Ethylene block copolymers with tetrahydrofuran

Ethylene-vinyl acetate (EVA) polymers (containing 65%-70% by weight of vinyl acetate) are of industrial interest as high-molecular weight plasticizers for PVC, mainly because of their low cost. A polymeric plasticizer PB-3041 available from Du Pont allows the preparation of a highly permanent plasticized PVC formulation. It is believed to be a terpolymer of ethylene, vinyl, acetate, and carbon monoxide. Also, butylene terephthalate-tetrahydrofuran block copolymers, with the trade name of Hytrel (Du Pont), are used as excellent permanent plasticizers of PVC. 

Polyacetylene latexes (48) have been prepared by polymerizing acetylene in the presence of poly[(fert-butylstyrene)-fo-(ethylene oxide)]. The use of a tetrahydrofuran/cyclohexane (THF/cyclohexane) solvent combination led to the formation of a stable dispersion of nearly uniform spherical polyacetylene particles 40-200 nm in diameter. The block copolymer was separated from the polyacetylene by several wash cycles with a good solvent for the block copolymer (cyclohexane), and after removing the solvent, a polyacetylene powder was obtained. On the basis of nitrogen adsorption... 

Block copolymers consisting of segments with widely separated solubility characteristics have generated considerable interest because of their unusual surfactant properties. In fact, one of the earliest commercial block copolymers were the Wyandotte "Pluronics." These were poly(propylene oxide-b-ethylene oxide) prepared by sequential addition of ethylene oxide to sodium alkoxide initiated propylene oxide (37,38). Szwarc (39) and others (40,41) prepared poly(styrene-b-ethylene oxide) by addition of ethylene oxide to polystyrene anions in tetrahydrofuran. Other syntheses of AB or ABA block copolymers of styrene-ethylene oxide include sequential addition in various solvents, and coupling reactions (42,43). 

Polyoxyalkylene block copolymers represent an important class of nonionic surfactants with different applications in the field of detergency. Even if, in principle, these compounds can be synthesized by the polymerization of several cyclic ethers such as, for example, ethylene oxide (EO), propylene oxide (PO), tetrahydrofuran, or 1,2-butylene oxide, in this chapter, our attention is focused exclusively on the derivatives of EO and PO. The initiators of the polymerization vary considerably and are mainly distinguished on the basis of their functionality. In most cases, for products with applications for detergency, tetrafunctional initiators can be adopted. 

It has been shown that in highly crystalline polymers having multiple transitions, such as poly(ethylene terephthalate), the glass transitions may be determined only by gas chromatography [170, 174, 177, 204]. The glass transition was also detected by gas chromatography in the copolymers acrylonitrile-vinyl acetate [201], acrylonitrile-a-methylsty-rene and the terpolymers of these monomers with vinyl acetate [207], polystyrene-butadiene [199], and styrene-tetrahydrofuran block copolymers [208]. 

Ethylene oxide/styrene block copolymers have been further free-radical copolymerized with other ethylenically unsaturated compounds such as methyl methacrylate and methacrylic acid in benzene, tetrahydrofuran, and dimethylformamide (176). Correlations were made between reactivity ratio and solvent dielectric constant, as well as between solubility parameters of reaction solvent and growing polymer chains with marked effects apparent. Gel permeation chromatography of diblock and triblock copolymers based on polystyrene and poly(ethylene oxide) has revealed interesting molecular characteristics (177). Such block copolymers have an amphiphilic character. In aqueous solution, the polymers form spherical micells with a polystyrene core and a poly(ethylene oxide) outer sheath. The investigations used an aqueous-methanolic solution and were able to ascertain block copolymer structures and to estimate the impurities in the diblock copolymer. 

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