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.     

Synthesis and structure of tetrakis(isopropylimino)bis-[tris(dimethylamino)silylamino]alane

A novel cage-type compound tetrakis(isopropylimino)bis[tris(dimethylamino)silylamino]alane, H₆Al₆(NⁱPr)₄[NSi(NMe₂)₃]₂, (1), was prepared by reaction of tris(dimethylamino)silylamine H₂NSi(NMe₂)₃ with poly(isopropyliminoalane) (HAlNⁱPr)₆. The molecular structure of 1 was determined and discussed on the basis of FTIR, NMR and X-ray crystallographic analysis.     

Anionic polymerization of styrene in tetrahydrofuran (THF) with cumylcaesium as initiator

The kinetics of the anionic polymerization of styrene initiated by cumylcaesium have been reinvestigated in tetrahydrofuran. Quite unlike earlier investigations, the ion pair rate constant $\text{k}{}_{\mathrm{p}}\text{(±)}$ was found to be 130 l/mole/sec at 25° and the dissociation constant of polystyrylcaesium to be about 5 × 10^?10 mole/l. In the presence of caesiumtriphenylcyanoborate used as a common ion salt addition, $\text{k}{}_{\mathrm{p}}\text{(±)}$ was measured over a wide range of temperature. The results are compared to the temperature behaviour of the ion pair rate constants obtained with polystyrylsodium in polar solvents; they indicate that the existence of solvent separated ion pairs cannot be excluded for polystyrylcaesium.     

阴离子聚合法合成PMMA-b-PMTFPS嵌段共聚物

以含缩醛官能团的有机锂为引发剂, 将甲基丙烯酸甲酯(MMA)与含氟硅氧烷单体1,3,5-三甲基-1,3,5-三(3',3',3'-三氟丙基)环三硅氧烷(F3)阴离子嵌段共聚, 获得了窄分子量分布的聚甲基丙烯酸甲酯-b-聚[甲基(3,3,3-三氟丙基)硅氧烷](PMMA-b-PMTFPS)嵌段共聚物, 并用GPC, 1H NMR, FTIR和DSC对嵌段共聚物进行了表征. 研究结果表明, 在THF中利用PMMA-OLi对F3进行阴离子开环聚合时, 单体F3浓度的选择对提高嵌段共聚物产率至关重要.     

Anionic polymerization of dodecamethyl-cyclohexasiloxane (D6) with lithium cryptate as a counterion

A kinetic study of the anionic polymerization of dodecamethylcyclohexasiloxane (D₆) has been carried out in toluene at 25°C with the cryptate Li⁺ + [211] as the counterion. The rate constants of propagation of D₆ and of the formation of cyclic oligomers have been determined. The results are in good agreement with those reported previously for the anionic polymerization of D₃ and D₄ under the same conditions. The rate constants of propagation and of formation of D₆ have been found to be equal to 1.1 l-mol⁻¹.h⁻¹ and 0.05 h⁻¹, respectively. In the case of the anionic polymerization of cyclosiloxanes with Li⁺ + [211] as the counterion, the order of reactivities of D_x as a function of × is as follows:      

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.     

Syntheses and rearrangements of tris(hydroxymethyl)phosphine and tetrakis(hydroxymethyl)phosphonium salts

Abstract

Tetrakis(hydroxymethyl)phosphonium (HOCH₂)₄P⁺ salts, particularly the chloride (THPC) and sulfate (THPS), are among the most accessible organophosphorus compounds that can be made quantitatively from PH₃ and formaldehyde in aqueous media under ambient conditions. These phosphonium salts are air-stable, and are widely used as reactants in organic syntheses, as well as in textile or oil industries. Synthesis of tris(hydroxymethyl)phosphine (THP), an active component of the salts, is more complicated because direct synthesis from PH₃ and CH₂O requires either pressure and high temperature, at which THP rearranges into bis(hydroxymethyl)methylphosphine oxide, CH₃P(O)(CH₂OH)₂, or a metal catalyst that is usually difficult or impossible to recover. Syntheses of THP based on neutralization of the salts are more convenient but require pH control and additional steps to separate THP from CH₂O. This review summarizes literature data on syntheses and purification of the salts and THP, and side reactions such as thermal rearrangement and oxidation.     

Di[tris(trimethysilyl)methyl]-zinc and -cadmium

Tris(trimethylsilyl)methyllithium reacts with the anhydrous halides MC1₂ (M = Zn or Cd) to give the compounds [(Me₃Si)₃C]₂M, which show high thermal and chemical stability. They decompose only above 300°C, with formation of (Me₃Si)₃CH, and are not attacked by water in refluxing THF. The zinc compound can be steam-distilled without decomposition, and does not react with boiling concentrated hydrochloric acid or with bromine in carbon tetrachloride.     

Solvent-free synthesis and purification of poly[2-(dimethylamino)ethyl methacrylate] by atom transfer radical polymerization

Solvent-free synthesis of well-defined poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) (co)polymers was performed by atom transfer radical polymerization conducted under very mild conditions (in bulk at 25 degrees C). The pH-dependence and the thermo-responsive behaviour of PDMAEMA in aqueous solution were operated to isolate and purify the (co)polymers without using any organic solvent or further catalyst extraction. The viscosity in aqueous solution of so-purified PDMAEMA homopolymers and their block copolymers with poly(ethylene glycol) (PEG) was studied as a function of molar mass and concentration and a typical polyelectrolyte behaviour was observed, these catalyst-deprived polycations are able to form stable and non toxic complexes with DNA, showing good transfection efficacies in gene therapy.     

Anionic polymerization with alkaline-earth counterion. I. Preparation and characterization of dicarbanionic oligostyrylbarium and -strontium in tetrahydrofuran

Dicarbanionic oligostyrylbarium or -strontium, PS⁼Ba⁺⁺ and PS⁼Sr⁺⁺, were prepared by reacting styrene with finely divided barium or strontium in THF or THP. The effects of reaction temperature, monomer, and metal concentration were described. Difunctionality of these living oligomers is confirmed from calculated and observed molecular weight data and also from conductivity measurements. λ_max of carbanions is found to vary with DP . At 25°C it decreases from 368 nm for dimers to 359 nm for DP > 10. As observed for monocarbanionic polystyrylbarium (PS^?)₂Ba⁺⁺, λ_max of PS⁼Ba⁺⁺ of high DP decreases with temperature, while λ_max of PS⁼Ba⁺⁺ of low DP increases with decreasing temperature. At ?100°C the difference between the two extreme values is about 30 nm. Similar results are obtained with PS⁼Sr⁺⁺. Such unusual spectral properties are interpreted, on the basis of excitation molecular theory, in terms of ring structures for the living oligomers.     

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.     

The effect of additives on the polymerization of methyl methacrylate. tris(1,2-dibromo-propyl)phosphate

The effect of the additive, Tris(1,2-dibromopropyl)phosphate, on the kinetics of free radical polymerization of methyl methacrylate is studied. No marked differences were observed in the homopolymerization despite the reported effect of this additive on the mechanical properties of the resulting polymer. It was concluded that the additive was a multifunctional transfer agent producing linear and branched polymer molecules. Several model transfer agents have been studied to confirm these conclusions. H-NMR spectra of the polymer confirm that there is no change in the stereoregularity of the polymer prepared in the presence of this additive, and no copolymerization of the phosphate unit.     

Phosphino[tris(trimethylsilyl)methyl]Boranes and 2,4‐Bis[tris(trimethylsilyl)methyl]‐1,3,2,4‐diphosphadiboretanes [1]

The reaction of tris(trimethylsilyl)methylboron dihalides (Me₃Si)₃CBX₂ (X = Cl, F) with the lithium phosphides LiPHtBu and LiPHmes leads to the phosphinoboranes (Me₃Si)₃CBX‐(PHR), (Me₃Si)₃CB(PHR)₂ or the 1,3,2,4‐diphosphadiboretanes [(Me₃Si)₃CB(PR)]₂, depending on the ratio of the reagents, the reaction temperature and concentration. High dilution and low temperatures are required for the synthesis of (Me₃Si)₃CB(Hal)PHR ( 1–3 ) in order to prevent the formation of (Me₃Si)₃CB(PHR)₂ ( 4 and 5 ). The latter compounds are best prepared in a two step phosphination from (Me₃Si)₃CBHal₂ and LiPHR. At higher temperatures the four‐membered 1,3,2,4‐diphosphadiboretanes [(Me₃Si)₃CB(PR)]₂ 6 and 7 are the most stable compounds. On the other hand, compounds of type (Me₃Si)₃CB(Hal)PR₂, 8 and 9 , are thermally more stable than the monophosphinoboranes 1 – 3 . Phosphinoboranes of type (Me₃Si)₃CB(PR₂)₂ (R = tBu, mes) could not be prepared. NMR and mass spectral data are in accord with the monomeric nature of compounds 1 to 9 .     

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.     

Micellization and applications of narrow-distribution poly[2-(dimethylamino)ethyl methacrylate]

Oxyanion-initiated polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA), initiated by potassium benzyl alcoholate (BzOK), produced a number of well-defined, water-soluble benzyloxy end-capped homopolymers of various molecular weights. The structure of these homopolymers was confirmed by FTIR and ¹H NMR. The molecular weights of the polymers were estimated by comparing the ¹H NMR peak integrals for phenyl protons of the benzyloxy group with those of the dimethylamino protons of the monomeric unit. GPC analysis showed that these homopolymers possess a narrow molecular weight distribution ( ) in the range of 1.15–1.28. Under acidic or neutral conditions, the polymers exhibit the behavior of polymeric surfactants bearing protonized tertiary amines in their pendants, with critical micelle concentration (CMC) between 0.5 to 1 g/L and surface tension dropping below 40 mN/m. It was also found that the lower critical solution temperature (LCST) of the polymeric surfactants (as determined by UV-visible spectroscopy) varied with properties such as molecular weight, concentration, and pH in aqueous media. The polymeric surfactants showed excellent pH-response and emulsifier properties when used in the emulsion polymerization of styrene.