Studies in ring-opening polymerization. I. 5,5-diethyl-1,3,2-dioxathiolan-4-one-2-oxide

The polymerization of 5,5-diethyl-1,3,2-dioxathiolan-4-one-2-oxide has been examined in various solvents at 60–100°C. Kinetic studies have shown that steric hindrance by the C₅ ethyl substituents prevents the occurrence of a bimolecular propagation reaction involving direct attack by a terminal hydroxyl group on the ring. In dry, nonhydroxylic solvents, the first-order rate-determining step in the sequence of reactions leading to polymer formation is a primary ring scission reaction in which a reactive intermediate is formed and sulfur dioxide eliminated. This intermediate, which is formally depicted as an α-lactone, then takes part in a very rapid chain-propagation process, the individual steps of which govern the molecular weight distribution of the polymer. The values of the activation energy (25–30 kcal/mole) and frequency factor (10¹¹?10¹³ sec^?1) for this polymerization reaction are, therefore, those associated with monomer decomposition and not the chain growth process. The molecular weight of the resultant polymer, poly-(3-pentylidene carboxylate) is controlled by adventitious traces of water which produce one carboxyl and one hydroxyl group per chain. Polymers having M?_n ～ 20,000 are readily obtained; these are materials of moderately high melting point (T_m ? 200°C) which crystallize from the melt into a banded spherulitic structure.     

Studies in ring-opening polymerization. III. 5-methyl-5-propyl and 5-methyl-5-isopropyl-1,3,2-dioxathiolan-4-one 2-oxide

5-Methyl-5-propyl-1,3,2-dioxathiolan-4-one 2-oxide (MPAS) and 5-methyl-5-isopropyl-1,3,2-dioxathiolan-4-one 2-oxide (MiPAS), which are isomers of the previously studied 5,5-diethyl-1,3,2-dioxathiolan-4-one 2-oxide (DEAS), have been synthesized and their polymerizability compared with that of the last compound. The two unsymmetrically substituted monomers polymerize by a mechanism which is substantially identical to that of their symmetrically substituted counterpart. In dry nonhydroxylic solvents the rate-determining process is the primary scission of the ring, which takes place with elimination of sulfur dioxide and concurrent ring contraction to form an α-lactone intermediate. In this reaction, the parent acid, produced by reaction of the monomer with adventitious traces of moisture, acts as the initiating species. The resultant polymers are all hydroxyl/carboxyl-terminated, but, whereas those derived from the two unsymmetrically substituted monomers are amorphous and readily soluble in a variety of organic solvents, those derived from the diethyl-substituted ring have been shown to be highly crystalline materials which dissolve in very few solvents. The relative polymerization rates are illustrated by the first-order rate constants for decomposition in nitrobenzene at 90°C: DEAS, 20.1 × 10^?5 sec^?1; MiPAS, 11.0 × 10^?5 sec^?1; MPAS, 9.7 × 10^?5 sec^?1. The role of the substituents in determining the magnitude of these constants is discussed in terms of both the Thorpe-Ingold effect and electron donation at C-5.     

Polymerization initiated by an electron donor–acceptor complex. Part I. Polymerization of methyl methacrylate initiated by liquid sulfur dioxide–pyridine complex in the presence of carbon tetrachloride

The polymerization of methyl methacrylate can be initiated by a charge-transfer complex of liquid sulfur dioxide and pyridine in the presence of carbon tetrachloride. The molar ratio of sulfur dioxide and pyridine which participated in the complex was found from a spectrophotometric study to be 2:1. The polymerization proceeds through free-radical intermediates. The overall rate of polymerization is proportional to the square root of the concentration of the complex, and the values of k_p/k_t^1/2 under the various polymerization conditions were satisfactorily consistent with the literature value. For the activation energy of the overall reaction, 8.2 kcal./mole was obtained, and for initiation, 9.7 kcal./mole was evaluated from the values of k_p/k_t^1/2. It was deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–pyridine complex and the monomer.     

Polymerization of α-Methylstyrene in Cyclohexane with Potassium as Initiator. IV. Thermodynamic Study and Gel-Permeation Chromatographic Analyses of the Polymers

Polymerization of α-methylstyrene in cyclohexane containing traces of tetrahydrofuran (THF) has been carried out at 40°C with potassium as initiator. The conversion of monomer to polymer was very slow, and a solution with [M]₀ of 5.15 mole/ liter, carrying 0.110 mole/liter of the living ends [LE], required two months to reach a stationary state. The gel-permeation chromatographic (GPC) analyses of these polymers showed them to have multimodal distributions which could be split into components D+A, B, and C similar to those found for poly-α-methylstyrene prepared in THF and α-dioxane as solvents. Furthermore, under identical conditions of [M]₀ and [LE], the GPC distributions of poly-α-methylstyrene prepared in cyclohexane, p-dioxane, and THF were the same, in spite of their different dielectric constants. Under identical conditions of [M]₀ but with different [LE], the effect of excessive [LE] on the GPC distributions of the polymers prepared in cyclohexane was not limited to the component D+A as was the case when THF or p-dioxane were the solvents, but also on the component C which increased its contribution [P]_e to the polymer.     

Thermal degradation of polymers with phenylene units in the chain. II. Sulfur-containing polyarylenes

Poly(p-phenylene sulfide), a poly(arylene sulfone), and a poly(arylene sulfonate) were subjected to thermal degradation in vacuo, at temperatures between 250 and 620°C. The volatile and solid degradation products were analyzed by mass spectroscopy, infrared spectroscopy, and elemental analysis. The major decomposition product of poly-(phenylene sulfide) is a condensate, which consists of di- and trimeric chain fragments, dibenzothiophene, and possibly thianthrene. The residual polymer loses two thirds of its sulfur as hydrogen sulfide, however, one third is retained even at 620°C. The most characteristic decomposition reaction of the polysulfone and of the polysulfonate is the almost complete removal of the sulfur as sulfur dioxide. The elimination of sulfur dioxide is practically complete at 450°C for the polysulfone and at 350°C for the polysulfonate.     

Studies on the charge transfer complex and polymerization. XVI. Spontaneous copolymerization of cyclopentene and sulfur dioxide

The alternating copolymerization of cyclopentene and sulfur dioxide was studied. It takes place spontaneously at ?15°C. The rate of copolymerization in toluene was found to be proportional to [CPT]³ and [SO₂]² with the overall activation energy of 16.5 kcal/mole. Terpolymerizations with eight different third monomers were carried out to examine the character and behavior of the copolymerization system of CPT and SO₂. However, the polymerizations with styrene and methyl methacrylate as the third monomers were found to be extraordinary, in that all the three components are not incorporated into the polymer chain.     

Hydroperoxide-initiated copolymerization of sulfur dioxide and cyclohexene. I. Characterization of charge-transfer complex and initiation

The copolymerization of cyclohexene and sulfur dioxide to form an alternating copolymer was initiated by tert-butyl hydroperoxide. The enthalpies and entropies of formation of the cyclohexene-sulfur dioxide charge-transfer complex, which is present during the copolymerization, were determined in two solvents by means of ultraviolet spectroscopy. The reduction of ultraviolet absorption during copolymerization afforded a convenient means of investigating reaction kinetics. No evidence of the direct involvement of the complex in polymerization initiation was found. The observation that the use of unpurified cyclohexene led to spontaneous initiation appears to point to adventitiously formed hydroperoxide rather than the charge-transfer complex as providing initiating radicals which are produced by the redox reaction of the hydroperoxide with sulfur dioxide. A competing heterolytic scission reaction was found to result in the formation of tert-butyl peroxide and sulfuric acid. This reaction caused the polymerization reaction to stop after a short period of time due to a time-dependent decrease in initiator concentration.     

Polymerization initiated by an electron donor–acceptor complex. Part IV. Kinetic study of polymerization of methyl methacrylate initiated by the charge-transfer complex consisting of poly-2-vinylpyridine and liquid sulfur dioxide

A kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge-transfer complex of poly-2-vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates, as with the pyridine-liquid sulfur dioxide complex system. The association constants K of acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that both K and overall rate of polymerization R_p of MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e., R_p is proportional to the square root of the concentration of the complex and to the 3/2-order of the monomer concentration; R_p is clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor and the monomer.     

Bond Energy Scheme for Estimating Heats of Formation of Monomers and Polymers. VI. Sulfur Compounds

The bond energy scheme is extended to sulfur compounds and heats of formation and atomization energy terms derived from thermochemical data reviewed to 1977, for bonds of sulfur with carbon, hydrogen, halogens, and oxygen atoms. A precision of ± 1 kcal/mole was attainable for the covalent bonds of divalent sulfur in the lowest oxidation state S(± II). The higher valency states: S(IV) and S(VI) involve polar contributions depending upon the electrouegativity of the combining atom as well as (d^π -p^π) orbital promotion energies which are specific to the compound and transferable to other molecules only with a limited precision, no better than about ± 3 kcal/mole. The atomization energy terms (E_a ^25°C) of various bonds of sulfur a are found consistent with the experimental bond dissociation energies and bear a relationship with bond lengths and force constants as observed in the previous work. Heats of polymer-forming reactions and heats of formation of sulfur-containing monomers and polymers are estimated from the newly derived bond energy terms.     

Surface treatment of poly(3-pentylthiophene) by ionizing radiation

The influence of radioactive krypton⁸⁵Kr on the surface properties of poly(3-pentylthiophene) has been studied. Irradiation by gaseous⁸⁵Kr leads to structural polymeric chain changes, which induce after iodine doping the formation of charge-transfer complexes with iodine as well as with gaseous sulfur dioxide manifesting itself by the increased electric conductivity. The presence of ammonia brings about reaction with iodine bound in the complex with a conducting polymer.     

Studies on the charge transfer complex and polymerization. XIV. Spontaneous copolymerization of 1-methylcyclopropene and sulfur dioxide

Copolymerization between 1-methylcyclopropene (MCP) and sulfur dioxide (SO₂) was studied. It took place spontaneously even at a low temperature, and was found to be consistent with polymerization by a “living” radical, as suggested by the increase of reduced viscosity with conversion and by the formation of block polymers in the presence of acrylates. The rate of copolymerization was proportional to [MCP]³ and [SO₂]², and the overall activation energy of copolymerization was about 15.1 kcal/mole. A tentative mechanism to explain the experimental results is discussed.     

Photochemistry of poly(vinyl cinnamylideneacetate) and related compounds

The photochemistry of the cinnamylideneacetyl group was investigated with respect to a photosensitive polymer, poly(vinyl cinnamylideneacetate). The photochemical reaction of 1,4-butanediol dicinnamylideneacetate was intramolecular cyclobutane formation. The photosensitive polymer underwent dimerization of the cinnamylideneacetyl moiety to form a cyclobutane ring. The reactivity of the double bond adjacent to the carbonyl group was larger than that of the double bond adjacent to the phenyl group in the chromophore. The quantum yield of the reaction was larger in the solid state than in solution: ? > 1.2 in crystalline state, ? = 0.5 in polymer film, ? = 0.1 in solution. The reaction was sensitized by triplet sensitizers (E_T > 42 kcal/mole). The thermal reaction of the polymer was completely different from the photochemical reaction. A radical initiator was very ineffective for reaction of the polymer.     

Initiation and propagation in γ-radiation-induced polymerization of ethylene

The initiation and propagation reaction in γ-ray-induced polymerization of ethylene was studied by the two-stage irradiation method, i.e., a first stage in which initiation and propagation occur at a high dose rate, and a second stage where only the growth of polymer radical occurs. The rate of initiation is calculated from the amount of polymerized monomer and the degree of polymerization as the rate of increase in the number of polymer chains. The initiation rate is shown to be proportional to the ethylene density in the reactor and dose rate. G_R of radical formation is found to be about 1.6 at 30°C. at a dose rate of 2.5 × 10⁴ rad/hr. and is almost independent of ethylene density but decreases slightly with increasing irradiation dose rate. The lifetime of the growing polymer chain radical is shown to be long at normal temperature. The absolute propagation rate is proportional to the square of ethylene fugacity and depends on dose rate to some extent. For chain growth, irradiation of low dose rate is necessary. The apparent activation energy for the propagation reaction is ?9 kcal./mole.     

Isothermal degradation of poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole

The isothermal degradation of poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole in vacuo has been studied. Measurement of the increase in pressure with time, coupled with infrared analysis, was used to determine the distribution of the degradation products. Processes A and B with different second-order rate laws were determined to be significant in the temperature range of 550–700°C. Process A leads to the formation of equimolar quantities of hydrogen and ammonia and has an activation energy of 68 kcal/mole. Process B leads to the production of HCN, NH₃, and H₂ in the ratio of 1:1:2.5 and has an activation energy of 77 kcal/mole. The activation energies and the rate laws are consistent with a mechanism in which the initial degradation step is the bimolecular reaction of two aromatic rings.     

Aggregation behavior of polystyrene‐b‐poly(ethylene/butylene)‐b‐polystyrene triblock copolymer in N‐methylpyrrolidone

Solution property of hydrogenated polystyrene‐b‐poly(ethylene/butylene)‐b‐polystyrene triblock copolymer (SEBS copolymer) was studied by using static light scattering and dynamic light scattering for cyclohexane and N‐methylpyrrolidone (NMP) solutions. From the values of dimensionless parameters ρ, defined as the ratio of radius of gyration 〈S²〉^1/2 to hydrodynamic radius R_H, and solubility parameters, SEBS copolymer proved to exist as single chain close to random coil in nonpolar cyclohexane, whereas aggregate into the core‐shell micelle consisting of poly(ethylene/butylene) (PEB) core surrounded by PS shell in polar NMP. The core‐shell micelle formed in NMP is composed of 65 polymer chains, having three times larger average chain density (d = 0.12 g cm^?3) than a single polymer chain (d = 0.04 g cm^?3) in cyclohexane. The comparison with the aggregation behaviors in other solvents demonstrated that the aggregate compactness of the copolymer depended largely on solvent polarity, resulting in formation of the highly dense PEB core (R_c = 4.5 nm) and the thick PS shell (ΔR = 22.9 nm) in high‐polar NMP. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 588–594, 2010     

Studies on the Polymerization of Bifunctional Monomers. XIX. Radical Cyclopolymerization of Divinylformal

Radical polymerizations of divinylformal were carried out with AIBN initiator in several solvents. In many solvents (benzene, cyclohexane, acetonitrile, DMSO, etc.), the polymers consisted of the cyclized monomer unit and 5 to 8= of the pendant formate group. The amounts of the residual vinyl group were quite small in these solvents. The formate group was probably formed by the hydrogen migration and the subsequent ring scission of the cyclic propagating radical. On the other hand, a polymer obtained in CS₂ contained about 30= of the pendant vinyl group but no formate group. In addition, the carbon and hydrogen contents of this polymer were lower than expected, and sulfur was detected instead. The polymerization in benzene-CS₂ mixtures indicated a much stronger influence of CS₂ than benzene. These results suggest that CS₂ molecules interact strongly with the propagating radical to the extent that it can be incorporated into polymer.     

Kinetics of styrylquinolinc formation

A comprehensive kinetic investigation of reactions occurring in the formation of styryl-quinolines has been conducted. Specific rate data such as rate equations, rate constants, and thermodynamic activation values have been determined and utilized in a study of which factors are of greatest importance in the reactions forming 2-styrylquinolines. A mechanism has been proposed for the condensation reaction which agrees with rate relationships found. Gas-liquid partition chromatography was used to follow the kinetics of the condensation reactions. A rate constant of 5.41 × 10^?2M^?1min^?1 was found for the reaction of benzaldehyde with 2-methyl-quinoline using zinc chloride as a catalyst at 104.0°. Rate constants of 1.28 × 10^?2 MT^?1 min^?1 and 1.05 × 10^?2 M^?1 min^?1 were found for the reactions of p-methylbenzaldehyde and p-methoxybenzaldehyde with quinaldine to form 2-(p-methylstyryl)quinoline and 2-(p-methoxystyryl)-quinoline, respectively at 92.4°. A linear relationship was found using the Hammett equation. An Arrhenius plot was constructed from rate constants determined at five different temperatures for the reaction of benzaldehyde and quinaldine to form 2-styrylquinoline, using zinc chloride as a catalyst. The energy of activation, E_a, was found to be 22.2 kcal/mole for this reaction. The enthalpy of activation, ΔH?, free energy of activation, ΔF?, and entropy of activation, ΔS?, were found to be 21.4 kcal/mole, 27.7 kcal/mole and -16.7 eu/mole, respectively, at 104.0°. The mechanism proposed in the formation of 2-styrylquinoline involves the fast formation of a carbanion-zinc chloride complex, which then attacks, in the rate determining step, the aldehyde utilized in the reaction. The lack of reaction of certain methylquinolines is attributed to the inadequacy of the carbanion formed and not to the difficulty involved in the initial formation of the carbanion.     

The pyrolysis of trimethylene sulfide. A unimolecular decomposition

The kinetics of decomposition of trimethylene sulfide to ethylene and thioformaldehyde was investigated in a single-pulse shock tube using the «relative rate» technique. The extent of reaction was measured in the reflected shock regime from 860° to 1170°K, but experimental difficulties limited the useful data to the temperature range of 980°–1040°K. The first-order rate constant was found to be k = 10^13.0 exp (?48,200/RT) sec^?1. This result sets an upper limit of 50 kcal/mole for the standard enthalpy of formation of CH₂S, with 35 kcal/mole as a more likely value. The isomerization of cyclopropane to propene was used for the reference reaction; in turn, this was checked, in a relative rate experiment, against the pyrolysis of cyclohexene.     

Studies in ring-opening polymerization. IV. Thermal polymerization of phenyl-substituted 1,3-dioxolan-2,4-diones

The effect of C-5 phenyl substituents on the thermal decomposition of the 1,3-dioxolan-2,4-dione ring has been examined. Unlike the dimethyl-substituted ring, 5-methyl-5-phenyl-1,3-dioxolan-2,4-dione decomposes smoothly in dry nonhydroxylic solvents to yield polymer and carbon dioxide. The introduction of a second C-5 phenyl substituent produces a similar but more rapid decomposition, with the added complication of a competing ring fragmentation leading to ketone formation. An analogy is drawn between the observed behavior of the phenyl-substituted 1,3-dioxolan-2,4-diones and that of the previously studied 1,3,2-dioxanthiolan-4-one 2-oxides. These monomers therefore provide another example of the thermal polymerisation mechanism first observed with 5,5-dimethyl-1,3,2-dioxathiolan-4-one 2-oxides. In these reactions the rate-determining step is the first-order ring-scission process leading to the formation of an α-lactone intermediate. This intermediate then takes part in a very rapid chain-growth process which governs the characteristics of the polymer formed.     

Two reaction routes for the preparation of aromatic polyoxadiazoles and polytriazoles: Syntheses and properties

Two reaction routes for the preparation of aromatic poly-1,3,4-oxadiazoles and poly-1,2,4-triazoles are studied and their influence on the physical properties, i.e., inherent viscosity, glass transition, degradation temperature, and film integrity of the final products are discussed. Aromatic poly-1,3,4-oxadiazoles are prepared by means of a polycondensation reaction of terephthaloyl chloride and isophthalic dihydrazide yielding a precursor polymer, poly(p, m-phenylene) hydrazide, which is converted into the corresponding poly-1,3,4-oxadiazole by means of a cyclodehydration reaction. Poly-1,3,4-oxadiazoles are also prepared by means of a polycondensation reaction between terephthalic and isophthalic acid and hydrazine yielding poly-1,3,4-oxadiazoles with higher inherent viscosities. Flexible poly-1,3,4-oxadiazole films are obtained only if the inherent viscosities of the polymers used are higher than 2.7 dL/g. The thermal stability is found to increase with increasing content of p-phenylene groups in the polymer backbone. Aromatic poly-1,2,4-triazoles are prepared using polyhydrazides with alternating para- and meta-phenylene groups and poly-1,3,4-oxadiazoles with a random incorporation of para- and meta-phenylene groups in the main chain as precursor polymers. The glass transition temperatures are found to increase with increasing content of p-phenylene groups in the main chain of these polymers. Cold crystallization is observed only for the alternating polymer. © 1994 John Wiley & Sons, Inc.