Kinetics of anionic polymerization of methylmetacrylate with caesium and sodium as counterions in tetrahydrofuran

The kinetics of the anionic polymerization of methylmethacrylate in tetrahydrofuran at ?75 are investigated. Cumylcaecium, α-methylstryrylcaesium and α-methylstyrylsodium were used as initiators. The results show that the polymerization proceeds practically without side reactions under these conditions; as for the anionic polymerization of styrene in polar solvents, ion pairs and anions contribute to the propagation. The rate constant of monomer addition to the ion pair has at ?75 values of 60 and 80 for polymethylmethacrylsodium and polymethylmethacrylcaesium, respectively, and for the anion about 5 × 10⁴ l mole^?1 sec^?1. The dissociation constant was measured as 3·5 × 10^?9 for polymethylmethacrylsodium and 2 × 10^?9 mole/l for the caesium compound at this temperature: the corresponding dissociation enthalpies are ?0·3 and ?1·3 kcal mole^?1. The relatively low activation energy for monomer addition to the ion pair of polymethylmethacrylsodium of 2·3 kcal mole^?1 suggests the existence of two types of ion pairs whereas the corresponding value for polymethylmethacrylcaesium of 4·5 kcal mole^?1 does not allow such an interpretation. The kinetic results are compared with those of the corresponding polystyrylcompounds: the differences are explained by the fact that, in the case of the polymethylmethacryl compound, the estergroup competes with the solvent for solvation of the cation.     

Tetraalkylammonium salts as additives in anionic polymerization of methyl methacrylate

The anionic polymerization of methyl methacrylate was carried out in the presence of t-BuOK/Quaternary ammonium salt (QAS) and α-lithio-ethylisobutyrate/QAS in toluene and THF. Seven QAS and one quaternary phosphonium salt of different size and shape were used as modifiers. With the aid of the model system alkali picrate/QAS, it was found that the interaction between the picrate salt and QAS in toluene does not proceed as a pure cation exchange reaction. Two types of adducts were distinguished: Initiator/QAS with a very long hydrocarbon chain (>C₁₂) promote isotactic placement, while the adducts t-BuOK/QAS with two or more bulky substituents produce a highly syndiotactic polymer with high conversion and comparatively low polydispersity in pure toluene.     

Mechanism of the anionic polymerization of methyl methacrylate initiated by tetramethylammonium–triphenylmethide in tetrahydrofuran

A tetramethylammonium (TMA)–triphenylmethide (TPM) initiator generated in situ by the reaction of trimethyltriphenylmethylsilane with tetramethylammonium fluoride in tetrahydrofuran was found to have greater stability than the corresponding tetrabutylammonium or tetrahexylammonium derivatives. The predominant mode of degradation of TMA–TPM was found to be the TMA‐mediated methylation of TPM anions. The initiation of methyl methacrylate by TMA–TPM in tetrahydrofuran at ?78 °C was demonstrated to produce quantitative yields of poly(methyl methacrylate) with polydispersities of less than 1.1. Although the initiator efficiencies were low (9–40%) because of relatively slow initiation on the polymerization timescale, the initiation appeared to be rapid enough to give relatively narrow molecular weight distributions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 237–244, 2004     

Metal‐free anionic polymerization of methyl methacrylate in tetrahydrofuran using bis(triphenylphosphoranilydene)ammonium (PNP+) as counterion

Bis(triphenylphosphoranilydene)ammonium (PNP⁺) triphenylmethanide (Ph₃C^–) is a new metal‐free initiator for the living polymerization of methyl methacrylate (MMA). The kinetics of the polymerization strongly depend on the metal counterion of the initiator precursor. When the initiator is made from the metathesis reaction of Ph₃CK and PNPCl, the polymerization follows first‐order kinetics up to 0°C with half‐lives below 0.1 s. The propagation rate constants are much higher than those obtained with tetraphenylphosphonium (TPP⁺) cations, indicating a smaller fraction of dormant ylides. When the initiator is synthesized from Ph₃CLi, polymerization proceeds much slower and molecular weight distributions of the obtained polymers are broadened indicating that the active species are mostly lithium enolates in this case.     

Kinetics of emulsion polymerization of methyl methacrylate

The kinetics of the emulsion polymerization of methyl methacrylate at 50°C have been studied in seeded systems using both chemical initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., ～0.7 for 10^?3 mol dm^?3 S₂O²₈ initiator). The data are quantitatively interpreted using a generalized Smith–Ewart–Harkins model, allowing for free radical entry, exit, biomolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k_t) on the weight fraction of polymer (w_p), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent re-entry into particles rather than hetero-termination. The results for k_t(w_p) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.     

Photopolymerization of methyl methacrylate using tetrahydrofuran sulphur dioxide complex as photoinitiator

Photopolymerization of MMA in visible light was studied at 40 using THF-SO₂ complex as the photoinitiator. Initiator exponent was 0.19 and monomer exponent lay between 1.0 and 1.5, depending on thenature of solvent. Analysis of kinetic and other data indicate that the polymerization proceeds by a radical mechanism and termination is initiator dependent. Chain termination via degradative chain (initiator) transfer appears to be significant feature.     

Synthetic and mechanistic aspects of anionic polymerization of methyl methacrylate using tetrabutyl ammonium thioimidate

The tetrabutylammonium salts of ionic organo-initiator containing N,N'-diisopropylthiourea (TUA-1) or N,N'-diethylthiourea (TUA-2) serve as inexpensive initiators for the anionic polymerization of methyl methacrylate (MMA) at room temperature. The molecular weights of obtained polymers are in the range of 1500–22,700 g mol⁻¹ and the molecular weight distributions are fairly broad (Đ = 1.9–2.5) in optimized cases. The molar ratio of monomer to initiator can be achieved up to 800. Side-reactions, for example, backbiting, transfer reactions result in the polymerization being a non-living manner, thus leading to broad molecular weight distributions of the resulting polymers. The effects of counterion nature were also studied from the polymerization of MMA using TUA-1 anion with sodium or potassium salts as counterions under identical conditions. Detailed investigation indicates that the polymerization proceeds via a sulfur anion initiated repeated 1,4-Machael addition. In general, thioimidate initiators induced MMA polymerization feature certain induction periods, which is ascribed to slow addition thioimidate to CC double bond of MMA as a result of low initiator efficiency.     

Poly(ethylene oxide) gel as a novel polymerization medium anionic polymerization of methyl methacrylate

Crosslinked poly(ethylene oxide)-(PEO-N) is used as a novel medium for the anionic polymerization of methyl methacrylate (MMA) initiated by t-BuOK and ethyl-α-lithioisobutyrate (α-LiEtIB) in toluene. Comparative studies with linear poly(ethylene oxide)-(PEO-L) are performed as well. It is found that PEO-N effectively binds both initiators, and the polymerization process takes place mainly in the gel phase. PEO-N accelerates the polymerization process initiated by t-BuOK enabling the formation of high-molecular-weight polymers with high yields. Part of poly(methyl methacrylate)-(PMMA) remains in the gel particles yielding semi-interpenetrating networks with amphiphilic properties. PEO additives do not influence profoundly the course of the polymerization, initiated by α-LiEtIB. The influence of PEO-N on the proceeding of the polymerization is discussed in some detail.     

Living anionic polymerization of lauryl methacrylate and synthesis of block copolymers with methyl methacrylate

Anionic polymerization of lauryl methacrylate (LMA) with 1,1‐diphenylhexyl lithium in tetrahydrofuran (THF) at ?40 °C resulted in a multimodal and broad molecular weight distribution (MWD) with poor initiator efficiency. In the presence of additives such as dilithium salt of triethylene glycol (G₃Li₂), LiCl, and LiClO₄, the polymerization resulted in polymers with a narrow MWD (≤ 1.10). Diblock copolymers of methyl methacrylate (MMA) and LMA were synthesized by anionic polymerization using DPHLi as initiator in THF at ?40 °C with the sequential addition of monomers. The molecular weight distribution of the polymers was narrow and without homopolymer contamination when LMA was added to living PMMA chain ends. Diblock copolymers with broad/bimodal MWD were obtained with a reverse‐sequence monomer addition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 875–882, 2004     

Kinetics and stereoregulation in the isotactic-specific and living polymerization of methyl methacrylate

Kinetic studies on the isotactic-specific living polymerization of methyl methacrylate with t-C₄H₉MgBr were carried out in toluene at −78°C and the kinetic orders with respect to the monomer and initiator were found to be unity. Propagation rate in the early stage of polymerization and the initiation rate were studied by kinetic measurement and analysis of oligomer distribution. The rate constants for the propagation of the unimer (k₁), dimer (k₂), and trimer anions (k₃) were found to be in the following order; k₁ >> k₂ > k₃. ¹³C NMR spectra of the oligomer anions indicated the coordination of penultimate and antepenultimate ester groups to Mg counterion. Possible mechanism for stereoregulation in the early stage of polymerization was discussed.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization

The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ S_p^?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ E_t^?) of complexed growing chain radicals.     

Photo-living radical polymerization of methyl methacrylate using alkoxyamine as an initiator

The photoradical polymerization of vinyl acetate was performed using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator in the presence of bis(alkylphenyl)iodonium hexafluorophosphate (BAI). The MTEMPO/BAI system using 2,2’-azobis(isobutyronitrile) or 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator did not succeed in controlling the molecular weight and produced polymers that showed a bimodal gel permeation chromatography with the broad molecular weight distribution. On the other hand, the polymerization using 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine and BAI proceeded by the living mechanism based on linear increases in the first order time–conversion and conversion–molecular weight plots. The molecular weight distribution also increased with the increasing conversion due to cloudiness of the solution as the polymerization proceeded. It was found that the polymerization had a photolatency because the propagation stopped by interruption of the irradiation and was restarted by further irradiation.     

Microstructure of the copolymers of methyl methacrylate with other methacrylates obtained by radical and anionic copolymerizations in tetrahydrofuran

Monomer reactivity ratios r₁ and r₂ were determined in the copolymerizations of methyl methacrylate (MMA, M₁) with 1, 1-diphenylethyl (DPEMA), α,α-dimethylbenzyl (DMBMA), tert-butyl (t-BuMA), diphenylmethyl (DPMMA), phenyl (PhMA), and 1-naphthyl (NpMA) methacrylates (M₂) in tetrahydrofuran (THF) by azobisisobutyronitrile (AIBN) at 60°C and butyllithium (n-BuLi) at ?78°C. The reactivities of the monomers were explained in terms of the polar effect of the ester groups in both copolymerizations. All the copolymers isolated in low yields were converted to PMMA either directly or by copoly(MMA—methacrylic acid) to determine the triad tacticities of the copolymers. Coisotactic parameters σ₁₂ and σ₂₁ were determined by assuming the terminal model statistics. The σ₂₁ values always accorded to the σ₂₁ values within experimental error, and in radical copolymerizations they were between isotactic parameters σ₁₁ and σ₂₂ of the homopolymerizations of MMA and M₂ monomers. In anionic copolymerizations, however, the σ₁₂ = σ₂₁ values varied, depending on the M₂ monomers. In copolymerization with DPEMA the values were less than both σ₁₁ and σ₂₂ with DMBMA they were between σ₁₁ and σ₂₂, with DPMMA, nearly equal to σ₁₁, and with PhMA and NpMA, greater than both σ₁₁ and σ₂₂. The application of these parameters to copolymerizations performed at high conversion was also investigated.     

Anionic polymerization of methyl methacrylate using tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium (P5+) as counterion in tetrahydrofuran

A novel metal‐free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P₅⁺) cation with the 1,1‐diphenylhexyl (DPH^–) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between –20 and +20°C using a flow tube reactor provide nearly linear first‐order time‐conversion plots with half‐lives below 0.1 s, a linear dependence of the number‐average degree of polymerization, and rather narrow molecular weight distributions (M_w/M_n ≈ 1.2). ¹³C NMR measurements on a model of the active chain end (the P₅⁺ salt of ethyl isobutyrate) in THF‐d₈ show 15 and 25 ppm upfield shifts of the α‐carbon compared to the dimers and tetramers of the lithium ester enolate, respectively, indicating a non‐aggregated structure and an increased charge density on the α‐carbon.