L40 - SUMMARY FROM LAST CLASS xi M i The number-average...

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Dr. P. Lucas U of A MSE 110 Polymers properties SUMMARY FROM LAST CLASS •T h e number-average molecular weight is expressed as: Where x i is the fraction of chain within the size range i. And M i is the mean molecular weight of the chain range i. The probability of entanglement increases with chain length hence the viscosity and consequently the Tg increases with polymer chain length. Cross-linking of the polymer chain limits sliding or “reptation” and improve the mechanical properties of the polymer. •A n elastomer stretches under applied stress but can regain its shape. Thermoplastic polymers can be reversibly melted. Thermosetting polymers undergo extensive covalent cross-linking when heated and become permanently rigid. The Elastic Modulus E of a linear chain polymer change from solid to rubbery to liquid when heated. Simple polymer chains can fold and align to form crystalline platelets. Crystalline polymers are a mixture of up to 70% crystallite embedded in a amorphous matrix. Elastic deformation corresponds to a reversible deformation Plastic deformation corresponds to an irreversible deformation Cold drawing of crystalline polymers align the chains in the direction of the stress and therefore improve the tensile strength by a factor up to ×5. = i i n M x
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Dr. P. Lucas U of A MSE 110 Network polymers Resin + hardener are mixed to initiate polymerization and form a highly cross- linked 3-D network polymer. POLYMERS
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This note was uploaded on 11/19/2009 for the course MSE 110 taught by Professor Lucas during the Spring '08 term at University of Arizona- Tucson.

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L40 - SUMMARY FROM LAST CLASS xi M i The number-average...

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