Introduction to polymers
Introduction to polymers

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Introduction to polymers

2.3.5 Repeat unit placement

A final kind of isomerism in homopolymers is possible when monomer units are added to a growing chain in reverse rather than in their normal position. Because monomer molecules have a particular shape in space, they will normally approach a growing chain end to minimise any spatial interaction, and a regular chain structure results from head-to-tail joints. A defective joint can sometimes occur, however, when heads combine to form a head-to-head joint (Figure 21). Although the chain units are fully chemically bonded together, it represents a weak link in the chain because less energy is needed to break the chain here than elsewhere. So in failure problems, such as thermal degradation, breakage will start here rather than in the normal chain. The occurrence of head-to-head joints is less than 1 per cent in normal polymers.

Figure 21
Figure 21 (a) Regular head-to-tail repeat units in polystyrene; (b) irregular head-to-head joint in polystyrene chain

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus