Chemical Properties :



The attractive forces between polymer chains play key role in determining a polymer's characteristics. cuase polymer chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules. Variouse side groups on the polymer can lend the polymer to hydrogen bonding between its own chains. These forces normally result in higher crystalline melting points and higher tensile strength.

The intermolecular forces could affect by dipoles in the monomer units. Polymers including amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between hydrogen atoms in H-C groups the oxygen atoms in C=O groups . Dipole bonding is weaker than hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar's (Twaron), flexibility is one of the polyesters characteristics .

Ethane, has no permanent dipole. The attractive forces between polyethylene chains arise from weak van der Waals forces. Molecules could imagine as being surrounded by a cloud of negative electrons. As two polymer chains get closer, their electron clouds reject one another. This may cause of lowering the electron density on one side of a polymer chain, creating a slight positive dipole on this side. This charge is enough to attract the second polymer chain.