Maurice Morton

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 th...

Swelling of latex particles

Abstract A theoretical relation has been derived for the equilibrium swelling of latex particles. The equilibrium solubility and rate of solution of solvents were measured on a series of polystyrene latex fractions of varying particle size. The solvents used were styrene, toluene, and chlorocyclohexane. It was found, as predicted by theory, that the equilibrium amount of solvent imbibed by latex particles is a direct function of the particle diameter and an inverse function of the interfacial energy at the surface of the particles. The molecular weight of the polymer has no effect on the equilibrium swelling, within the range from 100,000 to several million molecular weight units. The rate of imbibition of these solvents appears to be extremely rapid, indicating that equilibrium solubility would appear to be maintained in most polymerization reactions. The fact that a particular solvent is a “good” solvent for the polymer does not necessarily result in a greater swelling of the particles, since the solvent may show a higher interfacial energy against the aqueous phase. The soap titration method is best for determining the average particle size of a latex for purposes of predicting equilibrium swelling.

ABA Block Copolymers of Dienes and Cyclic Sulfides

Abstract ABA block copolymers have been synthesized in which the center block was polyisoprene or polybutadiene and the end blocks were polyethylene sulfide or polythiabutane. The latter were shown to crystallize, leading to mechanical properties analogous to those of the “thermoplastic elastomers.”

Structure-property relations in amorphous and crystallizable ABA triblock copolymers

Abstract The properties of the thermoplastic elastomers derived from ABA triblock copolymers depend largely on the nature of the A blocks, which form rigid, thermoplastic domains holding the elastic network together. These domains may be either amorphous or crystalline in nature, the former resulting from an inherent incompatibility between the A and B blocks, while the latter form by normal crystallization processes. It can be demonstrated convincingly that the formation of the amorphous (glassy) domains is enhanced by a higher degree of incompatibility between the A and B blocks and that the strength of the material depends on the degree of phase separation and on the integrity of the amorphous domains. However, the viscosity increases with increasing incompatibility between the two phases, presumably because the two-phase morphology persists even in the melt. On the other hand, the presence of crystallizable A blocks, which do not phase separate in the melt, leads to good flow properties. However, the ...

Anionic polymerization characteristics of the 1:1 complex of n-butylsodium and n-, s-dibutylmagnesium (sodium tributylmagnesiate)

Abstract The behavior of isoprene and styrene polymerizations initiated by the complex of n-butylsodium and n-,s-dibutylmagnesium (sodium tributylmagnesiate) has been examined. The styrene-benzene system was found to yield stable active centers and polymers of predictable molecular weight and narrow molecular weight distributions. Isoprene, however, did not follow this behavior and yielded polydisperse material having molecular weights lower than those predicted on the basis that only n-butylsodium is capable of initiating chain growth. The polyisprene microstructure was found to consist of ∼60% 3,4 and ∼40% 1,4 units.

History of Synthetic Rubber

Abstract Synthetic rubber undoubtedly represents the earliest development of the synthesis of macromolecules. It dates back to the historic discovery by Greville Williams in 1860 that isoprene is the “mother substance” of natural rubber. Attempts to convert isoprene, and later other 1,3-dienes, to a synthetic rubber began shortly thereafter, although the first commercial production of such a material did not take place until a half century later. The period between World War I and II witnessed the first development of a true synthetic substitute for natural rubber, i.e., sodium-polymerized butadiene, which was produced in Germany as Buna rubber and in the USSR as SK rubber. However, during the 1930s, Germany developed the emulsion copolymerization of butadiene-styrene (Buna S), whereas sodium polybutadiene continued as the principal general purpose synthetic rubber in the Soviet Union. The United States which, up till then, had only developed special-purpose synthetic rubbers like neoprene, entered the sy...

High Performance Elastomers

The term “high performance elastomers” can, of course, be rather broadly defined. This is because of the unusual situation which prevails in the field of elastomers, and which is not really paralleled in any other area of polymer science. It arises from the fact that the use of rubber in industry and commerce began over 150 years ago, and is still greatly concerned today with natural rubber. Hence the development of the synthetic rubbers, which only date back about 50 years, depended strongly on their “high performance”, compared with the natural product. Of course, since those early beginnings, synthetic rubber has also filled part of the need for “general purpose” rubber. However, in selecting the particular synthetic rubbers for discussion at this symposium, I defined “high performance” as the ability of the material to withstand rather extreme ambient conditions, involving heat, chemicals, solvents, etc. Hence the fact that any given elastomer could do “as good a job as”, or even slightly better than, natural rubber, or at lower cost, should not, in my opinion, put it in the class of high performance.

Introduction to Polymer Science

Polymer science is concerned with the composition and properties of a large number of substances classed as “polymer,” which include rubbers, plastics, and fibers. The meaning of the term “polymer” will become clear during the course of this chapter, but it does involve some understanding of basic chemistry. The science of chemistry concerns itself with the composition of matter and with the changes that it undergoes. To the layman, the methods and processes of chemistry appear quite baffling and difficult to comprehend. Yet these are essentially based on a simple, logical development of knowledge about the substances which comprise our physical world. Since this book is not intended exclusively for readers trained in chemistry, the subject of polymer chemistry will be developed from the type of first principles comprehensible to anyone.

Rubber Enters the Polymer Age

Abstract I hope that this review of the highlights of my research and educational activities over the past 40 years has demonstrated how polymer science has taken over the fairly “ancient” art of rubber technology; and how both the methods of research used in and the career training required for mans utilization of this unique material are now firmly established as part of the science of macromolecules.

BRANCHING IN DIENES

Considerable interest has been shown recently in the possibilities of interaction between free radicals and polymer chains during the course of a polymerization reaction. In the case of vinyl polymerizations, where the monomer possesses only one double bond, such a reaction is generally considered to lead to chain transfer from radical to polymer, resulting in the growth of a branch on the original polymer chain. For a hydrocarbon polymer this branching reaction may be visualized as follows: