Compared with ester derivatives, ester-free poly(trimethylene carbonate) (PTMC) derivatives have attracted increased interest because they do not create any acidic compounds after decomposition. Inspired by the chemical structure of poly(α-olefin)s or branched polyethylene (PE), various lengths of alkyl chains, such as -C8H17, -C12H25, -C16H33, -C18H37, and -C20H41, were introduced into trimethylene carbonate (TMC) with ester-free structures to improve the physical properties of PTMC, which can be labeled with trimethylolethane. These monomers were polymerized, and their thermal properties, hydrophobicity, and degradation behavior were investigated. When the length of the alkyl chain was longer than -C16H33, the polymer solidified with higher melting points than at room temperature. The poly(trimethylene carbonate) (PTMC) derivative with a -C18H37 group at the side chain was used for the hydrolysis test both in organic and aqueous solvents, resulting in 91% degradation after 9 weeks in a mixture of THF-d8, D2O, and NaOHaq at room temperature, whereas only 11% degradation was observed in NaODaq. after 9 weeks, suggesting that the hydrophobic long alkyl chains at the side chains influenced their hydrophobic nature and degradation manner. © The Author(s), under exclusive licence to The Society of Polymer Science, Japan 2024.