Factors Affecting the Size of Aqueous Poly(vinylphenol-co-potassium styrenesulfonate)/Poly(ethylene oxide) Complexes Rongjuan Cong, ² Robert Pelton,* ,² Paul Russo, ‡ and Garrett Doucet ‡ Department of Chemical Engineering, McMaster University, Hamilton, Ontario L8S 4L7, Canada, and Chemistry Department, Louisiana State University, Baton Rouge, Louisiana 70803 Received June 20, 2002; Revised Manuscript Received October 25, 2002 ABSTRACT: The diffusion properties of complexes formed between poly(ethylene oxide) (PEO) and poly- (vinylphenol-co-styrenesulfonate) (PKS) in aqueous medium were investigated by diffusion ordered NMR (DOSY), fluorescence photobleaching recovery (FPR), and viscosity measurements. All three techniques showed that PEO/PKS complexes range from single PEO coils with bound PKS molecules to large complex species containing many PEO chains. For a given PKS structure, there are two important transitional PEO molecular weights. The lowest one, ∼8000 Da, corresponds to the onset of PEO/PKS complex formation. The second transitional PEO molecular weight is between 10 5 and 10 6 Da and corresponds to the onset of multi-PEO chain complex species which are important for flocculation. PKS functions as a physical cross-linking agent for PEO. If there is too little PKS, multiple PEO chains are not bound together. Similarly, high concentrations of PKS give small complexes because there are few opportunities for connecting multiple PEO chains together, since all the PEO chains are saturated with bound PKS. Introduction Mixtures of high molecular weight poly(ethylene oxide), PEO, and water soluble phenolic polymers are used as flocculants (retention aids) in the papermaking process. 1,2 The active flocculating agent is a water soluble complex formed between the nonionic PEO and anionic phenolic polymers. These are unusual floccu- lants because they depend on electrostatic attraction to the target colloids, which makes them effective in dirty systems. All the commercial phenolic polymers used in papermaking retention are poorly defined condensation polymers. In an effort to understand mechanisms, our laboratory has investigated PEO/phenolic polymer com- plexes based on well defined, linear poly(vinylphenol- co-potassium styrenesulfonate) (PKS) 3 and tyrosine rich polypeptides. 4 Since typical phenolic polymers have molecular weights between 10 4 and 10 5 Da and the PEO molecular weight is usually greater than 2 × 10 6 Da, the complexes are large. Our attempts to understand the structure and function of the PEO/phenolic polymer complexes have focused on two distance scales. Our previous papers described NMR characterization of the complexes at the level of segmental interactions-both hydrogen bonding and hydrophobic interactions between the aromatic rings and the PEO ethylene groups oc- curred. 3,5 Described in this paper are the results of a systematic investigation of the sizes of PEO/PKS com- plexes determined by viscosity, fluorescence photo- bleaching recovery (FPR), and diffusion ordered NMR spectroscopy (DOSY) measurements. The literature describes the use of dynamic light scattering (DLS) to characterize the size of both PEO and PEO/phenolic polymer species in aqueous solution. Results for simple PEO solutions show the presence of very large species which must involve multiple PEO chains. The explanations have been controversial. Polver- ari and van de Ven summarize this literature and make the case for cluster formation. 6 Others have argued the observations reflect the presence of impurities in the PEO. 7-9 This controversy emphasizes the importance of careful control of the PEO dissolution process. 10 DLS measurements of PEO/phenolic polymer com- plexes have shown two extreme behaviors. Complexes formed with relatively hydrophobic phenolic polymer shrink 11 and often show phase separation. By contrast, more hydrophilic phenolic polymers cause the PEO chain to expand. 12 It is difficult to develop general mechanisms from the existing studies because the commercial phenolic polymers employed were poorly characterized as a result of their complexity. In this work we report the first application of fluorescence photobleaching recovery (FPR) to the characterization of PEO/phenolic polymer complexes. A FPR measurement is simple in concept: 13,14 the molecule of interest is labeled by covalent attachment of a fluorescent molecule; thus, only the fluorescently tagged species is observed. Measurements begin when a bright laser flash dye erases (bleaches) the dye from regions of the sample chamber not covered with a mask. With time, unbleached molecules from neighboring masked regions diffuse into the unmasked regions, giving an increase in fluorescent emission. The rate of recovery of the fluorescence signal can be used to obtain the self-diffusion coefficient. A comparison of dynamic light scattering and FPR techniques has appeared. 15 Diffusion ordered NMR spectroscopy (DOSY) is an- other option for the measurement of PEO/phenolic polymer diffusion properties. DOSY is based on pulsed field gradient NMR that encodes the information about the translational motion into NMR data. 16 It combines the selectivity of high-resolution NMR with the hydro- dynamic information provided by pulsed field gradient NMR. Information about chemical shift is present in one dimension, and the self-diffusion coefficient, in the second dimension of DOSY spectra. The most distin- guishable feature of DOSY is the fact that NMR active impurities are detected but do not interfere with mea- * To whom correspondence should be addressed. E-mail: peltonrh@mcmaster.ca. ² McMaster University. ‡ Louisiana State University. 204 Macromolecules 2003, 36, 204-209 10.1021/ma020965y CCC: $25.00 © 2003 American Chemical Society Published on Web 12/13/2002