Crystallinity in polymers refers to the degree of order and regularity in the molecular chains.

Linear polyethylene has straight, unbranched chains, which can pack tightly together, forming a highly ordered and crystalline structure. The close packing of chains leads to strong intermolecular forces and a higher melting point.

Branched polyethylene has side chains that disrupt the regular packing of the polymer chains. These branches create irregularities and prevent the chains from aligning perfectly, resulting in a lower degree of crystallinity. The lower packing density leads to weaker intermolecular forces and a lower melting point.

Therefore, linear polyethylene exhibits higher crystallinity due to its more ordered structure and closer chain packing.