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Downloaded by STANFORD UNIV on September 28, 2013 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1989-0223.ch021
Synthesis and Characterization of Hydrophobically Associating Polymers
1
P. L. Valint, Jr. , Jan Bock, and D. N. Schulz
2
Exxon Research and Engineering Company, Clinton Township, Route 22 East, Annandale, N J 08801 Novel polymerization techniques were used to synthesize new macromolecules that consisted of a water-soluble backbone with small amounts of hydrophobic functionality. Micellar polymerization is based on the capability of surfactant micelles to solubilize hydrophobic molecules into an aqueous medium; it was used to copolymerize acrylamide and hydrophobically substituted acrylamide monomers. A critical aspect of these polymerizations was the incorporation of the hydrophobic monomer into the water-soluble polymers. A method that used the UV chromophore of newly synthesized N-aryl substituted acrylamides was developed to quantify incorporation at the low levels of hydrophobe normally used (about 1 mol %). The synthesis of the substituted acrylamides, the UV technique, and results obtained with it are discussed.
H Y D R O P H O B I C A L L Y A S S O C L V T I N G W A T E R - S O L U B L E P O L Y M E R S have
been
investigated i n alternative approaches to aqueous viscosification b y u l t r a h i g h m o l e c u l a r w e i g h t a n d c h a i n expansion i n p o l y m e r s (1-12). A b o v e the o v e r l a p c o n c e n t r a t i o n , (i.e., the s e m i d i l u t e c o n c e n t r a t i o n regime) these p o l y m e r s associate i n t e r m o l e c u l a r l y i n solution to b u i l d h y d r o d y n a m i c size v i a the i n t r o d u c t i o n o f a s m a l l n u m b e r o f h y d r o p h o b i c groups a l o n g the b a c k b o n e 2 2
Current address: Bausch & Lomb, 1400 North Goodman Street, Rochester, NY 14692 Current address: Exxon Chemical Company, Linden, NJ 07036
0065-2393/89/0223-0399$06.00/0 © 1989 American Chemical Society
In Polymers in Aqueous Media; Glass, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.
400
POLYMERS IN A Q U E O U S M E D I A
of a water-soluble polymer. This association results in enhanced viscosification and altered response of other solution rheological properties (13, 14). Because the level of hydrophobic monomer in the feed is usually low (90% hydrophobe incorporation. 4
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Downloaded by STANFORD UNIV on September 28, 2013 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1989-0223.ch021
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The data just described were obtained on high-conversion polymer samples, which represent a composite of all polymer molecules produced from the beginning to the end of the polymerization. No information was obtained to discern the extent of compositional heterogeneity with regard to hydrophobe content. If incorporation is heterogeneous, polymer samples at various levels of conversion must be examined to gain an understanding of polymer composition. Our initial efforts to gain such information included sampling during polymerizations of N-4-butylphenylacrylamide and acrylamide at 1.5 h after initiation and comparing with the polymer obtained at complete reaction. The data presented in Table IV show that the polymer that formed at the early stages of the polymerization (i.e., about 30% conversion) had a much higher hydrophobe content than polymer produced toward the end Table III. Hydrophobe-Containing Polymer Absorptivities Absorptivity (Lg^cm- )
Hydrophobe
if
1
N-4-Alkylphenylacrylamide 0.75%C RAM 0.75%C HRAM 0.75%C HRAM 1.0%C HRAM 1.25%Ccm->) 1.93 1.35 2.80 1.79 3.29 2.37
r
2
0.9920 0.9840 0.9933 0.9903 0.9515 0.9948
Incorporation (%) 134 91 144 91 136 96.9
In Polymers in Aqueous Media; Glass, J.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.
21.
VALINT E T AL.
Hydrophobically Associating Polymers: Synthesis
409
of the reaction. Therefore, the resultant total polymer sample was heterogeneous with regard to hydrophobic monomer content. O n the basis of the solution properties of similar polymers, compositional heterogeneity was suspected; however, it was felt that the heterogeneity resulted from low initial hydrophobe incorporation followed by high incorporation toward the end of the polymerization. Originally, the hydrophobic monomer was thought to be relatively inaccessible, solubilized within the micelle. Apparently, the double bond of the hydrophobe is readily available to attack by the propagating radical moiety. More detailed study is required to fully understand incorporation Downloaded by STANFORD UNIV on September 28, 2013 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1989-0223.ch021
during micellar polymerization.
Summary A critical aspect of the micellar polymerization of hydrophobically substituted acrylamides and water-soluble monomers is the incorporation of the hydrophobic monomer into the resultant water-soluble polymers. Because of the low levels of hydrophobic monomer (
