NATIONAL BUREAU OF STANDARDS REPORT NBt PROJECT MBS REPORT 0708-20-3824 DecemlDer 31 , 1958 6308 Progress Report ANALYSIS OF METHYL METHACRYLATE COPOLYMERS BY GAS CHROMATOGRAPHY by John Strassburger* Gerhard M. Brauer* Alphonse F, Forziati** Claire L, Burns* * Chemist, Dental Research Section, National Bureau of Standards. ** Research Associate, American Dental Association Research Division, National Bureau of Standards This work is a part of the dental research program conduc- ted at the National Bureau of Standards in cooperation with the Council on Dental Research of the American Dental Association, the Army Dental Corps, the Dental Sciences Division of the School of Aviation Medicine, USAF, the Navy Dental Corps, and the Veterans Administrationo IMPORTANT NOTICE NATIONAL BUREAU Of STA regress accounting documonta Approved for Intended for use within the G public release by the malljf published It is subjected to additional evaluation and re director of the National Institute of reproduction, or open-literature listing of this Reporti either In lion is obtained In writing from Standards and Technology (NIST) the Oftice of the Dlrectofi Natl Such permission Is not needed, however, by the Government s on October 9, 2015 prepared If that agency wishes to reproduce additional copies U. S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS } ' ' A-'Ty. ?'.,• :»-. vs*- V fV ' 'i ( 1 :jifr ' f • ' i : ":’• 'v;. - i. ^ '“i r, Wi '"V’..' V./- ., -V ? *k .v . sv ^ ': -s .. 'Vr. '-K \ i » :.S- A V .r ^.'i ' • ! ’ .'<•’.»*•>•' ’ : •: ••:• ' 'i . 1 * ;• /;. ; '. *' ,;“ t ‘-V? n.'.; 'ii'' if. * ,r-‘ ’ ' X >. 6 . v> IM1h4‘D ''tf i; ' - ? * !* ' V ’ • r\y~Att0l’iy li. H. iv. sU fv V.- ?. / . ANALYSIS OF METHYL METHACRYLATE COPOLYMERS BY GAS CHROMATOGRAPHY Abstract The usefulness of gas chromatographic techniques for the identification of selected polymers and the quantitative determination of the composition of co- polymers was investigated In the procedure employed the polymer or copolymer was characterized from the chromatogram of its liquid pyrolysis products. Presence of copolymeric constituents even in amounts of Vfo or less was readily detected. A rapid method of improved accuracy for the quantitative determination of methyl methacrylate copolymers has been developed 1 . INTRODUCTION The detection and quantitative determination of copolymeric constituents in polymers such as methyl methacrylate is a diffi- cult and tedious tasko Especially difficult to analyze are the compositions of cross-linked insoluble polymers. Often the compositions cannot be determined with any degree of accuracy. Most practical procedures identify the pyrolysis products of the insoluble copolymers by infra-red or mass spectrometric techniques Recently gas chromatography has become one of the most use- ful tools for the separation^ identif ication and quantitative • [e.^^Ax' .m i " 1 V ''•f ^ * .' t I ^ ^ jr — ~ ''' ii'Ss'sis^A 'll f'-' e/P' bniB ’Prfa' *xo1^ •'' ^ " '. 'i™ " - {111 rov 1:q- nul.‘Ji:S'Qa/no'^ ectjt 1t<?' SHK Hi I’ »'..- -T I 4’. 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In this technique separa tion of components of a mixture is accomplished by selective sorp tion on a stationary medium. Although a number of books Il-3] and papers have described gas chromatographic separation of or- ganic mixtures, only a few investigators [4-7] have reported iden tification of polymers by gas chromatographic analysis of their pyrolysis products. The ^im of this study was to determine the suitability of gas chromatographic techniques for the identification of polymers used in dentistry. The materials were depolymerized and the / * liquid fractionsj of the depolymerization products were subjected to vapor chromatographic analysis. Among the materials studied were mixtures and copolymers of methyl methacrylate with methyl and ethyl acrylate, acrylic and methacrylic acid and ethylene dimethacrylate 2 . EXPERIMENTAL PROCEDURE 2.1 Sample Preparation The copolymers were bulk polymerized after removal of the inhibitor from the monomer either by extraction with sodium hy- droxide or by distillation. Solutions containing varying per- (by volume) centages of monomers /Were placed into clean test tubes and ni- trogen was bubbled through each sample for five minutes. The test tubes were immediately stoppered with an aluminum foil covered cork and placed in a 60°C oven and were kept at this temperature until the contents had polymerized to a solid mass. - 3 - They were then placed in a 100° C oven for two to three days to complete the polymerization. In later experiments the test tubes were sealed in order to avoid loss of volatile monomer due to evaporation during polymerization. The polymers were pyrolyzed in ap oven at 350° C and the liquid fraction of the pyrolysate was collected in a covered container kept in an ice bath. Although precautions were taken to avoid loss of highly volatile liquids^ slight errors in the subsequent analysis may have been caused by the evaporation of such components. No effort was made to collect gaseous pyrolysis products and hence they did not appear in the chromatograms. The pyrolysis condensates were stored in snap cap vials in a refrigerator prior to analysis which was usually conducted within 48 hours. Samples were removed from the vials by means of a Gilmont micropipet syringe and 20 microliters were introduced into the injection valve of the chromatograph. 2.2 Apparatus and Operating Procedures Analyses were made using a Consolidated Electrodynamics Corporation chromatograph, type X-26-201 . A schematic drawing is given in Figure 1. A small amount of sample was injected at the head of the partition column and was transported through the column by helium which acted as an inert carrier gas. The column was made up of an inert size-graded solid that functioned as the support for the stationary liquid phase. Johns -Manv i 1 le C-22 ground firebrick, mesh #30 to 70, was selected as the solid support for dinonyl phthalate, the liquid phase. " . c£ J S' •) -.'f'>i a. I *. J' *7 d.'- ... ^ '* 0 • :.' f' t: £ . : '"i uu ;> i. lit j. ';a g-.:cI ; Gj'wii Qct"': .1 . '•/^v. r: ^x£^ .gl. rer. : ^:::: ' ' '' i-'i'fi -• ::1 ”• S’ ar.^ C'^c ^-2 PBV“ b 3 s ^I'O^ X'-i ^W o'’' Ofr.Y. QC g. 'T - •’ : :.:} ::•• : £ A-3:V..Ii:>'i '.: — i. :g nv.'L .' V . /£.£ :*!/?. .">L rtx -.'Cr'aG fjl _fvGi£/0 •• - i A . ic't'j 3 ;:>3 . £ ;: oX-lielo'/ lo i •/: : .. .. )QBV^ Oil-:*’ : •'.vai:: G3-’ : GV£r: 3±^i.£ g -v;.g.. -.f.-'i;.3 - ••'• • • - . -'^Ol r.c . b:- t. 'bclle O.K' '(} b\;,;C|moc .dv^ps ' . i'l^G ; .e.r'v’r : ai: ' '3'. ....! - • 6 ri.'t civj.'. ifio qG..: G . 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J2 ! u • •;-:* " ' ' '*•:.' j ; £••;: ' bc:^v;r r 3* a£'v A0f vO;j . /It' ''‘I'Fi:-'’ •!•.'" :‘' ;;: .1 .a y y:£j; lv^ .’ ;;/ion .CMqi-'ii * *• * ^1 '• f ^ . „,, jiX . - 4 - Dinonyl phthalate^ a liquid with low vapor pressure^ was employed as the stationary phase since it is non-selective; that is, it will effect a satisfactory separation for a wide range of compounds, roughly according to their volatility and can be used at relatively high temperatures. The columns were prepared according to the procedure described by Dimbat, Porter and Stress [8 ] The temperature of the column was kept high enough to vaporize the sample. Thus, the carrier gas carried the vapor- ized components of the sample through the column at different rates in accordance with the relative degree of volatility of the components, causing them to emerge from the end of the column in the order corresponding to their affinity for the column material. Changes in the composition of the effluent were de- tected by a delicate sensing device, capable of indicating both qualitatively and quantitatively the presence of components in the effluent. This detector consisted of four thermal conductivity cells arranged in the form of a Wheatstone Bridge.