D16. Describe how complex side chains and molecular weight distributions influence the overall physical properties of a polymer.

Molecular weight

As the chains grow longer, the strength of the polymer increases. However, after they have reached a certain length, additional chain lengthening has little effect. Can be understood by imaging entangled chains. As the chains grow, their entanglement increases. At a certain length, they are so strongly entangled that any additional entanglement will not add significant strength to the system because the failure will occur within the chain rather than through chain slippage.

The above concept can be understood by looking at spaghetti, and how the lengths of the spaghetti strings affect the cohesiveness of the pasta.  

Protruding side chains

Long and complex side chains separate the main chains, which results in lower glass transition temperature and lower strength properties.  

Large molecular weight distribution

A large molecular weight distribution means that shorter chains will separate longer chains. The shorter chains act principally as an external plasticizer. Thus, a large molecular weight distribution decreases the glass transition temperature and results in a polymer with inferior mechanical properties.