Polystyrene-dimethylsiloxane block copolymer

Poly(dimethylsiloxane) (PDMS) is a well-known hydrophobic polymer with higher repellency for water than PS crosslinked siUcone elastomers (WCA = 112° for a smooth film) are commonly used for fabricating microfluidic devices. But forming solid fibers comprised solely of linear PDMS is not possible, due to its low glass transition temperature. Instead of using linear homopolymer PDMS, Ma et al. [21] electrospun fibers of poly(styrene-b-dimethylsiloxane) block copolymers blended with 23.4 wt% homopolymer polystyrene (PS-PDMS/PS) from a solution in a mixed solvent of THF and DMF. The resultant fiber mat, with fiber diameters in the range of 150-400 nm, exhibited a WCA of 163° and a hysteresis of 15°. An illustration of water droplets beaded up on such a mat is provided in Fig. 3. A PS mat of similar fiber diameter and porosity exhibited a WCA of only 138°. The difference was attributed to the lower surface tension of the PDMS component, combined with its spontaneous segregation to the fiber surface. X-ray photoelec-... 

Rutledge et al. showed that fiber mats composed solely of uniform fibers could be obtained by electrospinning a hydrophobic material (i.e., poly(styrene-block-dimethylsiloxane) block copolymer) blended with homopolymer polystyrene (PS) [24]. The roughness of the nonwoven mat, resulting from the small diameters of the fibers (150-400 nm), combined with the enrichment of the dimethylsiloxane... 

A. Mayer et al. examined poly(dimethylsiloxane)-bIock-poly(ethylene oxide) (PDMS-b-PEO), poly(styrene)-f)Iock-poly(ethylene oxide) (PS-b-PEO), polystyrene-block-poly(methacryhc acid) (PS-b-PMAA) as amphiphihc block copolymers with regard to their properties in stabilizing colloidal metal nanoparticles [37, 49]. All three polymers are successfully used to stabihze various transition metal coUoids... 

Dawkins and Taylor109 dispersed poly(methyl methacrylate) (PMMA) or polystyrene (PS) particles in n-alkanes stabilized by AB block copolymers of styrene and dimethyl-siloxane. In these cases, styrene blocks act as anchors and dimethylsiloxane blocks give a surface layer. The thickness 6 of the dimethylsiloxane layer was determined by viscosity measurements as a function of the molecular weight of dimethylsiloxane blocks. 

Besides the use of micromolecular multiinitiators, block copolymers can be obtained from macromolecular initiators. In a first step, a polymeric initiator is generally synthesized by reacting a mono- or difunctional polymer with a functional initiator. Various macromolecular initiators were prepared in this way including quite different sequences polystyrene [13, 18, 19, 25, 26], poly(dimethylsiloxane) [27], polymethylmethacrylate) [13,15,28], polyvinylacetate [28], polyvinylchloride [29, 30], polyesters [30], polycarbonate [31,32], polybutadiene [13, 25, 33], polyamide [34], polyethylene glycol) [35] or polyaromatic [36], An excellent review of the synthesis and uses of such macroinitiators was written by Nuyken and Voit [37]. Thus, only few typical examples are going to be mentioned below. 

Tphe surface activity of block copolymers containing dimethylsiloxane units as one component has received considerable attention. Silicone-poly ether block copolymers (1,2,3) have found commercial application, especially as surfactants in polyurethane foam manufacture. Silicone-polycarbonate (4, 5), -polystyrene (6, 7), -polyamide (8), -polymethyl methacrylate (9), and -polyphenylene ether (10) block copolymers all have surface-modifying effects, especially as additives in other polymeric systems. The behavior of several dimethylsiloxane-bisphenol A carbonate block copolymers spread at the air—water interface was described in a previous report from this laboratory (11). Noll et al. (12) have described the characteristics of spread films of some polyether—siloxane block co-... 

The amphiphilic block copolymers most conunonly used for the development of nanoreactors consist of hydrophiUc blocks, such as poly(aaylic acid) (PAA), poly(ethylene oxide) (PEO), poly(2-methyl oxazoline) (PMOXA), or poly[L-isocyanoalanine(2-thiophen-3-yl-ethyl)amide] (PIAT), and a hydrophobic block such as polystyrene (PS), polybutadiene (PB), or poly(dimethylsiloxane) (PDMS) [32-35]. Bionanoreactors have been obtained mainly by using polymer vesicles (polymersomes), but there are also a few reports based on other supramolecular assemblies (Table 11.1). 

As a continuation of this work, various analogs of these triblock copolymers were synthesized, such as a-methylstyrene-b-isoprene-b-a-methylstyrene, a-methylstyrene-b-(propylene sulfide)-b-a-methylstyrene and a-methylstyrene-b-dimethylsiloxane-b-a-methylstyrene. All of these showed similar morphology and structure-property relations as the styrene-diene triblocks, as might have been expected. It was noteworthy, however, that when the polystyrene end blocks were replaced by poly-a-methylstyrene, there was a noticeable increase in modulus and tensile strength, at any given temperature. This was presumably due to the enhanced ability of the poly-a-methylstyrene domains to withstand greater stresses and higher temperatures,... 

Yin, R. and Hogen-Esch, T.O. (1993) Synthesis and characterization of narrow molecular weight distribution polystyrene-poly(dimethylsiloxane) mactocychc block copolymers and their isobaiic precursors. Macromolecules,... 

Polyphosphazenes form amphiphilic block copolymers with organic polymers, such as poly (ethylene oxide), polystyrene, or poly(dimethylsiloxane). Comb, star, and dendritic architectures were also obtained. There are also... 

Thus, several block copolymers have been prepared by ITP among which we can cite polystyrene-b-poly(butyl acrylate),perfluoropolyethers-b-poly(VDF-co-HFP), ° poly-(VDF)-b-polystyrene, polystyrene-b-poly(acrylic add) as well as polystyrene-b-poly(dimethylsiloxane)-b-polystyr-ene and poly(VAc)-h-poly(dimethyl siloxane)-b-poly (VAc)." "- ... 

The first ternary star copolymers containing three different arms were presented by Fujimoto and coworkers [81], They used a special technique to combine three different blocks (tert-butyl methacrylate, styrene, and dimethylsiloxane) which were all synthesized by living anionic polymerization. PDMS was synthesized by initiation with a functionalized 1,1,-diphenyl ethylene (DPF). In a second step living polystyrene anions were reacted with the DPF linked to the PDMS, before the tert-butyl methacrylate was added to give the 3-miktoarm star terpolymer. Several years later the morphological properties of these star copolymers were published as well. TFM and SAXS support a threefold symmetry where the junction points between the three incompatible blocks are confined on one line [221]. 

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