- Email: [email protected]
The mechanism of surface graft formation during the radiation-induced graft copolymerization
2290
V. YA. T~an~ov eta/.
6. A. P. RUDAKOV and N. A. SEMENOV, Mekhanika polimerov, No. 3, 155, 1965 7. A. P. RUDAKOV, Dissertation, 1969 8. N. A. ADR0VA, M. I. BESSONOV, L. A. LAIUS and A. P. RUDAKOV, Poliimidy-novyi klass termostoikikh polimerov (The Polyimides--a ~ew Type of Heat-resistant Polymers). Izd. "Nauka", 1968 9. R. ][gEl)A, J. Polymer Sci. B4: 353, 1966 10. G. A. BERMER and D. E. KLINE, J. Appl. Polymer Sci. 12: 593, 1968 11. E. BUTTA, S. De PETRIS and M. PACQUONI, J. Appl. Polymer Sci. 18: 1073, 1969 12. T. I. BORISOVA, M. I. BESSONOV and A. P. RUDAKOV, Sb.: Sintez, struktura i svoistva polimerov (In: The Synthesis, Structure and Properties of Polymers). p. 94, Izd. "Nauka", 1970
THE MECHANISM OF SURFACE GRAFT FORMATION DURING THE RADIATION-INDUCED GRAFT COPOLYMERIZATION* V. YA. KABAI~OV, N. i%[.KAZIMIROVA a n d A. YE. CHALYKH Physical Chemistry Institute, U.S.S.R. Academy of Sciences (Received 8 February 1971)
A KIVOWLEDGE of the macro- a n d micro-structure of t h e surface l a y e r of t h e graft is v e r y i m p o r t a n t for the d e v e l o p m e n t of p o l y m e r modification b y radiation. Earlier work showed [1, 2] t h a t t h e conditions for r a d i a t i o n g r a f t copolymerization and t h e t y p e of surface of t h e original p o l y m e r will affect t h e s t r u c t u r e and t o p o g r a p h y of t h e grafted layer. N u m e r o u s reports, e.g. [3, 4], p r o d u c e d information only a b o u t t h e position o f the grafts in the copolymer. We were interested in t h e s t u d y of t h e m e c h a n i s m of surface grafting as a whole, i.e. f r o m t h e early stages to relatively large grafting percentages. I t was o f considerable practical interest to s t u d y t h e t o p o g r a p h y of t h e graft surface, which determines t h e surface properties of the p o l y m e r (adhesion, p i g m e n t a t i o n capacity, etc.). These studies were m a d e on s y s t e m p o l y e t h y l e n e - p o l y g l y c i d y l methacrylate (PE-PGMA). EXPERIMENTAL
The PE-PGMA graft eopolymers were produced by direct or prior irradiation, as previously described [1, 5I. High-pressure PE films 350/~ thick were used; the oriented PE samples were produced by first subjecting the filrn~ to a 4-5-fold mono-axial elongation at room temperature. Electron- and optical microscopy were employed on carbon replicas of the film surfaces; the instruments were UEMV-100A and MIN-8 respectively. The photographs were taken by * Vysokomol. soyed. AI4: No. 9, 2042-2047, 1972.
Mechanism of surface graft formation
22§i ~
transmitted light. The transverse sections of the films were 30/~ thick. The struoture present in the PE samples was made visible by etching with ozone [6], which quickly showed up the presence of a heterogeneous surface. The topography of the graft surface was studied by profilography by means of a highly sensitive profilograph-profilometer. RESULTS
The electron-microscopic studies of the early stages of grafting (1-3°/o~ showed the PGMA graft to consist of 0.05-0.1/~ diameter globules (Fig. 1). The etching of the samples with ozone led to the conclusion t h a t the observed globules represent the truly grafted phase. As the etching of PE was much faster t h a n t h a t of PGMA, the most stable structures (the globules) can be regarded a s grafted PGMA. The formation of globules was also detected when pure monomer or its solutions in polar and non-polar solvents (benzene, acetone) were used. The globular dimensions and the number of globules per unit surface area. increased, as the percentage of grafting increased. A 1 °/o grafting from a glyeidyl methacrylate (GMA) solution in acetone gave globule diameters of 0.05/~, while 14°/o showed it to be 2.0 p; the average distance between globules was 2.0 and 1.4 respectively. Electron microscopy showed the globular dimensions to increase a s the amount of grafted polymer increased, after which the globules coalesced and gave rise to the PGMA graft on the edges of the macromolecular structures of PE. The surface in later stages of graft copolymerization was convoluted, even at very large grafting percentages (about 160~/o). From approximately the stage of coalescence of the globules (10-15~/o grafting), one could see the effect of the solvent type on the nature of the grafted surface layer. Polar solvents for the monomer, in which P E hardly swelled, produced an accumulation of PGMA at the film surface, which did not happen with non-polar solvents it the same grafting %. The presence of surface structures was evident at small amounts of graft eopolymer when using the GMA solution irL polar solvents (acetone, methanol) for grafting (Fig. 1). The earlier use of infrared spectroscopy in polarized light [2] had shown t h e orienting effect of the support on the macromolecules of the PGMA graft. This effect was evaluated in the shape of 1--R, in which R--degree of dichroism in t h e infrared spectrum of the line belonging to the C-----O group oscillations. The plot. of the degree of orientation against the amount of graft copolymer became less s t e e p as soon as the grafting efficiency had reached 20-30°/o. We wanted to find out the nature of the orienting effect by the support during grafting from the liquid phase. We found an inverse linear correlation to exist between the degree of orientation and the relative thickness of the grafted layer during the study of transversal cross section of the film graft (Fig. 2), i.e. A1/l, in which A/--thickness of the grafted l a y e r , / - - t o t a l thickness of grafted film. The curve of the relative thickness of graft as a function of the grafting percentage was found to be subject to considerable slowing down from 30-40 /~ thickness onwards; this was equivalent to 20-30~/o grafting. The explanation for
V. YA.
KABANOV
~t a / .
I!i!i:iJii:ilili!! !ili!!!iii!il
?' CU;
., ..........
........ ....... . . . . . . .
,~;
j~!,~,'~:
;~":~
:;!~/~:~,~.:
/ , ,,:;7"
~i-~¢~*,~:'
:'
'
~;'2:
~'~ '~:.... ~#:
, . ,;
"
" 'i~
'; :
,'~'
" 4"
: ."
:;:~ :~ii >':~i,i'.:;¢~ '
~::'
, '?'~:,:~>?
PIG. 1. Photomicrography of the PE-PGMA graft copolymer surfaces: a--grafting from an ~etone solution of GMA (3~), b--grafting from a methanol solution of GMA (5~), c--surface structure of an oriented copolymer after etching with oxygen (7 ~), d--optical photo° microgram of the surface of an oriented grafting film (36~). The bracketted figure is that of the grafting efficiency. t h i s is t h a t the copolymerization is limited at this stage by the monomer diffusion into the film. The kinetic curve also led to the conclusion (Fig. 3) of diffusion affecting the progress of grafting. The much reduced degree of orientation of the g r a f t e d chains as the % grafting increased, and the corresponding increase of relative grafted layer thickness could explain the relatively large diffusion velocity o f t h e monomer into the film. The conclusions drawn from the findings are t h a t the orienting effect of the
2~9~
Mechanism of surface graft formation
support "will depend on the thickness of the grafted layer in the studied system and can be explained by grafting taking place in the inter-fibrillar ducts of P E . The orienting effect of the support will therefore apply to grafting not only from the gas phase, but also from the liquid phase of the monomer. 1-R 0,?0020
-
O.lO
0
I
I
I
lO
20
30
dl
~ lO0 ~
2
~ 6o ~-
.,('L-.-.-'-
20 L 0
o
4
12
20
l 23
Tl'me , hr
"-E' % Fio. 2
Fro. 3
~ G . 2. The degree of orientation 1 - - R as a function of the relative thickness of the grafted layer zll/l. FIe. 3. The grafting Yo as a function of irradiation time: 1 - graft of pure GMA, 2 - graft from an acetone solution of GMA on oriented samples, 3 - - a s 2 but grafted on a non-oriente~ sample.
We investigated the orienting effect of the support on the macromolecular structure of the grafted layer. The originally oriented sample had an orientation of supermolecular order, which was produced during the stretching of the film. As Fig. lc shows, the grafted polymer was positioned on the borders of the oriented structures; this was also the case at fairly high grafting percentages (50-60%). The start of the graft copolymerization on oriented and non-oriented samples was characterized by the formation of PGMA globules (Fig. 1). Electron-micro/
I20 80 _
/8
1
-I8
~
2
~6 Z
L
/0
JO
dO 7O Cpaf//ag ,
Fro. 4
~0
I0
80 ~0 70 Gpaftz'ng, %
~0
Fio. 5
F I e . 4. The degree of surface roughness of." 1--non-oriented, 2--oriented copolymers. F I e . 5. The amplitude and the number of peaks per 1 m m profile length of surface on t h e
profilogram: 1, 3--non-oriented, 2, 4--oriented copolymers, 5--copolymers produced after preliminary irradiation.
V. YA. K_~ANOVeta/.
~204
seopy showed these not to orient themselves on the edges of the macromoleealax structure when polar or non-polar, solvents were used; the distance between globales greatly differed in the direction of and at right angles to the orientation axis. That shown in Fig. i between globules in the direction o£ orientation was 1.2 ~, at right angles to it 0.8/l. The globules became larger in later stages of grafting, but the order of orientation of the original polymer was retained in the graft copolymer layer (Fig. 1). !
~/Oz7 2
~
z7
I
/0
I
z~7
I
]
,7# 4O ,1l -?-,%
Fro. 6. The degree of surface roughness of oriented and non-oriented (2) copolymers as a function of the relative thickness of the grafted layer. The study of the grafted layer surface of system GMA-polar solvent at 20-30% grafting [1] had shown the surface roughness to increase. The results of profilography on grafts from a GMA solution in acetone showed the surface roughness to increase in this stage of copolymerization (Fig. 4); it was due to an acceleration of growth in peak amplitude on the profilogram, but also of the numbers per unit length of the surface profile (Fig. 5). The degree of roughness is here the product o f average peak height and average number of peaks per 1 mm profile surface. The peaks were found to broaden in subsequent stages of the copolymerization; this resulted in a retaxdation of the increase of the degree of roughness. The changes of the latter, seen by optical microscopy, as a function of the grafted layer thickness, consisted e r a decrease above 30% grafting, which was equivalent to a 30-40/~ depth of grafted layer (Fig. 6). This change of surface roughness was due to the slower diffusion of monomer into the film, as shown in Fig. 3, and resulted in a slower rate of growth in the depth of the grafted layer. On the basis of our results one can say that the slower growth in thickness o f the graft in the bulk of the film changed the nature of the effect of the support on the topography of the grafted layer surface. The degree of surface roughness increased more slowly when the number of grafting centres inside the sample betomes smaller. The use of an acetone solution of GMA for grafting on an oriented P E film yielded a smaller surface roughness, measured in the direction of the axis of orientation and normal to it~ than with non-oriented samples in the same range of grafting percentages (2-90~/o) (Fig. 4). The reason appears to be the difference in the topography of such samples. The degree of surface roughness as a function
Mochanism of surfaoo graft formation
2295
of grafting percentage increased more uniformly in the case of non-oriented samples owing to diffusion being more difficult for the monomer in the case of oriented PE (Fig. 3). The peak numbers and peak amplitudes continued to grow steadily on the profilogram above a 30% grafting, but the rate was slower (Fig. 5). One can also see in Fig. 6 that the rate of growth of the degree of roughness as a function of thickness of grafted layer became smaller from 20-30% grafting onwards. Where preliminary irradiation was used, the amount of surface graft was small and the surface topography of the grafted layer hardly differed from that of the ungrafted sample within the studied grafting percentages; this is shown in Fig. 5. A clarification of the effects of various functional groups introduced into the grafted PGMA on the topography and macromolecular structure of the copolymer surface layer was sought in experimental polymer-analogue conversions of the grafted samples by treatment with nitric, phosphoric acids and mono-ethanolamine. The results of these experiments showed that new functional groups (--NO3,--H2P04,--NHC2H4OH) had no effect on the dimension and number of the globules which formed in the initial stages of grafting, nor on the topography of the copolymer surface, regardless of whether oriented or non-oriented samples were used. CONCLUSIONS
(1) The initial stage of grafting polyglycidyl methacrylate (PGMA) on polyethylene (PE) was found to take place in the form of PGMA globules which became larger and then coalesced as the grafting percentage increased; this happened independently of the type of solvent used for the monomer. (2) The effect of the monomer solvent on the grafted layer formation was evident during the stage in which the globules coalesced. The amount of graft copolymer at the surface was larger in the case of polar solvents than with non-polar at identical grafting percentage. (3) The oriented order of the macromolecules remained intact when grafting from the liquid monomer phase. The orienting effect of the support is explained by a grafting which takes place in the micro-ducts of the original film. (4) The degree of surface roughness on oriented and non-oriented samples was found to increase, as grafting progressed, in accordance with the thickness of the grafted layer; it depends on the monomer diffusion into the film. At larger than 20-30% grafting efficiency the rate of increase of surface roughness becomes smaller owing to the slowing down of monomer diffusion. (5) Oriented films gave a smaller degree of surface roughness than the nonoriented; it also increased more uniformly with the % grafting and this is explained by the topography differences between the original samples and their effects on diffusion rates of monomer. Translated by K . A . _AT.T~.r¢
2296
Yu. M. ]~AT.TI~'SKII¢A~al. REFERENCES
1. V. Ya. KABANOV, N. M. KAZIiKIROVA, A. A. NESTERENKO and V. I. SPITSYN,
Vysokomol. soyed. B10: 855, 1968 (Not translated is Polymer Sci. U.S.S.R.) 2. V. Ya. KABANOV, R. E. ALIEV and N. M. KAZIMIROVA, Vysokomol. soyed. BU: 834, 1969 (Not translated in Polymer Sci. U.S.S.R.) 3. K. Kh. RAZIKOV, Kh. U. USMANOV and U. A. AZIZOV, Vysokomol. soyed. 7: 1798, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 10, 1980, 1965) 4. M. L. ROLLINS, A. M. CANNIZZARO, F. A. BLOUIN and G. C. ARTHUR, J. Appl. Polymer Sci. 12: 71, 1968 5. V. Ya. KABANOV, N. M. KAZIMIROVA and V. I. SPITSYN, Vysokomol. soyed. Ag: 1758, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 8, 1983, 1967) 6. M. R. KISELEV, E. L YEVKO and V. M. LUK'YANOVICH, Zavod. labor. 32: 201, 1966
AN ELECTRON MICROSCOPE STUDY 0F CRYSTALIJ~ATION IN THIN POLYMER LAYERS* Yu. M. ~AT,TWSKH,M. B. KONSTAlVTIlVOPOL'SKAYA,N. l~I. TITOVA and V. A. KARGnV (dec.) L. Ya. Karpov Scientific Research Institute of Physical Chemistry
(Received 8 February 1971) THE behaviour of polymers situated at t he b o u n d a r y of two phases is known to differ from t h a t in t he bulk [1, 2]. The mobility is reduced in t he boundary layers due to interaction with the surface of the other phase and t he geometrical restriction of the number of macromolecular conformations. Earlier studies had shown polypropylene with a 60% v / v glass powder cont e n t [3] to be almost incapable of crystallization; this was regarded as evidence of a v e r y substantial restriction of movement of t he structural elements. The influence of the solid surface on the crystallization kinetics of the polymers in thin layers has been established [4]. The object of this work was to study the influence of a hard surface on structure formation in polymers. Electron-microscopic observations were made of the crystallization of polymers on solid surfaces of different chemical compositions. We assumed th e surface energy of the material in contact with t he polymer surface to affect molecular motion at the phase boundary, which would affect the crystallization characteristics. EXPERIMENTAL
We studied isotactic polypropylene (Moplen). The structures produced on fiat, solid surfaces and in systems filled with a dispersed fine powder were studied. The polymer ~lms were produced from solutions with different thermal histories be* Vysokomol. soyed. A14: No. 9, 2048-2052, 1972.
V. YA. T~an~ov eta/.
6. A. P. RUDAKOV and N. A. SEMENOV, Mekhanika polimerov, No. 3, 155, 1965 7. A. P. RUDAKOV, Dissertation, 1969 8. N. A. ADR0VA, M. I. BESSONOV, L. A. LAIUS and A. P. RUDAKOV, Poliimidy-novyi klass termostoikikh polimerov (The Polyimides--a ~ew Type of Heat-resistant Polymers). Izd. "Nauka", 1968 9. R. ][gEl)A, J. Polymer Sci. B4: 353, 1966 10. G. A. BERMER and D. E. KLINE, J. Appl. Polymer Sci. 12: 593, 1968 11. E. BUTTA, S. De PETRIS and M. PACQUONI, J. Appl. Polymer Sci. 18: 1073, 1969 12. T. I. BORISOVA, M. I. BESSONOV and A. P. RUDAKOV, Sb.: Sintez, struktura i svoistva polimerov (In: The Synthesis, Structure and Properties of Polymers). p. 94, Izd. "Nauka", 1970
THE MECHANISM OF SURFACE GRAFT FORMATION DURING THE RADIATION-INDUCED GRAFT COPOLYMERIZATION* V. YA. KABAI~OV, N. i%[.KAZIMIROVA a n d A. YE. CHALYKH Physical Chemistry Institute, U.S.S.R. Academy of Sciences (Received 8 February 1971)
A KIVOWLEDGE of the macro- a n d micro-structure of t h e surface l a y e r of t h e graft is v e r y i m p o r t a n t for the d e v e l o p m e n t of p o l y m e r modification b y radiation. Earlier work showed [1, 2] t h a t t h e conditions for r a d i a t i o n g r a f t copolymerization and t h e t y p e of surface of t h e original p o l y m e r will affect t h e s t r u c t u r e and t o p o g r a p h y of t h e grafted layer. N u m e r o u s reports, e.g. [3, 4], p r o d u c e d information only a b o u t t h e position o f the grafts in the copolymer. We were interested in t h e s t u d y of t h e m e c h a n i s m of surface grafting as a whole, i.e. f r o m t h e early stages to relatively large grafting percentages. I t was o f considerable practical interest to s t u d y t h e t o p o g r a p h y of t h e graft surface, which determines t h e surface properties of the p o l y m e r (adhesion, p i g m e n t a t i o n capacity, etc.). These studies were m a d e on s y s t e m p o l y e t h y l e n e - p o l y g l y c i d y l methacrylate (PE-PGMA). EXPERIMENTAL
The PE-PGMA graft eopolymers were produced by direct or prior irradiation, as previously described [1, 5I. High-pressure PE films 350/~ thick were used; the oriented PE samples were produced by first subjecting the filrn~ to a 4-5-fold mono-axial elongation at room temperature. Electron- and optical microscopy were employed on carbon replicas of the film surfaces; the instruments were UEMV-100A and MIN-8 respectively. The photographs were taken by * Vysokomol. soyed. AI4: No. 9, 2042-2047, 1972.
Mechanism of surface graft formation
22§i ~
transmitted light. The transverse sections of the films were 30/~ thick. The struoture present in the PE samples was made visible by etching with ozone [6], which quickly showed up the presence of a heterogeneous surface. The topography of the graft surface was studied by profilography by means of a highly sensitive profilograph-profilometer. RESULTS
The electron-microscopic studies of the early stages of grafting (1-3°/o~ showed the PGMA graft to consist of 0.05-0.1/~ diameter globules (Fig. 1). The etching of the samples with ozone led to the conclusion t h a t the observed globules represent the truly grafted phase. As the etching of PE was much faster t h a n t h a t of PGMA, the most stable structures (the globules) can be regarded a s grafted PGMA. The formation of globules was also detected when pure monomer or its solutions in polar and non-polar solvents (benzene, acetone) were used. The globular dimensions and the number of globules per unit surface area. increased, as the percentage of grafting increased. A 1 °/o grafting from a glyeidyl methacrylate (GMA) solution in acetone gave globule diameters of 0.05/~, while 14°/o showed it to be 2.0 p; the average distance between globules was 2.0 and 1.4 respectively. Electron microscopy showed the globular dimensions to increase a s the amount of grafted polymer increased, after which the globules coalesced and gave rise to the PGMA graft on the edges of the macromolecular structures of PE. The surface in later stages of graft copolymerization was convoluted, even at very large grafting percentages (about 160~/o). From approximately the stage of coalescence of the globules (10-15~/o grafting), one could see the effect of the solvent type on the nature of the grafted surface layer. Polar solvents for the monomer, in which P E hardly swelled, produced an accumulation of PGMA at the film surface, which did not happen with non-polar solvents it the same grafting %. The presence of surface structures was evident at small amounts of graft eopolymer when using the GMA solution irL polar solvents (acetone, methanol) for grafting (Fig. 1). The earlier use of infrared spectroscopy in polarized light [2] had shown t h e orienting effect of the support on the macromolecules of the PGMA graft. This effect was evaluated in the shape of 1--R, in which R--degree of dichroism in t h e infrared spectrum of the line belonging to the C-----O group oscillations. The plot. of the degree of orientation against the amount of graft copolymer became less s t e e p as soon as the grafting efficiency had reached 20-30°/o. We wanted to find out the nature of the orienting effect by the support during grafting from the liquid phase. We found an inverse linear correlation to exist between the degree of orientation and the relative thickness of the grafted layer during the study of transversal cross section of the film graft (Fig. 2), i.e. A1/l, in which A/--thickness of the grafted l a y e r , / - - t o t a l thickness of grafted film. The curve of the relative thickness of graft as a function of the grafting percentage was found to be subject to considerable slowing down from 30-40 /~ thickness onwards; this was equivalent to 20-30~/o grafting. The explanation for
V. YA.
KABANOV
~t a / .
I!i!i:iJii:ilili!! !ili!!!iii!il
?' CU;
., ..........
........ ....... . . . . . . .
,~;
j~!,~,'~:
;~":~
:;!~/~:~,~.:
/ , ,,:;7"
~i-~¢~*,~:'
:'
'
~;'2:
~'~ '~:.... ~#:
, . ,;
"
" 'i~
'; :
,'~'
" 4"
: ."
:;:~ :~ii >':~i,i'.:;¢~ '
~::'
, '?'~:,:~>?
PIG. 1. Photomicrography of the PE-PGMA graft copolymer surfaces: a--grafting from an ~etone solution of GMA (3~), b--grafting from a methanol solution of GMA (5~), c--surface structure of an oriented copolymer after etching with oxygen (7 ~), d--optical photo° microgram of the surface of an oriented grafting film (36~). The bracketted figure is that of the grafting efficiency. t h i s is t h a t the copolymerization is limited at this stage by the monomer diffusion into the film. The kinetic curve also led to the conclusion (Fig. 3) of diffusion affecting the progress of grafting. The much reduced degree of orientation of the g r a f t e d chains as the % grafting increased, and the corresponding increase of relative grafted layer thickness could explain the relatively large diffusion velocity o f t h e monomer into the film. The conclusions drawn from the findings are t h a t the orienting effect of the
2~9~
Mechanism of surface graft formation
support "will depend on the thickness of the grafted layer in the studied system and can be explained by grafting taking place in the inter-fibrillar ducts of P E . The orienting effect of the support will therefore apply to grafting not only from the gas phase, but also from the liquid phase of the monomer. 1-R 0,?0020
-
O.lO
0
I
I
I
lO
20
30
dl
~ lO0 ~
2
~ 6o ~-
.,('L-.-.-'-
20 L 0
o
4
12
20
l 23
Tl'me , hr
"-E' % Fio. 2
Fro. 3
~ G . 2. The degree of orientation 1 - - R as a function of the relative thickness of the grafted layer zll/l. FIe. 3. The grafting Yo as a function of irradiation time: 1 - graft of pure GMA, 2 - graft from an acetone solution of GMA on oriented samples, 3 - - a s 2 but grafted on a non-oriente~ sample.
We investigated the orienting effect of the support on the macromolecular structure of the grafted layer. The originally oriented sample had an orientation of supermolecular order, which was produced during the stretching of the film. As Fig. lc shows, the grafted polymer was positioned on the borders of the oriented structures; this was also the case at fairly high grafting percentages (50-60%). The start of the graft copolymerization on oriented and non-oriented samples was characterized by the formation of PGMA globules (Fig. 1). Electron-micro/
I20 80 _
/8
1
-I8
~
2
~6 Z
L
/0
JO
dO 7O Cpaf//ag ,
Fro. 4
~0
I0
80 ~0 70 Gpaftz'ng, %
~0
Fio. 5
F I e . 4. The degree of surface roughness of." 1--non-oriented, 2--oriented copolymers. F I e . 5. The amplitude and the number of peaks per 1 m m profile length of surface on t h e
profilogram: 1, 3--non-oriented, 2, 4--oriented copolymers, 5--copolymers produced after preliminary irradiation.
V. YA. K_~ANOVeta/.
~204
seopy showed these not to orient themselves on the edges of the macromoleealax structure when polar or non-polar, solvents were used; the distance between globales greatly differed in the direction of and at right angles to the orientation axis. That shown in Fig. i between globules in the direction o£ orientation was 1.2 ~, at right angles to it 0.8/l. The globules became larger in later stages of grafting, but the order of orientation of the original polymer was retained in the graft copolymer layer (Fig. 1). !
~/Oz7 2
~
z7
I
/0
I
z~7
I
]
,7# 4O ,1l -?-,%
Fro. 6. The degree of surface roughness of oriented and non-oriented (2) copolymers as a function of the relative thickness of the grafted layer. The study of the grafted layer surface of system GMA-polar solvent at 20-30% grafting [1] had shown the surface roughness to increase. The results of profilography on grafts from a GMA solution in acetone showed the surface roughness to increase in this stage of copolymerization (Fig. 4); it was due to an acceleration of growth in peak amplitude on the profilogram, but also of the numbers per unit length of the surface profile (Fig. 5). The degree of roughness is here the product o f average peak height and average number of peaks per 1 mm profile surface. The peaks were found to broaden in subsequent stages of the copolymerization; this resulted in a retaxdation of the increase of the degree of roughness. The changes of the latter, seen by optical microscopy, as a function of the grafted layer thickness, consisted e r a decrease above 30% grafting, which was equivalent to a 30-40/~ depth of grafted layer (Fig. 6). This change of surface roughness was due to the slower diffusion of monomer into the film, as shown in Fig. 3, and resulted in a slower rate of growth in the depth of the grafted layer. On the basis of our results one can say that the slower growth in thickness o f the graft in the bulk of the film changed the nature of the effect of the support on the topography of the grafted layer surface. The degree of surface roughness increased more slowly when the number of grafting centres inside the sample betomes smaller. The use of an acetone solution of GMA for grafting on an oriented P E film yielded a smaller surface roughness, measured in the direction of the axis of orientation and normal to it~ than with non-oriented samples in the same range of grafting percentages (2-90~/o) (Fig. 4). The reason appears to be the difference in the topography of such samples. The degree of surface roughness as a function
Mochanism of surfaoo graft formation
2295
of grafting percentage increased more uniformly in the case of non-oriented samples owing to diffusion being more difficult for the monomer in the case of oriented PE (Fig. 3). The peak numbers and peak amplitudes continued to grow steadily on the profilogram above a 30% grafting, but the rate was slower (Fig. 5). One can also see in Fig. 6 that the rate of growth of the degree of roughness as a function of thickness of grafted layer became smaller from 20-30% grafting onwards. Where preliminary irradiation was used, the amount of surface graft was small and the surface topography of the grafted layer hardly differed from that of the ungrafted sample within the studied grafting percentages; this is shown in Fig. 5. A clarification of the effects of various functional groups introduced into the grafted PGMA on the topography and macromolecular structure of the copolymer surface layer was sought in experimental polymer-analogue conversions of the grafted samples by treatment with nitric, phosphoric acids and mono-ethanolamine. The results of these experiments showed that new functional groups (--NO3,--H2P04,--NHC2H4OH) had no effect on the dimension and number of the globules which formed in the initial stages of grafting, nor on the topography of the copolymer surface, regardless of whether oriented or non-oriented samples were used. CONCLUSIONS
(1) The initial stage of grafting polyglycidyl methacrylate (PGMA) on polyethylene (PE) was found to take place in the form of PGMA globules which became larger and then coalesced as the grafting percentage increased; this happened independently of the type of solvent used for the monomer. (2) The effect of the monomer solvent on the grafted layer formation was evident during the stage in which the globules coalesced. The amount of graft copolymer at the surface was larger in the case of polar solvents than with non-polar at identical grafting percentage. (3) The oriented order of the macromolecules remained intact when grafting from the liquid monomer phase. The orienting effect of the support is explained by a grafting which takes place in the micro-ducts of the original film. (4) The degree of surface roughness on oriented and non-oriented samples was found to increase, as grafting progressed, in accordance with the thickness of the grafted layer; it depends on the monomer diffusion into the film. At larger than 20-30% grafting efficiency the rate of increase of surface roughness becomes smaller owing to the slowing down of monomer diffusion. (5) Oriented films gave a smaller degree of surface roughness than the nonoriented; it also increased more uniformly with the % grafting and this is explained by the topography differences between the original samples and their effects on diffusion rates of monomer. Translated by K . A . _AT.T~.r¢
2296
Yu. M. ]~AT.TI~'SKII¢A~al. REFERENCES
1. V. Ya. KABANOV, N. M. KAZIiKIROVA, A. A. NESTERENKO and V. I. SPITSYN,
Vysokomol. soyed. B10: 855, 1968 (Not translated is Polymer Sci. U.S.S.R.) 2. V. Ya. KABANOV, R. E. ALIEV and N. M. KAZIMIROVA, Vysokomol. soyed. BU: 834, 1969 (Not translated in Polymer Sci. U.S.S.R.) 3. K. Kh. RAZIKOV, Kh. U. USMANOV and U. A. AZIZOV, Vysokomol. soyed. 7: 1798, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 10, 1980, 1965) 4. M. L. ROLLINS, A. M. CANNIZZARO, F. A. BLOUIN and G. C. ARTHUR, J. Appl. Polymer Sci. 12: 71, 1968 5. V. Ya. KABANOV, N. M. KAZIMIROVA and V. I. SPITSYN, Vysokomol. soyed. Ag: 1758, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 8, 1983, 1967) 6. M. R. KISELEV, E. L YEVKO and V. M. LUK'YANOVICH, Zavod. labor. 32: 201, 1966
AN ELECTRON MICROSCOPE STUDY 0F CRYSTALIJ~ATION IN THIN POLYMER LAYERS* Yu. M. ~AT,TWSKH,M. B. KONSTAlVTIlVOPOL'SKAYA,N. l~I. TITOVA and V. A. KARGnV (dec.) L. Ya. Karpov Scientific Research Institute of Physical Chemistry
(Received 8 February 1971) THE behaviour of polymers situated at t he b o u n d a r y of two phases is known to differ from t h a t in t he bulk [1, 2]. The mobility is reduced in t he boundary layers due to interaction with the surface of the other phase and t he geometrical restriction of the number of macromolecular conformations. Earlier studies had shown polypropylene with a 60% v / v glass powder cont e n t [3] to be almost incapable of crystallization; this was regarded as evidence of a v e r y substantial restriction of movement of t he structural elements. The influence of the solid surface on the crystallization kinetics of the polymers in thin layers has been established [4]. The object of this work was to study the influence of a hard surface on structure formation in polymers. Electron-microscopic observations were made of the crystallization of polymers on solid surfaces of different chemical compositions. We assumed th e surface energy of the material in contact with t he polymer surface to affect molecular motion at the phase boundary, which would affect the crystallization characteristics. EXPERIMENTAL
We studied isotactic polypropylene (Moplen). The structures produced on fiat, solid surfaces and in systems filled with a dispersed fine powder were studied. The polymer ~lms were produced from solutions with different thermal histories be* Vysokomol. soyed. A14: No. 9, 2048-2052, 1972.