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The termination steps of free radical polymerization steps are of two types: recombination and disproportionation. [2] In a recombination step, two growing chain radicals (denoted by •) form a covalent bond in a single stable molecule. For the example of a vinyl polymer,
Combination of an active chain end with an initiator radical (Figure 16). [2] Figure 16: Termination of PVC by reaction with radical initiator. Interaction with impurities or inhibitors. Oxygen is the common inhibitor. The growing chain will react with molecular oxygen, producing an oxygen radical, which is much less reactive (Figure 17).
Many radical processes involve chain reactions or chain propagation with disproportionation and recombination occurring in the terminal step of the reaction. [8] Terminating chain propagation is often most significant during polymerization as the desired chain propagation cannot take place if disproportionation and recombination reactions ...
Termination: Chains in their active form react via a process known as bi-radical termination to form chains that cannot react further, known as dead polymer. Ideally, the RAFT adduct radical is sufficiently hindered such that it does not undergo termination reactions. Video 1. Visual representation of RAFT polymerization (main RAFT equilibrium ...
The steady-state concentration of the growing polymer chains is 10 −7 M by order of magnitude, and the average life time of an individual polymer radical before termination is about 5–10 s. A drawback of the conventional radical polymerization is the limited control of chain architecture, molecular weight distribution, and composition.
In polymer chemistry, chain transfer is a polymerization reaction by which the activity of a growing polymer chain is transferred to another molecule: [1] [2] P ∙ + XR PX + R ∙ {\displaystyle {\ce {P}}^{\bullet }+{\ce {XR -> PX + R}}^{\bullet }} where • is the active center , P is the initial polymer chain, X is the end group , and R is ...
Chain termination Two free radicals (chlorine and chlorine, chlorine and methyl, or methyl and methyl) combine: Methane chlorination: termination The last possibility generates in an impurity in the final mixture (notably, an organic molecule with a longer carbon chain than the reactants). The net reaction is: Methane chlorination overall reaction
It is defined as a chain polymerization from which chain transfer and chain termination are absent. [6] In the absence of chain-transfer and chain termination, the monomer in the system is consumed and the polymerization stops but the polymer chain remains active. If new monomer is added, the polymerization can proceed.