A series of twelve poly(ethylene oxide) (PEO)-polyacrylates and -polymethacrylates with PEO side chains, ranging in molecular weight from 164 to 1000, was studied by differential scanning calorimetry in order to analyse the behaviour of the glass transition temperature. It is shown that the glass transition temperature Tg first decreases with increasing side-chain length to attain a constant value corresponding to the Tg of linear PEO. Contrary to the n-alkyl homologous polymers, the influence of the side-chain crystallization is weak and only appears for long side chains (number-average molecular weight Mn > 450). The proposed reason is the higher content of amorphous side-chain units between the backbone and the crystallites in PEO as compared to alkyl chains. A relation predicting variations of Tg in comb-like polymers with the length of the side chains is proposed. This relation, based on variation of the Tg of the side chain with its length, fits the experimental results for n-alkyl and PEO side-chain polyacrylates and polymethacrylates using only one parameter characterizing the nature of the side chain.