RuH2(PPh3)(4) catalyzed Tishchenko type polyaddition of terephthalaldehyde gives aromatic polyester (1), which contains three structural units, [OCH2-C6H4-CH2O] (1a), [OCH2-C6H4-CO] (1b), and [CO-C6H4-CO] (1c). H-1-NMR spectrum shows the presence of the three units in a 1 : 2 : 1 ratio. Isophthalaldehyde also undergoes similar polyaddition to give another aromatic polyester (2), while 1,12-dodecanedial gives an aliphatic polyester (3) containing the following structural units : [OCH2-(CH2)(10)-CH2O] (3a), [OCH2-(CH2)(10)-CO] (3b), and [CO-(CH2)(10)-CO] (3c). The above polymers have M-n of 2.7 x 10(3)-5.4 x 10(3) and M-w of 4.3 x 10(3)-9.7 x 10(3), respectively. Mixtures of terephthalaldehyde and 1,12-dodecanedial produce copolymers, which contain the units 1a-1c and 3a-3c in a random sequence. In the copolymerization, terephthalaldehyde shows a strong tendency to give 1c units, whereas 1,12-dodecanedial predominantly affords 3a units. SmI2 also catalyzes polyaddition of terephthalaldehyde to give the corresponding polyester with M-n of 1.7 x 10(3) and M-w of 3.7 x 10(3), respectively.