Tg Table    

Glass transition Temperature
of Comb-like Polyvinyl esters

The effect of alkyl side chains on the glass transition temperature (Tg) has been reported for a number of polymers. The figure below shows as an example the variation in Tg for a homologous series of polyvinyl esters based on acrylic and methacrylic acid. The two related classes of polymers show a markedly different Tg, that is the difference in Tg is about 100 K. This is due to the steric hindrance effect of the additional methyl group of the methacrylates which is attached to the same carbon atom as the ester group (COOR).

 

 

However, both polymers show a similar variation in Tg, that is, with increasing length of the side chain, the glass transition temperature (Tg) first decreases, as one would expect, but when the n-alkyl side chain reaches a critical value, the Tg starts to rise again. In the case of acrylates, the critical value is about 10 carbon atoms (or 9 CH2 groups), whereas in the case of methacrylate the Tg drops until the side chain length reaches a value of about 13 CH2 groups.

References
  1. H.K. Reimschuessel, J. of Poly. Sc.: Polymer Chemistry, Edition, Vol. 17, 2447-2457 (1979)

  • Summary

    Comblike Polymers

    Macromolecules in which each monomer unit has a long side chain are called comblike polymers.

  • Brushlike Polymers

    Macromolecules in which each monomer unit carries two long side chains are known as brushlike polymers.

  • Polymers with Short Side Chains

    An increase in the length of side chains results in a larger free volume, reduced packing density, and thus, in a lower glass transition temperature, increased toughness, and flexibility.

  • Polymers with Long Side Chains

    Polymers with long side chains have an intrinsic tendency to side-chain "crystallization" which leads to an increase in the glass transition temperature.

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