Anionic oligomerization, styrene

Anionic initiator, PMMA H spectra, 4 Anionic oligomerization, styrene, 182... 

There are also examples where the non-cross-linked polymeric reagent is most readily available by direct polymerization of suitably functionalized monomers. For example, polymerization of a crown ether which contains styrene units is possible by free radical or anionic methods (15). In the case of anionic oligomerization (Equation 6) or in the case of the metalation shown in Equation 4, the reactive intermediate macromolecule is a nucleophilic polymer which can be derivatized with a variety of electro-... 

Anionic oligomerization with slow chain initiation or transfer Oligo-styrene and other vinyl oligomers 10" - 10 ... 

Examples include control of molecular weight in step-growth polymerization, number-average degree of polymerization in step-growth polymerization of nonstoichio-metric monomer mixtures, free-radical and anionic polymerizations of styrene, and ethene oligomerization to linear 1-olefins in the Shell Higher Olefins Process. 

Rhodium Catalysts. The catalytical behavior of Rh complexes in oligomerizations has been extensively studied " . A wide variety of olefins such as a-olefins, chlorinated olefins, styrene, and acrylates (but not acrylonitrile) are dimerized by RhClj-SHjO. The reactions are carried out at T from 20 to 200°C and are generally not very dependent on the solvent, although small amounts of alcohols lead to increased activity. A detailed insertion mechanism based on an anionic Rh(III)-H-intermediate has been suggested but a carbene mechanism and a metallacycle pathway have also been discussed. 

A few examples are in place. Carbanions are good initiators of polymerization of many vinyl and diene monomers. Their reactivities decrease along the series primary, secondary, tertiary. Thus, benzyl carbanion is a poor initiator of styrene polymerization, whereas the oligomeric a-methyl styrene anions or cumyl carbanions are very efficient110. ... 

Oligomerization Reactions. Lithium naphthalenide has long been a convenient initiator for anionic living polymerization reactions. Thus, styrenes, acrylates, dienes, and other monomers have been polymerized using lithium naphthalenide as an anionic initiator. In some circumstances, however, oligomerization can be controlled to furnish only dimers (eq 11). Also, in the presence of a secondary amine, 1,3-dienes can be persuaded to react in a formal 1,4-fashion to produce allyl amines (eq 12). ... 

The fact that alcohols are sufficiently nucleophilic to initiate the anionic polymerization of FO (a unique feature, not shared by other epoxides, including styrene oxide), provides a useful way of preparing block, star and graft copolymers from, respectively, diols, polyols and OH-bearing polymers such as cellulose and poly(vinyl alcohol). The FO blocks and grafts however, are oligomeric in size, because transfer reactions limit their growth [4d]. 

The polymerization of styrene anionically produces an atactic block. The typical end block molecular weight for polymers used in pressure-sensitive adhesives is below the 18,000 Da entanglement molecular weight of polystyrene (see Table 15.3). Thus the softening point of these polymers is less than that of pure polystyrene. Like the tackifiers and oils discussed below, the polystyrene end blocks are in the oligomeric region where properties still depend on molecular weight (see O Fig. 15.18). 

---