Growing Chain End Research Articles

Anionic polymerization of phenyl vinyl ketone initiated with a model compound possessing the same structure as the growing chain end

AbstractAnionic polymerization of phenyl vinyl ketone (PVK) was carried out in toluene at 0°C by use of an initiator, ethylzinc 1,3‐diphenyl‐1‐pentene‐1‐olate (I), which possesses the same structure as the growing chain end of PVK in the diethylzinc (ZnEt2)‐initiated polymerization. A unimodal molecular weight distribution was found in the obtained polymer. The polymerization system exhibited a “living characteristic” with the initiator efficiency being 1.0.

Specific solvent interactions in the stereo‐regular polymerization of methacrylic acid

AbstractA study has been made of the marked effect of solvent on the stereoregularity of poly (methacrylic acid) prepared by the radical polymerization of methacrylic acid initiated by Co60 gamma radiation. The specific interaction of the solvent with the monomer and the growing polymer chains, leading to particular structures at the growing chain end, leads to the observed effect on the stereoregularity of the polymer. It is apparent that solvents of intermediate hydrogen bonding strength and bulkiness lead to highly syndiotactic polymer. Thus poly (methacrylic acid) prepared at −78°CC in a 20% by volume solution of methacrylic acid in 2‐propanol contains 95% syndiotactic triads. The effect of the steric hindrance of the solvent is amply demonstrated by the fact that polymerization in 2‐methylcyclohexanol results in the highest degree of syndiotacticity at 0°CC (82% syndiotactic triads) but yields polymer having only 69% syndiotactic triads at −78°CC. This is in contrast to the usual effect on stereoregularity upon lowering the temperature of radical polymerization. The detailed mechanism of this polymerization and its relation to the polymerization of other monomers capable of hydrogen bonding to solvents will be discussed with specific reference to the particular structures that may give rise to the observed effects.

Synthesis of poly‐α,α‐diphenylglycine. II. Cationic polymerization of 4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one

Abstract4,4‐Diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one (I) was found to undergo a cationic polymerization under the influence of boron trifluoride etherate in an anhydrous solvent. The poly‐α,α‐diphenylglycine (III) thus formed contained a larger amount of oligomers than the polymer obtained by thermal decomposition as described in the preceding paper. The molecular weight distribution was further shown to depend on the monomer and catalyst concentration and on the nature of the solvent. A mechanistic rationalization is proposed, involving propagating triazolinium ion pairs (VII) which are not interrupted by chain transfer or termination in the absence of water or alcohol. In the presence of water or alcohol, no polymerization occurred, but the normal acid‐catalyzed decomposition products (IV and V) were then obtained. 1‐Methyl‐4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one (VIII) was also treated with BF3 · OEt2 in a dry solvent at room temperature and furnished 1‐methyl‐3‐phenyl‐indolin‐2‐one (XII) instead of a polyamide. This reaction constitutes a new method for the synthesis of these heterocycles.

Synthesis of poly‐α,α‐diphenylglycine. I. Thermal polymerization of 4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one

AbstractThe thermal decomposition of 4,4‐diphenyl‐Δ2‐1,2,3‐triazolin‐5‐one (I) was reinvestigated and shown to yield poly‐α,α‐diphenylglycine (III) instead of the previously reported 3,3,6,6‐tetraphenylpiperazine‐2,5‐dione (II). Differentiation between the two structures was made by molecular weight determinations and spectroscopic analyses. The infrared spectra were studied in detail and compared with model compounds. They showed that the absorption peak at 1470 cm−1 must be attributed to the trans‐amide II absorption of the polymer. Furthermore, the polymers were found to contain terminal CONH2 as well as triazolinone or ether functions (from alcohol). Fractionation was performed in three solvents based on solubility differences: dichloroethane (or chloroform), methanol, and n‐hexane. All the fractions were characterized by physical methods. A mechanistic investigation revealed that the polymerization process cannot be rationalized by a radical or cationic mechanism, but is compatible with a molecular mechanism involving triazolinone functions at the growing chain ends.

Cationic copolymerization of 1.3‐dioxolane with diketene

AbstractCationic copolymerization of 1.3‐dioxolane with diketene was carried out in toluene, methylene chloride and nitrobenzene at 0°C with triethyloxonium tetrafluoroborate as an initiator. NMR analysis of the microstructure of the copolymer has disclosed that both monomer units are distributed randomly in the copolymer chain, and that the growing chain end of the 1.3‐dioxolane unit adds to both the ring‐oxygen atom and the carboncarbon double bond of the diketene monomer. The fraction of the latter mode of addition, which reflects the selectivity of the active chain end of 1.3‐dioxolane in its reaction with diketene, was found to be 0.69–0.83 depending on the solvents.

Cationic copolymerization of anethole: Reactivity of geometric isomers of α,β‐disubstituted ethylenes

AbstractCationic copolymerizations of anethole were carried out under various conditions in order to confirm the relative reactivities of its geometric isomers. trans‐Anethole was more reactive than cis‐anethole in copolymerizations with p‐methoxystyrene or styrene, but less reactive in the mutual copolymerization of cis‐ and trans‐anethole; i.e., the trans isomer was more reactive to a growing chain end with little steric hindrance. Thus the intrinsic reactivity of an olefinic double bond to carbonium ion is greater for the trans isomer than for the cis isomer. This idea is supported by 13C NMR spectra, since the signal of the olefinic β‐carbon of the trans isomer is at higher field than that of the cis isomer. The behavior of anethole was compared with the results observed in vinyl ethers, where the cis isomer was always more reactive irrrspective of the structure of the growing chain end. In addition, the dependence of monomer reactivity ratios on polymerization conditions is discussed.

Polymerization of N‐CARBOXY‐α‐amino acid anhydride by organometallic compounds III. Mechanism of asymmetric selective polymerization of n‐carboxy alanine anhydride by organoaluminum catalysts

AbstractCopolymerizations of D‐ and L‐N carboxy alanine anhydride by Al(C2H5)3 and (i‐C4H9)2AlN(C2H5)2 were studied in order to elucidate the mechanism of stereospecific polymerization of the N‐carboxy‐α‐amino acid anhydride (NCA) with the two organoaluminum compounds.The enantiomer involved in higher concentration in the starting monomers was polymerized preferentially in the propagation step by these catalysts. The mechanism of the asymmetric selective polymerization was concluded to be the growing chain end control, neither the enantiomorphic catalyst sites control nor the control by the helical conformation of the growing polymer chains.It was found in Al(C2H5)3 initiated polymerization system that almost perfect stereoselective reaction took place at an early stage of the polymerization; that is, about five mole of the NCA initially reacted with one mole of Al(C2H5)3 and the amounts of L‐ and D‐enantiomer of the NCA reacted were always equal independently of enantiomer ratio in the starting NCA.

Influence of temperature on microstructure of anionic‐initiated polybutadiene

AbstractApplication of the Arrhenius relationship for temperature and ratio of isomeric units in polybutadiene made in the presence of butyllithium initiator is consistent with the existence of three simultaneous competing reactions. Evidence in the literature is cited to support the possibility that the growing chain end exists in a composite equilibrium producing localized structures which on reacting with monomer result in fixed isomeric units. The compliance of the data with the thermodynamic relationship permits the extrapolation of a narrow set of data to a broad temperature range.

Formation of spherulites during polymerization of lactams

AbstractThe mechanism of the crystal growth of nylon in the course of alkaline polymerization of lactams was studied in terms of kinetics and morphologies of the resultant crystals.It was found that in the bulk polymerization of α‐pyrrolidone, the resultant polymer precipitated in the form of spherulites. Spherulites formed in the early stage of polymerization were swollen, soft balls in which thin lamellar crystallites were radiating along the spherulitic radius. It is considered that the growing chain molecules, when they attained a critical length beyond which they lost the solubility in the system, will precipitate into the form of lamellae in which molecules are aligned perpendicularly to the lamellar surface. Such spherulites matured as the polymerization proceeded. In the early stage of the polymerization, the mutual coupling of the swollen spherulites occurred. In the subsequent stage, the vacant space was occupied by the product of further polymerization, so that the coupled spherulites grew into a sphere again. On the other hand, the propagation of the chains in the individual spherulites made the spherulites compact. It is postulated that the chains grown from the surface of the lamellar nuclei, precipitate in the interstices between the lamellae and a part of these chains will form molecular ties between the lamellae giving rise to compact spherulites.The decrease in the rate of polymerization observed may be attributable to the occlusion of the growing chain ends into the precipitates. The impurity in the system, i.e., water, seems to affect the rate of the monomer addition, but does not the morphology.Spherulites were also grown in the case of nylon 6, the polymerization of ϵ‐caprolactam.

Effects of Additives on the Alternating Copolymerization of Aziridines with Cyclic Imides

Abstract The effect of the addition of 2-methyl-2-oxazoline, which is an isomer of the growing chain end, was examined. The rate of the copolymerization of ethylenimine with succinimide increased upon the addition of 2-methyl-2-oxazoline. On the basis of this result and of the NMR spectrum of the copolymer, the mechanism of propagation via an activated state similar to oxazoline was proposed. The copolymerization was accelerated by the addition of sodium iodide, which is the catalyst of the isomerization of the growing chain end. The property of the copolymer obtained was different from that of the copolymer obtained without sodium iodide. Sodium iodide also affected the copolymerization of N-ethylethylenimine with succinimide, while it did not affect that of ethylenimine with N-ethylsuccinimide. The reduced viscosity of the copolymer increased with the reaction time. The reaction mechanism of the copolymerization in the presence of the catalyst was discussed on the basis of the facts mentioned above.

Polymerization mechanism of N‐carboxy‐α‐amino acid anhydride by organometallic compounds. II.. Reaction with organozinc compounds

AbstractReactions of N‐carboxy‐α‐amino acid anhydride (NCA) with dialkylzinc or related organozinc compounds were studied to elucidate the polymerization mechanism of NCA by dialkylzinc as initiator.The first stage of initiation reaction is a hydrogen abstraction reaction of dialkylzinc from NH group of α‐amino acid NCA resulting in the formation of an activated NCA. The second stage of initiation is a reaction between two molecules of the activated NCA forming a zinc carbamate group.Propagation reaction is a carbonyl addition of the zinc carbamate group to the activated NCA to form a mixed anhydride which changes into an amide group releasing carbon dioxide.Regeneration of the activated NCA is supposed to be done by the reaction of free α‐amino acid NCA with the zinc atom bonded to nitrogen atom at the growing chain end.

Tacticity of Poly (o-methoxystyrene) Obtained by Cationic Polymerization

Abstract o-Methoxystyrene was polymerized under various conditions with BF3 O(C2H5)2, SnC14, or A1(C2H5)Cl2 catalyst. The effect of polymerization conditions on the steric structure of poly(o-methoxy-styrene) was studied by NMR spectra of the methoxyl protons, and has been tentatively assigned to the triad tacticity of the polymer. Highly stereoregular polymers were not obtained by these catalysts. The tacticity of polymers was independent of the polarity of solvents, as observed in the cationic polymerization of α-methylstyrene. This behavior was completely different from the cationic polymerization of vinyl ethers. It was found that the heterotactic fraction increased with decreasing polymerization temperature upon polymerization in toluene solution. The fraction of the triad tacticity calculated from Bovey's equation coincided with the experimental results. This fact shows that the steric structure of the addition monomer is determined only by the growing chain end unit and that there is no penultimate...

Polymerization of propylene to syndiotactic polymer. V. Steric control and copolymerization

AbstractBinary copolymerizations of ethylene, propylene and butene‐1 were studied. The copolymers show a tendency to an alternating sequence distribution if prepared by syndiospecific catalysts, whereas they show a random distribution when prepared by non‐stereospecific or by isospecific catalysts.These facts indicate that syndiotacticity is due to steric interactions between monomer and last unit of the growing chain end and that isotacticity is due to steric interactions between monomer and counter‐ion. The propylene‐butene‐1 copolymerization shows that the side‐chain rotations of the last added unit are hindered in the presence of syndiospecific catalysts.

Cationic polymerization of α‐methylstyrene catalyzed by boron trifluoride etherate in 1,2‐dichloroethane under an electric field

AbstractThe cationic polymerization of α‐methylstyrene with boron trifluoride etherate was studied in 1,2‐dichloroethane under an electric field. The electric field was again found to increase the polymerization rate. This field effect was independent of monomer concentration, as was found previously. The effect, however, became greater as the catalyst concentration was lowered, unlike previous findings with various cationic systems. Furthermore, the field effect became smaller with rising temperature, whereas it had been practically independent of temperature in previous studies. The field effect increased linearly with the field strength. At 2.7 kv./cm. the rate was almost tripled. The field effect was small at lower dielectric constants, as had been observed previously. The large field effects observed and their “exceptional” behavior led to the interpretation that “partial” desolvation of free, growing chain ends, in addition to the field‐facilitated dissociation, was responsible for the effect. Specific conductivities of polymerizing solutions and catalyst solutions were measured and are discussed.

Kinetics of biopolymerization on nucleic acid templates.

AbstractThe kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocks L adjacent sites. Solutions are found for the probability nj(t) that a template has a growing center that occupies the sites j — L + 1,…, j at time t. Two special sets of solutions are considered, the uniform‐density solutions, for which nj(t) = n, and the more general steady‐state solutions, for which dnj(t)/dt = 0. In the uniform‐density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady‐state case, only L = 1 is discussed. For a steady‐state polymerization rate less than the maximum uniform‐density rate, the steady‐state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform‐density solutions corresponding to that polymerization rate. For a steady‐state polymerization rate equal to or slightly larger than the maximum uniform‐density rate, the steady‐state solutions are nearly uniform to the single uniform‐density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assumed in the uniform region(s).

Ionic Polymerization under Electric Field.* V. Cationic Polymerization of Styrene Catalyzed by Boron Trifluoride Etherate

Abstract The cationic polymerizations of styrene under an electric field have been investigated by using boron trifluoride etherate as a catalyst and binary mixtures of toluene, 1,2-dichloroethane, and nitrobenzene of various compositions as the solvent. The polymerization rate of styrene in dichloroethane was tripled in the presence of a rather low-intensity electric field of 0.25 kV/cm. The field-accelerating effects were found to be nil in pure toluene, increasing with increasing dielectric constant of the mixed solvents and, through the maximum value in pure dichloroethane, decreased with further increase in the dielectric constant. This observation might indicate that the ion pair of the growing chain ends is too “firm” to show the field effects in toluene, whereas the degree of dissociation of ion pairs in nitrobenzene is large to such an extent that the application of the electric field can no longer increase the population of free ions. This interpretation is in qualitative agreement with the pred...

NMR studies on the stereospecific polymerization of methyl vinyl ether. Part II. Polymerization by sulfuric acid–aluminum sulfate complex: Enantiomorphic catalyst sites model

AbstractHighly crystalline poly(methyl vinyl ether) (PMVE) was produced in toluene in a temperature range of 0 to −20°C. with the use of sulfuric acid–aluminum sulfate complex (SA catalyst). It was found from the NMR spectra that these polymers contained more than 50% of the triad isotactic fraction and the melting point of the unfractionated polymer was about 130°C. However, PMVE containing a large amount of the isotactic fraction was insoluble in nitromethane, so the triad tacticity of highly crystalline PMVE could not be quantitatively determined. The molecular weight of PMVE increased with increasing conversion and increasing polymerization temperature. This behavior is different from that in metal halide catalysts. Also, the stereoregularity of PMVE decreased with increasing monomer concentration. However, addition of a polar solvent and increasing the polymerization temperature had little effect on the stereoregularity of the polymer. The increase in the isotactic fraction at high catalyst concentration and the difference in the monomer composition in the copolymerization of methyl vinyl ether with 2‐chloroethyl vinyl ether by SA catalyst from that obtained by BF3·O(C2H5)2 suggest that the absorption of MVE on a catalyst surface is an important step in the propagation step by SA catalyst. The fraction of the triad tacticity calculated from the enantiomorphic catalyst sites model8 coincided with the experimental results. This fact shows that the steric structure of the adding monomer is determined only by the nature of the catalyst irrespective of the nature of a growing chain end. It is concluded, on considering also the results of the previous paper, that completely different factors can control the steric structure of a polymer even for the same monomer when different catalysts are used.

The mechanism of anionic polymerization of dimethylketene

AbstractIn the reaction of dimethylketene with GRIGNARD reagent of ether polyketonic type oligomers were formed, but the non‐distillable fraction was of polyester type. Therefore it is suggested that the propagation reaction to polyketone proceeds slowly, but those to polyester is a fast one.From the results of fractionations of polymers prepared under various conditions, the polymerization mechanism is explained by three kinds of growing chain ends which are in dynamic equilibrium.

Specific polymerization of vinylpyridinium salts. Polymerization on macromolecular “matrices”

Abstract4‐Vinylpyridinium salts could be spontaneously polymerized in organic and water media by unusual ionic mechanism. The growing active species were characterized with high chemical specificity. The growing chain end being intramolecular ionic pair (zwitterion) was able to add only the molecules of monomeric vinylpyridinium salt and does not react with other vinyl monomers, including vinylpyridine. The reaction described was used for polymerization of 4‐vinylpyridine on macromolecules of polystyrene sulfonic acid in water and in organic solvent. The chains of strong polyacid were operating as activating “matrices,” which adsorbed, neutralized, and polymerized strictly stoichiometric amount of monomer molecules. The morphology of polymerization products was studied with electron microscopy.

Rates of polymer formation and monomer consumption in the solution polymerization of trioxane catalyzed by BF3 · O(C2H5)2

AbstractIn the solution polymerization of trioxane catalyzed by BF3 · O(C2H5)2 at 30°C. the amount of the methanol‐insoluble polyoxymethylene is less than the amount of monomer consumed. This difference was much larger than the amount of formaldehyde determined in the polymerized system and could not also be explained in terms of the amount of the methanol‐soluble oligomer. Tetraoxane was detected in large quantities by gas chromatography in the polymerized solution of trioxane. Therefore, the difference between the amounts of the methanol‐insoluble polymer and the monomer consumed was ascribed partly to the formation of tetraoxane. In spite of the fact that tetraoxane was polymerized more easily than trioxane by BF3 · O(C2H5)2, an almost constant amount of tetraoxane was produced, independent of the kind of solvent and the polymer yield. This suggests the existence of an equilibrium concentration of tetraoxane. On the other hand, the formation of trioxane was observed in the solution polymerization of tetraoxane by BF3 · O(C2H5)2. This suggests that the formation of tetraoxane during the trioxane polymerization is due to a back‐biting reaction in which the growing chain end of trioxane attacks the oxygen atom in its own chain with depolymerization of tetraoxane.