By means of free radical polymerizations were made the copolymers of acrolein，acrolein-styrene and acrolein-divinyl benzene and the infrared spectra of which were taken．It was shown that polyacrolein contains ether linkage，carbon-carbon double bend earbonyl and hydroxyl groups．When treated either with hydroxyl-amine hydrochlorido or with sodium hydroxide solution，the polyacrolein lost or changed the carbonyl group and ether linkage as shown by infrared spectra．This indicated that both the carbonyl group and ether linkages of acrolein are sensitive．Different compositioEs of the copolymer of acrolein styrene possessed different infrared spectra．Comparatively speaking，the copolymer with a smaller amount of styrene contained a less amount of carbonyl groups and more ether linlmges while those with a higher amount，i．e．，approximately eqnimolecular，of styrene contained a higher。amount of carbonyl groups and a smaHer amount of ether linkages．This is probably due to the fact that the copolymerization of aerolein with styrene might cut down the possibility of cyelization．a-hydroxyphosphonic acids were obtained when polymers of the acrolein．acrolein-styrene and acrolein-divinylbenzene were treated with phosphorus triehloride． After the reaction'mixture had been kept at 20℃ for twenty-four hours，the phosphorus content and exchange capacity of the product approached the maximum value．The reaction took place faster at around 75℃ than that below 75℃．When the reaction was undertaken in a solvent with a higher d4eleetric constant or in a mixed solvent．a phosphoric acid with a higher phosphorus content a better exchange capacity could be obtained．Since the carbonyl groups of the homopolymer and eopolymer of acrolein could not be completely converted to the phosphoric acid by phosphorus triehloride and the remainder of carbonyl groups could undergo Cannizzaro reaction，the products after ha-ring been treated with sodium hydroxide solution usually gave a higher exchange ca-pacity than that of the sample without th is treatment．