The monomers are mainly arranged head-to-tail, meaning that there are chlorides on alternating carbon centres.
PVC has mainly an atactic stereochemistry, that means that the relative stereochemistry of the chloride centres is accidentally or random .
Some grade of syndiotacticity of the chain gives a few percent crystallinity that is influential on the properties of the material. About 57% of the mass of PVC is chlorine.
The presence of chloride groups gives the polymer very different properties from the structurally related material polyethylene.