Butyl lithium, as initiator

Polystyrene was prepared by the anionic polymerisation of styrene in toluene plus THF mixtures (4 1 volume ratio) using n-butyl lithium as initiator. After removing a sample for analysis at this stage, the remainder of the living polystyrene was reacted with a five molar excess of trichloromethylsilane for 15 min and then excess methanol introduced. The methoxy-terminated polystyrene was freeze-dried from dioxan. The method described here essentially follows the route proposed by Laible and Hamann (6). 

Polymerizations were carried out at 30°C in all glass, sealed reactors using breakseals and standard high vacuum techniques (3). For the calorimetric measurements, a 1 liter sample of a 0.03M solution of each polymeric lithium compound with M of ca. 4,000 was prepared in benzene solution using sec-butyl-lithium as initiator and transferred to the glove box. 

Rossi has synthetized block copolymers polyisoprene-poly(vinyl-2-pyridine) and polyisoprene-poly(vinyl-4-pyridine) of various composition and molecular weight by anionic polymerization under high vacuum205, 208. The polymerization in THF dilute solutions with Cumylpotassium as initiator yielded a 1,2 + 3,4-microstructure of the polyisoprene block. The polymerization in toluene solutions with sec-butyl-lithium as initiator yielded a 1,4-c/s-microstructure of the polyisoprene block. 

The data under discussion were obtained in the course of a study of the anionic polymerization of isoprene in benzene at 35.1° C. Earlier work on the polymerization using -butyl lithium as initiator in a number of hydrocarbon solvents had shown that the kinetic behaviour was complicated. For example, the isoprene concentration-time curves were sigmoidal and the ratio of the number of moles of isoprene consumed to the number of moles of n-butyl lithium reacted increased as the reaction proceeded. These and other complications showed that the rate of the reaction could not possibly be represented by an equation of the type... 

Table 22-15. The Anionic Copolymerization of Styrene (Md with Isoprene (M2) with Butyl Lithium as Initiator...

Styrene polymerization in hexane with sec-butyl lithium as initiator 135... 

Studies of the copolymerizations of 1,1-diphenylethylene and dienes showed rather different behavior compared with the copolymerizations of styrene and 1,1-diphenylethylene [125, 133-136]. The monomer reactivity ratios for copolymerizations of dienes with DPE are shown in Table 7. When butadiene was copolymerized with 1,1-diphenylethylene in benzene at 40 °C with -butyl-lithium as initiator, the monomer reactivity ratio for butadiene, ri, was 54 this means that the addition of butadiene to the butadienyl anion is 54 times faster than addition of 1,1-diphenylethylene to the butadienyl anion [133]. This unreactivity of poly(butadienyl)lithium towards addition to DPE was also observed in studies of end-capping of poly(butadienyl)lithium with DPE in hydrocarbon solution (see Sect.3.3) [109, 111]. Because of this unfavorable monomer reactivity ratio, few DPE units would be incorporated into the co-... 

The kinetic model describes the carbanion polymerization of styrene in a hydrocarbon solvent using n-butyl lithium as the initiator. The mechanism is characterized by four steps ... 

Polymer Synthesis and Characterization. This topic has been extensively discussed in preceeding papers.(2,23,24) However, we will briefly outline the preparative route. The block copolymers were synthesized via the sequential addition method. "Living" anionic polymerization of butadiene, followed by isoprene and more butadiene, was conducted using sec-butyl lithium as the initiator in hydrocarbon solvents under high vacuum. Under these conditions, the mode of addition of butadiene is predominantly 1,4, with between 5-8 mole percent of 1,2 structure.(18) Exhaustive hydrogenation of polymers were carried out in the presence of p-toluenesulfonylhydrazide (19,25) in refluxing xylene. The relative block composition of the polymers were determined via NMR. 

Polymers - The PS, PDMS, polyhexylisocyanate (PHIC), and polylso-prene (PI) samples had been extensively characterized to determine molecular weights, molecular sizes, and thermodynamic parameters (5, 6, 7 ). The samples were anionlcally polymerized using butyl lithium as the initiator. The pertinent data are shown in Table L Polylsobutylene/PIB polymers were obtained by fractionation of commercial polymers and their molecular weights were measured (8). 

A dramatic development in the anionic polymerization of acrylate and methacrylate monomers was the discovery that by addition of lithium chloride it was possible to effect the controlled polymerization of f-butyl acrylate [122]. Thus, using oligomeric (a-methylstyryl)lithium as initiator in THE at -78 °C, the molecular weight distribution of the... 

In contrast to block copolymers of two methacrylates, block copolymers of a methacrylate and styrene can only be prepared anionically by polymerizing styrene first. As shown in Scheme 25, well-defined (pdi = 1.03-1.11) diblock copolymers of styrene and 6- [4 -(4"-Methoxyphenyl)phenoxy]hex-yl methacrylate (PS - PMPPHM) were synthesized directly by sequential anionic polymerization of styrene and then the methacrylate in THF at -78 °C using 5-butyl lithium as the initiator [44]. The reactivity of the growing polystyrene anions were reduced by reaction with 1,1-diphenylethylene be-... 

Attempts to copolymerize 15 with styrene in an analogous manner failed due to decomposition of the cluster. However, copolymerization was accomplished by use of n-butyl lithium as an anionic initiator. In this case, a benzene solution of styrene and 15 (in a 100/1 mole ratio) was treated with a trace of n-butyl lithium. After 20 hours, methanol was added to the mixture in order to quench the reaction and cause precipitation of the resulting polymer, which was then purified by repeated precipitations from methylene chloride. Spectroscopic characterization of the polymer confirmed that the cluster had been chemically incorporated into the polymer, with a loading of 0.67 mole per cent. 

Myrcene is, to our knowledge, the only monoterpene which has been the object of living anionic polymerization (LAP) and copolymerization studies [91]. These systems involved A -butyl lithium as the initiator, and either benzene or THF as solvent. When the reaction was carried out in the former, 1,4-addition was favoured (85-90 per cent). 

The polystyryl monocarbanion 4 was prepared in THF at -78 C using sec-butyl lithium as the initiator while the polystyryl dicarbanion (Scheme 2) was prepared using sodium naphthalene as the initiator. The initiator was added first followed by the styrene. A bright, reddish orange-colored solution was obtained confirming the presence of the polystyryl carbanions. 

A dramatic development in the anionic polymerization of acrylate and methacrylate monomers was the discovery that by addition of lithium chloride it was possible to effect the controlled polymerization of f-butyl acrylate (86). Thus, using oligomeric (o -methylstyryl)lithium as initiator in THF at —78°C, the molecular weight distribution (M /Mn) of the polymer was 3.61 in the absence of lithium chloride but 1.2 in the presence of lithium chloride ([LiCl]/[RLi] = 5). In the presence of 10 equiv of LiCl, f-butyl acrylate was polymerized with 100% conversion and 95% initiator efficiency to provide a polymer with a quite narrow molecular weight distribution (My,/Mn = 1.05). More controlled anionic polymerizations of alkyl methacrylates are also obtained in the presence of lithium chloride. Other additives, which promote controlled pol5unerization of acylates and methacrylates, include lithium f-butoxide, lithium (2-methoxy)ethoxide, and crown ethers (47,48). The addition of lithium chloride also promotes the controlled anionic polymerization of 2-vinylpyridine. 

Styrenic block copolymers are made by anionic living polymerization using sec-butyl lithium as a preferred initiator in non polar solvents such as cyclohexane or toluene.In the normal sequential polymerization, the initiator reacts with a molecule of styrene to form a polystyryol lithium species which then propagates with transfer of the initiator anion to the active chain end. 

In our early work on the coupling reaction we used equimolar amounts of pyridine and sec-butyl lithium as the initiator in THF solvent at -78°C. When polymerization was complete an aliquot was removed to isolate a sample of uncoupled control polymer, and to the remainder was added a stoichiometric amount of 1,4-bis-(a-bromomethyl)benzene to effect the transformation. 

The end block of SAMS copolymer was polymerized first in some preparations in AMS solvent. In this case, AMS was added and blanked with butyl-lithium as before. Styrene monomer and s-butyllithium for initiation were then added to start the SAMS polymerization at temperatures above 50°C. At the time designated for butadiene addition, a small amount of the butadiene monomer was bled in first. The remaining butadiene was added after the reaction solution was cooled to near 5°C. The reaction solution was then brought back to about 50°C for a period of 70 to 80 minutes for the... 

Ito and co-workers [39] applied C-NMR to the determination of end groups in PS polymerised anionically with n-butyl lithium as the initiator. Polymers with molecular weights between 1000 and several million were included in this study. 

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