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The degree of polymerization, or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule. [1] [2] [3]For a homopolymer, there is only one type of monomeric unit and the number-average degree of polymerization is given by ¯ ¯ = ¯, where ¯ is the number-average molecular weight and is the molecular weight of the monomer unit.
The mass-average molecular mass, M w, is also related to the fractional monomer conversion, p, in step-growth polymerization (for the simplest case of linear polymers formed from two monomers in equimolar quantities) as per Carothers' equation: ¯ = + ¯ = (+), where M o is the molecular mass of the repeating unit.
M n is the number average molecular weight, M w is the weight average molecular weight, M o is the molecular weight of the repeating monomer unit, Đ is the dispersity index. (formerly known as polydispersity index, symbol PDI) The last equation shows that the maximum value of the Đ is 2, which occurs at a monomer conversion of 100% (or p = 1 ...
As a result the molecular weight decreases rapidly. As new free radicals with high reactivity are formed, monomers cannot be a product of this reaction, also intermolecular chain transfer and disproportion termination reactions can occur. CH 2-CH 2-CH 2-CH 2-CH 2-CH 2-CH 2 ’→ CH 2-CH 2-CH=CH 2 + CH 3-CH 2-CH 2 ’ or CH 2 ’+CH 2 =CH-CH 2 ...
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) (see below). [12] [14] RAFT reagent to initiator: determines the end groups on the polymer chains.
There are two important aspects with regard to the control of molecular weight in polymerization. In the synthesis of polymers, one is usually interested in obtaining a product of very specific molecular weight, since the properties of the polymer will usually be highly dependent on molecular weight. Molecular weights higher or lower than the ...
In contrast step-growth polymerization involves only one type of step, and macromolecules can grow by reaction steps between any two molecular species: two monomers, a monomer and a growing chain, or two growing chains. [17] In step growth, the monomers will initially form dimers, trimers, etc. which later react to form long chain polymers.
Multiplying the ratio of monomer consumed to the concentration of the CTA used by the molecular weight of the monomer (mM) a reliable estimate of the number average molecular weight can be determined. RAFT is a degenerative chain transfer process and is free radical in nature. RAFT agents contain di- or tri-thiocarbonyl groups, and it is the ...