- Email: [email protected]
Studies on thermal degradation of aliphatic polyamides by pyrolysis-glass capillary chromatography
STUDIES ON THERMAL DEGRADATIOS OF ALIPHATIC POLYAMIDES BY PYROLYSIS-GLASS CAPILIARS GAS CHRO!bZATOGRAPIIY
ISTRODL’CfIOS
Synthetic polqrnides. which are well kn0H-n as nylons. are widely utilized in \arir?us f&is as fibres. cngineerin_e plastics. etC The first s>-n&etic polyamide. nylon 66. was prepared by condensation of adipic acid and hexamethylenediaminmine in 1938. Subsequently. nylon 6 was synthesized b>ring-opening polymerization of l -caprolactam In recent years. there have been developed many additional ahphatic polyamides. such as nylon 7.9. 12. 6.10.6_12 and 12.12.Thermo-stable aromatic polyamides such as Kevlar and Yomex are also available Half-aromatic polyamides such as n_vlon MXD6 which have excellent gas-barrier characteristics,are now also in practical use_ Considerable work has &en carried out on the pyoi_vsis of polyamides &hammer et al_ [l] reported that nylon 6.6 yielded cycloperrtanone as one of the most characteristic p_\rolysisproducts. In studying the thermal decomposition of an aromatic polyamide. Chatfield et al. [2] identified aromatic
nitriles LEdmu-ald and co-workers [3-51 investigated various polyamides by pyrolysis-mass spectrometry (h--MS). and pr-ted an extensive discussion on the thermal degradation of the pol_vamides, Pyrolysis-gas chromsttography (Py-GC) hs also been applied to the compositional analysis of nylon 6-nylon 6.6 copolymers [6]In this work. a series of aliphstic pal>-amides were studied by Py-GC_ The polymer sampls were pyrol_\-sedat 550°C in a vertica1 microfurnace-Q-p= pyr+-str under a flou- of carrier gs. and the resultiq degradation producrs were continuously separated by a glass capiliac column to obtain high-rex~
lution pyrograms. The char;rcteristic ps;tks appearing on the p~~ograms were identified using 3 mass spectrometer din+attach& to 3 gas chromatoprdph. The _ecner31 degradation mechanisms of the aliph3tic poly3mides 3re discussed on the basis of the observed pyo_g3ms_
Table 1 shows twek kinds of polgmide pmvided b_\- the Plastics Laboratory. Tomy
samples utiIized. which w-ere Industry Inc. S3305_ J3pan-
X\;?-Ion4 ~-3s synthesized from Zpyrrolidone by anionic pril_vmerization. The other four kinds of c~rtminoc3rbox$ic acid-type poIymides were prepared by either rixg-openins polymcrizttion of the correqonding lactams or
4
6 s Ii 12 6.6 65 6-10 6-l’ 126 1210 13 -_ 17
+ SH(CH, !,CO+, + SHtCH, !sCO+, + SH(CH:),CO+, +SH(CH, )JOtrr f SH(CH= )JO+, + SHtCH, ),SHCOKHz )JO+, +SH(CH,),SHCO,CH,),CO+, +SH(CH=),SHCQCH:),CO+, +SH[CH,),SHCQCH-)&Of, +SH(CH- _ )..SHCO(Cti: j,CO+, I_ tSHiCH~),:SHC~CH:),CO+, +SH(CHz),,SHCOiCH:):jCOf,
119
polycondensation of exuninocarbox~lic acids The other seven kinds of dkunine-dic3rboxyl.k xid-type poI_vamides were prepared b_v condensation polymerization of the corrwonding d&nines and dicarboxylic acidsThe nylon samples were dissolved in formic scid and then precipitated with methanol to remove impurities The precipitates were filtered and n-ashed with methulol, Iind then dried 3t SOT under v3cuum for IS h &-~o&sis-gas
chromaxogmphic condirions
_A wrtical microfum3ce+yx p_vrolyser jYan3_srimoto GP-10 IS). which permitted instantaneous 3nd specific therm31 degmdrrtion of pol>mtr s3mpies [7]. ~-3s attached directly to a Shimadzu 7-A _easchromato_g3ph equipped with 3 high-resolution &ss capillcolumn (50 m X O-9 mm Q-D_ >i;O-3 mm I.D.) suspensionso3ted with OV-101 and Silanos (325 meshi. In order to obt3in 3 high resolution even for rektively polar components. the 36-c si:es of the inner surface of the @ss cslpillq column were treated with 3 dilute solution of PEG 2011. baked out at 25O=C for 30 h by p3ssinS nitrogen carrier gas thro@ it and washed uith chloroform prior to the final d_vnamic costing with OV-101. The column temperature 1x3s pro_g3mmcd from 50 to 250°C at 3°C.z~‘min. The flow-nte of the nitrosen 3t the pyroI_vstr of 55 ml,,.:-minwas reduced to I ml_/min 3t the capiil~ column throu_eh a splitter (55: l)_ The de3d \-olume of the splitter was p3ckcd with 5% of O\‘-101 on Dksolid H (SO-100 mesh). the temptzxture of which ~-3s maintained 31 25OOC. The p3ckinS in the splitter plays 3.n import3nt role in preventing contamin3tion of the column by the concomitant less volatile components in the degradation producrrw-tichotheruise tvauldresultinrrseriousdtcrtase in resolution [S]. Amounu of sample ran&S from O-1 t0 O-5 mS were p~~olysed at 55OT under a Rou- of nitrogen carrier gas_ Peak identification ~-3s mostly carried out using ZI directly connecrrd JEOL JMS-QlO_A qusdrupole maSS spectrometer. RESULTS ASD DISCCRSIOS Chcuacren3zic degradaxivn products J;O~ ru’phcric po@~~ides
T3bleZ summarizes the various classgs of chaMctcristic thtrm3l degmdation products from aliphatic pol_vamides which sppeared on the resultinS pyro_enms at 550°C (Fi_es. l- 12). Hylrocarbons (HCsj: As reported for the p>-rolysis of polyethyltnes [9]_ the norm3l hydrocarbon peaks from n_vlons also consist of trip!ets (saturatd a-olcfmic and a,wd.ioleftic). among u-hich the cz-olcftic pe&s h3ve the strongest intensities. However. for the HCs with the mxtimum -bon
T-ABLE Z Charzcterisdc dqradation chss of c0mpaxxis
prcxiucts from alipktic polyamides
Abbrc-
StnIffurc
xistion CH,-(CH, I,-CH, CH2 = CH-(CH, b_ _ ,-CH, CH,= CH-(CH,),_,-CH=CH: CH,-[CH- _ ) .x-C=S CH, =CH-(CH2),_,-C=S _#wH: 1”. SH
Lzsrams
L
o=c
Dinitriks
DS
S=C-(CHz,,-C=S
Cyi!opax;rront
CP
CH,-CH, ‘c=o ~~H,-CH/ OH CH,-,CH,,,-C-S-~CH:}~-CH; ov CH, =CH-tCH,
)%_ !- C - S -rCH,
I,-CH,
0y CH, =CH+CH,I,_~-C-I;‘-,CH2,,_,-CH=CH: OH CH, -tCH:
)m- C-;-(CH,),-CsS OH
CH, =CH-(CH,
b_ I- C-S-{CH,l_-C=S Ho
CH,-KH,
1, - S-C-(CH,),-C=S Ho
CH, = CH-(CH:
brn _ ?- k - C-(CHz),-C=S
number. the intensity of the a.=-diolefinic peak becomes wry close to that of the a-olefinic peak_ Siononitriles (XX): MX pea& are mostly doublets (saturated and aolefinic). among which the olefinic are the most intense.
Lactams (L): Some weminocarboxylic acid-type q-ions yield fairly straq L peaks. Dinitriles (DSs): Most of the diamine-dicarboxylic acid-t>-pt n_vlons yield characteristic DS peaks whose carbon numbers correspond to those of the dicarboxylic acids utilizedCyclopentanone (CP): This peak is chamctcristic of the adipic 3cid fractions in the polyner chain. Hydrocarbons containing one smidc group [HC\_Aj]: The possible sxructures shown in Table2 predict msny 3ssocisted pe3ks even for 3 &-en c3rbon number HC(_+). In f3ct. 3 srriu of complex multiplets 3re usu3lfy obscn-cd for HC(A)sMononitriles containing one 3rnide group [MS(A)]: The series of MS(A) peaks theoreticaliy should consist of doublets (sstunted and a-olcfinic,~. among which the olcfinic are the m3in p&sHowever. in the higher retention rqion where most of blS(A.)s 3ppe3r. the obser\-ed pe3ks 3pparent& become singlets bec3usc of the sm3ller differences in the boiling points between the isomers and the poorer res&-ing pow-er oi the separrttion column in the higher retention re@on. In the follovring discussion. the sbbreviations show-n in T3bleZ 3x u_wd for the chancteristic degmdation products.
FQs. 1 snd 2 show the pyrogr3ms of nylon 4 snd 6. respectivel_\-. 31 3 pyrolysis temperature of 55O’C_ -4s discussed in praioa p3ptrs [G-6]_ the main products 3re the 3ssociatcd lacL3ms such 3s butyolsctam [L( nr = 3!] and c-c3prol3ctam [ L( nr = 5)]. respectively. These 3re formed throqh thtrmal ckv3ge of the relativcl_\- wuk C-S bonds in the bzckbons of ht polymer chains follou-ed by cyclir;ltion. 3s the resultinS Ls 3re suifkientl~ stable at the p_vrol_vsistsmptr3ture:
.?.a
I
=
-.-.-.-A%
3:.
On the pyrog3m of nylon 6. addition31 minor nitriie pe3ks 3rc obscr\-cd. n: = 1-4 n = 5.L such 3s MS\‘(m = 4) and a series of MSC;I_AJ( Figs. 3.3 3nd 5 are the pyrognms of nylon S. 1I and IL resp~tively- The 3zfsoci3Lcd L peaks (m = 7. 10. 11) become vtn_ sm3ll. mainly became of the relstively small chance of rinS forrnstion resrttions forming theseloge ring compounds at hi& temperatures- It is well known that one of rhe mast chaxxtcristic therm31 dcgmdstion mechanisms is zssocistcd withcieaxqeof
_xs =-;
1a.:.
i
_-
I.
.1
_
=-I.
:
-
._
_
z i_
_________d.‘------_
. ..-. -
__. _. _
,,, __
__
xs
=I:--‘.r.::
A
.._
- -
z .=-:.
.
_.. 5
:_2
r.: A
-*-c -
Pgogrzm
the relative!?
ci.
5: mm. -mm ::zB
4
r,._L__k-h..n-._..
- _. .__.- ________-__--
_’
--.=_.':_3
;:
.__ --.-
*z I
fis
;:
*
_ .r.._--~~_‘;.
'5: TF_z.
-_ :
i: --s-r __.-
_._ ..__.
‘.‘
of nylcm 1l_
weak C-S
ar-olefinic acid-tines
bonds in the polymer chain, Thus, the formation 0
[CH, = CH-(CH,
I=:- C SH,]
of
U-S reported by Py-MS
studies [5]. However. in the present @--GC work. we could not find any a-oltfinic acid-amide peaks on the pyo_gams of the nylon samples Instead. fairly strong mononitrile peaks (XI&r uere obser\-ed. The major oltfir~ic MSs may be formed throu& the fcllowing C-S bond cleavages followed bthe dehydration reaction:
The maximum carbon number of the MSs cor~~ponds to that of the number of successive methylene groups in the pal_\-mer chain plus 1, The minor saturated MS peaks are always accompanied by the ma_ior olefinic peaks. It is interestins that. among the set-i- of the doublet MS peaks. the a-olefinic peaks are usuall_v stronger than the saturated ones. but the reverss tendency is always obsen-cd for the third maximum cxbon number MS pairs. This tendency can be seen not on& for the cxminocxbox_vlic acid-type qlons but also for the condensation-t_\penylons- These phenomena su_gest that. when 51% with carbon numbers fewer than the maximum are formed through C-C bond cleaqge. there might e.xist some sxceptionslly fwoured routes for the formation of the third maximum carbon number SISs. One
px~ibk sxpkmstion is that. among the competitive C-C bond clexqes to form the third masimum MSs from the maximum l\lSs_ route I to yield ~~~tuntcd MS pIus acetylsnt ma>- be more favoured than route II to yie!d a-otsfmic MS plus cth>-km:
On the other hand. the C-C bond clear\-a_eesto yield HCs with carbon numbers 1~a than and _ereater than 2 may proceed preferentially thrwgh routs II-tvps reactions to form a-&fink AiXs. On th; other hand. a series of trip!sts are observed for HCs whose maximum carbon number correponds exactI_v to those of the number of ?;uccesivc msthykne gwps in the poI>mtr chain, In the higher retention @on. a serk of MS(A) peaks 3~ also obse=ed. Except for nylon 8. these shrrrxrcristic 1IS;(_A) peaks are overlapped by the series of complex muIti~1st~ of HC(A) peaks.
Fig. 6 and 7 show the pyrograms of nylon 6.6 and 126, respectiv&. which were syahesized from C, and Cl2 diamincs and adipic acid- The mosr characteristic peak is cyclopentanone (CP). which is knoun to be formed from the adipic acid fractions in the polymer chain as follow-s [ 1.61:
.. : .; : :
__r-._: :. :
rr
-mi ._
-_._
c
-%-.-.-.-A,
_
In the earlier retention re@on. the corresyondirq HC peaks are al-so obsen-td. However. the $elds of HC(_A)s are very small_ Althou_eh that adipic acid-t>pe nylons do not yield any set-k of peaks of Xi% rexcept for !US\_Ai’ peaks small MS{ m = IO) peaks for n_vlon 12.6). the corraponding are obscr\-cd, Furthermore_ a vet small DS( nr = 41 peak appears on the pyrqrams of nylon 6-6 and 136_ On the p~~ograms of n_\-lon 6-9 (FigSI_ 6-10 fFi_e.9;. O-12 ~Fle !O)_ 1220 (Fig. 11) and 12.12 (Fig 12). w-here either the C,-. C::,- or C:z-dicarboxyl?c acid is used. one of the most characteristic peaks is thst of the dinitriles (DSs). These may be formed in a similar ~-a>-to the formation of _\lSs from cxuninocarboxylic acid-t_\pe nylons:
The series of HC and MS peaks on the pFro_gzrs zre asscxizted lx-31 cleavage of the C-C bonds along the pol>mtr chain In addition. a xriss of MS(A)’ peaks are also obsem-ed for each nylon sample_ Especially with hexamethylenediamine-t>p nylons such as nylon 6.9. 6_!0 and 6,lL the associated MS(A)’ peaks are clearly separated on the p>ro_gams. Further. it is interesting that a small l -caprolactam peak [L( M = 5); is obssrwd x\lth the he_xameth~lenediamin~type nylons (including nylon 6-61~ In between the 51X and MS;(A)’ peaks. a complex series of HC(_A) multipltts TLTt aho
observed. The mechanisms of mononitrile formation mentioned above predict that the maximum carbon numbers of MSs for nylon 1210 and 12 12 should be pmk nine and ele\-en respectively- However. on both p_\ro,erams, the MS
1: z-c I
-xc
*_&,
z
.-
.-
,:
_
-.
_..;
I i ‘.
!.
I
i ;
_-_.
..--\L.h_--.
___---. H,’ A’
of
nylon
- --
6.6.
__
-. ,_____-_
. -_.-
--
._-._----
.--;--
-
=::--.:::-I’ I’ ;
:s,
I.
-.-
Fi_e6. Pyogran
.
,‘:. .
.
-4i
z-3
t-3’
I
.-c
__
-.
r
.=I;.’
1
5:
. ..
--r
5: .
:=:
f. 2
t:x.?r =:z-:
: :_
-L-
;
T
i-
i5y.m”
-=-
CICSCI--
-.
. ‘-
__
. ..
_A
129
.
130
series continue to C,= Moreover. as mentioned above. n>-Ion 12.6 also yielded C,+lX peaks. These phenomena susest that some additional thermal rearrangement-t>pe reactions mi@t participate in the formation of the l\IXs from the C,,-diamine-t>pe nylons. As a SUM of the general thermal degradation of the aliphatic polyamides. the main characteristic peaks such as IA. HCs. 5fXs. CP and DSs which appeared in the relatively earlier retention regions of the p>.rograms are given in Table 3. In concl-usion. the Py-GC technique combined \:.ith high-resolution glass capillary separation has been demonstrated to be V~Q-effective in studies on the thermal degradation of polymides whose degradation products consist of many kinds of compounds. Hou-ever. this technique has a limitation associated uith the volatility of the products from the polymer samplesL’nder the ultimate gas chromatographic conditions utilized. the C&IX(A) peak barely appeared on the pyrograms at a retention time of about 65 min. As was reported by Ltiderwald and Mere [5]. the less volatile degradation products such as cyclic olisomers of polyamides would bt better studied by Py-MS. where the p>.rol>-sisof the polymer sample is performed under high vacuum in a mass spectrometer. Thus. PyGC and @-MS would provide L-q- useful complementary information about the thermal characterization of polymers. .4CKSOu.LEDGE!slEscT The authors are indebted to Plastics Laboratory. Torax Indusw Inc, Nagoya. Japan. for providing a series of well characterized aliphatic nylon samples.
REFERESCES 1 RG. Achynma. 2 DA Cbf%M. 3511.
F-M__Fkinhn and G-M_ Kline. J. Rtr. Sat B-s_ Stand_ 46 (1951) 391. 1.X Einhorn. R-W_ Mickclron md J-H. FuucX J. Pal>= S5_ I (1979)
ISTRODL’CfIOS
Synthetic polqrnides. which are well kn0H-n as nylons. are widely utilized in \arir?us f&is as fibres. cngineerin_e plastics. etC The first s>-n&etic polyamide. nylon 66. was prepared by condensation of adipic acid and hexamethylenediaminmine in 1938. Subsequently. nylon 6 was synthesized b>ring-opening polymerization of l -caprolactam In recent years. there have been developed many additional ahphatic polyamides. such as nylon 7.9. 12. 6.10.6_12 and 12.12.Thermo-stable aromatic polyamides such as Kevlar and Yomex are also available Half-aromatic polyamides such as n_vlon MXD6 which have excellent gas-barrier characteristics,are now also in practical use_ Considerable work has &en carried out on the pyoi_vsis of polyamides &hammer et al_ [l] reported that nylon 6.6 yielded cycloperrtanone as one of the most characteristic p_\rolysisproducts. In studying the thermal decomposition of an aromatic polyamide. Chatfield et al. [2] identified aromatic
nitriles LEdmu-ald and co-workers [3-51 investigated various polyamides by pyrolysis-mass spectrometry (h--MS). and pr-ted an extensive discussion on the thermal degradation of the pol_vamides, Pyrolysis-gas chromsttography (Py-GC) hs also been applied to the compositional analysis of nylon 6-nylon 6.6 copolymers [6]In this work. a series of aliphstic pal>-amides were studied by Py-GC_ The polymer sampls were pyrol_\-sedat 550°C in a vertica1 microfurnace-Q-p= pyr+-str under a flou- of carrier gs. and the resultiq degradation producrs were continuously separated by a glass capiliac column to obtain high-rex~
lution pyrograms. The char;rcteristic ps;tks appearing on the p~~ograms were identified using 3 mass spectrometer din+attach& to 3 gas chromatoprdph. The _ecner31 degradation mechanisms of the aliph3tic poly3mides 3re discussed on the basis of the observed pyo_g3ms_
Table 1 shows twek kinds of polgmide pmvided b_\- the Plastics Laboratory. Tomy
samples utiIized. which w-ere Industry Inc. S3305_ J3pan-
X\;?-Ion4 ~-3s synthesized from Zpyrrolidone by anionic pril_vmerization. The other four kinds of c~rtminoc3rbox$ic acid-type poIymides were prepared by either rixg-openins polymcrizttion of the correqonding lactams or
4
6 s Ii 12 6.6 65 6-10 6-l’ 126 1210 13 -_ 17
+ SH(CH, !,CO+, + SHtCH, !sCO+, + SH(CH:),CO+, +SH(CH, )JOtrr f SH(CH= )JO+, + SHtCH, ),SHCOKHz )JO+, +SH(CH,),SHCO,CH,),CO+, +SH(CH=),SHCQCH:),CO+, +SH[CH,),SHCQCH-)&Of, +SH(CH- _ )..SHCO(Cti: j,CO+, I_ tSHiCH~),:SHC~CH:),CO+, +SH(CHz),,SHCOiCH:):jCOf,
119
polycondensation of exuninocarbox~lic acids The other seven kinds of dkunine-dic3rboxyl.k xid-type poI_vamides were prepared b_v condensation polymerization of the corrwonding d&nines and dicarboxylic acidsThe nylon samples were dissolved in formic scid and then precipitated with methanol to remove impurities The precipitates were filtered and n-ashed with methulol, Iind then dried 3t SOT under v3cuum for IS h &-~o&sis-gas
chromaxogmphic condirions
_A wrtical microfum3ce+yx p_vrolyser jYan3_srimoto GP-10 IS). which permitted instantaneous 3nd specific therm31 degmdrrtion of pol>mtr s3mpies [7]. ~-3s attached directly to a Shimadzu 7-A _easchromato_g3ph equipped with 3 high-resolution &ss capillcolumn (50 m X O-9 mm Q-D_ >i;O-3 mm I.D.) suspensionso3ted with OV-101 and Silanos (325 meshi. In order to obt3in 3 high resolution even for rektively polar components. the 36-c si:es of the inner surface of the @ss cslpillq column were treated with 3 dilute solution of PEG 2011. baked out at 25O=C for 30 h by p3ssinS nitrogen carrier gas thro@ it and washed uith chloroform prior to the final d_vnamic costing with OV-101. The column temperature 1x3s pro_g3mmcd from 50 to 250°C at 3°C.z~‘min. The flow-nte of the nitrosen 3t the pyroI_vstr of 55 ml,,.:-minwas reduced to I ml_/min 3t the capiil~ column throu_eh a splitter (55: l)_ The de3d \-olume of the splitter was p3ckcd with 5% of O\‘-101 on Dksolid H (SO-100 mesh). the temptzxture of which ~-3s maintained 31 25OOC. The p3ckinS in the splitter plays 3.n import3nt role in preventing contamin3tion of the column by the concomitant less volatile components in the degradation producrrw-tichotheruise tvauldresultinrrseriousdtcrtase in resolution [S]. Amounu of sample ran&S from O-1 t0 O-5 mS were p~~olysed at 55OT under a Rou- of nitrogen carrier gas_ Peak identification ~-3s mostly carried out using ZI directly connecrrd JEOL JMS-QlO_A qusdrupole maSS spectrometer. RESULTS ASD DISCCRSIOS Chcuacren3zic degradaxivn products J;O~ ru’phcric po@~~ides
T3bleZ summarizes the various classgs of chaMctcristic thtrm3l degmdation products from aliphatic pol_vamides which sppeared on the resultinS pyro_enms at 550°C (Fi_es. l- 12). Hylrocarbons (HCsj: As reported for the p>-rolysis of polyethyltnes [9]_ the norm3l hydrocarbon peaks from n_vlons also consist of trip!ets (saturatd a-olcfmic and a,wd.ioleftic). among u-hich the cz-olcftic pe&s h3ve the strongest intensities. However. for the HCs with the mxtimum -bon
T-ABLE Z Charzcterisdc dqradation chss of c0mpaxxis
prcxiucts from alipktic polyamides
Abbrc-
StnIffurc
xistion CH,-(CH, I,-CH, CH2 = CH-(CH, b_ _ ,-CH, CH,= CH-(CH,),_,-CH=CH: CH,-[CH- _ ) .x-C=S CH, =CH-(CH2),_,-C=S _#wH: 1”. SH
Lzsrams
L
o=c
Dinitriks
DS
S=C-(CHz,,-C=S
Cyi!opax;rront
CP
CH,-CH, ‘c=o ~~H,-CH/ OH CH,-,CH,,,-C-S-~CH:}~-CH; ov CH, =CH-tCH,
)%_ !- C - S -rCH,
I,-CH,
0y CH, =CH+CH,I,_~-C-I;‘-,CH2,,_,-CH=CH: OH CH, -tCH:
)m- C-;-(CH,),-CsS OH
CH, =CH-(CH,
b_ I- C-S-{CH,l_-C=S Ho
CH,-KH,
1, - S-C-(CH,),-C=S Ho
CH, = CH-(CH:
brn _ ?- k - C-(CHz),-C=S
number. the intensity of the a.=-diolefinic peak becomes wry close to that of the a-olefinic peak_ Siononitriles (XX): MX pea& are mostly doublets (saturated and aolefinic). among which the olefinic are the most intense.
Lactams (L): Some weminocarboxylic acid-type q-ions yield fairly straq L peaks. Dinitriles (DSs): Most of the diamine-dicarboxylic acid-t>-pt n_vlons yield characteristic DS peaks whose carbon numbers correspond to those of the dicarboxylic acids utilizedCyclopentanone (CP): This peak is chamctcristic of the adipic 3cid fractions in the polyner chain. Hydrocarbons containing one smidc group [HC\_Aj]: The possible sxructures shown in Table2 predict msny 3ssocisted pe3ks even for 3 &-en c3rbon number HC(_+). In f3ct. 3 srriu of complex multiplets 3re usu3lfy obscn-cd for HC(A)sMononitriles containing one 3rnide group [MS(A)]: The series of MS(A) peaks theoreticaliy should consist of doublets (sstunted and a-olcfinic,~. among which the olcfinic are the m3in p&sHowever. in the higher retention rqion where most of blS(A.)s 3ppe3r. the obser\-ed pe3ks 3pparent& become singlets bec3usc of the sm3ller differences in the boiling points between the isomers and the poorer res&-ing pow-er oi the separrttion column in the higher retention re@on. In the follovring discussion. the sbbreviations show-n in T3bleZ 3x u_wd for the chancteristic degmdation products.
FQs. 1 snd 2 show the pyrogr3ms of nylon 4 snd 6. respectivel_\-. 31 3 pyrolysis temperature of 55O’C_ -4s discussed in praioa p3ptrs [G-6]_ the main products 3re the 3ssociatcd lacL3ms such 3s butyolsctam [L( nr = 3!] and c-c3prol3ctam [ L( nr = 5)]. respectively. These 3re formed throqh thtrmal ckv3ge of the relativcl_\- wuk C-S bonds in the bzckbons of ht polymer chains follou-ed by cyclir;ltion. 3s the resultinS Ls 3re suifkientl~ stable at the p_vrol_vsistsmptr3ture:
.?.a
I
=
-.-.-.-A%
3:.
On the pyrog3m of nylon 6. addition31 minor nitriie pe3ks 3rc obscr\-cd. n: = 1-4 n = 5.L such 3s MS\‘(m = 4) and a series of MSC;I_AJ( Figs. 3.3 3nd 5 are the pyrognms of nylon S. 1I and IL resp~tively- The 3zfsoci3Lcd L peaks (m = 7. 10. 11) become vtn_ sm3ll. mainly became of the relstively small chance of rinS forrnstion resrttions forming theseloge ring compounds at hi& temperatures- It is well known that one of rhe mast chaxxtcristic therm31 dcgmdstion mechanisms is zssocistcd withcieaxqeof
_xs =-;
1a.:.
i
_-
I.
.1
_
=-I.
:
-
._
_
z i_
_________d.‘------_
. ..-. -
__. _. _
,,, __
__
xs
=I:--‘.r.::
A
.._
- -
z .=-:.
.
_.. 5
:_2
r.: A
-*-c -
Pgogrzm
the relative!?
ci.
5: mm. -mm ::zB
4
r,._L__k-h..n-._..
- _. .__.- ________-__--
_’
--.=_.':_3
;:
.__ --.-
*z I
fis
;:
*
_ .r.._--~~_‘;.
'5: TF_z.
-_ :
i: --s-r __.-
_._ ..__.
‘.‘
of nylcm 1l_
weak C-S
ar-olefinic acid-tines
bonds in the polymer chain, Thus, the formation 0
[CH, = CH-(CH,
I=:- C SH,]
of
U-S reported by Py-MS
studies [5]. However. in the present @--GC work. we could not find any a-oltfinic acid-amide peaks on the pyo_gams of the nylon samples Instead. fairly strong mononitrile peaks (XI&r uere obser\-ed. The major oltfir~ic MSs may be formed throu& the fcllowing C-S bond cleavages followed bthe dehydration reaction:
The maximum carbon number of the MSs cor~~ponds to that of the number of successive methylene groups in the pal_\-mer chain plus 1, The minor saturated MS peaks are always accompanied by the ma_ior olefinic peaks. It is interestins that. among the set-i- of the doublet MS peaks. the a-olefinic peaks are usuall_v stronger than the saturated ones. but the reverss tendency is always obsen-cd for the third maximum cxbon number MS pairs. This tendency can be seen not on& for the cxminocxbox_vlic acid-type qlons but also for the condensation-t_\penylons- These phenomena su_gest that. when 51% with carbon numbers fewer than the maximum are formed through C-C bond cleaqge. there might e.xist some sxceptionslly fwoured routes for the formation of the third maximum carbon number SISs. One
px~ibk sxpkmstion is that. among the competitive C-C bond clexqes to form the third masimum MSs from the maximum l\lSs_ route I to yield ~~~tuntcd MS pIus acetylsnt ma>- be more favoured than route II to yie!d a-otsfmic MS plus cth>-km:
On the other hand. the C-C bond clear\-a_eesto yield HCs with carbon numbers 1~a than and _ereater than 2 may proceed preferentially thrwgh routs II-tvps reactions to form a-&fink AiXs. On th; other hand. a series of trip!sts are observed for HCs whose maximum carbon number correponds exactI_v to those of the number of ?;uccesivc msthykne gwps in the poI>mtr chain, In the higher retention @on. a serk of MS(A) peaks 3~ also obse=ed. Except for nylon 8. these shrrrxrcristic 1IS;(_A) peaks are overlapped by the series of complex muIti~1st~ of HC(A) peaks.
Fig. 6 and 7 show the pyrograms of nylon 6.6 and 126, respectiv&. which were syahesized from C, and Cl2 diamincs and adipic acid- The mosr characteristic peak is cyclopentanone (CP). which is knoun to be formed from the adipic acid fractions in the polymer chain as follow-s [ 1.61:
.. : .; : :
__r-._: :. :
rr
-mi ._
-_._
c
-%-.-.-.-A,
_
In the earlier retention re@on. the corresyondirq HC peaks are al-so obsen-td. However. the $elds of HC(_A)s are very small_ Althou_eh that adipic acid-t>pe nylons do not yield any set-k of peaks of Xi% rexcept for !US\_Ai’ peaks small MS{ m = IO) peaks for n_vlon 12.6). the corraponding are obscr\-cd, Furthermore_ a vet small DS( nr = 41 peak appears on the pyrqrams of nylon 6-6 and 136_ On the p~~ograms of n_\-lon 6-9 (FigSI_ 6-10 fFi_e.9;. O-12 ~Fle !O)_ 1220 (Fig. 11) and 12.12 (Fig 12). w-here either the C,-. C::,- or C:z-dicarboxyl?c acid is used. one of the most characteristic peaks is thst of the dinitriles (DSs). These may be formed in a similar ~-a>-to the formation of _\lSs from cxuninocarboxylic acid-t_\pe nylons:
The series of HC and MS peaks on the pFro_gzrs zre asscxizted lx-31 cleavage of the C-C bonds along the pol>mtr chain In addition. a xriss of MS(A)’ peaks are also obsem-ed for each nylon sample_ Especially with hexamethylenediamine-t>p nylons such as nylon 6.9. 6_!0 and 6,lL the associated MS(A)’ peaks are clearly separated on the p>ro_gams. Further. it is interesting that a small l -caprolactam peak [L( M = 5); is obssrwd x\lth the he_xameth~lenediamin~type nylons (including nylon 6-61~ In between the 51X and MS;(A)’ peaks. a complex series of HC(_A) multipltts TLTt aho
observed. The mechanisms of mononitrile formation mentioned above predict that the maximum carbon numbers of MSs for nylon 1210 and 12 12 should be pmk nine and ele\-en respectively- However. on both p_\ro,erams, the MS
1: z-c I
-xc
*_&,
z
.-
.-
,:
_
-.
_..;
I i ‘.
!.
I
i ;
_-_.
..--\L.h_--.
___---. H,’ A’
of
nylon
- --
6.6.
__
-. ,_____-_
. -_.-
--
._-._----
.--;--
-
=::--.:::-I’ I’ ;
:s,
I.
-.-
Fi_e6. Pyogran
.
,‘:. .
.
-4i
z-3
t-3’
I
.-c
__
-.
r
.=I;.’
1
5:
. ..
--r
5: .
:=:
f. 2
t:x.?r =:z-:
: :_
-L-
;
T
i-
i5y.m”
-=-
CICSCI--
-.
. ‘-
__
. ..
_A
129
.
130
series continue to C,= Moreover. as mentioned above. n>-Ion 12.6 also yielded C,+lX peaks. These phenomena susest that some additional thermal rearrangement-t>pe reactions mi@t participate in the formation of the l\IXs from the C,,-diamine-t>pe nylons. As a SUM of the general thermal degradation of the aliphatic polyamides. the main characteristic peaks such as IA. HCs. 5fXs. CP and DSs which appeared in the relatively earlier retention regions of the p>.rograms are given in Table 3. In concl-usion. the Py-GC technique combined \:.ith high-resolution glass capillary separation has been demonstrated to be V~Q-effective in studies on the thermal degradation of polymides whose degradation products consist of many kinds of compounds. Hou-ever. this technique has a limitation associated uith the volatility of the products from the polymer samplesL’nder the ultimate gas chromatographic conditions utilized. the C&IX(A) peak barely appeared on the pyrograms at a retention time of about 65 min. As was reported by Ltiderwald and Mere [5]. the less volatile degradation products such as cyclic olisomers of polyamides would bt better studied by Py-MS. where the p>.rol>-sisof the polymer sample is performed under high vacuum in a mass spectrometer. Thus. PyGC and @-MS would provide L-q- useful complementary information about the thermal characterization of polymers. .4CKSOu.LEDGE!slEscT The authors are indebted to Plastics Laboratory. Torax Indusw Inc, Nagoya. Japan. for providing a series of well characterized aliphatic nylon samples.
REFERESCES 1 RG. Achynma. 2 DA Cbf%M. 3511.
F-M__Fkinhn and G-M_ Kline. J. Rtr. Sat B-s_ Stand_ 46 (1951) 391. 1.X Einhorn. R-W_ Mickclron md J-H. FuucX J. Pal>= S5_ I (1979)