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Polymer Blends:
Students Involved: Sathish Sukumaran, PhD Candidate.
SukumaSH@email.uc.edu
Polymer Blends/Chain Conformational Studies: Current Funding Sources, ACS PRF-G (20K), P&G Paper Division (50K/year)
PB1: Persistence Length of i-Poly(Hydroxy-Butyrate), G. Beaucage, S. Rane, S. Sukumaran, M. M. Satkowski, L. A. Schechtman, Y. Doi, Accepted Macromolecules, 1997.
PB2: Symmetric, Isotopic Blends of Poly(dimethylsiloxane), Beaucage, G.; Sukumaran, S.; Clarson, S. J.; Kent, M. S.; Schaefer, D. W., Macromolecules (1996), 29(26), 8349-8356.
PB3: Small-angle scattering from polymeric mass fractals of arbitrary mass-fractal dimension, Beaucage, G., J. Appl. Crystallogr. (1996), 29(2), 134-146.
PB4: Mechanical behavior and morphology of tactic poly(vinyl methyl ether)/polystyrene blends, Beaucage, G.; Stein, R. S., Polymer (1994), 35(13), 2716-24.
PB5: Light scattering from random coils dispersed in a solution of rodlike polymers, Jamil, T.; Russo, P. S.; Negulescu, I.; Daly, W. H.; Schaefer, D. W.; Beaucage, G., Macromolecules (1994), 27(1), 171-8.
PB6: Tacticity effects on polymer blend miscibility. 2. Rate of phase separation, Beaucage, G.; Stein, R. S., Macromolecules (1993), 26(7), 1609-16.
PB7: Tacticity effects on polymer blend miscibility. 3. Neutron scattering analysis, Beaucage, G.; Stein, R. S., Macromolecules (1993), 26(7), 1617-26.
PB8: Tacticity effects on polymer blend miscibility. 1. Flory-Huggins-Staverman analysis, Beaucage, G.; Stein, R. S.; Koningsveld, R., Macromolecules (1993), 26(7), 1603-8.
PB9: Polymer blend miscibility and phase separation kinetics analyzed using Flory-Huggins-Staverman theory, Stein, R. S.; Beaucage, G.; Berard, M. T.; Koningsveld, R., Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) (1991), 32(1), 475-6.
PB10: Tacticity effects on polymer blend miscibility, Beaucage, G.; Stein, R. S.; Hashimoto, T.; Hasegawa, H., Macromolecules (1991), 24(11), 3443-8.
PB11: Phase separated polymer alloys with reduced brittleness, G. Beaucage and R. S. Stein, US Patent 533,828 (1994).
PB12: Time-of-Flight Secondary Ion Mass Spectrometry of Deuterated Linear Poly(dimethylsiloxane) X. Zhang, J. O. Stuart, S. J. Clarson, A. Sabata, G. Beaucage, Macromolecules (1994), 35, 2716-24.
1) Initial Work, i-PVME/PS. Our work in the polymer blends area began with an industrially based project aimed at the development of phase-separated, rubber reinforced polystyrene using LSCT behavior [PB4 and 6-10]. Tactic PVME is a rubbery material with physical crosslinks based on crystallites. In phase-separated bulk samples shear banding can be introduced as a competitive energy absorption mechanism with crazing to lead to extremely tough styrenics. This work lead to a patent granted to Polysar Corporation. The work also required a detailed study of tacticity effects on miscibility in the PVME/PS system. Our approach was to look at structural changes in the PVME chains as a basis for changes in the interacting unit which are manifested in a shift in thermodynamic equilibrium. One of the most important conclusions from this work was that there is an association between the crystalline melting point and miscibility in blends where the crystalline component is too dilute to crystallize. This association explains strong dependencies of the statistical segment length on tacticity and temperature in the vicinity of the melting point.
2) Model Isotope Blends, PS/dPS, PDMS/dPDMS. In work at Sandia, these efforts were, to some extent, continued with the aim of focusing on model systems where complicating effects such as tacticity and polydispersity did not play a role. We initially focused on PS/dPS system with the aim of determining the molecular weight dependence of the interaction parameter. In addition to molecular weight effects one aim of this work was to determine the reason that data fits to the RPA equation are usually constrained to the first 10-15 data points of a data set consisting of about 250 points. This model system seemed ideal to study such features. Parallel to this work we were developing new tools to substitute for the Debye-equation for polymeric structures in inorganic mass-fractals as discussed above [ST1-3]. The conclusion from the PS studies were that a normal analysis using RPA approach and the Debye equation lead to unexplainable dependencies of the interaction parameter on molecular weight. This molecular weight dependency could be completely removed by allowing a slight deviation in the dimension of coils in this model blend from 2.0 for Gaussian chains to 2.1 for slightly collapsed chains. Additionally, the use of slightly collapsed coils allowed for fits to the entire data range [PB3].
In work at UC, in collaboration with Sandia, we have focused on the most flexible chain polymer, PDMS, in the hope of observing true Flory-Huggins behavior. Isotopic blends of PDMS were used in these studies. The results of this work support Gaussian scaling, yet a variable persistence length is still necessary to describe the behavior of Rg with temperature[PB2]. The unexpected dependence of statistical segment length on temperature can be explained using the "blob" approach of Degennes/Edwards coupled with Flory-Krigbaum approach for coil expansion. If this approach is taken a true Flory-Huggins interaction parameter can be obtained with no non-combinatorial entropy. This represents the first observation of an interaction parameter which follows the Flory-Huggins definition, i.e. the absence of a non-combinatorial entropy term. We believe that many of the deviations from Flory-Huggins behavior can be attributed to incorrect accounting of chain scaling in polymer blends.
3) Application of the Unified Equation to Chain Statistics, PHB's. We have also, been extending work on chain statistics and physical description using the unified function to describe the scaling transition from Gaussian to persistence scaling at the persistence length in biosource polyesters from P&G [PB1]. Our analysis of these systems shows an extremely large persistence length, associated with local coiling of these chains, yet a global Gaussian behavior for size-scales larger than the persistence length. These results are consistent with rheological measurements.
4) Extension of Chain Statistics Approach to Non-woven Fabrics. Current funding for our blends/chain structure work comes from PRF-G and Procter and Gamble, paper division. The PRF grant supports basic research aimed at polymer blends. The paper/diaper division of P&G is aimed at a novel application of these concepts in the parameterization of structure in non-wovens used for the production of diapers on a micron to millimeter scale. We have used a novel ultra-low angle light scattering instrument, pinhole SALS and Bonse-Hart x-ray camera to describe structure from about 1 mm to 100 in these materials. The main focus of these studies is to obtain a polymer-like description of these materials which would yield a fractal dimension, persistence length and overall radius of gyration for non-woven fibers just as we have obtained these values for real polymer chains. Several features of this work can be discussed in the open literature. In Glass Microfiber systems (very fine fiber-glass) the scaling of non-woven fibers can be easily determined using the unified function and light scattering data [paper in preparation]. It is interesting that in this non-interacting system the equivalent of a chain scaling regime leads to a fractal dimension of 5/3 which matches theoretical predictions for self-avoiding walks. The persistence length measured with scattering corresponds with the average kink-length of these fibers. Scattering results such as persistence length and overall radius of gyration can be verified on a local scale using optical and scanning electron microscopy in this system. It is quite encouraging that scattering predictions for capillary absorption isotherms for this material match data obtained directly. Inherent to the scattering data is an understanding of the morphology which underlies features in the capsorption isotherm, indicating directions for the design of non-wovens with enhanced capillary absorption. We have recently investigated orientation in these materials using an adaptation of the Hermans Orientation function and SALS data. This information is being used to describe directionality in fluid flow and absorption in non-wovens on a millimeter to micron scale.
5) Chemically Driven Spinodal Decomposition. In addition to work on scaling effects in miscible polymer blends and chain conformation and adaptations in non-woven materials, we have recently been investigating the production of spinodal-like structures in chemically driven systems [APS Meeting this last spring, ACS meeting Las Vegas, ACS Fall Meeting this Year Polymer Preprint submitted 1997, paper in preparation]. Our focus here has been in PDMS/sol-gel systems where we have extensive exposure as described in the next section. We serendipitously found that some sol-gel/polymer systems can be chemically driven to produce irreversible, micron scale spinodal-structures which can be observed with the optical microscope or using pinhole SALS. The systems go through two stages of structural development. In a matter of minutes the PDMS chains are terminally crosslinked into a gel by a hydrolysis/condensation reaction with TEOS and TEOS like siloxanes (also for silane crosslinked systems). These gelled systems then develop spinodal structure over a period of hours to days depending on the PDMS network crosslink density and the chemical reaction driving the production of silica, i.e. the nature of the crosslinker/silica precursor. We believe that the spinodal structure is composed of silica domains and partially condensed TEOS. Current efforts are aimed at optimization of this structure for improved mechanical properties. Spinodal structures have been produced from a variety of silica precursors which involve a wide variety of chemistries. We have received assistance in the synthetic chemistry in this project from Jim Mark's group at UC and Mohamad Saraf of the University of Cairo.
Copyright (c) 1998