b-PPDO triblock copolymer were synthesized and characterized. In the first step, PPDO-b-PEG-b-PPDO triblock copolymer was synthesized via a ring-opening polymerization of P-Di Oxanone (PDO) monomer with Poly (Ethylene Glycol) (PEG) using stannous octoate (Sn(Oct) 2) as the catalyst. In the second step, L-lactide monomers (60 or 80 mole ratio) as the end blocks were added to the resulting prepolymer in presence of stannous octoate (Sn(Oct) 2) catalyst. In the first step, Poly (Ethylene Glycol) (PEG) and, in the second step, triblock copolymer acts as the macro-initiator. The obtained pentablock copolymers were identified by 1 H and 13 CNMR spectroscopy. Intrinsic viscosity of the resulting copolymers was measured via dilute solution viscometry in chloroform as the solvent. The thermal properties (such as melting points, melting enthalpy and crystallinity) and thermal degradation behavior were studied by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). From the obtained results, it was seen that the poly ( L-lactide) end blocks show similar crystallization behavior like poly ( L-lactide) homopolymer and also melting temperature of pentablock copolymers rise with an increase in L-lactide content.

The mechanism of selective transfection mediated by pentablock copolymers; Part II: Nuclear entry and endosomal escape

Transfection efficiencies of non-viral gene delivery vectors commonly vary with cell type, owing to differences in proliferation rates and intracellular characteristics. Previous work demonstrated that the poly(diethylaminoethylmethacrylate) (PDEAEM)/Pluronic F127 pentablock copolymers exhibit transfection in vitro selectively in cancer cell lines as opposed to non-cancerous cell lines. This study continues the investigation of intracellular barriers to transfection using this vector in “normal” and cancer cell lines to understand the underlying mechanisms of the selectivity. Results from Part I of this investigation showed, using conjugated epidermal growth factor, that cellular uptake of these polyplexes is not a major barrier in these systems. Part II of this work continues the investigation into the other potential intracellular barriers, endosomal escape and nuclear entry, using a lysosomotropic agent chloroquine (CLQ), and a nuclear localization signal (NLS) SV40, respectively. Lack of effectiveness of NLS peptide in improving the transfection efficiency suggests that nuclear uptake might not be the major intracellular barrier using the pentablock copolymer vectors, or that the nuclear transport might not be primarily achieved through nuclear pores. However, inclusion of CLQ led to a dramatic enhancement in the level of gene expression, with an almost two orders of magnitude increase in expression seen in normal cell lines, compared with that the increase observed in cancer cell lines. The different lysosomal pH values in normal vs cancer cells was believed to cause the pentablock copolymer vectors to behave distinctly during transport through endocytic pathways, with greater loss of functional DNA occurring in normal cells containing more acidic endocytic vesicles in contrast to cancer cells with less acidic vesicles. Interestingly, CLQ introduced almost no enhancement in the transfection with the control vector ExGen which lacked selectivity of transfection. Exploiting intracellular differences between normal and cancer cells for gene delivery vector design offers a new paradigm to achieve transfection selectivity based on intracellular differences rather than conventional approaches involving vector modification using specific ligands for targeted delivery.

Characterization of a sulfonated pentablock copolymer for desalination applications

Water and salt transport properties were determined in a family of sulfonated pentablock copolymers to characterize their potential as chlorine-tolerant desalination membrane materials. The degree of sulfonation, block molecular weight, and casting conditions can be independently varied to tune the transport properties of these materials. Data for water uptake, water permeability, salt permeability, and apparent surface charge are presented. Apparent diffusion coefficients of water in these materials were calculated using the solution-diffusion theory. Generally speaking, water sorption, water diffusivity, water permeability, and salt permeability increase with increasing degree of sulfonation. As ion exchange capacity increases from 0.4 to 2.0 meq/g (dry polymer), water uptake values vary between 21% and 118%, and water permeability values, in units of cm2 s−1, vary over 4 orders of magnitude. Salt permeability depends on both the upstream sodium chloride concentration, between 0.01 and 1.0 mol L−1, and the degree of sulfonation. Both water permeability and salt permeability are sensitive to the conditions used when casting the polymer films. Apparent surface charge, as characterized by zeta potential, has been shown to be related to the fouling tendency of several membrane materials. In these materials, zeta potential is most negative in samples with low levels of sulfonation and is near neutral in samples with the highest level of sulfonation.

Thermal and pH‐sensitive gold nanoparticles from H‐shaped block copolymers of (PNIPAM/PDMAEMA)‐b‐PEG‐b‐(PNIPAM/PDMAEMA)

AbstractWell‐defined H‐shaped pentablock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM), poly(N,N‐dimethylaminoethylacrylamide) (PDMAEMA), and poly(ethylene glycol) (PEG) with the chain architecture of (A/B)‐b‐C‐b‐(A/B) were synthesized by the combination of single‐electron‐transfer living radical polymerization, atom‐transfer radical polymerization, and click chemistry. Single‐electron‐transfer living radical polymerization of NIPAM using α,ω azide‐capped PEG macroinitiator resulted in PNIPAM‐b‐PEG‐b‐PNIPAM with azide groups at the block joints. Atom‐transfer radical polymerization of DMAEMA initiated by propargyl 2‐chloropropionate gave out α‐capped alkyne‐PDMAEMA. The H‐shaped copolymers were finally obtained by the click reaction between PNIPAM‐b‐PEG‐b‐PNIPAM and alkyne‐PDMAEMA. These copolymers were used to prepare stable colloidal gold nanoparticles (GNPs) in aqueous solution without any external reducing agent. The formation of GNPs was affected by the length of PDMAEMA block, the feed ratio of the copolymer to HAuCl4, and the pH value. The surface plasmon absorbance of these obtained GNPs also exhibited pH and thermal dependence because of the existence of PNIAPM and PDAMEMA blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis, self‐assembly, drug‐release behavior, and cytotoxicity of triblock and pentablock copolymers composed of poly(ε‐caprolactone), poly(L‐lactide), and poly(ethylene glycol)

AbstractBiocompatible and biodegradable ABC and ABCBA triblock and pentablock copolymers composed of poly(ε‐caprolactone) (PCL), poly(L‐lactide) (PLA), and poly(ethylene glycol) (PEO) with controlled molecular weights and low polydispersities were synthesized by a click conjugation between alkyne‐terminated PCL‐b‐PLA and azide‐terminated PEO. Their molecular structures, physicochemical and self‐assembly properties were thoroughly characterized by means of FT‐IR, 1H‐NMR, gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, dynamic light scattering, and transmission electron microscopy. These copolymers formed microphase‐separated crystalline materials in solid state, where the crystallization of PCL block was greatly restricted by both PEO and PLA blocks. These copolymers self‐assembled into starlike and flowerlike micelles with a spherical morphology, and the micelles were stable over 27 days in aqueous solution at 37 °C. The doxorubicin (DOX) drug‐loaded nanoparticles showed a bigger size with a similar spherical morphology compared to blank nanoparticles, demonstrating a biphasic drug‐release profile in buffer solution and at 37 °C. Moreover, the DOX‐loaded nanoparticles fabricated from the pentablock copolymer sustained a longer drug‐release period (25 days) at pH 7.4 than those of the triblock copolymer. The blank nanoparticles showed good cell viability, whereas the DOX‐loaded nanoparticles killed fewer cells than free DOX, suggesting a controlled drug‐release effect. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Micellar Morphology in Sulfonated Pentablock Copolymer Solutions

The morphology of solutions of poly[t-butyl styrene-b-hydrogenated isoprene-b-sulfonated styrene-b-hydrogenated isoprene-b-t-butyl styrene] (tBS-HI-SS-HI-tBS) pentablock copolymers with a range of sulfonation levels was studied by small-angle X-ray scattering and transmission electron microscopy. For dilute pentablock copolymer solutions, TEM confirms the spherical micellar morphology. Small-angle X-ray scattering results and their interpretation using the Kinning−Thomas model reveal that sulfonated pentablock copolymer solutions with all levels of sulfonation exhibit spherical micellar morphologies with a core of SS and a corona of solvated HI-tBS. Both the radius of the micelle core and the closest approach distance between cores increase with sulfonation level, while the number density of micelles decreases. The calculated fraction of micelles per unit volume shows an increase and then a plateau with sulfonation level. The manipulation of micelle size dramatically impacts the processability.

Picolyamine based pH/temperature sensitive hydrogels

pH/temperature-sensitive hydrogels have attracted increasing attention as drug/protein delivery systems. This study reports a new pH sensitive moiety of picolyamine (PCA) and its pentablock copolymer hydrogels made from triblock PCL-PEG-PCL and picolyamine oligomer (OPCA). The picolyamine monomer (PCAM) was synthe- sized using the picolyamine and methacryloyl chloride coupling reaction. OPCA was synthesized by conventional rad- ical polymerization from PCAM. The pKa of the pH sensitive moiety, OPCA, was found to be 6.65. The moiety was used to couple with PCL-PEG-PCL to produce the pentablock copolymer, OPCA-PCL-PEG-PCL-OPCA. The sol-gel phase transition of the aqueous solution of this material was affected by the pH and temperature change. In addition, the gel phase region could be controlled by the molecular weight of OPCA, the PCL/PEG ratio and chain length of PEG. This material could be used as an injectable hydrogel for drug/protein delivery.

Synthesis and Characterization of PDMS-, PVP-, and PS-Containing ABCBA Pentablock Copolymers

Amphiphilic ABCBA pentablock copolymers based on PVP, PS, and PDMS were synthesized using a combination of ATRP and RAFT polymerizations. The PVP-block-PS-block-PDMS-block-PS-block-PVP pentablock copolymer was characterized using a variety of chromatography and spectroscopic methods which showed that a high degree of end group and molecular weight control can be achieved. Preliminary analysis of the aqueous solution behavior of the pentablock copolymer showed that it self-assembles in water in order to shield the PDMS and PS segments from the water.

Thermoplastic Elastomers with Composite Crystalline−Glassy Hard Domains and Single-Phase Melts

We report the synthesis and characterization of thermoplastic elastomers (TPEs) containing both crystalline and glassy hard segments, with the aim of capturing the mechanical properties of conventional all-amorphous triblock TPEs, while forming the solid-state structure by crystallization from a single-phase melt. To accomplish this, we used living ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation to synthesize symmetric pentablock copolymers with the architecture crystalline−glassy−rubbery−glassy−crystalline. Analogous crystalline−rubbery−crystalline triblocks show a high initial modulus, yielding, and poor recovery, resulting from platelike crystalline hard blocks. By contrast, with the pentablock architecture and appropriate selection of block lengths, crystallization from a single-phase melt causes a layer rich in the glassy block to form around the crystallites, limiting their lateral growth and generating composite hard domains with both crystalline and glassy components. The pentablocks show the low initial modulus, strain-hardening behavior, and small permanent set desired for TPEs, while retaining an easily processed single-phase melt.

CHEMOENZYMATIC SYNTHESIS OF A PENTABLOCK COPOLYMER AND ITS SELF-ASSEMBLY BEHAVIOR STUDY

A triblock copolymer PCL-b-PEG-b-PCL was prepared by enzymecatalyzed ring-opening polymerization of e-caprolactone in the presence of catalyst Novozyme 435 and initiator PEG.The αbromoester terminated Br-b-PCL-b-PEG-b-PCL-b-Br macroinitiator was obtained in the subsequent esterification of end hydroxyl groups with α-bromopropionyl bromide and was used in the ATRP of 2,2,3,4,4,4-hexafluorobutyl methacrylate(HFMA).A pentablock copolymer consisting of poly(ethylene glycol)(PEG),polycaprolacrone(PCL) and poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)(PHFMA) was synthesized.The structures of the polymers were characterized by NMR and GPC.Because of the industrial and scientific significance,increasing interest has been arising on the aggregates of complicated block copolymers in selective solvents.The self-assembly of the pentablock copolymer was investigated in aqueous solutions.The size and shape of the resulting micelles were investigated using dynamic light scattering and tapping-mode atomic force microscopy.The results demonstrated that the copolymeric micelles had a spherical shape with a mean diameter of about 77 nm.In addition,the micellar morphologies were influenced remarkably by changing the initial copolymer concentration in organic solvents.

Controlling the degradation of pH/temperature-sensitive injectable hydrogels based on poly(β-amino ester)

Poly (ethylene glycol) (PEG) — poly(e-caprolactone(CL)-co-D,L-lactide (LA)) (PCLA-PEG-PCLA) was synthesized by ring-opening polymerization to form a temperature sensitive hydrogel triblock copolymer. Poly(β-amino ester) (PAE) obtained from 1,4-butanediol diacrylate (BDA), and 4,4′-trimethylene dipiperidine (TMDP) was used as a pH sensitive moiety to conjugate to the triblock copolymer. The physicochemical properties of the temperature-sensitive triblock and pH/temperature-sensitive pentablock copolymers (PAE-PCLA-PEG-PCLA-PAE) were characterized by 1H NMR spectroscopy and gel permeation spectroscopy. The sol-gel phase transition behavior of the PAE-PCLA-PEG-PCLA-PAE block copolymers was investigated. An aqueous solution of the copolymers (20 wt%) changed from a sol phase at pH 6.4 and 10°C to a gel phase at pH 7.4 and 37°C. In addition, the degradation of PAE-PCLA-PEG-PCLA-PAE was compared with that of poly(ethylene glycol) — poly(e-caprolactone) — poly (β-amino ester) (PAE-PCL-PEG-PCL-PAE) using both in vitro and in vivo experiments. The relationship between the insulin release profile from the matrix and the degradation of these materials also investigated.

Tunable hydrogel morphology via self-assembly of amphiphilic pentablock copolypeptides

Download options Please wait... Supplementary files Table S1 (molecular weights and molecular weight distributions of pentablock copolymers), Table S2 (minimum gelation concentrations) and Fig. S1–S6 (additional rheology, confocal microscopy, DLS, cryoTEM, TEM and SAXS data) PDF (794K) Article information DOI https://doi.org/10.1039/B927137F Article type Paper Submitted 23 Dec 2009 Accepted 07 Apr 2010 First published 30 Apr 2010 Download Citation Soft Matter, 2010,6, 2546-2551 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Tunable hydrogel morphology via self-assembly of amphiphilic pentablock copolypeptides Z. Li and T. J. Deming, Soft Matter, 2010, 6, 2546 DOI: 10.1039/B927137F To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Zhibo Li Timothy J. Deming

New amphiphilic fluorescent CBABC-type pentablock copolymers containing pyrene group by two-step atom transfer radical polymerization (ATRP) and its self-assembled aggregation

Abstract A series of novel amphiphilic fluorescent CBABC-type pentablock copolymers ( Py – PMMA – PEG4600 – PMMA – Py ) were prepared from BAB-type amphiphilic triblock copolymer ( PMMA – PEG4600 – PMMA ) as macroinitiator with various contents of 1-(methacryloyloxyethylamino-carboxylmethyl) pyrene ( PyMOI ) by atom transfer radical polymerization (ATRP) in toluene using CuBr/2,2-bipyridine as catalyst system. Triblock copolymer ( PMMA – PEG4600 – PMMA ) was prepared by ATRP and obtained from Br – PEG4600 – Br as macroinitiator with methyl methacrylate in tetrahydrofuran using the same catalyst. The molecular weights of pentablock copolymers which were reinitiated by PMMA – PEG4600 – PMMA macroinitiator were calculated from 1 H NMR spectra up to 42,400 gmol −1 . The polydispersity of pentablock copolymers obtained from GPC analysis was narrow between 1.10 and 1.38. The crystallinity of triblock copolymer ( PMMA – PEG4600 – PMMA ) was decreased slightly with incorporating PMMA segment. Introducing the bulky pyrene substituent into pentablock copolymer, the melting temperature was not observed and all pentablock copolymers showed amorphous patterns in wide-angle X-ray scattering (WAXS) due to decrease in the degree of crystallinity of polymer chain because of disturbing regular packing. The temperatures at 10% weight loss (Td 10 ), examined by TG analysis, showed values ranging from 265 to 323 °C in nitrogen and 264 to 313 °C in air. Fluorescence spectra of Py – PMMA – PEG4600 – PMMA – Py exhibited stronger excimer emission at ca . 480 nm due to the aggregations of pyrene group formed via interaction of the hydrophobic chains. The more content of PyMOI segment in pentablock copolymers can obtain the higher emission intensity ca . 480 nm. When there were higher PyMOI contents (84.9 wt% PyMOI ) in pentablock copolymers, they formed larger aggregates (210 nm) in SEM micrographs. On the other hand, while increasing the concentration of the polymer solution in THF, the morphology was changed from spherical (0.1 mg/mL) to chainlike (1.0 mg/mL) aggregates.