Self-condensing ring-opening

SCROP Self-condensing ring-opening polymerization... 

Almost at the same time, Hedrick et al. published a reaction based on the same concept, where the term self-condensing ring-opening polymerization (SCROP) was introduced. The inimer 4- [2,2-bis(hydroxymethyl)propanoyl]oxy hexano-6-lactone (Scheme 28) was reacted in the presence of a catalytic amount of SnOct2 to yield hyperbranched polyesters. 

YAN D Y, Hou J, ZHU X, KOSMAN J J and wu H s (2000), A new approach to control crystallinity of resulting polymers self-condensing ring opening polymerization ,... 

HO—R—COOH, or an amino acid, H2N—R—COOH. In some cases, such monomers self-condense to a cycHc stmcture, which is what actually polymerizes. For example, S-caprolactam (1) can be thought of as the self-condensation product of an amino acid. Caprolactam undergoes a ring-opening polymerization to form another... 

Less important methods are the self condensation of w-hydroxy acid and the ring opening of lactones and cyclic esters. In self condensation of w-hydroxy acids, cyclization might compete seriously with linear polymerization, especially when the hydroxyl group is in a position to give five or six membered lactones. 

There are three methods by which we commercially manufacture nylons. We make nylons of the AB type by hydrolytic ring opening reactions of lactams and the self condensation of co-amino acids. Nylons of the AABB type are made from diamines and diacids via an intermediate know as a nylon salt. 

The base-catalyzed self-condensation of diketene is a similar type of reaction and yields dehydroacetic acid together with the tripyranone (322) (49JOC460, B-68MI22400). Ring opening of diketene and attack of the oxyanion on a second molecule of diketene followed by an intramolecular condensation accounts for the formation of the pyranone. The selfcondensation of malonyl dichloride in the presence of a ketone, which acts as a weak base, is a similar reaction (52JCS4109). 

After purification, the lactam is polymerized by heating at elevated temperatures in an inert atmosphere. During self-condensation, the ring structure of the lactam is opened so that the monomer acts as an epsilon-aminocaproic acid radical. Unlike that of nylon 66, the polymerization of caprolactam is reversible the polymer remains in equilibrium with a small amount of monomer. As with nylon 66, nylon 6 is extruded in thin strands, quenched, and cut into chips for subsequent spinning, or the molten polymer is pumped directly to the spinning equipment. 

The derivatives of ethylene oxide and aziridine can be used to build macrocycles. Substituted aziridine or ethylene oxide self-condenses on ring opening to form cyclic trimers, tetramers, and so on (Dale and Daasvatn, 1976 Dale et al., 1974 Hansen and Burg, 1968 Tsuboyama et al., 1970). The size of the macrocycle depends mainly on what starting material is used. In the case of N-benzylaziridine, the macrocycle formed was the tetraaza-12-crown-4. 

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