For the following pairs of polymers, do the following: (1) state whether or not

Question

For the following pairs of polymers, do the following: (1) state whether or not it is possible to decide whether one polymer has a higher tensile modulus than the other; (2) is possible, note which has the higher tensile modulus and then cite the reason(s) for your choice; and (3) if it is not possible to decide, then state why. [Also consider their repeat unit structure] Branched polyethylene with a number-average molecular weight of 250,000 g/mol; linear and isotactic poly(vinyl chloride) with a number-average molecular weight of 200,000 g/mol

Explanation / Answer

Crystalline materials have lower tensile modulus compared to amorphous material. Polyethylene (PE), which is a crystalline materials has lower tensile modulus compared to Poly vinylchloride (PVC), which is a amorphous material. Branching in material increases the amorphous nature of the material. So, Branched PE has higher tensile modulus compared to unbranched PE. Tensile modulus increases with molecular weight. So, Branched PE (250, 000 g/mol) has higher tensile modulus than PVC (200, 000 g/mol). However the molecular weight and the structural information alone is not sufficient to judge which has higer tensile modulus. % of Crystallinity in addition is required to judge which has higer tensile modulus.

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