Polymerization 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... 

Polyesters contain the ester group —COO— in the main chain. Many methods are suitable for their synthesis self-condensation of a,o>-hydroxy acids, ring-opening polymerization of lactones, the polycondensation of dicarboxylic acids with diols, transesterification, the polycondensation of diacyl chlorides with diols, polymerization of O-carboxy anhydrides of a- and jS-hydroxycarboxylic acids, and the copolymerization of acid anhydrides with cyclic ethers. The last reaction is commercially used in the curing of epoxides with anhydrides. 

Nylons are prepared by (1-a) eondensation of diamines and dibasie acids or (1-b) condensation of diamines and dibasic acid chlorides, (2) ring-opening polymerization of eyelie lactams, (3) self-condensation of bifimctional amino acids, etc. Some important polymerization reactions and citations to the reviews covering them are given in Table 2. 

Nylon 6,6 continues to be the major commercial nylon but several other nylons have now achieved commercial status. The principal nylons which are currently commercially available are shown below. For the preparation of these nylons, three general methods have been developed, namely reaction of a diamine and a dicarboxylic acid self-condensation of an co-aminoacid and ring-opening polymerization of a lactam. The method usually applied for each nylon is also shown below. The various nylons are distinguished from one another by a numbering system based on the number of carbon atoms in the starting materials. 

In the late 1990s, Penczek and co-workers described the synthesis of highly branched (star) polymers by reacting oligomeric alcoholates obtained by ring-opening polymerization of ethylene oxide (EO) with various diepoxides. One possible reaction sequence of the reaction is shown in Scheme 1. This approach can be seen as the first self-condensing ROP (SCROP) synthesis (see below) to obtain hyperbranched polymers. 

Aliphatic polyamides are produced commercially by condensation of diamines with dibasic acids, by self-condensation of an amino acid, or by self-condensation of an amino acid, or by ring-opening polymerization of a lactam [14,40,41]. To obtain polymers of high molecular weight, there should be stoichiometric equivalence of amine and acid groups of the monomers. For amino acids and lactams the stoichiometric balance is ensured by the use of pure monomers for diamines and dibasic acids this is readily obtained by the preliminary formation of a 1 1 ammonium salt, often referred to as a nylon salt. Small quantities of monofunctional compounds are often used to control the molecular weight. 

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. 

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. 

Hyperbranched polymers are synthesized in a one-step method, often from AB monomers but also by combining A +B (x>3) monomers or variations of those. Polymerization methods have been applied that involve polycondensation, polyaddition, and ring-opening or self-condensing vinyl polymerization. Even though the one-pot synthetic approach leads to imperfectly branched structures because of uncontrolled growth, it is more suitable for the preparation on a larger scale and thus for commercial use. Nowadays, different... 

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