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We found a polyphenylacetylene(PPA)derivative with a simple chemical structure synthesized by polymerization of 3,5-substituted phenylacetylene,which possessed high molecular weight(MW)and high cis content,could self-organize into hexagonal columnar phase with intracolumnar order at low temperatures and without intracolumnar order at higher temperatures.The observation is similar to that of dendronized polyacetylene reported.1 The transition between the columnar phases is reversible.During the transition process,the diameter of the column decreases due to the cis-cisoidal to cis-transoidal isomerization of the backbone,which lead to the contract of the alkyl tails.Simultaneously,the length along c-axis elongates to quite a high extent(20%-30%).The large structural change has potential to be applied to nanomechanical function.