Polystyrene polystyryl anions

Polystyrene bisperoxides can be prepared by the termination of polystyryl anion with bromo methyl benzoyl peroxide [9] ... 

The order of reactivities could be also reversed by a change of solvent. For example, in THF styrene is more reactive than butadiene towards salts of polystyryl anions, whereas in hydrocarbon solvents butadiene is more reactive than styrene towards lithium polystyrene. This reversal of reactivities presumably is caused by a change in the mechanism of propagation. The monomers react directly with carbanions in THF, but become coordinated to Li+ in hydrocarbon solvents. 

Figure 9.2 Size exclusion chromatography traces for raw grafting products formed in the coupling reaction of chloromethylated polystyrene with polysty-ryllithium (a) without 1,1-diphenylethylene capping, and (b) with capped polystyryl anions (adapted from ref. [4])...

Preparation of desired molecular weight polystyryl carbanion ( Living Polystyrene ) by anionic polymerization (Fig. 2). Anionic polymerization has been used extensively to provide control over molecular weight with narrow molecular weight distribution. 

When a tetra-chain, star-shaped polystyrene is prepared by a coupling reaction between living polymer and coupler (e.g 1,2,4,5-tetrachloromethyl benzene), the reaction is often carried out with the polystyryl anion in slight excess in order to avoid by-production of types of branched polystyrene other than the tetra-chain. 

By virtue of this reaction, the whole product is apt to contain a certain amount of precursor polystyrene. Such a crude product, coded S-A, for which the polystyryl anion was added in high excess, was used as the sample. The precursor polystyrene had a weight-average molecular weight (Mw) of 2 x 104, and 8 x 104 was expected for the molecular weight of star-shaped component. 

A bimolecular process was reported by two independent groups, i.e., Hocker [19] and Rempp [20] in 1980. Macrocyclic polymers have been successfully prepared by the coupling reaction of a two-ended living polystyryl anion with a difunctional electrophile such as a, a -dibromo-p-xylcnc under high dilution to yield cyclic and linear mixtures. The cyclic polymer was isolated by a fractional precipitation. This bimolecular end-to-end reaction process has been used for synthesizing cyclic polystyrene by many researchers [21-25]. 

The reactions are just like the ones that produce polystyrene. First, a molecule of methyl methacrylate reacts with a polystyryl anion to form a methyl methacrylate anion (crossover). Then the methyl methacrylate block grows in a series of propagation steps, followed by the addition of methanol to effect termination as before. We can draw the structure for the block copolymer, named poly styrene-6/oe -methyl methacrylate) as is shown here. 

A method for preparing star-shaped polystyrene by either the incremental or single addition of divinyl benzene to a living polystyryl anion is described. Star-shaped polymers containing up to 34 arms were prepared with polydispersities of less than 1.1. 

The styrene/methyl methacrylate pair contains monomers with different relative reactivity levels in Table 9-1. Polystyryl anion will initiate the polymerization of methyl methacrylate, but the anion of the latter monomer is not sufficiently nucleophilic to cross-initiate the polymerization of styrene. Thus the anionic polymerization of a mixture of the two monomers yields polyfmethyl methacrylate) while addition of methyl methacrylate to living polystyrene produces a block copolymer of the two monomers. 

One of the most useful properties of polymerization systems involving styrene or the dienes is the appearance in the solutions of colour associated with the actual active centres. For example, living polystyrene solutions in tetrahydrofuran show a strong red colouration which disappears immediately on the introduction of a trace of oxygen, water or carbon dioxide. The source of this colour is a strong absorption band (e 10 ) in the near-ultraviolet region of the spectrum. The positions of the maximum and intensity of absorption are not very sensitive to changes in solvent or counter-ion (Fig. 1) [Xmax polystyryl anion 328—346 mp, 1.2—1.4 x 10 Xmax polyisoprenyl anion 270—315... 

The living nature of polystyryl anion has been applied for the system of diblock, triblock, and multiblock copolymers [67 70]. Examples for commercial products are Kraton rubber (Shell Oil Co.), a styrene butadiene styrene triblockcopolymer, and Styrolux (BASF AG), a styrene-butadiene-styrene starblockcopolymer. First, a block polystyrene can be prepared that remains active then a new monomer can be added. Termination with dimethylsilicium dichloride yields a triblock copolymer ... 

The chemical structures of the highly branched living linked polystyryl anion using 4 chloro dimethylsilyl styrene (CDMSS) end-capped polystyrene is depicted below ... 

Anionic polymerisation of hydrocarbon monomers is initiated by lithium butyl to produce a living polymer the association number of which in solution is required to elucidate the kinetics. When the living polymer (for example polystyryl lithium) is terminated, the polystyrene can be isolated and a solution then made to determine its molecular weight, M. If the living polymer is associated in solution, the ratio of its... 

Thus polystyryl carbanions and polyacrylonitrile carbanions prepared by anionic polymerization were reacted with cellulose acetate or tosylated cellulose acetate in tetrahydrofuran under homogenous reaction conditions. The carbanions displaced the acetate groups or the tosylate groups in a S v2-type nucleophilic displacement reaction to give CA-g-PS and CA-g-PAN. Mild hydrolysis to remove the acetate/tosylate groups furnishes the pure cellulose-g-polystyrene (Figure 3). 

The use of polysilanes as photoinitiators of radical polymerization was one of the hrst means whereby they were incorporated within block copolymer structures [38 0], albeit in an uncontrolled fashion. However the resulting block copolymer structures were poorly defined and interest in them principally lay in their application as compatibilisers for polystyrene (PS) and polymethylphenylsilane blends PMPS. The earliest synthetic strategies for relatively well-defined copolymers based on polysilanes exploited the condensation of the chain ends of polysilanes prepared by Wurtz-type syntheses with those of a second prepolymer that was to constitute the other component block. Typically, a mixture of AB and ABA block copolymers in which the A block was polystyrene (PS) and the B block was polymethylphenylsilane (PMPS) was prepared by reaction of anionically active chains ends of polystyrene (e.g. polystyryl lithium) with Si-X (X=Br, Cl) chain ends of a,co-dihalo-polymethylphenylsilane an example of which is shown in Fig. 2 [43,44,45]. Similar strategies were subsequently used to prepare an AB/ABA copolymer mixture in which the A block was poly(methyl methacrylate) (PMMA) [46] and also a multi- block copolymer of PMPS and polyisoprene (PI) [47]. 

A variation of the sequential monomer addition technique described in Section 9.2.6(i) is used to make styrene-diene-styrene iriblock thermoplastic rubbers. Styrene is polymerized first, using butyl lithium initiator in a nonpolar solvent. Then, a mixture of styrene and the diene is added to the living polystyryl macroanion. The diene will polymerize first, because styrene anions initiate diene polymerization much faster than the reverse process. After the diene monomer is consumed, polystyrene forms the third block. The combination of Li initiation and a nonpolar solvent produces a high cis-1,4 content in the central polydiene block, as required for thermoplastic elastomer behavior. 

Nucleophilic substitution with the phenolate anion derived from EC-20 and K2C03 induced 30% substitution, along with elimination of hydrogen bromide.331 Phosphonium groups can be introduced at the polystyrene and poly(MA) terminal via reaction with EC-21,355 and methyl groups with Me3Al (EC-22).356 An allyl terminal is obtained also via an ionic pathway, where the polystyryl carbocation generated... 

Blocks. The synthesis of block copolymers were attempted in the following manner. "Living" polystyrene was first prepared by conventional anionic techniques using n-BuLi as the initiator in THF at -78 C. In initial experiments, this polystyryl lithium product was treated with AICI3 to afford a polystyryl A1 species which could be capable of alkylating Ti(0Bu)4. However, we find it to... 

A typical polymer-modified organoclay for the preparation of PS nanocomposites could be a PS polymer with some cationic sites to be attached to the clay surface. Polystyryl quaternary ammonium salts (PSQAS) were synthesized via three different polymerization routes anionic polymerization (AP), free radical co-polymerization (CP), and chloromethy-lation of polystyrene (CM) [67] (Table 3.6). TGA results indicated that CP-PSQAS and CM-PSQAS were thermally stable, because the C-C bonds in aromatics are much stronger than those in aliphatic compounds. The polystyryl-modified clays exhibited intercalated or partially exfoliated structures. 

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