Solvent effects on free-radical polymerization, 3. Solvent effect on polymerization rate of methyl methacrylate and N-vinyl-2-pyrrolidone

The homopolymerizations of methyl methacrylate (MMA) in N-methyl-2-pyrrolidone (NMP) and of N-vinyl-2-pyrrolidone (NVP) in methyl isobutyrate (MiB) were investigated at 60°C using AIBN as initiator. Reaction rate and dynamic viscosity of the medium were determined as function of monomer dilution. It follows from the estimated monomer exponent n that MMA reacts in NMP faster (n = 0,739) and NVP in MiB slower (n = 1,495) in comparison with reaction rates obtained from the direct proportionality of monomer concentration. The observed deviation was quantitatively separated in partial deviations caused by chain initiation, propagation and termination. It was found that the viscosity effect on chain termination plays a dominant role in the global solvent effect. Chain propagation is influenced by electron donor-acceptor interactions between monomers and solvent.     

Solvent effects on free-radical polymerization, 2. IR and NMR spectroscopic analysis of monomer mixtures of methyl methacrylate and N-vinyl-2-pyrrolidone in bulk and in model solvents

Binary systems of methyl methacrylate (MMA)/N-vinyl-2-pyrrolidone (NVP) and MMA/N-methyl-2-pyrrolidone (NMP) with NMP as saturated model of NVP and of NVP/methyl isobutyrate (MiB) with MiB as saturated model of MMA were investigated by means of IR and NMR spectroscopy. Investigations were carried out at room temperature or at 60°C in CHCl₃ (IR) or CDCl₃ and C₆H₁₂/C₆D₁₂ (NMR). It can be concluded from IR and NMR spectra that the polarity of MMA increases in the presence of NVP and the polarity of NVP decreases in the presence of MMA. Equilibrium constants K of complex formation were determined to: K = 0,169 ± 0,037 L · mol^?1 for MMA/NVP at 30°C, 0,112 ± 0,024 L · mol^?1 for NVP/MiB at 60°C and 0,125 ± 0,030 L · mol^?1 for MMA/NMP at 60°C.     

Bestimmung der geschwindigkeitskonstanten und der effektivitäten beim zerfall von 2,2′-azoisobutyronitril in styrol,N-vinyl-2-pyrrolidon und methylmethacrylat

The decomposition rate constants k_d of initiators can be determined by a new method directly in monomers as solvents. If a suitable inhibitor is added to a monomer mixture with the initiator the latter decomposes nearly without monomer conversion. The initiator concentration—after the inhibitor is consumed—can be found by means of the dilatometrically determined polymerization rate after the induction period. The functional connection between polymerization rate and initiator concentration found without inhibitor is used as a calibration curve for that purpose. The dilatometrical measurements were made in the monomers styrene and N-vinyl-2-pyrrolidone using 2,2′-azoisobutyronitrile (AIBN) as initiator and p-quinone as inhibitor. The following decomposition rate constants were found: k_d=1,52 · 10^?5 S^?1 (styrene) and k_d=1,62 · 10^?5 S^?1 (N-vinyl-2-pyrrolidone), which is in agreement with literature values. Initiator efficiencies f were calculated: f=0,46 (styrene), f=0,47 (N-vinyl-2-pyrrolidone). In methyl methacrylate (MMA) 2,2′-diphenyl-1-picrylhydrazyl (DPPH) was used as inhibitor. Under certain conditions the product k_df can be calculated from the consumption rate of DPPH. The value found in MMA (k_df=3,7 · 10^?6 s^?1) is lower than that reported in literature (6,45 · 10^?6 s^?1).     

Kinetik der startreaktion der radikalischen homo- und copolymerisation von styrol,N-vinyl-2-pyrrolidon und methylmethacrylat

In one, two and three component polymerizations of the monomer system styrene (St = M₁), N-vinyl-2-pyrrolidone (NVP = M₂) and methyl methacrylate (MMA = M₃) the rate constants of the initiation step 2k_df were measured in bulk at 60°C by means of the inhibition method with the stable Banfield radical as inhibitor and AIBN as initiator. The obtained 2k_df-values depend non-linearly on the monomer feed. It results from the evaluation of initiator decomposition constant k_d that the chain initiation step is mainly determined by the rate of initiator decomposition. In all polymerizations the efficiency factor f was almost equal to 0,5.     

Kinetische analyse der copolymerisationsgeschwindigkeit von N-vinyl-2-pyrrolidon mit styrol und methylmethacrylat

The polymerization rate of two binary monomer systems styrene (St)/N-vinyl-2-pyrrolidone (NVP) and NVP/methyl methacrylate (MMA) was investigated dilatometrically in bulk at 60°C with AIBN as initiator. While the copolymerization rate of the system St/NVP can be satisfactorily described by means of the classical reaction model, this is not the case for the system NVP/MMA. This deviation from the classical model can be explained by a charge-transfer interaction between NVP and MMA which was measured by means of ¹H and ¹³C NMR spectroscopy.     

Nitroxide‐Mediated Polymerization of Methyl Methacrylate Using an SG1‐Based Alkoxyamine: How the Penultimate Effect Could Lead to Uncontrolled and Unliving Polymerization

Summary: The nitroxide‐mediated polymerization (NMP) of MMA initiated with a new crowded SG1‐based alkoxyamine was performed. Contrary to the results expected after a kinetic analysis (Fischer's diagram), the polymerization of MMA at 45 °C with SG1 showed only partial control and livingness during the first 15% of conversion. Simulations using PREDICI highlighted that the kinetic rate constants currently in use had not been correctly estimated and that a strong penultimate effect drastically increased the equilibrium constant K (7 × 10⁻⁷), preventing a well‐controlled polymerization. Experimental determination of the k_c value (1.4 × 10⁴ L · mol⁻¹ · s⁻¹) confirmed a strong penultimate effect on the recombination reaction, whereas for the dissociation reaction this effect is lower (k_d = 10⁻² · s⁻¹).

Nitroxide‐mediated polymerization of MMA at 45 °C initiated with a new crowded SG1‐based alkoxyamine.     

Pressure Dependence of Iron‐Mediated Methyl Methacrylate ATRP in Different Solvent Environments

Iron‐mediated atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in N‐methylpyrrolidin‐2‐one (NMP) solution is investigated via online VIS/NIR spectroscopy up to 2500 bar. The activation–deactivation equilibrium constant, K_ATRP, decreases towards higher NMP content due to the formation of catalytically less active Fe^II/NMP species. The reaction volume increases from 1 to 15 cm³ mol^?1 in passing from 16 to 92 mol% NMP. The same effects are observed for monomer‐free model systems with poly(MMA)–Br as the initiator. Investigations into iron‐catalyzed ATRP of MMA in less polar solvents or even without an additional solvent (i.e., for bulk ATRP) yield K_ATRP values, which are by two to three orders of magnitude higher than in the presence of NMP.

     

The influence of charge-transfer complexes on the copolymerization behavior of cyclic maleic acid derivatives with donor monomers

The acceptor monomers maleic anhydride (MSA), itaconic anhydride (ISA), N-phenylmaleimide (NPI) and N-cyclohexylmaleimide (CMI) were combined with the donor monomers styrene (ST), butyl vinyl ether (BV) and N-vinyl-2-pyrrolidone (NVP) and studied by means of UV spectroscopy using CT bands. In this manner, the 1:1 stoichiometry of the CT complexes, the equilibrium constant in the range of 20°C to 60°C, and the thermodynamic equilibrium data were determined. Additionally, Monte-Carlo simulations of the donor-acceptor combinations in the presence of solvent molecules were run. The cohesion energies calculated from these simulations were used to quantify the donor-acceptor interactions and showed good agreement with the UV spectral data. The acceptor strength decreases in the order MSA > NPI > ISA > CMI, the donor strength in the order of NVP > ST > BV. In the free radical solution copolymerization of the systems NVP/NPI, BV/NPI, acrylonitrile (AN) AN/CMI, AN/NPI, MSA/CMI and MSA/NPI, the reaction rate and molecular weight dependence on the monomer combination, as well as the r-values were determined. Using the K_c-values, conclusions were drawn concerning the different reaction mechanisms. The properties of the polymers were investigated using differential scanning calorimetry (DSC) and thermogravimetry.     

Phenyl-2,4,6-trimethylbenzoylphosphinates as water-soluble photoinitiators. Generation and reactivity of OṖ(C6H5)(O−) radical anions

Lithium- and magnesium phenyl-2,4,6-trimethylbenzoylphosphinates (TMPPL and TMPPM) are effective water-soluble photoinitiators for the free-radical polymerization of appropriate monomers such as acrylamide (AA) and methacrylamide (MAA) in aqueous solution. They are also capable of initiating the polymerization of other olefinic compounds such as styrene (St), methyl methacrylate (MMA) or acrylonitrile (AN) in water-containing solvent mixtures such as 1:1 water-acetonitrile mixtures. This is due to the fact that TMPPL and TMPPM undergo α-scission with a rather high quantum yield (?(α) ≈ 0,35) resulting in the formation of 2,4,6-trimethylbenzoyl radicals and O?? (C₆H₅)(O^?) radical anions. The latter are very reactive toward olefinic monomers. Bimolecular rate constants k_R+M/(L/(mol · s)) were determined by flash photolysis at room temperature, e. g. in neat water: 3,8 · 10⁸ (MAA), 2,2 · 10⁸ (AA), and in H₂O/CH₃CN (1:1, v/v): 1,8 · 10⁷ (St), 1,2 · 10⁸ (MMA), 8,4 · 10⁷ (AN).     

On the photoinitiation of free radical polymerization-laser flash photolysis investigations on thioxanthone derivatives

Laser flash photolysis studies and stationary polymerizations were carried out with the aim to elucidate kinetics and mechanisms of photoinitiation processes based on thioxanthone (TX)/amine interactions. During these studies prominence was given to reactions which significantly influence the initiator efficiencies. Thus, rate constants of the reactions ³TX^* + monomer (k_q), ³TX^* + amine (k_XH), and ketyl radical + monomer (k) were determined; k_q decreases according to the series: styrene (St) > N-vinyl-2-pyrrolidone (VP) > methyl methacrylate (MMA) > acrylonitrile (AN) > butyl vinyl ether (BVE) > vinyl acetate (VA) from 6 ·10⁹ l·mol^?1·s^?;1 to 2·10⁴ l·mol^?1·s^?1. Substitution in the 2-position of TX by methyl (MTX), isopropyl (ITX) and Cl (CTX) generally causes a decrease of k_q, except for the systems CTX/VP and CTX/BVE. The k_XH values range from 6 to 8·10⁹ l·mol^?1·s^?1 for typical amines, e.g. ethyl 4-((dimethylamino)benzoate). Ketyl radicals react rather slowly with monomers; for CTX k in l·mol^?1·s^?1: 7·10³ (St), 4·10² (VP), 4·10¹ (MMA), ? 10 (BVE). O₂ reacts rapidly with ketyl radicals: k = 2·10⁹ l·mol^?1·s^?1 (TX). Rates of polymerization ν (monomer consumption) determined at [M] = 5 mol/l and [amine] = 10^?1 mol/l are equal for TX, ITX, MTX, and CTX, but increase according to the series AN < MMA < VP; ν depends on the thioxanthone and the monomer concentration according to ν ∝ [TX]^1/2[M].     

Role of bulky α-substituent in free-radical polymerization and copolymerization of methyl α-(alkoxymethyl)acrylates

Methyl α-(alkoxymethyl)acrylates were prepared from methyl α-(bromomethyl)acrylate in 80–90% yield. The monomers homopolymerize fast to yield low-molecular-weight polymers. The monomers bearing a linear alkoxymethyl group except for the ethoxymethyl group are characterized by a relatively low ceiling temperature. The rate constants for propagation k_p and termination k_t of methyl α-(butoxymethyl)acrylate were evaluated to be k_p = 298 dm³ · mol^?1 · s^?1 and k_t = 8 · 10⁶ dm³ · mol^?1 · s^?1 at 60°C, respectively. The α-(alkoxymethyl)acrylates are more reactive than methyl methacrylate toward polystyrene radical, except for the α-(dodecyloxymethyl)acrylate which is slightly less reactive, indicating that an increase in the reactivity by the electron-withdrawing character of the alkoxy group prevails over the steric hindrance against addition of the polymer radical, except for the large dodecyloxymethyl group.     

Synthesis,polymerization, and copolymerization of lactams containing vinyl groups

Two new lactam monomers containing vinyl groups were synthesized, namely 1-benzyl-3-methylene-5-methyl-2-pyrrolidone ( 1 ) and 5-oxo-2-pyrrolidinylmethyl methacrylate ( 2 ). Their homopolymerization and copolymerizations with methyl methacrylate (MMA), styrene, or methylacrylate were studied. The copolymerization parameters r₁ and r₂ were also evaluated. Poly( 1 ) is a stable polymer which decomposes at ≈ 300°C under nitrogen and at 250°C in air. Its pyrrolidone ring is resistant towards acids and bases.     

Solvent effect on the propagation rate constant in the radical polymerization of bis(2-ethylhexyl) itaconate

Polymerization of bis(2-ethylhexyl) itaconate ( 1 ) with dimethyl azobis(isobutyrate) ( 2 ) was carried out at 50°C in various solvents. Polar solvents caused a significant decrease in the polymerization rate (R_p) and the molecular weight of resulting poly( 1 ). The propagating poly( 1 ) radical could be observed as a five-line ESR spectrum in the actual polymerization systems used. The stationary concentration of poly( 1 ) radical was determined by ESR to be 4,2–6,4 · 10^?6 mol · L^?1 at 50°C when the concentrations of 1 and 2 were 1,03 and 3,00 · 10^?2 mol · L^?1. Using R_p the monomer concentration and the polymer radical concentration, the propagation rate constant (K_p) was estimated to be 1,4–6,8 L · mol^?1 · s^?1, depending on the solvents used. The k_p value was smaller in more polar solvents. The solvent effect is explained in terms of the solvent affinity for the propagating polymer chain.     

4-[Diphenyl(trimethylsilyl)methyl]benzophenone as initiator in the photopolymerization of methyl methacrylate and styrene

The polymerization of methyl methacrylate (MMA) and styrene (St) has been studied using 4-[diphenyl(trimethylsilyl)methyl]benzophenone 1 as photoinitiator. The polymerization follows a free radical mechanism; the polymerization rate increases linearly with the monomer concentration and was found to be proportional to the 0.33 and 1.40 power of the photoinitiator and the monomer (MMA) concentration, respectively. The overall activation energy in the case of MMA photopolymerization was calculated to be 25.0 kJ/mol. From ¹H NMR studies it is concluded that the obtained polymers contain two different trimethylsilyl moieties, one at the head and the other at the tail of the polymer chain, showing primary termination reactions even at low initiator concentrations. The p-benzoyltrityl radical 1^· is incorporated into the polymer chain to a very small extent, acting as a scavenger. This is also concluded by laser flash photolysis (LFP) and ESR spectroscopy measurements. A “living” character of the polymerization was observed only at very low initiator concentrations. The triplet state (³ 1 ^*) of the initiator was quenched by styrene, reducing its efficiency. The rate constant k_q of the quenching process of ³ 1 ^* was measured by LFP (k_q = 3.1 · 10⁹ M⁻¹ · S⁻¹). The triplet state and the photodissociation efficiency of the initiator is unaffected by MMA at various concentrations.     

Über die elementarreaktionen der radikalischen polymerisation von benzylmethacrylat

The influence of various solvents on the rate constants of chain growth and chain termination of benzyl methacrylate has been determined. The absolute rate constants were obtained by combination of stationary and nonstationary methods (rotating sector). The initiator efficiency f depends on the viscosity of the monomer solvent system and on the type of monomer. f is nearly independent of the monomer concentration and of the initiation rate. From that one may conclude that a considerable proportion of the twin recombination reactions takes place outside the primary cage formed by the solvent. The rate constant of chain growth k_w is nearly identical to k_w of methyl methacrylate and shows a slight increase with increasing solvent viscosity. This has been found in the case of methyl methacrylate too. The rate constant of chain termination k_a increases less than proportionally to the reciprocal value of the viscosity of the monomer solvent system. A possible correlation to the internal viscosity is discussed.     

Conductivity studies on living poly(methyl methacrylate) in tetrahydrofuran

The change in conductivity with concentration has been studied for living poly(methyl methacrylate) at ?78°C in tetrahydrofuran as solvent and using lithium, sodium, and potassium as gegen-ions. The experimental conditions of MMA polymerizations have been similar to those used to prepare monodisperse samples. Biphenyl-alkali metal complexes have been used as initiators. Their dissociation constants have been determined at 25°C with values 2.7·10^?6, 0.83·10^?6, and 0.18·10^?6 mole/l., for Li^⊕, Na^⊕, and K^⊕ as gegen-ions, respectively. Log Λ vs. log c plots for living polymers yield straight lines with slopes varying between ?0.17 and ?0.28, depending on the cation. At dilute concentrations the slopes sharply jump up to ?0.50. The values for the dissociation constants, calculated by FUOSS method, are 4.4·10^?10 and 2.1·10^?10 mole/l., with Li^⊕ and K^⊕ as gegen-ions, respectively. In the case of Na^⊕ a quantitative estimation of K_d was not possible, but, qualitatively, it appears to be intermediate between those for Li^⊕ and K^⊕.     

Reactivities of ω‐Unsaturated Methacrylate Oligomers toward tert‐Butoxy Radicals: Investigation of the Effect of Degree of Polymerization and Ester Alkyl Group

The reactivities of ω‐unsaturated methacrylate oligomers (RMA‐n; n = 2–5) toward tert‐butoxy radicals (t‐BuO^·) as a model of the addition step in addition‐fragmentation chain transfer (AFCT) have been investigated by the nitroxide trapping technique in combination with HPLC and electrospray ionization mass spectrometry. The ratio of the rate coefficients for the addition of ω‐unsaturated methyl methacrylate oligomers (MMA‐n) to t‐BuO^· to the β‐fragmentation of t‐BuO^· (k_add/k_β), where k_β can be treated as a constant, has been shown to decrease with increasing n due to increased steric hindrance of the α‐substituents. However, the value of k_add/k_β reaches a constant value at n = 3–4, and the greatest extent of suppression of the addition rate compared with MMA is less than a factor of four. Comparison of the values of k_add/k_β for ω‐unsaturated cyclohexyl methacrylate oligomers (CHMA‐n; n = 2 and 3) with MMA‐n revealed that the extent of suppression increased with increasing n without regard to the ester alkyl group. Hydrogen abstraction by t‐BuO^· from RMA‐n appears to occur mainly at the ester alkyl groups, and the extent is much greater from CHMA‐n than from MMA‐n.

     

Synthèse et polymérisation de monomères acryliques fluorés substitués en position α, 4. Applications à l'α-acétoxyacrylate et à l'α-propionyloxyacrylate de 2-perfluorooctyléthyle

The synthesis of the two monomers 2-perfluorooctylethyl α-acetoxyacrylate ( 1 ) and 2-perfluorooctylethyl α-propionyloxyacrylate ( 2 ) was performed in two steps starting from ethyl pyruvate and 2-perfluorooctylethanol with overall yields of about 56% and 50%, respectively. Transesterification of ethyl pyruvate with the adequate fluorinated alcohol followed by enol acylation gave 1 and 2 , respectively. The kinetic study of polymerization of monomers 1 and 2 , led to the determination of the values of the ratio of the square of the rate constant of propagation over the rate constant of termination k²_p/k_te equal to 9,2 · 10^?3 and 9,1 · 10^?3 L · mol^?1 ·s^?1, respectively, and were compared to those of commercially available fluorinated acrylates and methacrylates.     

Über die radikalpolymerisation einiger monomerer in dimethylformamid

The polymerization of acrylonitrile, methyl acrylate, methyl methacrylate, α-chloromethyl acrylate and α-bromo methyl acrylate in dimethylformamide has been investigated using α.α′-azobisisobutyronitrile as initiator. The following relations have been derived at 60°C: for methyl acrylate v = 15.15·10^?4·[I]^0.5·[M], for methyl methacrylate v = 3.46·10^?4·[I]^0.5·[M], for α-chloro methyl acrylate v = 5.25·10^?4·[I]^0.5·[M], and for α-bromo methyl acrylate v = 4.12·10^?4·[I]^0.5·[M]. It has been found that (k_p/k_t^0.5)₆₀ is 14.4·10^?2 for α-chloro methyl acrylate and 12.15·10^?2 for α-bromo methyl acrylate. The relation between the kinetic data obtained and the HAMMETT σ_p constants has been discussed for the substituents in α-position to the double bond which are considered to be the characteristic parameters for the chemical structure of the monomers.     

Kinetic and ESR studies on the radical polymerization. radical-initiated copolymerization of the diethyl itaconate-SnCl4 complex and styrene

The copolymerization of diethyl itaconate (1) (M₁) and styrene (2) (M₂) with dimethyl 2,2′-azoisobutyrate ( 3 ) was performed in benzene at 50°C, and the following copolymerization parameters were obtained: r₁ = 0,34, r₂ = 0,35, Q₁ = 0,93 and e_l = +0,66. The copolymerization system was found to involve ESR 1

1 Electron spin resonance.

-observed propagating polymer radicals at low monomer feed composition (f₂) of 2 . The apparent rate constant of termination increased rapidly with f₂. The ESR-determined values of the apparent propagation rate constant of the copolymerization were lower than those calculated on the basis of the Mayo-Lewis model, suggesting a significant penultimate effect in the copolymerization. On the other hand, the copolymerization of the 1 -SnCl₄ complex (M₁) and 2 (M₂) at 50°C yielded a nearly alternating copolymer independently of the monomer feed composition. The propagating polymer radicals were ESR-observable even up to f₂ = 0,8. The ESR-determined apparent rate constant (k_p) of propagation showed a maximum near f₂ = 0,5. From the relationship between k_p and f₂, the rate constants of cross-propagations of the present alternating copolymerization were evaluated as k₁₂ = 483 and k₂₁ = 510 L. mol^?1 · s^?1. Comparison of the k₂₁ value and the reported propagation rate constant (209 L · mol^?1 · s^?1) of homopolymerization of 2 leads to the conclusion that the alternating copolymerization via free-monomer propagation mechanism originates from a pronounced penultimate effect suppressing homopropagation of 2 , but not from enhanced cross-propagation.