The chain flexibility of polymethacrylic systems prepared by the free-radical polymerization of 4-(methacryloyloxy)acetanilide (MOA), 4-(2-(methacryloyloxy)ethyloxy)acetanilide (MOEA), and 4-(6-(methacryloyloxy)hexyloxy)acetanilide (MOHA) and copolymers with 2-hydroxyethyl methacrylate (HEMA) is analyzed on the basis of the glass transition temperature of the corresponding homo- and copolymers. This is done taking into consideration the effect of the length of the side spacer group (ethyleneoxy or hexyleneoxy) introduced between the acrylic ester group and the aromatic polar side residue, which correspond to the chemical structure of a well-known drug, paracetamol. The glass transition temperature of copolymers with HEMA are analyzed according to empirical treatments which consider the influence of the distribution of monomeric units on the T-g of the copolymer samples. The T-g of the pure alternating diads is determined by the application of equations suggested by Barton and Suzuki and Mathot, based on the entropic theory, giving values of T-gMOEA-HEMA = 347.5 K and T-gMOEA-HEMA = 273 K, sensibly lower than the average value expected from the additive contribution of the T-g of the corresponding homopolymers. The behavior is related to the flexibility introduced by the alkylene spacer segments.