Drying and water uptake of poly(acrylic acid) rubidium and cesium salts with different degrees of neutralization were studied. Though the equilibrium water. uptake increased with increasing neutralization %. the slope of the plot above ca. 45 % neutralization was greater than that below this neutralization %

Hiraoka Kyoko

Tabuchi Kumiko

Yokoyama Tetsuo

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Report o.f The Faculty of'Eng'ineering, Nagashki University, vol. 14, No. 22, January 1984 81         Hydration of Poly(acrylic Acid) Rubidium         and Cesium Salts                                      '                                                      '                                          by                        '                  Kyoko HIRAOKA*, Kumiko TABUCHI**                     and Tetsuo YOKOYAMA*                                                 '                            '                          '                            tt                                                    ''                                                         '                                                                  '   Drying and water uptake of poly(acrylic acid) rubidium and cesium salts with differentdegrees of neutralization were studied. Though the equilibrium water uptake increased with in-XeaatStnegioXeXi.saikZeautitOrgiiil(atiotnhe%Si.OPe  Of the piot above ea 4s % neutralization was greatel, than              INTRODUCTION    The authors have been studying the hydration  tlof poly(acrylic acid) alkali metal salts in solidor very concentrated state. The preceding papersin this seriesi'2'3) have shown the drying processand equilibrium water uptake of poly(acrylic acid)lithium (PALi), sodium (PANa), and potassiumsalts (PAK). In the present paper the authorswish to call further attention to the hydration be-havior of poly(acrylic acid) rubidium (PARb) andcesium salts (PACs). .... ... '         '･. EXPERIMENTAL   PAA was prepared by the radical polymeriza-tion of acrylic acid in toluene with benzoy! per-oxide initiator. The detail of the synthesis ispractically the same as that used previously4).Molecular weight, which was determined fromintrinsic viscosity in dioxane solution at 300C usingthe published correlation5) (n) =8.5×10-`Ml!2,was loo,ooo. .                          .t. PARb and PACs with degrees of neutraliza-tion varying from O% to 100 % were preparedby adding the calculated amounts of 1 N aqueoussolution of rubidium and cesium hydroxide to the1 N aqueous solution of PAA.Received September 30, 1983. *Department of Materials Science and Engineering**Present address: Analysis and Treatment Center for     The drying processes of PARb and PACs at    '  1000C under atmospheric pressure were folloWed  by weighing them at appropriate time intetvals.  Ordinary air oven was used for drying experiments.gg,2iliei･/ig,M,gX,EhZS.s.f,s.age.p,!gvesse'swere.,.pr?.--    .' Water uptake of PARb and PACs at 250C in                                       '  an atmosphere of 73 % relative humidity wds fol-  lowed by weighing at appropriate time intervals.  Glycerine solution (60 %) was used f6r maintain-  ing constant humidity. A sensitive spring balance  made of thin phosphor bronze wire was used for                                            'continuous weighing device. ' /' '' ''..                '            '         RESULTS AND DISCUSSION  1. Drying process                         '''  .' Drying processes of PARb and PACs are very similar to those of PALi, PANa, and PAKi,2,3). The previous idea that the drying process of PAA salts is not governed by Tg (diffusion-controlled)  but is governed by the release of water molecule  from hydrated state (dehydration-controlled) was confirmed by this study. ' l                                          '                                        ' 2. Water uptake ..     Fig. 1 and 2 show the equilibrium water up- take as a function of the degree of neutralization,               . t..1                            ./     ttttttt /t tt ttt t tt t tt tt ttt t ttt t tttt tttt t ttt tt ttttt t tt ttttt t t ttt tt ttt ttt t t tt                                        '       ･･ 1   tt tt ttttt l      t tt                       'Environmental Protection, Nagasaki University  82･ , Hydration of Poly(acrylic Acid)for PARb and PACs, respectively. It is apparentthat the equilibrium water uptake does not increaselinearly with neutralization %. This is similarto the case of the other PAA salts studi'ed before.The slope of the plots increased distinctly aboveca. 45% neutralization. In the case of PALi andPANa, the bending of the plots appeared at 33% neutralization, whereas PAK had the bendingof the plot at 25% neutralization. These surpris--ing phenomena that PAA salts become much morehygroscopic at certain ion content were reasonablyTEN¢pdi36rlg4p-r-I-:ppal¢2SL,opt    oFig. 1    Neutralization % 'Equilibrium water uptake at 250C and73% relative humidity for poly(acrylicacid) rubidium salts with differentdegrees of neutralization                      ' TABLE 1. Iohic radii and the possibilities            to the alkali metal ionsRubidium and Cesium Salts explained by assuming the octet coordination-structure of carboxyl oxygen atoms to lithium and sodium ion by chelation, and the bodycentered cubic (b. c. c.) coordination of those to potas- sium ion by chelationi'2'3). In the case of rubidi- um and cesium ion, it can be expected that the octet and the b. c. c. coordination by chelation are difficult because the ionic radii of the both metal atoms are considerably greater than those of the internal spheres of the two coordination struc- ture composed of the chelation of carboxyls. TablerlosNopes3o-Hp-rlqp･pesoqooc                Neutralization %    Fig, 2 Equilibrium water uptake at 250C and          73% relative humidity for poly(acrylic          acid) cesium salts with different deg-          rees of neutralizationof coordination of carboxyls by chelationIonic Radius (A) Radius of Internal SphereIon-H.C.p.a) Paulingb)Tetrahedral       o･ O.462 A Octet      eO.923 A b.c.c.      e1.131 ALi+Na+K+Rb+Cs+op111.68.97.33.47.67O.60O.951.331.481.69fitfitfitfitfita)b)HandbookHandbookof chemistry and physics, Theof chemistry, Edtd. by Lange,chemical Rubber CoMcGraw-Hill Bopk. (1971), p. F-152.Co. (1967), p. 122,                              K. Hiraoka, K.                                   '                               '! shows the ionic radii and the possibilities of co-ordination of carboxyls by chelation to the alkalimetal ions, It is considered that PARb and PACscan not form even b. c. c. coordination of car-boxyl groups to metal atoms. The detailed discus-sion for the Pending at 45 % neutralization willbe given in a subsequent paper with other exper-imental evidences, .                            '               REFERENCES1) K. Hiraoka and T. Yokoyama, Polym. Bull.,  2, 183 (1980).Tabuchi and T. Yokoyama ' 83      2) K. Hiraoka, M. Gotanda, and T. Yokoyama,        Polym. Bull., 2, 631 (1980)･      3) K. Hiraoka and T. Yokoyama, Polym. Bul-        l,, 3, 225 (1980).      4) A. Eisenberg, T. Yokoyama, and E. Sam-        balido, J. Polym. Sci.: Part A-1, 7, 1717 (1        969). - .      5) S. Newman, W. R. Krigbaurn, C. Laugier,        and P. J. Fiory, Polym. Sci., 14, 451 (1954).

Hydration of Poly(acrylic Acid) Rubidium and Cesium Salts

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Hydration of Poly(acrylic Acid) Rubidium and Cesium Salts

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