Hydrophilic block copolymers synthesis

Colfen, H. (2001) Double-hydrophilic block copolymers synthesis and application as novel surfactants and crystal growth modifiers. Macromotecular Rapid Communications, 22, 219-252. 

Qi, L. Colfen, H. and Antonietti, M. (2001). Synthesis and Characterization of CdS Nanoparticles Stabilised by Double Hydrophilic Block Copolymers. Nano Lett, 1, 61-65. 

ATRP is a powerful synthetic tool for the synthesis of low molecular weight (Dp < 100-200), controlled-structure hydrophilic block copolymers. Compared to other living radical polymerisation chemistries such as RAFT, ATRP offers two advantages (1) facile synthesis of a range of well-defined macro-initiators for the preparation of novel diblock copolymers (2) much more rapid polymerisations under mild conditions in the presence of water. In many cases these new copolymers have tuneable surface activity (i.e. they are stimuli-responsive) and exhibit reversible micellisation behaviour. Unique materials such as new schizo-... 

FIGURE 54.27 Macro-CTAs and schematic representation of the RAFT precipitation polymerization process. (Reprinted with permission from J. Am. Chem. Soc., 129(46), An, Z., Shi, Q., Tang, W., Tsung, C.K., Hawker, C.J., and Stucky, G.D., Facile RAFT precipitation polymerization for the microwave-assisted synthesis of well-defined, double hydrophilic block copolymers and nanostructured hydrogels, 14493. Copyright 2007 American Chemical Society.)... 

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. 

Recently, this combination was also used in the synthesis of double-hydrophilic block copolymers such as PEO-l -PNIPAM and PEO-l -PSS. In these applications, the hydroxyl groups of mono- or difimctional PEOs were converted to dithiobenzoyl groups and used as macro-RAFT agents. Depending on the functionality of the initial PEO-, AB-, and ABA-type block copolymers, well-defined structures were prepared from the polymerization of NIPAM and styrenesulfonate (SS). The overall procedure is summarized in Scheme 45. 

Gianneschi and coworkers [29] have utilized a similar approach in functionalizing ROMP copolymers with hydrophilic peptides. This work involves a block copolymer synthesis incorporating a phenyl NBE moiety as the hydrophobic block and an NHS moiety as the chemically addressable block. Subsequent conjugation of peptides via their N-termini affords amphiphilic block copolymers in which the hydrophilic shell is defined by a short peptide sequence programmed to be an enzyme substrate. For graft-to functionalization, A/ ,A/ -diisopropylethylamine was added to the activated ester diblock copolymer in DMF, followed by the addition of peptide (with respect to NHS units). 

More specific topics, such as block copolymer synthesis by changing the polymerization mechanism [18], by step-growth polymerization [19], via macroinitiators [20], living free-radical polymerization [21, 22] or ionic polymerization [23] were reviewed later on, as well as the synthesis of selected block copolymer types, for example hydrophilic-hydrophilic copolymers [24], copolymers based on PEO [10,16]. 

Cai, Y., Tang, Y. and Armes, S.P. (2004) Direct synthesis and stimulus-responsive micellization of Y-shaped hydrophilic block copolymers. Macromolecules, 37,972S-97 i7. 

Bouyer F, Gerardin C, Fajula F, Putaux JL, Chopin T (2003) Role of double-hydrophilic block copolymers in the synthesis of lanthanum-based nanoparticles. Colloids Surf A 217 179-184. doi 10.1016/s0927-7757(02)00574-5... 

Kizakkedathu, J.N., Kumar, K.R., Goodman, D., and Brooks, D.E. 2004. Synthesis and characterization of weU-defined hydrophilic block copolymer brushes by aqueous ATRP. Polymer 45 7471-89. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

In their efforts to construct stimuli-responsive, supramolecular amphiphiles, Frechet et al. [126-129] reported the synthesis of a novel series of AB and ABA block copolymers via the Williamson ether synthesis (e.g., 47, Fig. 21). Polyethylene glycols (PEGs) of different lengths were used as the linear hydrophilic B block while polyaryl ether dendrons of different sizes were used as the hydro-phobic A block. These copolymers were characterized by optical microscopy,... 

In a very recent set of papers [48,54,59,60,131,132,324-328], the synthesis and characterization of metallosupramolecular amphiphilic block copolymers containing a hydrophilic PEO block linked to a hydrophobic PS or PEB block through a fozs-2,2/ 6/,2/terpyridine-ruthenium(II) complex have been described. These copolymers form the so-called metallosupramolecular micelles . 

We have shown that polymeric micelles constmcted of block copolymers of poly(ethylene oxide) (PEG) and poly(L-asparate) containing the anticancer dmg (adriamycin, ADR) selectively accumulate at solid tumor sites by a passive targeting mechanism. This is likely due to the hydrophilicity of the outer PEG chains and micellar size (<100 nm) that allow selective tissue interactions [17,18]. Polymeric micelle size ranges are tailored during polymer synthesis steps. Carefully selection of block polymer chemistry and block lengths can produce micelles that inhibit nonselective scavenging by the reticuloendothelial system (RES) and can be utilized as targetable dmg... 

---