Cationic polymerization of methoxyallene with protonic acids

The cationic polymerization of methoxyallene (1) was carried out with some protonic acids at ?50°C in dichloromethane. Polymer yield and molecular weight increase with the degree of acidity of the protonic acid (CF₃CO₂H < CH₃SO₃H < CF₃SO₃H), whereas the remaining double bond content in the polymer decreases with the acidity of protonic acids. Consequently, to obtain a polymer with high molecular weight and high double bond content (i. e., low degree of side reactions), the polymerization of 1 with medium acidic CH₃SO₃H gives the best results. It gives a highly unsaturated polymer in moderate yield, which can not be obtained with Lewis acids such as BF₃OEt₂.     

Radiation polymerization of perhydrotriphenylene-included butadiene

The planar isomer of perhydrotriphenylene (PHTP) is a new host molecule for the inclusion polymerization of butadiene. By γ-irradiation of the PHTP-monomer adduct an inclusion compound between PHTP and the polymer is obtained, as revealed by its melting point. The recovered polymer has a highly regular trans-1.4-structure. The effect of different variables (dose, dose-rate, PHTP/monomer ratio) has also been studied.     

Cationic polymerization of styrenes by protonic acids and their derivatives, 3. Propagating species in the polymerization of styrene by trifluoroacetic acid

The nature of the propagating species in the cationic polymerization of styrene by trifluoroacetic acid was investigated with special attention to the possibility of ester propagation. The molecular weight distribution (MWD) of polymers formed at 50°C in 1,2-dichloroethane (DCE) and mixtures of DCE and benzene was found to be bimodal, and increasing solvent polarity facilitated the formation of the higher polymers. From this evidence, coupled with the effects of a common ion salt on the MWD, it was concluded that the bimodal MWD results from concurrent propagation of two ionic species. ¹⁹F NMR spectra of the polymerization system in DCE at 50°C showed two peaks, one of which was assigned to the acid and the other to its styryl and polystyryl esters. The esters were formed slowly and the polymerization rate fell more rapidly than corresponded to the fall in monomer concentration. The styryl ester (1-phenylethyltrifluoroacetate) could not initiate the polymerization under the same conditions. These results indicate that an ester is not the propagating species in the present system. A kinetic treatment based on the inertness of the ester gave a satisfactory interpretation of the results.     

Cationic polymerization of styrenes by protonic acids and their derivatives, 2. Two propagating species in the polymerization by CF3SO3H

The bimodal molecular weight distribution (MWD) of the polymers and the polymerization rate in the cationic polymerization of styrene by CF₃SO₃H were studied under a variety of conditions. Both the decrease of the dielectric constant of the reaction mixture and the addition of a common-ion salt (Bu₄N⁺SO₃CF) reduced the polymerization rate and the formation of the higher molecular weight portion of the polymers (the high polymer). It appears that of the two propagating species the one which forms the high polymer is more ionically dissociated and more reactive in propagation. Salt effects indicate that in nitrobenzene the propagating species is a solvent-separated ion pair and/or a free ion. The effects of monomer concentration on the bimodal MWD have shown that there are different chain-breaking reactions for the two propagating species. The possibility that the monomer is complexed with one of the growing species is also discussed.     

Cationic polymerization of methoxyallene with Lewis acids

The cationic polymerization of methoxyallene ( 1 ) was carried out with some Lewis acids at ?50°C in dichloromethane. BF₃OEt₂ was found to be an effective catalyst for the cationic polymerization of 1 . From analyses of ¹H and ¹³C NMR spectra, the obtained polymers consist of units with the 1,2-double bond of 1 being opened, although the 2,3-double bond is consumed also to an amount of 24 to 43 mol-%. This decrease in 2,3-double bond content in the polymer may be attributed to intramolecular cyclization of the propagating cation and/or the intermolecular reaction of the propagating cation with polymer to produce a graft polymer. Moderately polar solvents such as dichloromethane proved to be best suited for obtaining polymers with high double bond content.     

Cationic polymerization of styrenes by protonic acids and their derivatives, 1. Rates and molecular weight distributions of polystyrenes formed by some sulfonic superacids

The cationic polymerizations of styrene by sulfonic superacids (CF₃SO₃H, FSO₃H, and ClSO₃H) and by methanesulfonic acid (CH₃SO₃H) were investigated with respect to the polymerization rate and the molecular weight distribution (MWD) of the polymer at 0°C. The superacids initiated the polymerization at low concentrations. CF₃SO₃H is the most active initiator among the protonic acids investigated so far. The polystyrenes formed in methylene chloride showed a MWD with two distinct peaks irrespective of the kind of initiators. In benzene only the low molecular weight polymer is formed, in nitrobenzene only the high molecular weight polymer. This indicates that in methylene chloride all the initiators generate two kinds of propagating species which grow simultaneously and independently. The time-course of the polymerizations depended on the kind of initiators, in that CF₃SO₃H gave first-order polymerizations to completion, while FSO₃H and ClSO₃H gave limited yields. The termination mechanism is also discussed.     

Cationic polymerization of styrenes by protonic acids and their derivatives, 4. Homo- and Co-polymerizations of para-substituted styrenes by CF3SO3H

p-Methyl- and p-chlorostyrenes (pMeSt and pClSt) were polymerized by CF₃SO₃H in methylene chloride at 0°C and gave polymers with a bimodal molecular weight distribution (MWD). This indicates that the polymerizations involve two independent propagating species: a dissociated and a non-dissociated species. Their selectivities toward monomers were compared in the copolymerizations of pMeSt and pClSt with styrene (St) by CF₃SO₃H in benzene, methylene chloride, and nitrobenzene solvents. Decreasing solvent polarity and the presence of a common-ion salt ((n-C₄H₉)₄N⁺SO₃CF^?₃) greatly increased the reactivity difference between the monomers. Thus the non-dissociated species is more selective than the dissociated species. In contrast, the composition of pMeSt-St copolymers produced by BF₃O(C₂H₅)₂ did not change with the solvent polarity. The difference in nature between the propagating species generated by CF₃SO₃H and by BF₃O(C₂H₅)₂ is discussed.     

Emulsion polymerization of butadiene, 4. Effect of thiols

The role of thiols of low water solubility, commonly used in the emulsion polymerization of butadiene, has been considered. The following effects have become apparent: (1) dodecanethiols act as efficient chain transfer agents in limiting the formation of heavily cross-linked polymer networks; (2) the monomer concentration within the particles is not influenced by such thiols; (3) C₁₂-thiol radicals do not desorb because of their extremely low water solubility. The ‘promoting effect’ of thiols in emulsion polymerizations of diene-hydrocarbons is still poorly understood, but it appears to be related to impurities present in the emulsifier, as it was found completely absent in emulsifier-free polymerizations.     

Copolymerization of polar vinyl monomers with butadiene in the presence of Lewis acids

The copolymerization of acrylonitrile (AN), methacrylonitrile (MAN), methyl acrylate (MA), and methyl methacrylate (MMA) with butadiene (BD) in the presence of ethylaluminium dichloride, zinc chloride, and stannic chloride was investigated. The reactivity of polar monomers in the copolymerization was found to decrease in the following order: AN>MAN>MMA>MA. It was also found that AN and MAN form with BD copolymers of essentially 1:1 composition; MMA, and particularly MA were found, however, to form with BD copolymers of a composition different from 1:1. In competition with the copolymerization, a Diels-Alder reaction was shown to occur in the investigated systems. The reactivity of polar monomers in the Diels-Alder reaction was found to increase in the following order: MAN<AN<MMA<MA. In the presence of aluminium bromide and of antimony chloride these monomers were found to produce with BD the corresponding Diels-Alder adducts but not the copolymers. The obtained results are discussed in terms of the electron-accepting properties of polar vinyl monomers and of the stability of transient charge-transfer complexes between the monomers involved in the copolymerization and the Diels-Alder reaction.     

Effects of halogen ligands on 1,3‐butadiene polymerization with cobalt dihalides and methylaluminoxane

We conducted 1,3‐butadiene polymerization at 0 and 18 °C using CoX₂ (X = halogen) combined with MAO to elucidate the role of halogen ligands attached to cobalt. With increasing the polymerization time, the molecular weight distribution curves of the polymers obtained progressively shifted to higher molecular weight regions accompanied by narrowing polydispersity, irrespective of the cobalt halides employed. The polymer yield linearly increased after an exponential induction stage, while the number‐average molecular weight linearly increased vs. polymerization time. Thus, the number of polymer chains calculated from the polymer yield and the number‐average molecular weight increased with polymerization time. After a certain polymerization time, the number of polymer chains was saturated to be about 60% catalyst efficiency in the CoCl₂ and CoBr₂ systems but only about 2% in the CoI₂ system. The number‐average molecular weight increases linearly vs. polymer yield from a small positive intercept. These phenomena were interpreted by a slow initiation system without any termination and chain transfer reaction. The kinetic analysis indicated that the rates of initiation were significantly influenced by the nature of the halides and descended in the following order, CoCl₂ > CoBr₂ > CoI₂ > CoF₂ = 0, whereas the rates of propagation were independent on variation of halogen ligands. ¹H and ¹³C NMR analyses of the polymers indicated that the microstructure of the resulting polymer was high cis‐1,4 irrespective of the halogen ligands.

The number of polymer chains of CoI₂ as a function of polymerization time.     

Terpolymerization of polar vinyl monomers with butadiene and styrene in the presence of Lewis acids

Terpolymerizations of polar vinyl monomers, acrylonitrile, methyl acrylate, or methyl methacrylate with butadiene and styrene in the presence of ethylaluminium dichloride, zinc chloride, or other Lewis acids were carried out. The yield and the contents in monomer units of the terpolymer and the yields of the polar vinyl monomer/butadiene 1,4-cycloaddition byproduct formed in these systems were determined. Butadiene conversions in the above terpolymerizations and 1,4-cycloaddition side reactions were related to those in the copolymerization and 1,4-cycloaddition proceeding in corresponding binary systems without styrene. The results are discussed in terms of a radical polymerization and a polar 1,4-cycloaddition mechanisms.     

Condensation polymerization of N-dithiocarbonyl alkoxycarbonyl-amino acids. Part I. Synthesis and condensation polymerization of N-dithiocarbonyl ethoxycarbonyl-amino acids

N-dithiocarbonyl ethoxycarbonyl-amino acids (III), were synthesized in crystalline form from various amino acids by the addition of ethyl chlorocarbonate to dithiocarbamic acid salt obtained from amino acid and CS₂ at low temperature. When the reaction was performed above room temperature, polypeptides could directly be obtained without getting III. Compounds such as III were synthesized from glycine, DL -α-alanine, DL -valine, DL-methionine, L-leucine, glycylglycine, β-alanine, γ-amino-n-butyric acid and ε-amino-n-caproic acid in this paper. III were polymerized to polypeptides in high yields in the presence of a basic catalyst or by heating; acid inhibited the polymerization of III.     

Emulsion polymerization of butadiene, 1. The effects of initiator and emulsifier concentration

The kinetics of the emulsion polymerization of butadiene was investigated using Dresinate 214 as emulsifier and three dissociative initiators, viz. potassium peroxodisulfate, 4,4′-azobis-(4-cyanopentanoic acid) and 2,2′-azoisobutyronitrile. All experiments were conducted in the presence of a thiol as chain transfer agent, as usual in diene-polymerizations. The polymerization rate in interval II, R_pol, was found to be highly insensitive to changes in the initiator concentration (R_pol ∝ [I]^0,08). Primary radicals are generated in large abundance in interval I as compared with the final particle number, indicating that the initiator efficiency with regard to particle nucleation is very low. The development of particle number as a function of conversion at several emulsifier concentrations shows that limited coagulation is occurring in the present system. R_pol depends on the emulsifier concentration with an exponent of 0,61, while the final particle number after cessation of coagulation depends on the emulsifier concentration to the 1,6th power. As a consequence the average number of radicals per particle must be a function of particle size, because the monomer concentration in the latex particles is approximately constant in interval II. A certain analogy in behaviour between the emulsion polymerization of various polar monomers, kinetically dominated by radical desorption, and the emulsion polymerization of butadiene, suggests that similar events determine the kinetic course in the present system.     

The initiation of polymerization of unsaturated tertiary amines with carboxylic acids

The polymerization rate (R_p) of N-methyl-N-phenyl-2-aminoethyl methacrylate (MPAEMA) initiated with 2,2' -azodiisobutyronitrile (AIBN) at 50°C increased considerably after the addition of CCI₃COOH, and distinctly after the addition of CH₃COOH. R_p in a benzene solution of 2 mol. dm^?3 MPAEMA and 5 · 10^?2 mol. dm^?3 CCl₃COOH (without AIBN) was 13% · h^?1. [η] of the obtained polymer corresponded to 64 cm³ · g^?1. The polymerization order of MPAEMA initiated with CCl₃COOH is 0,93 with respect to monomer and 0,51 with respect to CCl₃COOH. The overall activation energy of polymerization of MPAEMA calculated from the temperature dependence of R_p between 20 and 50°C is 43 ± 1,2 kJ · mol^?1. In a benzene solution of 2 mol.dm^?3 MPAEMA, 5 · 10^?2 mol · dm^?3CCl₃COOH and 5 · 10^?3 mol · dm^?3 1,4-benzoquinone at 50°C the polymerization does not proceed for 6 h. In a benzene solution of 2 mol · dm^?3 4-dimethylaminostyrene (4-DMAS) and 2 mol · dm^?3 CH₃COOH (without AIBN), 40% of monomer polymerized within one hour. [η] of the polymer was 4 cm³ · g^?1. The overall activation energy of polymerization of 4-DMAS in the presence of CH₃COOH is ca · 54 kJ · mol^?1. The addition of 5 · 10^?3 1,4-benzoquinone slows down the polymerization rate only slightly. The effect of acids on the elementary polymerization reactions is characterized.     

Particle growth in butadiene emulsion polymerization, 4. The promoting effect of mercaptans

The observation that butadiene emulsion polymerizations in the presence of fatty acid emulsifiers need minimal amounts of tertiary or n-dodecanethiols to polymerize at a reasonable rate is often referred to as the promoting effect of mercaptans and is evaluated in this paper. Experimental evidence is presented which shows that fatty acid emulsifiers can actively reduce the average number of radicals per particle. In this paper it will be shown that three components are necessary for retardation of the rate of polymerization in the absence of dodecanethiol to occur: (1) Only diene monomer polymerizations show retardation. (2) Only peroxodisulfate-initiated polymerizations show retardation. (3) Retardation of the rate of polymerization only occurs in the presence of fatty acid emulsifiers. These three components are combined for the first time in a reaction scheme which is an extension of a reaction scheme proposed by Kolthoff in 1951. Experimental evidence justifies the suggestion that reaction between a fatty acid radical and butadiene play an important role in the promoting effect.     

Mechanism of the polymerization of hexamethylcyclotrisiloxane (D3) in the presence of a strong protonic acid

The polymerization of hexamethylcyclotrisiloxane (D₃) was studied in methylene chloride solution in the presence of trifluoromethanesulfonic acid as catalyst. The reaction occurs mostly by addition of monomer to the ends of growing molecular chains. However, an important role is played by cleavage of a siloxane bond in the monomer by acid or water as well as by reverse processes of silanol and/or +ylester end group condensation to siloxane linkages. The latter account for the formation of large amounts of cyclic products and for the coupling of linear chain fragments. They are also responsible for the regeneration of the catalyst leading to establishment of stationary concentrations of reactive species in the polymerization system. The involvement of the above mentioned processes of condensation and siloxane bond cleavage contributes to a dramatic change in kinetics of the polymerization with introduction of water into the reaction system. In particular, the polymerization when carried out without water addition shows three interconnected features: 1 Strong acceleration of the rate with addition of small amounts of water to the system. 2 An apparent negative value of the activation energy. 3 Increase of the rate with decreasing initial concentration of the monomer. Above a certain level of water content the polymerization rate is only slightly dependent on the concentration of water. The energy of activation is 50 kJ/mol and the reaction is of 1st order in monomer, internally as well as externally.     

Particle growth in butadiene emulsion polymerization, 3. Radical adsorption and desorption rate coefficients

The kinetis of the emulsion polymerization of butadiene at 60°C in Smith-Ewart interval III were investigated using peroxodisulfate as initiator. The aim of this work was to obtain insight in the radical adsorption and desorption rate coefficients through monitoring non-steady state kinetics. The acquired data shows an initiator concentration dependence of the desorption rate coefficients. This dependence explains the independences of the rate of butadiene emulsion polymerization of the peroxodisulfate concentration in the presence of tertiary dodecylthiols.     

Use of controlled radical polymerization of butadiene with AIBN and TEMPO for the determination of the NMR characteristics of hydroxymethyl groups

The controlled radical polymerization of butadiene initiated with 2,2′-azoisobutyronitrile (AIBN) and in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) is presented. The produced oligomers which have number average degrees of polymerization ranging between 3 and 12 were characterized by NMR. This led to the determination of both the end-groups and the functionality. The hydrolysis of these oligomers yields α-hydroxy-ω-cyano-polybutadiene. ¹³C and ¹H NMR spectra of these products exhibit two characteristic signals of hydroxymethyl groups. The mechanism of the polymerization allows the assignments to cis- and trans-CH₂CH=CH—CH₂OH groups. In fact, this method also shows that geraniol end-groups are negligible in commercially available products obtained by the polymerization initiated with hydrogen peroxide.     

Alternating copolymerization of acrylonitrile with butadiene in the presence of binary and ternary catalytic systems of Lewis acids type

Acrylonitrile (AN) and butadiene (BD) were copolymerized in the presence of binary C₂H₅AlCl₂? MtX_n (MtX_n = metal halide or metal alkoxide) and ternary ZnCl₂? R_mMtX_n? VOCl₃ (R_mMtX_n = metal alkyl or alkylmetal chloride) catalytic systems. The yield of the copolymer (mole ratio of units AN/BD = 1:1) formed in the presence of the above systems, and the effects of the molar proportion of catalyst components, of the reaction temperature and time on the copolymer yield in some systems were determined. The role of individual components of binary and ternary catalytic systems in the copolymerization is discussed.     

Emulsion polymerization of butadiene, 3. Kinetic effects of stirring conditions and monomer/water ratio

The stirring speed n influences the emulsion polymerization of butadiene, (1) by reducing the effective emulsifier concentration [E]_eff available for particle nucleation and stabilization at high n, and (2) by limiting diffusion of monomer to the latex particles at low n. The large density difference between butadiene and water promotes the breaking up of droplets at high n, while the same condition constitutes a large driving force for (partial) phase separation at low n. Increasing the monomer/water ratio at constant [E] decreases [E]_eff, and thus the final particle number. At monomer volume fractions >0,6 mixed emulsions are likely to be formed initially, reducing [E]_eff even further. In the presence of mixed emulsions, polymerization in the monomer phase may no longer be neglected, giving rise to a complex kinetic behaviour.