18
Downloaded by MONASH UNIV on December 8, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch018
Three-Stage Latex Interpenetrating Polymer Networks Zhang Liucheng, Li Xiucuo, and Liu Tianchang Department of Chemical Engineering, Hebei Institute of Technology, Tianjin, People's Republic of China 300130
Three-stage latex interpenetrating polymer networks (LIPNs) have been reported in many patents, but reported investigations on the effect of particle diameter, morphology, and dynamic mechanical properties have been limited in the literature. We have prepared a poly(butyl acrylate)-polystyrene-poly(methyl methacrylate) LIPN by three-stage emulsion polymerization. The morphology of this system was studied by transmission electron microscopy using RuO4 staining. The particle diameters and their distribution, as well as the dynamic mechanical properties of the material, were determined, and the influence of monomer feeding rate and initiator and emulsifier doses on particle diameter and morphology was investigated.
LATEX INTERPENETRATING POLYMER NETWORKS
(LIPNs) are a unique type of polymer blend that is prepared by seeded emulsion polymerization (multi stage emulsion polymerization) (1, 2). The preparation involves creation of a seed latex of cross-linked polymer (polymer 1). Then a second monomer (monomer 2) together with its cross-linking agent is introduced into the reaction vessel and monomer 2 is polymerized. Because no fresh emulsifier is added during the second-stage polymerization, it is assumed that no new nucleation takes place during the monomer 2 polymerization. Hence growth occurs on the established latex particles. Transmission electron microscopy ( T E M ) and dynamic mechanical analysis ( D M A ) studies led to the proposal of an essentially core-shell model for the resulting latex particles ( 1 - 7 ) . Previous research (4-6, 8-10) has shown that the particle morphology depends on the miscibility of monomer 2 in polymer 1, the mutual compati0065-2393/94/0239-0373$06.00/0 © 1994 American Chemical Society
In Interpenetrating Polymer Networks; Klempner, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
Downloaded by MONASH UNIV on December 8, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch018
374
N I TERPENETRATING POLYMER NETWORKS
bility of polymers 1 and 2, the cross-link density of the networks, the hydrophilicity of the polymers, the addition method of the second monomer, the type and amount of initiator, and the polymerization temperature. Latex interpenetrating polymer networks based on acrylic polymers have great practical value in adhesives, foams, paints, paper coatings, textile sizings, and polymer modifications (I, 2, 7). Most of the works reported hitherto are limited to two-stage latex interpenetrating polymer networks. Recently, three-stage L I P N s based on acrylic polymers have been reported in many patents (11-15). The apparent kinetics of the polymerization process for three-stage L I P N has been studied by Liucheng et al. (16), but reported investigation on the effect of the particle diameter, morphology, and dynamic mechanical properties has been limited in the literature. W e prepared a three-stage L I P N by a three-stage emulsion polymerization of η-butyl acryl ate, styrene, and methyl methacrylate ( L I P N P B A - P S - P M M A [poly(butyl acrylate)-polystyrene-poly(methyl methacrylate)]). The particle diameters and distribution as well as the dynamic mechanical properties and morphol ogy of this material are reported herein.
Experimental Details The emulsion polymerization was carried out in a 1000-mL tetraneck bottle (2). The reaction temperature change was no more than ± 0 . 2 °C and the agitation speeds were 250 rpm. In the first stage of the three-stage emulsion polymeriza tion, deionized and deoxidized water was placed in the tetraneck bottle. Then emulsifier (sodium dodecyl sulfonate) and P-modifying agent (sodium borate) were added and dissolved while stirring thoroughly. The polymerization and cross-hnking of η-butyl acrylate (BA) with ethylene glycol dimethacrylate (EGMA) were carried out in a nitrogen atmosphere while K S 0 water solution was added. After the first-stage polymerization was completed, styrene (ST), cross-hn king agent, divinylbenzene (DVB), and initiator K S O were fed into the bottle and the second-stage polymerization was carried out. At the third stage, methyl methacrylate ( M M A ) and K S O were charged. Three-layer L I P N P B A - P S - P M M A was produced. The composition and the polymerization condi tions of the samples are tabulated in Table I. 2
2
2
2
2
2
8
s
s
Determination of Particle Diameter and Distribution. The latex parti cle diameters and distribution were determined by electron microscopy (Hitachi600) and the micrographs were analyzed with a photography-analyzing instrument (Ibasi model II). The specimens were prepared by dilution ol the L I P N and bromination for 10 min. Then the specimens were coated onto small copper grids with supporting wafers (used for observation and for taking the micrographs). The size and distribution of the latex particle diameters were obtained by analyzing the micrographs. The polydispersity index (distribution width) was denned as
_ EiV D /ElV D
c
EN D /EN D
c
p
D
n
p
w
n
p
p
In Interpenetrating Polymer Networks; Klempner, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
18.
LIUCHENG ET AL.
Three-Stage Latex IPNs
375
Table I. Polymerization Condition and Composition of the Samples Stage First
PBSN PBSN PBSN PBSM PBSM PBSN PBSN -CSS-4 -CSS-6 -CSS-8 -CSS-11 -CSS-14 -CSS-20 -CSS-22
Components Deionized water (mL) Emulsifier (g) BA (g) E G D M A (g)
400 0.7 40 2.5
(g/L water) Second ST (g) DVB (g/100 ST) Initiator K S 0 (g/L water) AWN (g) Sodium borate
Downloaded by MONASH UNIV on December 8, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch018
2
2
8
b
1.0
1.0
30 3.5
30 3.5
0.6 0
1.0 0
M M A (g) Initiator K S 0 (g/L water) AIBN (g) 2
2
C
Polymerization temperature (for all three stages) (°C)
400 0.7 40 2.5 1.0 30 0
400 0.7 40 2.5 1.0 30 0
400 0.7 40 2.5
400 0.7 40 2.5
400 0.7 40 2.5
1.0
1.0
1.0
30 4.0
30 3.5
30 3.5
0.6 0
0.6 0
0.6 0
a
0.3
(g) Third
400 0.7 40 2.5
0 1.24
0.3
55
55
0.4 55
0.6 0 0.3 55
0.3 55
0.3
0.3 55
55
8
0.55 0
0.55 0
0 0.22
0.55 0
0.55 0
0.55 0
0.55 0
70
70
70
70
70
80
60
NOTE: Dropwise feeding mode. The residual concentration of K S 0 from the first-stage reaction is 0.85 g/L of water. Therefore, the K S O concentration in the second-stage has this additional amount of K S O . Azobis(isobutyronitrile). a
2
2
2
2
8
s
2
2
s
where, D and D are the weight-average and number-average diameters of the particles, respectively, and N is the number of latex particles with diameter within a range of central value D . w
N
p
c
Determination of Dynamic Mechanical Properties. The emulsion ob tained in the three-stage polymerization was coagulated with aluminum sulfate, filtered, washed to neutrality, and stove-dryed at 80 °C. The resultant powder was then hot-pressed at 180 °C to form wafers of 0.20-0.30-mm thickness. The dynamic mechanical properties of the wafer were determined in a viscoelastometer (Rheovibron model DDV-II-EA). The measuring frequency was 100 Hz and the heating rate was 2 °C/min. Characterization of Latex Particle Morphology. The use of osmium tetroxide as a staining agent is limited to polymers that have some level of unsaturation. Hobbs et al. (17) reported that mercuric trifluoroacetate can effectively stain poly(phenylene ether) (PPO) and styrene-butadiene-styrene (SBS) three-block copolymers, but is ineffective for polystyrene. Trent et al. (18) reported that ruthenium tetroxide ( R u 0 ) is a good staining agent for polymers that contain polystyrene (PS). 4
In Interpenetrating Polymer Networks; Klempner, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
376
INTERPENETRATING POLYMER NETWORKS
The morphology of the three-stage latex particles was observed with a transmission electron microscope (Hitachi EM-H-800) after the specimen was stained with R u 0 . For P B A - P S - P M M A latex, the dry-staining method was found to be preferable to the wet-staining method. The dry-staining method consisted of mixing powdered N a l O with powdered R u 0 * 2 H 0 . Reaction of the mixture with aqueous water vapor in air resulted in the R u 0 used for staining. Exposure for 14 h was required to achieve adequate staining. The general procedures for electron microscopy were as follows: The threestage latex was spread on clean slide glass and dried in air. Because of the high glass-transition temperature of PS and P M M A , the latex formed small flat fragments rather than a film. The fragments were dried overnight at 60 °C under vacuum and then carefully transferred into capsules. Epoxy resin (Epon 812) that contained a curing agent was poured into the capsules to embed the L I P N and the capsules were cured at 38, 45, and 65 °C for 24 h, respectively. The cured blocks were ultramicrotomed into thin sections that were mounted on copper grids, dried in air, and stained with R u 0 . Then the electron micrographs were taken. 4
2
2
Downloaded by MONASH UNIV on December 8, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch018
4
4
Results and Discussion Particle Diameters and Distribution. The influence of monomer feeding type and initiator concentration on particle diameter and distribution is tabulated in Tables I I - V and shown graphically in Figure 1. The data in Table II demonstrate that the distribution width that corresponds to the batch process is slightly wider than the distribution width of the semibatch Table II. Number- and Weight-Average Diameters and Distribution (conversion > 97%) Feeding Type
D (μηι)
D (μπι)
Batch process Drop feeding for 0.5 h
0.0670 0.0792
0.0722 0.831
n
w
D^/D, 1.078 1.048
Table III. Influence of MMA Feeding Type on LIPN PBA-PS-PMMA Particle Diameters and Distribution (conversion > 97%) Feeding Type
D (μηι)
Batch process Drop feeding for 0.5 h
0.0657 0.0839
Ό (μηι)
n
ιν
0.0848 0.0879
D./D
n
1.292 1.047
Table IV. Influence of K S G Concentration on LIPN PBA- PS Particle Diameters and Distribution 2
KSO 2
2
2.13 3.94
s
X10M
2
8
Ό (μηι) η
0.0556 0.0543
O (μηι) w
0.0625 0.0600
1.124 1.105
In Interpenetrating Polymer Networks; Klempner, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.
LIUCHENG ET AL.
18.
377
Three-Stage Latex IPNs
Table V. Influence of K S O Concentration on LIPN PBA-PS-PMMA Particle Diameters and Distribution 2
KSO 2
2
s
X 10M
D
1.85 2.70 3.90
2
N
s
O
(μπι)
w
(μπι)
D^/D 1.055 1.045 1.062
0.0892 0.0831 0.0762
0.0845 0.0795 0.0717
N
REL. FREQUENCY %
Downloaded by MONASH UNIV on December 8, 2014 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0239.ch018
20 H
10H
0.08
Ο μΓΠ η
•
b \
-
1
