If some head-to-head configuration is detected in a polymer chain known to propa

Question

If some head-to-head configuration is detected in a polymer chain known to propagate by head-to-tail addition, what type of termination has occured?

What effect does the increase of solvent polarity have on a free-radical polymerization?

Why does polymerization not take place in the droplets instead of in the micelles in emulsion polymerization?

In general, which is more rapid: A) addition or B) condensation polimerization?

What species in addition to deed polimer, is produced in a chain transfer reaction with a microcarbonation in a cationic chain polymerization?

Name a common initiator cationic and anionic chain polymerization

Explanation / Answer

1.

For example, when propylene is polymerized, the monomers can arrange themselves along the chain in three different ways. If we call the CH2 end of the propylene the "head" and the CH(CH3) end the "tail", then a head-to-tail polymerization would lead to a polymer chain with a methyl group (CH3) located on every other carbon .On the other hand, if the polymerization occurred in a head-to-head, tail-to-tail fashion, methyl groups would be located on adjacent carbons in pairs. A third possibility involves random orientation of monomer units along the polymer chain. These three different structural forms of polypropylene would be expected to have different physical properties. Generally, the head-to-tail polymer is produced using heterogeneous Ziegler-Natta or homogeneous cyclopentadienyl-zirconium catalysts.

The polymer is terminated by hydrogens.

2. The polymerization is strongly accelerated in the aqueous medium, with the polymerization rate increasing one order of magnitude when the solvent is changed from an organic one to aqueous medium. These results were analysed in terms of macroradical conformation, effect of medium viscosity, aggregate formation, hydrogen bond formation and effect of temperature. The results suggest that the main factor that controls the polymerization rate is a kinetic effect due to the hydrogen bonding between the amide carbonyl group and water molecules.

3. At the beginning of the reaction it exists in the form of micelles. Part of the monomer enters the micelles, but most of it exists as droplets a micrometer or more in diameter. In the ideal case no polymer is formed in the monomer droplets.

4. addition reactions,in general,are more rapid than the condensation reactions and area,therefore,more difficult to interrupt and modify.

5. a carbocationic species in addition to deed polimer, is produced in a chain transfer reaction with a microcarbonation in a cationic chain polymerization.

6.A common initiator in an anionic polymerization is sodium naphthalide

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