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What is chain branching?

What is chain branching?

So-called branching chain reactions are a form of chain reaction in which the number of chain carriers increases in each propagation. As a result the reaction accelerates very rapidly, sometimes being completed in less than 1/1,000th of a second.

What is long chain branching?

Long-chain branches are defined as those long enough to entangle, i.e., the branch molecular weight is more than two times the entanglement molecular weight (Me) of the polymer (Graessley 1974).

How is branching in the polymer chain?

In polymer chemistry, branching occurs by the replacement of a substituent, e.g., a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. Polymers which are branched but not crosslinked are generally thermoplastic.

What causes branching in LDPE?

Branching is caused during polymerization at high pressure by growth sometimes starting from an initiation point in a chain rather than at the end. An alternative way of making polyethylene is at low pressure using a special catalyst, and this usually results in a highly linear chain without branching (HDPE).

Which polymerization branching chain Cannot be possible?

Since we can see that it is linear in shape (no branching present) it cannot be a branched chain polymer. -About Bakelite: It is a cross linked polymer and thermosetting type of polymer. It is formed using phenol (C6H5OH) and formaldehyde (HCHO) monomers and hence is known as phenol-formaldehyde polymer.

What is stationary chain reaction?

VI) Chain Reactions In chain reactions, a product from a step in the mechanism is a reactant for a previous step (i.e. the reaction feeds itself). a) Stationary or stable chain reactions. The concentration of reactive intermediates is constant in time or slowly decreasing.

Does branching affect viscosity?

The smaller coil size of a branched chain will tend to decrease the viscosity, although branches long enough to entangle produce a broadened terminal zone and larger viscosity.

What are long chain polymers made by linking of several ester units?

Answer: Polyester, a class of synthetic polymers built up from multiple chemical repeating units linked together by ester (CO-O) groups. Polyesters display a wide array of properties and practical applications.

What is the effect of branching?

The effect of long chain branching depends on the differences in their chemical structure from that of the main chain and to a lesser extent on the degree of long chain branching. The physical characteristics of the polymer show the sharpest changes when tree-like branching occurs.

How does branching affect crystallization?

Short branches interfere with the formation of crystals, that is, they reduce the amount of crystallinity whereas long branches undergo side chain crystallization because they are able to form lamellar crystals of their own.

How can you tell the difference between LDPE and HDPE?

LDPE’s long- and short-chain branches keep the material from packing tightly in its crystalline form. This gives it less tensile strength than HDPE, but greater ductility….In a nutshell: the chemistry of LDPE and HDPE.

LDPE HDPE
Flexible Semi-rigid; tough
Good compression set Good compression set

How can you tell the difference between HDPE and LDPE?

LDPE’s long- and short-chain branches keep the material from packing tightly in its crystalline form. This gives it less tensile strength than HDPE, but greater ductility….In a nutshell: the chemistry of LDPE and HDPE.

LDPE HDPE
Good abrasion resistance Excellent abrasion resistance
Lightweight Lightweight

What are the results of a branching chain reaction?

description and results. In chain reaction So-called branching chain reactions are a form of chain reaction in which the number of chain carriers increases in each propagation.

Which is the first step in the chain mechanism?

Photooxidation of polyethylene proceeds by a free radical chain mechanism. There are four steps: initiation, propagation, chain branching, and termination. Initiation is caused by either the presence of initiator or the presence of hydroperoxide. The following equations show the initiation step:1

Which is an example of a chain reaction?

For example, the chlorination of ethane is a chain reaction, and its mechanism is explained in the following way. If we mix chlorine, , and ethane, , together at room temperature, there is no detectable reaction. However, when the mixture is exposed to light, the reaction suddenly initiates, and explodes.

What happens to radicals in a chain reaction?

Chain termination steps are elementary steps that consume radicals. When reactants are exhausted, free radicals combine with one another to give stable molecules (since unpaired electrons become paired). These elementary steps are responsible for the chain reactions’ termination: In chain reactions, many products are produced.