Anionic Polymerization of Vinyl Monomers

Abstract

Addition polymerizations involving soluble organometallic species have received intensive attention in recent years with special reference to the type of counterion and solvent. An anionic mechanism is proposed for those systems where there is good reason to assume that the metal is strongly electropositive relative to the carbon (or other) atom at the tip of the growing chain. Hence, the metal, e.g. lithium, becomes a cation either in the free state or coupled with the growing carbanion. Under the appropriate experimental conditions, spontaneous termination is avoidable in many of those systems when one of the metals of Group I is used as the counterion. The alkali metals sodium and potassium were revealed to be polymerization initiators of isoprene in the disclosures of Matthews and Strange in 1910 and Harries in 1911. The first unambiguous report of the use of lithium in reactions with diolefins appears to be that of Ziegler and coworkers in 1934. Their work consisted of an investigation of the reaction between the alkali metals (lithium, sodium) or alkyllithium species and butadiene, isoprene, 2,3-dimethylbutadiene, or piperylene.

Interaction of Paraffin Wax Gels with Random Crystalline/Amorphous Hydrocarbon Copolymers

“…For higher paraffin content (Figure 6c) 3-D paraffin crystals indicated by the Q -4 power law at low Q seem to coexist at low temperatures with the hairy plate structures that define the scattering at high Q. From a more detailed analysis presented in ref 27 a cocrystallization process of C 24 and polymer into platelet structures is proposed where the very thin paraffin plates are monolayer tetracosane crystals with a thickness of 32 Å while the polymer structures are about five times as thick. Figure 7 displays the scattering patterns of the mixed solutions of PEB-7.5 with different tetracosane contents for several temperatures of interest.…”

“…This indicates that a sufficient amount of wax must precipitate from solution before a percolating gel network is formed. Indeed, because the C 24 wax is the most soluble examined, the strength of this gel is most sensitive to temperature since C 24 precipitates over the widest range of temperatures. The longer chain paraffins, on the other hand, precipitate over a relatively narrow temperature range, ln…”

Thermodynamics and Phase Behavior of Block Copolymer/Homopolymer Blends with Attractive and Repulsive Interactions

“…A partially deuterated poly(ethylene-block-head-to-head propylene) copolymer (PE-PP) and a fully hydrogenous polyisobutylene (PIB) homopolymer were synthesized and characterized by methods described in refs [43][44][45]. The chemical structures of the polymers (ignoring the deuterium labels) are shown in Figure 1.…”

Experimental techniques in high‐vacuum anionic polymerization

“…A round-bottom flask is attached to the vacuum line, and the stopcock is opened to the vacuum for a few seconds until the liquid begins to bubble, at which point the stopcock is closed. The following sequence is now repeated: (1) freeze the liquid, (2) open the stopcock to the vacuum line for a couple of minutes, (3) close the stopcock, and (4) thaw the liquid and stir it briskly for a couple of minutes. Each time the liquid is refrozen, the equilibrium is shifted so that dissolved gases may escape and be removed by the vacuum pump.…”

“…Classic reviews of these techniques that remain relevant today were written by Fetters 1 and by Morton and Fetters. 2 Hadjichristidis et al 3 published a more recent technical review that very well captures many of the advances made within this synthetic discipline over the last 20 years and contains excellent descriptions of the basic high-vacuum procedures, reagent preparation and purification, polymerization techniques, and some details on the synthesis of complex architectures using anionic polymerization.…”