Polystyrene-polyethylene oxid

Polystyrene/polyethylene oxide dendrimers were prepared by ATRP using tri- and tetra (bromomethyl) benzene as the initiators [207]. Each bromine end-group of the resulting stars was transformed first to two - OH groups and subsequently to potassium alcholate, as shown in Scheme 114. These - OK sites served to initiate the anionic polymerization of EO. The synthesized dendritic copolymers were found to display monomodal and narrow molecular weight distribution. 

Fig. 8 (a) Structure-based and (b) source-based Sgroup representation of a polystyrene/ polyethylene oxide block-copolymer... 

Extensive neutron reflectivity studies on surfactant adsorption at the air-water interface show that a surfactant monolayer is formed at the interface. Even for concentration cmc, where complex sub-surface ordering of micelles may exist,the interfacial layer remains a monolayer. This is in marked contrast to the situation for amphiphilic block copolymers, where recent measurements by Richards et al. on polystyrene polyethylene oxide block copolymers (PS-b-PEO) and by Thomas et al. on poly(2-(dimethyl-amino)ethylmethacrylamide-b-methyl methacrylate) (DMAEMA-b-MMA) show the formation of surface micelles at a concentration block copolymer, where an abrupt change in thickness is observed at a finite concentration, and signals the onset of surface micellisation. 

Self-assembled block copolymers are basically amphilic molecules which contain distinctively different polymers. This block copolymer contains two or more polymers quantitatively in the form of blocks. Some of the block copolymers are polyacrylic acid, polymethylacrylate, polystyrene polyethylene oxide, polybutadiene, polybutylene oxide, poly-2-methyloxazoline, polydimethyl sUoxane, poly-e-caprolactone, polypropylene sulfide, poly-A -isopropylacrylamide, poly-2-vinylpyridine, poly-2-diethylamino ethyl methacrylate, poly-2-(diisopropylamino) ethyl methacrylate, poly-2-(methacryloyloxy) ethyl phosphorylcholine, and polylactic acid. These copolymers contain more than polymers to form certain configurations like linear, branched, patterned. For example, if we take three polymers named A, B, and C, they can be combined to form arrangements AB, BA, AA, BAB, ABCAB, ABCABC, ABABAB, etc. in the form of branched configuration it forms (ABQa, (ABA)a, (AB)4, etc. Depending on the above-mentioned number of blocks, they are named as AB diblock copolymers, ABC triblock copolymers, ABC star block copolymers, etc. The covalent linkage between these different blocks of polymers makes macroscopic phase separation impossible, that is, in its place the phase separation... 

Several other di- and triblock copolymers have been synthesized, although these are of limited commercial availability. Typical examples are diblocks of polystyrene-block-polyvinyl alcohol, triblocks of poly(methyl methacrylate)-block poly(ethylene oxide)-block poly(methyl methacrylate), diblocks of polystyrene block-polyethylene oxide, and triblocks of polyethylene oxide-block polystyrene-polyethylene oxide [4]. 

An alternative (and perhaps more efficient) polymeric snrfactant is the amphipathic graft copolymer consisting of a polymeric backbone B (polystyrene or polymethylmethacrylate) and several A chains (teeth) snch as polyethylene oxide [4], This graft copolymer is sometimes referred to as a comb stabilizer. This copolymer is nsnally prepared by grafting a macromonomer such methoxy polyethylene oxide methacrylate with polymethylmethacrylate. The grafting onto technique has also been nsed to synthesize polystyrene-polyethylene oxide graft copolymers. 

The grafting into technique has also been used to synthesize polystyrene-polyethylene oxide graft copolymers. These molecules are not commercially available. 

Problem 12.7 A combination of core rst and coupling onto approaches often offers a simple strategy to synthesize star block copolymers. Suggest, accordingly, a synthetic strategy for the preparation of 3-arm star block copolymers consisting of diblock polymeric arms, polystyrene- polyethylene oxide (PSt-fc-PEO). 

XPS spectra of polystyrene (top), polyethylene oxide (middle) and a polystyrene-polyethylene oxide diblock copolymer (bottom). 

Notes PEO-PPO = Polyethylene oxide-polypropylene oxide PEO-PPO-PEO = Polyethylene oxide-polypropylene oxide-polyethylene oxide PEO-PS-PEO = Polyethylene oxide-polystyrene-polyethylene oxide PS-PVOH = Polystyrene-polyvinylalcdiol. 

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