Dale J. Meier

Prediction and manipulation of the phase morphologies of multiphase polymer blends: II. Quaternary systems

The dispersed phases of a multiphase polymer blend will either form an encapsulation-type phase morphology or the phases will remain separately dispersed, depending on which morphology has the lower free energy. We have developed a model to predict phase morphologies of multiphase polymer blends. Calculations based on the model suggest that interfacial tensions play the major role in establishing the phase structure of a multiphase system, with a less significant role played by the surface areas of the dispersed phases. The model further shows that the phase structure of a multiphase polymer blend can be converted from one type to another by changing the interfacial tensions between one or more pairs of the components using interfacially-active agents such as block or graft copolymers. We have applied the model to different ternary blends of polystyrene, polyethylene, polypropylene and poly(methyl methacrylate), and have compared the predicted morphologies of these blends with experimental results. In each case, the predicted morphologies agree with those found experimentally. In addition, we have successfully converted the phase structures of these blends from one type to another by using interfacially-active block copolymers.

An AFM study of the properties of passive films on iron surfaces

The electrochemical corrosion processes of iron in a borate solution have been investigated by in situ electrochemical atomic force microscopy (ECAFM). A freshly polished iron surface is easily passivated electrochemically in a borate solution to give a film which is different from the oxide layer which forms on the iron surface in air. Most areas of the passive film are uniform, but some defects still exist in the film which allow localized corrosion to occur. In situ ECAFM can be used to examine these defects directly and to observe the initial corrosion processes in which ferric oxide particles are both formed and reduced by cyclic voltammetry.

Compatibilizing effects of block copolymers in low-density polyethylene/polystyrene blends

Abstract The phase and mechanical properties of a low-density polyethylene/polystyrene 70/30 (LDPE/PS 70/30) blend has been determined after compatibilization with various styrene-ethylene, styrene-ethylene/butene and styrene-ethylene/propylene type block copolymers. It is shown that high interfacial activity, as reflected in the reduction of the dispersed phase size, does not necessarily bring about an improvement in the mechanical properties of the blend. Although the diblock copolymers were more efficient in reducing the phase size, the triblock copolymers were more effective in improving the mechanical properties. The effect of poly(styrene- b -ethylene)(S-E) block copolymer on the particle coalescence and rheological properties of the LDPE/PS 70/30 blend has been investigated. It is shown that small amounts of the block copolymer can significantly retard or actually suppress the coalescence of the dispersed phases, and thus stabilize the morphology of the blend. The addition of the S-E copolymer increases the elastic modulus and dynamic viscosity of the blend, and the samples become more non-Newtonian as the block copolymer concentration increases.

Synthesis and properties of diarylsiloxane and (aryl/methyl)siloxane polymers: 1. Thermal properties

Abstract Poly(diarylsiloxane)s are highly crystalline, high-melting polymers with excellent high-temperature properties. As a consequence of the rigid polymer backbone, they show crystal-liquid-crystal transitions, and both nematic and smectic states have been observed by optical microscopy. The polymers of greatest interest in this investigation have been those containing phenyl and p-tolyl substituents on the siloxane backbone. We have prepared a series of polymers with various combinations of these substituents, as well as the end members of the series, poly(diphenylsiloxane) and poly(di(p-tolyl)siloxane). The polymers are prepared with controlled molecular weights and distribution by ring-opening anionic polymerization of the cyclic trimers in solution. The crystal-liquid-crystal transition temperatures, T1c, for poly(diphenylsiloxane) and poly(di(p-tolyl)siloxane) are very high (265 and 300°C, respectively) and the polymers are only soluble in a few solvents at temperatures above 150°C. However, the T1c values are reduced for the mixed poly((phenyl p- tolyl)siloxane)s and the polymers become soluble at lower temperatures. The symmetric poly((phenyl p- tolyl)siloxane) is of particular interest since T1c is reduced to 150–160°C, and the polymer is soluble at room temperature in common solvents such as toluene, tetrahydrofuran and chloroform. In contrast to the retention of the crystalline and liquid-crystalline character in the mixed diarylsiloxanes, the replacement of a single phenyl group by a methyl group in the repeat hexaphenyl triad sequence of poly(diphenylsiloxane) is sufficient to destroy both the crystalline and liquid crystalline character of the polymer.

Ultra-high modulus polyethylene. 1 Effect of drawing temperature

Abstract Drawing behaviour and the properties of ultra-drawn high density polyethylene have been investigated as a function of the drawing temperature. An optimum temperature has been found for each type of polyethylene, at which the best drawing behaviour is found. It appears that the temperature range for effective drawing (leading to a high draw ratio and high Youngs modulus) depends on the molecular weight and its distribution. The temperature range of the effective drawing is shifted towards higher temperatures for polyethylene exhibiting broader molecular weight distribution and higher weightaverage molecular weight. Ultra-high modulus and transport samples have been obtained by drawing high density polyethylene with broad molecular weight distribution ( M w M n ∼ 20 and M w ∼ 200 000 ) at higher drawing temperatures. It has been found that in the range of drawing temperatures 80–105°C the modulus of this polyethylene is higher for samples drawn at higher temperatures. Transparent samples with draw ratios of 35–40 and with Youngs moduli of 600–650 kbar (at room temperature) have been obtained by drawing the polyethylene at 100°–105°C. We conclude that the high molecular fraction in the polyethylene, forming tie molecules in the drawn material, is responsible for the high modulus, while the low molecular weight fraction facilitates alignment of the long chains and retards the internal voiding (whitening) to a very high draw ratio during drawing at the higher temperatures.

Latex film formation: atomic force microscopy and theoretical results

Abstract We have critically examined the kinetics of latex film formation using an atomic force microscope to obtain corrugation height data as a function of time, temperature, molecular weight, particle size, etc. The results show that the film forming process obeys viscoelastic time/ temperature superposition principles, thus indicating a direct relationship between the kinetics of film formation and rheological properties. Film formation kinetics are examined under ‘wet’ and ‘dry’ conditions, with film formation occurring almost ten-times faster under wet conditions than dry. This proves for the latex system examined that capillary pressure from the water meniscus is the dominant driving stress for film formation. Past theories for latex film formation are reviewed, and problems and deficiencies are noted. A new theory for film formation from a dry latex system is presented, which is based on the use of the Boltzmann Superposition Principle to relate the changing stress and strain fields as the latex particles deform. The predictions of theory and the experimental data show excellent agreement over nearly four decades of time.

New techniques for determining domain morphologies in block copolymers

Abstract We have developed several new techniques for examining the domain morphologies of microphase-separated block copolymers. By selective degradation and removal of the matrix component of suitable block copolymers, the domain-forming component can be left intact in its original morphological form and available for characterization. Thus we have selectively removed the polydiene (polybutadiene or polyisoprene) matrix component of poly(styrene- b -diene) copolymers by treatment with ozone. The remaining polystyrene domains were stained with ruthenium tetroxide or shadowed with platinum and examined by electron microscopy. A marked improvement in the ability to distinguish domain morphologies and their three-dimensional character was found when these degradation techniques were used. Details of domain morphologies that were not apparent when using conventional osmium tetroxide staining methods on undegraded films often became clearly apparent with this new technique.

Synthesis and properties of diarylsiloxane and (aryl/methyl)siloxane polymers: 2. Solution and rheological properties

Polydiarylsiloxanes and polydialkylsiloxanes, with alkyl groups larger than methyl, have liquid-crystalline states, presumably as the result of a chain-rigidifying effect from steric interactions of the bulky aryl or alkyl groups along the chain. In the first paper of this series, we reported on the thermal behaviour of a number of diarylsiloxane polymers with phenyl and/or p-tolyl substituents, all of which showed liquid-crystalline behaviour at high temperatures. The solution properties of several of the ‘mixed’ poly(phenylp-tolyl)siloxane polymers have now been investigated in order to characterize their chain stiffness properties and to relate these to the tendency to form a liquid-crystalline state in bulk. The ‘mixed’ poly(phenylp-tolyl)siloxanes were chosen for investigation since they have a major advantage in experimental convenience over the ‘unmixed parent’ polymers, polydiphenylsiloxane and polydi(p-tolyl)siloxane. The former are soluble at room temperature in common solvents, whereas the latter polymers are only soluble at temperatures above 150°C. The various diarylsiloxane polymers were prepared by anionic polymerization of the cyclic trimers, and the preservation of the triad sequences (absence of ‘scrambling’) was confirmed by 29Si n.m.r. Values of the Mark-Houwink-Sakurada exponent, a, for three different types of poly(phenylp-tolyl)siloxanes are essentially equal, at ∼0.83. This value of the exponent is below the value expected for a rigid chain (a>1.0) but is above the maximum value expected for a flexible random-coil polymer in a good solvent (a⩽0.8). The shear viscosity of solutions of the mixed poly(phenylp-tolyl)siloxane polymers increases monotonically with increasing polymer concentration up to 60 wt%, and does not show an abrupt drop in viscosity above a critical concentration, as is often observed with rigid-rod polymers. This observation, together with the value of the Mark-Houwink-Sakurada exponent, a<1, indicates that these polymers do not behave in solution as rigid-rod polymers, but most likely as worm-like chains with a relatively large persistence length.

Synthesis and properties of diarylsiloxane and (aryl/methyl)siloxane polymers: 3. New aryl substituents

Abstract In this paper we describe the synthesis and characterization of a new series of diarylsiloxane polymers, in which the aryl substituents are either m-tolyl, 4-methoxyphenyl or 4-propylphenyl. The polymers were prepared by the ring-opening anionic polymerization of cyclic trimers in solution at high temperatures. The structure and compositions of the cyclic trimers were confirmed by 1H and 29Si n.m.r. The new diaryl polymers are all highly crystalline, and each melts to a liquid crystalline state. The crystal-liquid crystal transition temperatures depend on the nature of substituents and follow the order: di(4-methoxyphenyl)≅di(p-tolyl)>di(phenyl)>di(4-propylphenyl)>di(m-tolyl). The transition temperatures of polydi(4-methoxyphenyl)siloxane and polydi(p-tolyl)siloxane are both very high (300°C). The solubility of the diarylsiloxane polymers is strongly affected by the nature of the aryl substituents. Polymers having di(4-methoxyphenyl), di(p-tolyl) or di(phenyl) substituents are only soluble at temperatures above 150°C in solvents such as dimethylsulfoxide and diphenyl ether. Polydi(m-tolyl)siloxane and the mixed poly (p- tolyl phenyl)siloxanes are soluble in toluene and chloroform at room temperature. Polydi(4-propylphenyl)siloxane crystallizes slowly, and if recovered and tested before becoming fully crystalline it will dissolve in common solvents such as toluene and chloroform at room temperature. However, after annealing it becomes soluble only at high temperatures. The cyclic trimer of di(o-tolyl)siloxane could only be prepared in trace quantities, and we were unsuccessful in preparing polydi(o-tolyl)siloxane, probably because of the steric interactions of the o-tolyl groups.

Phase-Selective Curing of Poly(p-Methylstyrene-b-Butadiene-b-p-Methylstyrene)

The preparation, properties and phase-selective crosslinking reactions of poly(p-methylstyrene-b-butadiene-b-p-methylstyrene), PMS-BD-PMS, have been examined. The PMS-BD-PMS triblock copolymer was synthesized anionically by sequential monomer addition. The ability to selectively crosslink the poly(p-methylstyrene) end-block segments was examined by curing with various polymers containing hydroperoxide end groups. Both polystyrene hydroperoxide, PSO2H, and poly(p-methylstyrene) hydroperoxide, PMSO2H, were found to significantly increase tensile stress at break and the percent elongation-at-break of the PMS-BD-PMS triblock copolymer. In addition, the modified triblock copolymer was insoluble in toluene, heptane and methyl ethyl ketone. When unfunctionalized styrene homopolymer was added the effects were quite different. These results have been compared to the unselective, non-phase-selective peroxide, dicumyl peroxide, which dramatically decreases the elastomeric properties of the triblock copolymer after curing. In addition, the specificity of this effect has been investigated by carrying out equivalent experiments with an analogous poly(styrene-b-butadiene-b-styrene), PS-BD-PS, triblock copolymer. No enhancement of tensile properties was observed on the treatment. of the PS-BD-PS triblock copolymer with PS02H, followed by curing. The phase-selective curing of PMS-BD-PMS resulted in a product with better tensile properties at 70oC than that observed for the corresponding uncured PMS-BD-PMS and PS-BD-PS triblock copolymers.