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Investigation of the molecular characteristics of polyvinyl chloride obtained in presence of polyfunctional additives
2474
V.I. KOLEGOVet aL
3. L. M. VOLKOVA, Tez. dokl. V Vsesoyuz. konf. on khimii i primeneniyu kremniiorganicheskikh soyedinenii (Summaries of Reports to Fifth All Union Conference on the Chemistry and Uses of Organosilicon Compounds). p. 32, Riga, 1986 4. N. A. PLATI~ and V. P. SHIBAYEV, Grebneobraznye polimery i zhidkiye kristally (Comb-Like Polymers and Liquid Crystals). Moscow, 1980 5. K. A. ANDRIANOV, L. M. VOLKOVA, A. A. ZHDANOV and Ye. P. PARSEGOVA, Zh. obshch, khim. 50: 1088, 1980
Polymer Science U.S.S.R. Vol. 31, No. I t , pp. 2474-2479, 1989 Printed in Poland
0032-3q50/89 $ I 0.00 + .00 O 1991 Pergamon Press pie
INVESTIGATION OF THE MOLECULAR CHARACTERISTICS OF POLYVINYL CHLORIDE OBTAINED IN PRESENCE OF POLYFUNCTIONAL ADDITIVES* V. I. KOLEGOV, M. A. LYSOVA, A. YA. PESSINA, V. N. POTAPOV and V. G. MARININ (Received 14 March 1988) The influence on the MMD of polyvin~l chloride of the addition during the course of polymerization of additives of polyfunctional monomers containing allyl groups and an allyl ester of methacrylic acid has been studied. A branchid polymer forms with a wide MMD and also a crosslinked polymer. Addition of triallyl isocyanurate raises the MM of polyvinyl chloride to a greater extent than does a monomer containing two allyl groups. IN I N D U S T R Y PVC of different grades is used. The high molar mass grades are obtained at low polymerization temperatures 36-40cC, the duration of the process reaching 15-20 hr. The rate of polymerization of vinyl chloride (VC) may be increased by raising the temperature of polymerization but this reduces the MM. Increase in the M M without reducing the rate of the process may be achieved by introducing into the polymerization system pol3functional monomers [1, 2] causing branching of the PVC molecules. We studied the M M D of polyvinyl chloride obtained by the methods of block and suspension polymerization of VC with small additions of monomers contaning several double bonds: the diallyl esters of adipic (DAA), sebacic (DAS), phthalic (DAP), isophthalic (DAIP) acids, the allyl ester of methacrylic acid (AMA) and triallyl isocyanurate (TAIC). The MMD of polyvinyl chloride was determined with a GPC apparatus with a set of five styrogel columns with a porosity 104, 3 x 103, 103, l02 and 25 nm with the Waters R-403 refla:tometric (USA) and LCD-2563 ultraviolet (CSSR) detectors [3]. THF served as eluent. To destroy the asso* Vysokomol. soyed. A31: No. 11, 2260-2265, 1989.
Investigation of molecular characteristics of polyvinyl chloride
2475
ciates the PVC solutions in THF before analysis were treated thermally at 100°C for 1 hr. To prevent clogging of. the filters and entry into the columns of large crosslinked particles the PVC solutions were first centrifuged and filtered throdgh bard textured paper filters. To determine the crosslinked insoluble polymer in PVC we prepared solutions in MEK which were also heated at 100°C for 1 hr. The insoluble polymer was separated from the soluble on a laboratory centrifuge at 8000 rpm and with centrifugal acceleration 7500 g and its content determined by weighing. Block polymerization of VC with polyfunctional monomer additives was carried out at 63°C with lauroyl peroxide as initiator. On suspension polymerization we used di-2-ethylhexylperoxydicarbonate. To determine the copolymerization constants the PVC samples were obtained by block polymerization with a molar ratio VC : TAIC from 11 to 72. On copolymerization of VC with monomers containing several double bonds each of which may take part in the acts of attachment to the glowing polymer radicals, branched macromolecules formed. The monomer with two double bonds may lead to a branching node in the PVC molecule containing as many as four branches and the monomer with three double bonds to a branching node of six branches. The branching of the macromolecules may be characterized by the values of the number average b, and weight average bw branching densities [4]
b . = ~ : ' b:o
(1)
xflb:O
b.=X=lb=o x=
=xflb
1 b=O
(2)
x=
1 b=O
Here P~. ~ is the number of molecules with degree of polymerization x with b branching nodes; 2. is the number average degree of polymerization; b. is the mean number of branching nodes per molecule. Since expression (1) for b. with an identical mass includes large branched molecules and small most probably unbranched ones forming a fraction small in mass but large in the number of molecules then b. has lower values than b~,. The large branched molecules forming a fraction of the molecules large in mass make the greatest contribution to the magnitude bw. TABI.,B 1.
MOLECULAR
CHARA~TICS
OF BLOCK
PVC
OBTAINED
WITH
ADDITIONS
OF D ~ N T
1 ) O L Y F U N CTEONA.L M O N O M E R S
Monomer h
TAIC DAS DAP DAIP DA.A
M~ x 10-3 36-9 4@4
M,, x 10-3 76 194
42"8
89 89
41 4 38"8
38'3
90 93
M,/M,
b.
b,,
2.06
0 @195
0 1-872
@O25 @046
@ 108 @213 @282
4-80 2.08
2.16 2. 32 2.43, |
@058
,
[
V.I. KOLEOOVet aL
2476
Block and suspension PVC have an M M D close to the most probable Flory distribution with a polydispersity index Mw/M,,=2 [5]. Characteristic of branched polymers is a wider M W D and Mw/M,,>2. Deviation o! the magnitude Mw/M,, fiom 2 is theoretically described in the work of Stockmayer [6] for polycondensation of biand tri-functional and bi- and tetra-functional monomers and in the work of Beasley [7] for radical polymerization with trifunctional branchings. Since the M M D of linear PVC does not differ from of that linear polycondensation polymers and the polyfunctional additives to VC used in the work give branching nodes of four and six branches, to calculate the branching densities of our PVC sarnples it is better to use the Stockmayer expressions for macromolecules with tetrafunctional branching nodes Mw _ 2 _ 1 bw M. l-3b. 2 b.
(3)
whence
1
b"=3
2
b~,--- 2 b.
3(Mw/M.)'
MW
(4)
Mn
Table 1 gives the results of study of the influence of the additives of different allyl monomers (0-022 mole~o of VC) on the mean MMs and degree of branching of block PVC. It will be seen that the additives lead to appreciable rise in Mew and M,,/M~ and hence to the formation of a branched polymer. The magnitude M~ changes insignificantly. It will also be seen that the greatest branching is observed with the TAIC additive containing three allyl groups. Change in the M M D and the content of the crosslinked polymer with increase in the amount of TAIC was studied on samples of suspension PVC obtained at 63°C (Table 2). TABLE 2.
EFFECT OF
TAIC ADDITIVES DURING SUSPENSION POLYMERIZATION OF V C
CHARACTERISTICS AND CONTENT OF THE CROSSLINKI~D
TAIC, mole
ON THE MOLECULAR
POLYMER
CROSS-
M~xl0 -a Mwxl0 -s
0 ff016 0-022 0-034*
45-4 50'4 " 51.2 47-6 ,
77 127 184 205
M,,/M,
b,
b, =,,
bw
1-69 2"52 3'58 4-31
0 0-068 O"147 0-179
0 O- 128
0 O- 342 1-053 I'543
O-180 O' 361
linked PVC, % 0 0'82 2-5 5"1
TAIC was introduced in portions: half at the start of polymerization and a half after reaching 3 0 ~ conversion.
TAELE 3. MWD OF SUSPENSIONPVC AS A FUNCTIONOF THe AMA ADDITIVE AMA, mole% 0 0"035 O"069
M, x 10-3
M~,x I0 -a
I
Mw/M,
45"4 37'6 45"3
77 77 84
[ ]
1"74 2.02 1.86
I
Cr°sslinked PVC, ~o 0 15'2 25'0
1
Investigation of molecular characteristics of polyvinyl chloride
2477
As will be seen increase in the amount of T A l C governs the increase in Mw and practically does not change. We calculated the maximum number of branching nodes b,m.~ per PVC molecule starting from the assumption that all the T A l C molecules become branching nodes. The closeness of the b, and b~ max values points to the soundness of the method chosen for calculating bianching. From the b. values obtained it may be concluded that there are not more than two branched molecules per ten PVC molecules. Figure 1 gives the gel chromatograms of the samples from Table 2, Increase in the amount of crosslinking agent leads to growth in the high molar mass tail, the low molar mass tail remains unchanged and the maxima have the same retained volume and M M as PVC obtained without crosslinking agent at the same temperature.
Mw/M. and the content of the crosslinked polymer while M,
j,
45
I
I
5
3O
#5 -,Vrel.un. I 35
1
q
E
130
lttO0
I
30
I
130
V, reLun.
35
1#00
M . I0 -a
M,iO-a FIG. 1 FIo. 2 Fio. 1. Gel chromatograms of PVC samples with content of TAIC 0 (I); 0-016 (2) and 0.034 (3) mole~. FIG. 2. Gel ehromatograms of PVC sample obtained with addition of 0-045 moley, DAP (1), samples C-90 (3) and C-70 (4). Curve numbers correspond to sample numbers in Table 4. The influence of AMA on the mean MMs and the content of the crosslinked polymer on suspension polymerization of VC at 63°C is indicated in Table 3. A large amount of crosslinked polymer is observed proportional to the AMA additive. The soluble fraction does not differ in M M D from PVC obtained without crosslinking agent. The differences in the M M D of polyvinyl chloride and the amount of crosslinked polymer depending on the nature of the polyfunctional comonomer added on polymerization of VC may be explained from the mechanism oI copolymeiization of VC with the aUyl compounds used and the allylmethacrylate. The Fineman and Ross method [8] was used to detelmine the copolymerization constants of VC with TALC: rl = 24.0, r2 ~ 0. These results match the findings of review [9] on the copolymerization of VC with monoallyl compounds. Since rl >>1, in the growing PVC chains the capacity for attachment of VC is considelably higher than for the allyl compound. The ailyl radical is also prone to interact with VC. As a result in the polymer chains rare penetrations of the TAlC molecules form possibly becoming branching nodes and leading to the formation of branched molecules. Finding the copolymerization constants of VC with A M A is a more complicated problem and, therefore, we used the values
2478 TABLE 4.
V.I. KOLEOOVet aL MOLECULAR CHARACTERISTICS OF SUSPENSION
PVC
WITH KB ~ 9 0 ,
OBTAINED WITH ADDI-
TION OF D A P I
Sample I DAP, No. mole %
I
M, xlO -3
Mwxl0 -s
74' 5 77"3 105-0 55-4
263 260 201 104
O"045 I O"067* 0t 0t
•
3'53 3-37 1.90 1-88
b~
bw
0"145 0.135 0 0
1' 024 0-910 0 0
Crosslinked PVC, %
* D A P was supplied in portions: half at the start of polymerization and half after depletion of 30,% VC. t PVC of grade C-90 with Kj,=90. PVC of grade C-70 wlth Kp = 70.
ri =0, r2= 12.5 for the VC and M M A pair [10]. On copolymerization of VC with AMA vinyl chloride reacts more preferentially with AMA via the MMA group which is also prone to attach AMA. Therefore, the copolymer of VC with AMA enriched with AMA is the first to form. The high concentration of the non-reacting allyl groups in this copolymer promotes the crosslinking of the copolymer. This also may explain the large amount of crosslinked polymer presented in Table 3. After rapid depletion of AMA pure PVC forms. This assumption confirms the absence of the influence of AMA on the M W D of polyvinyl chloride (Table 3).
z/
Ae
I -
55 ]
]
5
30
- -
n
-
z/5 I
130
-
-
-'--"
[
35 ~ r e t un.
lqO0 MwlO"3
Flo. 3. Gel chromatograms of two PVC samples obtained in presence of DAP (1, 2) and TAIC (3, 4) and recorded with the aid of the refractometric (1, 3) and ultraviolet (2, 4) detectors. PVC with the Fickentscher constant Kr = 90 is obtained at 36°C. It can be synthesized with KF = 90 by introducing the allyl monomeric additives at considerably higher temperatures and duration of polymerization reduced 2-3 times. The characteristics ot the M M D ot such samples obtained at 53°C corresponding to the conditions of preparing PVC with K r = 7 0 are given in the two upper lines of Table 4. The PVC samples contain a crosslinked polymer. They greatly differ in M M D from PVC of C-90 grade although they have a similar Kr. From the chromatograms in Fig. 2 it will be seen that sample 1 differs from PVC C-90 (sample 3) and in the position of the low molar mass maximum coincides with PVC C-70 (sample 4). But unlike PVC C-70 sample 1 has a large high molar mass fraction with a small maximum for an elution volume V= 37, mostly consistin$ of a branched polymer,
Investigation of molecular characteristics of polyvinyl chlol ide
2479
An attempt was made to determine the distribution of the D A P units in the PVC molecules. Since the D A P units absorb light at ~.= 254 nm and PVC does not, one may use the LCD-2563 ultraviolet detector. Figure 3 presents the gel chromatograms of sample 1 from Table 4 obtained with refractometric and ultraviolet detectors. It will be seen that the D A P units are contained in all the PVC molecules (curve 2). But chrom a t o g r a m 2 as compared with 1 has a disproportionately large high molar mass maximum, the value of which is determined not by the high content of the D A P units but by strong light scatter of the large branched molecules. To allow foI the contribution of light scatter we recorded chromatograms 3 and 4 of the PVC s~mple (Table 2) obtained in presence of T A I C (0.022 mole ~o of VC) poorly absorbing at ~.= 254 nm as compared with D A P but promoting to a greater degree the branching of PVC. It will be seen that the ultraviolet detector registered heavy light scatter on the largest branched molecules and crosslinked microparticles (curve 4) [11]. It is not possible to allow quantitatively for the contribution of scatter in curve 2. However, the probability of folmation of branches-is higher for the molecules containing a large number of D A P units. Therefore, the largest macromolecules containing branches may also contain a large fraction of D A P units. Translated by A. Cltoz~ REFERENCES
1. P. SCHWAB, U.S. Pat. 3979366; RZhKhim, No. 8, 8C21 lrI, 1977 2. G. ARNAUTU, C. UGLEA and P. CLUCK, Roumanian Pat. 66871; RZhKhim., No. 4, 4S28II, 1980 3. V. 1. KOLEGOV, V. N. POTAPOV, T. M. SOROKINA, V. M. ARTEMICHEV and S. V. LAPIN, Plast. massy, 12, 36, 1982, 4. V. A. GRECHANOVSKH, Usp. khim. 38: 2194, 1969 5. V. I. KOLEGOV, Plast. massy, 5, 31, 1978 6. W. H. S T O C K M A Y E R , J. Chem. Phys. 12: 125, 1944 7. J. K. BEASLEY, J. Amer. Chem. Soc. 75: 6123, 1953 8. R. H. WILLEY and E. E. SAYLE, J. Polymer Sci. 42: 491, 1960 9. I. B. KOTLYAR and Ye. N. ZIL'BYERMAN, Uspekhi khimii i fiziki polimerov (Advances in Polymer Chemistry and Physics) (Ed. by Z. A. Rogovin). p. 258, Moscow, 1973 10. K. S. MINSKER, Entsikiopediya polimerov (Polymer Encyclopaedia) (Ed. by V. A. Kaxgin). p. 455, Moscow, 1972 11. V. I. KOLEGOV, V. N. POTAPOV, V. N. KOCHERYAYEV and Ye. I. VARAVINA, Vysokotool. soyed. B28: 391, 1986 (Not translated in Polymer Sci. U.S.S.R.)
V.I. KOLEGOVet aL
3. L. M. VOLKOVA, Tez. dokl. V Vsesoyuz. konf. on khimii i primeneniyu kremniiorganicheskikh soyedinenii (Summaries of Reports to Fifth All Union Conference on the Chemistry and Uses of Organosilicon Compounds). p. 32, Riga, 1986 4. N. A. PLATI~ and V. P. SHIBAYEV, Grebneobraznye polimery i zhidkiye kristally (Comb-Like Polymers and Liquid Crystals). Moscow, 1980 5. K. A. ANDRIANOV, L. M. VOLKOVA, A. A. ZHDANOV and Ye. P. PARSEGOVA, Zh. obshch, khim. 50: 1088, 1980
Polymer Science U.S.S.R. Vol. 31, No. I t , pp. 2474-2479, 1989 Printed in Poland
0032-3q50/89 $ I 0.00 + .00 O 1991 Pergamon Press pie
INVESTIGATION OF THE MOLECULAR CHARACTERISTICS OF POLYVINYL CHLORIDE OBTAINED IN PRESENCE OF POLYFUNCTIONAL ADDITIVES* V. I. KOLEGOV, M. A. LYSOVA, A. YA. PESSINA, V. N. POTAPOV and V. G. MARININ (Received 14 March 1988) The influence on the MMD of polyvin~l chloride of the addition during the course of polymerization of additives of polyfunctional monomers containing allyl groups and an allyl ester of methacrylic acid has been studied. A branchid polymer forms with a wide MMD and also a crosslinked polymer. Addition of triallyl isocyanurate raises the MM of polyvinyl chloride to a greater extent than does a monomer containing two allyl groups. IN I N D U S T R Y PVC of different grades is used. The high molar mass grades are obtained at low polymerization temperatures 36-40cC, the duration of the process reaching 15-20 hr. The rate of polymerization of vinyl chloride (VC) may be increased by raising the temperature of polymerization but this reduces the MM. Increase in the M M without reducing the rate of the process may be achieved by introducing into the polymerization system pol3functional monomers [1, 2] causing branching of the PVC molecules. We studied the M M D of polyvinyl chloride obtained by the methods of block and suspension polymerization of VC with small additions of monomers contaning several double bonds: the diallyl esters of adipic (DAA), sebacic (DAS), phthalic (DAP), isophthalic (DAIP) acids, the allyl ester of methacrylic acid (AMA) and triallyl isocyanurate (TAIC). The MMD of polyvinyl chloride was determined with a GPC apparatus with a set of five styrogel columns with a porosity 104, 3 x 103, 103, l02 and 25 nm with the Waters R-403 refla:tometric (USA) and LCD-2563 ultraviolet (CSSR) detectors [3]. THF served as eluent. To destroy the asso* Vysokomol. soyed. A31: No. 11, 2260-2265, 1989.
Investigation of molecular characteristics of polyvinyl chloride
2475
ciates the PVC solutions in THF before analysis were treated thermally at 100°C for 1 hr. To prevent clogging of. the filters and entry into the columns of large crosslinked particles the PVC solutions were first centrifuged and filtered throdgh bard textured paper filters. To determine the crosslinked insoluble polymer in PVC we prepared solutions in MEK which were also heated at 100°C for 1 hr. The insoluble polymer was separated from the soluble on a laboratory centrifuge at 8000 rpm and with centrifugal acceleration 7500 g and its content determined by weighing. Block polymerization of VC with polyfunctional monomer additives was carried out at 63°C with lauroyl peroxide as initiator. On suspension polymerization we used di-2-ethylhexylperoxydicarbonate. To determine the copolymerization constants the PVC samples were obtained by block polymerization with a molar ratio VC : TAIC from 11 to 72. On copolymerization of VC with monomers containing several double bonds each of which may take part in the acts of attachment to the glowing polymer radicals, branched macromolecules formed. The monomer with two double bonds may lead to a branching node in the PVC molecule containing as many as four branches and the monomer with three double bonds to a branching node of six branches. The branching of the macromolecules may be characterized by the values of the number average b, and weight average bw branching densities [4]
b . = ~ : ' b:o
(1)
xflb:O
b.=X=lb=o x=
=xflb
1 b=O
(2)
x=
1 b=O
Here P~. ~ is the number of molecules with degree of polymerization x with b branching nodes; 2. is the number average degree of polymerization; b. is the mean number of branching nodes per molecule. Since expression (1) for b. with an identical mass includes large branched molecules and small most probably unbranched ones forming a fraction small in mass but large in the number of molecules then b. has lower values than b~,. The large branched molecules forming a fraction of the molecules large in mass make the greatest contribution to the magnitude bw. TABI.,B 1.
MOLECULAR
CHARA~TICS
OF BLOCK
PVC
OBTAINED
WITH
ADDITIONS
OF D ~ N T
1 ) O L Y F U N CTEONA.L M O N O M E R S
Monomer h
TAIC DAS DAP DAIP DA.A
M~ x 10-3 36-9 4@4
M,, x 10-3 76 194
42"8
89 89
41 4 38"8
38'3
90 93
M,/M,
b.
b,,
2.06
0 @195
0 1-872
@O25 @046
@ 108 @213 @282
4-80 2.08
2.16 2. 32 2.43, |
@058
,
[
V.I. KOLEOOVet aL
2476
Block and suspension PVC have an M M D close to the most probable Flory distribution with a polydispersity index Mw/M,,=2 [5]. Characteristic of branched polymers is a wider M W D and Mw/M,,>2. Deviation o! the magnitude Mw/M,, fiom 2 is theoretically described in the work of Stockmayer [6] for polycondensation of biand tri-functional and bi- and tetra-functional monomers and in the work of Beasley [7] for radical polymerization with trifunctional branchings. Since the M M D of linear PVC does not differ from of that linear polycondensation polymers and the polyfunctional additives to VC used in the work give branching nodes of four and six branches, to calculate the branching densities of our PVC sarnples it is better to use the Stockmayer expressions for macromolecules with tetrafunctional branching nodes Mw _ 2 _ 1 bw M. l-3b. 2 b.
(3)
whence
1
b"=3
2
b~,--- 2 b.
3(Mw/M.)'
MW
(4)
Mn
Table 1 gives the results of study of the influence of the additives of different allyl monomers (0-022 mole~o of VC) on the mean MMs and degree of branching of block PVC. It will be seen that the additives lead to appreciable rise in Mew and M,,/M~ and hence to the formation of a branched polymer. The magnitude M~ changes insignificantly. It will also be seen that the greatest branching is observed with the TAIC additive containing three allyl groups. Change in the M M D and the content of the crosslinked polymer with increase in the amount of TAIC was studied on samples of suspension PVC obtained at 63°C (Table 2). TABLE 2.
EFFECT OF
TAIC ADDITIVES DURING SUSPENSION POLYMERIZATION OF V C
CHARACTERISTICS AND CONTENT OF THE CROSSLINKI~D
TAIC, mole
ON THE MOLECULAR
POLYMER
CROSS-
M~xl0 -a Mwxl0 -s
0 ff016 0-022 0-034*
45-4 50'4 " 51.2 47-6 ,
77 127 184 205
M,,/M,
b,
b, =,,
bw
1-69 2"52 3'58 4-31
0 0-068 O"147 0-179
0 O- 128
0 O- 342 1-053 I'543
O-180 O' 361
linked PVC, % 0 0'82 2-5 5"1
TAIC was introduced in portions: half at the start of polymerization and a half after reaching 3 0 ~ conversion.
TAELE 3. MWD OF SUSPENSIONPVC AS A FUNCTIONOF THe AMA ADDITIVE AMA, mole% 0 0"035 O"069
M, x 10-3
M~,x I0 -a
I
Mw/M,
45"4 37'6 45"3
77 77 84
[ ]
1"74 2.02 1.86
I
Cr°sslinked PVC, ~o 0 15'2 25'0
1
Investigation of molecular characteristics of polyvinyl chloride
2477
As will be seen increase in the amount of T A l C governs the increase in Mw and practically does not change. We calculated the maximum number of branching nodes b,m.~ per PVC molecule starting from the assumption that all the T A l C molecules become branching nodes. The closeness of the b, and b~ max values points to the soundness of the method chosen for calculating bianching. From the b. values obtained it may be concluded that there are not more than two branched molecules per ten PVC molecules. Figure 1 gives the gel chromatograms of the samples from Table 2, Increase in the amount of crosslinking agent leads to growth in the high molar mass tail, the low molar mass tail remains unchanged and the maxima have the same retained volume and M M as PVC obtained without crosslinking agent at the same temperature.
Mw/M. and the content of the crosslinked polymer while M,
j,
45
I
I
5
3O
#5 -,Vrel.un. I 35
1
q
E
130
lttO0
I
30
I
130
V, reLun.
35
1#00
M . I0 -a
M,iO-a FIG. 1 FIo. 2 Fio. 1. Gel chromatograms of PVC samples with content of TAIC 0 (I); 0-016 (2) and 0.034 (3) mole~. FIG. 2. Gel ehromatograms of PVC sample obtained with addition of 0-045 moley, DAP (1), samples C-90 (3) and C-70 (4). Curve numbers correspond to sample numbers in Table 4. The influence of AMA on the mean MMs and the content of the crosslinked polymer on suspension polymerization of VC at 63°C is indicated in Table 3. A large amount of crosslinked polymer is observed proportional to the AMA additive. The soluble fraction does not differ in M M D from PVC obtained without crosslinking agent. The differences in the M M D of polyvinyl chloride and the amount of crosslinked polymer depending on the nature of the polyfunctional comonomer added on polymerization of VC may be explained from the mechanism oI copolymeiization of VC with the aUyl compounds used and the allylmethacrylate. The Fineman and Ross method [8] was used to detelmine the copolymerization constants of VC with TALC: rl = 24.0, r2 ~ 0. These results match the findings of review [9] on the copolymerization of VC with monoallyl compounds. Since rl >>1, in the growing PVC chains the capacity for attachment of VC is considelably higher than for the allyl compound. The ailyl radical is also prone to interact with VC. As a result in the polymer chains rare penetrations of the TAlC molecules form possibly becoming branching nodes and leading to the formation of branched molecules. Finding the copolymerization constants of VC with A M A is a more complicated problem and, therefore, we used the values
2478 TABLE 4.
V.I. KOLEOOVet aL MOLECULAR CHARACTERISTICS OF SUSPENSION
PVC
WITH KB ~ 9 0 ,
OBTAINED WITH ADDI-
TION OF D A P I
Sample I DAP, No. mole %
I
M, xlO -3
Mwxl0 -s
74' 5 77"3 105-0 55-4
263 260 201 104
O"045 I O"067* 0t 0t
•
3'53 3-37 1.90 1-88
b~
bw
0"145 0.135 0 0
1' 024 0-910 0 0
Crosslinked PVC, %
* D A P was supplied in portions: half at the start of polymerization and half after depletion of 30,% VC. t PVC of grade C-90 with Kj,=90. PVC of grade C-70 wlth Kp = 70.
ri =0, r2= 12.5 for the VC and M M A pair [10]. On copolymerization of VC with AMA vinyl chloride reacts more preferentially with AMA via the MMA group which is also prone to attach AMA. Therefore, the copolymer of VC with AMA enriched with AMA is the first to form. The high concentration of the non-reacting allyl groups in this copolymer promotes the crosslinking of the copolymer. This also may explain the large amount of crosslinked polymer presented in Table 3. After rapid depletion of AMA pure PVC forms. This assumption confirms the absence of the influence of AMA on the M W D of polyvinyl chloride (Table 3).
z/
Ae
I -
55 ]
]
5
30
- -
n
-
z/5 I
130
-
-
-'--"
[
35 ~ r e t un.
lqO0 MwlO"3
Flo. 3. Gel chromatograms of two PVC samples obtained in presence of DAP (1, 2) and TAIC (3, 4) and recorded with the aid of the refractometric (1, 3) and ultraviolet (2, 4) detectors. PVC with the Fickentscher constant Kr = 90 is obtained at 36°C. It can be synthesized with KF = 90 by introducing the allyl monomeric additives at considerably higher temperatures and duration of polymerization reduced 2-3 times. The characteristics ot the M M D ot such samples obtained at 53°C corresponding to the conditions of preparing PVC with K r = 7 0 are given in the two upper lines of Table 4. The PVC samples contain a crosslinked polymer. They greatly differ in M M D from PVC of C-90 grade although they have a similar Kr. From the chromatograms in Fig. 2 it will be seen that sample 1 differs from PVC C-90 (sample 3) and in the position of the low molar mass maximum coincides with PVC C-70 (sample 4). But unlike PVC C-70 sample 1 has a large high molar mass fraction with a small maximum for an elution volume V= 37, mostly consistin$ of a branched polymer,
Investigation of molecular characteristics of polyvinyl chlol ide
2479
An attempt was made to determine the distribution of the D A P units in the PVC molecules. Since the D A P units absorb light at ~.= 254 nm and PVC does not, one may use the LCD-2563 ultraviolet detector. Figure 3 presents the gel chromatograms of sample 1 from Table 4 obtained with refractometric and ultraviolet detectors. It will be seen that the D A P units are contained in all the PVC molecules (curve 2). But chrom a t o g r a m 2 as compared with 1 has a disproportionately large high molar mass maximum, the value of which is determined not by the high content of the D A P units but by strong light scatter of the large branched molecules. To allow foI the contribution of light scatter we recorded chromatograms 3 and 4 of the PVC s~mple (Table 2) obtained in presence of T A I C (0.022 mole ~o of VC) poorly absorbing at ~.= 254 nm as compared with D A P but promoting to a greater degree the branching of PVC. It will be seen that the ultraviolet detector registered heavy light scatter on the largest branched molecules and crosslinked microparticles (curve 4) [11]. It is not possible to allow quantitatively for the contribution of scatter in curve 2. However, the probability of folmation of branches-is higher for the molecules containing a large number of D A P units. Therefore, the largest macromolecules containing branches may also contain a large fraction of D A P units. Translated by A. Cltoz~ REFERENCES
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