Poly bifunctional initiator formed

The synthesis of triblock copolymers B-A-B can be achieved by means of a bifunctional initiator a bifunctional a,u-dicarbanionic poly-A precursor is formed, and is used in a second step as the initiator for the polymerization of monomer B, with the same conditions to be observed as above. A number of efficient bifunctional initiators are commonly used, in polar solvent media. Recent work, carried out in several laboratories -- t aimed at the preparation of efficient bifunc-tional Initiators soluble in non polar solvents. Such systems... 

As the example of 2-vinyl butadiene has already shown, the free radical polymerization of dienes is particularly interesting. Because of the two bifunctional double bonds, 1,4-dienes, CH2=CH—R—CH=CH2, are normally tetrafunctional and therefore lead to branching and cross-linking even at relatively low yield. With certain initiators, however, 1,3-dienes such as CH2=CH—CH=CH2, butadiene, or CH2==C(CH3)—CH=CH2, isoprene, react bifunctionally to form unbranched 1,4-poly (dienes). Symmetric 1,6-dienes, and frequently also symmetric 1,5-dienes, likewise give more or less unbranched molecules. In contrast to the l,4-poly(dienes), however, the 1,6- and l,5-poly(dienes) only possess slight unsaturation. That is, intramolecular ring formation by a cyclopolymerization occurs, for example, in the 1,6-diene acrylic acid anhydride. 

Cyclic Amines. The three-membered cyclic amines and the four-membered cyclic amines can be polymerized only by cationic mechanism (324). Monofunctional initiators, such as methyl triflate (325), produce monofiinctional telechelics from f-butylaziridine (TEA). Addition of the monomer to a bifunctional living PTHF solution (326) gives bifimctional poly(TBA). This is a method of making ABA block copolymers. The aziridinium end groups react with acrylic acids to form the corresponding esters (327). 

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