AbstractThe reactivity ratios for the copolymerization of lauryl methacrylate (LMA) with diallyl phenylphosphonate (DAPP), diallyl butylphosphonate (DABP), and diethyl allylphosphonate (DEAP), respectively, have been measured at 80°.\documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{l} {\rm LMA - DAPP, }r_1 = 19.5,{\rm }r_2 = 0.072 \\ {\rm LMA - DABP, }r_1 = 18.7,{\rm }r_2 = 0.091 \\ {\rm LMA - DEAP, }r_1 = 52.5,{\rm }r_2 = 0.066 \\ \end{array} $\end{document}None of the phosphonates are active for copolymerization with LMA but the DAPP and DABP have similar activities which are greater than that of DEAP. The variation with conversion in composition of the LMA‐DAPP copolymer formed at any instant has been calculated using Skiest's equation and the calculations have been extended to show the variation of the overall composition of the copolymer with conversion. Intrinsic viscosities and molecular weights have been measured for some LMA‐DAPP copolymers and these values are found to depend on the phosphorus contents of the copoly