Radical polymerization of methyl methacrylate with ethane-1,1,2-triyltribenzene as an initiator and ethane-1,1,2-triyltribenzene-end polymers as macroinitiators

An unsymmetrical triphenylethane, ethane-1,1,2-triyltribenzene (ETB), was successfully prepared from phenyl lithium, trans-1,2-diphenylethylene, and methanol. Characterization of the compound was performed by ¹H and ¹³C nuclear magnetic resonance spectroscopy (NMR). The polymerization of methyl methacrylate (MMA) was performed in the presence of ETB at 85 °C or higher. The free radicals obtained were characterized by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS). Gel permeation chromatography (GPC) traces of the average molecular weight of poly(MMA) (PMMA) showed a series of translations with increasing time. The average molecular weight of PMMA indicated narrow polydispersity, and a linear relationship was found between ln([M]₀/[M]) and polymerization time. These results indicated the “living” nature of the polymerization of MMA in the presence of ETB. The structure of ETB was also introduced to the end of polystyrene (PS), polyisoprene (PI), and polyisoprene-b-polystyrene (PIS) chains which were obtained by living anionic polymerization. Hence, they initiated radical polymerization of MMA as ETB-end-macroinitiators to obtain block copolymers. Thus, living anionic polymerization and this radical polymerization method were combined together to prepare block copolymers without the intermediate transformation step.     

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.     

Free‐radical polymerization of methyl methacrylate with a tetrafunctional peroxide initiator

This study examined the use of a new tetrafunctional peroxide initiator in the bulk free‐radical polymerization of methyl methacrylate. The objective was to investigate the effect of using a multifunctional initiator through an examination of the rates of polymerization and the polymer properties. The molecular weights and radii of gyration were obtained with a size exclusion chromatograph equipped with an online multi‐angle laser light scattering detector. The performance of the tetrafunctional initiator was compared to that of a monofunctional counterpart [tert‐butylperoxy 2‐ethylhexyl carbonate (TBEC)]. The results showed that the new tetrafunctional peroxide initiator produced a faster rate of polymerization than TBEC at an equivalent concentration but also generated a polymer of a lower molecular weight. This trend was the opposite of what was observed in a previous study with styrene. When TBEC was used at a concentration four times that of the new tetrafunctional peroxide initiator, both produced equal rates of polymerization and similar molecular weights. The degree of branching was also investigated with radius‐of‐gyration plots. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5647–5661, 2004     

Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl methacrylate)

Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed isotactic PMMA (iMA) with about 90% isotactic triads and different M?_v's, viz., iMA-1: 7.2 × 10⁵; iMA-2, 5.0 × 10⁵; iMA-3, 3.5 × 10⁵; iMA-4, 1.25 × 10⁵; and iMA-5, 1.15 × 10⁵. The MMA:iMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. It is found that the M?_v of the polymer formed ran parallel to the M?_v of iMA. In all cases syndiotactic PMMA (s-PMMA) was produced which associated with the isotactic substrate to form acetone-insoluble stereocomplexes. The syndiotactic polymers probably consist of long syndiotactic and heterotactic sequences. The syndiotacticity decreased with conversion and was generally highest in the presence of iMA-1. With iMA-1 even the formation of some additional i-PMMA (in the acetone-insolubles) was indicated, especially in the later stages of the polymerization. Characterization of the acetone-soluble fractions indicated that i,s-stereoblock polymers were also produced, of which the persistence ratios ρ increased with the M?_v of iMA. From these results it is concluded that this reaction differs from the conventional radical polymerization and can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i- and s-PMMA to associate. The formation of i,s-stereoblock polymers and additional i-PMMA indicates that s-PMMA in its turn can also act as a polymer matrix.     

Radical polymerization of methyl methacrylate in the presence of low-molecular-weight poly(methyl methacrylate)

The kinetics of the bulk radical polymerization of methyl methacrylate and the structure and properties (physicomechanical and thermomechanical, as well as diffusion and sorption) of the polymers were examined in relation to the amount of low-molecular-weight poly(methyl methacrylate) added.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). II. Syndiotactic PMMA as matrix

Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed syndiotactic PMMA (sMA) with about 90% syndiotactic triads and of different M?_v, viz., sMA-1, 1.6 × 10⁵; sMA-2, 3.0 × 10⁵; and sMA-3, 8.7 × 10⁵. The MMA:sMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. In all cases isotactic PMMA (i-PMMA) was produced, especially in the initial reaction stages, which associated with the syndiotactic substrate to form acetone-insoluble 1:2 i/s-stereocomplexes. The isotacticity decreased with conversion and was highest in the presence of sMA-3. Characterization of the acetone-soluble fractions indicated that i,s-stereoblock polymers were also produced. From these results it is concluded that this reaction can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i-PMMA and s-PMMA to associate. With sMA of M?_v below about 1.2 × 10⁵, no i-PMMA is formed; in other words, no replica polymerization occurs. For polymerizations in the presence of sMA-2, the critical M?_v of propagating chains, with has to be exceeded before stereoassociation is strong enough to effectuate replica polymerization, has been estimated to be 0.6 × 10⁵.     

Azobenzene‐based initiator for atom transfer radical polymerization of methyl methacrylate

2‐Bromopropionic acid 2‐(4‐phenylazophenyl)ethyl ester, 2‐bromopropionic acid 6‐(4‐phenylazophenoxy)hexyl ester (BPA₆), 2‐bromopropionic acid‐(4‐phenylazoanilide), and 2‐bromopropionic acid 4‐[4‐(2‐bromopropionyloxy)phenylazo]phenyl ester (BPPE) were used as initiators with monofunctional or difunctional azobenzene for the heterogeneous atom transfer radical polymerization of methyl methacrylate with a copper(I) chloride/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalytic system. The rates of polymerizations exhibited first‐order kinetics with respect to the monomer, and a linear increase in the number‐average molecular weight with increasing monomer conversion was observed for these initiation systems. The polydispersity indices of the polymer were relatively low (1.15–1.44) up to high conversions in all cases. The fastest rate of polymerization and the highest initiation efficiency were achieved with BPA₆, and this could be explained by the longer distance between the halogen and azobenzene groups and the better solubility of the BPA₆ initiator. The redshifting of the UV absorptions of the polymers only occurred for the BPPE‐initiated system. The intensity of the UV absorptions of the polymers were weaker than those of the corresponding initiators in chloroform and decreased with the increasing molecular weights of the polymers in all cases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2358–2367, 2005     

Poly(methyl methacrylate)-kaolinite nanocomposites prepared by interfacial polymerization with redox initiator system

Interfacial intercalative polymerization of methyl methacrylate (MMA) was developed to prepare PMMA-kaolinite nanocomposites using a redox initiator system, based on dodecylamine as reductant, immobilized into kaolinite by successive intercalation while the oxidant component of the redox system (K₂S₂O₈) was applied from aqueous phase. The X-ray diffraction (XRD) was used to prove the functionalization of the clay with the amine before starting the polymerization reaction. The progress of the polymerization reaction through the involvement of the amine in the initiation process was confirmed not only by successfully performing the reaction at 50 °C, a temperature at which the K₂S₂O₈ cannot start the polymerization alone, but also by the enhancement of polymerization rate and drop in activation energy required to start the polymerization. The produced PMMA/kaolinite nanocomposites were examined by XRD and transmission electron microscope as well; both confirmed the defoliation of the kaolinite layers into homogeneously distributed platelets within the polymer phase which supports the effectiveness of the redox initiation in the intercalative polymerization. Furthermore, more explanation about the interfacial structure of the nanocomposites was given using Fourier transform infrared. The thermal gravimetric analysis revealed a very similar behavior above 300 °C with respect to the pure PMMA prepared under the same reaction conditions while in the range from 220 °C to 320 °C, the degradation was earlier in the case of the nanocomposites due to the presence of the dodecylamine; on the other hand, the glass transition temperatures were increased remarkably as assigned by differential scanning calorimetry in comparison with the pure PMMA.     

Unsymmetrically substituted ethane as a new and efficient initiator for the polymerization of methyl methacrylate and styrene

In this paper, we present a compound, 2,3-diphenyl butyronitrile (DPBN), which can be used as a new and efficient radical initiator for the polymerization of methyl methacrylate (MMA) and styrene (St). Very different from other compounds as a carbon-carbon initiator, DPBN is an unsymmetrically substituted ethane and works with high initiation reactivity at lower temperatures. This new compound as an initiator exhibits various advantages, such as easy preparation, high initiation reactivity, safe use and storage, and convenient handling.     

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.     

Radical polymerization of methyl methacrylate initiated by an enolizable ketone–carbon black system

The polymerization of methyl methacrylate (MMA) initiated by an enolizable ketone (R₁? CO? CH₂? CO? R₂)-carbon black system was investigated. Although enolizable ketone itself could not do so, the polymerization of MMA was initiated by enolizable ketone in the presence of carbon black. In addition, a chloranil-enolizable ketone system was able to initiate the polymerization of MMA. It was found that the enol form of the ketone and quinonic oxygen groups on the carbon black surface played an important role in the initiation system; namely, it was considered that the polymerization was begun by the ketone radical (R₁? CO? CH? CO? R₂) formed by a one-electron transfer reaction from enolate ion to quinonic oxygen groups. The effect of solvent on the process was also studied. The rate of the polymerization increased, depending on the solvent used, in the following order: benzene < 1,4-dioxane < dimethyl sulfoxide < N,N-dimethylformamide < N-methyl-2-pyrrolidone. Furthermore, it became apparent that during the polymerization poly(methyl methacrylate) was grafted onto the carbon black surface (grafting ratio was ca. 40% when benzene was used as solvent) and the carbon black obtained gave a stable colloidal dispersion in organic solvent.     

Miniemulsion polymerization of methyl methacrylate with dodecyl mercaptan as cosurfactant

Miniemulsions of methyl methacrylate with sodium lauryl sulfate as the surfactant and dodecyl mercaptan (DDM) as the cosurfactant (or hydrophobe) were prepared and polymerized. The emulsions were of a droplet size range common to miniemulsions and exhibited long-term stability (greater than 3 months). Results indicate that DDM retards Ostwald ripening and allows the production of stable miniemulsions. When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of the concentration of surfactant, cosurfactant and initiator were determined. Rates of polymerization, monomer droplet sizes, polymer particle sizes, molecular weights of the polymer, and the effect of initiator concentration on the number of particles vary systematically in ways that indicate predominant droplet nucleation in these systems. © 1996 John Wiley & Sons, Inc.     

The use of ylide (4-picolinium 4-chloro phenacyl methylide) as an initiator for the polymerization of methyl methacrylate

The thermal polymerization of methyl methacrylate [MMA] was carried out using ylide (4-picolinium 4-chloro phenacyl methylide) as an initiator. The rate of polymerization (R_p) increases with increasing monomer and initiator concentrations; The exponent value has been computed to be 1 ± 0.02 and 0.5, respectively. The reaction was carried out at four different temperatures and the overall activation energy has been computed to be 16.01 kcal/mol. The polymerization was inhibited in the presence of hydroquinone as a radical scavanger. Kinetic studies indicates that the overall polymerization takes place by a radical mechanism.     

Polymerization of methyl methacrylate with cupric laurate–benzoin system as initiator

The polymerization of methyl methacrylate initiated by cupric laurate in combination with benzoin has been investigated in carbon tetrachloride medium at 60°C. The rate of polymerization was found to be proportional to the square root of both cupric ion and benzoin concentrations, and to the 1.5th power of the monomer concentration. Spectral studies indicated that there is a complex formation between cupric ion and the monomer methyl methacrylate. A reaction scheme, based on initial formation of the complex and its subsequent reaction with benzoin to produce the free radicals responsible for initiation has been postulated to explain the observed results.     

Polymerization of methyl methacrylate with cupric laurate-N,N-dimethyl formamide as initiator system

The polymerization of methyl methacrylate with cupric laurate in combination with N,N-dimethyl formamide as initiator was studied in carbon tetrachloride medium at 60°C. The rate of polymerization was found to be proportional to the 3/2th power of the monomer concentrations and to the square root of both cupric laurate and DMF concentrations. Spectroscopic investigations indicated a ternary complex formation involving cupric ion, methyl methacrylate, and DMF. A reaction scheme is suggested on the basis of these results and various kinetic constants have been evaluated.     

Solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate initiator: Kinetics of polymerization and activation parameters for the primary decomposition of the initiator

The kinetics of solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate (aliquat persulfate) at 60°C has been studied in t-butyl alcohol, N,N-dimethyl formamide, acetonitrile, dioxane, acetone, and methyl ethyl ketone. The rate of polymerization depends markedly on the solvent used. The initiator exponent is close to 0.5 in the first three solvents but larger than this value in the other three solvents. The overall activation energy of the polymerization has been determined in all the solvents. The rate constants and activation parameters for the primary decomposition of the initiator have been determined in the first three solvents where ideal polymerization conditions prevail. The activation parameters for the decomposition of AQ₂S₂O₈ in the organic solvents depend on the type of solvent. They are very different from those of the free S₂O^2?₈ ion in water. These differences have been explained taking into consideration the various ionic forms in which the initiator exists in the studied solvents using a previously postulated model of the activated state.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). III. Influence of temperature

Methyl methacrylate (MMA) was polymerized by radical initiation at 0, 25, 50, 75 and 100°C in DMF in the presence of preformed isotactic PMMA (iMA) or preformed syndiotactic PMMA (sMA) with different M?_v and also without preformed PMMA (“blank” polymerizations). From the tacticities of the formed polymers it is concluded that blank polymerization does not conform to simple Bernoulli statistics, but follows at least first-order Markov statistics. The formation of long syndiotactic sequences in the presence of iMA and long isotactic sequences in the presence of sMA denotes still higher-order Markov statistics. The stereoregulating action is improved by higher M?_v of the preformed polymer (matrix) and lower reaction temperature. These influences can be explained by assuming an equilibrium between polymer growth on the matrix and in the “free” solution. For polymerizations in the presence of iMA or sMA below 300°K, the differences in activation enthalpies (ΔH_s/i? – ΔH_i/s?) are practically equal to that for the blank polymerization, ca. 900 cal/mole, whereas the differences in activation entropies (ΔS_s/i? – ΔS_i/s?) differ considerably. (ΔS_s/i? – ΔS_i/s?) values are highly negative in the presence of iMA and highly positive in the presence of sMA. From these results it is concluded that the isotactic and syndiotactic polymer matrices exert a steric influence on the monomer addition process, thus promoting so-called stereospecific replica polymerization.