Anionic polymerization, lactams

In anionic polymerization the reaction is initiated by a strong base, eg, a metal hydride, alkah metal alkoxide, organometaHic compounds, or hydroxides, to form a lactamate ... 

Nylon 4 is produced hy ring opening 2-pyrrolidone. Anionic polymerization is used to polymerize the lactam. Cocatalysts are used to increase the yield of the polymer. Carhon dioxide is reported to he an excellent polymerization activator. 

Two-shot techniques for acyclic diene metathesis, 435-445 for polyamides, 149-164 for polyimides, 287-300 for polyurethanes, 241-246 for transition metal coupling, 483-490 Anionic deactivation, 360 Anionic polymerization, 149, 174 of lactam, 177-178 Apolar solvents, 90 Aprotic polar solvents, 185, 338 Aprotic solvents, low-temperature condensation in, 302 Aqueous coating formulations, 235 Aqueous polyoxymethylene glycol, depolymerization of, 377 Aqueous systems, 206 Ardel, 20, 22... 

Anionic polymerization of lactams was shown to proceed according to what is called the activated monomer mechanism. With bischloroformates of hydroxy-terminated poly(tetramethyleneglycol) and poly(styrene glycol) as precursors for a polymeric initiator containing N-acyl lactam ends, block copolymers with n-pyrrol-idone and e-caprolactam were obtained by bulk polymerizations in vacuum at 30 and 80 °C, respectively361. ... 

It is well known that the anionic polymerization of lactams in general is markedly facilitated by the addition of N-acetylated lactams60-62. The polymerization of 61 is also accelerated by the addition of its N-acetylated compound 65 (Table 8). 

Azolides used as promotors in the anionic polymerization of lactams,1231,1241 and as plasticizers for PVC 1251... 

K. Hashimoto, Ring-Opening Polymerization of Lactams. Living Anionic Polymerization and Its Applications , Prog. Polym. Sci. 2000, 25, 1411-1462. 

The details of the anionic polymerization of nylon 6 have been extensively reviewed (1-8) and will only be discussed briefly as they affect the star-polymerization of nylon 6. Nylon 6 is polymerized anionically in a two-step process (Figure 1). The first step, creation of the activated species 3, is the slow step. The e-caprolactam monomer reacts in the presence of a strong base (such as sodium hydride) to form the caprolactam anion 2. This anion reacts with more caprolactam monomer to form 3. The reaction of this activated species with lactam anions occurs rapidly to form the nylon 6 polymer 4. 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

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. 

Polymerizations initiated by strong bases (R-, IIO, RO-) and tertiary amines (which are poor nucleophiles) proceed at much faster rates than do polymerizations initiated hy primary amines. Also, unlike the latter, where each polymer chain contains one initiator fragment (i.e., RNH—), these polymerizations do not result in incorporation of the initiator into the polymer chain. Polymerization proceeds by an activated monomer mechanism similar to that in the anionic polymerization of lactams. The reacting monomer is the NCA anion XLIV... 

Sebenda, J., Anionic Ring-Opening Polymerization Lactams, Chap. 35 in Comprehensive Polymer Science, Vol. 3, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, London, 1989. 

What are the roles of an acylating agent and activated monomer in the anionic polymerization of lactams ... 

For sodium/hexamethylene-l,6-bis-carbamidocaprolactam system, Sibal et al. [64] found the value of the constant k in Equation 1.4 to be 17.5. Note that the values of the constant k in Equation 1.4 that defines the relative complex viscosity rise during anionic ring opening polymerization of caprolactam are comparable for both caprolactam-magnesium-bromide/isophthaloyl-bis-caprolactam and sodium/hexamethylene-l,6-bis-carbamidocapro-lactam as the catalyst/initiator systems even though the kinetic constants for anionic polymerization for these systems are extremely different (see Table 1.2). 

Successive addition of monomers to the end of macromolecular initiator is the usual technique for the synthesis of tailored blockcopolymers. Anionic polymerization of pivalolactone, a-pyrrolidone— and the NCA of T-methyl-D-glutamate -2 was started from the end group of a prepolymer consisting carboxylate group or acyl lactam group or amino group. Living polymer of C-capro-lactone was expected to be formed by the initiated polymerization from polymer carbanion under kinetic controlled condition. 

The mechanism for the production of nylon-12 from the lactam is similar to that for nylon. However, in the case of nylon-12, the ring opening is more difficult and the rate of polymerization is slower, at least in part owing to the lower solubility of the lactam in water. A catalyst such as an acid, amino acid, or nylon salt can serve as a ring-opening agent. Nylon-12 can also be produced via anionic polymerization, ie, polymerization using an anhydrous alkali catalyst. This process can be quite fast even at low temperatures, eg, a few minutes at 130°C. 

A large number of inorganic compounds can be used as the activators of acid-ion (anionic) activated lactam polymerization. The activator in anionic activated lactam polymerization not only increases the process rate, but also changes the structure and functionality of a polymer formed, and, as a result an activator can regulate the properties of the end-product.1... 

Anionic polymerization of s-caprolactam is used to make cast or RIM polyamide-6. Using a premade lactam chain end and a metal catalyst, it proceeds rapidly at 100-160°C, well below the melting temperature of the polymer, Tm 220°C. The propagation differs from anionic propagation of most unsaturated monomers because the growth center at the chain end is not represented by an anionically activated group but by a neutral N-acy-lated lactam, and the anionically activated species is the incoming monomer (Table 2.26). 

Semicrystalline polyamide fine powders have been used as toughening agents for epoxy networks. The powders can be obtained by grinding granules, or directly by anionic polymerization of lactams, 6 or 12, in an organic solvent from which the formed semicrystalline polymer precipitates. Microporous powders with an average particle size in the range of 10 pm and a narrow particle-size distribution, are obtained. 

The anionic polymerization of 58 shows typical equilibrium polymerization behavior. From the temperature dependence of the equilibrium monomer concentration, the thermodynamic parameters for the polymerization of 58 in dimethyl sulfoxide were evaluated to be AHSS = -23.8 1.5 kJ/mol and ASss = — 71.5 + 4.2 kJ/mol deg (subscript ss refers to a solution state). [67] The ceiling temperature for 1 mol/L solution is about 60 °C. The enthalpy change in the polymerization of 58 is considerably larger than those for monocyclic lactams, pyrrolidone and piperidone, but no quantitative comparison of these data can be made, because the reported data refer to different experimental conditions. The significant entropy decrease in the polymerization is ascribable to the presence of the six-membered tetrahydropyran ring in the repeating unit. 

Anionic polymerization of 58 activated by N-benzoyl lactam proceeds without side reactions. Since side reactions in the anionic polymerization of lactams are mainly caused by protonabstraction, the pKa value for the bridge-head methine proton adjacent to the lactam-carbonyl group in 58 must be higher than that for the a-methylene protons in 2-pyrrolidone. This is because the former monomer has a rigid bicyclic structure. 

Fig. 2. Number-average molecular weight and molecular weight distribution of the polyamide obtained by anionic polymerization of bicyclic lactam 58 as a function of conversion. Polymerization conditions [M]0, 2.11 mol P potassium pyrrolido-nate, 0.5 mol% activator, N-benzoyl derivative of 58, 2 mol% solvent, Me2SO temp., 25 °C...

Anionic polymerization of a sodium salt (61) of a bromosubstituted bicyclic lactam (60) is very unusual. It proceeds in dimethylformamide at 0 and 25 °C with elimination of sodium bromide and gives oligomers 62 having a bicyclic oxalactam ring in each repeating unit. [70]... 

This adduct is presumably formed by the mechanism illustrated in Scheme 15 [74]. As in the conventional anionic polymerization of other lactams, 69 reacts with potassium pyrrolidonate to give a lactam anion 71. However, as soon as 71 is... 

In anionic polymerization, monomer complexes are less important. e-Ca-prolactam forms a strongly bound complex with LiCl, with a pronounced effect on the polymerization kinetics [175]. The formation of similar complexes is probably typical for all lactams. 

The opening of lactam rings by strong bases and their anionic polymerization proceed by means of a complicated disproportionation [173]. The reaction is usually initiated by an organometallic lactam derivative with the alkali... 

This statement has its limitations. Ionic polymerization in hydrocarbons is always kinetically complicated, it often starts only after the addition of a polar compound (co-initiator), and it is affected by the aggregation of initiating and propagating particles. In strongly polar media, activation of initiator by dissociation of acids and bases is easy. Such solvent is simultaneously a reactive transfer agent. Propagation usually does not occur, and only low molecular products are formed. Exceptions can, of course, be found. During anionic polymerization of lactams in DMF, the solvent only increases the amount of dissociated initiator [27]. 

Some heterocycles have both nucleophilic and electrophilic atoms in their molecule. Thus they can be opened and polymerized by the anionic, cationic or coordination mechanisms. Examples are lactams, lactones, and cyclic siloxanes. Investigations of the mechanism of lactam propagation are complicated by the occurence of side reactions. In principle, the mechanism described in Chap. 3 by the schemes (55)—(57) and (71) is accepted. Anionic polymerization of cyclic esters consists, in most cases (see Chap. 4, Sect. 2.2) of repeated reversible attacks on the carbonyl carbon by the anion 0]-. From e-caprolactone, polyester chains grow according to [315]... 

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). 

The catalyst used in this reaction is sodium hydride therefore, this is referred to as an anionic polymerization. The sodium hydride removes the acidic lactam proton to form an anion (1) that attacks the coinitiator, acetylcaprolactam (2), which has an electron-attracting acetyl group at-... 

Frequently, the order of rates of polymerization of various lactams is different from that of the thermodynamic parameters for polymerization. For example, the initial rates of hydrolytic polymerization were practically the same for capro-, enantho- and capryllactam [25—27], whereas the corresponding heats of polymerization differed significantly for these monomers [27] —AH = 3.3, 5.3 and 7.8 kcal mole", respectively). Similarly, for substituted caprolactams the sequence of free energies of polymerization is just opposite to the order of rates of anionic polymerization (Fig. 1). 

Under substantially anhydrous conditions, the anionic polymerization of lactams possessing an unsubstituted amide group may be initiated by any strong base capable of forming the free lactam anion... 

The high speed of anionic polymerization is due to the fact that both reacting species are chemically activated and hence highly reactive the lactam anion represents an activated monomer with increased nucleo-philicity and the terminal N-acylated lactam unit represents an activated end group (growth centre) with increased acylating ability. 

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