Cyclic amides polymerization

The polymerization of lactams (cyclic amides) can be initiated by bases, acids, and water [Reimschuessel, 1977 Sebenda, 1976, 1978 Sekiguchi, 1984]. Initiation by water, referred to as hydrolytic polymerization, is the most often used method for industrial polymerization of lactams. Anionic initiation is also practiced, especially polymerization in molds to directly produce objects from monomer. Cationic initiation is not useful because the conversions and polymer molecular weights are considerably lower. 

The anionic polymerization of lactams proceeds by a mechanism analogous to the activated monomer mechanism for anionic polymerization of acrylamide (Sec. 5-7b) and some cationic polymerizations of epoxides (Sec. 7-2b-3-b). The propagating center is the cyclic amide linkage of the IV-acyllactam. Monomer does not add to the propagating chain it is the monomer anion (lactam anion), often referred to as activated monomer, which adds to the propagating chain [Szwarc, 1965, 1966]. The propagation rate depends on the concentrations of lactam anion and W-acy I lactam, both of which are determined by the concentrations of lactam and base. 

The initiator used is important for copolymerizations between monomers containing different polymerizing functional groups. Basic differences in the propagating centers (oxonium ion, amide anion, carbocation, etc.) for different types of monomer preclude some copolymerizations. Even when two different monomer types undergo polymerization with similar propagating centers, there may not be complete compatibility in the two crossover reactions. For example, oxonium ions initiate cyclic amine polymerization, but ammonium ions do not initiate cyclic ether polymerization [Kubisa, 1996]. 

Ring-Opening Polymerization of Cyclic Amides (Lactams)... 

The reaction of dibasic acids with diamines was reported in the early literature [6-13] to give low molecular weight cyclic amides as infusible and insoluble products. It was Carothers [14-18] who first recognized that polymeric amides were formed by the reaction of diamines with dibasic acids. Many of the polyamides were able to be spun into fibers and the fibers were called Nylon by du Pont [14-20]. 

Tam et al. (1). Ring-opening polymerization of cyclic amides using this agent are also reported by Tam et al. (2). 

The five-membered cyclic amide pyrrolidone has achieved widespread attention in the area of heterocyclic polymers since the first preparation and polymerization reactions of l-vinylpyrrolidin-2-one (1) were reported in the early 1940s. Poly(vinylpyrrolidone) (2) and its copolymers are among the most thoroughly studied heterocyclic addition polymers (B-74MI11100). Monomer (1) is readily polymerized (B-77MI11100) both free radically and ionically (Scheme 1). The former method is by far the most important, and allows the preparation of a wide variety of copolymers. Interestingly, in the homopolymerization of vinylpyrrolidone (1), the molecular weight of the polymer obtained does not appear to be influenced by the initiator concentration or the reaction temperature. 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

The industrial manufacture of nylon relies upon the alkaline polymerization of a cyclic amide known trivially as caprolactam. Caprolactam can be produced by the action of sulfuric acid on the oxime of cyclohexanone in a rearrangement known as the Beckmann rearrangement. 

After the first amide is formed, one end of the new molecule is nucleophilic and the other electrophilic so that it can grow at both ends. The polymer is made up of alternating -NH(CH2)6NH-and -(CH2)4CO- units, each having six carbon atoms, and is called nylon 6.6 . Another and much simpler way to make nylon is to polymerize caprolactam. This monomer is a cyclic amide and the polymer does not have alternating units—instead, each unit is the same. 

A few papers have examined the range of Lewis bases that are effective for isobutene controlled/living polymerization [91,149,156]. One proposal is that effective nucleophiles (electron donors) should have relatively high donor numbers (DN > 26) [149]. Another screening shows that triethylamine is exceedingly effective for isobutene [156]. Pratap et al., also reported recently the use of cyclic amides (lactams l-methyl-2-pyr-rolidone) [158] and cyclic amines [152] for the dicumyl acetate/BCL initiating system. 

Although several cyclic amides (lactams) can be polymerized by cationic mechanism, this method of polymerization is of little practical importance because the anionic or hydrolytic polymerization provides much more convenient route to corresponding polyamides. Polyamides obtained by cationic polymerization of lactams are less stable and oxidize faster than those obtained by anionic polymerization [213). 

Cyclic amids can be polymerized by an ionic mechanism. Most attention has been given to the aliphatic lactams which polymerize to polyamids ... 

Joyce and Ritter (1) in 1941 obtained a patent on the base catalyzed polymerization of caprolactam. They described the reaction of a small amount of sodium or other alkali metal in caprolactam to form sodium caprolactam and the rapid, exothermic polymerization of caprolactam above 200°C to form molten nylon polymer. The polymerization reaction is an isomerization of the low viscosity cyclic amide to a high viscosity, high molecular weight polyamide. 

In addition to step and chain polymerizations, another mode of polymerization is of importance. This is the ring-opening polymerization of cyclic monomers such as cyclic ethers, esters (lactones), amides (lactams), and siloxanes. Examples of commercially important types are given in Table 10.1. Of those listed, only the polyalkenes are composed solely of carbon chains. Those that have enjoyed the longest history of commercial exploitation are polyethers prepared from three-membered ring cyclic ethers (epoxides), polyamides from cyclic amides (lactams), and polysiloxanes from cyclic siloxanes. 

Lactams are cyclic amides formed by the intramolecular amidation of amino acids. The polymerization of lactams [Eq. (10.48)]... 

H. Sekiguchi, Lactams and Cyclic Amides, Chap. 12 in Ring Opening Polymerization, Vol. 2, (K. J. Ivin and T. Saegusa, eds.), Elsevier, London (1984). 

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