Лако-красочные материалы — производство

-r CH2— CHX-j — CH2— c L -*n-1 The radical formed by abstraction above is available to initiate propagation of another polymer chain. CH2— CHX- L CH2- CHX + RSH mercaptan 1 r CH2— CHX- b CH2- X о + RS *n mercapto radical The effectiveness of a chain transfer agent is measured in terms […]

Modifiers are species that contain a labile atom (most usually hydrogen or halogen) which can be abstracted by the propagating chain. Propagation of the chain is terminated and the radical is transferred to the modifier. R — f CH — CHxT — CH2 — CHX + R — H L Jn R — f CH […]

Transfer to monomer can occur in one of two ways. Both involve an abstraction process through which a hydrogen atom is transferred to the propagating chain. The free radical is transferred to the monomer to form a monomer radical. a) Abstraction from the Vinyl Carbon Atom. The monomer radical formed is free to initiate the […]

(i) Transfer to Solvent Here the polymerisation solvent acts as a transfer medium. Consider the following example of polystyrene homopolymerisation in carbon tetrachloride solvent:

This involves the removal of the radical from the propagating chain and the transfer of the radical to another chemical species. Both combination and disproportionation reactions result in the extinction of radicals. However, in the case of transfer reactions, the radical is not destroyed, but merely removed from the propagating chain and transferred to another […]

In order to terminate a growing polymer chain, it is necessary to effect the removal of the free radical from the polymer chain. This may be accomplished in one of several ways, but all involve either a “combination” reaction, a “disproportion” reaction or a “transfer” reaction. The exact mechanism will be dependent on the chemical […]

Once the monomer radical has been formed, propagation proceeds rapidly as the number of monomer units increases successively to produce a growing polymer chain. After each successive addition, the free radical is retained on the vinyl carbon atom of the end chain unit. RO—CH2— CHX + CH2 = CHX————- ► RO—CH2— CHX — CH2— CHX […]

Polymerisation may be initiated by one of three mechanisms: a) Free Radical Initiation b) Anionic Initiation B+A“ + CH2 = CHX -> A-CH2-CHX“B+ c) Cationic Initiation A~B++CH2 = CHX -> B-CH2-CHX+A“ Although most vinyl and acrylic monomers will undergo any of the above types of initiation, some of the polyether monomers can only be polymerised […]

Long chain molecules can be formed by the addition polymerisation of monomers of the general formula CH2 = CRX. Where R may be H, CH3 or a halogen and X includes halogen, aryl, amide, ester, substituted ester, nitrite and carboxyl groups. The polymerisation reaction can be represented as пСНг = CRX -> [CH 2 — […]

by PETER JONES Grad PRIEdited by Peter Oldring PhD BA Chapter One I INTRODUCTION The vinyl and acrylic group of resins is one of the most widely used in surface coating applications. Vinyl and acrylic resins may be used on their own or in blends with other resins. Coating resins can be divided into two […]