Effect of Pendant Pyrene Groups on the Topology and Thermal Properties of Poly(Trimethylene Carbonate)

Planar aromatic side chains offer a promising strategy for regulating polymer topology and segmental dynamics. Here, a pyrene‐substituted trimethylene carbonate (TMCM‐Py) was synthesized and polymerized by DBU‐catalyzed ring‐opening polymerization using benzyl alcohol as an initiator. Its polymerization behavior and properties were compared with those of related monomers bearing biphenyl (Bp), triphenyl (Tr), or dibenzyl (DBp) substituents. The resulting polymers exhibited apparent number‐average molecular weights of 2.3–10.8 × 10 3 with dispersities (Đ) of 1.16–1.36. MALDI‐TOF MS revealed both linear and cyclic species for polymers bearing bulky aromatic substituents, whereas cyclic species in PTMCM‐Py remained below the detection limit, qualitatively suggesting preferential linear chain propagation over backbiting‐induced cyclization. Thermogravimetric analysis showed comparable thermal stability across the series, while the glass‐transition temperature strongly depended on the side‐chain structure and reached 87°C for PTMCM‐Py. Fluorescence spectroscopy of PTMCM‐Py in dilute dichloromethane solution revealed pronounced excimer emission, indicating strong pyrene–pyrene association. Collectively, these results suggest that planar pyrene side chains promote π–π stacking networks that act as physical crosslinks, suppress backbiting, restrict segmental mobility, and substantially increase the glass‐transition temperature.