The answer I got is: As n increases, the side chains become flexible, and the overall stiffness of the polymer decreases.
Could you explain why the side chain become flexible? Is it because of molecular weight? crystallinity? copolymerization? and why when the side chains become flexible then the overall stiffness decreases?
Hello dear it occur because this chains reduce the crystallinity of the system, since structural packing is reduce, because the chain increase the mobility. Therefore the melting temperature will decrease.
As the number of methylene groups (CH2) increases, the side chain becomes more flexible because these groups are able to rotate easily. On the other hand, as n increases the side chain becomes more bulky and hinders the rotation and mobility of the backbone. The flexibility of the backbone is one of the factors that determines the stiffness of the polymer.
As n increases, the dangling chains have greater rotation above Tg. In such a case, these long chain repeating units act more like plasticisers and lead to the polymer being less stiff. This is a form of internal plasticization which involves the introduction of side chains (either substituents or grafted branches). This effect is well known with the polyacrylates and polymethacrylates, and is caused by lowering of the forces between the polymer chains owing to the bulkiness of the substituent groups. The reason for the minimum in the curve is that side chain crystallization occurs as the substituent chain increases beyond a certain length. Another example of internal plasticization is the alkylation of polyamides which gives elastic fibers by lowering crystallinity and Tg through reduction of intermolecular forces. These fibers were the forerunners of the present elastic fibers such as Lycra, Vyrene, and
others.
Hi, it's basically what people call "elbow room".
So if you have longer and flexible side groups the free volume will increase (i.e. the chains will have more space to move and slide past each other) leading to a drop in stiffness and viscosity. The Tg will decrease as well.
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