Kinetics of inhibited or retarded polymerization. Investigations on the cerium(IV)/toluene/acrylonitrile system

The kinetics and mechanism of the inhibiting action of toluene on the Ce(IV) initiated polymerization of acrylonitrile were studied together with the effects of [M], [Ce(IV)], [Toluene], [HClO₄], [NaClO₄], and [Acetic acid] on the rate of polymerization. The values of composite rate constant kk_t/k_pk_ok_i for toluene (and substituted toluenes) was calculated by plotting [M]/R_p versus [M]^?1. A very significant observation in the present study was that the plot of [M]/R_p versus [M]^?1 gave a negative intercept, which seems to be a general observation for all inhibiting substrates. On the basis of the experimental data, it could be concluded that the benzyl radical obtained by hydrogen abstraction, and not a chain transfer, is responsible for the inhibition.     

Studies on aqueous polymerization of acrylamide. Potassium persulfate/2-mercaptoethylamine hydrochloride redox system

The kinetics of aqueous polymerization of acrylamide, initiated by the potassium persulfate(K₂S₂O₈)/2-mercaptoethylamine hydrochloride (MEAH) redox pair was studied under nitrogen atmosphere at 30 ± 0,1 °C. The initial rates of polymerization were found to be proportional to [K₂S₂O₈]^1,5 (in the range of 0,8 to 1,2 mmol^?1), to [acrylamide]¹ (in the range of 0,8.10^?1 to 1,2.10^?1 mol 1^?1), and to [MEAH]¹ (in the range of 1,0 to 7,0mmol 1^?1), respectively. The overall energy of activation was found to be 9,8 kcal mol^?1 (40kJ mol^?1). Water miscible alcohols and common salts (NaF, NaCl, (CH₃)₄NI) appeared to depress both the polymerization rate and the maximum conversion. With MnSO₄.4H₂O the reverse influence was found.     

Studies on aqueous polymerization of acrylamide, 2. Potassium persulfate/2-mercaptoethanol redox system

The polymerization of acrylamide in aqueous media initiated by the potassium persulfate/2-mercaptoethanol redox pair was studied at 30°C under nitrogen atmosphere. The initial rate of polymerization was found to be proportional to nearly the 1,5th power of the potassium persulfate concentration within the range of 0,6 to 2,0 mmol l^?1 and to the first power of acrylamide concentration in the range of 0,1 to 0,14 mol l^?1. The rate was also found to be proportional to the first power of the 2-mercaptoethanol concentration within the range 4,0 to 8,0 mmol l^?1. The overall activation energy was found to be 134 kJ mol^?1. Further the effect of salts (NaCl, KCl, NH₄Cl, Na₂C₂O₄, K₂C₂O₄·H₂O, (NH₄)₂C₂O₄,MnSO₄·4H₂O, and NaF) and aliphatic alcohols (methanol, ethanol, and propanol) was tested.     

Studies on aqueous polymerization of acrylamide, 4. Potassium persulfate/thioglycolic acid redox system

Aqueous polymerization of acrylamide, initiated by the potassium persulfate-thioglycolic acid redox pair, was studied at 30°C under introgen. The initial rate of polymerization R was found to be approximately proportional to the 0,5th power of potassium persulfate concentration within the range of 0,6 to 1,0 mmol^?1. R was also found to vary linearly with the monomer concentration between 0,8 · 10^?1 and 1,0·10^?1 mol l^?1 and to increase with the thioglycolic acid concentration in the interval of 3,0 to 4,0 mmol l^?1. The activation energy was estimated to be 126 kJ mol^?1. Addition ot NaCl, NaF, and (CH₃)₄NI lowered the initial rate R while MnSO₄ increased it. Some aliphatic alcohols were observed to be polymerization retarders.     

Studies on the aqueous polymerization of acrylamide by the acidified potassium permanganate-thioglycolic acid redox system

The polymerization of acrylamide in aqueous media, initiated by the acidified potassium permanganate/thioglycolic acid ( 1 ) redox pair was studied at 30±0,1°C in an inert atmosphere of dry and oxygen-free nitrogen. The initial rate of polymerization was found to be proportional to nearly the first power of potassium permanganate concentration within the range of 2,0.10^?3 to 6,0.10^?3 moll^?1. The rate was also found to be proportional to the first power of [acrylamide] in the range of 8,0.10^?2 to 10,0.10^?2 moll^?1. The rate of polymerization appears to be independent of thioglycolic acid ( 1 ) concentration in the range of 1,0.10^?2 to 1,2.10^?2moll^?1. At still higher concentrations, however, the amount of 1 depresses the rate and maximum conversion. An excess of sulphuric acid was found to affect the rate of polymerization to a slight extent and a deficiency of the acid makes the reaction to stop at an early stage, during the range studied. This indicates, therefore, the presence of an optimum concentration of H₂SO₄ for the smooth initiation of polymerization. A study on the effect of salts reveals that KCl and NH₄Cl lower the initial rate of polymerization, whereas the reverse is true for MnSO₄.H₂O and Na₂C₂O₄. The water-miscible aliphatic alcohols e.g. CH₃OH, C₂H₅OH, (CH₃)₂CHOH, and C₄H₉OH were found to depress the extent of polymerization.     

The polymerization of acrylonitrile by tetraaziridotitanium(IV)

The polymerization of acrylonitrile by tetraaziridotitanium(IV) is very much more rapid than the same reaction initiated by tetrakis(dimethylamino)titanium(IV). The former reaction has dead-end kinetics but both can be fitted with the same kinetic scheme. Polymerization is accompanied by initiator wastage via unidentified reactions. Insertion of saturated nitriles into the Ti? N bonds of tetrakis(dimethylamino)titanium can be monitored by NMR and gives products with high activity for the polymerization of acrylonitrile. Despite their high reactivity towards acrylonitrile none of the initiators will polymerize less reactive monomers.     

Mechanism of the polymerization of acrylamide initiated by the glycerol/Ce(IV) redox system

The mechanism of the polymerization of acrylamide in aqueous medium initiated by the glycerol (R)/Ce(IV) redox system was studied. The rate of monomer disappearance was found to be directly proportional to [M]^3/2, and R^1/2 at lower concentrations of Ce(IV). The rate of the disappearance of ceric ions was found to be inversely proportional to [M] and directly proportional to [Ce(IV)] and [R]. Consistent with the findings of earlier investigations, a complex formation between monomer, acrylamide, and ceric ion is indicated. The experimental results show the termination to be mutual. On the basis of these and other kinetic results, an appropriate mechanism is proposed. At higher concentration of Ce(IV), a different mechanism seems to operate. The rates of disappearance of both the monomer and ceric ions are retarded on addition of anions like HSO₄^?, SO₄^{? ?}, or CIO₄^?, but they are accelerated on the addition of Mn(II) ions. Interpretations of the above observations are furnished.     

Redox polymerization, 3. Kinetics of acrylonitrile polymerization initiated by the redox systems cyanoacetic acid/Mn(III) and 2-butanone/Mn(III) in aqueous sulfuric acid

The kinetics of Polymerization of acrylonitrile initiated by the redox systems cyanoacetic acid/Mn(III) and 2-butanone/Mn(III) were investigated in the temperature range of 30 – 50°C in aqueous sulfuric acid. The kinetics are consistent with the formation of a 1 : 1 complex between the reducing agent and Mn(III), its unimolecular decomposition yielding the initiating radical. Extensive oxidation of the primary radical with exclusively mutual termination of growing radicals accounts for the kinetics of the polymerization. Rate and equilibrium constants as well as thermodynamic parameters were evaluated and their significance is discussed.     

Kinetics of the aqueous polymerization of acrylamide initiated by the permanganate- tartaric acid redox system

The kinetics of the aqueous polymerization of acrylamide, initiated by the permanganate/tartaric acid redox system was studied at 35±0,2°C under nitrogen. The initial rate of polymerization remains independent of the tartaric acid concentration in the range 3,3.10^—3 to 9,9.10^—3mol/dm³. The order of the reaction with respect to the catalyst concentration (catalyst exponent) is found to be 0,55, indicating a bimolecular mechanism for the termination reaction. The rate of polymerization varies linearly at low monomer concentrations (1,25.10^—2 to 5,0.10^—2mol/dm³). With increase in temperature above 35°C, the initial rate increases but the conversion decreases. The overall energy of activation is found to be 18,68 kcal/mol (78,10kJ/mol) in the temperature range 30 to 50°C. Water miscible organic solvents and neutral salts depress both the rate and the conversion. Addition of MnSO₄ or the injection of more catalyst at intermediate stages raises both the initial rate and the maximum conversion. NaF decreases the rate but increases the conversion.     

Vinyl polymerisation of acrylonitrile by the vanadium(V)-glycerol redox system

A kinetic study of the thermal polymerisation of acrylonitrile initiated by the redox system V⁵⁺ -glycerol in sulfuric acid and perchloric acid was made in the temperature range 35–45°C. The rates of polymerisation and V⁵⁺ disappearance wee measured with respect to their dependence on time, monomer, metal ion, glycerol, acid, and ionic strength. Experimental evidences provide support to a mechanism involving initiation by a free radical produced by the decomposition of the acyclic complex between V⁵⁺ and glycerol. The kinetics are consistent with a linear termination of polymerisation (1st order in respect of growing radicals) at higher concentration of V⁵⁺. The various rate and activation parameters were evaluated and an appropriate reaction scheme is proposed. The induction period and the polymerisation rate of the V⁵⁺ -glycerol system were compared with those involving polyhydroxy alcohol systems such as sorbitol and mannitol.     

Effect of some additions on the aqueous polymerization of acrylamide,initiated by permanganate-oxalic acid redox system

The effect of different additives on the aqueous polymerization of acrylamide, initiated by MnO-oxalic acid redox pair, was studied at 25°C in an atmosphere of nitrogen. It was observed that the rate of polymerization increased in the presence of alkali metal (Li⁺ to Rb⁺) chlorides. Cupric chloride and ferric chloride were found to be polymerization retarders. Anionic and cationic detergents showed marked influence on the rate of polymerization. Also, the presence of water-soluble alcohols lowered the polymerization rates to a sufficient extent.     

Kinetic evidence for the mechanistic difference in the aqueous polymerization of acrylonitrile

Kinetic evidence indicated two different mechanistic pathways in the polymerization of acrylonitrile initiated by peroxodiphosphate-vanadyl ion redox system in aqueous solution depending upon the concentration of the reducing metal ion employed. The mechanistic difference lies in the termination reaction, exclusively mutual termination occurring in the concentration range [VO²⁺]=2,5·10^?3 to 5·10^?3 mol·dm^?3 and exclusively linear termination taking place in the concentration range [VO²⁺] =10^?2 to 25·10^?3 mol·dm^?3.     

Acrylamide polymerization initiated with the redox system Ce(IV)-cyclohexanone in micellar phase: A kinetic study

The effect of an organized anionic surfactant, i.e. sodium dodecyl sulfate (SDS), on the acrylamide (AM) polymerization initiated with the redox system Ce(IV)-cyclohexanone (CH) in aqueous nitric acid was kinetically studied over a temperature range of 25–45°C. With increasing concentration of SDS, above its critical micelle concentration (CMC) the rate of polymerization, R_p(obs), as well as the rate of Ce(IV) consumption, −R_Ce(obs), were found to increase, while in the presence of cetyltrimethylammonium bromide (CTAB) these rates decreased considerably. R_p(obs) is proportional to [Ce(IV)]^0.5, [CH]^0.5 and [AM]^1.5. −R_Ce(obs) also increases with increasing concentration of Ce(IV), cyclohexanone and acrylamide. The overall activation energy for the process, in the presence and absence of 15 × 10⁻³ M of SDS, was calculated to be 15.1 and 21.4 kcal/mol, respectively. The viscosity average molecular weight of polyacrylamide was found to increase with increasing SDS concentration. A suitable mechanistic scheme for the polymerization process is proposed.     

Studies on the mechanism of redox polymerization initiated by N-haloamines and iron(II)

The mechanism of the redox polymerization of methyl methacrylate in aqueous medium in the dark was studied for the redox initiator systems N-halodiethylamine + Fe(II) and triethylamine + halogen + Fe(II), by analysis of the polymer end groups using the dye partition method. In the case of chlorine, both these initiator systems incorporate only the amino group into the polymer to an extent of about one group per polymer molecule. The polymers are found to be free from chlorine. Furthermore, a large portion of the total amino groups introduced into the polymer, using the initiator system triethylamine + halogen + Fe(II) are quaternary in nature. In the case of bromine, both the initiator systems introduce only a bromine atom and no amino group into the polymer. The initiator systems containing chlorine prove to be useful for the preparation of polymers containing amino groups at the one end only.     

Aqueous polymerisation of acrylonitrile initiated by the V(V)-ethylene glycol redox system

The kinetics of acrylonitrile polymerisation initiated by the redox system V(V)-ethylene glycol were investigated in aqueous sulfuric acid in the temperature range 40–50°C. The rate of polymerisation, of V(V) disappearance, and the chain lengths of polyacrylonitrile were measured. The effect of certain water miscible organic solvents and certain neutral salts on the rate of polymerisation was investigated. The kinetics are consistent with the formation of an intermediate complex between the diol and the oxidant whose decomposition leads to the initiating radical. A suitable kinetic scheme is proposed and the various rate and energy parameters are computed.     

Studies on organometallic compounds as polymerization catalysts. IV. Polymerization of propylene oxide catalyzed by zinc chloride-alkali metal alkoxide system

Binary system of zinc chloride-alkali metal alkoxide was studied as catalyst for propylene oxide polymerization. The reaction of zinc chloride with alkali metal alkoxide was found to proceed steppwise according to the equations: Formation of high molecular weight polymer in the propylene oxide polymerization catalyzed by zinc chloride-alkali metal alkoxide system is found to be caused by zinc dialkoxide formed in the reaction system. The results support our previous conclusion that the presence of alkyl-zinc bond in zinc alkyl-alcohol system is not necessarily an indispensable factor for high molecular weight polymer-forming reaction.     

Polymerization of acrylonitrile initiated by the redox system manganese (III) acetate/ethylene glycol

The kinetics of polymerization of acrylonitrile initiated by the redox system manganese (III) acetate/ethylene glycol was studied in aqueous sulfuric acid medium in the temperature range from 30 to 40°C. The effect of varying the concentrations of monomer (M), acetic acid, and sulfuric acid and the addition of some electrolytes on the rate of polymerization (R_p) was investigated. Based on the experimental observations of the dependence of (R_p) on various parameters, a suitable kinetic scheme could be proposed. The plot of R_p²[M]² vs. [M] was found to be linear, a striking general phenomenon observed for all the substrates we have studied in this laboratory.     

Studies on organometallic compounds as polymerization catalysts. II. Diethylzinc/water system for epoxide polymerization

Diethylzinc/water system was studied using infrared spectroscopy, X-ray diffraction, and vapor phase chromatography. The main reactions of diethylzinc with water are considered to be as follows: Relative LEWIS acidity for ether is found to be in the order: Initiators for the polymerization of propylene oxide by diethylzinc/water system are found to be Et(ZnO)_nZnEt, Et(ZnO)_nH, or HO(ZnO)_nH, which have disordered wurtzite structures concerning zinc-oxygen bond. On the hydrolysis of the polymerization system, 2-methyl-l-butanol, 2-pentanol, and propylene glycol are found as initial products. The main reaction of the polymerization of propylene oxide catalyzed by diethylzinc/water system was discussed in terms of the coordinate ionic mechanism.     

Effect of oxygen on acrylonitrile polymerization in water solutions

The kinetics of polymerization of acrylonitrile initiated by iron(III) salts and hydrogen peroxide in water solution in an atmosphere of nitrogen containing varying amounts of oxygen was investigated at 26.0 ± 0.1°C. Increased amounts of oxygen decrease the rate of polymerization as well as the average molecular weight of the formed polymer. The rate of polymerization falls to zero with the increasing content of oxygen. There is, however, no difference in the rate of polymerization or the molecular weight of the formed polymer if the oxygen content of the nitrogen was decreased by careful deoxygenation from 13.5 ppm to less than 1 ppm. The length of the induction period is in agreement with the inhibition scheme as proposed by SCHULZ and HENRICI.