Question

A sample of poly(ethyl acrylate) (structure shown below) is composed of the following mixture: Mol% of chains 20 30 DP 1,000 2,000 3,000 50 Calculate Mn, Mw and PDI. Clearly show ALL work for full credit

Answer 1

Mol% of chains DP 20 1,000 30 2.000 50 3,000

Number average molecular weight: Mn The number average molecular weight is the statistical average molecular weight of all the polymer chains in the sample, and is defined by: EN M; Mn = EN where M is the molecular weight of a chain and N is the number of chains of that molecular weight. Mn can be predicted by polymerization mechanisms

Mn 20*1000 +30% 2000 + 50x3000 204 30+50 * Mn = 2300

Weight average molecular weight: Mw The weight average molecular weight is defined by: ENM? MW - EN M; Compared to Mn, Mw takes into account the molecular weight of a chain in determin- ing contributions to the molecular weight average. The more massive the chain, the more the chain contributes to Mw.

Mw - NM, 2 & N₂ M2² of No M3² NIMI + N2 M₂ + Ng Mg 20x(1000)2 + 30 x(2000)2480 x(3000) 20x1000 +30x2000 +50 x 3000 Mw = 20 %106 + 120 *106 + 450 x 106 230,000 590 X 106 - 29565-217 23 4104 E

The polydispersity index is used as a measure of the broadness of a molecular weight distribution of a polymer, and is defined by: Polydispersity index = Mn

PDI - MW 2565.217 2300 PDI :_10115 #