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Study of the mechanism of structure formation during the production of an epoxide surface coating
STUDY OF THE MECHANISM OF STRUCTURE FORMATION DURING THE PRODUCTION OF AN EPOXIDE SURFACE COATING* L. A. SUKHAREVA, S. S. IVANOVA and
P. I. ZUBOV
Physical Chemistry Institute, U.S.S.R. Academy of Sciences (Received 6 March 1972)
Epoxide solutions are structured systems consisting of molecular associations which alter their rheological properties during storage as a result of the aggregation of the structural elements and bond formation between them. The processes taking place in the epoxide solutions at various stages with and without a thermosetting agent present, have much in common, and determine the structure of the surface coating. The pitting (eratering) which occurs during the formation of the coating is typical of epoxides with a broad molecular weight distribution (MWD). I t is thought to be linked with the creation of a supermolecular structure around the molecular associations of the oligomer, which play the part of structuring centres. THE p o l y m e r i z a t i o n to low mol.wt, p o l y e p o x i d e s d u r i n g t h e f o r m a t i o n of surface coatings was f o u n d to be a t w o - s t a g e process. T h e first stage consists of c h e m i c a l b o n d s f o r m i n g inside t h e m a c r o m o l e c u l a r s t r u c t u r e s , t h e second o f b o n d s f o r m i n g a m o n g s t t h e l a t t e r [1]. T h e s t r u c t u r a l order increases w i t h t h e t e m p e r a t u r e o f t h e s u r f a c e - c o a t i n g p r o d u c t i o n , g r e a t e r a d h e s i o n of t h e l a t t e r to t h e surface o f t h e s u p p o r t , t h e a d d i t i o n of r e a c t i v e fillers, a n d t h e c r e a t i o n of a t h i x o t r o p i c s t r u c t u r e in t h e oligomerie s y s t e m s b y m e a n s of a modifier [2, 3]. T h e s t u d y deals w i t h t h e s t r u c t u r a t i o n which t a k e s place in t h e e p o x i d e solutions a n d its effect on t h e s t r u c t u r e a n d p r o p e r t i e s o f t h e surface coatings. EXPERIMENTAL
Oligo-epoxides were studied which had broad mol.wt, distribution (MWD) (600-20,000) and a larger average mol.wt. (1200) than was used before; polyamlde (PO-200) was used
as the hardener. All the investigations were carried out at 20°C. The structuration which took place in the epoxide solutions in P-5 and paints based on them was assessed on the basis of rheological data from a Shvedov-type instrument. The polymerization kinetics were studied by infrared (IR) spectroscopy. The inhibition rate of the relaxation processes was assessed from the internal stress changes [4]. Electron microscopy was used in the structural study of the coating after etching with oxygen [5]. RESULTS
A 3 0 % oligo-epoxide solution, as Fig. l a shows, is a slightly s t r u c t u r e d s y s t e m w h i c h will d i s i n t e g r a t e w h e n a r e l a t i v e l y small s h e a r stress is a p p l i e d to it ( a b o u t 1 dyne/cm~). T h e s a m e t y p e of theological curves h a d b e e n o b t a i n e d earlier [6] * Vysokomol. soyed, h15: Iqo. 11, 2506-2511, 1973. 2837
L. A. SUgl:[AREVA e$ a~.
2838
with association systems containing a small number of crosslinkages between structural elements; these formed as a result of weak molecular interactions. The upper viscosity limit dropped after 7 hr of structuration while the lower limit rose slightly. The structural elements disintegrated at smaller shear stress (0.5 dyne/cm~) which means that the number of bonds between them decreased.
a
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b ZO00~4-
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2
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2
8
I0 N
~ 1 20 60 100
I 500
I
1000
[
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5000 11,000 #,d#ne/em~
:F~G. 1. The viscosity as a function of shear stress in: a - - a n oligo-epoxidc solution; b - - i n the oligomer with hardener, a : / - - o r i g i n a l solution; 2--after 7 hr; 3--after 1 day, b: / - - o r i g inal solution; 2 - 9 - - a f t e r 1, 2, 3, 5, 22, 27, 46 a n d 54 hr respectively.
However, both the viscosity limits became greater after several days and the transition between them became smoother. The critical shear stress at which the structural elements disintegrated also became greater. In order to clarify the reasons for the substantial changes in the shape of the
Mechanism of structure formation during production of epoxide surface coating 2839 theological curves as a function of structuration time of the oligomer solutions, t h e y were compared with those of the same solutions after a setting agent addition at a 0.5 : 1.0 ratio. Figure lb shows the presence of the setting agent to make the system more structurated, more viscous, and to produce a greater critical shear stress. The nature of the viscosity changes did not alter however, although the structuration time was shorter. The upper viscosity limit dropped b y a factor of 2 after one hour structuration time, while the lower limit remained the same. There was a slight reduction of the critical shear stress required for the disintegration of the structural elements. Hardly any changes took place during the second hour. The greatest critical shear stress was reached after 3 hr, the lower level of the viscosity range being raised slightly, while the upper one reached its original value. This was followed b y a slow increase in viscosity and in critical shear stress. The viscosity reached 30 poise after 27 hr, the critical shear stress 4 dyne] /cm ~. Typical throughout is the abrupt change from the upper to the lower viscosity level. The rate of structuration rapidly increased after this; the viscosity reached 400 poises after 46 hr, the critical shear stress 14 dyne/cm ~. The values were 6000 poises and 500 dyne/cm 2 respectively after 54 hr. The change between the viscosity levels became much smoother and the curve became an almost straight line after 54 hr. One gathers from these results that the oligo-epoxide solutions of M ~ 1200, compared with low mol.wt, epoxides, are a structured system. There will be a slight decrease in viscosity at the start of storage without the hardener; this appears to be due to strengthening of the structural elements and weakening of the bonds between them. This is followed b y an increase in the number of the physical bonds, chemical bond formation and increase in viscosity, and in the critical shear stress of the system. These stages of theological changes can also be detected when the epoxide solutions are stored in the presence of (with) hardener. Typical for the behaviour of the solutions is that the first stage is rapid and that, in addition to increases in viscosity and cirtical shear stress in the first two stages, there is a third in which these two parameters increase, while the type of rheological curve changes become smoother. To clarify the structuration characteristics during the hardening of the oligoepoxide solutions, we compared the changes in rhcological properties during polymerization with the conversions of the epoxy groups and the IR-spectral changes during the formation of the surface coating. The kinetics of the IR-spectral absorption line intensities are reproduced in Fig. 2. Those of the epoxy-group participations in the polymerization are illustrated by curve 1 which shows that the concentration of epoxy groups up to 3 hr from the start of polymerization remains almost constant. This period of hardening is equivalent to strengthening of the associations formed in the solution and is accompanied by decrease in viscosity and critical shear stress. This period is followed by a polymerization in which the concentration of epoxy groups steadily decreases while the number of H-bonds increases as a result of reactions between
2840
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eta/.
hydroxyl- and amino-groups. The beginning of this period corresponds with an increase in critical shear stress to a value typical of the original solutions, which indicates that the polymerization chiefly progresses inside the macromolecular structures in this stage. Continuation of polymerization for up to 2 days brings about a decrease in the number of epoxy groups, and increase in viscosity increase b y two orders of magnitude, as well as an increase in critical shear stress due to chemical bonds forming between macromoleeular structures in this stage.
120
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,
,I ~
I
I
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~ I
9
I
60 110
da~s
:Fxo. 2. The kinetics of absorption line intensity changes in the IR spectrum (cm-X): 1--925; 2--1370; 3--1390; 4--3340. Figure 2 also shows a sudden change of the content of epoxy groups during polymerization, and the existence of induction periods at the start of the separate hardening stages. o;,kS/tree
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8
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.
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.
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3
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Fro. 3. The kinetics of: /--internal stress changes; 2--solvent evaporation from the surface coating as a function of time. Curves 2 and 3 show line intensity changes of the symmetrical deformation vibrations of the H-bonds of the two methyl groups situated on one C-atom. The lines are equidistant either side of the average value (1380 cm -z) and should have
Mechanism of structure formation during production of epoxide surface coating 2841
the same intensity. The intensity of the 1370 cm -1 line however, was 3 times that of the 1390 cm -1 line in the original spectrum. This could be the case only ff tert.butyl group would be present, which is not the case here; neither are there
3~
FIe. 4. Electron microscope pictures of the oligo-epoxide surface coating: a - - s t r u c t u r e of the film on a level part; b - f - - s t r u c t u r e of a 1.5 m m crater; g - i - - s t r u c t u r e of a 0.25 m m crater; b, c, g--central part of crater; d-f, h, / - - a r e a around the crater in order of distance from the centre.
a n y branches with a methyl group present. The intensity difference between these lines must therefore be explained b y stereoehemical factors, particularly the effect of the vibrations of two in-series benzne rings. One day after the surface coating started to form the 1370 cm -1 line intensity begins to decrease to become the same as that of the other line after 60 days; this can be interpreted as due to a conformational rearrangement of the benzene rings, after which both the methyl groups will have sterically identical conditions [7, 8]. The induction periods of the seperate hardening stages are due in the epoxy coatings to orientational changes of the oligomer molecules and a structural rearrangement of the elements due to the internal stress created in the coating.
2842
L. A. S u ~ L m ~ v A e~ a/.
The drying of the coating can be divided into two stages (Fig. 3, curve 2), in which the first is linl~ed with the solvent removal (more than 60%) from the system and a slight increase of the internal stresses (up to 1 kgf/em~); according to Fig. 2 no chemical bonds are produced in this process. The second stage of drying is characterized by a lower drying intensity. The kinetic curves of polymerization and internal stresses show this as an induction period; the coating will still contain 20% of the solvent, which slowly evaporates in the next 10 days while intense polymerization takes place, which is accompanied by abrupt internal stress increases. The coating will still contain 15°/o of the solvent in the final stage. These findings make it clear that the polymerization starts in epoxy-group coatings when the solvent content is small (about 20%). In order to clarify the structnration characteristics during solvent evaporation and polymerization, we examined the macromoleeular structure of a coating produced from an oligo-epoxide solution with and without a setting agent present (Fig. 4a). No significant differences were detected. The production of a coating from epoxides with a relatively large mol.wt. showed the formation of complex macromolecular structures at the boundary between the surface film and air; these were circular and consisted of rings with varying morphology of their structural elements, also in dimension and packing density [9]. The presence of these structures was linked with the appearance of pitting (crater formation) in the polymer coating which greatly reduced its decorative and protective qualities. The formation of these structures did not depend on the polymerization conditions and happened during the solvent evaporation. It also is a feature of paint compositions when no hardener had been added to the system. Figure 4b-f show the structure of an individual crater of 1-5 mm diameter; this was obtained by the replica technique. One can see a nucleus in the crater centre, which consists of rod-like structures of 300-500/~. Its removal caused its density and structure to change. A dimensional reduction of the nucleus to 1-8/1 caused a morphological change of the structural elements forming the crater. Figure 4g-/show the defects of smaller dimensions to have a typically globular structure which differed from that present in the coating surrounding the foreign body [9]. From these results one can assume the causes of crater formation in the surface layers of coatings to be due to the specific features of structuration in the oligomer solutions having a broad MWD, in which the molecules of larger mol.wt form associates with an ordered structure fulfilling the role of structuratiou centres. Translated by K. A. A~y_~N REFERENCES 1. L. A. SUKHAltEVA, V. A. VORONKOV and P. I. ZUBOV, Vysokomol. soyed. A l l : 407, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 458, 1969) 2. L. A. SUKHAREVA, V. A. VORONKOV and P. A. ZUBOV, Kolloid. zh. 32: 261, 1970
Viscosity of polypropylene glycol oligomers
2843
3. L. A. SUKHAREVA, V. A. VORONKOV and P. I. ZUBOV, Kolliod. zh. 3a: 592, 1971
4. L. A. LEPILKINA and P. I. ZUBOV, Vestnik Akad. Nauk SSSR, No 3, 49, 1962 5. P. I. ZUBOV, M. R. KISELEV and L. A. SUKHAREVA, Dokl. Akad. Nauk SSSR 176: 336, 1967 6. P. I. ZUBOV, L. A. SUKHAREVA, N. I. SERAYA and V. A. VORONKOV, Vysokomol. soyed. A l l : 486, 1969 (Translated in Polymer Sei. U.S.S.R. 11: 3, 547, 1969) 7. L. BELLAMY, Infrakrasnye spektry slozhnykh molekul (The Infrared Spectra of Complex Molecules). p. 33, Izd. inostr, lit., 1963 8. A. CROSS, Vvedenie v prakticheskuyu infrakrasnuyu spektroskopiyu (Introduction to Practical Infrared Spectroscopy). p. 86, Izd. inostr, lit., 1961 9. L. A. SUKtLkREVA, S. S. IVANOVA and P. I. ZUBOV, Kolloid. zh. 35: 69, 1973
THE VISCOSITY OF POLYPROPYLENE GLYCOL OLIGOMERS AS A FUNCTION OF TEMPERATURE AND MOLECULAR WEIGHT* O, A. OL'KHOVIKOV, V. IV[. GOLUBEV a n d G. A. GLADKOVSKII All-Union Synthetic Resins Research Institute (Received 9 March 1972) The temperature dependence of the viscosity of linear polypropylene glycols (PPG) of various mol.wt, was studied in the range from -- 56 to + 56°C, amongst them that of a sample in which the hydroxyl end groups had been substituted by methyl groups. The temperature--viscosity functions of all the samples were found to be described by the Williams-Landell-Ferri empirical formula. The type of dependence in this formula of the parameters on the mol.wt, and the hydroxyl group content of the PPG was well explained by the theories dealing with the relaxation processes as a consideration of the free volume.
THE v i s c o s i t y of p o l y - e t h e r s has a considerable effect on t h e process t e c h n o l o g y d u r i n g t h e m a n u f a c t u r e of p o l y u r e t h a n e s . F o r e x a m p l e , t h e s t a b i l i t y o f f o a m p r o d u c i n g s y s t e m s d u r i n g p o l y u r e t h a n e f o a m p r o d u c t i o n s t r o n g l y d e p e n d s on t h e v i s c o s i t y of t h e p o l y e t h e r as a n original c o m p o n e n t of t h e s y s t e m [1]. T h e m a n u f a c t u r e o f such c o m p o s i t i o n s b y m i x i n g also s t r o n g l y d e p e n d s on this f a c t o r [2]. T h e oligo-ethers w i t h m o l e c u l a r weights (mol.wt.) of several h u n d r e d s or t h o u s a n d s are i n t e r m e d i a t e in p o s i t i o n b e t w e e n low- a n d high mol.wt, s u b s t a n c e s . T h e y are t h u s s u i t a b l e m o d e l c o m p o u n d s for rheological p r o p e r t y studies of p o l y m e r s a t r e l a t i v e l y low mol.wt. T h e s t u d y o f p o l y p r o p y l e n e glycol ( P P G ) is t h u s of c o n siderable i n t e r e s t in this respect. This simple oligoether is a n o n - c r y s t a l l i z i n g * Vysokomol. soyod. A15: No. ll, 2512-2516, 1973.
P. I. ZUBOV
Physical Chemistry Institute, U.S.S.R. Academy of Sciences (Received 6 March 1972)
Epoxide solutions are structured systems consisting of molecular associations which alter their rheological properties during storage as a result of the aggregation of the structural elements and bond formation between them. The processes taking place in the epoxide solutions at various stages with and without a thermosetting agent present, have much in common, and determine the structure of the surface coating. The pitting (eratering) which occurs during the formation of the coating is typical of epoxides with a broad molecular weight distribution (MWD). I t is thought to be linked with the creation of a supermolecular structure around the molecular associations of the oligomer, which play the part of structuring centres. THE p o l y m e r i z a t i o n to low mol.wt, p o l y e p o x i d e s d u r i n g t h e f o r m a t i o n of surface coatings was f o u n d to be a t w o - s t a g e process. T h e first stage consists of c h e m i c a l b o n d s f o r m i n g inside t h e m a c r o m o l e c u l a r s t r u c t u r e s , t h e second o f b o n d s f o r m i n g a m o n g s t t h e l a t t e r [1]. T h e s t r u c t u r a l order increases w i t h t h e t e m p e r a t u r e o f t h e s u r f a c e - c o a t i n g p r o d u c t i o n , g r e a t e r a d h e s i o n of t h e l a t t e r to t h e surface o f t h e s u p p o r t , t h e a d d i t i o n of r e a c t i v e fillers, a n d t h e c r e a t i o n of a t h i x o t r o p i c s t r u c t u r e in t h e oligomerie s y s t e m s b y m e a n s of a modifier [2, 3]. T h e s t u d y deals w i t h t h e s t r u c t u r a t i o n which t a k e s place in t h e e p o x i d e solutions a n d its effect on t h e s t r u c t u r e a n d p r o p e r t i e s o f t h e surface coatings. EXPERIMENTAL
Oligo-epoxides were studied which had broad mol.wt, distribution (MWD) (600-20,000) and a larger average mol.wt. (1200) than was used before; polyamlde (PO-200) was used
as the hardener. All the investigations were carried out at 20°C. The structuration which took place in the epoxide solutions in P-5 and paints based on them was assessed on the basis of rheological data from a Shvedov-type instrument. The polymerization kinetics were studied by infrared (IR) spectroscopy. The inhibition rate of the relaxation processes was assessed from the internal stress changes [4]. Electron microscopy was used in the structural study of the coating after etching with oxygen [5]. RESULTS
A 3 0 % oligo-epoxide solution, as Fig. l a shows, is a slightly s t r u c t u r e d s y s t e m w h i c h will d i s i n t e g r a t e w h e n a r e l a t i v e l y small s h e a r stress is a p p l i e d to it ( a b o u t 1 dyne/cm~). T h e s a m e t y p e of theological curves h a d b e e n o b t a i n e d earlier [6] * Vysokomol. soyed, h15: Iqo. 11, 2506-2511, 1973. 2837
L. A. SUgl:[AREVA e$ a~.
2838
with association systems containing a small number of crosslinkages between structural elements; these formed as a result of weak molecular interactions. The upper viscosity limit dropped after 7 hr of structuration while the lower limit rose slightly. The structural elements disintegrated at smaller shear stress (0.5 dyne/cm~) which means that the number of bonds between them decreased.
a
2
~?.0
4tO
b ZO00~4-
*!
sO
×z
~a
A8 o~
~" 1810
-I: 0 5
2
i
2
8
I0 N
~ 1 20 60 100
I 500
I
1000
[
I
5000 11,000 #,d#ne/em~
:F~G. 1. The viscosity as a function of shear stress in: a - - a n oligo-epoxidc solution; b - - i n the oligomer with hardener, a : / - - o r i g i n a l solution; 2--after 7 hr; 3--after 1 day, b: / - - o r i g inal solution; 2 - 9 - - a f t e r 1, 2, 3, 5, 22, 27, 46 a n d 54 hr respectively.
However, both the viscosity limits became greater after several days and the transition between them became smoother. The critical shear stress at which the structural elements disintegrated also became greater. In order to clarify the reasons for the substantial changes in the shape of the
Mechanism of structure formation during production of epoxide surface coating 2839 theological curves as a function of structuration time of the oligomer solutions, t h e y were compared with those of the same solutions after a setting agent addition at a 0.5 : 1.0 ratio. Figure lb shows the presence of the setting agent to make the system more structurated, more viscous, and to produce a greater critical shear stress. The nature of the viscosity changes did not alter however, although the structuration time was shorter. The upper viscosity limit dropped b y a factor of 2 after one hour structuration time, while the lower limit remained the same. There was a slight reduction of the critical shear stress required for the disintegration of the structural elements. Hardly any changes took place during the second hour. The greatest critical shear stress was reached after 3 hr, the lower level of the viscosity range being raised slightly, while the upper one reached its original value. This was followed b y a slow increase in viscosity and in critical shear stress. The viscosity reached 30 poise after 27 hr, the critical shear stress 4 dyne] /cm ~. Typical throughout is the abrupt change from the upper to the lower viscosity level. The rate of structuration rapidly increased after this; the viscosity reached 400 poises after 46 hr, the critical shear stress 14 dyne/cm ~. The values were 6000 poises and 500 dyne/cm 2 respectively after 54 hr. The change between the viscosity levels became much smoother and the curve became an almost straight line after 54 hr. One gathers from these results that the oligo-epoxide solutions of M ~ 1200, compared with low mol.wt, epoxides, are a structured system. There will be a slight decrease in viscosity at the start of storage without the hardener; this appears to be due to strengthening of the structural elements and weakening of the bonds between them. This is followed b y an increase in the number of the physical bonds, chemical bond formation and increase in viscosity, and in the critical shear stress of the system. These stages of theological changes can also be detected when the epoxide solutions are stored in the presence of (with) hardener. Typical for the behaviour of the solutions is that the first stage is rapid and that, in addition to increases in viscosity and cirtical shear stress in the first two stages, there is a third in which these two parameters increase, while the type of rheological curve changes become smoother. To clarify the structuration characteristics during the hardening of the oligoepoxide solutions, we compared the changes in rhcological properties during polymerization with the conversions of the epoxy groups and the IR-spectral changes during the formation of the surface coating. The kinetics of the IR-spectral absorption line intensities are reproduced in Fig. 2. Those of the epoxy-group participations in the polymerization are illustrated by curve 1 which shows that the concentration of epoxy groups up to 3 hr from the start of polymerization remains almost constant. This period of hardening is equivalent to strengthening of the associations formed in the solution and is accompanied by decrease in viscosity and critical shear stress. This period is followed by a polymerization in which the concentration of epoxy groups steadily decreases while the number of H-bonds increases as a result of reactions between
2840
L.A. S ~ v A
eta/.
hydroxyl- and amino-groups. The beginning of this period corresponds with an increase in critical shear stress to a value typical of the original solutions, which indicates that the polymerization chiefly progresses inside the macromolecular structures in this stage. Continuation of polymerization for up to 2 days brings about a decrease in the number of epoxy groups, and increase in viscosity increase b y two orders of magnitude, as well as an increase in critical shear stress due to chemical bonds forming between macromoleeular structures in this stage.
120
"x'---x~--#
O0 ,
, H
,
,I ~
I
I
I /~ffl
20 60 ~! 2 1¢ G J rm'n hn T/me
~ I
9
I
60 110
da~s
:Fxo. 2. The kinetics of absorption line intensity changes in the IR spectrum (cm-X): 1--925; 2--1370; 3--1390; 4--3340. Figure 2 also shows a sudden change of the content of epoxy groups during polymerization, and the existence of induction periods at the start of the separate hardening stages. o;,kS/tree
2 - 20 ~- ~ L.~-
~
. I,,
ZO
6o"
m 1"17.
~ I
I
_ I
0
~ I.
8
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.
~
.
1
3
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]
~ f0 30
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Fro. 3. The kinetics of: /--internal stress changes; 2--solvent evaporation from the surface coating as a function of time. Curves 2 and 3 show line intensity changes of the symmetrical deformation vibrations of the H-bonds of the two methyl groups situated on one C-atom. The lines are equidistant either side of the average value (1380 cm -z) and should have
Mechanism of structure formation during production of epoxide surface coating 2841
the same intensity. The intensity of the 1370 cm -1 line however, was 3 times that of the 1390 cm -1 line in the original spectrum. This could be the case only ff tert.butyl group would be present, which is not the case here; neither are there
3~
FIe. 4. Electron microscope pictures of the oligo-epoxide surface coating: a - - s t r u c t u r e of the film on a level part; b - f - - s t r u c t u r e of a 1.5 m m crater; g - i - - s t r u c t u r e of a 0.25 m m crater; b, c, g--central part of crater; d-f, h, / - - a r e a around the crater in order of distance from the centre.
a n y branches with a methyl group present. The intensity difference between these lines must therefore be explained b y stereoehemical factors, particularly the effect of the vibrations of two in-series benzne rings. One day after the surface coating started to form the 1370 cm -1 line intensity begins to decrease to become the same as that of the other line after 60 days; this can be interpreted as due to a conformational rearrangement of the benzene rings, after which both the methyl groups will have sterically identical conditions [7, 8]. The induction periods of the seperate hardening stages are due in the epoxy coatings to orientational changes of the oligomer molecules and a structural rearrangement of the elements due to the internal stress created in the coating.
2842
L. A. S u ~ L m ~ v A e~ a/.
The drying of the coating can be divided into two stages (Fig. 3, curve 2), in which the first is linl~ed with the solvent removal (more than 60%) from the system and a slight increase of the internal stresses (up to 1 kgf/em~); according to Fig. 2 no chemical bonds are produced in this process. The second stage of drying is characterized by a lower drying intensity. The kinetic curves of polymerization and internal stresses show this as an induction period; the coating will still contain 20% of the solvent, which slowly evaporates in the next 10 days while intense polymerization takes place, which is accompanied by abrupt internal stress increases. The coating will still contain 15°/o of the solvent in the final stage. These findings make it clear that the polymerization starts in epoxy-group coatings when the solvent content is small (about 20%). In order to clarify the structnration characteristics during solvent evaporation and polymerization, we examined the macromoleeular structure of a coating produced from an oligo-epoxide solution with and without a setting agent present (Fig. 4a). No significant differences were detected. The production of a coating from epoxides with a relatively large mol.wt. showed the formation of complex macromolecular structures at the boundary between the surface film and air; these were circular and consisted of rings with varying morphology of their structural elements, also in dimension and packing density [9]. The presence of these structures was linked with the appearance of pitting (crater formation) in the polymer coating which greatly reduced its decorative and protective qualities. The formation of these structures did not depend on the polymerization conditions and happened during the solvent evaporation. It also is a feature of paint compositions when no hardener had been added to the system. Figure 4b-f show the structure of an individual crater of 1-5 mm diameter; this was obtained by the replica technique. One can see a nucleus in the crater centre, which consists of rod-like structures of 300-500/~. Its removal caused its density and structure to change. A dimensional reduction of the nucleus to 1-8/1 caused a morphological change of the structural elements forming the crater. Figure 4g-/show the defects of smaller dimensions to have a typically globular structure which differed from that present in the coating surrounding the foreign body [9]. From these results one can assume the causes of crater formation in the surface layers of coatings to be due to the specific features of structuration in the oligomer solutions having a broad MWD, in which the molecules of larger mol.wt form associates with an ordered structure fulfilling the role of structuratiou centres. Translated by K. A. A~y_~N REFERENCES 1. L. A. SUKHAltEVA, V. A. VORONKOV and P. I. ZUBOV, Vysokomol. soyed. A l l : 407, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 458, 1969) 2. L. A. SUKHAREVA, V. A. VORONKOV and P. A. ZUBOV, Kolloid. zh. 32: 261, 1970
Viscosity of polypropylene glycol oligomers
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3. L. A. SUKHAREVA, V. A. VORONKOV and P. I. ZUBOV, Kolliod. zh. 3a: 592, 1971
4. L. A. LEPILKINA and P. I. ZUBOV, Vestnik Akad. Nauk SSSR, No 3, 49, 1962 5. P. I. ZUBOV, M. R. KISELEV and L. A. SUKHAREVA, Dokl. Akad. Nauk SSSR 176: 336, 1967 6. P. I. ZUBOV, L. A. SUKHAREVA, N. I. SERAYA and V. A. VORONKOV, Vysokomol. soyed. A l l : 486, 1969 (Translated in Polymer Sei. U.S.S.R. 11: 3, 547, 1969) 7. L. BELLAMY, Infrakrasnye spektry slozhnykh molekul (The Infrared Spectra of Complex Molecules). p. 33, Izd. inostr, lit., 1963 8. A. CROSS, Vvedenie v prakticheskuyu infrakrasnuyu spektroskopiyu (Introduction to Practical Infrared Spectroscopy). p. 86, Izd. inostr, lit., 1961 9. L. A. SUKtLkREVA, S. S. IVANOVA and P. I. ZUBOV, Kolloid. zh. 35: 69, 1973
THE VISCOSITY OF POLYPROPYLENE GLYCOL OLIGOMERS AS A FUNCTION OF TEMPERATURE AND MOLECULAR WEIGHT* O, A. OL'KHOVIKOV, V. IV[. GOLUBEV a n d G. A. GLADKOVSKII All-Union Synthetic Resins Research Institute (Received 9 March 1972) The temperature dependence of the viscosity of linear polypropylene glycols (PPG) of various mol.wt, was studied in the range from -- 56 to + 56°C, amongst them that of a sample in which the hydroxyl end groups had been substituted by methyl groups. The temperature--viscosity functions of all the samples were found to be described by the Williams-Landell-Ferri empirical formula. The type of dependence in this formula of the parameters on the mol.wt, and the hydroxyl group content of the PPG was well explained by the theories dealing with the relaxation processes as a consideration of the free volume.
THE v i s c o s i t y of p o l y - e t h e r s has a considerable effect on t h e process t e c h n o l o g y d u r i n g t h e m a n u f a c t u r e of p o l y u r e t h a n e s . F o r e x a m p l e , t h e s t a b i l i t y o f f o a m p r o d u c i n g s y s t e m s d u r i n g p o l y u r e t h a n e f o a m p r o d u c t i o n s t r o n g l y d e p e n d s on t h e v i s c o s i t y of t h e p o l y e t h e r as a n original c o m p o n e n t of t h e s y s t e m [1]. T h e m a n u f a c t u r e o f such c o m p o s i t i o n s b y m i x i n g also s t r o n g l y d e p e n d s on this f a c t o r [2]. T h e oligo-ethers w i t h m o l e c u l a r weights (mol.wt.) of several h u n d r e d s or t h o u s a n d s are i n t e r m e d i a t e in p o s i t i o n b e t w e e n low- a n d high mol.wt, s u b s t a n c e s . T h e y are t h u s s u i t a b l e m o d e l c o m p o u n d s for rheological p r o p e r t y studies of p o l y m e r s a t r e l a t i v e l y low mol.wt. T h e s t u d y o f p o l y p r o p y l e n e glycol ( P P G ) is t h u s of c o n siderable i n t e r e s t in this respect. This simple oligoether is a n o n - c r y s t a l l i z i n g * Vysokomol. soyod. A15: No. ll, 2512-2516, 1973.