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The linear thermal expansion coefficients of oriented films of poly(p‐phenylene‐2,5‐didodecyloxy‐terephthalate) in the three structures B, A, and Lf are reported. The results are interpreted in terms of a molecular laminate model in which the rigid main‐chain layers are separated by the aliphatic side chains. In a film oriented unidirectionally the rigid mainchain layers provide a negative contribution to the thermal expansion coefficient, while the side chains supply a positive contribution. Therefore, the resulting expansion coefficient α depends on the details of the main‐ and side‐chain packing and low‐temperature values between α = +0.3 × 10−5 K−1 (A and Lf and α = −1.2 × 10−5 K−1 (B) are found in highly oriented films. Measurements on undrawn films are in accordance with the molecular laminate model. © 1994 John Wiley & Sons, Inc.