D17. Identify the spatial configuration of polymer chains and define linear polymer, branched polymer, and cross-linked polymer. Describe how these three structures may be formed.

Linear polymers

The classical example regarding a linear polymer is the polymerization of ethylene. When ethylene polymerizes, the chains grow in one single direction.

Branched polymers

Copolymerizing a rather small molecule (e.g. ethylene) with a larger molecule (e.g. propylmethacrylate) can form a branched polymer.

Cross-linked polymers

A cross-linked polymer is formed when a dimethacrylate (or any molecule with two or more methacrylate groups) molecule is polymerized. During the polymerization, one end of the dimethacrylate forms a branch that can participate in the chain growth of an adjacent chain.