The infrared spectrum analysis showed that the polymerization reaction was complete, and the polymer was a kind of thermoplastic material without branched chains.

Branching polymer chains, copolymerizing with another monomer, and blending branched or cross-linked polymers are the basic methods to increase its viscosity so that it can be suitable for foaming.

Polymers may consist of long chains of unbranched or branched monomers or may be cross-linked networks of monomers in two or three dimensions.