Intermolecular interaction, supermolecular structure and paramagnetism in polyconjugated systems

Intermolecular interaction in polyconjugated systems

2727

11. V. A. KARGIN, G. P. ANDRIANOVA and G. G. KARDASH, Vysokomol. soyed. A 9 : 267, 1967 (Translated in Polymer Sei. 9: 2, 289, 1967) 12. V. A. KARGIN and G. L. SLONIMSKII, Kratkie ocherki po fiziko-khimii polimerov (Short Essays on the Physical Chemistry of Polymers). p. 152, Izd. " K h i m i y a " , 1967 13, N. Ya. RAPOPORT-MOLODTSOVA, T. A. BOGAYEVSKAYA, T. A. KORETSKAYA, T. I. SOGOLOVA a n d V. A. KARGIN, Dokl. Akad. Nauk SSSR 155: 1171, 1964 14. G.L. SLONIMSKII, A. I. KITAIGORODSKII, V. M. BELAVTSEVA, V. B. TOLSTOGUZOV and I. I. MAL'TSEVA, Vysokomol. soyed. BI0: 640, 1968 (Not translated in Polymer Sci. U.S.S.R,)

INTERMOLECULAR INTERACTION, SUPERMOLECULAR STRUCTURE AND PARAMAGNETISM IN POLYCONJUGATED SYSTEMS* A. A. BERLIN Institute of Chemical Physics, U.S.S.R. Academy of Sciences

(Received 17 April 1970) IT can be taken as established that as the length of a polyconjugated sequence increases the energy gap and energy of the excited state decrease. Also the ionization potential (I) decreases, and the electronic polarizability and the affinity for electrons (A) increase. I t can be shown that the variation in the difference I - A with increase in polyconjugation correlates with the variation in the physicochemical properties of polyconjugated homologues [1, 2]. This is illustrated b y data relating to aromatic hydrocarbons from which polarization and the sterie effect of groups and hereto-atoms are excluded. I t is seen from Figs. 1 and 2 that as I - A decreases the melting points and heats of sublimation of polyacenes and poly-p-phenylenes increase and the solubility (L) and energy of activation for conductivity fall. These results show that the melting points of crystalline, linear and multinuclear aromatic chain hydrocarbons containing four or five rings, are higher than the melting points of such metals as zinc, lead and tin. In addition to this it is well known t h a t substances such as m a n y dyestuffs are soluble with greater difficulty and associate in solution if they do not contain bulky substituents. In our opinion the above correlations can be attributed to formation of u-complexes [3], the polarization of which increases with increase in the length of the polyconjugated chain and with decrease in the difference I - A . Taking into account the fact t h a t polarization of the end atoms of a polyeonjugated chain * Vysokomol soyed. A13: No. I I , 2429-2439, 1971.

~.728

A.A.

B~.RLI~

(linear polyenes, poly-lv-phenylenes , molecules with terminal hetero-atoms} or of atomic centres within the molecule (polyacenes, hetero-chain polyconjugated ~ystems (PCS's)), it m a y be assumed that more favourable conditions for intermolecular ~-electron interaction will_" exist when the molecules are packed in bundles and the ends of the chains are in close p r o ~ m i t y . In such associations, Tm,°C

I-A,eV E,eV

I

/ogL -3

Tm'°O

h

500

~,5 300

rg .o1o FIG. 1

I

2o%

1"5

I00 -

2 z/ 6 No. of'benzene nuc/ei

ti

FIG. 2

:FIG. 1. Dependence of the physieechemical properties of hydrocarbons on the number of n-electrons: /---difference between the ionization potential and electron affinity (Z-A), eV; 2--energy of activation for electrical conductivity (E), eV, 3--melting point, °C, 4--logarithm of the methyl-group affinity constant (log KeHs). FIG. 2. Dependence of the melting point of polyphcnylenes (1), m-phenylenes (2) and the logarithm of the solubility in benzene (L, g/1. at 20°1 (3} of individual polyphenylenes on the number of conjugated phenylene groups. w i t h a suitable length of the conjugated chain and a suitable value of I - A , the polarization favours reduction in the intermolecular distances in comparison with the first members of the homologous series. This increase in packing density with decrease in I - A in crystalline complexes has been predicted theoretically a n d demonstrated experimentally in a number of systems [3]. The approach of the chains to one another in polarized ~-complex associations o f PCS's gives an additional energy gain as a result of intermolecular overlapping o f the u-electron orbitals in the direction perpendicular to the a-bonds, and for terminal hetero-atoms in the direction of the axis of the molecules. This special feature of intermolecular interaction in polyconjugated systems is the cause of their anomalously high melting points and heats of sublimation, their low solubility, the formation of associations in solution and a number of other properties [4] (see Figs. 1 and 2). Deviations from a linear or series distribution of conjugated nuclei, the presence of bulky side substituents, causing steric hindrance, and lack of structural order in the conjugated chain, decrease or upset the regular variation in 1-.,4

Intermolecular interaction in polyconjugatod systems

2729

with increase in the number of conjugated ~-bonds, and reduce the possibility of close packing of the molecules. Therefore such systems should be less heat-resistant and more soluble than compounds of the type under consideration. This is in accord with experimental findings. Despite the fact that the problem of the special intermolecular forces in PCS's and their decisive role in the physics and chemistry of polyeonjugated systems was discussed as long ago as 1958 [4], it has not received much attention from research workers. Only recently has this question been raised again in connection with specific features of the formation of polyeonjugated chains [1, 5] and the structure of organic semiconductors [6]. To elucidate this problem calorimetric investigations were carried out for determination of the energy of conjugation, and to find the contribution to this of intermolecular u-electron interaction in individual and polymeric hydrocarbons, the main chains of which are constructed of conjugated units (oligoarylvinylenes) or aromatic nuclei (polyarylenes) [5]. In these papers the difference between the total energy of conjugation and the energy of conjugation in benzene rings was taken as the criterion for assessment of the intermolecular exchange interaction of the ~-electrons of the polyconjugated chains, and was called the "energy of stabilization of structure" (Table). I t is seen that in individual polyene hydrocarbons with end groups there is an additional contribution to the energy of stabilization, -- AH~ = 6.0-12.0 keal/mole, which :is much higher than the energy of conjugation of 1,3-butadiene and its analogues (2-4 kcal/mole). It would be incorrect to explain this difference by intramolecular delocalization. It is reasonable to suppose that the observed values of AH~ are mainly due to intermolecular interaction. It is also seen from the Table that on passing to polymers with a conjugated system there is an anomalously high energy of stabilization of tens and hundreds of kilocalories when calculated on the unit and average molecular weight respectively. It is obvious that such high values of AH~ are the result of special intermoleeular forces, present even in polymeric hydrocarbons, i.e. substances without hetero-atoms, dipolar groups or hydrogen bonds. It is interesting to note that for polymers of 1,4-diphenylbutadiyne-l,3, prepared by thermal polymerization, the experimental values of AHz are lower than those calculated for a linear structure, whichcould be formed by polymerization through one triple bond (23.5 as against 54-4 kcal/mole). This is supported by evidence indicating that the thermal polymerization of diphenylbutadiyne involves two triple bonds, resulting in formation of polyconjugated polymers contaflfing strained, rubrene-like fragments. It has been shown that AH~ for rubrene has the positive value of 44-46 kcal/ /mole, due to mutual repulsion of the phenyl radicals situated close to one another. From this it follows that the comparatively large negative value of AHr¢ for polydiphenylbutadiyne indicates a large contribution by u-electron interaction between the polymer molecules.

2730

A. A . B~.l~IN ENERGIES

OF

0 STABILIZ_&~vION O F P O L Y C O I ~ J U G A T E D

O

SYSTEMS

- - A U,$ kcal/mole

--ztH,$ kcal/mole

~,~ Compound of polymer

Uni~

~-~

Styrene Trans-stilbene

C6H~CH----CH2 CeHsCH=CH----C6H~

I04.1~ 180.2f

found

calc.

1048.2 1762.1+0.9 (1758-2-4-0.2)

1050.0

1.8

1768-8

unit

m~cromolecule

Trans-trans- 1, 4- C6HsCH-----CH 206.2~ / diphenylbutadiene CH---~CH--C6H Polyphenylaee1100.( tylene (~herreal polymeriL C.H, 3. zation)* Polyphenylace5700.£ tylene (catalytic polymeriL O.H. zation)~ C~Hs

2027.5i0-5 (2024.7-4-0.3)

2039.4

6-1 11.9 (14"71

984.4-4-0.7

993.5

9.1

977.1-~0.2

994*4

17-3

960

Polytolane

890.0

1695.2+0.1

22.7

113.5

135.69

5059.7 (50; 57.5)

1150.0

1901.4± 1.4

[

o!.£ C.Hs

C.H6

Rubrene

-

Polydiphenylbutadiyne- 1,3

J_-/ /\c=~ r

p-Polyphonylene (acc. to Kovachich)

--41.6 (--43.8)

C+Hs -

C6Hs 4,4-Diphenyl

97-4

23-5

249.4

\ 154.0 ,O00

1492.7

3.0

672.0

45.0

* Conjugatedblockwith n~**j=2~-8unit~. ? Conjugatedblockwith n~.j=5-7 units. ~: The flgunmIn brackets are taken from the literature or calculatedfrom publisheddata.

3600

Intermoleeular i~teraction in polyconjugated systems

2731

Thus experimental confirmation of the existence in polyconjugated systems of strong intermolecular interaction has been obtained, and this is largely responsible for their thermodynamic stability and specific properties. It is evident t h a t in polyconjugated systems t h a t are not sterically hindered intermolecular u-electron interaction makes an incomparably greater contribution than the energy of intramolecular delocalization. The consequent high tendency of poIymers with a conjugated system to form strong associations gives grounds for the assumption that such substances have a micro-heterogeneous structure [1, 7].

Fin. 3. Supermoleeular formations in polytolane; Pt--shadowed carbon replica (× 33,000). Examination in the electron microscope has confirmed this conclusion [7] (Fig. 3). Shadowed replicas of fracture surfaces from block specimens and particles of amorphous polyphenylacetylene and polytolane clearly show the presence of secondary, spherical particles of size up to 250-500 rag. From the photographs shown it is seen t h a t small and large spheres arise from anisodiamctric particles of size ~ 10-50 mg (100-500 A). We have observed similar superstructural formations in other PCS's (polytolane, polydiphenylbutadiync). It is reasonable to assume that the presence of the secondary, spherical formations indicates the fact t h a t associations of macromolecules form a micro-phase in the system. When the polymer is moulded these particles tend to reduce their surface of separation, becoming packed into spherical aggregates. I t has been shown recently t h a t when polyconjugated blocks are included in the molecule of an elastomer closer packing of the associations is possible t h a n in PCS's not joined to elastic fragments. I t has been found, for example, t h a t initiation of polymerization of polyisoprene by the bisdiazonium radical in the presence of reducing agents, or by nitrosodiacetates of aromatic amines

3732

A.A.

B~.~Lnv

(benzidine for example), block eopolymers containing polyazophenylene fragments are formed [8] •N s O

~ _ ~

N i" + C H I = O_~ H = C H ,

-N,

CH,

Such block copolymers when they contain a small proportion of P0S blocks (n----15--20%) are thermoelastoplasts, giving the E P R signal characteristic of polyazophenylene and the anomalous curve of the dependence of reduced viscosity on concentration, with increase in t//¢ at c ~ 0.2-0-3 g/100 ml, typical of associated substances. A very important point is t h a t t h e y are black-violet in colour, whereas polyazophenylene prepared under the same conditions is a yellow or light-brown substance. D 1.0

O',T

0

~'00

580

A,r~

600

700

Fxo. 4. Absorption spectrum of a benzene solution (0-21 g/1.) of po]yazophenylene (.~, =2200) (1) and a block copolymer of polyazophenylene and polyisoprene (PAP eontenb 15.5yo, ~/n =22,000) (2); D--optical density. I t is seen from Fig. 4 t h a t an elastomer containing no more t h a n 15% of polyazophenylene blocks, in contrast to pure polyazopheny!ene, has an absorption m a x i m u m in the region of 560 m#, and absorption in the longwave region (2> >500 m#) is much higher in general. To this it must be added t h a t increase in the content of polyazophenylene blocks above 30% produces lighter coloured, yellowbrown products t h a t are not elastomers at 20-50 °. They approach polyazophenylene in their absorption spectra. The cause of these anomalies is evidently t h a t when a rigid polyconjugated block is situated in a flexible matrix (a rubber) its packing in associations of the bundle type is much easier. Consequently intermoleoular n-electron interaction is more fully effeeted, which to some extent has the same effect as increase in conjugation, and hence there is a decrease in the energy gap and a bathochromie shift in the absorption spectra. The fact t h a t this bathechromic shift in the electronic spectra is due to the presence of strong associations is supported also by the fact t h a t when their solutions are heated a marked hypsoehromic shift occurs.

Intermolecular interaction in polyconjugated systems

2733

The idea of a micro-heterogeneous structure of polymers containing a conjugated system is in complete accord with the micro-heterogeneous model of polymeric semiconductors put forward in references [9] and [10]. As a result of studies of EPR spectra, of the frequency and temperature dependence of the energy of activation for conductivity and of the thermal E1VfF, and the use of the method of injection of carriers, it has been shown convincingly with polytetracyanoethylene, its gelation complexes and thermally degraded, irradiated polyethylene as examples, that in such systems there is a region of polyconjugation in which the conductivity is several orders of magnitude higher than the average value, and where the energy of activation for conductivity approaches zero. Measurements were made, indicating a high mobility of the carriers in these regions of polyconjugation (10-100 cm~/V/sec), whereas the average mobility in these same polymers is not more than 10-~-10 -s cm2/V/see. The minimal length of the conducting regions in polytetracyanoethylene is 40 A. Heat treatment of the polymer (above 360 °) brings about an increase in conductivity and increase in the length of these regions to 300 A. It may therefore be asserted that in the structure of PCS's there are "metal-like" associations, forming a micro-phase in the system. These associations are collected together in more loosely packed, spherical formations, distributed in a disordered fashion among weakly associated macromolecules. Obviously the limited mobility and short life of the carriers in polymeric semiconductors are associated with the disordered, micro-heterogeneous structure of the latter. This conclusion is supported by recently published data, according to which the drift mobility of the carriers in polyphenylaeetylene can be increased by four or five orders of magnitude, by suitable treatment of the polymer to alter its supermolecular structure [11]. THE PARAMAGNETISM OF PCS's BY INTERMOLECULAR INTERACTION AND THE ~ L O C A L A C T I V A T I O N ~ EFFECT

The most general property of PCS's, distinguishing them from "saturated' polymers, is the existence of spins in the former, detected by the EPI% method. The paramagnetie centres (PMC's) affect the physical and physicochemieal properties of PCS's, including their dark and photo-initiated electrical conductivity, absorption and luminescence spectra, and reactivity. The effect of a PMC on molecules with a conjugated system complexing with it, was discovered in our laboratory in 1962 and named "the local activation effect" [12-15]. Nevertheless the problem of the conditions of formation and the nature of the PMC's cannot yet be considered to be finally solved. Of the hypotheses concerning the nature of the paramagnetism of a PCS previously put forward, two are still of value. 1) The biradical hypothesis [12, 15], postulates that the paramagnetic centres arise as a result of unpairing of ~-electrons in the longer polyconjugated macromolecules. Here it is assumed that the S-T transition can occur as a result of thermal excitation and the triplet formed is converted to a stable bir~ical. I t is assumed also that the possibility

2734

A.A.

BERLIN

of such transitions requires small values of the energy gaps in the bundle-type associations of' homologous polymer fractions with long conjugated sequences, disruption of coplanarity in the systems and a large resonance energy gain b y delocalization of the unpaired spin in the conjugated system. 2) The hypothesis that charge-transfer states play a decisive part [16, 17] is based on the assumption of the presence in PCS's of polar states in close proximity, brought about b y one-electron intermolecular transfer, with formation of stable, radical-ion complexes. These hypotheses can explain more or less satisfactorily a number of experimental facts concerning the generation of PMC's or their effect on the properties , of PCS's [18, 19]. The biradleal hypothesis has now been developed further on the basis of a quantum-chemical consideration of polyene chains as the sum of = C H - g r o u p s with an odd number of electrons [20]. Interaction between two close neighbours is dependent on the sum of the spins of the two of their electrons involved. Two cases are possible. 1) The sum of the neighbouring spins S = 0 and the energy of interaction is equal to Q. 2) The sum of the spins S = 1 and the energy of interaction is equal to /~. For organic molecules antiparallel orientation of the spins is advantageous (case 1). In order for this ordering to be disturbed so that S-~I (triplet excitation) and expenditure of energy o f / ~ - Q is necessary. When it is remembered that this excitation is not localized in one unit, b u t is distributed along the conjugated sequence, then instead of one level with an excitation energy of ~ - Q we have a band of width Ema~(Pma,~)--Emin(Pmin), determined b y the probability of the triplet excitation transition. It must be emphasized that this transition and the width of the band are due to exchange interaction of spins, consequently the energy of triplet excitation is spread over a zone, the lower edge of which borders on the fundamental level. Quantum-chemical calculations have shown that the energy spectrum of the lower triplet states has a quasi-homopolar character and En for polyenes is expressed by

E,,=lnl~/~. Here En is the excitation energy in the transition to the triplet state, d = 4 r f l I 1 (2~fl/y)/I e (2~fl/~), n = ± l , ~ 2 , ± 3 ..., fl is the resonance integral, the coulomb integral, characterizing the repulsion of electrons on the same centre, I e and 11 the Bessel functions of the imaginary argument of zero and first order, and ~hr the number of ~-electrons. When account is taken of the fact that according to references [21] and [22] alternation of the lengths of the bonds does not occur in polyene and similar structures, it becomes obvious that it is possible to take into account only one value of the exchange integral ft. Then when 2~fl/~, is small the energy spectrum of the lower triplet states from the above formula takes the form E n ~ [nld~2fl~/.N~ ,, and for given values of N and ~, will be less the lower the value of ft. Reduction in fl is possible b y disturbance of the coplanarity

Intermolecular interaction in polyconjugated systems

2735

of the arrangement of the structural elements of the PCS macromolecules, as has been observed experimentally [23], and higher values of N in these can be obtained in fractions of higher molecular weight. Taking into account the intermolecular exchange interaction of the u-electrons the total number of conjugated u-electrons is considerably increased. From analysis of the above considerations we come to the conclusion that in PCS fractions of higher molecular weight there are low triplet states, and an increased probability of occupation of triplet levels as a result of reduction in eoplanarity and increase in the number of u-electrons taking part in exchange interaction.

2 2"0

2"5-

1+5- i 25

I

r, o0

FIG. 5

75

I

0

3o 7¥me , hp

I

6O

Fro. 6

FIG. 5. Temperature dependence of the EPR signal strength of OPA. The ordinate represents the ratio of the signal strength of the specimen (Ispec) to the signal strength of the standard (/st). FIG. 6. Rate of change in the EPR signal strength of oligophenylacetylene at room temperature (corresponding to section 3-1, Fig. 5):/--solid specimen of OPA, 2--OPA in solution in benzene (c =0'3 mole/1.). Calculation shows that the singlet-triplet transition can take place with energies commensurate with kT. The spins thus arising are stabilized by delocalization along the conjugated system of the maeromolecules and of the u-complex associations formed from them, and it is this that gives rise to. unusually long life of the triplet state in PCS's. In cases where formation of an ionized state is energetically favourable (the presence of polar groups and hetero-atoms, solvation b y a medium with high ~ etc.), one-electron intermolecular transfer of triplet spins with formation of charge-transfer complexes is possible [16, 17]. The above ideas about the presence of low triplet states in PCS's explain the occurrence of paramagnetic centres in them under mild conditions of synthesis. In this respect they supplement our previously formulated ideas about the nature of the paramagnetic centres in PCS's, and do not exclude the possibility of transition from a triplet-excited state to stable radicals, as was stated in references [12-15]. The recently discovered phenomenon of thermal excitation of paramagnetism in PCS's [24] is in good agreement with the above views.

2736

A.A. Bm~r~

Figure 5 shows a curve of the temperature dependence of the intensity of t h e E P R signal in oligophenylacetylene (OPA) subjected to heat treatment at 400 ° for a short time. It is seen that during the course of heating for 5-10 rain (section 1-2) the strength of the signal increases by a factor of about 2.5, but during subsequent cooling for 30 min (section 2-3) the signal strength does not return to its original value. Then at constant temperature (section 3-1, Fig. 5 and curve 1, Fig. 6) the intensity falls almost to its original value. This behaviour of the E P R signal is seen not only in a solid OPA specimen, but also in a solution of OPA in degassed benzene. The time to reach equilibrium is shorter in solution, however, than in a solid specimen (Fig. 6, curve 2), and it has been proved experimentally that this is not due to saturation. From this it may be assumed that part of the E P R signal of a PCS, even at room temperature, is attributable to thermal excitation. This assumption is confirmed by the decrease in the E P R signal strength of an OPA sample kept for 3 months at --78% This experimentally observed conformity with Curie's law can be attributed to very long times of relaxation of the E P R signal strength. I t has been mentioned previously that a characteristic of polyconjugated systems is the existence in them of strong associations of the macromolecnles, in which intermolecular delocalization of ~-electrons is possible. In assuming the occurrence of exchange (intermolecular) delocalization of ~-eleetrons it is logical to suppose that in PCS associations intermolecular spin transfer is possible, as a result of exchange interaction of the spin with ~-bonds and also spin-spin interaction. According to these ideas the PCS associations should be regarded as quasi-molecular formations with common energy levels. The above data on coordination energy, associations and a number of other physicochemical properties of PCS's are in good agreement with the ideas expressed here. Compounds in which exchange interaction of spins with ~-eleetrons or ungeneralized electrons of hetero-atoms occurs we propose to regard as "spin transfer" complexes (STC's). A specific characteristic of STC's is transfer of excitation from a triplet-excited particle to the molecule complexing with it. This should increase the probability of occupation of their triplet levels and consequently alter their reactivity and physicoehemieal properties (the "local activation" effect [13-15]). The part played by the local activation effect has been demonstrated in pyrolysis [25, 26], thermal- and photo-oxidative degradation [27-29], polymerization [30-32], reaction of PCS's with radicals [33-35], catalysis by polyconjugated systems [36, 37] and activation of cis-trans isomerization [38]. The effect of paramagnetie centres on the physical properties of polyconjugated systems is exhibited in change in the intensity of fluorescence, the life of photo-carriers and the energy of activation for conductivity [39-42]. The increased probability of intermoleeular transitions in complexes of stable, nitrogen-containing radicals was studied by the NlVIR method in references [43-45]. On the example of a complex of a stable radical with dibutyl maleate

Intermolecular interaction in polyconjugated systems

2737

it was shown t h a t t he orbital of the unpaired electron crosses the double-bond orbitals. I n such a system the nitroxide radical is a catalyst of cia-trans isomerization and a n u m b e r of other reactions. Thus the "local activation" effect embraces a v er y wide circle of phenomena of great scientific and practical interest. CONCLUSIONS Analysis of experimental information on the relationship between the struct u r e and physicochemical properties of polyconjugated systems (PCS's) leads to th e conclusion t h a t the change in the energy gap, t he difference in ionization potential and in affinity for electrons correlate with the difference in solubility, t e n d e n c y for association, electrophysical characteristics and radical react i vi t y of homologues differing in the length of the conjugated sequence. The formation of strong associations of molecules of polymers with a conjugated system is easily brought about by attaching the polyconjugated block to the flexible " m a t r i x " of a r u bber (block or graft copolymers). Thermochemical data, electronic spectra and the viscosity properties of solutions show t h a t in association of PCS macromolecules large intermolecular forces are involved, evidently on account of u-electron and spin-spin interaction. These associations must be regarded as quasi-molecular formations with common electronic levels and a lower energy gap. As a result of this such systems contain free spins (PMC's), delocalized along the conjugated zone. These PMC's facilitate intermolecular transitions in the u-bonds of th e complexing molecules and affect their reactivity and physicochemical properties (the "local activation effect"). Translated by E. O. Pm~r.n~s

REFERENCES

1. A. A. BERLIN, International Symposium on Macromolecular Chemistry, Brussels, 1967 2. A. A. BERLIN and V. P. PROMYSLO~r, Zh. strukt, khim. 11: 1076, 1970 3. L. J. ANDREWS and R. M. KEEFER, Molekulyarnye kompleksy v organicheskoi khimii (Molecular Complexes of Organic Chemistry). Izd. "Mir", 1967 (Russian translation) 4. A. A. BERLIN and V. P. PARINI, Khim. i khim. teklmol. 1: 122, 1958 5. A. A. BERLIN, M. I. C,HERKASHIN, Ye. A. 1KIROSHNICHENKO, Yu. A. LEREDEV and M. G. GAUSER, Izv. Akad. Nauk SSSR, ser. khim., 1501, 1969 6. Ya. F. FREIMANIS, Trudy II seveshchaniya po organicheskim poluprovodnikam (Trans. 2nd Conference on Organic Semiconductors). p. 63, Izd. "Znanie", 1960 7. A.A. BERLIN, Sb. dokladov yubilcinoi sessii po vysokomolekulyarnym soyedineniyam (Col]ected Reports of the Jubilee Session on Macromolecular Compounds). p. 98, Izd. IKhF, 1970 8. A. A. BERLIN, B. G. GERASIMOV and L. I. SAKHAROVA, Dok]. Akad. Nauk SSSR 196: 1108, 1971 9. A. A. BERLIN, L. I. BOGUSLOVSKII, R. Kh. BURSHTEIN, N. G. MATVEYEVA, A. I. SHERLE and N. A. SHUMOVSKAYA, Dokl. Akad. l~auk SSSR 186: 1127, 1961

10. L. I. BOGUSLOVSKIIand A. V. BANNIKOV,Organicheskie po]uprovodniki i biopolimery (Organic Semiconductors and Biopo]ymers). p. 52, Izd. "l~anka", 1968

2738

A . A . BERLII~

11. A. A. BERLIN, N. A. BAKH, Ye. N. MERKULOV, A. V. VANNIKOV, M. I. CHERKASHIN a n d I. M. CHERBAKOVA, Izv. Akad. l~auk SSSR, ser. khim., 2345, 1969 12. A. A. BERLIN, K h ~ . prom., No. 12, 23, 1962; K h i m i y a i tekhnol, polhnerov, Nos. 7-8, 139, 1960 13. A. A. BERLIN, V. A. VONSYATSKII a n d L . O. LYUBCHENK0, Izv. Akad. Nauk SSSR, Otd. khim nauk, 1312, 1962 14. A. A. BERLIN a n d S. I. BASS, Izv. Akad. l~auk SSSR, Otd. khim nauk, 1494, 1962; Dokl. Akad. Nauk SSSR 150: 795, 1963 15. A. A. BERLIN, Izv. Akad. Nauk SSSR, ser. khim., 59, ]962; International Symposium on Macromolecular Chemistry, p. 281, Prague, 1965 16. L. A. BLYUMENFEL'D, V. A. BENDERSKII and P. A. STUNZHAS, Zh. strukt, khim. 7: 868, 1966 17. V. A. BENDERSKII, Dissertation, 1964 18. A. V. TOPCHIEV (Ed.), Organicheskie poluprovodniki (Organic Semiconductors). p. 232, Izd. Akad. Nauk SSSR, 1963 19. W. HAUGEN and M. TRACTTEBARY, Acta Chem. Scaud. 20: 1726, 1966 20. A. A. BERLIN, G. A. VINOGRADOV and A. A. OVCHINNIKOV, Izv. ~ a d . Nauk SSSR, ser. khim., 1378, 1971 21. L A. MISURKIN a n d A. A. OVCHINNIKOV, Zh. teor. i eksp. khim. 3: 431, 1967; Zh. eksp. i teor. fiz., Pis'ma 4: 248, 1966 22. N. A. POPOV, Zh. strukt, khim. 1O: 422, 1969 23. N. Ya. SLONIM, Ya. B. URMAN, V. A. VONSYATSKH, B. I. LIOGON'KH and A. A. BERLIN, Dokl. Akad. Nauk SSSR 154: 914, 1964 24. A. A. BERLIN, G. A. VINOGRADOV and V. M. KORBYANSKII, Izv. Akad. Nauk SSSR, ser. khim., 1192, 1970 25. A. A. BERLIN, V. A. GRIGOROVSKAYA, V. K. SKACHKOVA and V. Ye. SKURAT, Vysokomol. soyed. A1O: 1578, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 7, 1826, 1968) 26. A. A. BERLIN, V. A. GRIGOROVSKAYA, V. P. PARINI a n d K. H. GAFUROV, Dokl. Akad. Nauk SSSR 156: 1371, 1964 27. A. A. BERLIN a n d S. I. BASS, Sb. Starenie i stabilizatsiya polimerov (Collected papers. Ageing a n d Stabilization of Polymers). p. 129, Izd. " K h i m i y a " , 1966 28. V. K. AFONSKII, A. A. BERLIN and D. M. YANOVSKII, Vysokomol. soyed. 8: 699, 1966 (Translated in Polymer Sci, U.S.S.R. 8: 4, 767, 1966) 29. A. A. BERLIN, International Symposium on Macromolecular Chemistry, Budapest, 1969 30. A. A. BERLIN a n d N. G. MATVEYEVA, Dok]. Akad. Nauk SSSR 167: 91, 1966 31. A. A. BERLIN, M. I. CHERKASHIN and B. G. ZADONTSEV, Vysokomol. soyed. Bg: 91, 1967 (Not translated in Polymer Sci. U.S.S.R.); B. G. ZADONTSEV, M. I. CHERKASHIN and A. A. BERLIN, Izv. Akad. Nauk SSSR, set. khim., 2065, 1967 32. A. A. BERLIN, A. P. FIRSOV and V. V. YARKINA, Vysokomol. soyed. BI0: 724, 1968 (Not translated in Polymer Sci. U.S.S.R.) 33. A. A. BERLIN and V. A. VONSYATSKII, Dokl. Akad. Nauk SSSR 154: 627, 1964; V. A. VONSYATSKII, G. I. KALYAYEV and A. A. BERLIN, Izv. Akad. Nauk SSSR, ser. khim., 304, 1964 34. A. A. BERLIN, G. N. BELOVA and A. N. FIRSOV, Dokl. Akad. Nauk SSSR 180: 140, 1968; Vysokomol. soyed. B10: 366, 1968 (Not translated in Polymer Sei. U.S.S.R.) 35. A. A. BERLIN and G. N. BELOVA, Vysokomol. soyed. B9: 718, 1967 (Not translated in Polymer Sei. U.S.S.R.) 36. J. GALLARD, T. LAEDERICH, R. SALLE and P. TRAYNARD, Bull. Soc. Chim. France, 2204, 1963; J. GALLARD, M. NECHTSCHEIN, M. SOULIF and P. TRAYNARD, Bull. Soc. Chim. France, 2209, 1963

S t u d y of structural parameters of a phenol-formaldehyde resite

2739

37. M. NEgHTSCHEIN a n d A. REBOUL, Compt. rend. 264g: 1220, 1967 38. A. A. BERLIN, V. P. P A R I N I a n d K. AL'MANBETOV, Dokl. Akad. l~auk SSSR 166: 595, 1966 39. A. A. BERLIN, Kh. M. GAFUROV, V. F. GA{~HI~OVSKII a n d V. P. PARINI, Izv. A k a d . N a u k SSSR, set. khim., 728, 1966; A. A. BERLIN, Kh. M. GAFUROV, N. S. MAIOROV a n d V. P. PARINI, Izv. A k a d N a u k SSSR, set. khim., 746, 1966 40. Kh. M. GAFUROV, V. M. MULIKOV, G. F. GACHKOVSKII, V. P. PARINI, A. A. BERLIN a n d L. A. BLYUMENFEL'D, Zh. strukt, khim. 6: 649, 1965 41. Kh. M. GAFUROV, Dissertation, 1967 42. R. M. VLASOVA and A. V. AIRAPETYANTS, F i z i k a tverdogo tcla 7: 13, 1965

STUDY OF THE STRUCTURAL PARAMETERS OF A PHENOL-FORMALDEHYDE RESITE* A . 2X_. BERLIN, R . ~V[. ~J~SEYEVA, K . A~'MA~I'BETOV, O. k . ~V~OCHALOVA

and I. YA. SLO~¢I~I Institute of Chemical Physics, U.S.S.R. Academy of Sciences

(Received 23 April 1970) DURI~G recent years considerable success has been achieved in establishing the structure of hardened phenol-formaldehyde polymers (PF's) and in studies of the reactions involved in their formation. Experimental evidence obtained b y various physical and physicochemical methods has led to the conclusion that crosslirrked P F ' s consist of macromolecnles with widely spaced chemical crosslinkages and a larger number of physical bonds. Many authors are inclined to the opinion that an "infinite" spatial network is not attained in resites. Despite the successes in studies of PF's, quantitative determination of the structural parameters of resites, and their relationship to the properties of the resin, has been the subject of only a very small number of papers. To a certain extent this is attributable to the complexity of the structure of the polymers and to limitations in the methods of analysis resulting from the infusibility and insolubility of resites. The aim of the work reported here was to determine the structural parameters of P F ' s hardened b y hexamethylenetetramine, and to find the effect of certain additives on formation of the spatial network of a resite. EXPERIMENTAL

The original PF resin, obtained by condensation of phenol with formaldehyde in the presence of HCI as catalyst, was subjected to fractional precipitation b y petroleum ether a t 20~0.1 °, from a 4 ~ solution in acetone. After separation into nine fractions, fractions 1-3,

* Vysokomol. soyed. AI3: No. 11, 2440-2446, 1971.