Poly block copolymer effect

JorzikU, Wolf BA (1997) Reduction of the interfacial tension between poly(di-methylsiloxane) and polyethylene oxide) by block copolymers Effects of molecular architecture and chemical composition. Macromolecules 30(16) 4713-4718... 

The metallocene-ATRP route has been expanded by Matsugi etal. [164], to produce polyethylene-b-poly(methyl methacrylate). In the first step, hydroxyl-functionalized polyethylene was successfully prepared through the copolymerization of ethylene with aluminum-capped allyl alcohol, using a specific zirconium metaUocene/methylaluminoxane catalyst system. In the next step, the terminal alcohol was converted to hahde by 2-bromoisobutyryl bromide to obtain bromide-functionalized polyethylene, which could initiate the ATRP of MMA (Scheme 11.40). The block copolymers obtained exhibited unique morphological features that depended on the content of PMMA segment. Moreover, the block copolymers effectively compatibiUzed the corresponding homopolymer blend at the nanometer level. 

Polyall lene Oxide Block Copolymers. The higher alkylene oxides derived from propjiene, butylene, styrene (qv), and cyclohexene react with active oxygens in a manner analogous to the reaction of ethylene oxide. Because the hydrophilic oxygen constitutes a smaller proportion of these molecules, the net effect is that the oxides, unlike ethylene oxide, are hydrophobic. The higher oxides are not used commercially as surfactant raw materials except for minor quantities that are employed as chain terminators in polyoxyethylene surfactants to lower the foaming tendency. The hydrophobic nature of propylene oxide units, —CH(CH2)CH20—, has been utilized in several ways in the manufacture of surfactants. Manufacture, properties, and uses of poly(oxyethylene- (9-oxypropylene) have been reviewed (98). 

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

Hydrosilation reactions have been one of the earlier techniques utilized in the preparation of siloxane containing block copolymers 22,23). A major application of this method has been in the synthesis of polysiloxane-poly(alkylene oxide) block copolymers 23), which find extensive applications as emulsifiers and stabilizers, especially in the urethane foam formulations 23-43). These types of reactions are conducted between silane (Si H) terminated siloxane oligomers and olefinically terminated poly-(alkylene oxide) oligomers. Consequently the resulting system contains (Si—C) linkages between different segments. Earlier developments in the field have been reviewed 22, 23,43> Recently hydrosilation reactions have been used effectively by Ringsdorf 255) and Finkelmann 256) for the synthesis of various novel thermoplastic liquid crystalline copolymers where siloxanes have been utilized as flexible spacers. Introduction of flexible siloxanes also improved the processibility of these materials. 

Deschamps AA, Grijpma DW, and Feijen J. Poly(ethylene oxide)/poly(butylenes terephthalate) segmented block copolymers The effect of copolymer composition on physical properties and degradation behavior. Polymer, 2001, 42, 9335-9345. 

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

These poly(MMA) obtained could induce the photopolymerization of St to give a star block copolymer, butgelation was partly observed, similar to thepoly-merization of St with 51. The addition of 13 in the photopolymerization of MA with 51 was effective in preventing gelation [175]. 

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]. 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acryhc acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubihty in water and retain this property after functionahzation with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by coohng the solution to 0 °C [92]. Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

SBS is a three-block copolymer of styrene and butadiene. Incompatibility of PS and poly-butadiene (BR) causes segregation of the chain parts a two-phase system results in which PS and BR each have their own individuality and their own Tg. The fact that the highest Tg is lower than the Tg of normal PS, is a result of the relatively low molar mass of the PS chain ends. In general the effect of M on Tg is insignificant Tg= - K/ M, but when K is, e.g. 10 and M = 10,000, Tg can be 10°... 

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