Organic polymers with near-zero uniaxial thermal expansion coefficients

A process for obtaining an organic polymer having a near-zero uniaxial thermal expansion coefficient, characterized in that a highly chain alinged polyacetylene obtained by solid-state polymerization of an acetyleneic monomer selected from the group of cyclic and acyclic acetylenic monomers containing at least two conjugated acetylene groups per monomer molecule and having a negative uniaxial thermal expansion coefficient is subjected to at least one cycle comprising (a) heating from a first temperature to a second temperature, the first temperature being below and the second temperature being above the lowest temperature at which a first order phase transformation or chemical degradation occurs, (b) holding at the second temperature for a period of time sufficient to induce sufficient chain misaligned fractions in the polyacetylene to produce a uniaxial thermal expansion coefficient therein having an absolute value of less than about 5.0 .times. 10.sup.-.sup.6 .degree.C.sup.-.sup.1 and (c) cooling to a temperature below the firt-order phase transition temperature or temperature at which substantial chemical degradation occurs.