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Polystyrene (PS) / ˌ p ɒ l i ˈ s t aɪ r iː n / is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. [5] Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to air and water vapor and has a relatively low ...
The Flory–Fox equation relates the number-average molecular weight, M n, to the glass transition temperature, T g, as shown below: =, where T g,∞ is the maximum glass transition temperature that can be achieved at a theoretical infinite molecular weight and K is an empirical parameter that is related to the free volume present in the polymer sample.
The molecular mass of a polymer differs from typical molecules, in that polymerization reactions produce a distribution of molecular weights and shapes. The distribution of molecular masses can be summarized by the number-average molecular weight, weight-average molecular weight, and polydispersity .
The number average molar mass is a way of determining the molecular mass of a polymer.Polymer molecules, even ones of the same type, come in different sizes (chain lengths, for linear polymers), so the average molecular mass will depend on the method of averaging.
The degree of polymerization, or DP, is the number of monomeric units in a macromolecule or polymer or oligomer molecule. [1] [2] [3]For a homopolymer, there is only one type of monomeric unit and the number-average degree of polymerization is given by ¯ ¯ = ¯, where ¯ is the number-average molecular weight and is the molecular weight of the monomer unit.
The number-average molecular weight (M n) and weight-average molecular weight (M w) are most commonly reported. [28] [29] The ratio of these two values (M w / M n) is the dispersity (Đ), which is commonly used to express the width of the molecular weight distribution. [30]
There are two important aspects with regard to the control of molecular weight in polymerization. In the synthesis of polymers, one is usually interested in obtaining a product of very specific molecular weight, since the properties of the polymer will usually be highly dependent on molecular weight. Molecular weights higher or lower than the ...
As a liquid or a gas, pure styrene will polymerise spontaneously to polystyrene, without the need of external initiators. [29] This is known as autopolymerisation. At 100 °C it will autopolymerise at a rate of ~2% per hour, and more rapidly than this at higher temperatures. [22]