Poly diblock copolymers

As previously described, all microspheres discussed in this chapter were synthesized from AB type diblock copolymers. Precursor block copolymers, poly(styrene-b-4-vinyl pyridine) (P[S-b-4VP]) diblock copolymers, were synthesized using the additional anionic polymerization technique [13]. The basic properties of the block copolymers were determined elsewhere [24,25] and are listed... 

With diblock copolymers, similar behavior is also observed. One component is enriched at the surface and depending on miscibility and composition a surface-induced ordered lamellar structure normal to the surface may be formed. Recent investigations include poly (urethanes) [111], poly(methoxy poly (ethyleneglycol) methacrylate)/PS [112] and PS/PMMA [113, 114]. In particular the last case has been extensively studied by various techniques including XPS, SIMS, NR and optical interferometry. PS is enriched at the surface depending on blockcopolymer composition and temperature. A well ordered lamellar structure normal to the surface is found under favourable conditions. Another example is shown in Fig. 6 where the enrichment of poly(paramethylstyrene), PMS(H), in a thin film of a di-... 

Fig. 6. Hydrogen depth profile of a thin film of poly(p-methylstyrene)(H)/ PS(D) diblock copolymer, PMS(H)-b-PS(D), on a silicon wafer as obtained by the l5N-NRA technique [57]. The sample has been annealed for 1 h at 140 °C. PMS(H) is largely enriched at the surface. The solid line is a guide to the eye...

Fig. 7a, b. PMIM-image of (a) a poly-p-bromostyrene surface [118], (b) a PS/polybutadiene diblock copolymer, PS-b-PB, at approximately 100 fold magnification. The lateral resolution is of the order of 1 pm while the height resolution is of the order of 0.6 nm. The root-mean-square roughness averaged over the area shown is 0.8 nm in (a) close to the resolution limit of the technique. It is much larger (10 nm) in (b) due to the formation of steps after annealing. The scale in z-direction in (a) and (b) is different by a factor of 7... 

Poly(styrene-/7-isobutylene-/ -styrene) (PS-PIB-PS), triblock copolymers can be prepared via coupling of living PS-PIB diblock copolymers in a one-pot procedure [12]. 

FIGURE 5.17 Temperature versus G —the shear storage modulus at a frequency of 1.6 Hz for diblock copolymer poly(ethylene propylene)-poly(ethylethylene) (PEP-PEE). The order-disorder transition (ODT) calculated to be 291°C 1°C. (From Rosedale, J.H. and Bates, F.S., Macromolecules, 23, 2329, 1990. With permission of American Chemical Society.)... 

Papadopoulos, P. etal. Nanodomain-induced chain folding poly(gamma-benzyl-L-glutamate)-b-polyglycine diblock copolymers. Biomacromolecules, 6, 2352, 2005. 

Wang, Z., Masuo, S., Machida, S. and Itaya, A. (2007) Site-selective doping of dyes into polystyrene-fclock-Poly(4-vinyl pyridine) diblock copolymer films and selective laser... 

Even more complex structures have been described. For example, chirality of blocks may lead to other morphologies. A polystyrene-fc-poly-(L-lactide) diblock copolymer, PS-fr-PLLA, constituting both achiral and chiral blocks was reported to form an array of hexagonally packed PLLA nanohelices with a left-handed helical sense in the bulk state (Fig. 3). The structure was found... 

Although being qualitatively in agreement with experimental results, disagreements between experiment and theory remain. Besides the composition, /a, and the total degree of polymerization, N, all theoretical works refer to the segmental interaction parameter x This parameter can be estimated from a relationship to the solubility parameters. The ODT as a thermodynamic measure of the incompatibility was used to compare a set of symmetrically composed diblock copolymers from different hydrocarbons, polydimethyl-siloxane and poly(ethylene oxide) (PEO) [33]. While the behaviour of hydrocarbon diblock copolymers was successfully described by a consistent set of solubility parameters, this procedure failed for systems containing PEO. The... 

The pathway and kinetics of the C to S transition have been studied on shear-aligned cylinders of the commercial diblock copolymer of PS and poly(ethylene-co-butylene) (KRATON G 1657 Shell Chemical Company) [143, 144], A complete dissolution of the cylindrical structure before the epitaxial... 

As an example of blends with attractive interactions, Fig. 65 shows a superstructure in which interactions between methacrylic acid groups and pyridine side groups of a polystyrene-fc-polybutadiene-fo-poly(f-butyl methacry-late-staf-methacrylic acid) (PS-b-PB-b-P(MAA-sfaf-fBMA)) triblock quater-polymer and a PS- -P2VP diblock copolymer lead to a wavy lamellar structure with cylinders from mixed P2VP and P(MAA-sfaf-fBMA) blocks [194],... 

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. 

Arimura H, Ohya Y, Ouchi T (2005) Formation of core-shell type biodegradable polymeric micelles from amphiphilic poly(aspartic acid)-Wock-polylactide diblock copolymer. Biomacromolecules 6 720-725... 

Fig. 13 The structure of DOX-conjugated PEG-b-poly (aspartic acid) diblock copolymer. DOX molecules are covalently bonded to a diblock copolymer via hydrazine linkage, which can be cleaved in acidic conditions, enabling the release of DOX in a site-specific manner...

Anchoring of Diblock Copolymers of Polystyrene and Poly(dimethyl siloxane) on Polymer Particles... 

Much work on the preparation of nonaqueous polymer dispersions has involved the radical polymerization of acrylic monomers in the presence of copolymers having the A block the same as the acrylic polymer in the particle core 2). The preparation of polymer dispersions other than polystyrene in the presence of a PS-PDMS diblock copolymer is of interest because effective anchoring of the copolymer may be influenced by the degree of compatibility between the PS anchor block and the polymer molecules in the particle core. The present paper describes the interpretation of experimental studies performed with the aim of determining the mode of anchoring of PS blocks to polystyrene, poly(methyl methacrylate), and poly(vinyl acetate) (PVA) particles. 

Liu et al. prepared palladium nanoparticles in water-dispersible poly(acrylic acid) (PAA)-lined channels of diblock copolymer microspheres [47]. The diblock microspheres (mean diameter 0.5 pm) were prepared using an oil-in-water emulsion process. The diblock used was poly(t-butylacrylate)-Wock-poly(2-cinna-moyloxyethyl) methacrylate (PtBA-b-PCEMA). Synthesis of the nanoparticles inside the PAA-lined channels of the microspheres was achieved using hydrazine for the reduction of PdCl2, and the nanoparticle formation was confirmed from TEM analysis and electron diffraction study (Fig. 9.1). The Pd-loaded microspheres catalyzed the hydrogenation of methylacrylate to methyl-propionate. The catalytic reactions were carried out in methanol as solvent under dihydro-... 

AB diblock copolymers, 20 485-487 AB diblock poly ampholytes, 20 478 Abierixin, 20 132... 

Loo et al. [21,42,44,91] reported a simple exponential decay (n = 1) for polyethylene-fc-poly(styrene-ran-ethylene-ran-butene) [PE-fo-poly(SEB)] diblock copolymers in which the PE blocks form isolated spheres or cylin-... 

The technique of self-nucleation can be very useful to study the nucleation and crystallization of block copolymers that are able to crystallize [29,97-103]. Previous works have shown that domain II or the exclusive self-nucleation domain disappears for systems where the crystallizable block [PE, PEO or poly(e-caprolactone), PCL] was strongly confined into small isolated MDs [29,97-101]. The need for a very large number of nuclei in order to nucleate crystals in every confined MD (e.g., of the order of 1016 nuclei cm 3 in the case of confined spheres) implies that the amount of material that needs to be left unmolten is so large that domain II disappears and annealing will always occur to a fraction of the polymer when self-nucleation is finally attained at lower Ts. This is a direct result of the extremely high number density of MDs that need to be self-nucleated when the crystallizable block is confined within small isolated MDs. Although this effect has been mainly studied in ABC triblock copolymers and will be discussed in Sect. 6.3, it has also been reported in PS-fc-PEO diblock copolymers [29,99]. 

There have been relatively few reports dealing with double-crystalline diblock copolymers [102-110,197-200]. The particular case of ABC triblock copolymers with two semicrystalline blocks will be presented in a separate section. Works pertaining to one of the most studied systems PCL-fo-PEO have already been previously reviewed [43]. Recently, probably the most comprehensive studies on double-crystalline diblock copolymer systems were performed on poly(p-dioxanone)-fc-PCL diblock copolymers, PPDX-fr-PCL, and therefore several important aspects of these works [102,103,107] will be summarized in this section. 

Fig. 6 a DSC cooling scans (10°Cmin ) for poly(e-caprolactone) (PCL) and poly(p-dioxanone) (PPDX) homopolymers, diblock copolymers and a 50/50 blend, b Subsequent heating scans (10 °Cmin 1). (From [103], Reproduced with permission of the Royal Society of Chemistry)... 

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