Side-chain crystallisation

A large number of organic acrylic ester polymer have been prepared in the laboratory. Poly (methyl acrylate) is tough, leathery and flexible. With increase in chain length there is a drop in the brittle point but this reaches a minimum with poly-(n-octyl acrylate) (see Figure 15.12.). The increase in brittle point with the higher acrylates, which is similar to that observed with the poly-a-olefins and the poly(alkyl methacrylate)s, is due to side-chain crystallisation. 

The presence of long (linear) side chains in branched polymers can cause side chain crystallisation. It is important to distinguish main chain from side chain crystallisation for the effect of this difference on the product properties can be considerable. 

The Tm- and Tc-values of a polymeric system increase in general as a function of the chainlength i.e. the system s molecular weight. Both values become constant at higher molecular weights or go through a kind of maximum value [2]. This makes discrimination between main chain and side chain crystallisation on basis of the side chain length easy ... 

Side chains are in comparison with the main chains usually short and the Tm- and Tc-values of side chain crystallisation effects will, therefore, in general increase with increasing side chain length. 

Values for n higher than 8 are meaningless in chapter 1.4.2 it is shown that the Tg-value determination for samples with n > 7 is seriously hampered by side-chain crystallisation effects. 

Side chain crystallisation or side chain interactions ( with partial and/or full intercalation) occur and play a dominant role in the determination of the structure of many organic polymethylenic systems such as liquid crystal oligomers and polymers etc. X ray structure determinations on polyalkylthiophenes are presently being performed by various groups [164-165]. 

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