A Novel Associative Polymer Network based on Cyclodextrin Inclusion with Tunable Rheological Properties
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0947-A09-10
A Novel Associative Polymer Network based on Cyclodextrin Inclusion with Tunable Rheological Properties Lin Fu1, Xuhong Guo1, Stephen Lincoln2, and Robert K. Prud'homme1 1 Chemical Engineering, Princeton University, Equad, Olden Street, Princeton, NJ, 08540 2 School of Chemistry&Physics, University of Adelaide, Adelaide, SA, 5005, Australia
ABSTRACT A novel associative polymer network with tunable rheological properties is developed based on cyclodextrin-hydrophobe inclusion. The network is formed from mixtures of two polyacrylic acid (PAA) backbone polymers, one with pendant cyclodextrin groups and one with pendant hydrophobic alkyl groups. The lifetime of the cyclodextrin-hydrophobe inclusion can be well controlled by the length of alkyl chains inserted into the cyclodextrins; also, the binary nature of cyclodextrin-hydrophobe inclusion prevents hydrophobes from forming nonstoichiometric multiple associations. This system can serve as a model associative polymer network to test associative polymers theories. Dynamic rheological properties of this mixture solution can be tuned by adding free cyclodextrins or sodium dodecylsulfate (SDS) to displace polymer-to-polymer associations. Dynamic moduli change three orders of magnitude from a gel state to a sol state. The phase behavior of this mixture solution is experimentally studied by light scattering measurements and rheology. The thermodynamics of the cyclodextrin-hydrophobe interaction is independently studied using isothermal titration calorimetry and surface plasmon resonance study. INTRODUCTION Water soluble associative polymers, which are usually composed of hydrophilic backbones and hydrophobic side chains, are widely used as rheology modifiers in coatings, paints, cosmetics and pharmaceutics. It is desirable to control the properties of associative polymers in a quantitative way [1-3]. The hydrophobic groups in associative polymers tend to aggregate into clusters to avoid being exposed to the polar environment in aqueous solution. These clusters play the role of reversible junctions between different polymer chains. However, the stoichiometry (i.e. the number of hydrophobic groups in a cluster) is not fixed. It increases with polymer concentration. The qualitative features of the phase and gelation behavior of associative polymers have been understood for about two decades. However, quantitative understanding of the solution properties of associative polymers is very limited [4-6]. We designed a novel associative polymers system based on the inclusion between cyclodextrins and hydrophobes: mixtures of hydrophobically modified polyacrylic acid polymers (HMPAA) and cyclodextrin modified polyacrylic acid (CDPAA). The two distinctive differences of this system compared to the traditional associative polymers are that the lifetime or energy of the association between cyclodextrin and hydrophobe is controllable, and the binary nature of cyclodextrinhydrophobe inclusion ensures a one-to-one association. We first study the rheological behavior of HMPAA-C
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