EAA Properties

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  • 8/3/2019 EAA Properties


    244 E. P. OTOCKAN D T. K. KWEI Macromolecules

    TABLEConstants in eq 5 I've S

    Present work 6 10Ackers work& 5 13-

    a See ref 33 .rv = r,,, + s erfcc1(Kd) ( 5 )

    The cons tan t rqo s the posi t ion of the maximum ordi-nate of the distr ibution, s the measure of s tan dard dev-iation, and erfc-1 the inverse error function comple-ment.Ackers showed for several gels that a plot of rq GS .erfc-(Kd) was linear and that r,,, a n d s could be takento be cal ibrat ion constants for a given gel. I n presentwork, the available values of Kd = (V, - Vo)jViweregraphed in terms of the inverse error function comple-m ent, e r f ~ - l ( K ~ ) , ~ ~s. the corresponding estimatedmolecular radii, r7 , to yield the approximately l inear(34) Tables of the Erro r Funct ion and I t s Derivat ives ,Nat ional Bureau of Standards, Appl ied Mathemat ics Series 41 ,

    U. S. Government Prin t ing Office, Washington , D. C., 1954.

    relationship shown in Figure 8. Cons tan ts f ound f orthis line, together with those estimated from Figure 2of Ackers pap er33 re given in Table V. The proximityof rV aa n d s values found in the present work withthose repo rted by Ackers-although his plot is based ondat a from fractionation of dextrans-gives sup por t tothe above discussed co ncepts of the molecular size andthe swelling relationships of NaL S molecules. Ou rexperimental results seem to provide further evidencefavoring G orings interpretations as well as the presentideas concerning the mechanism of gel chromatograph yseparations.

    Acknowledgments. The authors appreciate the help-ful counsel of Dr. Bjorn F. Hrutfiord of the College ofFores try and the De par tmen t of Chemical Engineer ing,and the substantia l ass is tance given by Mr. R oger W adeof the Department of Biochemistry, of the Universityof Washington. They are also grateful to D r . D. A. I.Goring of the Pulp and Paper Research Ins t i tute ofCanada , and to Dr . Ka j For s s and P r ofes sor W . Jensenof the Finnish Pulp and Paper Research Ins t i tute ofHelsinki for helpful discussions of their i mp ortan t wo rk.

    Properties of Ethylene-Acrylic Acid CopolymersE. P. Otocka and T. K. KweiBell Telephone Laboratories, Inc., Mur ray Hill, ew JerseyReceived January 25, 1968 07974.

    ABSTR ACT: The effects of carboxylic acid comonomers on polyethylene are studied using calorimetry, dynamicmechanical testing, and infrared spectroscopy. Infrared studies indicate that the fraction of acid groups hydrogenbonded is determined by a temperature-dependent equilibrium with thermodynamic p arameters similar to smallmolecule acids in ordinary solvents. During elongation, the planes of the acid dimer become perpendicular tothe direction of stretch. The resultsshow that the acid groups are not crystallizable, and the dimerization takes place in the amorphous phase. Theincreases in T, with increasing acid content as determined by E are more correctly described by cross-linkingequations than by the simple copolymer relationships.

    The melting points of the copolymers are tested using Florys equation.

    variety of effects arise from the incorporation ofA comonomers with functional pendent groups inotherwise nonpo lar vinyl polymers. In the cases ofcarboxylic acids, alcohols, amines, or amides, changesin physical properties are often identif ied with thehydroge n bon ded structures formed. Systematic in-vestigation of how relatively isolated functional gro upsalter polymer behavior is necessary in understandingthe behavior of systems where they are major con-stituents.Early investigations have shown that the presence ofcarboxylic acid or carboxylate comonomers generallyincreased matrix cohesion but did not lead to mechan-ically stabl e networks.1-3 Th e pictu re of acid dimeri-zation and acid-base interactions in amo rpho us poly-

    ( I ) H. P. Brown (to B. F. Goodrich Co.), U . S. Pa t en t( 2 ) W. C o o p e r , J . Polj,m. Sci., 28 , 195 (1958).( 3 ) W . E. Fitzgerald and L . Nielscn, Proc. RO J . SOC.London),

    2,662,874 (1953).

    mers has mo re recently been refined. Below T, thefunctional groups are highly associated and immobile.Above T , chain mobility allows relatively free diffusionof the gro ups and t he fraction associated is determinedby a temperature-dependent equilibrium. --6 Super-ficially this lat ter beha vior is identical with that of smallmolecule analogs in non pol ar solvents. Th e thermo-dynamic parameters of the association, however, maydiffer from th e low molecular weight systems.In this work the effects of acrylic acid comon omer onthe properties of branched polyethylene are discussedwhere th e additional variable of crystallinity is present.Several other authors have discussed such changes forthe case of methacrylic acid and its metal salts. Theseexperiments have shown that ionization of the aciddepresses crystal formation m ore severely than does the

    (4 ) R. Longworth and 13. Morawetz , J . P O ~ J , V I .c i . , 29 , 307( 5 ) E. P. O t o ck a an d F. R . Eirich, ibid. , in press.( 6 ) E. P. Otocka a n d F. R. Eirich, ibid., i n prcss.

    (1958).12282, 137 (1962).

  • 8/3/2019 EAA Properties


    V O ~ ., NO.3, MLiJV-June IYh8 ErHYLENt-AC'KYLIC ACID C O P O L Y M E R S 245

    init ia l incorporat ion of the comonomer , yet s t i f fensthe sample as a whole.7-9 O n the othe r han d, it isindicated that the p t rans i t ion of the copolymers israised mo re by the incorpo rat ion of the acid alone thanby its univalent metal salt. 0Four ethylene-acrylic acid copolymers of varyingcompos i t ion wer e ob ta ined f r om the Dow Chemica lCo. and Union C ar b ide Cor p . and the ac id content waschecked by t i t ra t ion. The methyl grou p content wasdetermined by infrared analysis. These findings aresummarized in Table I .Experimental Section

    Infrared Spectra. Three separate series of infrared ex peri-ments were carried o ut on the acid copolymers to determinethe effects of composition, temperature, and elongation ontheir spectra. All data were taken on a Perkin-Elmer Model21 prism instrument. For the elongation studies, a pair ofPerkin-Elmer AgCl polarizers were employed.Two special mounting techniques were used fo r thestretching and heating experiments. A steel frame wasconstructed to fi t the spectropho tometer mounting slide. Onthis frame was a single screw, threaded in opposite directionson its upper and lower portions. As the screw is turned,the sample grips travelling on each threaded section moveapart. allowing the midpoint of the film to remain i n thecenter of the ir beam. Spectra were taken a t a number ofelongations to 200 with polarizations parallel and per-pendicular to the direction of stretch.A heated cell1' was modified to allow study of the copoly-mer films above T,,,without changes in thickness. The gasspace of the existing design was eliminated and circularaluminum foil shims equal to the sample thickness wereused as spacers. Circular samples were cut from thecopolymer films to fit snugly within the area defined by thespacer. The sample and spacer were held by moderatemechanical pressure between salt plates during the experi-ments. Isothermal (+1') scans of the 2-15-p region weretaken at about 10' intervals, and again during cooling. Theintensities of the major bands of the spectra here virtuallyidentical before and after heating.Finally, series of three films of differing thickness fromeach copolymer were scanned to determine the extinctioncoefficient of one oft he acid absorptions.Calorimetry. The melting points and heats of fusion forthe branched polyethylene reference and the four acid co-polymers were determined on the Perkin-Elmer differentialcalorimeter, DSC-1B. The instrument was calibrated usingthe melting points of water and benzoic acid, 0 an d 122".Samples were cut from copolymer films, melted, then crystal-lized by cooling at 5.0c/min. After 24 h r at 25 ' the samplewas remelted at 10'/min. The areas under the latter curveswere determined by planimeter for crystallinity calculations.The maxim um excursion from the base line was taken as themelting point. In a like manner, the maximum i n the crystal-lization exotherm was taken as the crystallization tempera-ture. Solutions of the copolymers inxylene (0.01 solids) were used i n an effort to grow crystalsfrom solution. While no single crystals could be obtained.al l the samples yielded at least some very small, open,spherulitic crystal sheaths. Nucleation would not occur

    Solution Crystallization.

    (7 ) R. W. Rees ,and D. J . V au g h n , P o / r m . Prepr in t s , 6 , 28 7(1965).( 8 ) R . W . Rees an d D . J. Vaughn, ib id . , 6, 296 (1965).(9 ) W . J . M acK n i y h t , e t a/ . , . A p p l . Phj , s . , 38 , 4208 (1967).( I O ) W. J . M acI< n i g h t , e t a[ . , bid., in press.( 1 1 ) M . G. C h a n and W. L . Hawkins , P o / J ~ .a g . Sci . , 7, 264( I 967).


    A 2 0 3 5 0 0 918B 4 8 - 2 0 0 66 0 926C 5 0 -2 0 I 57 0 935D 4 8 > I 5 2 26 0 94 6E 6 9 > 1 . 5 2 78 0 953

  • 8/3/2019 EAA Properties


    24 6 E. P. OT OC KA AND T. K. KWEI Mucroniolecules


    Acid, e,Polymer mol/cc cm2/m ol- ~BCDE



    20- 0.vY 4



    4 24 x 10-4 3 . 5 8 x 1049.71 X 3 . 4 5 x 101.66 x 10-3 3 52 X 1042.00 x 10-3 3.46 X loJ

    O / A

    kcal /mole0

    4 2.6 2. 8 3.0 3.2 3.4 3IO I T ( K - )

    Figure 1.i n ethylene copolymers: 0 ,heating; 0 , ooling.Association constants for the carboxylic acids

    28.0I- 2 .6 5 2.4: .2m 2.0-212 1.81.6I 41.2

    C - AD -E - v

    2.2 1