Spontaneous homopolymerization of 2,5-dimethylene-2,5-dihydrofuran (DDF) was studied. The polymerization rates in two different initial monomer concentrations of DDF were analyzed with the first-order and second-order kinetics, and the homopolymerization of DDF was found to obey the first-order kinetics. The Arrhenius plot of the apparent rate constants at 30, 40, 50, and 60 degrees C gave an overall activation energy of 68.0 kJ/mol for the polymerization of DDF. From the comparison of the apparent rate constants at -78 degrees C and the time (the so-called half-life time) to decrease in half the monomer concentration for DDF with the corresponding values for p-xylylene (QM), DDF was found to be a less reactive monomer than QM. The copolymerizations of DDF with vinyl monomers such as acrylonitrile (AN), alpha-chloroacrylonitrile (ClAN), diethyl fumarate (DEF), and fumaronitrile (FN) were carried out in chloroform at 50 degrees C in the presence of AIBN to obtain the monomer reactivity ratios r(1)(DDF) = 30.0 +/- 3.0 and r(2)(AN) = 0 for the DDF-AN system, r(1)(DDF) = 1.55 +/- 0.2 and r(2)(ClAN) = 0 for the DDF-ClAN system, r(1)(DDF) = 3.88 +/- 0.2 and r(2)(DEF) = 0 for the DDF-DEF system, and r(1)(DDF) = 2.41 +/- 0.1 and r(2)(FN) = 0 for the DDF-FN system, respectively. As the monomer reactivity ratios of r(2) for all systems were zero, and and e values of DDF were calculated from the combination of two r(1)(DDF) values of any two copolymerization systems to be the 7.64 to 6.63 X 10(21) range for and and the -0.70 to -6.31 range for e, indicating that DDF is a highly conjugative and electron-donating monomer.