Lecture 2: Molecular weight of polymers

These flashcards cover key concepts found in the polymer physics lecture, focusing on definitions, methods, and properties related to polymer molecular weight and characterization.

What does molecular weight influence in polymers?

It affects viscosity, mechanical strength, solubility, and thermal properties.

What is degree of polymerization (DP)?

The average number of repeating units per chain; molecular weight M = DP × M₀.

What is dispersity (Đ)?

The ratio Mw/Mn, indicating the width of the molecular weight distribution.

What is a monodisperse polymer?

A polymer where all chains have the same molecular weight; Đ = 1.

What is a polydisperse polymer?

A polymer with chains of varying lengths; Đ > 1.

What is number-average molecular weight (Mn)?

An average representing the total mass divided by the number of molecules.

What is weight-average molecular weight (Mw)?

Averages weighted by the mass of each molecule, the longer polymer chains have greater chance of being included in the weight calculation.

What is the Mark-Houwink-Sakurada equation used for?

It gives the relationship between n (viscosity of a polymer solution) and the molecular weight.

What does the exponent a in the Mark-Houwink equation indicate?

It reflects polymer–solvent interactions; a = 0.5 in theta solvent, a ≈ 0.8 in good solvent.

What does Size Exclusion Chromatography (SEC) measure?

It separates polymers by hydrodynamic volume to estimate Mn, Mw, and Đ (relative method). “large comes out first”

Why is SEC a relative method?

Because it requires calibration with known polymer standards.

What does light scattering measure?

It measures absolute Mw, radius of gyration (Rg), and polymer–solvent interaction parameter (A2), by measuring scattering from solutions. 

What is MALDI–MS used for?

It is used for analyzing the molecular weight of polymers. Gives absolute values and dispersion factor

What is the principle of colligative methods?

Colligative methods är sätt att bestämma molekylvikt genom att mäta hur lösningsmedlets egenskaper förändras (tex. kokpunkt, fryspunkt, osmotiskt tryck)

De fungerar eftersom effekten beror på antalet polymermolekyler och inte deras typ.

What is end-group analysis?

A chemical method for Mn determination by titrating or detecting specific end-groups.