Below are three polymers to be examined for use as vascular graft materials: Pol

Question

Below are three polymers to be examined for use as vascular graft materials: Poly(styrene) Poly(acrylonitrile) Polytetrafluoroethylene Which two do you believe would exhibit the highest and the lowest crystallinity, respectively, and why? What analytical technique would you use to determine the crystallinity of each material? Assume that the values below represent the Tg and Tm for each of the three materials: Based on this information, which of these materials would you select for this application?

Explanation / Answer

a) As a general rule, if a polymer is regular and orderly, then it forms crystals easily. Among these three polymers,

   Polytetrafluoroethylene would be highly crystalline as it has no side chain; it is nearly 100% crystalline. The branched, i.e., when there is side chain on the polymer then the probablity of packing in order is less comparatively. These have two polymers, one atactic (irregular, amorphous) and the other syndiotactic (regular, crystalline). a In case of polyacrylonitrile and polystyrene, the branch is nitrile is a polar group which can hold the polymer to give strong crystals.

Therefore, among these three, Polytetrafluoroethylene and polyacrylonitrile are highly crystalling when compared to given polystyrene.

b) Crystallinity of all three materials can be evaluated by density measurement and Differential scanning calorimetry (DSC). The other important method that could be used is X-ray diffraction technique.

c) By considering the following points we could choose which of these three polymers is best.

i) A plastic product is flexible at room temperature if its Tg (glass transition temperature) is below room temperature and rigid at room temperature if its Tg is above room temperature

ii) Tg - temperature range where molecules start to soften) and Tm - temperature where molecules start to melt.

As Tm stands for melt temperature of the polymer, we need higher Tm valued polymer. And Tg with lower values.

Hence, from the given Tm values, polytetrafluoroethylene should be the best choice for making vascular materials.

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