ABA triblock B5 Cin copolymers were prepared by attaching photoreactive poly(2-cinnamoyloxyethyl methacrylate) (PCEMA) segments to both ends of main-chain smectic BB-5(3-Me) polyesters. The copolymers with PCEMA volume fraction (phi) ranging from 23% to 50% formed lamellar microdomains, and the BB-5(3-Me) block formed smectic layers parallel to the lamellae. When the B5 Cin melt was drawn into film and annealed at a liquid crystal (LC) temperature of BB-5(3-Me), the lamellae and smectic layers lay perpendicular to the longitudinal direction. The PCEMA block in the monodomain films was cross-linked by UV irradiation leading to 20% conversion. When heated, the cross-linked films with phi > 37% contracted reversibly on the isotropization of the LC segment, coinciding with the reversible decrease in the lamellar spacing (D). The film elongated on the liquid crystallization by a factor which increased from 1.07 to 1.24 with decreasing phi.