Materials Science and Engineering Practice Exam 2026 – The All-in-One Guide to Mastering Your Exam!

Heat travels in polymers mainly through vibrational energy (phonons), and how well those vibrations can propagate depends on how orderly the chain packing is. Isotactic polypropylene has all the methyl groups on the same side, which promotes regular, close packing and a high degree of crystallinity. The crystalline regions form orderly pathways that let phonons move with less scattering, so heat can be transported more efficiently along those ordered regions. In contrast, atactic polypropylene has a random arrangement of side groups, leading to an amorphous structure with many irregularities and defects that scatter phonons and hinder heat flow. Because of this, isotactic polypropylene has higher thermal conductivity than atactic polypropylene.