Reactivity of lactams in anionic polymerization

The rate of anionic lactam polymerization is greatly affected by variation of the permittivity of lactams with ring size and substitution, as well as by changes of permittivity during polymerization. Therefore, an estimation of reactivities under comparable conditions is possible in solution only. The lack of any solvent permitting anionic lactam polymerization at low temperatures was circumvented by using living polymers soluble in aprotic solvents as carriers. Such polymers are able to remain in solution even after the addition of a few monomer units of a lactam, the polymer of which is insoluble. In this way, relative reactivities of a series of four-membered lactams, as well as that of the five-membered one were established.     

Block copolymerization. V. Block anionic polymerization of lactams

Bischloroformates of hydroxy-terminated poly(tetramethylene glycol) (PTG) and polystyrene (PSt) were prepared and used as the initiators for the anionic polymerization of α-pyrrolidone and ε-caprolactam in bulk at 30°C and 80°C, respectively. Initiation efficiency was sufficiently high to give well-defined nylon–PTG(or PSt)–nylon block copolymers. Both the yield and the viscosity of the block copolymer increased with polymerization time up to 50% conversion of the lactam.     

Studies on anionic polymerization of lactams. Part II. Effect of cocatalysts on the polymerization of pyrrolidone

The rates of addition of pyrrolidonate magnesium bromide (PyMgBr) to N-benzoyl-, N-acetyl-, and N-methylpyrrolidone were measured in solution in tetrahydrofuran (THF). The values found for the rate constants at 25°C. were 9.5 × 10^?2, 2.8 × 10^?2, and 5 × 10^?4 l./mole-sec., respectively. The rate constant for addition of PyMgBr to pyrrolidone was also measured and found to be 3 × 10^?9l./mole-sec. Possible causes for the large difference between the values of these constants are discussed.     

Studies on anionic polymerization of lactams. Part III. Copolymerization of pyrrolidone and caprolactam

On reacting acetylcaprolactam (AcCL) and pyrrolidonate MgBr (Py^?) in tetrahydrofuran solution, transacetylation takes place, giving acetylpyrrolidone (AcPy) and caprolactamate MgBr (CL^?). The rate constants for the transacetylation reactions were measured at 25°C. Their values in units of liters/mole-second were: The rate constants for the addition reactions measured were: As the transacetylation is much faster than the addition reaction the copolymer composition should be given by the equation: where K_trans, the transacetylation equilibrium constant, equals 0.3 while K_acidity reflects the relative acidities of the monomers and its value (from the literature) is about 0.4. Pyrrolidone is, therefore, more reactive than caprolactam in anionic copolymerization by a factor of about 8.     

Synthesis and ring-opening metathesis polymerization of eight-membered unsaturated lactams and related monomers

Novel eight-membered ring unsaturated lactams were synthesized and tested as monomers for the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). The reaction of a N-protected cyclic alkeneamine was also investigated. The Grubbs’ benzylidene complexes RuCl₂(=CHPh)(PCy₃)₂ or RuCl₂(=CHPh)(PCy₃)(IMesH₂) and selected ruthenium–arene species bearing either phosphine or stable Arduengo-type N-heterocyclic carbene ligands served as catalyst precursors. In most cases, isomerization of the starting materials took place and only 1-benzyl-1-aza-2-ketocyclooct-5-ene afforded a polymeric product. This polyamide was characterized by numerous analytical techniques.     

Polymerizability of norbornene in ring-opening metathesis polymerization initiated by Mo-based complexes

Concerning the study on the relation between structural parameters and reactivity in ring-opening metathesis polymerization of cyclo-olefins, the “living” polymerization of norbornene initiated by Schrock's-type complexes was considered as a reference and studied from the kinetic point of view. First kinetic orders with respect to both monomer and active species allow the values of absolute rate constants of propagation to be determined. The thermodynamic parameters obtained from kinetic experiments performed at different temperatures seem to indicate that monomer coordination and metallacycle formation are rate-determining steps in the process studied. © 1994 John Wiley & Sons, Inc.     

On the anionic polymerization of cyanogen

The reaction of anionic initiators with cyanogen was investigated by ultraviolet, visible, and infrared spectroscopy. It is argued that the reaction proceeds via formation of an analog of the heterocyclic anion C₇N₇? previously known from the reaction of KCN with (CN)₂. The analytical results and spectra of the final black product were indicative of the possible formation of open-structured C₇N₇? dimers. A molecular model of the dimer suggests why the polymerization might terminate at the dimer stage. The pyrolysis of the cyclic acid HC₇N₇ was studied with the aim of determining the structure and mechanism of the formation of the resulting black product. It is suggested that this thermally induced polymerization reaction probably proceeds via formation of azomethine-type intermolecular crosslinks and may serve as a model for the investigation of the mechanism of nitrile polymerization in pyrolyzed acrylonitrile polymers.     

Molecular weight distribution of polyamides obtained in anionic polymerization of methyl-substituted β-lactams and aminolysis of their N-benzoyl lactams

The anionic ring-opening polymerization of 3-methyl-2-azetidinone ( 3 ) in a mixture of N,N-dimethylacetamide with lithium chloride proceeded quantitatively in a homogeneous phase at 25°C, as well as the living anionic polymerization of 3,3-dimethyl-, 4,4-dimethyl-2-azetidinone ( 1 and 2 respectively) in a similar condition. However, the molecular weight dispersion of the polyamide obtained from 3 was found to be higher than that obtained from 1 and 2. The aminolysis reaction of their N-benzoyllactams and N-acyllactams corresponding to their growing species with benzylamine was investigated kinetically, and one of the reasons for broadening of the molecular weight distribution of the polyamide obtained in the anionic polymerization of 3 was speculated to result from a low value of the ratio of the initiation reaction constant to the propagation one. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1831–1838, 1997     

Kinetics and mechanisms in anionic ring-opening polymerization

Recent advances in the anionic ring-opening polymerization (AROP), including covalent (pseudoanionic) polymerization, are reviewed. Thermodynamics, kinetics, and mechanisms of AROP are discussed, covering mostly polymerization of oxiranes, lactones and cyclic siloxanes as monomers. The following general problems of AROP are discussed: anionic polymerizability, thermodynamics - particularly of the monomers exhibiting low ring strain, chemistry of initiation, structures and reactivity of active species. New phenomena, particularly polymerization with reversibly aggregating species are analyzed in more detail. Chain transfer to polymer - the major side reaction - is analyzed quantitatively, by introducing the selectivity parameter β, expressed by the ratio k_p/k_tr. This parameter has been determined for the anionic and pseudoanionic polymerization of ϵ-caprolactone.     

Stereochemistry of anionic vinyl polymerization

The stereochemistry of anionic polymerization of vinyl monomers: CH₂=C(R)C(Y)=X where X and Y are O, N or C and R = H or alkyl is discussed in terms of a: the geometry of the -CH₂C-(R)C(Y)=X intermediate existing as E- or Z-isomers; b: the interactions of cation (Li, Na, etc.) with the anion and coordinating groups on the penultimate or antepenultimate asymmetric carbon. The E/Z ratio appears to be determined directly by the s-trans/s-cis approach of the monomer. The nature of the coordination of the counter ion is considerably more complicated and is discussed in detail.     

Equilibrium anionic polymerization of n-valeraldehyde

This paper describes an anionic polymerization of n-valeraldehyde (VA) in tetrahydrofuran (THF) initiated by benzophenone-monolithium complex in a high vacuum system. In spite of the deposition of the resulting polymer an equilibrium state between the monomer and the polymer was observed at a temperature range of ?90 to ?68°C. From the linear relationship between the equilibrium monomer concentration and the polymerization temperature, values of ?5.3 ± 0.3 kcal/mole and ?25.7 ± 1.4 cal/mole-deg, respectively, were evaluated for the enthalpy change and the entropy change in the present system. The effect of polar substituents on the polymerizability of aldehydes is discussed from the comparison of these values with those in the case of β-methoxypropionaldehyde.     

Tailored heterogeneity indices in anionic polymerization

Equations are derived for the differential molecular weight distribution curve and for the heterogeneity index for several types of delayed initiator addition in anionic polymerization. All the results are in closed and easily used form, and depend only upon the product of the rate constant of the propagation reaction, the total initiator concentration, and a parameter representative of the rate of initiator addition. The results are plotted versus the above-mentioned product, so that one can determine the heterogeneity index to be expected under a wide range of the variables involved.     

Polybromostryl macromers and their anionic polymerization

The decomposition of polybromostyryl carbanions (PBS^?), obtained by anionic polymerization of 4-bromostyrene in tetrahydrofuran (THF), was investigated in the dark in a temperature range of ?6–?21°C. It was accompanied by the evolution of bromine anions and by the formation of polymeric allylic carbanions (λ_max = 575 nm; ε_max = 6800 eq^?1·L·cm^?1). The reaction mechanism was elucidated. The rate constant of the unimolecular rate-determining step of the process was 1.3 × 10^?5 s^?1 and 9.7 × 10^?5 s^?1 at ?21 and ?6°C, respectively. Its apparent energy of activation E_app = 18.38 Kcal/mol. The polybromostyrenes with allylic carbanions at their ends may decompose further. Their “dark” decomposition yielded 1,3-butadiene-1,3-diphenyl-macromers. The mechanisms of decomposition of the PBS^? carbanions and the dark decomposition of the polybromostyryl allylic carbanions are analogous. The rate constant of the latter process was 2.5 × 10^?6 s^?1 at ?6°C. The anionic polymerization of prepared macromers can be initiated in THF at ?78°C by α-methylstyryl carbanions, which do not react, however, with PBS^? carbanions. “Comblike” polymacromers were prepared in which each branch had a molecular weight of about 50,000. The overall molecular weight of the polymacromer was estimated to be about 1 × 10⁶. It has been assumed that the 2–1 mode of addition to the diene group of the macromer is predominant during its polymerization. The 3–4 mode of addition followed by proton shift represents the termination step. The 4–3 mode of addition was ruled out on the basis of spectroscopic evidence.     

Radiation-induced grafting polymerization by the anionic mechanism

The radiation-induced grafting polymerization of phenylacetylene and 2-methyl-5-vinylpyridine (2M-5VPy) onto low-density polyethylene has been investigated under strict identical conditions, using crude and thoroughly dried monomers. In the case of thoroughly dried monomers, the radiation-induced grafting is performed by the combined (radical + anionic) mechanism. The kinetics of radical and anionic grafting of 2M-5VPy are investigated in detail. The activation energies are 4.8 ± 0.3 and ?2.7 ± 0.3 kcal/mole for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to the dose rate to the 0.47 ± 0.03 and 0.92 ± 0.03 power for the radical and anionic grafting, respectively. The initial rate of grafting is approximately proportional to monomer concentration to the 1.55 ± 0.05 and 2.1 ± 0.05 power for the radical and anionic grafting, respectively. These data conform to the contribution of the anionic mechanism in a thoroughly dried system. The mechanism of radiation-induced anionic grafting is discussed.     

Active centres in the anionic polymerization of methoxypolyethyleneglycol methacrylates

The nature of the propagation sites in the anionic polymerization of methoxypolyethyleneglycol methacrylates in the presence of Li counterion has been studied through i.r. spectra of the model compounds, Li derivatives of isobutyric acid esters, (CH₃)₂CLiCOO(CH₂CH₂O)_nCH₃ with n from 1 to 4, and of 2,2,4-trimethylglutaric acid esters. The wavelength of the absorption band of lithioisobutyrates, due to the vibration of the

grouping, is independent of the nature of the solvent. This fact has been explained by intramolecular solvation of Li⁺ by the polyethereal alcoholic residue. The spectra of the metalated trimethylglutarates give evidence of concurrent solvation of Li⁺ by the alkoxy carbonyl group in the γ-position and the alcoholic residue of the ester group bound to the metalated carbon atom. When the number of ethyleneoxide units in the polyethereal chain is increased, the coordination of Li⁺ to it prevails over the interaction with the γ-malkoxycarbonyl group.     

Mechanism of anionic polymerization of phenylacetylene

Anionic polymerization of phenylacetylene in the presence of butyllithium has been studied. It was shown that the process of polymerization is accompanied by the appearance and growth of the ESR signal with pronounced superfine structure. The model of polymerization was suggested according to which formation of low molecular polyphenylacetylene is caused the destruction of the active centers by means of electron transfer from the active center to the conjugated chain. This type of electron transfer may also be the fundamental reaction limiting the chain length in cationic polymerization of acetylene monomers. © 1992 John Wiley & Sons, Inc.     

Active centre structure and the stereoregulation process in anionic polymerization

The mechanism of stereoregulation in the anionic polymerization of butadiene and isoprene is discussed in terms of what is known about the structure of the active centres. This includes the effect of the presence of cis and trans isomers and the dynamics of their interconversion and in the isoprene case, the effect of two distinct types having 1,4 and 4,1 structures.     

Functionalization during anionic polymerization of heterocycles

General approaches to the synthesis of functional polymers based on heterocycles are considered. Most attention is paid to the living anionic polymerization with functionalization through initiation or deactivation. It is shown that demands of both high molecular weight and quantitative functionalization cannot be completely satisfied. Some examples of preparing functional polyethers and polyesters are given, namely dinitrophenyl derivatives and vinyl ether macromonomers of poly(ethylene oxide) as well as methacrylate macromonomers of β-propiolactone. Some of perspective applications of these polymers are also touched upon.