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Heats of Copolymerization of Butadiene and Styrene from Measurements of Heats of Combustion

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Heats of Copolymerization of Butadiene and Styrene from Measurements of Heats of Combustion Journal of Research of the National Bureau of Standards Vol. 48, No.4, April 1952 Research Paper 2313 Heats of Copolymerization of Butadiene and Styrene from Measurements of Heats of Combustion Raymond A. Nelson/ Ralph S. Jessup/ and Donald E. Roberts The h eats of combustion of two samples of polybutadiene and four cop olvm ers of buta­ cli ene and styrene prepared at 50° C (122° F ), and one sample of polybutadiene and four copolym ers polym eri zed at 5° C (41 ° F) were m easured in a bomb calorimeter. The stn ene contents in th e copolymers varied from approximately 8 to 55 weigh t percent. A value for the heat of polymerization (or copolym eri zation) was calculated for each sample by combining th e exper im ental value for t he h eat of combustion wi th other known thermoche.mical data. The m ean value obtained for th e heat of polymerization (- tlI-J p 0) of polybutad lene IS 17.4 kcal per monomer unit, and the values obtained for t he heat of co­ polymerization varied from 17.1 to 17.7 kcal p er m onomer uni t. No app er ciable difference was found betweep ti? e heats of copolymerization of t he 5° C and 50° C pol.vmers. The h eat of copolymeriza t IOn can be r e pr ese n~ e d as a function of styr ene content of the polym er b.v a n equatIOn of a form den ved theor etICall y by Alfrey ancl Lewis, although th e co ncli t ions under whICh th e polymers were formed were such t hat some of the a s~ u m pt i o n s underl Yinp: the de ri vation of the equation wer e not satisfi ed. 1. Introduction T A TlL" l. Analyses oj polymer sa m/)/es M easurements have been made, by means of a Phenyl. Polymer Sly- Car- H ydro- Ox),- 8ul- A sh beta- bomb calorimeter, of the heats of combustion of rene bon gon gcn fur naphthyl- three samples of polybutadiene and eight copolymers a lll ine of butadiene and styrene, ranging in styrene content from approximately 8 to 55 percent by weight (5 to 50° C (122° F ) POI)'llWrS 40 mole %). Two of the samples of polybutadi ene I lrt cQ I 'let c ~ 'lrt 00 II A __________ '1I'1 ~ 'ld ~ 'wI c:o 't "t ~ and four of the copolymers 'werc prepared by poly­ 0 88. 48(j 11. 166 O. 14 5 0. 109 O. 100 0.00 G L- 65i ____ 0 88.05(; 11. I i9.) · 145 '. 072 . 09i . 12 merizatiol1 at 50 ° C (122° F ), whereas the others GL- 658 ____ 8.58 88.00i 10.8982 . 16 . 136 . 104 . 1 were polymerized at 5° C (41 ° F ). The data have X-452 _____ 23 89 89. 42 10.36 .090 . 08i . 13 . Oi GL-OG2 __ __ '12.98 VO . 1OO 9. i 100 · 14 . 081 . 111 I been combined with other thermochemi cal data to 48-B _______ 55. i3 00.561 9. 2643 · 15 . 0·16 . 158 . 07 obtain values for heats of polymerization and co poly­ merization. 5° C (41 ° F) polymers B _____ __ ___ 0 88.4i4 11. 1000 O. 12 0. 083 0. 34 O. J4 2. Source and Purity of Material X-45'L ____ 8.58 88.869 10.872 .235 '. 056 . 18 . 13 X-4i8 _____ _ 22.61 89. 443 10. '1008 . 15 . 048 . 098 . Il G r.- 600 ____ 36.20 89.913 9.93'12 . 08 . 050 . 095 . 11 The materials used in this investigation were made GL-66L ___ 53.09 90.513 9.3585 . 11 . 045 .09i . 11 available by the R econstruction Finance Corp., Office of Rubber R eserve, and were purifLCd in the , Added after analysis. " rhe values reported here arc corrected val ues for sulfur content. For G L-657 Rubber Section of the Bureau. Some of the prop­ the experimelltall y determined ,-slue is 0. 150% S 81ld for X-454 0.087% S. See erties of the purified materials are given in table 1. text p. 2ib. The pol ymers were prepared by emulsion polymer­ ization. The " modifiers" used were commercial described above and after further evacuation to n- dodecyl mercaptan (DDM) for the 50° C polymers, about 10- 4 mm of mercury for several days at room and commercial tert-dodecyl mercaptan (S ulfole) for temperature. the 5° C polymers. The purified samples were analyzed quantita­ The purification procedure involved dissolving the tively, and the results arc reported in table 1. The sample in benzene and precipitating it by pouring styrene contents reported in this table were calcu­ the solution slowly into methyl alcohol while stirring. lated from the carbon-hydrogen ratios (corrected for This was done three times. Then the purified mercaptan) . sample was again dissolved in benzene, a small A part of the experimentally determined sulfur amount of phenyl-beta-naphthylamine was added content of sample X-454 was found to be present a as an antioxidant, the mixture was frozen, and the an inorganic impurity, rather than a mercaptan benzene was removed by sublimation in vacuum to attached to the polymer chain_ The sulfur con ten t give a product similar to foam rubber in appearance. r eported in table 1 for this sample is the excess of This procedure removed soap, fatty acid, and stabi­ the total observed ulfur over that found to be pres­ lizer, as well as som e of the low-molecular-weight ent in the inorganic impurity. The experimentally polY111.e1'. In the presen t work no significant dif­ determined sulfur content of sample GL-657, which ference was found in the heats of combustion of contained no styrene, wa high er than that calculated samples burned as received after the treatment from th e observed carbon-hydrogen ratio on the as- 275 -- sumption that the sample consisted entirely of do­ decrease in intrinsic energy accompanying the reac­ decyl mercaptan and polybutadiene. It was assumed tion that the difference was due to sulfur in inorganic im­ purity (as in the case of sample X-454) , and the b-?c sulfur content reported is that calculated from the CaH bOcSd(solid polym er) + (a + d + -:f- ) 0 2(g)~ carbon-hydrogen ratio. (1) 3 . Method and Apparatus aC02(g) + d S02(g) + %H20 (liq) , The apparatus and procedure used in the bomb using the Washburn procedure [7] modified so as to calorimetric measurements have been described pre­ apply to 28° C and to the energy con ten t of the gases viously [1 , 2, 3, 12).1 The bomb used has a capacity at zero pressure instead of 1 atm. of 381 ml. One milliliter of water was placed in th e The measuremen ts were made in terms of the abso­ bomb before each combustion experimen t. The lu te joulc as the unit of energy. Conversion to the polymer samples used were first compressed into conventional thermochemical caloric was made by pellets. means of the rela tion The calorimetric system was calibrated with NBS Standard Sample 39g of benzoic acid , using the valu e 1 cal= 4.1840 abs j . 26433.8 abs jig for the heat of combustion of this material under the conditions of the standard bomb 4. Results of the Calibration Experiments process [3, 4, 5]. In calculating the resul ts of the h eat of combustion All the measurem en ts of heat of combustion re­ measuremen ts, the amount of the combustion reac­ ported in this paper were made with the same calo­ tion in each experimen t was determined from the rimetric system . However, the work was carried out mass of carbon dioxide formed, using the value 44.010 over a period of about 2 years, and, because of nec­ g for the molecular weight of carbon dioxide [21 ]. essary repairs to the calorimetric system , it was re­ T ests were made for carbon monoxide in the gaseous calibrated several times during the course of the products of combustion after the carbon dioxide had work. T able 2 presents a summary of the valu es been removed, using a colorimetric method developed obtained for the energy equivalent of the calorimeter at the Bureau [6]. No carbon monoxide was found, and the numbers of th e polymer samples whose heats and no soot or other evidence of incomplete combus­ of combustion were measured, using each value fo r tion was found in the bomb in any experiment. the energy eq uivalent. Corrections were applied to the observed h eat of combustion in each experimen t for hea t of stirring, T A BLE 2. Enel'YY equivalent of calorimetej' heat transfer b etween calorimeter and surroundings, ignition energy (22 j), and energy produced by the Energy equivalen t Polymr l's inn:'stigatcd formation of aqueou s nitric (58 .8 kj /mole) and sul­ furic (3 05 .7 kj/mole) acids in the bomb. The last jre 13784.4 ± 0. i " II two corrections were made on the basis of the anal­ 13372.2± 0.8 48-n , X - 452. 01,- 658 ysis of the washings from the bomb after each com­ 1~970.2 ± 1. 8 0L-657 13964 .9± 1. 8 01,-662 bustion experiment. The air initially in the bomb 1395o.7 ± 1. 4 { 0L-660 o T~f\6 1 (e xperiment, 1 and 2) was not Hushed out with oxygen in these experimen ts.
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