Polymer M e n ~ U.S.S.R. Vol. 20, pp. 2909-2918. (~) Pergamon Preu Ltd. 1970. Printed in Poland
STUDY OF SOLIDIFICATION OF EPOXY RESINS BY OLIGOESTER TITANATES OF DIFFERENT CHEMICAL STRUCTURES* A. L. SUVOROV, A. I. SUVOROVA, L. D. DUL'TSEVA, M. A. KOC~NEVA, N. Y u . YEZHOVA a n d YE. F. LOGINOVA Institute of Chemistry of the Urals Scientific Centre, U.S.S.R. Academy of Sciences A. M. Gorky State University, Urals
(Received 27 January 1978) It was shown by dielectric and mechanical investigations that crosslinked polymers are formed by the interaction of epoxy resins with oligoester titanates of different chemmal structures. These polymers have high physical and mechanmal parameters. I f ohgoester titanates are regarded as tetrafunctional, a network of highest density is formed with a component ratio considerably lower than the stoichiometrm. To explain features of solidification, a study was made 0fseveral model systems. Results suggest that both OH end groups and Ti-O-C bonds take part in network formation of epoxy-titanium-polyester polymers, while ohgoestor fragments of the organotitanium solidifier function as internal plasticizers of the polymer obtained. ORGANOTITANIUM p o l y e s t e r s - - o l i g o e s t e r t i t a n a t e s  were previously recomm e n d e d as solidifiers of e p o x y resins . These solidifires ensure the p r e p a r a t i o n o f strong, fairly elastic a n d heat resistant polymers w i t h o u t f u r t h e r i n t r o d u c t i o n o f modifiers. I n view of the f a c t t h a t oligoester t i t a n a t e s h a v e several reactive eentres which can p a r t i c i p a t e in crosslinking, it was interesting to explain special features o f this process. Oligomer a n d m o n o m e r c o m p o u n d s with a n d w i t h o u t h y d r o x y l e n d groups a n d a t i t a n i u m a t o m were used as solidifiers for this purpose. I t was interesting to explain the dependence of properties of e p o x y - t i t a n i u m polyester p o l y m e r s o b t a i n e d on the chemical s t r u c t u r e of a t i t a n i u m - p o l y e s t e r solidifier a n d its c o n t e n t in initial compositions. ED-16 and ED-22 industmal Diane resins with epoxy numbers of 15.4 and 21.8%, respectively, purified by filtration and dried in vacuum and ohgoestor titanates with different structures of the oligoeste~ block were examined. The latter were obtained by the interaction  of one mole ethylorthotitanate with four moles of ethylene glycol oligoester and phthalic, hexahydrophthallc and adipic acids. The reaction was carried out in methylene chloride at room temperature and stirring vigorously. The solvent and ethanol obtained during the reaction were distilled in vacuum at 60-80 °. * Vysokomol. soyed. A20: No. 11, 2592-2600, 1978. 2909
-- CO) ~.4,CH.CH,0H]4
* Calculated value is shown In the numerator and the value found in the denominator. I" Calculated from molecular wcishts of initial olisoester8 determined experimentally.
T i - - ( -- OCIH~) 4 - - t e t r a e t h o x y t l t a n i u m C - - ( -- C H 2 O H h - - p e n t a e r y t h r i t o l
T t - - [ - - O - - (CH~CH~OC -- C6H4-- CO) ~ 35CHzCH2OCCH3]~
T i - - [ - - O - - ( C H ~ C H 2 0 C - - CeH10CO) 1 4CHsCHzOH]~
T~ -- [-- 0 -- (CH,CH~0C
Ti -- [-- 0 -- (CH~CH~0C
TABLE 1. C~A3~ACTERISTICS OF SOLIDIFIERS
Saponification number, m g KOH/g
130/2 n m M.p. 260 °
B . p . , °C
Solidification of epoxy resins
In addition to oligoester titanates with OH end groups, a compound was used as model solidifier, in which these groups were replaced by acetoxy groups. This product was obtained by methods similar to those previously described, by the interaction of ethylorthotltanate with low molecular weight diaeetate ethylenephthalate. Tetraethoxytitanimn and pentaerythrite used as model solidlfiers were purified before use--the former by vacuum distillation, the latter, by recrystalhzatlon from wa£er. Titanium content was determined by a method previously described  and saponificatmn numbers of oligoester tltanates used by methods specially developed for compounds conraining titamum . Results and molecular weights calculated are shown in Table 1. The wscosity of unsohdffied rm'xtures was measured by the dropping sphere method at 25 °. I R spectroscopic investigations of initial products and their mixtures were carried out in a UR-20 device with KBr and NaC1 prisms with a layer thickness of 228/~m. 6~o solutions of substances in methylene chloride were examined. Resins were solidified under conditions described previously  with gradual increase of temperature from 150 to 200 ° m 15 hr. Compositions contained 10 to 60~o solidifier which corresponded to 30, 20, 12, 8, 3 and 2 moles resin per mole sohdifier. Solidified polymers were m the glassy state at room temperature. The soluble fraction was determined by prolonged extraction with methylene chlomde in a Soxhlet apparatus. The retmular nature of polymers solidified wa~ characterized by the molecular weight of the chain segment between crosslink units Me, determined from the equilibrium modulus of elongation of non-swollen samples at temperatures higher than the glass temperature [6, 7]. Mechanical properties in compression, elongation and bending were determined in FM250 and ZDM-5/91 tensile testing machines; specific impact strength was established with an MK-0.5 pendulum impact device and glass temperature evaluated from temperature/ /deformation curves plotted using a device with constant loading of the sample . Dmlectric properties (tangent of dielectric loss anglo tan J, dielectric constant e') were determined using a TR-9701 bridge in the interval of frequencies of 0-5-200 kc/s and temperatures of -- 150--4- 200% I t was established t h a t e p o x y compositions containing different a m o u n t o f oligoester t i t a n a t e s do n o t solidify a t r o o m t e m p e r a t u r e for a long period of t i m e . H o w e v e r , viscosity increases during storage. F o r e x a m p l e , t h e viscosity of a c o m p o s i t i o n containing 8 0 % E D - 2 0 a n d 2 0 % E G P T increases f r o m 11 to 150-260 poise 3-5 m o n t h s a f t e r p r e p a r a t i o n . Possible causes of increasing viscosity m a y be processes of chemical i n t e r a c t i o n of e p o x y groups w i t h functional g r o u p s of t h e solidifier a n d s t r u c t u r e f o r m a tion preceding a n d facilitating crosslinking. T o explain this process, a s t u d y was m a d e of I R s p e c t r a of some compositions during storage a n d p r o p e r t i e s of polym e r s o b t a i n e d f r o m t h e m . I R s p e c t r a were o b t a i n e d 7, 14 days, 1,2,3 a n d 5 m o n t h s a f t e r p r e p a r i n g t h e compositions; some of t h e m are shown in Fig. 1. B a n d s were o b s e r v e d in I R s p e c t r a a t 840, 925 a n d 1240 cm -1, t y p i c a l of e p o x y groups [9, 10]. A c o m p a r i s o n of s p e c t r a (Fig. la) confirms a slight d e p e n d e n c e of t h e i n t e n s i t y of these b a n d s on t h e storage t i m e o f compositions. F o r b a n d s o f b o n d stretching v i b r a t i o n s of the o x y r a n e ring a t 925 c m -1, which are m o s t sensitive to solidification  optical d e n s i t y was calculated  a n d f o u n d to decrease b y 0.05 units, w h i c h c o r r e s p o n d s to a utilization o f ~ 10% e p o x y groups.
A. L. Suvoxov eta/.
Therefore, in spite of the slight utilization of epoxy groups both during the storage of compositions at room temperature and during heating at temperatures far from initial gel formation (Fig. lb), viscosity increases considerably. I t m a y
FIo. 1. Variation of IR spectra, optical density and the viscosity of epoxy-titanium-poly. ester compositions based on ED-20, containing 20% EGPT and kept under different conditions: a--freshly prepared (1) and stored at room temperature for 2 (2) and 5 months (3); b--freshly prepared (1) and heated to 120° for 3 (2) and 12 hr (3). A cross indicates the bands which were used for the calculation of optical density. be assumed that an increase in viscosity is mainly due to the formation of ordered units as a result of molecular interaction [12, 13]. Their formation facilitates crosslLnking and the formation of a more perfect network. This is confirmed b y a reduction of the content of a soluble polymer fraction as the retention time of compositions at room temperature increases (Fig. 2) and b y an improvement of physical and mechanical properties. Results in Table 2 indicate that prolonged retention at room temperature and preliminary heating of compositions produce stronge~ polymers. Moreover, polymers obtained from compositions kept for a long time at room temperature have the most satisfactory properties, while further heating of these compositions either does not change properties, or results in some deterioration. These results are in agreement with the assumption concerning the formation of ordered units since their formation, no doubt, depends on temperature.
Solidification of epoxy resins
Bearing in mind the effect of past history of compositions, polymers obtained
using compositions kept at room temperature for the same length of time (2-3 months), were compared in subsequent investigations.
Fie. 3 Fio. 2 FIG. 2. Relation between the content of soluble fraction m polymers based on ED-16, solidified with 10% E D P T a n d the retention time of the initial composition at room temperature. FIG. 3. Relation between three dimensional network density of polymers based on ED-16, solidified with E G P T (1), E G G P T (2) and EGAT (3) a n d compositions.
Three dimensional network density was determined for all polymers crosslinked with oligoester titanates; the dependence of network density on component ratio is shown in Fig. 3. It can be seen that a network of maximum density is formed in every case during the interaction of 1 mole solidifier with 8-12 moles of resin. OT EPOXY-TITAT~JtUMopOLYESTER COMPOSITIONS CONTAINING ED-20 and 20% E G P T and polymers obtained from them Conditions of storage of Mechanical properties of samples compositions before solidisolidified fication q, poise stress causing yield point retention at (at 25 °) failure, kg/cm s impact retention a t in comroom strength, 120 °, hr pression, in elonga- in bending kg.cm/cm j temperature kg/cm I tion ae
days 2 months 3
•5 year .5 9~ days 7
7 3 months
2O 8 4 2O 2O
12 70 124 > 300 > 300 290 100 >300 > 300
1000 1180 1250 1225 1260 715 1100 1300 1160
420 860 850 875 550 740 720 710 790
880 1280 1360 1340 1100 1195 1050 1170 1400
2.0 23.0 15.0 24.5 13.5 20 14.0 5"0 16.0
A. L. SUVOROVet al.
During the formation of a crosslinked polymer the mobility of structural units varied considerably, which can be easily evaluated from dielectric parameters. Figure 4 shows the typical temperature-frequency relation of the tangent of dielectric loss angle for one of the systems examined; two maxima on the curve are attributed to the region of dipole segmental (DS) and dipole group (DG) loss. ~'an I',IO2 D8 x2 AO "6
FIG. 4. Temperature dependence of the tangent of dielectric loss angle tan ~ for a polymer obtained by solidification with 12 moles ED-16 resin and 1 mole EGPT. Frequency, ke/s: 1--0.5; 2--1, 3--5, 4--10, 5--50, 6--100, 7--200. Relaxation time v and the heat of activation AH of DG and DS processes were calculated from curves of tan ~ - f ( T , m). Figure 5a shows the dependence on composition for the three systems examined of the time of dipole-segmental relaxation, which is most sensitive to network formation. In view of considerable differences in the mobility of systems it is impossible to quote comparable values of the dependence of T on composition for the same experimental temperature. The type of dependence of the time of relaxation on composition is, however, of major importance: the mobility of structural elements with composition varies according to a curve with an extremum, systems of maximum crosslinking having the lowest mobility (Figs. 3 and 5). Heats of activation of DG and DS processes in solidified systems also vary according to composition, as shown b y a curve with a maximum, the position of which corresponds to the composition range of 8-12 moles resin per mole of solidifier, i.e. the range of formation of networks of highest density (Fig. 5b). The extremal dependence of the degree of crosslinking on composition is also reflected b y physical and mechanical properties of crosslinked polymers. As shown b y Fig. 6, the dependence of these properties on composition is also
S o l i d i f i c a t i o n o f e p o x y resins
extremal, although maximum values of various parameters are somewhat displaced in relation to each other on the axis of compositions, still they correspond to an interval of 8-20 moles of resin per mole of solidifier. An exception is the dependence on composition of impact stress (IS) for polymers solified with EGAT. An increase in the amount of the latter in the mixture results in a considerable increase of IS up to a composition with 3 moles of resin per mole of solidifier. From results in Figs. 5 and 6 it may be concluded t h a t the oligoester unit influences physical, mechanical and dielectric properties of epoxy-titanium-polyester polymers. Systems solidified with EGPT have the highest AH value of the DS process and those solidified with EGAT, the lowest (Fig. 5b). This is due to
10g.z" Q °I x2
o-',,10"; k..q~m Z 14
./ xZ oJ
ReMn/so/idz~'eP , mole/mole FIG. 5
/?esin//sol/d/,~er, mole/mo/e FIG. 6
FIG. 5. Relation between the lime of dipole segmental relaxation (a), the heat of activation DS (I-III) and DG (IV) processes (5) and the composition of systems obtained using ED-16 and sohdifiers: 1--EGPT, 2--EGGPT, 3--EGAT; a: 1--100, 2--80, 3--110 °.
FIG. 6. Relation between ~l (I), ~r (II) and impact strength (III) and the composition of systems obtained using ED-16 and oligoester titanates: /--EGPT, 2--EGGPT, 3--EGAT.
A. L. S w o R o v
the structure of the polyester fragment in the solidifier molecule: the existence of a methylene chain between polar groups - - C O O - - makes the system solidified with EGAT more mobile, compared with the system solidified with EGPT. The structure of the solidifier molecule has practically no effect on DG loss. The value of •H of DG loss is 8-15 kcal/mole in every case, which is typical of epoxy solidified polymers and, as shown previously [14, 15], is due to the motion of - - C H 2 - - C H - - C H 2 - - O - - groups.
OH The dependence of strength parameters on the structure of the oligomer unit of the solidifier (Fig. 6) is only apparent on transition from aromatic to aliphatic particles. On transition from an aromatic to a cyclo-aliphatic radical these properties remain practically unchanged; the highest value of parameters measured in the optimum is observed for systems solidified with EGPT. fan 6"~10z
1PzG. 7. Temperature dependence of tan J for polymers based on ED-16, solidified with pentaerythritol in the presence of a plasticizer (1), with tetraethoxytitanium (5), tetraethoxytitanium in the presence of a plastmlzer (2), EGPT (3) and I)AEPT (4). Results of dielectric and mechanical studies therefore prove that during the interaction of epoxy resin with oligoester-titanates of different chemical structure crosslinked polymers are formed with high physical and mechanical parameters. ~Highest network density is formed with a component ratio considerably lower than the stoichiometric if oligoester-titanates are regarded as tetrafunctional. I t m a y be assumed that this is caused b y the presence in the oligoester titanate molecule of several reactive centres, in which crosslinl~ing m a y take place.
Solidification of epoxy resins
To explain features of solidification, a study was made of dielectric properties of polymers obtained from the model solidifiers described. Solidification was carried out under the same conditions, with a molar ratio of resin: solidifier of 12: 1. Considering the structure of oligoester titanates (Table 1), a plasticizer--oligoethylene phthalate HsCH~C--(O--C--C6H4--C--OCH~CH~--)I.4~H was added
O O to the systems with tetraethoxy titanium and pentaerythritol, which repeats the structure of oligoester unit of EGPT and has the same molecular weight. Figure 7 shows the temperature dependence of tan 5 at a frequency of 100 kc/sec (similar measurements were made at seven fixed frequencies) for all model systems and for a system consisting of 12 moles-resin and 1 mole EGPT. It is well known that the position of Tmax of DS loss characterizes the glass temperature at a selected frequency of the electric field and the varying heat stability of the material, dependent on the structure of the network obtained may be determined from this position. Since oligoeste,r titanates contain free OH end groups that can interact with the epoxy ring  it was assumed that these groups take part in the formation. of a network of polymers examined. Pentaerythritol was used as model tetrafunctional solidifier free from titanium atom. Solidification of epoxy resin by this compound under conditions optimum for oligoester titanates results in the formation of a solid product,* soluble in methylene chloride, which has a low value of Tmax of dielectric loss and high values of tan ~ (curve 1, Fig. 7) due to the presence of a large number of polar groups. A comparison of curves 1 and 3' of Fig. 7 indicates that under the conditions selected, in contrast with pentaerythritol, E G P T ensures the preparation of a polymer with fairly high Tmax. At. the same time it follows from Fig. 7 (curve 5) that tetraethoxy titanium has the highest value of Tmax; the addition to this system of a plasticizer displaces Tmax to the region of lower temperatures (curve 2). These results, compared with results of a system solidified with pentaerythritol, confirm our assumption t h a t T i - - O - - C bonds t a k e part in network formation of epoxy-titanium-polyester polymers to form a unit containing a titanium atom. This agrees with results o f dielectric investigations of an ED-16-DAEPT system, in which OH groups of the solidifier are replaced by acetoxy groups (curve 4, Fig. 7). These results prove t h a t a crosslinked polymer with a high value of Tmax is formed. A comparison of curves 2, 3 and 5 in Fig. 7 shows t h a t the system solidified with oligoester titanate occupies an intermediate position regarding values o f Tmax and tan ~, which suggests that the oligoester unit of the oligoester titanate molecule has a plasticizing role in the solidified polymer. Results therefore suggest that both OH end groups and T i - - O - - O bonds take part in network formation of epoxy-titanium-polyester polymers, while oligoester* A crosslinked product with a molar ratio of resin : pentaerythritol close to the stoichiometric (and at 230-250 °) is formed.
A . L . S~voRov et al.
particles of the organotitanium solidifier function as internal plasticizers of the polymer obtained. Finally, the authors wish to thank A. A. Tager for his advice and discussing results. Tranalated by E. SE~RE REFERENCES
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