D. G. Peiffer

Phase behaviour and solution properties of sulphobetaine polymers

Abstract Aqueous polyelectrolytes have been extensively studied and comprehensively described in numerous books and reviews. In contrast, systematic investigations of aqueous polyzwitterions are few. This paper describes the detailed phase behaviour and solution properties of a homopolymer based upon a recently available sulphobetaine monomer, N -(3-sulphopropyl)- N -methacrylooxyethyl- N , N -dimethyl ammonium betaine (SPE). In addition, such properties are probed at the molecular level by static and dynamic light scattering, as well as laser Raman spectroscopy. Poly[ N -(3-sulphopropyl)- N -methacrylooxyethyl- N , N -dimethyl ammonium betaine], P(SPE), of 4.35 × 10 5 M w shows remarkable phase behaviour. It exhibits both an upper critical solution temperature ( UCST ) and an ‘apparent inverted’ lower critical solution temperature ( LCST ), i.e. a 1-phase region flanked by two 2-phase regions. Moreover, the UCST occurs at an order of magnitude lower polymer concentration than predicted by theory or demonstrated by experiment with conventional polymers. The aqueous solubility of (SPE) depends upon polymer molecular weight, as well as the concentration and structure of added salts. ‘Soft’ salt anions and cations are more effective solubilizers than ‘hard’ anions and cations. Furthermore, solutions of P(SPE) display ‘antipolyelectrolyte behaviour’, i.e. viscosities which increase with increasing salt concentrations. Static light scattering experiments indicate that the solvent quality for P(SPE) increases with increasing salt concentration. Dynamic light scattering measurements show that the polymer diffusion coefficients decrease and the chain dimensions increase with increasing salt concentrations. Moreover, laser Raman spectroscopy indicates that the local environment around the zwitterion functionalities is also modified by changes in salt concentration. Based upon such molecular level probes, models have been proposed to account for the P(SPE) phase behaviour and solubility. Thus, P(SPE) is depicted as a collapsed coil in water because of intra-group and intra-chain associations. The unusual phase behaviour of P(SPE) in water is rationalized in terms of a shift from intra- to interinteractions. In turn, NaCl breaks up the intra-associations and promotes polymer solubility.

Synthesis and viscometric properties of low charge density ampholytic ionomers

Abstract The addition of ionic groups onto the molecular structure of a macromolecule produces marked changes in its physical properties. A large volume of literature exists pertaining to the solution and solid phase properties of these charged species spanning a broad range of charge densities. Until recently, however, little work has been published on ionomers containing opposite chargess (i.e., polyampholytes) except with regard to highly charged species. In this study, we focus on the synthesis and solution properties in fresh and high ionic strength solutions of low charge density acrylamide-based polyampholytes not necessarily possessing an equimolar ratio of anionic and cationic units. The results show that the separation of these oppositely-charged monomer units via neutral acrylamide moieties establishes a control over physical properties not readily attainable in the highly-charged polyampholytes (generally insoluble in fresh water) or conventional polyelectrolytes. At low charge densities, typically

Reinforcement of EPDM-based ionic thermoplastic elastomer by carbon black

Abstract High abrasion furnace carbon black improves the physical properties of zinc sulfonated ethylenepropylenediene terpolymer of high (75 wt%) ethylene content. Properties studied include hardness, stress-strain characteristics, tear strength, hysteresis and abrasion resistance. Scanning electron photomicrographs of the tear fractured and abraded surfaces show changes in failure mode of the polymer on incorporation of carbon black. Results of dynamic mechanical analyses and dielectric thermal analyses show that carbon black reinforces the ionomers, presumably through weak rubber—filler interaction involving the backbone chains and strong interaction between the active sites of the filler surface and the ionic aggregates present in the ‘multiplets’ and ‘clusters’. Reprocessability studies in the Monsanto Processability Tester (MPT) show that the carbon black filled polymer can be reprocessed like a thermoplastic elastomer and there was no fall in properties even after three cycles of extrusion through the MPT.

Hydrophobically associating polymers and their interactions with rod-like micelles

Abstract Several families of anionic and cationic hydrophobically associating acrylamide-based copolymers have been synthesized. This study focuses on the characterization in aqueous environments of water-soluble copolymers in which low levels of alkyl, i.e. methylene, units are incorporated into the polymer chain structure. These hydrophobic monomers have built-in surfactant character; therefore, no non-polymerizable surfactants are required in the preparation of these copolymer materials. These hydrophobically associating copolymers are shown to possess both polyelectrolyte and hydrophobic character, especially as the ionic strength of the solution is varied. The results confirm that, even at low concentrations of hydrophobe (typically ≤ 1 mol%), interesting solution properties are observed, i.e. enhanced rheology as compared to its non-associating parent, marked time-dependent rheology at low shear rates, ‘anti-polyelectrolyte effect’ in high-ionic-strength solutions and the ability to interact preferentially with hydrophobically associating rod-like micelles. These latter materials are capable of forming highly viscoelastic solutions themselves. The rheological properties of these latter solution mixtures are very sensitive to the fraction of each component in the mixture and to the length of the alkyl chain copolymerized into the acrylamide chain backbone.

Bonding between epoxidized natural rubber and clay in presence of silane coupling agent

Based on the results of bound-rubber determination, Monsanto rheometric studies, solvent swelling, measurement of physical properties, and infrared spectroscopic studies, it is revealed that epoxidized natural rubber (ENR) and hard clay interact chemically to form Si–O–C bond during high-temperature (180°C) molding. It is also observed that addition of the silane coupling agent N-3-(N-vinyl benzyl amino)ethyl-γ-amino propyl trimethoxy silane monohydrogen chloride enhances the extent of the chemical interaction with the formation of coupling bonds of Si–O–Si type between clay and the coupling agent and C–N bonds between ENR and the coupling agent.

Nearly monodisperse spherical domain morphology in polycarbonate/poly(methylmethacrylate) blends following spinodal decomposition coupled with an interchange reaction

The morphological development in blends of bisphenol‐A polycarbonate (PC) and poly(methylmethacrylate) (PMMA) blends during isothermal annealing above 200 °C has been investigated where competition between liquid–liquid phase separation by spinodal decomposition and interchange reactions take place. Interchange reactions between PC and PMMA occurs at temperatures above 200 °C and leads to the formation of in situ graft copolymers from an ester–ester interchange reaction. During spinodal decomposition, graft copolymers are produced mainly at the interface region between the interconnected microphase domains. Instead of the usual ‘‘coarsening’’ process which is characteristic of the late‐stage of spinodal decomposition, the mixture exhibits nearly monodisperse spherical domains as revealed by optical microscopy. This phenomenon is further studied through extensive small angle light scattering measurements. Resonance peaks up to fourth order are noted, a rare observation. The result clearly demonstrates that...

Immiscibility in polystyrene/sulfonated polystyrene blends

Abstract Miscibility in the binary system of deuterated polystyrene and lightly sulfonated polystyrene has been investigated. Small-angle neutron scattering was used to evaluate the physical state of deuterated polystyrene/polystyrene—1.67% sulfonic acid blends over a wide composition range. Scattering behaviour was found to agree with the Debye—Bucche theory indicating that the blends were phase-separated at all compositions. A large positive interaction between styrene and styrenesulfonic acid monomers is believed to be responsible for the observed immiscibility.

Effect of sulfonation level on the single chain dimensions and aggregation of sulfonated polystyrene ionomers in xylene

Abstract Small angle neutron scattering has been used to determine the dimensions and extent of aggregation of dilute solutions of sodium sulfonated polystyrene (SPS) ionomers of molecular weight 10 5 g mol −1 and sulfonation levels of 0.95 and 1.65 mol% in p -xylene. At concentrations below 0.1 × 10 −2 g ml −1 the 0.95 mol% SPS was present as mainly single chains of considerably smaller dimension than that of the ‘parent’ polystyrene. Above this concentration small compact aggregates consisting of three chains were formed. These data could be analysed using the closed association model. The higher sulfonation level ionomer was present as even more compact single chains in very dilute solution. It associated, however, to form a distribution of much less dense aggregates with an average size that increased as the polymer concentration was raised. This type of behaviour was interpreted using the open association model and used to explain why semi-dilute solutions of this latter ionomer can gel.

Effect of interfacial tension on micellization of a polystyrene-poly(ethylene oxide) diblock copolymer in a mixed solvent system

Abstract The micellization of a polystyrene–poly(ethylene oxide) (PS–PEO) diblock copolymer in a mixed solvent of water and tetrahydrofuran (THF) was studied in terms of an aggregation number as measured by laser light scattering. The results show the aggregation number (f) of the micelle decreases monotonically as the amount of THF is increased. These experimental results are compared with a theoretical model that includes the variations in the interfacial tension. Experimentally, the interfacial tension is adjusted with the addition of relatively low levels of THF. The theory indicates that the aggregation number decreases as the interfacial tension is decreased. The theoretical prediction is in very good agreement with the experimental results. The main conclusion of this study is that the interfacial tension is the key factor in determining the aggregation number of the diblock copolymer micelle in a water–THF solvent system.

Influence of an elongational flow field on random coil and rod-like polymers in solution

Abstract The conformational response and spatial arrangement of random coil and rod-like macromolecules in solution was investigated utilizing an opposing jet device. This device is capable of generating a well-defined elongational flow field, which is quite useful for probing intra- and intermolecular interactions of sulphonated polystyrene (random coil) and xanthan (rod-like chain). With regard to the random coil in an aqueous environment, it was determined that its behaviour below the critical overlap concentration ( C∗ ) follows the anticipated trends as predicted by theory. Above C∗ , the elongational behaviour is determined by the intermolecular entanglement structure. However, changes in the ionic strength in these latter solutions reverts behaviour to that observed below C∗ . One implication of this finding is briefly discussed. Interestingly, intermolecular interactions dominate the behaviour of rod-like polymers, such as xanthan, below and above C∗ . Superimposed on these interactions is the subtle influence of the flow field both outside and along the axis connecting the centre of the jets. These results confirm that the xanthan macromolecule behaves as a liquid crystal at all concentrations investigated, even with relatively large changes in ionic strength.