Color-changing polymeric material

A method for applying a tamper resistant seal to a container, the tamper resistant seal comprising a polymeric material that is formed from a thermoplastic composition containing a continuous phase that includes a matrix polymer, colorant, microinclusion additive, and nanoinclusion additive,

• wherein the colorant includes an inorganic pigment, an organic pigment, a carbon pigment, or a combination thereof,
• wherein the microinclusion additive and nanoinclusion additive are dispersed within the continuous phase in the form of discrete domains,
• wherein a porous network is defined within the polymeric material that contains a plurality of pores, wherein the polymeric material exhibits an initial color, the method comprising:
• treating the polymeric material via heat treatment to reduce the size of one or more of the pores;
• and
• applying the tamper resistant seal to a container and the tamper resistant seal exhibiting the initial color when applied to the container and being configured to exhibit a second color when subjected to a deformational strain, the second color being different than the initial color, the second color providing a visual cue of tampering.