Coordination Polymerization

In the early 1950's a major new polymerization tecnique was dissolved that led to the production of polymers with unusual stereospecific structures. Although there were earlier indications of this type of polymerization, the field actually came into existence with the work of Ziegler (1955) and Natta (1955), who developed new polymerization catalyst with unique stereoregulating powers. Their Nobel Prize addresses (Ziegler 1964, Natta 1965) form excellent introductions to the field.

Since the earliest days, a number of names have been applied to the polymerization technique using what have become known as Ziegler or Ziegler Natta catalyst. Some have emphasized the stereoregulating features of certain of these polymerization, but that is not an essential feature. The term polyinsertion is still used, suggestive of chain propagation by the insertion of a monomer between the catalyst and the polymer chain to which it is attached, but the term coordination polymerization, used early to suggest the essential feature of a coordination complex with the catalyst, has remained and has been justified by mechanistic studies.

Coordination polymerization is far from simple in term of mechanism, kinetics, or application. The most important catalyst systems are known. Additional complications to the study of coordination systems arise because the same catalysts, under other conditions, can initiate polymerization by cationic, anionic, or even free radical mechanisms. One often coordination polymerization is carried out using a catalyst in the form of a slurry of small solid particles in an inert medium or a supported solid catalyst. Heterogeneous polymerization is not essential for coordination and the development of stereospecificity, however, for sufficient polar monomers.

Propagation and Termination Reaction

The chain radical formed in the initiation step is capable of adding successive monomers to propagate the chain:

R-(CH₂CHX-)CH₂CHX• + CH₂=CHX -----> R-(CH₂CHX--)_x+1CH₂CHCHX•

Termination
Propagation would continue until the supply of monomer was exhausted were it not the strong tendency of radicals to react in pairs to form a paired-electron covalen bond with loss of radical activity. This tendency is compensated for in radical polymerization by the small concentration of radical species compared to monomers.

The termination step can take place in two ways, combination or coupling:

-CH₂CHX• + •CHXCH₂-  -----> -CH₂CHX-CHXCH₂-

or disproportionation:

-CH₂CHX• + •CHXCH₂-  ------->  -CH₂CH₂X + CH₂XCH₂-

in which hydrogen transfer result in the formation of two molecules with one saturated and one unsaturated end group. Each type of termination is known. For example, studies of the number of initiative fragments per molecule showed that polystyrene terminates predominantly by combination, whereas poly(methyl methacrylate) terminates entirely by disproportionation at polymerization temperatures above 60^oC, and partly by each mechanism at lower temperatures. The termination reaction, controlled by diffusion in many cases, has been reviewed.

Raw Material For Plastic

Raw material for plastic currently use mostly from plastic waste in order they can sell cheaper than use original plastic seed. The quality of product is not good enough but the price is cheaper than other plastic. Many product sell with bad quality but people only find cheap plastic product don't see the quality of material. The raw material is accumulated from plastic waste material usually from thermoplastic type. This waste then grinding into small piece and then heated, melted and molded into plastic seed material.

Not all plastic waste can be recycled and reprocess into plastic material again, only plastic from thermoplastic source can be recycled again. Other kind of plastic can't be recycled usually they can't melt after heat with certain temperature, they tend to burn and not melt.