Processable poly(cycloacetals) with high molar masses (Mn) up to 38 kDa were synthesized in a systematic manner. Di-trimethylolpropane (Di-TMP) was used as tetravalent alcohol and was combined with a series of available dialdehydes, after a model reactivity study. These polymers have a high thermal stability with degradation temperatures (Td) up to 370 °C while the glass transition temperatures (Tg) ranged from room temperature to 115 °C. Trends in Tg modulation were confirmed by a theoretical simulation. Moreover, the poly(cycloacetals) showed favourable mechanical and optical properties.