Anionic polymerization of cyclosiloxanes in heterogeneous medium

Anionic polymerization of various cyclosiloxanes [octamethylcyclotetrasiloxane (D₄), 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V₄), and hexamethylcyclotrisiloxane (D₃)] was performed. As catalysts, IRA-900 and PB-100 type anionites with benzyltrimethylam-monium and 3-acrylamidopropylbenzyldimethylammonium groups, respectively, were used. The anionite with higher strongly basic exchange capacity (IRA-900) is more efficient in dimethylcyclosiloxane polymerization. PB-100 anionite with less strongly basic capacity is more active for polymerization of the V₄ monomer with bulky and electronegative sub-stituent. © 1996 John Wiley & Sons, Inc.     

Anionic polymerization of methyl methacrylate initiated by thiophenol

Methyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non-radical process. Since other monomers with an x,β-unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1-diphenyl-2-picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol-initiated polymerization supporting the postulated mechanism.     

Anionic block copolymerization of cyclotetrasiloxanes initiated by p-bis(dimethyllithiioxysilyl)benzene

The triblock copolymers of poly(diphenyl-b-dimethyl-b-diphenyl)siloxane (PMP) and poly(diphenyl-b-dimethyl-co-methylvinyl-b-diphenyl)siloxane (PMVP) have been synthesized by the dianionic polymerization procedure. The polymerization of the cyclotetrasiloxane monomers initiated by lithium-based initiator has been carried out so as to avoid equilibration reactions. The new initiator, p-bis(dimethyllithiioxysilyl)benzene, was used. Dimethyl formamide (DMF) was used as a promotor. The effects of initiator concentration, polymerization temperature, and polymerization time on the reaction were investigated. The block copolymers have been determined by ¹H-NMR, infrared, ultraviolet, and differential scanning calorimetry. Progressive precipitation separation has been used to study the molecular weight distribution, and the integral distribution curves of the molecular weight have been given. © 1996 John Wiley & Sons, Inc.     

Anionic block copolymerization of cyclotetrasiloxanes initiated by 4,4'‐bis(dimethyllithiioxylsilyl)diphenyl ether

The anionic copolymerization of cyclotetrasiloxanes initiated by 4,4′‐bis(dimethyllithiioxylsilyl)diphenyl ether (BDMOLiPE) was carried out for the preparation of poly(diphenyl‐dimethyl‐diphenyl)siloxane block copolymers (PMP). To reduce redistribution reaction, the lithium‐based dianionic initiator (BDMOLiPE) was first used for the copolymerization of the cyclotetrasiloxane monomers without solvent, with dimethyl formamide (DMF) as a promotor. The cyclotetrasiloxanes used involved octamethylcyclotetrasiloxane (D₄), octaphenylcyclotetrasiloxane (P₄), and tetramethyl‐tetravinylcyclotetrasiloxane (V₄). The copolymers obtained were characterized withproton nuclear magnetic resonance spectroscopy, infrared spectroscopy, intrinsic viscosity([η]) determination, transmission electron microscopy, and wide‐angle X‐ray diffraction analysis. The results illustrate that the products should belong to block copolymers but not be too perfect because the block copolymers were scrambled to a certain extent during the copolymerization process. However, we can approximately express them as PMP and PMVP, according to the different order of the feeding in raw materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1203–1210, 2001     

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature-preparation and polymerization of miniemulsion

Miniemulsions of styrene and butyl acrylate with sodium dodecyl sulfate (SDS) as the surfactant and hexadecane (HDE) and cetyl alcohol (HDL) as cosurfactants were prepared under high-speed stirring or ultrasonification. Results indicate that the stability of miniemulsions produced with HDE is more stable than that with HDL, when the feeding method, in which the cosurfactant is mixed with monomers, is used. There is an optical ratio (¼) of the surfactant to the cosurfactant for maximum stabilization of the miniemulsions. The miniemulsions prepared by ultrasonification are much more stable than those by high-speed stirring. Also, a stable miniemulsion can be prepared at lower temperature (45°C) when homogenizing way of ultrasonification is used. The emulsions were of a droplet-size range common to miniemulsions and some of them exhibited long-term stabilities (3 months). When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of temperature, ultrasonification time, ratio of monomers, and concentrations of surfactant, cosurfactant, and initiator on the polymerization rate, conversion, and particle size were determined. It was found that the miniemulsion copolymerization of styrene and butyl acrylate with a midial amount of a redox initiator ((NH₄)₂S₂O₈/NaH SO₃) at lower temperature (45°C) can be carried out successfully by using a suitable amount of the surfactant SDS (10 mM) and the cosurfactant HDE (40 mM), when a homogenizing way of ultrasonification is applied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2029–2039, 1998     

Anionic polymerization initiated by lamellar compounds of LiC12: 1. Kinetics of the polymerization of styrene and isoprene — initiator efficiency

The polymerizations of styrene and isoprene initiated by LiC₁₂ in cyclohexane are far slower than those observed in homogeneous media. The initiator's efficiency is estimated from a determination of the polymer molecular weight at differents reaction steps. Keeping in mind the monomer diffusion inside the graphite layers and in allowing some assumptions, some of the propagation rate constants were estimated. These values are much lower than those found in homogeneous polymerization. Temperature speeds up the reaction. The initiator's efficiency depends on the rate at which the graphite separates under the conjugated action of temperature and polymer growth.     

Anionic ring‐opening polymerization of adipic anhydride initiated by potassium poly(ethylene glycol)ate

Poly(adipic anhydride) (PAA) was prepared by the ring‐opening polymerization of adipic anhydride (AA) initiated by potassium poly(ethylene glycol)ate. The effects of various factors, such as the amount of initiator, concentration of the monomer, reaction time and temperature, and polarity of the solvent on the polymerization were investigated. The crude polymerized product was a mixture of PAA homopolymer and poly(ethylene glycol)–poly(adipic anhydride) block copolymer, as confirmed by ¹H‐NMR and gel permeation chromatography. Chain‐transfer reactions occurred intensively for the AA polymerization in both the nonpolar solvent toluene and the polar solvents CHCl₃ and tetrahydrofuran, which predominantly determined the molecular weight and the monomer conversion for the polymerized product. The lower monomer conversion in toluene was ascribed to a lower livingness for the initiator in the nonpolar solvent when compared with other two, polar solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2194–2201, 2003     

Anionic polymerization of vinylsilanes

Summary The anionic polymerization of dimethylphenylvinylsilane with sec-butyllithium/N,N,N,N-tetramethylethylenediamine (TMEDA) was investigated. The polymerization proceeded up to 100% yield and afforded the polymer having isomerized-structure units. The polymerization was accompanied by chain transfer reaction to the monomer and the polymerization rate in the presence of TMEDA was much lower than in the absence of TMEDA.     

Anionic polymerization of acrylates

Summary The article presents preliminary results of the anionic polymerization of 2-ethylhexyl- and butyl acrylates initiated by ester enolate in the presence of Li 3-methylpentoxide-3. Compared with the Li t-butoxide which has been widely used earlier, this alkoxide is a more efficient stabilizer of active centers. Under selectively chosen reaction conditions, polymerizations of both monomers proceed quantitatively with a small extent of the selftermination event at-40 and-20°C producing polymers with narrow MWD's.     

Anionic polymerization of MMA initiated by organolithium/cuprum diphenylphosphide (Ph2PCu) and synthesis of its block copolymer

Organolithium/cuprum diphenylphosphide (Ph₂PCu) was used as a novel initiator to polymerize methyl methacrylate (MMA) and styrene in tetrahydrofuran (THF) at −50 to −10°C. The polymerizations initiated by n-BuLi/Ph₂PCu, Ph₂PCu/Li (Ip)_3-6Li/Ph₂PCu, and PSLi/Ph₂PCu were studied in detail. The polymerization of alkyl methacrylate initiated by n-BuLi/Ph₂PCu showed a narrow molecular weight distribution (MWD) (1.08–1.25) and 100% initiation efficiency. The experimental number average molecular weight increased linearly with increasing [MMA]/[n-BuLi/Ph₂PCu]. After the second monomer addition, the molecular weight increased proportionally while the MWD remained constantly narrow. These results reveal partial living characteristics. Ph₂PCu/Li (Ip)_3-6Li/Ph₂PCu showed a similar behavior and was used to prepare PGMA-b-PBMA-b-PMMA-b-PBMA-b-PGMA successfully. The initiation efficiency of n-BuLi/Ph₂PCu for styrene was low. The macromolecular initiator PSLi/Ph₂PCu was prepared and PS-b-PMMA with a narrow distribution was synthesized. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Anionic copolymerization of butadiene and styryl-terminated polystyrene macromonomers

Summary For the preparation of graft copolymers of the type poly (butadiene-g-styrene), possibilities were investigated both of obtaining a living anionic copolymerization of butadiene and styryl-terminated polystyrene macromonomers and of assessing the necessary analytical prerequisites for determining the conversion. The course of this copolymerization can be observed by combining gravimetry with SEC. With the initiator system sodium tert-butoxide /n-butyl lithium there are only a few deviations from the statistically ideal course of copolymerization and the macromonomer is almost completely incorporated into the copolymer.     

Electrochemically initiated copolymerization of some acetylenic derivatives

Summary Electrochemically initiated copolymerization of some donor and acceptor acetylenic monomers (phenylacetylene and diphenyldiacetylene as donors and methyl propiolate as acceptor) was studied.     

Anionic polymerization of methyl acrylate

The homogeneous polymerization of methyl acrylate in tetrahydrofuran using a variety of sodium aryl catalysts has been investigated at ?75°C and ?30°C. The mode of action of each catalyst is discussed and its efficiency in producing high polymer has been calculated from the yields and polymer characteristics. Sodium trityl is the most effective catalyst at both temperatures. Dilatometry has shown that with sodium naphthalene at ?70°C, rapid initial polymerization to about 10% conversion in 4 min is followed by a very low rate period which proceeds at low temperature for at least 24 h when conversions up to 50% have been observed. Throughout this period a species is present which absorbs at 320 nm and which is immediately lost on addition of a proton donor. There is evidence suggesting that this dormant form of the poly(methyl acrylate) anion is an oxyanion. It is postulated that carbanions are formed initially and are responsible for the rapid polymerization rate. They also isomerize in an equilibrium reaction to form the unreactive oxyanions. The rate of further propagation is thus controlled by the value of the equilibrium constant which in this system is strongly in favour of the oxyanions. On the basis of this mechanism some rate constants have been calculated.     

Anionic polymerization of vinylsilanes VII

Summary. The anionic polymerization of tetravinylsilane (TeVS) was carried out in the presence and absence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Without TMEDA, the polymerization proceeded extremely slowly and the polymer yield was still low even after an extended polymerization time. When TMEDA was added to the system, the polymerization was remarkably accelerated and gelation was suppressed. Such polymerization behavior of TeVS is closely similar to that of methyltrivinylsilane under similar conditions. The effects of TMEDA are explained by its coordination to the propagating end that increases the selectivity in the reaction of the propagating end with vinyl groups. Received: 29 March 1997/Revised: 14 July 1997/Accepted: 18 July 1997     

Electroinitiated polymerization and copolymerization of phenylacetylene

Summary A linear conjugated polymer [(C₆H₅C=CH)] _n, with a trans rich, cis-trans copolymer structure results from the electropolymerization of phenylacetylene.     

APS-RH引发氯化二甲基二烯丙基铵与丙烯酰胺溶液共聚合反应

利用过硫酸铵-亚硫酸氧钠(APS-RH)引发体系,研究了聚合反应的温度、丙烯酰胺(AM)对氯化二甲基二烯丙基铵(DMDAAC)的物质的量比等因素以及几种不同的氧化-还原体系对DMDAAC-AM共聚反应规律的影响.在w(DMDAAC+AM)=30%;w(APS)=0.01%时,适宜的反应条件为:n(AM):n(DMDAA...     

Cationic polymerization of cyclopentadiene initiated by bifunctional trityl salts evidence for a direct addition of the initiator and application to block copolymerization

A chemical evidence for the fixation of triphenylmethyl cation in the initiation step is given in the case of cyclopentadiene polymerization initiated by stable trityl salts. With SbCl₆ as counter ion, negligible transfer reaction takes place at 0°C. The situation is more complex with SbCl₅OH^–. Mono and bifunctional trityl salts have also been used for the synthesis of AB and ABA block copolymers.     

六亚甲基亚氨基锂引发的丁二烯负离子聚合动力学

研究了以六亚甲基亚氨基锂(LHMI)为引发剂、环己烷为溶剂、TMEDA为极性调节剂的丁二烯自聚。其中LHMI可以预先制备,也可以在聚合体系中原位合成。当TMEDA/LHMI质量比小于2时,速率常数(Kp')随着TMEDA/LHMI的增大而升高。与正丁基锂引发体系的Kp'相比,相同条件下LHMI引发体系的Kp'变化不大,说明LHMI不起调节剂的作用。     

Ring-opening polymerization of lactide initiated by magnesium and zinc alkoxides

A mono methylether Salen-type ligand, SalenMe-H (1) is prepared in a one flask reaction by condensation of trans-1,2-diaminocyclohexane with 2-methoxybenzenaldehyde and followed by the addition of 2,4-di-tert-butylsalicylaldehyde. Further reaction of 1 with Mg(OBn)₂ in THF produces a magnesium alkoxide, [(SalenMe)Mg(OBn)]₂ (2). Compound 1 reacts with ZnEt₂ yields monomeric complex (SalenMe)ZnEt (3), which further reacts with 1 molar equiv of benzyl alcohol giving [(SalenMe)Zn(OBn)]₂ (4). Experimental results show that complexes 2 and 4 efficiently initiate the ring-opening polymerization of l-lactide and rac-lactide in a controlled fashion, yielding polymers with very low polydispersity indexes. Kinetic studies show a second-order dependency on [LA] and a first-order on [2] with magnesium complex 2 as an initiator. While zinc complex 4 is used as an initiator, the polymerization rate has a first order dependency on both [LA] and [4].