Anionic polymerization of ε-caprolactam with lithium aluminum hydride and with N-acetyl-caprolactam and phenyl isocyanate activators

The anionic polymerization of ε-caprolactam in the presence of lithium aluminum hydride proceeds similarly as other processes initiated by various organometallic and hydride catalysts. When using N-acetylcaprolactam or phenyl isocyanate as activators, the course of polymerization changes completely. Thus the polymerization can be carried out at low temperatures near the melting point of caprolactam, and the molecular weights, formed during polymerization, are stabilized.     

Polysiloxane-based activators in the anionic block copolymerization of ϵ-caprolactam

The activator used in the anionic polymerization of ?-caprolactam is systematically anchored onto the growing polyamide chain. The use of a macromolecular activator, as an isocyanate-terminated polymer, provides an attractive pathway to block copolymerization. However, this procedure is not compatible with a polysiloxane activator, because of the degradtion of the siloxane backbone under conditions needed for ?-caprolactam polymerization. The degradation process was unambiguously evidenced through model-reactions. This conclusion is in contradiction with a previously published report on this subject.     

Anionic polymerization of ε-caprolactam, 63. Catalysis by potassium-graphite intercalate

The overall rate constants of the isothermal bulk polymerization of ε-caprolactam were determined for the non-activated polymerization with a heterogeneous catalyst (KC₂₄) and a homogeneous catalyst (potassium ε-caprolactamate), and also for the corresponding polymerizations activated with N-benzoyl-ε-caprolactam. In comparison to the homogeneous catalysis, the non-activated polymerizations with KC₂₄ are slower, proceed with an induction period and give polyamide with a low molecular weight that does not diminish when the polymerization approaches equilibrium.     

Adiabatic polymerization of ϵ-caprolactam in presence of lithium chloride, 3. Oligomer formation

The activated anionic polymerization of ?-caprolactam is strongly affected by LiCl addition to the polymerizing medium. Large variations in the yield of the polymerization products are induced by increasing salt content: both high polymer and cyclic dimer yields sharply decrease as functions of the salt concentration, whereas monomer and (in part) higher oligomers show a relevant increase. Also the production of low molecular weight side products is influenced by LiCl: higher salt concentrations induce the formation of larger amounts of side compounds. Monomer equilibrium data reveal that the salt negatively affects the thermodynamics of polymerization. ΔG variation as a function of LiCl content shows an increasingly relevant influence of the entropic contribution to the standard free energy change. The effects of LiCl on ring-ring equilibria are qualitatively interpreted on the basis of both the strong ion-ion interactions between Li⁺ ions and carbonyl groups and the interchain densification process.     

Adiabatic polymerization of ε-caprolactam in presence of lithium chloride, 1. Thermodynamic and Kinetic aspects

The activated anionic polymerization of ε-caprolactam in presence of LiCl (up to 10 wt.-%) is studied under quasi-adiabatic conditions. The temperature increase of the system, after proper corrections for the heat exchange with the surroundings, allows to evaluate the enthalpies of polymerization δH_p and to correlate their variations with the specific interactions of LiCl with monomer and polymer. The sharp decrease of ?δH_p as function of LiCl content is attributed to the stabilizing effect of the ion-dipole interactions, which is higher for the monomer-salt pair than for the polymer-salt mixture. The initial rates of polymerization are enhanced by a few percents of added LiCl, with a maximum at about 3 wt.-%. The relative influence of various physical factors on the polymerization kinetics and thermodynamics is discussed.     

Polymerization of lactams, 81. Anionic polymerization of lactams accelerated with N-iminolactams, 2 ϵ-caprolactam (6-hexanelactam)

The anionic polymerization of ?-caprolactam (CL), initiated with the sodium or potassium salt of CL, was shown to be accelerated with 1-(1-pyrrolin-2-yl)-2-pyrrolidone (1) , 1-(1-azacyclohept-1-en-2-yl)-2-pyrrolidone (2) , 1-(1-azacyclonon-1-en-2-yl)-2-pyrrolidone (3) , 1-(1-azacyclohept-1-en-2-yl)-1-azacycloheptan-2-one (4) and 1-(phenyliminomethyl)-2-pyrrolidone (5) , both above the below the melting temperature of the polymer (150-230°C). The postpolymerization of the product was followed at 180°C for certain cases.     

The fast activation of ε-caprolactam polymerization in quasi-adiabatic conditions

Two carbamoyl-type activators of ε-caprolactam (CL) anionic polymerization have been used in quasi-adiabatic conditions with sodium caprolactamate as initiator, at different concentrations and relative ratios. The reaction products have been characterized in terms of high-polymer content and extent of crosslinking. Correlations between the various polymerization parameters on one side, and amount of crosslinked fraction and resultant polymer properties on the other side, have been found. Potential implications on a fine control of PCL properties, exerted by the experimental conditions chosen for the anionic synthesis, are envisaged.     

Polymerization by [3 + 2]-cycloaddition, 5. Telechelics with isocyanate end-groups

The “criss-cross” cycloaddition reaction between derivatives of benzaldehyde azine and several diisocyanates is used for the synthesis of polymers with an uncommon structure element: the 1,3,5,7-tetrazabicyclo[3.3.0]octane-2,6-dione. The nature of the diisocyanate determines the reactivity in this cycloaddition polycondensation and the solubility of the new polymers. A degree of polymerization up to P _n = 72 could be achieved. Due to the nature of the polycondensation reaction, the polymers have two isocyanate end-groups, independent of the stoichiometry of the monomer mixture at the beginning of the reaction. Thus, a prepolymer was synthesized and the chain extension by reaction of its isocyanate end-groups with diamines was studied in some detail.     

Cationic Polymerization of (3‐Aminopropyl)‐tris‐furfuryloxysilane Derivatives—a New Strategy for Complex Hybrid Material Synthesis

The trifunctional (3‐aminopropyl)‐tris‐furfuryloxysilane monomer ( 1 ) is able to undergo both twin polymerization and reaction with electrophilic compounds such as isocyanates. 1 can be readily synthesized from 3‐aminopropyptrimethoxysilane (APTMS) and furfuryl alcohol (FA). The reaction of 1 with three different aromatic isocyanates, namely phenyl isocyanate, diphenylmethane‐4,4′‐diisocyanate (MDI), and a prepolymer consisting of MDI end‐capped polytetramethylene ether glycole (PTMEG), to the corresponding substituted urea derivatives is presented. Three urea derivatives 1‐phenyl‐3‐(3‐tris‐furfuryloxysilyl)propylurea ( 2 ), diphenylmethan‐4,4′‐bis[3(tris‐furfuryloxysilyl)propyl]urea ( 3 ), bis[3(tris‐furfuryloxysilyl)‐propyl]urea‐capped PTMEG‐MDI‐prepolymer ( 4 ) as well as 1 were polymerized to multicomponent organic/inorganic hybrid materials in a one step procedure using methane sulfonic acid as catalyst. The simultaneous formations of poly furfuryl alcohol and polysiloxane networks within the hybrid material are proven by means of solid‐state NMR spectroscopic measurements. The homogeneous distribution of silicon within the solidified hybrid materials is analyzed by scanning electron microscopy, energy dispersive X‐ray spectroscopy, and high‐angle annular dark field‐scanning transmission electron microscopy (HAADF)‐STEM. Homogeneous nanostructured hybrid materials with silicon cluster sizes in the range of 2 nm have been obtained by polymerization of the urea derivatives 2 , 3, and 4 .     

Kuhn-Mark-Houwink-Sakurada-Beziehung für poly(ϵ-caprolactam)

The Kuhn-Mark-Houwink-Sakurada relationship for poly(?-caprolactam), (polyamide 6), is established, based on the absolute determination of the weight-average molecular weight by light scattering. It is obtained ([η] in cm³.g^?1): The unperturbed dimensions of this polymer in both solvents are also determined by using the Stockmayer-Fixman method.     

Synthesis of α,ω‐Isocyanate–Telechelic Poly(methyl methacrylate)

The preparation of α,ω‐isocyanate–telechelic poly(methyl methacrylate) using RAFT polymerization and two postpolymerization modification steps is presented. The synthetic strategy includes the RAFT polymerization of methyl methacrylate, which results in a hetero telechelic polymer. In the first modification step by radical exchange, a carboxylic acid homo telechelic PMMA was successfully prepared. Second, the carboxylic acid end groups are reacted with hexamethylene diisocyanate in excess and magnesium chloride as a catalyst. Under mild reaction conditions (80 °C, 4 h), the isocyanate homo telechelic PMMA is obtained. A conversion of 86% of the carboxylic acid end groups was achieved.     

Copolymerization of N-vinyl-ε-caprolactam with maleic anhydride

The copolymerization of N-vinyl-ε-caprolactam (VCL) with maleic anhydride (MA) in homogeneous solution of N,N-dimethylformamide at 70°C, initiated by benzoyl peroxide, is studied. VCL and MA form a 1:1 charge-transfer complex which is confirmed by spectroscopic analysis. The complex is decisive in the copolymerization reaction and has an equilibrium constant of 0,2 l/mol. The reactivity ratios of the VCL-MA pair are determined as follows:      

Hydroxytelechelic polybutadiene, 12. Polymerization reactions between hydroxytelechelic polybutadiene with hexamethylene diisocyanate or 4,4′-methylenedi(phenyl isocyanate). Kinetics of polymerization in toluene and in the bulk

Addition polymerization of hydroxytelechelic polybutadiene (HTPB) with hexamethylene diisocyanate (HMDI) with a mole ratio NCO/OH = 0,8 in dilute solution of toluene as well as in bulk follows apparent 3rd order kinetics. The polymerization rates are twice as sensitive to temperature as in toluene, an effect which is attributed to intra- and/or intermolecular (OH, OH) auto-association. The three alcoholic functions in HTPB are catalyzed equally by dibutyltin dilaurate. Even with high excess of NCO, free alcoholic functions were found in the product. They were determined quantitatively in moulded polyurethane sheets from HTPB + HMDI and HTPB + 4,4′-methylenedi(phenyl isocyanate) which should be partially crosslinked:     

Polymers based on p-aminophenol, 2. Poly(oxycarbonylimino-1,4-phenylene) and related polyurethanes

The simplest AB-type aromatic polyurethane, poly(oxycarbonylimino-1,4-phenylene) ( 1 ), was successfully synthesized by pyrolysis of phenyl N-p-hydroxyphenylcarbamate. The resulting polyurethane was colorless and soluble in some organic polar solvents. It was also confirmed to undergo “apparent sublimation” by first thermal dissociation to p-hydroxyphenyl isocyanate and subsequent repolymerization to the polyurethane on a cool surface. Three other polyurethanes with related structures were prepared by solution addition polymerization to compare the unique properties. The most remarkable difference was observed in thermal behavior. The polyurethane 1 was found to dissociate much more readily at elevated temperatures than a similar AABB-type polyurethane derived from hydroquinone and p-phenylene diisocyanate.     

Systèmes réactifs polyuréthannes bloqués, 1. Dissociation thérmique en fonction du type d'isocyanate et du type d'agent de blocage. etude par DSC et IRTF

The preparation of blocked isocyanates and their thermal dissociation into isocyanate and blocking agent was studied by DSC and IR spectroscopy. Thermal deblocking was found to be possible only with isocyanates blocked with ε-caprolactame or 2-butanone oxime, but not with β-ketoesters. With 2-butanone oxime — the most convenient blocking agent — the dissociation of blocked aromatic isocyanates starts at ≈ 80°C and is fast at 120°C. With blocked aliphatic isocyanates, the temperature of dissociation (T_d) is higher (≈ 120°C). Ether or tertiary amines have only a poor catalytic effect on the dissociation, and metal naphthenates have no apparent effect. The thermal and viscosity properties of prepolymers with terminal blocked isocyanate groups were investigated. The molecular interactions decrease in the order 1,4-phenylene diisocyanate (7) ? 4,4′-methylenediphenylene diisocyanate > trans-1,4-cyclohexylene diisocyanate ≈ 2,4- and 2,6-toluene diisocyanate.     

Polymorphie,Kristallinität und Schmelzwärme von Poly(ε-caprolactam), 1. IR-spektroskopische Untersuchungen

Poly(ε-caprolactam), (polyamide-6) crystallizes in different modifications, which show different characteristic IR absorption bands. The absorption coefficients of the bands were evaluated from the dependence of their intensity on temperature and specific volume of different polyamide-6 samples. A method is described how to determine quantitatively the amounts of α- and γ^*-modifications and of the amorphous phase. On the basis of these data the densities of the samples were calculated and shown to agree with the values determined experimentally. The specific volume of the amorphous phase is v = 0,917 cm³/g, and is independent of any contents of α, γ^*-, or γ-modifications the samples may contain.     

13C cross polarization/magic-angle spinning NMR and infrared spectroscopic study of poly(ε-caprolactam) and of poly(ε-caprolactam)/polystyrene blends

Infrared and ¹³C cross polarization/magic-angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectra and T relaxation times of differently treated poly(ε-caprolactam) 1

1 Systematic IUPAC name: poly[imino(1-oxohexamethylene)].

(PCL) and of poly(ε-caprolactam)/polystyrene blends were measured and the fractions of the α- and α-crystalline and mesomorphous PCL forms were determined. The amounts of the α-form obtained from the infrared and ¹³C CP/MAS NMR spectra are in agreement. In the blends, the fraction of the PCL α-crystalline form is higher as compared with extruded pure PCL. The existence of a single T parameter for PCL in each of the samples indicates small dimensions of the crystalline regions; the obtained T values correspond to the PCL phase composition.     

Polymerization of Lactides and Lactones, 8. Study on the Ring‐Opening Polymerization of 3‐Phenyl‐ε‐caprolactone and 5‐Phenyl‐ε‐caprolactone

Ring‐opening polymerization of 3‐phenyl‐ε‐caprolactone (3‐ph‐CL) and 5‐phenyl‐ε‐caprolactone (5‐ph‐CL) by tin(II) salt, Al(OⁱPr)₃ and CpNa has been studied; 3‐ph‐CL cannot be initiated by Al(OⁱPr)₃. Polymerization of 5‐ph‐CL initiated with Al(OⁱPr)₃ in toluene at 15°C yielded a polymer of a predictable molecular weight and a narrow molecular weight distribution. 3‐ph‐CL and 5‐ph‐CL can be polymerized by initiating with tin(II) salt, and CpNa. In CpNa‐based polymerization, high molecular weight P(3‐ph‐CL) and P(5‐ph‐CL) were obtained. DSC studies indicate that P(5‐ph‐CL) is an amorphous material, exhibiting a rubber state at room temperature. Compared with PCL, the glass transition temperature of P(3‐ph‐CL) and P(5‐ph‐CL) is higher (–60°C), in contrast to the melting temperature, which is higher for PCL. These new monomers give a route to novel aliphatic polyesters.     

Adiabatic polymerization of ε-caprolactam in presence of lithium chloride, 2. Properties of the resultant polymer

Physical and mechanical properties of poly(ε-caprolactam) synthesized in presence of various amounts of lithium chloride are measured on compression moulded films and correlated to the molecular organization, both in the amorphous and in the crystalline regions. By increasing the amount of LiCl present in the system it can be observed a heigtening of T_g and density of the amorphous phase as well as an increase of tensile modulus and yield strength. A transition from ductile to brittle failure occurs for both semicrystalline and amorphous samples in dry conditions, when the salt content in the amorphous phase is about 6 wt.-%. These phenomena and the capability of the salt to reduce the crystallinity of the polymer are interpreted in the frame of the already accepted model of ion-dipole interactions between lithium ion and the carbonyl groups of the polyamide. Effects due to moisture uptake are also discussed.     

Polylactones, 15. Reactions of δ-valerolactone and ϵ-caprolactone with acidic metal bromides

δ Valerolactone and ?-caprolactone were reacted with BBr₃, AIBr₃, TiBr₄, SnBr₄ or Bu₂SnBr₂ in dichloromethane or chloroform in a 1 : 1 mole ratio. When these exothermic reactions were conducted with cooling, complexation of the lactones at the exocyclic oxygen was detectable by means of IR and ¹H NMR spectroscopy as the first reaction step. However, heating to 60°C causes in all cases ring cleavage, and after hydrolytic removal of the metal bromides ω-bromocarboxylic acids or oligomers with ω-bromoalkanoyl end groups were obtained. SnBr₄, Bu₂SnBr₂ and ZnBr₂ proved to be good initiators of the polymerization of both lactones. At low monomer/initiator (M/I)-ratios (high initiator concentrations) most of the initiator remained unchanged, and the average degrees of polymerization of the resulting polylactones largely exceeded the value expected for the M/I-ratio. By means of viscosity and GPC measurements weight-average molecular weights up to 70 000 were found. All polylactones obtained by initiation with these three metal bromides contain ?-bromoalkanoyl end groups. Furthermore, high-molecular-weight poly(?-caprolactone) could be prepared at polymerization temperatures up to 150°C. The results do not indicate a cationic polymerization mechanism, but an insertion mechanism involving the metal-O bond formed after the first cleavage of the lactone rings.