1. The molecular weight between crosslinks (MC) is one of the most important parameter that describes...

1. The molecular weight between crosslinks (MC) is one of the most important parameter that describes the thermoset network structure. Describe how the MC is related to the following properties:(a) T_g, (b) modulus, (c) elongation to break, and (d) solvent resistance. How do you measure MC value?

Solutions

Expert Solution

A). Relationship between molecular weight between cross links (Mc) and Tg

Neilsen has described an empirical relationship which relates the rise in the Tg at a full conversion to network with Mc the number average molar mass between elasticity effective network junctions.

Tg= 3.9 x 10⁴/Mc

B). Relationship between molecular weight between cross links (Mc) and Modulus

Molecular weight between crosslinks, lz;i,, was calculated using equation (1) based on rubber elasticity”. Mc, = p RT/G where p is the density, R is the gas constant, T is absolute temperature and G is the shear modulus.

c). Relationship between molecular weight between cross links (Mc) and elongation at break

The failure representation of data indicates maximum possible breaking , ebmax for the material. This is found to be well correlated with degree of cross linking, specifically with the molecular weight between crosslinks Mc, as predicted by elasticity theory

Lambda max =1+ e_b max proportional to Mc ^1/2

Measurement of MC value

Mc is the molecular weight between crosslinks is defined by following equation

Mc= average molecular weight between cross links

V bar= specific volume of polymer

V1= molar volume of swelling agent

V_2m= polymer volume fraction in equilibrium swollen state

V_2r= poilymer volume fraction in relaxed state

= no. of branches originating from cross link site

queen_honey_blossom answered 1 month ago

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