Diblock copolymers poly -based

A different pH-triggered deshielding concept with hydrophilic polymers is based on reversing noncovalent electrostatic bonds [78, 195, 197]. For example, a pH-responsive sulfonamide/PEl system was developed for tumor-specific pDNA delivery [195]. At pH 7.4, the pH-sensitive diblock copolymer, poly(methacryloyl sulfadimethoxine) (PSD)-hZocA -PEG (PSD-b-PEG), binds to DNA/PEI polyplexes and shields against cell interaction. At pH 6.6 (such as in a hypoxic extracellular tumor environment or in endosomes), PSD-b-PEG becomes uncharged due to sulfonamide protonation and detaches from the nanoparticles, permitting PEI to interact with cells. In this fashion PSD-b-PEG is able to discern the small difference in pH between normal and tumor tissues. 

A. Benahmed, M. Ranger and J. C. Leroux, Novel polymeric micelles based on the amphiphilic diblock copolymer poly(N-vinyl-2-pyrrolidone)-Wocfc-poly(D,L-lactide). Pharm. Res., 18,323-328 (2001). 

The work by Ciferri and coworkers [128-130] focused on the supramolecular organization of aromatic rod-coil copolyamides in diluted (isotropic) and moderately concentrated (lyotropic) phases. Their diblock copolymers were based on a rigid block of poly(p-benzamide) (PBA) having a DP about 100, and different comparable lengths of flexible blocks, such as poly(m-phenylene isophthalamide) (MPD-I), poly(/n-benzamide) (MBA), or poly(ethylene glycol) (PEG). The use of end-capped prepolymers and selective extraction techniques assured a strict two-block sequence, the absence of free homopolymers not strongly bound to the copolymers, and a fractionation in terms of the rigid/flexible compositional distribution ratio. 

A simple procedure to pattern proteins onto surfaces was developed. The carbohydrate-based amphiphilic diblock copolymer, poly(styrene-Woc -[2-(p-D-galactosyloxy)ethyl methacrylate-co-styrene] [PS-fi-P(GalEMA-co-S)], was used for micellization and the production of honeycomb-stmctured porous films. Lectin binding assays using UV-vis spectroscopy and DLS showed that fluorescent PNA was successfully conjugated with the sugar moieties on the micelles and inside the pores of the porous films (Fig. 4) [62]. 

Poly(alkylene oxide)-based (PEO-PPO-PEO) triblock and diblock copolymers are commercially successful, linear non-ionic surfactants which are manufactured by BASF and ICI. Over the last four decades, these block copolymers have been used as stabilisers, emulsifiers and dispersants in a wide range of applications. With the development of ATRP, it is now possible to synthesise semi-branched analogues of these polymeric surfactants. In this approach, the hydro-phobic PPO block remains linear and the terminal hydroxyl group(s) are esteri-fied using an excess of 2-bromoisobutyryl bromide to produce either a monofunctional or a bifunctional macro-initiator. These macro-initiators are then used to polymerise OEGMA, which acts as the branched analogue of the PEO block (see Figures 2 and 3). 

Riess demonstrated recently that poly(styrene-b-oxirane) copolymers could act as non-ionic surfactants and lead to water/ toluene microemulsions (29, 30). Using isopropanol as cosurfactant, both 0/W and W/0 microemulsions are obtained (3l). This is a very important conclusion, since PO based diblock copolymers give rise only to 0/W microemulsions under the same experimental conditions (8, 31,). In this respect the "branched structure" of the PO hydrophilic component could favor a decrease in the packing density of the inverse micelle forming molecular and explain the different behavior of the linear and star-shaped PS/PO block copolymers in the W/0 microemulsification process. 

Kim and coworkers observed the formation of micelles in aqueous solutions by synthesizing a amphiphilic linear-dendritic diblock copolymer based on poly(ethylene oxide) (PEO) (Figure 5)50,62. In this case, the PEO can be considered as the core upon which the dendrimer was synthesized via a divergent process. In an aqueous phase, the hydrophilic... 

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