3.2. 3 Effect of initiator. Free radical polymerization is the most usual process of MIPs synthesis that needs an initiator and monomers (either functional and cross-linker agent) that have vinyl functional groups. Free radical polymerization has three stages including initiation, propagation, and termination [2].
What are three steps involved in free radical mechanism?
- Step 1: Initiation. Initiation breaks the bond between the chlorine molecule (Cl 2 ). ...
- Step 2: Propagation. ...
- Step 3: Termination.
What are the three stages of polymerization?
The polymerization reaction consists of three stages: (1) initiation, (2) propagation, and (3) termination .
What is the last step in free radical polymerization?
Termination . Chain termination is inevitable in radical polymerization due to the high reactivity of radicals. Termination can occur by several different mechanisms. If longer chains are desired, the initiator concentration should be kept low; otherwise, many shorter chains will result.
What are the steps of free radical polymerization?
There are three general stages of free radical polymerization: 1) initiation, 2) propagation, 3) termination. Let’s consider these stages in the order which they occur.
Why are free radicals a problem?
Free radicals damage contributes to the etiology of many chronic health problems such as cardiovascular and inflammatory disease, cataract, and cancer. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition.
How do radical initiators work?
In chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical reactions . These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical initiators are utilized in industrial processes such as polymer synthesis.
What is the characteristic of a radical chain initiation step?
The three phases of radical chain reactions
The initiation phase describes the step that initially creates a radical species . In most cases, this is a homolytic cleavage event, and takes place very rarely due to the high energy barriers involved.
What is a propagation step?
Chain propagation (propagation): A free radical reaction mechanism step having radical reactant(s) and gives radical product(s).
Which are free radical reaction?
A free-radical reaction is a chemical process in which molecules having unpaired electrons are involved . The radical species could be a starting compound or a product, but in organic chemistry the most common cases are reactions that involve radicals as intermediates.
What is the key to polymerization?
Usually at least 100 monomer molecules must be combined to make a product that has certain unique physical properties—such as elasticity, high tensile strength , or the ability to form fibres—that differentiate polymers from substances composed of smaller and simpler molecules; often, many thousands of monomer units are ...
What is polycondensation process?
Polycondensation is the process of forming polymers by the combination of different monomers . The process is frequently accompanied by the release of various subsidiary low-molecular products (water, alcohol, salt). ... different functional groups which may react among each other and thus form polymers (amino acids);
How does polymerization stop?
In chain growth polymerization, two growing chains can collide head to head causing the growth of both of the chains to stop . ... With step-growth polymerization, the reaction can be terminated by adding a monofunctional species containing the same functionality as one or more of the types of monomer used in the reaction.
In which step is the final polymer produced?
Termination . The third and final stage in the polymerisation process is known as termination. Termination of the reaction process can occur through the addition of a terminating free radical or when two chains combine.
Why is it impossible to polymerize propylene using free radical polymerization?
Polypropylene cannot be synthesized using free radical polymerization since you cannot make a stable propagating species with propylene . ZN polymerization is an example of chain growth since monomers are added one at a time to a growing chain that is tethered to an active catalyst site.
Why is polymerization exothermic?
Polymerization reactions are exothermic, which means they generate heat . Ideally, the total heat produced is small and harmlessly dissipates into the reaction container. However, if there is a large amount of monomer present and the reaction is strongly exothermic, the monomers may combine too quickly.
