- Email: [email protected]
The behaviour of a polyimide based on aniline phthalein and pyromellitic dianhydride under γ-irradiation
Po~l~mf Sohu~s U.8.S.R. VoL 25, i~o. II, PlP.~08--2~16, 19e0 Prtat~ tn Potsad
00~-$950fS0/1L1~}~ogJ07.5010 O 1~1 ~ ~ Ltd.
THE BEHAVIOUR OF A POLYIMIDE BASED ON ANII.INE PHTHALEIN ANI) PYROMELLVI~IC D I A N H Y D R I D E U N D E R y-IRRADIATION* V. V. KORSm~Z, V. V. LYASKZVICH, V. V. RoD~ and YA. S. VYaoDsg.u Hereto-organic Compounds Institute, U.S.S.R. Academy' of Scienoes (R6c,dt~d 29 October 1979) The radioly~is of a cazdJc polyimide, poly-[3,3.bis-(4-phenyleno)phthalJde]pyro. meilltimide has been investigated under F-irradiation under vaccum. The good radm. tion stability of the polymer has been demonstrated. Reasons for the stability of the polyimide m~n-ochains under F-irrad~tion are discussed. TEE demands of atomic and cosmic science and engineering call for the development of polymers capable of long-term high-temperature service-ability under the action of ionizing radiation. Notable in this connection axe axom~tic polymers with main chains containing heterorings, partieulaxly polyimides, which axe characterized by their good thermal stability [1]. Moreover it is known from the literature [2] that good radiation stability is a feature of individual representatives of aromatic polymers of the type in question. However, litle information is available in literature regarding the radiolysis of aromatic caxdic polyimides. In the present instance we investigated the effect of ? irradiation of some properties of a cardic polyimide, namely poly-bis-[3,3-(4'-phenylene)phthalide] pyromeUitimide (PI-2). 0 0 C _//-~
c
\(y / \ 0_= • \c/'~Ac / c
x _ / - ; Ic - o
II
U
0
0
0
This polymer was selected for investigation in view of the feasibility of soluble specimens being prepared in the cyclized form, which means that on the one hand the method of sol-gel analysis m a y be used to shed light on structural transitions occurring in polymers under irradiation, while on the other * Vysokorrg)l. soyed. A22: No. 11, 2559--2566, 1980. 2808
Polyitmde based on ~niline phthalein and pyromollitic dlmd~ydride
2809
h a n d a m o r e c o m p l e t e p u r i f i c a t i o n o f i n i t i a l c y c l i z e d s p e c i m e n s m a y be c a r r i e d o u t to r e m o v e r e s i d u e s o f s t a r t i n g m a t e r i a l s , as well as s t a b l e i m p u r i t i e s a p I ~ , a r i n g during synthesis of the polymer. The polyimide under study had 37/~= 98.000 and wa.q synthesized by lugh-temperature p,,lyc, mdensati,,n ~f pyromelhtnc diaxdlydrnde and aniline phthalein m ~,~luttor~ ,n nttr,,. benzene [3]. I r r , d m t t o n of the ~-peeimens (in powder form w,th a part,eh, size }~.low 30/an, - r fihn~ of thtckne.~ ix, low 30/zm) was carried ollt ill LtO~.UOat. [xx)iil t*,rnperatur~, i:~ - lo0 ¢.ma Zhtas aml:umh'~ ~mder initial pressure of 1o -~ t.rr. Depending of the irradiation do.,~. ~t t.l~lle¢i t~wtions of powd,.r were varied within limits of 0.3 to (}.6 g. Films were prepared fr,,tn *l 200 m~lutlon in D.%IAA by the method ofea~tmg tm a ,.,laoa support with s u b t ~ , t l u e n t heating nt Tab . ,~flv~nt ro~ldtv.s were, removed from the resulting films by oxtrs.L'tiOll (24 hr} wRh hot ii{'(.. t.one fi,lh}wr,d by dr3"im, in t,acuo at 9 0 ' . The *°Co radioactive i.~,tope was tmoti as t],. tin-iv,,. t , , n ~ouree. RaAmU,m dosimetry was performed by a st,u,lard fi.rromflphat,t. meth-d. Th,. r,uliation intens,ty was 700 r/sec. The tensile strength as of b~th the imtial and th,. trr,,ltat,,d flh.~ wa~ determined with the aid of ~ ZT-4 tensile test~.r. The initial films h~ul ,,~ ~i!u~ 3') k~x'm:. The gel fracti,,n formed under lrradmti~,, was dvtermm-d m PS. ° type- p,,r,,u~ t~la~u¢filters hv extracting the soluble fraction of polbmaer with DMAA at room temp;,r,,tur,.. "l'h," ESR spectra were r , e o r d e d at liquid nitrogen temperat.ur~, uamg al~ RE.13~I ~a,tv.. ~l~,etrometer. "Ft, do so $pec,mens wer(. irradiated in hquid nitro/dell ill s,~al~.d ti,l~lFtZ ilnli~mles tinder lnlt l~ll p r ~ u r o of 10-* t o r r . l~'e, floration of irradiated 8 p e o l n | t . n ~ . %vfl~. v a r r u . d . ,lit ; I t t h e w a v e l o n ~ h interval ;.) 380 rim e.t 77 K. using a DRSh-25{~ mercury lame. Gla.~s p}tot~ filters were tt~,M U) isolat4~ the required wavoleng,th inte~'al fro,n t}," |igh! flux. Cal. culation of t h 0 coneentrat op of paxarnagnetic centre8 wa.~ b,,tsed on staztdard proc,dun-, as ,~, [4]. CuC]t'2H:O monoerystal wtm used aa the standaxd. The spectra wen. reeord,.d at ultra.hi~ fro<:lueney level, wattage 0.1 inV. TABLE
]. V A L U E S
OF QI~AN"rITIEM CHA.RA(TT~RIZING CROMSLI.N"K/NG
AND D E O K A D A T r V E PROCESRKS, AS ~ ' E L L AS ~ OF
PI-~
~ A D I A T I O N STABILFrY
MAC'ROCHAJN8 U~qDER rR,RA.DLATION t ~
Paras neters Density of (chain) fractures per unit irradiation d o ~ p,, M r a d - ' C r o s s h n k i n g d e n s i t y per unit dose q,, M r a d - ' P,/qo
Radiation yield of fractures Gr, 1/100 eV Rmiiation yield of cromlinking (7¢,, 1/100 eV Energy expended per maerochain fracture, E l, e V Energy expended on cro~slinking of a single chain unit. Ec~ E t - Ecu, eV
t,~o~o
Va ]ues
0.27 × 10 -8 0.58 x 10 -S 0.47 0.52 x 10 -t 0"58 × 10-* 19,15O
893o 28,08O
I r r a d i a t i o n o f t h e p o l y i m i d e u n d e r v a c u u m is a c c o m p a n i e d b y c o m p e t i n g reactions r e l a t i n g to scission a a d erosslinking of the p o l y m e r ' m a i n ehain, with t h e e r o s s l i n k i n g p r o c e s s e s p r e d o m i n a t i n g . A gel f r a c t i o n a p p e a r s a f t e r i r r a d i a t i o n w i t h 1500 Mrs~t. O n f u r t h e r i r r a d i a t i o n t h e a m o u n t o f gel f r a c t i o n is i n i t i a l l y g r e a t l y inerea.,~d, t h e r e a f t e r e h a n g i n g o n l y i n s i g n i f i c a n t l y , a p p r o x i m a t i n g ~ s y m p t o t i e a l l y t o a l i m i t i n g v a l u e (92°~,). T h e a m o u n t o f sol f r a c t i o n 8 o n coor-
2810
V.V.
KomsRax
e~
aL
dinates s~-~/8 --f(1/r), where • is the dose, increases linearly (Fig. I), which meant that equations in [5] could be used to calculate parameters quantitatively characterizing the radiation stability of the PI-2 polyimide macrochains, as well as the probability of degradation and crosslinking processes. The calculated values in Table l evidence the extremely high radiation stability of polyimide PI-2. On comparing the radiation stability of cardic polyimide PI-2 with that of polystyrene*, which is one of the most radiation-resistant carbochain polymers [5], it is seen that the loss of energy, required for a single step of scission and crosslinking of PI-2 macrochains (28080 eV) is approximately four times tbe corresponding value for polystyrene [6]. s*V~"
I"2
~'~1~ lO ~-
04
I
l
1
o
o
O
1
O.q 0"8 tOa/r,, Mr,ad -I F~o. l
q
12
I
2O
Ooze e, lO-J,M~'ad Fro. 2
Fro. 1. Plot of s - b ~ vs. reciprocal of the do~, for poryimide PI.2. Fie. 2. Relative strength of polyimide PI-2 films versus the irradiation dose. The main experimental material that has appeared on the behaviour of polyimides under ionizing irradiation is an analysis of the strength and breaking elongation of films of a polyimide based on pyromeilitic dianhydride and 4,4'-diaminodiphenyi oxide ( " K a p t o n " films) [7-10], and the extremely good radiation stability of the films is pointed out. For instance, it was found [9] t h a t electron bombardment of the films (dose rate -~ 1800 Mrad/hr) in air up to a dose of the order of 5000 Mxad left the strength of the films practically unimpaired; a 25% reduction in strength was observed for films irradiated with 40,000 Mrad. The high irradiation dose used in the present work means that the " K a p t o n " film underwent irradiation approximating to vacuum conditions. In vie~v of this it'was desired to carry out a comparative analysis of the radiation ~tabillty of polyimide PI-2, and a study was accordingly made of strength changes in PI-2 films exposed to ~/-irradiation under vacuum. As m a y be seen from Fig. 2, the film strength remains practically constant under an enormous (for polymers) " We were unfortunately unable to find c o r r o d i n g literature.
data for other polyimide~"in
Polyirmde based on aniline phthale/n and pyromellitic dianhydride
281 !
dose amounting to 20,000 Mrad. This shows that the radiation stability of the PI-2 films is at any rate close to that of a " K a p t o n " film. When processes of crosslinking and degradation take place simultaneously in a linear polymer under irradiation, as occurs in the case. of PI-2. it b e c o m ~ impossible for all the molecules in a specimen to be involved in erosslinking [5]. This means that. depending on the number of main chain fraetures, an irradiated specimen will invariably contain a certain protx)rtion of insoluble fraction. It follows that under these conditions a three-dimensional network will in addition be filled and surrounded by molecules not participating in network formation. but undergoing major degradative changes in the irradiation process. The strength of a polymer of this type, in contradistinction to a completely crosslinked polymer, is determined both by properties of the resulting network, and by those of molecules remaining in the sol fraction, and moreover the strength is a function of the quantitative amounts of the latter components in the specimen. For instance, where the weight amount of sol fraction is insignificant, the properties of the carcass formed by the three-dimensional network will be the determining properties, whereas, as the weight amount of sol fraction increases, the properties of the latter will be superposed more and more on the network properties, and, when a definite limit has been reached, will become the dominant properties. This being so, the strength of the specimen will dopend on the same parameters as in the ease of uncrosslinked polymers. The overwhelming direction of crosslinking processes po/qo=0"47) in the case of the cardic polymide P1-2 leads in the final analysis to the appearance of a gel fraction (an analysis of the results depicted in Fig. 1 shows that the onset of gelation coincides with a dose of 1140 Mrad). At the same time the marked energetic stability of the PI-2 macromolecules ensures t h a t there is only an insignificant change in the film strength prior to the point where a gel fraction appears. The marked increase in the amount of gel fraction under subsequent irradiation (~ 70~o already with a dose of 4000 Mrad) and the adequate network TABLE
2. A ' E T W O R E P A R A M E T E R S OF PI-2 in vocuo
Amount of Dose, M r a d ! sol fraction, R
v~tsus THE IRRADIATION DOSE
N u m b e r of Crosslinking ', crosslinks coefficient, per b M e . m o J le. n~ × 10 -I~
Mc
m
1500 200O
~
3000
400O 5O00 ! 0,000 20,000
:.
0.72 0.59 0.39 0.30 0.28 0.18 0-16
1.27
1-96
58,240
1.48 1.98 2.35 2.47 3"28 3.57
2-28 3-07 3.63 3.81 5.06 5.51
43.650
I ~ i
29.100 21.820 17.460 8730 4360
2812 .
V . V . KO~SSJLX~ ~.
density (see Table 2) determines further maintenance of film strength for those irradiated even with 20,000 ~V~rad. The results obtained point to the good radiation stability of PI-2 and to fmfitful prospects of applications of PI-2 articles used in equipment exposed to a high degree of irradiation. However, the radiation stability of PI-2 exposed to 7-irradiation calls for a special explanation of the reasons for this stability. The results of an ESR analysis show that the low-temperature radiolysis of PI-2 specimens is accompanied by the formation of paramagnetic centres, whose concentration increases linearly up to a dose of 10 Mrad (Fig. 3, curve 1). The radiation yield of paramagnetic centres is inconsiderable and amounts to only 0.051 PMC*/100 eV, which provides additional confirmation of the good radiation stability of PI-2. If the polyimide is exposed to light with a gradually decreasing wavelength, the number of the resulting paramagnetic centres declines 'completely on photo irradiation with ). >1400 nm, after which a subsequent increase in the incident photon energy all the way ~ >i 280 nm brings no change either in the concentration of paramagnetic centres or in the shape of the ESR spectra. The rate of accumulation of photostable (at). I> 400 nm) paramagnetic centres is proportional to the irradiation dose (Fig. 3, curve 2), and the radiation yield of the latter amounts to 0.004 PMC/100 eV. N.
10"Tgt
30 t
/o
q
8
Oose,M ~ d
Fxo. 3. Plot of concenta'stion N of psz~zu~q~etzc cetzt~ in po]yimide PI-2 specimens
v~. the irradiation dose: I - a f t e r y-irrmiiation; 2-after ~,.irradiation followed by" phototreatment (~.;m400 rim}. It is noteworthy that most of the paramagnetic centres (~80%) disappear on exposing the specimens to light with ~ >~650 nm. It is seen in ~his case that the violet colouring acquired by PI-2 specimens after the low-temperature radiolyais disappears, and there is also a change in the shape of the ESR spectra. In particular, the narrow singlet of width of ~ 10 Oe disappears along with the broad singlet with a poorly resolved superfine structure. Changes of this type observed in 7-irradiated specimens of cardic polymers exposed to the action * Paramagnetic centree.
Pol3nmzde ba~,d on aniline phtlmlem and pyromellitic chmflLvdride
o81:¢
of light lgfint.s, as was demonstrated in earlier work [12], to electron and ion-radical st~bilization in irradiated specimens (the paramagnetic centres disappearing under the action of light with ,;. 1>400 nm) along with stabilization of relativeh" stable radicals (paramagnetic eentres stable on exposure to light with ;.~>4(,) rim). A feature of the radiol.vsis of PI-'2 wa.~ the high proportion of electrons and ion-radicals (.,-92°o) in the, total yiehl of paramagnetie centres. The radiation stability of polymer molecules depends both on the tYl~. of primar.v products of radiolysis, and on the recover 3 power of polymer molecules affected by irradiation procegses. The primary products of ra~liolysis are a large number of electrons ions and excited molecules having differing energy sI~ctra. Further changes occurring in polymers under irradiation are due to subseq~ent reactions of the latter products. For instance, one of the processes occurring after the ionization of a tx~lymer molecule is the recombination of a polymeric ion with a free electron leading to a marked probability of formatioa of two free radicals via a stage of excited molecule appearance and decay. The result of radiolysis of the polymer molecule by this mechanism is that further changes of t he molecule are determined by t he direction of reactions of the resulting radicals. This being so there may be both degradation of the polymer chain, leading to the formation of two stable but smaller molecules, and rebuilding of the chain. There may also be other reactions leading to structural transitions in the molecule, e.g. isomerization or three-dimensional x~etwork formation. However, disintegration of the excited molecafles into razlicals may be aeeompsnied by a process of reversion of the molecule to its initial state (without any chemical changes occurring) on account of various types of excitation energ3." scattering (radiation, radiationlegs transitions, etc.I. In this case the original structure of the polymer molecule will be preserved. In other words, the contribution of these reactions to the total number of reactions stemming from the variety of ways in which excited molecules may be transformed increases the radiation stability of the polymer. From this standlxfint the ESR data obtained by us do to some extent account for the good radiation stability of the polyimide. The following reactions of ion radicals and charges may take place in an irradiated specimen during the absorption of a light quantum [13] R - s'~ R + [ e ] o r R * M'+[e] M-+[+]
h,. M* /iv
. M*
• R~[+]
{1)
• M-kphoton
(2)
• M+photon
(:3)
If charges are trapped by polar groups, photoneutralization of charges may be accomptmiod either by radical formation at the expense of the neutralization energy M÷-4-(e]
. M*
, R~-Rt,
(4)
or by a process of neutralization energy dissociation in the form of radiation and
2814
V.V. KoB,sm~.x a a/.
heat M*+[e]
~ M*
. photon+M radiationless . process+M
(5)
It is seen from Fig. 3 that treatment of the 7-irra~tiated PI-2 specimens with visible light leads to a lower concentration of paramagnetic eentres, whereas in the case of reactions (1) and (4) this need not be so. Thus the decay of particles formed in PI-2 takes place mainly via a stage of formation of excited molecules, with subsequent transition of the latter to the basic state without damaging the polymer chains, ~ 9 2 % of the primary particles being neutralized by this mechanism, which is one of the factors underlying the good radiation stability of the polymer chains of PI-2. The feasibility of energy being absorbed in this w a y stems, in our view, from a considerable degree of saturation of PI-2 macrochains by phenylene fragments, which are radiation-resistant both on account of the marked stability of C - - H bonds of the benzene ring, and also because of special characteristics of the electron structure of the latter, allowing e x c e ~ energy scattering without breakdown of the molecular structure. In addition, the presence of a conjugated system in individual parts of the polymer chain should make a definite contribution to the radiation stability of PI-2 molecules. It follows that in the case of PI-2 the conjugation system must at least cover microblocks of the polymer molecule incorporated between central C atoms of the origirml diamine. This means that there will be a high "degree of collectivization of n-electrons, which will increase the number of low-level excited states, and make for abscrbed energy dissipation without chemical bond scission. At the same time a collectivized n-electron system likewise favours excitation energy transfer from weaker (as regards radiation) heterobonds to phenyl rings. Let us now turn to the radiation stability of the polyimide from the point of ~riew of the influence of subsequent reactions generating radicals that are stable on exposure to light with )./> 400 nm. In view of the poor resolution of the E S R spectrum remaining after visible light treatment of a 7-irradiated PI-2 specimen, one is unable to identify any concrete type of remaining radicals. However, we may deduce that some of the latter stem from transformations of the main chain heterogroup since carbonic oxides were found among the radiolysis products, as well as traces of aniline phthalein and diaminodiphenyhnethane. Moreover molecular hydrogen was present among the gaseous degradation products. In view of the composition of the degra~lation products we woukl assume that degradation of the polymer main chain must be accompanied by simnltaCO, '/ \ S",,/ neous or subsequent scission of bonds 1 and 2 of the imide ring --N ' \../x~/\ CO
Polyimide baaed on aniline phthalein and pyromelhtie dianhydride
:2815
resulting in the evolution of carbon monoxide, or along with P h - - N bond opening. At the same time there could well be a reduction in the molecular weight of the polymer on account of main ahain bond scission involving the central C atom of the original diamine. However, decay of the macromoleeule in the latter two directions is improbable in ~ e w of the cage effect. Certainly, in the case of a hemolytic direction of roactiorm the degradation proneness of polymers depends, in particular, on the mobility and stability of the emerging radicals. Radicals generated in the ease of P h - - N or Ph--(" bond scission are sufficiently stable, whereas their mobility is limited by the rigidity and size of the polymeric matrix. It is precisely under such conditions that there must be a greatly increa.~d probability of mutual recombination of radicals taking place in a cage. This fact along with the good radiation stability of the PI-2 molecules favours restoration of the original chain. Indirect evidence confirming the marked probability of recombination reactions involving the radicals in question in PI-2 is seen in the fact that practically no gaseous hydrocarbons were found in the radiolysis products of the "Maltrolon" polycaxbonate or in the polyarylate based on terephthalic acid chloride and 4,4'-dipnehylolpropane, whereas considerable amounts of carbonie oxides axe prooent [15, 16]. Thus the most probable process leading to main chain degradation must be one involving N - - C O bond scission, since, the poor'stability of the carbonyl radical [17] leads to dissociation of the latter, resulting ia carbon monoxide evolution. The carbon monoxide yield in tuxat increases the spacing in a cage between radicals remaining after dissociation. which results in an increased probability of remaining paramagnetic (,entres recombining with mobile radicals (e.g. with a hydrogen atom) and leading to formation of a stable molecule. However, it is clear from the chemical structure of the chain unit that even in the latter case energy losses required to lower the molecular weight will be double those required for a linear acvclic polymer of similar structure. Thus the remllts obtained in regard to the radiolysis of cardic v d y i m i d e PI-2 are in good agreement with published information highlighting the exceptional radiation stability of polyimide type polyrrlers. The good radiation stability of the PI-2 cardic polyimide itsoff stems from a set of properties of the polymer macrochains due to their chemical structure. Trar~/at~ by R. J. A. HEI~'DRY RF.F~t E~gF.$ f
I. V. V. KORSHAK. Termostoiklyo polinaory (Heat.statble P(,lymers). Izd. "Nauka", 1969 2. G. LEE, D. STOIrFEY and C. NEV~J.E, No~,b'(, linemy(' pohmery (Novel Lmcu~r Polymer). lzd. "'Khimiya", 1972 3. V. V. KORSHAK, S. V. VINOGRADOVA, Ya. S. VYGODSKII. S. A. PAVLOVA and L. V. BOIKO. Izv. AN SSSR. seriya khimtch. 2267, 1967 4 Yu. N. blOLIN and V. M. CHIBRIKIN, Zavc,dsk. l,tb. B2: 933, 1962 5. A. CHARLESBY, Nuclear Radiations aad PolyTnors. 1962
2816
Yu. G. YA,','OVSKn and G. V. V~XOORADOV
6. W. W. GRAF~%LY and L. M. ALBERUNO, J. Phys. Chem. 72: 4229, 1968 7. A. M. KOEIq[LEI~, D. F. MEASADAY and D. H. MORRIL, Nuel. Jtlst. Methods 33:34 I, 1965 8. Chem. F.ng. News, 43: 20, 38, 1965 9. V. G. ML'DYUGLN and P. N. FEFELOV, Mekhanika polimerov 111 I. 1969 10. H. L. PRICE and V. L. BELL, Nat. SA~LPE. 33'5, 1969 1]. V. V. KORSHAK, S. V. VLNOGRADOVA, V. A. PANKRATOV, S. A. PAVLOVA t~nd G. I. TLMOFEYEVA, Izv. AN SSSR, seriya khimich. 743, 1967 12. V. V. LYASHEVICH, V. V. KORSHAK and V. V. RODE, V y s o k o m o l . . ~ y e d . 19B: 742, 1975 {Not translated in Polymer Sci. U.S.S.R.) 13. V. K..VrrLINCH~'K and V. Ya. DUDAREV, Khimiya vysokikh energil 3: 133, 1969 14. V. K. BELIKOV and V. A. KO$OBL'TSKII. Vysokomol. soyed. 18A: 2452, 1976 (Trans. lated m Polymer Sci. U.S.S.R. 18:11, 2798, 1976) 15. CHZH.AO AYAN-TSZUN, P. M. VALETSKI], S. V. VINOGRADOVA, P. Ya. GLAZL'NOV, V. V. KORSHAK, S. R. RAFIKOV and B. L. TSETLLN, In sbornik enhtlcd Khirmcheskiyo ~voistva i mc~ii.fikat~iya polimerov (Chemical Properties of Polymers and their Modification). Izd. "Nauka"~ p. 126, 1964 16. J. H. G O L D E N , Makromolek. Chem. 66: 73, 1963 17. S. Ya. PSHEZHETSKII, A. G. KOTOV, V. K. MrLrNCHUK,. V. A. ROGINSl~Iq[ and V. I. T U P I K O V , E P R svobodnykh rmlikalov v radiatsionnoi khimfi ( E S R of Free Radi 'ca~ in Radiation Chemistry). Izd. "Khimiya", 1972
Polymer ~ U.S.$.B,. Vok .°2, No. 11. pp. 281&-Z82T. I ~ 0 Printed in Poland
00~I~50/801 t I ~ 1 6 - ~ . ~ 0 / 0 C) I~¢~II~tll~mOu]h'e~ Ltd.
THE, IMPORTANCE AND EVALUATION OF TEMPERATURE TRANSITIONS OF AMORPHOUS LINEAR POLYMERS FROM ONE PHYSICAL STATE INTO ANOTHER USLNG MODERN DYNAMIC METHODS* Yu. G. YANOVSE_Uand G. V. Vr~ooe.ADov A. V. Topchiyev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Received 30 October 1979) A study was made of results of inv~stigs'ting visco.elastie dynamic characteristics of 1,2.polybutadienes of narrow MWD and different molecular weights obtained under conditions of transition from the fluid to the high-elastic and from the high.elastic to the g l a ~ y stats for the case of low.aanplitude periodic shear deformation in a wide range of frequency and temperatttre. Limiting possibilities were i n d i c a t ~ for using the method of temperature.froquency reduction. Results of dynamic investigations were compared under different conditions of deformation: at constant frequency and variable temperature, at variable frequency and constant temperature and at constant frequency and temperature. * Vy~okomol. soyed. A22: No. 11, 2567-2576, 1980.
00~-$950fS0/1L1~}~ogJ07.5010 O 1~1 ~ ~ Ltd.
THE BEHAVIOUR OF A POLYIMIDE BASED ON ANII.INE PHTHALEIN ANI) PYROMELLVI~IC D I A N H Y D R I D E U N D E R y-IRRADIATION* V. V. KORSm~Z, V. V. LYASKZVICH, V. V. RoD~ and YA. S. VYaoDsg.u Hereto-organic Compounds Institute, U.S.S.R. Academy' of Scienoes (R6c,dt~d 29 October 1979) The radioly~is of a cazdJc polyimide, poly-[3,3.bis-(4-phenyleno)phthalJde]pyro. meilltimide has been investigated under F-irradiation under vaccum. The good radm. tion stability of the polymer has been demonstrated. Reasons for the stability of the polyimide m~n-ochains under F-irrad~tion are discussed. TEE demands of atomic and cosmic science and engineering call for the development of polymers capable of long-term high-temperature service-ability under the action of ionizing radiation. Notable in this connection axe axom~tic polymers with main chains containing heterorings, partieulaxly polyimides, which axe characterized by their good thermal stability [1]. Moreover it is known from the literature [2] that good radiation stability is a feature of individual representatives of aromatic polymers of the type in question. However, litle information is available in literature regarding the radiolysis of aromatic caxdic polyimides. In the present instance we investigated the effect of ? irradiation of some properties of a cardic polyimide, namely poly-bis-[3,3-(4'-phenylene)phthalide] pyromeUitimide (PI-2). 0 0 C _//-~
c
\(y / \ 0_= • \c/'~Ac / c
x _ / - ; Ic - o
II
U
0
0
0
This polymer was selected for investigation in view of the feasibility of soluble specimens being prepared in the cyclized form, which means that on the one hand the method of sol-gel analysis m a y be used to shed light on structural transitions occurring in polymers under irradiation, while on the other * Vysokorrg)l. soyed. A22: No. 11, 2559--2566, 1980. 2808
Polyitmde based on ~niline phthalein and pyromollitic dlmd~ydride
2809
h a n d a m o r e c o m p l e t e p u r i f i c a t i o n o f i n i t i a l c y c l i z e d s p e c i m e n s m a y be c a r r i e d o u t to r e m o v e r e s i d u e s o f s t a r t i n g m a t e r i a l s , as well as s t a b l e i m p u r i t i e s a p I ~ , a r i n g during synthesis of the polymer. The polyimide under study had 37/~= 98.000 and wa.q synthesized by lugh-temperature p,,lyc, mdensati,,n ~f pyromelhtnc diaxdlydrnde and aniline phthalein m ~,~luttor~ ,n nttr,,. benzene [3]. I r r , d m t t o n of the ~-peeimens (in powder form w,th a part,eh, size }~.low 30/an, - r fihn~ of thtckne.~ ix, low 30/zm) was carried ollt ill LtO~.UOat. [xx)iil t*,rnperatur~, i:~ - lo0 ¢.ma Zhtas aml:umh'~ ~mder initial pressure of 1o -~ t.rr. Depending of the irradiation do.,~. ~t t.l~lle¢i t~wtions of powd,.r were varied within limits of 0.3 to (}.6 g. Films were prepared fr,,tn *l 200 m~lutlon in D.%IAA by the method ofea~tmg tm a ,.,laoa support with s u b t ~ , t l u e n t heating nt Tab . ,~flv~nt ro~ldtv.s were, removed from the resulting films by oxtrs.L'tiOll (24 hr} wRh hot ii{'(.. t.one fi,lh}wr,d by dr3"im, in t,acuo at 9 0 ' . The *°Co radioactive i.~,tope was tmoti as t],. tin-iv,,. t , , n ~ouree. RaAmU,m dosimetry was performed by a st,u,lard fi.rromflphat,t. meth-d. Th,. r,uliation intens,ty was 700 r/sec. The tensile strength as of b~th the imtial and th,. trr,,ltat,,d flh.~ wa~ determined with the aid of ~ ZT-4 tensile test~.r. The initial films h~ul ,,~ ~i!u~ 3') k~x'm:. The gel fracti,,n formed under lrradmti~,, was dvtermm-d m PS. ° type- p,,r,,u~ t~la~u¢filters hv extracting the soluble fraction of polbmaer with DMAA at room temp;,r,,tur,.. "l'h," ESR spectra were r , e o r d e d at liquid nitrogen temperat.ur~, uamg al~ RE.13~I ~a,tv.. ~l~,etrometer. "Ft, do so $pec,mens wer(. irradiated in hquid nitro/dell ill s,~al~.d ti,l~lFtZ ilnli~mles tinder lnlt l~ll p r ~ u r o of 10-* t o r r . l~'e, floration of irradiated 8 p e o l n | t . n ~ . %vfl~. v a r r u . d . ,lit ; I t t h e w a v e l o n ~ h interval ;.) 380 rim e.t 77 K. using a DRSh-25{~ mercury lame. Gla.~s p}tot~ filters were tt~,M U) isolat4~ the required wavoleng,th inte~'al fro,n t}," |igh! flux. Cal. culation of t h 0 coneentrat op of paxarnagnetic centre8 wa.~ b,,tsed on staztdard proc,dun-, as ,~, [4]. CuC]t'2H:O monoerystal wtm used aa the standaxd. The spectra wen. reeord,.d at ultra.hi~ fro<:lueney level, wattage 0.1 inV. TABLE
]. V A L U E S
OF QI~AN"rITIEM CHA.RA(TT~RIZING CROMSLI.N"K/NG
AND D E O K A D A T r V E PROCESRKS, AS ~ ' E L L AS ~ OF
PI-~
~ A D I A T I O N STABILFrY
MAC'ROCHAJN8 U~qDER rR,RA.DLATION t ~
Paras neters Density of (chain) fractures per unit irradiation d o ~ p,, M r a d - ' C r o s s h n k i n g d e n s i t y per unit dose q,, M r a d - ' P,/qo
Radiation yield of fractures Gr, 1/100 eV Rmiiation yield of cromlinking (7¢,, 1/100 eV Energy expended per maerochain fracture, E l, e V Energy expended on cro~slinking of a single chain unit. Ec~ E t - Ecu, eV
t,~o~o
Va ]ues
0.27 × 10 -8 0.58 x 10 -S 0.47 0.52 x 10 -t 0"58 × 10-* 19,15O
893o 28,08O
I r r a d i a t i o n o f t h e p o l y i m i d e u n d e r v a c u u m is a c c o m p a n i e d b y c o m p e t i n g reactions r e l a t i n g to scission a a d erosslinking of the p o l y m e r ' m a i n ehain, with t h e e r o s s l i n k i n g p r o c e s s e s p r e d o m i n a t i n g . A gel f r a c t i o n a p p e a r s a f t e r i r r a d i a t i o n w i t h 1500 Mrs~t. O n f u r t h e r i r r a d i a t i o n t h e a m o u n t o f gel f r a c t i o n is i n i t i a l l y g r e a t l y inerea.,~d, t h e r e a f t e r e h a n g i n g o n l y i n s i g n i f i c a n t l y , a p p r o x i m a t i n g ~ s y m p t o t i e a l l y t o a l i m i t i n g v a l u e (92°~,). T h e a m o u n t o f sol f r a c t i o n 8 o n coor-
2810
V.V.
KomsRax
e~
aL
dinates s~-~/8 --f(1/r), where • is the dose, increases linearly (Fig. I), which meant that equations in [5] could be used to calculate parameters quantitatively characterizing the radiation stability of the PI-2 polyimide macrochains, as well as the probability of degradation and crosslinking processes. The calculated values in Table l evidence the extremely high radiation stability of polyimide PI-2. On comparing the radiation stability of cardic polyimide PI-2 with that of polystyrene*, which is one of the most radiation-resistant carbochain polymers [5], it is seen that the loss of energy, required for a single step of scission and crosslinking of PI-2 macrochains (28080 eV) is approximately four times tbe corresponding value for polystyrene [6]. s*V~"
I"2
~'~1~ lO ~-
04
I
l
1
o
o
O
1
O.q 0"8 tOa/r,, Mr,ad -I F~o. l
q
12
I
2O
Ooze e, lO-J,M~'ad Fro. 2
Fro. 1. Plot of s - b ~ vs. reciprocal of the do~, for poryimide PI.2. Fie. 2. Relative strength of polyimide PI-2 films versus the irradiation dose. The main experimental material that has appeared on the behaviour of polyimides under ionizing irradiation is an analysis of the strength and breaking elongation of films of a polyimide based on pyromeilitic dianhydride and 4,4'-diaminodiphenyi oxide ( " K a p t o n " films) [7-10], and the extremely good radiation stability of the films is pointed out. For instance, it was found [9] t h a t electron bombardment of the films (dose rate -~ 1800 Mrad/hr) in air up to a dose of the order of 5000 Mxad left the strength of the films practically unimpaired; a 25% reduction in strength was observed for films irradiated with 40,000 Mrad. The high irradiation dose used in the present work means that the " K a p t o n " film underwent irradiation approximating to vacuum conditions. In vie~v of this it'was desired to carry out a comparative analysis of the radiation ~tabillty of polyimide PI-2, and a study was accordingly made of strength changes in PI-2 films exposed to ~/-irradiation under vacuum. As m a y be seen from Fig. 2, the film strength remains practically constant under an enormous (for polymers) " We were unfortunately unable to find c o r r o d i n g literature.
data for other polyimide~"in
Polyirmde based on aniline phthale/n and pyromellitic dianhydride
281 !
dose amounting to 20,000 Mrad. This shows that the radiation stability of the PI-2 films is at any rate close to that of a " K a p t o n " film. When processes of crosslinking and degradation take place simultaneously in a linear polymer under irradiation, as occurs in the case. of PI-2. it b e c o m ~ impossible for all the molecules in a specimen to be involved in erosslinking [5]. This means that. depending on the number of main chain fraetures, an irradiated specimen will invariably contain a certain protx)rtion of insoluble fraction. It follows that under these conditions a three-dimensional network will in addition be filled and surrounded by molecules not participating in network formation. but undergoing major degradative changes in the irradiation process. The strength of a polymer of this type, in contradistinction to a completely crosslinked polymer, is determined both by properties of the resulting network, and by those of molecules remaining in the sol fraction, and moreover the strength is a function of the quantitative amounts of the latter components in the specimen. For instance, where the weight amount of sol fraction is insignificant, the properties of the carcass formed by the three-dimensional network will be the determining properties, whereas, as the weight amount of sol fraction increases, the properties of the latter will be superposed more and more on the network properties, and, when a definite limit has been reached, will become the dominant properties. This being so, the strength of the specimen will dopend on the same parameters as in the ease of uncrosslinked polymers. The overwhelming direction of crosslinking processes po/qo=0"47) in the case of the cardic polymide P1-2 leads in the final analysis to the appearance of a gel fraction (an analysis of the results depicted in Fig. 1 shows that the onset of gelation coincides with a dose of 1140 Mrad). At the same time the marked energetic stability of the PI-2 macromolecules ensures t h a t there is only an insignificant change in the film strength prior to the point where a gel fraction appears. The marked increase in the amount of gel fraction under subsequent irradiation (~ 70~o already with a dose of 4000 Mrad) and the adequate network TABLE
2. A ' E T W O R E P A R A M E T E R S OF PI-2 in vocuo
Amount of Dose, M r a d ! sol fraction, R
v~tsus THE IRRADIATION DOSE
N u m b e r of Crosslinking ', crosslinks coefficient, per b M e . m o J le. n~ × 10 -I~
Mc
m
1500 200O
~
3000
400O 5O00 ! 0,000 20,000
:.
0.72 0.59 0.39 0.30 0.28 0.18 0-16
1.27
1-96
58,240
1.48 1.98 2.35 2.47 3"28 3.57
2-28 3-07 3.63 3.81 5.06 5.51
43.650
I ~ i
29.100 21.820 17.460 8730 4360
2812 .
V . V . KO~SSJLX~ ~.
density (see Table 2) determines further maintenance of film strength for those irradiated even with 20,000 ~V~rad. The results obtained point to the good radiation stability of PI-2 and to fmfitful prospects of applications of PI-2 articles used in equipment exposed to a high degree of irradiation. However, the radiation stability of PI-2 exposed to 7-irradiation calls for a special explanation of the reasons for this stability. The results of an ESR analysis show that the low-temperature radiolysis of PI-2 specimens is accompanied by the formation of paramagnetic centres, whose concentration increases linearly up to a dose of 10 Mrad (Fig. 3, curve 1). The radiation yield of paramagnetic centres is inconsiderable and amounts to only 0.051 PMC*/100 eV, which provides additional confirmation of the good radiation stability of PI-2. If the polyimide is exposed to light with a gradually decreasing wavelength, the number of the resulting paramagnetic centres declines 'completely on photo irradiation with ). >1400 nm, after which a subsequent increase in the incident photon energy all the way ~ >i 280 nm brings no change either in the concentration of paramagnetic centres or in the shape of the ESR spectra. The rate of accumulation of photostable (at). I> 400 nm) paramagnetic centres is proportional to the irradiation dose (Fig. 3, curve 2), and the radiation yield of the latter amounts to 0.004 PMC/100 eV. N.
10"Tgt
30 t
/o
q
8
Oose,M ~ d
Fxo. 3. Plot of concenta'stion N of psz~zu~q~etzc cetzt~ in po]yimide PI-2 specimens
v~. the irradiation dose: I - a f t e r y-irrmiiation; 2-after ~,.irradiation followed by" phototreatment (~.;m400 rim}. It is noteworthy that most of the paramagnetic centres (~80%) disappear on exposing the specimens to light with ~ >~650 nm. It is seen in ~his case that the violet colouring acquired by PI-2 specimens after the low-temperature radiolyais disappears, and there is also a change in the shape of the ESR spectra. In particular, the narrow singlet of width of ~ 10 Oe disappears along with the broad singlet with a poorly resolved superfine structure. Changes of this type observed in 7-irradiated specimens of cardic polymers exposed to the action * Paramagnetic centree.
Pol3nmzde ba~,d on aniline phtlmlem and pyromellitic chmflLvdride
o81:¢
of light lgfint.s, as was demonstrated in earlier work [12], to electron and ion-radical st~bilization in irradiated specimens (the paramagnetic centres disappearing under the action of light with ,;. 1>400 nm) along with stabilization of relativeh" stable radicals (paramagnetic eentres stable on exposure to light with ;.~>4(,) rim). A feature of the radiol.vsis of PI-'2 wa.~ the high proportion of electrons and ion-radicals (.,-92°o) in the, total yiehl of paramagnetie centres. The radiation stability of polymer molecules depends both on the tYl~. of primar.v products of radiolysis, and on the recover 3 power of polymer molecules affected by irradiation procegses. The primary products of ra~liolysis are a large number of electrons ions and excited molecules having differing energy sI~ctra. Further changes occurring in polymers under irradiation are due to subseq~ent reactions of the latter products. For instance, one of the processes occurring after the ionization of a tx~lymer molecule is the recombination of a polymeric ion with a free electron leading to a marked probability of formatioa of two free radicals via a stage of excited molecule appearance and decay. The result of radiolysis of the polymer molecule by this mechanism is that further changes of t he molecule are determined by t he direction of reactions of the resulting radicals. This being so there may be both degradation of the polymer chain, leading to the formation of two stable but smaller molecules, and rebuilding of the chain. There may also be other reactions leading to structural transitions in the molecule, e.g. isomerization or three-dimensional x~etwork formation. However, disintegration of the excited molecafles into razlicals may be aeeompsnied by a process of reversion of the molecule to its initial state (without any chemical changes occurring) on account of various types of excitation energ3." scattering (radiation, radiationlegs transitions, etc.I. In this case the original structure of the polymer molecule will be preserved. In other words, the contribution of these reactions to the total number of reactions stemming from the variety of ways in which excited molecules may be transformed increases the radiation stability of the polymer. From this standlxfint the ESR data obtained by us do to some extent account for the good radiation stability of the polyimide. The following reactions of ion radicals and charges may take place in an irradiated specimen during the absorption of a light quantum [13] R - s'~ R + [ e ] o r R * M'+[e] M-+[+]
h,. M* /iv
. M*
• R~[+]
{1)
• M-kphoton
(2)
• M+photon
(:3)
If charges are trapped by polar groups, photoneutralization of charges may be accomptmiod either by radical formation at the expense of the neutralization energy M÷-4-(e]
. M*
, R~-Rt,
(4)
or by a process of neutralization energy dissociation in the form of radiation and
2814
V.V. KoB,sm~.x a a/.
heat M*+[e]
~ M*
. photon+M radiationless . process+M
(5)
It is seen from Fig. 3 that treatment of the 7-irra~tiated PI-2 specimens with visible light leads to a lower concentration of paramagnetic eentres, whereas in the case of reactions (1) and (4) this need not be so. Thus the decay of particles formed in PI-2 takes place mainly via a stage of formation of excited molecules, with subsequent transition of the latter to the basic state without damaging the polymer chains, ~ 9 2 % of the primary particles being neutralized by this mechanism, which is one of the factors underlying the good radiation stability of the polymer chains of PI-2. The feasibility of energy being absorbed in this w a y stems, in our view, from a considerable degree of saturation of PI-2 macrochains by phenylene fragments, which are radiation-resistant both on account of the marked stability of C - - H bonds of the benzene ring, and also because of special characteristics of the electron structure of the latter, allowing e x c e ~ energy scattering without breakdown of the molecular structure. In addition, the presence of a conjugated system in individual parts of the polymer chain should make a definite contribution to the radiation stability of PI-2 molecules. It follows that in the case of PI-2 the conjugation system must at least cover microblocks of the polymer molecule incorporated between central C atoms of the origirml diamine. This means that there will be a high "degree of collectivization of n-electrons, which will increase the number of low-level excited states, and make for abscrbed energy dissipation without chemical bond scission. At the same time a collectivized n-electron system likewise favours excitation energy transfer from weaker (as regards radiation) heterobonds to phenyl rings. Let us now turn to the radiation stability of the polyimide from the point of ~riew of the influence of subsequent reactions generating radicals that are stable on exposure to light with )./> 400 nm. In view of the poor resolution of the E S R spectrum remaining after visible light treatment of a 7-irradiated PI-2 specimen, one is unable to identify any concrete type of remaining radicals. However, we may deduce that some of the latter stem from transformations of the main chain heterogroup since carbonic oxides were found among the radiolysis products, as well as traces of aniline phthalein and diaminodiphenyhnethane. Moreover molecular hydrogen was present among the gaseous degradation products. In view of the composition of the degra~lation products we woukl assume that degradation of the polymer main chain must be accompanied by simnltaCO, '/ \ S",,/ neous or subsequent scission of bonds 1 and 2 of the imide ring --N ' \../x~/\ CO
Polyimide baaed on aniline phthalein and pyromelhtie dianhydride
:2815
resulting in the evolution of carbon monoxide, or along with P h - - N bond opening. At the same time there could well be a reduction in the molecular weight of the polymer on account of main ahain bond scission involving the central C atom of the original diamine. However, decay of the macromoleeule in the latter two directions is improbable in ~ e w of the cage effect. Certainly, in the case of a hemolytic direction of roactiorm the degradation proneness of polymers depends, in particular, on the mobility and stability of the emerging radicals. Radicals generated in the ease of P h - - N or Ph--(" bond scission are sufficiently stable, whereas their mobility is limited by the rigidity and size of the polymeric matrix. It is precisely under such conditions that there must be a greatly increa.~d probability of mutual recombination of radicals taking place in a cage. This fact along with the good radiation stability of the PI-2 molecules favours restoration of the original chain. Indirect evidence confirming the marked probability of recombination reactions involving the radicals in question in PI-2 is seen in the fact that practically no gaseous hydrocarbons were found in the radiolysis products of the "Maltrolon" polycaxbonate or in the polyarylate based on terephthalic acid chloride and 4,4'-dipnehylolpropane, whereas considerable amounts of carbonie oxides axe prooent [15, 16]. Thus the most probable process leading to main chain degradation must be one involving N - - C O bond scission, since, the poor'stability of the carbonyl radical [17] leads to dissociation of the latter, resulting ia carbon monoxide evolution. The carbon monoxide yield in tuxat increases the spacing in a cage between radicals remaining after dissociation. which results in an increased probability of remaining paramagnetic (,entres recombining with mobile radicals (e.g. with a hydrogen atom) and leading to formation of a stable molecule. However, it is clear from the chemical structure of the chain unit that even in the latter case energy losses required to lower the molecular weight will be double those required for a linear acvclic polymer of similar structure. Thus the remllts obtained in regard to the radiolysis of cardic v d y i m i d e PI-2 are in good agreement with published information highlighting the exceptional radiation stability of polyimide type polyrrlers. The good radiation stability of the PI-2 cardic polyimide itsoff stems from a set of properties of the polymer macrochains due to their chemical structure. Trar~/at~ by R. J. A. HEI~'DRY RF.F~t E~gF.$ f
I. V. V. KORSHAK. Termostoiklyo polinaory (Heat.statble P(,lymers). Izd. "Nauka", 1969 2. G. LEE, D. STOIrFEY and C. NEV~J.E, No~,b'(, linemy(' pohmery (Novel Lmcu~r Polymer). lzd. "'Khimiya", 1972 3. V. V. KORSHAK, S. V. VINOGRADOVA, Ya. S. VYGODSKII. S. A. PAVLOVA and L. V. BOIKO. Izv. AN SSSR. seriya khimtch. 2267, 1967 4 Yu. N. blOLIN and V. M. CHIBRIKIN, Zavc,dsk. l,tb. B2: 933, 1962 5. A. CHARLESBY, Nuclear Radiations aad PolyTnors. 1962
2816
Yu. G. YA,','OVSKn and G. V. V~XOORADOV
6. W. W. GRAF~%LY and L. M. ALBERUNO, J. Phys. Chem. 72: 4229, 1968 7. A. M. KOEIq[LEI~, D. F. MEASADAY and D. H. MORRIL, Nuel. Jtlst. Methods 33:34 I, 1965 8. Chem. F.ng. News, 43: 20, 38, 1965 9. V. G. ML'DYUGLN and P. N. FEFELOV, Mekhanika polimerov 111 I. 1969 10. H. L. PRICE and V. L. BELL, Nat. SA~LPE. 33'5, 1969 1]. V. V. KORSHAK, S. V. VLNOGRADOVA, V. A. PANKRATOV, S. A. PAVLOVA t~nd G. I. TLMOFEYEVA, Izv. AN SSSR, seriya khimich. 743, 1967 12. V. V. LYASHEVICH, V. V. KORSHAK and V. V. RODE, V y s o k o m o l . . ~ y e d . 19B: 742, 1975 {Not translated in Polymer Sci. U.S.S.R.) 13. V. K..VrrLINCH~'K and V. Ya. DUDAREV, Khimiya vysokikh energil 3: 133, 1969 14. V. K. BELIKOV and V. A. KO$OBL'TSKII. Vysokomol. soyed. 18A: 2452, 1976 (Trans. lated m Polymer Sci. U.S.S.R. 18:11, 2798, 1976) 15. CHZH.AO AYAN-TSZUN, P. M. VALETSKI], S. V. VINOGRADOVA, P. Ya. GLAZL'NOV, V. V. KORSHAK, S. R. RAFIKOV and B. L. TSETLLN, In sbornik enhtlcd Khirmcheskiyo ~voistva i mc~ii.fikat~iya polimerov (Chemical Properties of Polymers and their Modification). Izd. "Nauka"~ p. 126, 1964 16. J. H. G O L D E N , Makromolek. Chem. 66: 73, 1963 17. S. Ya. PSHEZHETSKII, A. G. KOTOV, V. K. MrLrNCHUK,. V. A. ROGINSl~Iq[ and V. I. T U P I K O V , E P R svobodnykh rmlikalov v radiatsionnoi khimfi ( E S R of Free Radi 'ca~ in Radiation Chemistry). Izd. "Khimiya", 1972
Polymer ~ U.S.$.B,. Vok .°2, No. 11. pp. 281&-Z82T. I ~ 0 Printed in Poland
00~I~50/801 t I ~ 1 6 - ~ . ~ 0 / 0 C) I~¢~II~tll~mOu]h'e~ Ltd.
THE, IMPORTANCE AND EVALUATION OF TEMPERATURE TRANSITIONS OF AMORPHOUS LINEAR POLYMERS FROM ONE PHYSICAL STATE INTO ANOTHER USLNG MODERN DYNAMIC METHODS* Yu. G. YANOVSE_Uand G. V. Vr~ooe.ADov A. V. Topchiyev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences
(Received 30 October 1979) A study was made of results of inv~stigs'ting visco.elastie dynamic characteristics of 1,2.polybutadienes of narrow MWD and different molecular weights obtained under conditions of transition from the fluid to the high-elastic and from the high.elastic to the g l a ~ y stats for the case of low.aanplitude periodic shear deformation in a wide range of frequency and temperatttre. Limiting possibilities were i n d i c a t ~ for using the method of temperature.froquency reduction. Results of dynamic investigations were compared under different conditions of deformation: at constant frequency and variable temperature, at variable frequency and constant temperature and at constant frequency and temperature. * Vy~okomol. soyed. A22: No. 11, 2567-2576, 1980.