Reactivity of 6‐Hexanelactam Cyclic Oligomers, 1. Acidolysis

The acidolysis of 6‐hexanelactam and its cyclic dimer and trimer performed in an excess of anhydrous acetic acid at 200°C was studied. The products of the acidolysis present in the reaction mixtures were analyzed by the RP HPLC method. For the acidolysis of the cyclic substances studied, reaction schemes were suggested and, based on them, a set of kinetic equations was established. It follows from the values of the rate constants obtained by solving the set of equations that the reactivity of the cyclic trimer in the system under study is about five times higher than that of the cyclic dimer. The reactivities of the cyclic dimer and 6‐hexanelactam are comparable.     

Polymerization of lactams, 93. Formation of 6-hexanelactam cyclic oligomers

The formation and decay of cyclic oligomers during hydrolytic polymerization, cationic polymerization, and autocatalytic polymerization of 6-hyxanelactam carried out at 260°C was followed by means of the high performance liquid chromatography (HPLC) analysis of portions extracted with methanol from the polymerization products. It was proved that the type of initiation system substantially affects the formation mechanism of cyclic oligomers. In the autopolymerization of 6-hexanelactam, the concentration of cyclic oligomers as a function of monomer conversion confirms a change of the predominant reaction mechanism during the polymerization.     

Solid state polymerization of zinc methacrylate

Zinc methacrylate has been polymerized in the solid state by the post-irradiation technique at 89.5°C. The polymer produced was less isotactic than that obtained from barium methacrylate dihydrate when polymerized under similar conditions. The tacticity of the poly(zinc methacrylate) differed markedly from the polymer produced in the liquid phase from methyl methacrylate or methacrylic acid. X-ray studies of the zinc methacrylate showed the monomer to have an orthorhombic unit cell with lattice constants of a = 17.94Å, b = 9.16 Å, and c = 13.2 Å. There are 8 molecules per unit cell and the symmetry can be classified as either Pnam or Pna2. The anhydrous monomer shows pronounced thermal polymerization at 89.5°C and the radiation-induced reaction shows no measurable intensity dependency over a 6 fold change in dose rate.     

Syntheses and characterization of poly(aminophenazines)

The oxidative polymerization of o-phenylenediamine was studied under a variety of conditions. At room temperature the reaction of o-phenylenediamine with ammonium persulfate in HCl acid medium gives a dimer, 2,3-diaminophenazine. The same reaction at 70°C results in a trimer with an open structure, [3-amino-2(3,4-diaminophenylamino)]-phenazine hydrochloride. At 118°C, the oxidative polymerization in glacial acetic acid medium gives poly(aminophenazine) acetate, analogous to polyaniline. However, either because of the atactic nature of the polymer and the consequences of this on the stability of charge carriers or because protonation occurs at localized amines, no electrical conductivity was found.     

Anionic copolymerization of ω-lactams with ω-lactones

Copolymerizations of ε-caprolactam, α-pyrrolidone or α-piperidone with ε-caprolactone or δ-valerolactone have been carried out in the presence of alkali metal. It has been shown that in copolymerizations of ε-caprolactam or α-pyrrolidone with ε-caprolactone and α-pyrrolidone with δ-valerolactone conversions of above 70 % and reduced viscosities of above 0.5 in m-cresol at 35°C for all compositions were obtained. In the case of copolymerization of ε-caprolactam with δ-valerolactone at 180°C a conversion of 25 % and a reduced viscosity of 0.5 were obtained, but the polymer was polycaproamide, while at 90°C the conversion was 50 % but the polymer was polyvalerolactone. In copolymerizations of α-piperidone with ε-caprolactone or δ-valerolactone the copolymer contained only polyester. A mechanism is proposed for the copolymerization of ω-lactams with ω-lactones with alkali metal, which involves chain propagation by the stepwise addition of the lactam ring at an end of the chain molecule and by the stepwise addition of the lactone ring at the other end of the chain molecule, resulting to a certain extent in the formation of polyester and polyamide segments. This mechanism is supported by experimental results obtained through the reaction in the presence of alkali metal salts of ω-lactam, data on infrared analyses and elementary analyses, and by experimental results obtained through measurements of physical properties of these copolymers.     

Thermal crosslinking of styrene/p-methylstyrene copolymers

Thermal crosslinking of polydisperse styrene/p-methylstyrene copolymers with compositions of between 0 and 100 mol-% of styrene and weight-average molecular weights of about 300000 was investigated under oxygen-free conditions at 260°C and 275°C. At these temperatures the formation of oligomers was negligible. The reaction products were analysed by gel permeation chromatography and by swelling experiments. Two competing reactions — degradation and crosslinking — were found which occur to an extent proportional to copolymer composition. By comparing the properties of the treated copolymer samples—molecular weights, amount and characteristics of the gel—with the properties of pure poly(p-methylstyrene) samples degraded at 275°C it can be concluded that samples with 83 mol-% and 79 mol-% of styrene treated at 275°C and 260°C, respectively, should remain unchanged with respect to molecular weight and composition, because degradation and crosslinking compensate each other. In the samples containing less styrene crosslinking predominates. The ratio of the reaction rates determined experimentally agrees well with the value calculated from the reaction rates of the homopolymers given in the literature. A simple radical-chain mechanism is proposed that explains the experimental results.     

Polymerization of cis- and trans-7,9-dioxabicyclo [4.3.0] nonane

The polymerization of cis- and trans-7,9-dioxabicyclo[4.3.0]nonane ( 1a ) and ( 1b ) was investigated in bulk and in solution with phosphorus pentafluoride and triethyloxonium hexachloroantimonate as initiators. The cis-isomer 1a forms in high yield the cyclic dimer 2a . The trans-isomer 1b polymerizes readily under similar conditions to relatively low molecular weight polymers, whereas in 1,1,2,2-tetrachloroethane solution predominantly the cyclic dimer 2b is formed. The polymerization of the trans-isomer 1b in toluene-d₈ solution is of first order with respect to monomer, and the concentration of active species appears to remain constant throughout the reaction. The polymerization of 1b in toluene-d₈ with PF₅ as initiator is completely reversible with temperature change, and the standard ceiling temperature T is 118°C (cone.: 1 mol/dm³ in toluene-d₈). The cyclic dimer 2b polymerizes at ?25°C to the same equilibrium product composition as the corresponding monomer 1b .     

Effect of phosphoric acid on the polycondensation of ε-caprolactone with δ-valerolactone and biodegradation of their copolyesters

Copolycondensation of ε-caprolactone (CL) and δ-valerolactone (VL) was performed in the presence and absence of phosphoric acid, in order to clarify the competition between the ring-opening reaction of lactones and the polycondensation of linear compounds produced by this reaction. The gel permeation chromatography data showed that the monomer peaks remained in the system even after 7 h from start of the reaction when polymerized in the absence of phosphoric acid and, on the contrary, in the presence of phosphoric acid the peaks disappear perfectly within 1 h. The weight-average molecular weights (M?_w) of poly(CL-co-VL), obtained by copolycondensation with and without phosphoric acid at 200°C for 1 h, were approximately 540 and 8900, suggesting that phosphoric acid markedly accelerates not only the rate of ring-opening but also the rate of copolycondensation. On the other hand, the biodegradation of the copolyesters obtained is characterized by the action of a lipase-type enzyme, showing a typical parabolic-type degradation pattern.     

Cationic polymerization of hexamethylcyclotrisiloxane by trifluoromethanesulfonic acid and its derivatives, 1. Initiation by trifluoromethanesulfonic acid

Polymerization of hexamethylcyclotrisiloxane (D₃) initiated by trifluoromethanesulfonic acid (triflic acid TfOH) was carried out under vacuum, in methylene chloride solution at 20°C. The reaction rate is first order in [D₃] and the constant active sites concentration [P*] varies as [P*] = k · [TfOH] · [D₃]. The two main products of the reaction, both formed in similar amount from the beginning, are the dimer D₆ and a high-molecular-weight polymer (HP). The other cyclic products also formed are the multiples of D₃ (D₉, D₁₂, …), macrocycles MC (number-average molecular weight M?_n ≈ 10₄) and small amounts of D₄, D₅ … (with [D₅] > [D₄]). The concentration of HP, MC, D₆, D₉, D₁₂, … and the M?_n of the high polymer grow proportionally to conversion. The main reaction giving the high polymer and D₆ is interpreted as a chain reaction, the growing HP bearing at each end potentially reactive silyl triflates which may be activated by the residual acid. D₆ is mainly formed by a special type of back-biting reaction involving transitory tertiary siloxonium ions. The other cycles D_3x and the macrocycles mainly result from cyclization reactions of a second population of growing macromolecules which bear a silyl ester at one end and a nucleophilic silanol group at the other end.     

A method of determining the active centers in cationic polymerization,applied to polymerization of dioxolane,trioxane, and formaldehyde

In order to determine the concentration of active centers, polymerizations are terminated by addition of sodium alkoxide. This yields alkoxy endgroups which after acid hydrolysis of the isolated and purified polymers are determined by gaschromatography of the produced alcohol. In cationic polymerization of anhydrous formaldehyde at −78°C under certain reaction conditions a fast and quantitative initiation reaction and no kinetic chain termination have been observed. Presumably living polymers are obtained. The unexpected decrease in the rate of polymerization after a certain conversion is ascribed to hindrance of monomer diffusion in the crystalline polymer in which the active centers are imbedded. Cationic chainends have been detected in the ⁶⁰Co γ-ray induced polymerization of crystalline trioxane. This proves a cationic mechanism of chain propagation in the radiation-induced polymerization of trioxane. In polymerization of 1.3-dioxolane by HClO₄ at 20°C a gradual but quantitative initiation reaction and no kinetic termination reaction have been observed. Termination by addition of alkoxide and determination of alkoxy endgroups also helped to distinguish between several different mechanisms of chain propagation proposed in the literature. It is assumed that the active center in dioxolane polymerization is a tertiary oxonium ion which propagates by an SN 2 reaction with monomer.     

Cationic polymerizations initiated by high energy radiation

Ionizing radiations generate both free radicals and ions upon interaction with matter and under appropriate conditions either free radical or ionic polymerizations are observed. Cationic polymerizations are favored by the presence of halogenated solvents and by low reaction temperatures. Selective inhibitors and copolymerization studies make it possible to determine the relative proportions of the cationic and the free radical contributions to the overall process under a variety of experimental conditions (temperature, reaction medium, radiation dose-rate). Pure, carefully dehydrated hydrocarbon monomers undergo cationic polymerization when irradiated at room temperature. This reaction proceeds at a very high rate and is believed to involve free propagating cations. Propagation rate constants are available for the following monomers: styrene (k_p = 3,5·10⁶ at 15°C), α-methylstyrene (k_p = 4.10⁶ at 0°C), cyclopentadiene (k_p = 6.10⁸ at ?78°C), isobutene (k_p = 1,5·10⁸ at 0°C), and isobutyl vinyl ether (k_p = 3.10⁵ at 30°C). The present views on the mechanism of radiation induced cationic chain initiation and chain propagation are briefly discussed.     

Mechanisms and kinetics of the anionic polymerization of acrylates, 1. Oligomerization of tert-butyl acrylate and characterization of products

The anionic polymerization of tert-butyl acylate (tBuA) initiated by tert-butyl α-lithioisobutyrate was investigated in THF at 25°C. The individual oligomers were isolated and characterized by UV, IR and NMR spectroscopy. The distribution of products was determined in the range of reaction times 0,02 s ≤ t ≤ 1800 s. The oligomerization is extremely fast. Even after 0,02 s at -30°C, no residual monomer could be detected. After short reaction times the reaction mixture almost exclusively consists of linear oligomers of tBuA. This indicates that there is no termination reaction by Claisen condensation during polymerization. Nevertheless, the molecular weight distribution is rather broad (M?_w/M?_n = 2,1₅). The very large amount of dimer observed is an indication of its low reactivity. A two-state mechanism is proposed to account for the high polydispersity. Only after longer reaction times side products are formed by Claisen condensation (“back-bitting”). The termination product of the trimer is an enolized cyclic β-ketoester.     

Cyclic Poly(l‐lactide) via Ring‐Expansion Polymerization by Means of Dibutyltin 4‐Tert‐Butylcatecholate

Five new catalysts are prepared from dibutyltin oxide and catechol (HCa), 2,3‐dihydroxynaphthalene (NaCa), 4‐tert‐butyl catechol (BuCa), 4‐cyano catechol (CyCa), and 4‐benzoyl catechol (BzCa), but only BuCa gives useful results. When benzyl alcohol is used as an initiator, linear chains having benzyl ester end groups are formed in a slow polymerization process. In contrast to cyclic or noncyclic dibutyltin bisalkoxides, neat BuCa yields cyclic poly(l ‐lactide)s via a fast ring‐expansion polymerization. Under certain conditions, a high‐melting crystalline phase (T _m = 191 °C) is obtained. At 160 °C and short reaction times even‐numbered cycles are slightly prevailing, but, surprisingly, at 120 °C, odd‐numbered cycles are predominantly formed. These results definitely prove that a ring‐expansion mechanism is operating.     

Synthesis and properties of quasi-rigid polyesters containing 2,5-disubstituted tetrahydropyran rings in their main chains

A polyester composed of trans-2,5-linked tetrahydropyran rings ( 4t ) was synthesized by direct polycondensation of trans-5-hydroxytetrahydropyran-2-carboxylic acid ( 5t ) using N-methyl-2-chloropyridinium iodide or triphenylphosphine and hexachloroethane as condensing agents in pyridine at 25 or 50°C. The hydroxycarboxylic acid 5t was polymerized also with dibutyltin oxide, although longer reaction times were required. The polyester 4t is soluble in m-cresol and halogenated protic solvents such as 2,2,2-trifluoroethanol, trifluoroacetic acids and dichloroacetic acid, but insoluble in chloroform and dichloromethane in which the corresponding cis-isomer ( 4c ) composed of cis-2,5-linked tetrahydropyran rings is soluble. According to conformational energy calculations, the repeating unit exists predominantly as a conformer in which both the exocyclic oxygen and the carbonyl carbon in the backbone of the chain are located in the equatorial positions of the tetrahydropyran ring; in other words, the chain of 4t takes a linear conformation. On the other hand, the exocyclic oxygen in the repeating unit of 4c occupies an axial position of the tetrahydropyran ring and the chain is winding. Conformational energies for dimer models for 4c and 4t were also estimated by means of force field calculations. These polyesters are partially crystalline according to their X-ray diffraction patterns. Both polyesters show birefringence at or above 200°C. The polyesters 4c and 4t decompose at 300°C in nitrogen atmosphere, approximately 150°C higher than the isomeric polyester 2 .     

Polymerization of lactams, 88. Copolymers poly(ϵ-caprolactam)-block-polybutadiene prepared by anionic polymerization,part III. Model polymerizations initiated with potassium salt of ϵ-caprolactam and accelerated with isocyanates and their derivatives

Anionic polymerization of ?-caprolactam was initiated with the potassium salt of ?-caprolactam and accelerated with phenyl isocyanate, toluylene diisocyanate, 4,4′-diphenylmethane diisocyanate, some derivatives of these isocyanates (urethanes, ureas, and allophanates), or combinations of phenyl isocyanate with its derivatives at 150°C. The effect of individual structures on the polymerization kinetics and their contribution to the preparation of block copolymers of ?-caprolactam with hydroxy-terminated prepolymers, in-situ functionalized with diisocyanates, are discussed on the basis of a detailed analysis of time functions of polymer yield and degree of polymerization.     

Polymerization of lactams, 92. Non-activated anionic polymerization of ϵ-caprolactam initiated with the sodium salt of ϵ-caprolactam

The non-activated polymerization of ε-caprolactam initiated with the sodium salt of ε-caprolactam (CLNa), which was prepared in situ with sodium methoxide, was studied in the temperature range 170–230°C and at CLNa concentrations from 0.20 to 1.0 mol-%, and at 190°C in the presence of 2.0–10.0 mol-% CLNa. Apparent rate constants and values of apparent activation energy (E_a) were determined for the initial autoaccelerated stage of polymerization (E_a = 230 kJ·mol^–1) as well as for the stage characterized by a zero-order reaction with respect to the monomer (E_a = 120 kJ·mol^–1). Non-integral orders of the polyreaction with respect to the initiator indicate a highly complex polymerization mechanism. Degradation reactions accompany the polymerization at high polymer contents.     

Side reactions during the initiation step in oligomerization of methacrylic esters by electron transfer reaction

Anionic oligomerization of methacrylic esters (methyl (MMA), ethyl (EMA), butyl (n-BMA), tert-butyl (t-BMA) methacrylates) was conducted in a one-step process by mixing, in tetrahydrofuran, the monomer, an alkali metal (sodium) and a deactivating agent (sulfur or tert-butyl alcohol). The formation of alcohol due to a nucleophilic attack of the ester group by the methacrylic carbanion was quantified and related to the monomer structure, temperature and nature of the living ends. It was shown that this side reaction is not limited to the propagation step but can occur during the initiation step. From mass spectra and nuclear magnetic resonance (NMR) spectroscopy of the protonated oligomers (tert-butyl alcohol as deactivating agent), it was concluded that this side reaction led to five-membered cyclic β-keto esters during the initiation step of MMA, EMA and n-BMA monomers only. This implies an intramolecular reaction between one carbanion of the dianionic dimer and the penultimate ester group. It was found that this reaction involves primarily dianionic tail-to-tail dimer, even though head-to-tail dimer was also formed.     

Über N-(isothiocyanatoacylamino)carbonsäuren und ihre kondensationspolymerisation zu copolyamiden mit alternierender sequenz

N-Isothiocyanatoacylamino carboxylic acids are crystalline monomers, which were prepared from ω-isothiocyanato carboxylic acid chlorides and various aliphatic or aromatic amino carboxylic acids. Their condensation polymerization to copolyamides was investigated under various conditions. At reaction temperatures ≤200°C exclusively copolyamides with an alternating sequence were formed, whereas at 250°C amide exchange reactions brought about copolyamides with short homologous blocks. The sequence analysis was achieved by ¹H-NMR- or by ¹³C-NMR-spectroscopy. The average molecular weights of all copolyamides were found to be in the range of 5–10000.