User:LittleJellies/sandbox1

Role of Z and R groups on RAFT agent
Including the guidelines for Z and R groups depending on their functions and which types are adequate depending on the monomers to be polymerized.

R group  :


 * It must be a good homolytic leaving group relative to Pn (shifts main equlibrium towards macro-CTA and R radical)
 * It should reinitiate polymerisation efficiently

Choice of Z group affects:


 * Rate of addition of propagating polymer to the thiocarbonyl of intermediate species
 * Rate of fragmentation of intermediate radicals

Guidelines have been provided for selection of R and Z groups based on the desried monomer to be polymerised and these are summarised in Figures x1 and x2. Monomers can be divided into more actived and less actived, called MAM and LAM, respectively. MAM will yield less active propagating radical species, and vice versa for LAM. Therefore, MAM require more active RAFT reageants, while LAM require less active reagents.

Important ratios between components
Describe the three important ratios (monomer to CTA, monomer to initiator and CTA to initiator) and how these affect the reaction and can be used to predict such things as degree of polymerization and average polymer molecular weight. Add the equations!

All ratios are relative to initial moles:


 * 1) Monomer to RAFT reagent: gives the expected degree of polymerization (that is, the number of monomer units in each polymer chain) and can be used to estimate the molecular weight of the polymer by Equation (1)
 * 2) RAFT reagent to initiator: determines the end groups on the polymer chains. For the α end, this ratio gives the number of chains that come from the R group (step IV?) to the number of chains that come from the initiator (step II?). For the ω end, it gives the proportion of dormant polymer chains (those with a thiocarbonylthio at the end) to dead chains.
 * 3) Monomer to initiator: similar to other radical polymerization techniques, for which the rate of propagation is proportional to the concentration of monomer and the square root of initiator concentration.

Equation (1):

$$MW_n = \frac{(M_0 - M_t)}{RAFT_0}MW_M + MW_{RAFT}$$

Where MWn is the molecular weight of the polymer, M0 and Mt are the initial and final moles of monomer, respectively, RAFT0 is the initial moles of RAFT reagent, MWM is the molecular weight of the monomer and MWRAFT is the molecular weight of the RAFT reagent. M0 - Mt could also be rewritten as M0*X (where X is conversion), so that the molecular weight of the polymer could be estimated based on conversion.

Relevant references to be added:

Perrier (2017)

Keddie (2014)

Keddie et al. (2012)