The attached paper explains both the ideal conditions for the storage of primers and also the mechanism behind the degradation of primers by freeze thawing.
The paper explains that repeated freeze-thawing leads to the potential loss of bases/phosphate groups from the terminus of DNA strands due to 'the fact that during the freezing/thawing process the oligonucleotide and buffer components isolate from the solvent system.'.
Article Analysis of the Degradation of Oligonucleotide Strands Durin...