The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

The kinetics of the anionic polymerization of methyl methacrylate in presence of N,N,N ′,N ′‐tetramethylethylenediamine (TMEDA) in THF are investigated using 1,1‐diphenyl‐hexyllithium as initiator in a temperature range between –20°C and 0°C in a flow‐tube reactor. The rate constants of propagation determined in the presence of TMEDA are compared to those obtained in the absence of a chelating agent. For propagation, the reaction order with respect to active centers is found to be 0.5 in both cases which indicates that the chelation of the lithium cation does not effectively perturb the aggregation of the enolate ion pair. Both the rate constants of propagation via non‐aggregated ion pairs, k_±, and the equilibrium constants of aggregation, K_A, are not significantly affected by TMEDA. The rate constants of termination in absence and presence of TMEDA are also comparable. Thus, it is concluded that TMEDA is not a better ligand for lithium ester enolates than THF. Even the addition of a cyclic tertiary polyamine (“crown amine”) such as 1,4,8,11‐tetramethyltetraazacyclotetradecane, does not lead to a significant change in the propagation rate constant, however, no termination is observed at –20°C. Extrapolation of the observed rate constants at two temperatures gives estimates for the equilibrium constants of aggregation, K_A, and the corresponding enthalpy and entropy. It is shown, that aggregation of PMMA‐Li in THF is an endothermic, entropy‐driven process (ΔH_A; ΔS_A > 0), similar to the dimer‐tetramer equilibrium of model ester enolates.     

Synthesis of a cationic polyelectrolyte by successive quaternization of 1,4-bis(2-diethylaminoethyl)benzene

1,4-Bis(2-diethylaminoethyl)benzene ( 4 ), synthesized from 1,4-divinylbenzene ( 1 ) and diethylamine ( 2 ) with lithium diethylamide as catalyst, was successively quaternized with 1,4-dibromobutane ( 5 ) to prepare a cationic polyelectrolyte 6 of the ionene type. Apparent molecular weights of the ionene samples were estimated by the sedimentation equilibrium method, and the result is discussed in connection with the true molecular weight. The rate constants for quaternization of first and second nitrogen atom of 4 (k₁ and k₂) were determined by the use of ¹³C NMR. It was found that the ratio of the rate constants, (k₂/(k₁/2)), markedly decreased in the 4/5 system, though it remained unity in the 4 ethyl bromide system.     

Ammonium salt catalyzed copolymerization of 2-hydroxy-4-(2,3-epoxypropoxy)benzophenone with phthalic anhydride

Ammonium salt catalyzed copolymerization of 2-hydroxy-4-(2,3-epoxypropoxy)benzophenone with phthalic anhydride was studied. The conversion curves could be linearized by the first order equation and the experimental rate constants k_exp for the initiation by various ammonium salts were determined. The rate of copolymerization was found to depend on the size of the cation but not on the type of anion. k_exp is a function of the first power initiator concentration but is independent of epoxide and anhydride concentration. The activation energy for the cetyltrimethylammonium bromide (CAB) initiated copolymerization in nitrobenzene was determined to be 73,5 kJ/mol. The kinetic scheme of copolymerization, which agrees well with the experimental results, was solved. The rate constant of the copolymerization of 2-hydroxy-4-(2,3-epoxypropoxy)benzophenone with phthalic anhydride catalyzed by CAB in nitrobenzene was found to be 2,76·10^?2l.mol^?1·s^?1. The ratio of rate constants for both propagation steps, i.e. reaction of carboxylate anion with epoxide (k₃) and reaction of alkoxide anion with anhydride (k₂), was determined to be k₃/k₂ = 0,2 ± 0,1.     

Untersuchungen zur kationischen polymerisation von oxepan

The ring-opening cationic polymerization of oxepane ( 3 ) was examined in bulk and in solution (1,2-dichloroethane). The initiators used were diethoxycarbenium hexachloroantimonate ( 2 ) and ethylhexamethyleneoxonium hexachloroantimonate ( 4 ). The preparation of 4 is described for the first time. Kinetic experiments showed that the polymerization of 3 is of S_N2-type (analogous to tetrahydrofuran). The propagation rate constants k_p were found to be 1,38·10^?4dm³mol^?1s^?1 at 10°C and 4,38·10^?4dm³mol^?1s^?1 at 20°C. The equilibrium monomer concentrations determined at 0 and 20°C were found to be 0,052 and 0,071 mol dm^?3. Because of the occurence of termination reactions, these equilibrium monomer concentrations, however, were not achieved in all cases. As a possibility for a termination reaction a hydride-abstraction from the monomer is discussed in detail.     

A kinetic study of the emulsion copolymerization of N,N′-methylenebis(acrylamide) and an unsaturated polyester

The emulsion copolymerization of N,N′-methylenebis(acrylamide) (MBA) and an unsaturated polyester (UP) initiated by potassium peroxodisulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization, the size of latex particles and the number of polymer particles were determined as a function of MBA concentration. The rate of MBA polymerization was found to be proportional to the 0,8th (at 0–15% conversion) and 0,9th (at 20–40% conversion) order with respect to [MBA] at 0,0231 mol · dm^?3 of UP. The values of the reaction order on the monomer concentration are discussed in terms of homogeneous and emulsion polymerization and crosslinking effects. The rate of UP polymerization in the emulsion copolymerization of MBA and UP does not depend on the total monomer concentration. The specific rate of MBA (or UP) polymerization increases with increasing monomer concentration and reaches a maximum at a certain concentration of monomer. The size of polymer particles decreases and the number of particles increases with increasing UP fraction. The stability of polymer particles increases with increasing UP fraction in the monomer feed. The ratio (k_p/k_t^0,5)₀ of the relative rate constants for propagation k_p and termination k_t calculated for the MBA or UP polymerizations at zero conversion increases with increasing MBA concentration. The growth of the polymer particles proceeds via polymerization in particles and by interparticle crosslinking reactions.     

Kinetics and stereocontrol of phenylalanine N-carboxyanhydride polymerizations

L -, D -, and various D ,L -phenylalanine N-carboxyanhydrides (NCA's) were polymerized with benzylamine and various concentrations of N-methylbenzylamine, respectively, in N,N-diethylformamide at 25°C. Three kinetic stages were observed for all systems: a fast “initiation” stage (I) followed by a slower stage (II) and a faster pseudo-first order propagation stage (III). The initiation rate is higher for N-methylbenzylamine than for benzylamine. The propagation rate constants, k_p^L, of the stage II polymerization of the L-monomer are independent of initiator type and concentration, whereas the corresponding stage III rate constants vary with the initial monomer/initiator ratio. For each propagation stage, the ratios of rate constants, k_p^D,L/k_p^L and k_p^D,L/k_p^D, respectively follow the pattern predicted by the absence of crossover reactions. Molar masses calculated from monomer conversion are higher than those determined from amine end group concentration for N-methylbenzylamine initiated polymerizations, but lower for benzylamine initiated ones.     

Branching in high molecular weight polyhydroxyethers based on bisphenol A

The polyaddition reaction of bisphenol A with the diglycidyl ether of bisphenol A is treated statistically on the basis of cascade theory to describe the branching process. The chain lengthening step is based on the reaction of the epoxide functional group with the phenolic hydroxyl group and leads to the formation of a 1,3-diphenoxy-2-propanol link. The peculiar feature of this polyaddition reaction is the possibility of further addition of an epoxide to a secondary hydroxyl group to form branched molecules. This branching reaction does not, however, lead to a loss of hydroxyl groups since a new secondary hydroxyl group is created when an epoxide functional group reacts with a secondary hydroxyl group. Closed analytic expressions are derived for the weight-average (M_w) and number-average (M_n) molecular weights in terms of the mole ratio R = m_b/m_a and the extents of reaction of the functional groups α(phenolic hydroxyl), β(epoxide), and p(branching), i.e. the probability p that an epoxide group has reacted with a secondary hydroxyl group, where m_b and m_a are the mole fractions of the diglycidyl ether of bisphenol A and of bisphenol A, respectively. Consideration of a simple kinetic mechanism shows that α,β and ρ are related to the ratio b = k₂/k₁, where k₁ and k₂ are the rate constants of the chain lengthening step and the chain branching step, respectively. The equations derived for M_w and M_n as a function of a α allow the determination of the branching probability p (or the kinetic rate constant ratio b). An equation for the gel point (M_w → ∞) is given which states a relationship between α_c and p_c where the subcript c refers to the critical point of gelation. Thus location of the gel point and measurement of α_c, either directly or by extrapolation on samples taken prior to gelation, enables p to be measured.     

Novel Fluorinated Hybrid Polymer by Radical Polyaddition of Bis(α‐trifluoromethyl‐β,β‐difluorovinyl) Terephthalate onto Dialkoxydialkylsilanes

To develop the radical polyaddition of bisperfluoroisopropenyl esters, the reactions of bis(α‐trifluoromethyl‐β,β‐difluorovinyl) terephthalate [CF₂?C(CF₃)OCOC₆H₄COOC(CF₃)?CF₂] (BFP) with dialkoxydialkylsilane were examined to prepare fluorinated hybrid polymers bearing dialkylsilyl groups in the main chain. Prior to polyaddition, the radical addition reaction of 2‐benzoyloxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅] (BPFP) has been investigated to afford the results that diethoxydimethylsilane (DEOMS) or dimethoxydimethylsilane with BPFP initiated by oxo radical are the best combination for the preparation of polymers. The mechanism of the addition reaction was proposed. Radical polyaddition of BFP with DEOMS initiated by benzoyl peroxide or di‐tert‐butyl peroxide has yielded polymers of up to molecular weight 1 × 10⁶ with rather broad molecular weight distribution. A mechanism for the polyaddition reaction is proposed based on the radical addition reaction between BPFP and DEOMS. The step‐growth polymerization is initiated by hydrogen abstraction of DEOMS to add a perfluoroisopropenyl group, followed by a 1,7‐shift of the radical in the intermediate. The relationship between addition reaction mechanism and polyaddition mechanism was also discussed.

     

Catalytic hydrolysis of activated aromatic esters by branched polyamines

Two polymeric amines, poly[(2-aminopropyl)propyleneimine] ( P _I ) and poly[(2-aminoethyl)-ethyleneimine] ( P _II ), as well as the dodecyl- and imidazolylmethyl-substituted derivative of P _I , were used for the hydrolysis of p-nitrophenyl acetate (PNPA), 4-acetoxy-3-nitrobenzoic acid (ANBA) and some of their homologues, in order to elucidate the relations between their overall structure and their catalytic activities. All reactions were carried out at 28,7°C in aqueous solution, and followed spectrometrically using a catalyst concentration in large excess with respect to the substrate concentration (10^?4 mol · L^?1). The reactions were found to obey pseudo-first order kinetics. By plotting log[substrate] against time, k₂(cat) and consequently the second-order rate constants k₂ were evaluated. The above mentioned polymers show hydrolysis constants which exceed the values obtained for tailor-made partially substituted polyethyleneimines. Even when linear polythyleneimine was substituted for 42% with 2-(2-aminopropylamino)propyl groups, P _I and P _II give k₂ values which are 8 times higher towards PNPA, and 10 times higher towards ANBA, under the same reaction conditions.     

Polymérisation anionique de l'acroléine, 2. Influence de la nature du contre-ion et de la température sur la cinétique de la réaction

In tetrahydrofuran, with Na⁺ and Li⁺ as counter-ions, the kinetic order of the anionic polymerization of acrolein is unity for monomer and for initiator. These results indicate that the living ends are not associated at the studied concentrations of initiator. The polymerization rate depends on the nature of the counter-ion. Transfer reactions to monomer do not affect the polymerization rate but greatly change the molecular weights M _n of polyacroleins. The experimental M are much lower than the theoretical M . The propagation constants k_pr and the transfer constant h_m are determined using these experimental values of M . From these results, we can conclude that with Li⁺ as counter ion, transfer reactions are much more numerous than with Na⁺. Furthermore, the polymerization rate increases with temperature. The activation energies of the propagation (E_a,pr) and transfer reactions (E_a,t) can be determined separately. When the temperature increases the propagation reaction is promoted in comparison to the transfer reaction to monomer, and simultaneously transfer reactions to polymer take place. This last phenomenon restricts the upper value of the polymerization temperature.     

Aqueous polymerization of vinyl monomers in the presence of surfactants, 1. Acrylamide

The kinetics of the polymerization of acrylamide initiated by potassium peroxodisulfate in water were studied in the presence of the anion-active emulsifier sodium dodecylphenoxybenzenedisulfonate. The emulsifier was found to affect the relative molecular mass of polyacrylamide, but it showed no effect on the rate of polymerization. The transfer constants to the emulsifier and the initiator were determined and amounted to of 3,6 · 10^?3 and 5 · 10^?3. The ratio of rate constants of termination and propagation k_t / k_p² = 6,9 · 10^?2 mol · dm^?3 · s, determined for the polymerization of acrylamide in the presence of the emulsifier, is almost identical with the value for the polymerization without emulsifier. Thus, propagation and termination reactions of the potassium peroxodisulfate initiated polymerization of acrylamide in water are not influenced by the emulsifier.     

Online Monitoring of Chain Transfer in Free‐Radical Polymerization

A recently introduced, automated method for online monitoring of polymerization reactions was used to study free‐radical transfer reactions. The persulfate initiated polymerization of acrylamide (AAm) in water was chosen as the test system. Chain transfer properties of ethanol (EtOH) and propanol (PrOH) were investigated. Different methods of computing the transfer constant are compared, including those based on the slope and intercept behavior of the monitored cumulative weight‐average molecular mass as a function of conversion, M̄_w (f), the reduced viscosity, and corresponding size exclusion chromatography analysis of the reaction end products. To a close approximation, the chain transfer agents were found to obey the form expected when ideal free‐radical polymerization takes place and radical transfer from propagating radicals to the chain transfer agent (CTA) is slower than from the CTA to monomer, that is, the polymer molar mass decreases with increasing chain transfer agent, but there is no appreciable effect on the kinetics of monomer conversion. The AAm kinetics were characterized in terms of the ratio k_p² /k_t, where k_p and k_t are the propagation and termination rate constants, respectively.     

Cationic polymerization of cyclic sulphides. I. Kinetic study of the polymerization of 3.3-dimethylthietane initiated by triethyloxonium tetrafluoroborate

The kinetics of the cationic polymerization of 3,3-dimethylthietane with triethyloxonium tetrafluoroborate in methylene chloride at 20°C have been studied. The polymerization is characterized by a very fast initiation reaction. The propagation occurs most probably via cyclic sulphonium ions. The existence of a termination by reaction of the growing chains with sulphur atoms of the polymer chain was demonstrated by kinetic and molecular weight measurements. The propagation constants k_p and termination constants k_t at different temperatures were calculated. The enthalpies of activation for the propagation and termination reactions are, respectively, ΔH^≠_p = 12.5 kcal mole^?1, ΔH^≠_t = 7.4 kcal mole^?1, and the corresponding entropies of activation are ΔS^≠_p = -26 cal deg^?1 mole^?1, ΔS^≠_t = -49 cal deg^?1 mole^?1.     

The Stability of Free Radicals in Densely Crosslinked Acrylate Polymer Networks

The four types of crosslinked polymer samples based on pentaerythritol tetraacrylate (PETA) and propylene glycol‐425‐diacetoacetate (PGDAA) were prepared in two steps. At first the Michael dark addition of vinyl groups of PETA to PGDAA results in polymer network (cf. Scheme 1). The higher conversion of residual vinyl monomer and pendant double bonds built up in the Michael network was achieved by a photo‐initiated free radical polymerization in the second step of polymer network synthesis. The lifetime of trapped radicals was estimated by following the decay of radicals in the dark period of intermittent illumination directly in the resonator cavity of ESR spectrometer. The determined values of bimolecular termination rate constants k_t are of order 10^–1 to 10² kg/mol·s in dependence on composition, structure of network, and environment. It was observed that oxygen facilitates the decay of free radicals. The k_t values are of about 1 to 2 decimal orders higher than that determined in nitrogen. Moreover, as in each subsequent light–dark cycle the k_t was increased, we believe that it is a consequence of enhancement the diffusion of free radicals by assisted oxygen chain reaction with formation of hydroperoxides. The exception is the sample B with the highest final crosslinks density and conversion of monomers to network. More tightly trapped free radicals were present in polymer networks photo‐cured in nitrogen. The k_t values in all four types of networks decreased in each consecutive light–dark cycle.     

Computer simulation of the steady state in reversible polymer-analogous reactions, 3. Flows and statistics in detailed balance

The steady state of reversible polymer-analogous reactions was simulated by Monte Carlo calculations. The length of the simulated copolymer chains was chosen large enough to yield data with an acceptable degree of statistical fluctuation. Two types of sets of relative rate constants K were investigated, first K₁ = K₂ = K₃, and second K₁ ≠ K₂, K₁ ≠ K₃, K₂ ≠ K₃, with K₁ · K₃ = K²₂. The relative rate constants K are defined as K₁ = k(AAA)/k(ABA), K₂ = k(AAB⁺)/k(ABB⁺), and K₃ = k(BAB)/k(BBB), where k is the ordinary rate constant pertaining to the reaction of the central monomeric unit in the triad given in parentheses, with two different types of monomeric units A and B in the binary copolymer. For both types of sets of relative rate constants the simulation showed a detailed balance to prevail for the kinetics in the steady state. It was also shown that the same kinetics and statistics were obtained in the steady state when starting the simulation first from a homopolymer consisting of A-monomeric units, and then from a homopolymer of B-monomeric units. Based on the finding of a detailed balance and on the definition of K, it could be shown by analysis that the first type of the sets of K leads to a Bernoullian statistics of the copolymers in the steady state, while the second type leads to a first-order Markov statistics. Correspondingly, equations are given which allow to calculate the relative rate constants from statistics and vice versa. The equations have also been confirmed by Monte Carlo simulation. In addition, the equations for the interrelations between the standard Gibbs free energies of the individual reactions for the central units in the triads are given.     

In vivo determination of transport and metabolism of deoxyglucose in intestinal tissues

Experiments were carried out on 11 anesthetized cats (Na-pentobarbital). Uptake of a glucose analogue (2-deoxy-d-glucose) by intestinal mucosa and muscularis from arterial plasma was studied in order to determine net rate of transport and phosphorylation of the material. The theoretical basis for calculating the rate constants of forward (k ₁ ^x ) and reverse (k ₂ ^x ) transport between plasma and tissue and also phosphorylation (k ₃ ^x ) and dephosphorylation (k ₄ ^x ) of¹⁴C labeled deoxy-glucose (DG) was determined. The method can also be used for estimating tissue glucose uptake. The rate constants were found to be:k ₁ ^x =0.669 and 0.873;k ₂ ^x =2.285 and 4.656;k ₃ ^x =0.057 and 0.067;k ₄ ^x =0.091 and 0.097 [s⁻¹] in the mucosa and muscularis, respectively. Glucose utilisation of intestinal mucosa was 2.69 and that of muscularis 2.46 mg/(min×100 g) tissue, respectively. Arterial glucose concentration was constant during the studies, however, it showed a variation from 120 to 250 mg/100 ml of plasma from animal to animal. Tissue glucose uptake or any of the rate constants were not influenced by the plasma level over this range.     

Kinetics of the polymer-analogous reaction of poly[(methyl methacrylate)-co-(methacrylic acid)] with epichlorohydrin

Poly[(methyl methacrylate)-co-(glycidyl methacrylate)] (poly(MMA-co-GMA)) was obtained by polymer-analogous reaction of poly[(methyl methacrylate)-co-(methacrylic acid)] with an excess of epichlorohydrin (ECH) in the presence of a quaternary ammonium salt R₄NX as catalyst. The kinetics of the addition reaction and the consecutive transepoxidation reaction was studied at 50–90°C. The rate constant of the addition reaction is one order of magnitude higher with E₁ = 71 kJ · mol^?1 than that of the transepoxidation reaction with E₂ = 83 kJ · mol^?1. The rate constants rise linearly with increasing concentration of the catalyst R₄NX. The equilibrium constants K ≈ 2,3 of transepoxidation of glycidyl methacrylate (GMA) as well as of poly(MMA-co-GMA) both with 1,3-dichloropropane-2-ol were determined in butyl acetate and dimethylformamide as solvent at 80–100°C. During the reverse transepoxidation reaction of 3-chloro-2-hydroxypropyl methacrylate (CHPM) as well as of its MMA-copolymer with equimolar amounts of ECH, side products were formed from the beginning of the reaction and the equilibrium was not established. The addition of ECH to CHPM was observed as a side reaction.     

Chain-coupling reaction of amine-terminated oligomers by bis(4-monosubstituted-5(4H)oxazolinones)

Bis(5(4H)oxazolinones) derived from naturally occurring α-amino acids were reacted with amine-terminated polyethers and polyamides in the bulk at 175–200°C. Model reactions were also carried out using primary alkylamines. The reactions were studied by means of SEC, and ¹H and ¹³C NMR, and the resulting polymers were characterized by DSC and TGA. The chain-coupling reaction is extremely fast and yields high molar mass copolymers containing peptide linkages in less than 5 min. The NMR spectra of model compounds and polymers were fully assigned, showing that the oxazolinone/amine polyaddition reaction proceeds in the expected way, without any noticeable side reaction. The polymers exhibit lower crystallinity, higher T_g and a melting temperature close to or lower than that of the starting oligomers.     

Synthesis and copolymerization of a polyamine macromer: Molecular design of a new functional graft copolymer

To develop a new method for molecular design of functional polymers, polyamine macromers 4, 10, and 16 were synthesized by lithium alkylamide catalyzed polyaddition reactions of N,N'-diethylethylenediamine (1), 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (7), and piperazine (12) to 1,4-divinylbenzene (2), respectively. Copolymerization of these macromers with styrene gave a new type of graft copolymers 6, 11, and 19, having polyamine grafts. Copolymerization data indicated that the length and number of graft chains could be controlled by adjusting the molecular weight of the macromer and its initial concentration in the copolymerization system. The crystallinity of 16, 19, and other macromers (17, 18) having piperazine units was discussed.     

Etude de la réaction de télomérisation d'un monomère tensioactif anionique

The synthesis of a new anionic polymerizable surfactant is described. It is obtained by reaction between methacryloyl chloride and 5-phenyl-1-pentanol. In a last step, the aromatic group is alkylated with succinic anhydride in order to obtain an ionic group. All products were characterized by ¹H nuclear magnetic resonance and the transfer constant C_T with C₈H₁₇C₂H₄SH and the ratio k_p²/k_t were determined. C_T is in agreement with that of classical acrylates whereas k_p²/k_t is lower because of the long methacryloyl chain which reduces the propagation rate.