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DHBCs copolymers

Amphiphilic block copolymers containing a cationic block may carry as the second block a hydrophilic or a hydrophobic one. Those containing a hydrophilic second block belong to the so called double-hydrophilic block copolymers (DHBC), which have recently been reviewed [60]. This promising class of polymers has potential applications in drug-carrier systems, gene therapy, desalination membranes, as switchable amphiphiles, and others [45, 60, 77]. [Pg.13]

A novel route to DHBC is outlined in Scheme 11. Reaction of TEMPO-ter-minated poly(VBC) with PEG-monomethyl ether results in reactive block copolymers 47, which can be converted readily to polymers 48 and 49 containing a cationic or a betainic block besides a PEG block [84]. [Pg.19]

Double hydrophilic block copolymers (DHBCs) are a class of polymers that combine the self assembly ability of block copolymers with the water solubility of hydrophilic macromolecular chains. Numerous sophisticated works have been already described in the literature, indicating the potential of this class of copolymers in emerging technologies. The synthesis of novel DHBCs, using either new monomers or post polymerization functionalization schemes, is the subject of intense investigation during the current years. [Pg.291]

Anionic polymerization is known to give model block copolymers with controlled molecular weights, narrow molecular weight distributions and versatile architecture. Anionic polymerization has been used for the synthesis of DHBCs in several eases although this type of polymerization teehnique is relatively intolerant to the presence of polar functionalities on the monomers utilized. A recent example has been described by Hadjichristidis and coworkers [6]. They have presented the synthesis of a series of poly (2-vinylpyridine-b-... [Pg.292]

Combination of anionic polymerization and post polymerization reactions has been used for the synthesis of poly(acrylic acid-b-N,N-diethylacrylamide) (PAA-PDEA) copolymers [9]. Initially the synthesis of a precursor poly(tert-butylacrylate-b- N,N-diethylacrylamide) (PtBMA-PDEAAm) block copolymer was realized via sequential anionic polymerization of the tert-butyl acrylate and diethylacrylamide monomers. However, an amount of PtBMA homopolymer was detected in the crude reaction product. In order to remove the vast majority of the homopolymer, the authors proposed the precipitation of the crude product in hexane, where the homopolymer is highly soluble, in contrast to the block copolymer. The piuified block copolymer was subjected to deprotection of the tert-butyl group in acidic media, leading to the desirable DHBC. The final block copolymer showed pH and thermosensitive solution aggregation. [Pg.293]

DHBCs of the type poly(p-hydroxystyrene-b-methaciylic acid) (PHOS-PMAA) were also synthesized via anionic polymerization followed by acidic hydrolysis [10]. Both blocks of the precursor poly(p-tert-butoxystyrene-b-tert-butylmethacrylate) (PtBOS-PtBMA) copolymers, formed by sequential addition of the protected monomers, could be deprotected in a single step giving the desired pH-responsive block copolymers. Figure 2. Hydrolysis was found to be nearly quantitative and resulted in a series of copolymers with well defined molecular characteristics and of variable composition. [Pg.293]

Different series of DHBCs were prepared from anionically synthesized poly(p-tert-butoxystyrene-b-ethylene oxide) (PtBOS-PEO) precursors [12], Post polynnerization acidic hydrolysis of the PtBOS block resulted in poly(p-hydroxystyrene-b-ethylene oxide) (PHOS-PEO) copolymers. Further functionalization of the PHOS block via a Mannich type aminomethylation reaction gave the poly[3,5-bis(dimethylaminomethylene)hydroxystyrene-b-ethylene oxide] (PNHOS-PEO) copolymers, as testified by FT-IR and NMR experiments. In these copolymers the PNHOS block carries two dimethylamino groups per monomeric imit that can be protonated in acidic media and weakly acidic phenolic groups that have their own pH sensitivity. The PNHOS-PEO block copolymers were further quatemized with... [Pg.294]

The synthesis of an interesting DHBC, namely poly (4-vinylbenzoic acid-block-2-(diethylamino)ethyl methacrylate) (PVBA-PDEAEMA), has been presented by Armes and Liu [13], The synthesis was performed by ATRP using protecting group chemistry in three steps. Initially the polymerization of a tert-butyl protected PVBA macro-initiator was performed followed by the polymerization of the second monomer, DEAEMA. Finally the hydrolysis of the tert-butyl protected block was realized giving rather monodisperse block copolymers. [Pg.295]

The synthesis of a novel, primary amine containing, DHBC has been described by Liu and coworkers [31]. The synthesis of the amine-containing monomer was performed by a two step click reaction. The preparation of the block copolymer, namely poly(N-isopropylacrylamide)-b-1 -(3 -aminopropyl)-4-acrylamido-1,2,3 -triazole hydrochloride)... [Pg.298]

The synthesis of a well defined poly(vinyl alcohol)-b-poly(aciylic acid) (PVA-PAA) DHBC has been recently reported in the literature [32] by a two step synthetic scheme. First the synthesis of a poly(acrylonitrile) (PAN) block was realized via cobalt-mediated radical polymerization, using a poly(vinyl acetate) (PVAc) macroinitiator, followed by hydrolysis of both blocks. The polymerization was performed in DMF, a very good solvent for PAN, and at low temperature, where block copolymers with low polydispersity were obtained. The polymerization procedure led to well defined macromolecules with relatively high molecular weights. The obtained copolymers were transformed to the desired DHBCs by hydrolysis, using large excess of potassium hydroxide in a water/ethanol mixture. The successful completion of the hydrolysis reaction was monitored by NMR and IR spectroscopy. An additional macroscopical indication of the DHBC formation was the aqueous solubility of the reaction product. [Pg.299]

In the concept of water soluble ABC block copolymers one has also to mention a huge amount of work that has been presented on the synthesis and solution behavior of copolymers with two hydrophilic blocks and one hydrophobic. However, the presence of a permanently hydrophobic block in this type of block polymers makes difficult their categorization as DHBCs. The synthesis of ABC triblock terpolymers with at least two hydrophilic blocks has been realized via a number of polymerization methodologies, like GTP and cationic polymerization, and has been studied in detail [42,43,44,45,46,47,48,49]. In most of the cases, the terpolymers were based on suitably functionalized methacrylate monomers and have been produced by the sequential monomer addition method. [Pg.301]

Finally, the synthesis of multiblock DHBCs has been also reported. The desired multiblocks have been obtained via RAFT polymerization, using polytrithiocarbonate as the chain transfer agent [50]. The synthesis of two mulhblocks with different molecular characteristics was achieved. Both block copolymers were consisted of PDMA and PNIPAM sequences. The molecular characteristics of the synthesized macromolecules were studied... [Pg.301]

One of the first syntheses of non-linear DHBCs has been described by Armes and coworkers [51]. They have prepared a series of A2B miktoarm star copolymers via ATRP of several hydrophilic methacrylate monomers by utilizing Jeffamine macroinitiators. The macroinitiators (which were the B blocks of the eopolymers) were synthesized by reaction of the terminal amino group of the polyalkyleneoxide ehain with two equivalents of 2-hydroxyethylmethacrylate, followed by esterification with 2-bromoisobutyryl bromide. The A blocks carried pH responsive substituted amine groups (water soluble and positively eharged at low pH) or zwitterionic phosphatidylamine groups. The expeeted ehemieal struetures for the macroinitiators and the resulting star copolymer where confirmed by NMR, MALDI-TOF-MS and SEC techniques. [Pg.302]

The synthesis of a miktoarm star copolymer of the type AnBn has been also demonstrated. The synthesis was performed via ATRP using divinylbenzene, as the core cross-liking agent. PEO macroinitiator chains were utilized for the polymerization of divinylbenzene forming a star polymer, with a random number of branches. The above star polymer was used as a multi-functional initiator for the polymerization of methacrylate monomers. Therefore, the synthesis of an amphiphilic miktoarm star copolymer was realized [54]. Finally, the hydrolysis of the protected methacrylate block led to the preparation of the desired DHBCs, namely the PEOn-PMAA stars. SEC analysis of the preeursor PEOn-PMMA copolymer revealed a relatively broad molecular weight distribution. Nevertheless, this is a good example for the synthesis of A Bn double hydrophilic star copolymers. [Pg.303]

Schizophrenic solution behavior has been also observed in a PMAA-PDEAEMA DHBC. The particular copolymer formed core-shell micelles at extreme pH ranges, i.e. pH < 5.5 or pH > 9.2, while it was phase separated at intermediate pH values. Micelles having PMAA cores were formed in acidic solutions, while micelles with PDEAEMA cores were formed in alkaline solutions [15]. [Pg.308]

An interesting example of a DHBC system that can self assemble tmder the influence of two different stimuli is the PVBA-PMEMA copolymer, presented by Liu and Armes [14]. The particular system formed small well defined micelles with a PVBA core at pH values lower than 5.5 at room temperature and in the absence of salt. No precipitation was observed at the isoelectric... [Pg.312]

Another example of a DHBC, which responds to two different stimuli, is the PNIPA-PSPP copolymer [93], This copolymer presents both UCST (PSPP block) and LCST (PNIPAM block) in aqueous solutions. However, the addition of salt increases the hydrophilicity of the PSPP block leading to a disappearance of the UCST. In contrast, the hydrophilicity of the PNIPAM block, is decreased upon addition of salt. Therefore, the size of the supramolecular aggregates formed is altered not only upon changes in solution temperature but also upon changes in the salinity. Copolymer concentration was also found to play a crucial role on the dimensions of the self-assembled structures. [Pg.313]

The micellization of a polypeptide eontaining DHBC has been also studied under variable solution pH and temperature [30]. A sehizophrenic solution behavior was observed for a PNIPAM-PGA block copolymer. At room temperature and low pH values micelles having polypeptide cores were formed, while at elevated temperatures and increased pH values micelles with PNIPAM cores were observed. It has to be noted that the formation of PGA eoie micelles was accompanied by a coil-to-helix transition of the polypeptide sequence. The above transition had as a result a different micellization kinetic profile for the system in eomparison with other conventional pH responsive systems. [Pg.313]

Another example of schizophrenic behavior has been observed in the case of A-b-(B-co-C) DHBCs. The copolymers P(EGMA-co-MMA)-PDEA (with various contents of MAA) associated in water either at elevated temperature and low pH values or at low temperature and increased pH values [28], Inverse micelles were observed in each case. Moreover, both the solution salinity and the content of MAA had a great influence on the critical micellization temperature, as was revealed by the experimental observations. [Pg.314]

Temperature and pH responsiveness has been also recorded for a non covalently bonded DHBC inclusion complex, namely P4VP-PNIPAM [33]. The non-covalently connected copolymer tends to create micelles with PNIPAM cores at low pH values and at elevated temperatures. However, at room temperature and high pH values, the polymer formed vesicles instead of core-shell micelles. The formation of vesicles was confirmed by a number... [Pg.314]

The use of double hydrophilic block copolymers in biomimetic mineralization processes has been investigated in recent years. In contrast to rigid templates (like carbon nanotubes and porous aluminum templates which predefine the final structure) water soluble polymers could be used as soluble species at various hierarchy levels. Usually, in the case of DHBCs, one of the block acts as scaffold for the development of the crystal, while the other acts as a soluble-stabilizing matrix. Therefore, both of the blocks play a crucial role on the development of the crystals. There is a plethora of reports on the emerging bio-inspired mineralization field. Various crystal structures have been presented during the last years, following versatile synthetic routes. A very detailed and illustrious review has been recently given by Colfen [3]. The above review describes in detail all aspects of the specific field. Herein, we present just a few selected examples. [Pg.316]

The development of CaCOs tablet-like arrays was achieved at the air/water interface through the cooperative mineralization regulated by a polypeptide and a DHBC, namely PEO-PMAA [95]. The experimental data indicate that the role of the block copolymer is focused on the regulation of the arrangement and orientation of the CaCOs tablets. The cooperative action of a polypeptide is essential for the formation of CaCOs tablet at the air/water interface. In the absence of the polypeptide, the formation of calcite CaCOs particles in the water phase was observed. [Pg.316]

An outstanding approaeh for the development of drug delivery systems has been recently presented by Zhang and Ma [99], In this work, the use of a P-cyclodextrin (P-CD) containing DHBC has been proposed for the inclusion of many hydrophobic substances. In their work, the synthesis of a bloek eopolymer with a PEG block and a polyaspartamide block carrying some P-CD units has been described. The P-CD imits are used as host sites for a plethora of hydrophobic small molecules, like pyrene and comnarine, as well as for hydrophobic polymers. However, the formation of inclusion complexes leads to the creation of located hydrophobic areas within the copolymer domain, which, in turn, has as a result the formation... [Pg.317]


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DHBCs

Double-hydrophilic block copolymers DHBCs)

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