On the behavior of organophosphorus lactam derivatives during anionic polymerization of ε-caprolactam

This article deals with the anionic polymerization of ε-caprolactam in the presence of N-substituted phosphorus-containing derivatives of ε-caprolactam: diethyl-(N-caprolactam)-phosphonite (PL₁); diethyl-(N-caprolactam)-phosphonate (PL₂), and 2,5-dichlorophenyl-bis-(N-caprolactam)-phosphinate (PL₃). It has been found out that PL₁ and PL₃ had an accelerating effect on the anionic polymerization of ε-caprolactam. The polymerization runs at high velocity and high degree of conversion. PL₂ does not accelerate the anionic polymerization of ε-caprolactam, but when the polymerization is activated by a strong activator of acyl lactam type, and the PL₂ concentration is commensurate with that of the activator, the process runs at a slightly lower rate and at a relatively high degree of conversion. The kinetics of the anionic polymerization in the presence of the three compounds was investigated. Equations describing the effect of the reagents on the polymerization rate were suggested. The activating energy of the polymerization was found out. The different actions of PL₁, PL₂, and PL₃ during the anionic polymerization of ε-caprolactam were explained by their structural differences.     

Al(Cap)3 as initiator in the anionic polymerization of ε-caprolactam at high temperature

Mechanism for polymerization of ε-caprolactam in the presence of both sodium and aluminum caprolactamate was investigated at 171°C. The role of Al(Cap)₃ as an initiator was revealed. The apparent rate constant of propagation reaction decreased with the increase in the concentration of Al(Cap)₃, as the two different metal salts interact even at 171°C. The activation energy of the overall polymerization reaction with this catalyst system was estimated to be 41.18 kcal/mole.     

Equilibrium anionic polymerization of β-methoxypropionaldehyde

Anionic polymerization of β-methoxypropionaldehyde (MPA) was carried out in tetrahydrofuran (THF) by using benzophenone–monolithium complex as an initiator. An equilibrium between polymerization and depolymerization was observed at a temperature range of ?90 to ?70°C. From the temperature dependence of the equilibrium monomer concentration, thermodynamic parameters for the polymerization of MPA in THF were evaluated as follows: ΔH_ss = ?4.8 ± 0.2 kcal/mole, ΔH_SS = ?22.4 ± 1.3 cal/mole-deg, and (T_c)_ss = ?59°C. The thermodynamic change upon the conversion of liquid monomer to condensed polymer was computed from both the partial mixing energy of MPA with THF and the linear relationship between the equilibrium volume fraction of MPA monomer and that of the resulting polymer: ΔH_1c = ?4.7 ± 0.2 kcal/mole, ΔS_1c = ?19.5 ± 1.3 cal/mole-deg, and (T_c)_1c = ?35°C.     

Equilibrium anionic polymerization of β-methoxycarbonylpropionaldehyde

β-Methoxycarbonylpropionaldehyde (MCPA) was polymerized in tetrahydrofuran (THF) with benzophenone–monolithium complex as the initiator. An equilibrium between the monomer and its polymer was observed in the temperature range of ?96 to ?78°C. MCPA had lower polymerizability than ether-substituted aldehydes and their corresponding unsubstituted aliphatic aldehydes in the temperature range. The thermodynamic parameters were evaluated from the temperature dependence of the equilibrium monomer concentration: ΔH_ss = ?4.3 ± 0.2 kcal/mole, ΔS_ss = ?21.9 ± 1.0 cal/mole deg, Tc_ss = ?76°C. Not only an ether substitution but also an ester substitution in propionaldehyde caused the decrease in the absolute values of the thermodynamic parameters for the aldehyde polymerization. These substituent effects may have been the result mainly of the strong intermolecular dipole–dipole interactions of polar groups in monomer states.     

Anionic polymerization of ϵ-caprolactam activated with phosphadiazines

Phenylphosphonyl-N,N′-biscaprolactam (I) and phenylphosphonyl-N,N′-bis(3,5-dimethylpyrazole) (II) were synthesized and found to be very efficient activators for the anionic polymerization of caprolactam when used in combination with strong bases such as sodium caprolactam. Polymers obtained in the presence of I and II had generally higher molecular weights and were less sensitive to thermal degradation upon molding than those whose preparation entailed the use of N-acetyl-caprolactam (III) as an activator. Thermal behavior and tensile properties indicated that the structure of these polyamides differs from that encountered in nylon 6 prepared with conventional anionic catalyst systems.     

Novel chemistry of β-lactones anionic polymerization

Some examples of novel chemistry of lactones polymerization are presented. New evidences on β-lactones polymerization by akali metal alkoxides and, also unusual in organic chemistry, C-C bond scission in β-lactones polymerization induced by alkali metal supramolecular complexes are discussed. Preparation of functional polyesters and various block polymers exhibiting “tailored” properties are also described.     

Regioselective ring-opening anionic polymerization of β-lactones

New aspects of anionic polymerization of 4-membered lactones are presented, attention being paid to regioselectivity of ß-lactones ring-opening reactions. It has been demonstrated that supramolecular complexes of alkali metal alkoxides used as initiators enable control of lactones polymerization, and due to anion activation yield polymers with specific molecular architecture. Synthesis of the analogue of natural polymer poly(3-hydroxybutyrate) via anionic polymerization of ß-butyrolactone is discussed.     

Cyclic oligomers content in anionic poly (ϵ-caprolactam)

The influence of initiator and activator concentrations on the anionic polymerization of ϵ-caprolactam and, in particular, on the methanol – extractable fraction of the final polymer has been widely studied. Due to the increasing interest of this polymerization in the field of reaction injection molding (RIM) technology, a thorough investigation has been also carried out to find the best experimental conditions for this reaction in the mold. The effect of postpolymerization annealing on the overall amount of low-molecular mass substances, among which cyclic oligomers, has been evaluated. Thermal properties as well as crystallinity of the resultant materials have been examined. A comparison with literature data is given; the suggested correlation between the amount of the oligomeric fraction and the molecular arrangement of the polymer in the solid state is discussed.     

Equilibrium anionic polymerization of α-methylstyrene in p-dioxane

The equilibrium anionic polymerization of α-methylstyrene in p-dioxane, with potassium as initiator, has been investigated at 5, 15, 25, and 40°C by using high-vacuum techniques. The comparison of these results with those obtained previously for the equilibrium polymerization of α-methylstyrene in tetrahydrofuran revealed that, although the values of ΔG_1c, the free-energy change upon the polymerization of 1 mole of liquid monomer to 1 bases-mole of liquid amorphous polymer of infinite chain length, are the same for both systems, there is a distinct effect of the solvent. This effect is reflected in the value of monomer equilibrium concentration and its variation with polymer concentration and is explained in terms of a solvent–monomer and solvent–polymer interaction parameter.     

Novel evidence on the chemistry of β-Lactone anionic polymerization

The mechanistic aspects of the β-lactones anionic polymerization initiated by both classical initiators, i.e. alkali metal alkoxides, and non-traditional ones, such as supramolecular complexes of alkali metals and alkali metal naphthalenes, are discussed in this paper.     

Anionic block copolymerization of ϵ-caprolactam

?-Caprolactam anionic homopolymerization was studied in the presence of different model activators. On the basis of the results ester- and isocyanate-terminated polymers were used as macroactivators and nylon-6–polyvinyl or polydiene block copolymers were synthesized in high yields. The physical properties and morphology of a nylon–polybutadiene triblock copolymer were characterized.     

Hydrogen bonded complexes of ϵ-caprolactam

The ultraviolet absorption band of a complex between 9-ethyladenine and ∈-caprolactam has been observed at a wavelength longer than that of the absorption band for the 9-ethyladenine monomer. Absorbance values (at 277.5 mμ) of solutions that contained 9-ethyladenine and different concentrations of ∈-caprolactam in cyclohexane were determined at different temperatures. Linear plots were utilized to determine the apparent association constant (K′ ) of the 9-ethyladenine-caprolactam complex over the range of 25° to 60°. The K′ values for the complex of 4-aminopyrimidine and ∈-caprolactam were determined for the same temperature range from the absorbance of cyclohexane solutions at 282.5 mμ. The K' values of the two complexes are the same at 25°, but ∈-caprolactam is more strongly bonded to 9-ethyladenine than to 4-aminopyrimidine at elevated temperatures. The synthesis of 4-amino-1-ethylbenzimidazole hydro-chloride was performed. An attempt to detect a complex between ∈-caprolactam and 4-amino-1-ethylbenzimidazole in a cyclohexane solution was not successful.     

Lipase-catalyzed ring-opening polymerization of α-methyl-δ-valerolactone and α-methyl-ε-caprolactone

Lipase-catalyzed ring-opening polymerization of α-methyl-substituted medium-size lactones, α-methyl-δ-valerolactone and α-methyl-ε-caprolactone, were carried in bulk. Immobilized lipase derived from Candida antarctica is active in the polymerization of both monomers. The polymerization proceeds under mild reaction conditions to give the corresponding aliphatic polyester having a hydroxy group at one end and a carboxylic acid group at the other.     

Grafting of polyamide 6 by the anionic polymerization of ε‐caprolactam from an isocyanate bearing polystyrene backbone

The grafting of polyamide 6 (PA6) onto polystyrene (PS) can rely on the use of a copolymer of styrene (St) and 3‐isopropenyl‐α, α‐dimethylbenzene isocyanate (TMI), PS‐co‐TMI, to activate the polymerization of ε‐caprolactam (CL) in the presence of sodium ε‐caprolactam (NaCL) as an anionic catalyst. This article is aimed at answering the following key questions. First, do all the isocyanate moieties of the PS‐co‐TMI participate in the activation of the polymerization of CL? Second, what are the composition of the resulting polymer product and the structure of the resulting graft copolymer? The results show that the isocyanate moieties had all participated in the activation of the polymerization, implying that each isocyanate moiety has led to the formation of a PA6 graft. The as‐polymerized product was composed of a pure PS‐g‐PA6 graft copolymer, homo‐PA6, and unreacted CL. Moreover, when the composition of a PS‐co‐TMI/CL/NaCL system was fixed, the mass ratio between the PA6 grafts and PS backbone of the pure PS‐g‐PA6 graft copolymer was almost a constant and was almost independent of its molar mass. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4766–4776, 2008     

γ-Ray-induced polymerization of α-haloacrylic acids

The γ-ray induced polymerizations of α-chloroacrylic acid, mp 66°C, and α-bromo-acrylic acid, mp 72°C, were investigated in the temperature range from 35°C to 85°C. An analysis of polymerization kinetics was made, and results were similar to those reported in the literature for other vinyl monomers. On heating of the polymer obtained, elimination of hydrogen halide takes place, and intramolecular lactone formation is observed. The rate of lactone formation of poly(α-chloroacrylic acid) obtained in the solid-state polymerization was found to be higher than that in the liquid state, because a highly isotactic configuration of polymers, tends to be formed in the solid-state polymerization, and elimination of hydrogen chloride is facilitated with an isotactic 5₂ helix structure.     

Kinetics of ε-caprolactone polymerization on dialkylaluminum alkoxides

Polymerization of ε-caprolactone initiated with dialkylaluminum alkoxides is a living system; formation of macrocyclics is fully depressed. Polymerization initiated with diethylaluminum alkoxide and diisobutylaluminum alkoxide proceeds on monomeric (deaggregated) active species, reversibly aggregating into trimers for the former and into dimers for the latter initiator. Kinetic treatment of this system allowed to determine simultaneously the aggregation-deaggregation equilibrium constant and the rate constant of propagation. Propagation most probably proceeds with insertion (pseudoanionically). Application of amines, complexing the growing species, allowed to break down the aggregates; polymerization became firstorder in initiator. Only secondary amines complexed strongly enough with growing species, the tertiary ones did not affect polymerization, at least up to the ratio 2:1 ([amine]/[initiator]^o). Rate constants of propagation in all of the studied^o systems, whether aggregated or not, have been found to be the same and equal to 0, 04 1·mol⁻¹·s⁻¹ at 25° in THF solvent. This value is approx. 10² times lower than for ion-pairs at these conditions. Moreover, rate constants are almost the same for the growing species …-OAl(C₂H₅)₂ and …-OAl(i-C₄H₉)₂, although aggregation is very much influenced by the size of the alkyl groups.