The initiation reaction is third order with respect to monomer M, and proceeds with the rate constant k_i.  In each initiation event, three monomer molecules M are consumed, and a polymer chain is born consisting of three links - two end links P and a mid chain link Q.

The propagation reaction is first order with respect to both monomer M and free radical chain ends P.  In each propagation event, the net change is that one monomer molecule M is consumed and a polymer mid chain link Q is generated. 

In any small volume element within the growing parylene film, the chemical changes occurring by these two reactions are:

                                             Initiation:

                                             Propagation:

:                    

Here, M, P and Q represent the concentrations of the individual structural elements M, P and Q.  Regrouping, we find for the total rate of disappearance of monomer and the total rates of formation of chain elements in that volume element are:

It should be recognized that the P and Q chain elements are linked together, and overall movement of the chains is severely restricted.  While monomer can diffuse about quite freely to various parts of the growing film, polymer chain motion is limited to segmental motion, such as might be involved in crystallization or in the relocation of monomer molecules. Hence, equations 10b and 10c in the 1978 paper are inappropriate.

Both rate constants, k_i and k_p, are of course have an Arrhenius temperature dependence characterized by different activation energies.

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