A single polymer pair (BR and EPDM) was used to confirm experimentally rheology-morphology relationships that have been previously gleaned from comparison of a variety of blend systems. The relative importance of the primary factors which govern blend morphology (composition and relative mixing viscosity of the components) was determined over the range of practical interest. In addition, correlation of mixing rheology with more accurate and complete shear modulus data allowed (a) molecular interpretation of rheological behavior in terms of network parameters, such as physical entanglements, and (b) estimation of the elastic and loss components of the shear modulus during mixing. An attempt was made at explaining the dependence of blend morphology on the viscoelastic properties of the components in terms of a fracture or tearing mechanism.

The morphology of heterogeneous blends of polybutadiene (PBD) and EPDM was selectively varied by a change of either the rheology of the blend components during mixing or of the blend composition. Under a given set of mixing conditions, the blend system approaches a "steady state morphology", which was found to be relatively independent of sample history. However, during subsequent compression molding, the morphology of the sample may be altered substantially with phase inversion occurring in some cases. A mechanism is proposed for the observed rheology-morphology behavior.The strain moduli of the vulcanizates prepared by irradiation of the elastomer blends were similar to those predicted using the parallel Takayanagi models. A positive synergism with respect to energy to break and stress at break was noted particularly in cases where the blend components showed a significantly different mechanical response. The sensitivity of the stress-strain response of these blends to changes in morphology was less than anticipated. This is attributed to restrictions imposed on the movement of the softer phase by the hard phase component of the blend. ZUSAMMENFASSUNG:Die Morphologie heterogener Polymermischungen aus Polybutadien (PBD) und Athylen-Propylen-Dien-Terpolymeren (EPDM) wurde selektiv variiert, indem entweder die Rheologie der Mischungskomponenten wahrend der Mischung oder die Zusammensetzung der Mischung geandert wurden. Bei gegebenen Mischungsbedingungen nahert sich das Mischungssystem einer ,,Steady-State-Morphologie", die sich als relativ unabhangig * Paper presented at the joint meeting of the GDCh-Fachgruppe "Makromolekulare Chemie" and the FachausschuR "Physik der Hochpolymeren" of the Deutsche Physikalische Gesellschaft on "Multiphase Polymer Systems" in Bad Nauheim (Germany) on March 30th 1976. jedoch die Morphologie wesentlich andern, wobei in einigen Fallen Phasenumwandlung eintritt. Fur das rheologisch-morphologische Verhalten wird ein Mechanismus vorgeschlagen.Die Dehnungsmoduln der durch Bestrahlung der Elastomermischungen hergestellten Vulkanisate glichen denjenigen, die durch die Takayanagi-Modelle vorausgesagt wurden. Ein positiver Synergismus hinsichtlich der Bruchenergie und der Zugspannung beim Bruch wurde speziell in den Fallen beobachtet, in denen die Mischungskoponenten ein ausgesprochen unterschiedliches mechanisches Verhalten zeigten. Die Empfindlichkeit des Zug-Dehnungsverhaltens dieser Mischungen bezuglich der hderungen in der Morphologie erwies sich geringer als vorher angenommen. Dies wird auf Einschrankungen in der Bewegungsmoglichkeit der weicheren durch die harte Phase in der Mischung zuruckgefuhrt.

No abstract

More than a million miles of tire testing is generally required to prove the utility of a new elastomer. For example, such a program has recently demonstrated that an alkyllithium solution polymerized butadiene styrene copolymer (Duradene rubber) has improved abrasion resistance over that of emulsion SBR1. It is, thus, extremely important to find meaningful relationships between the structure of an elastomer and its commercial importance to further guide the polymer chemist toward the development of new general purpose or specific application elastomers from laboratory sample through to final tire evaluation. Butadiene homopolymers and butadiene styrene copolymers prepared by alkyllithium catalysis in hydrocarbon solution offer unique opportunities to relate basic polymer structure parameters to tire compound performance. Their mixed micro-structure (cis-1, 4, trans-1, 4, and vinyl) preclude crystalline transitions which would otherwise complicate the interpretation of structural behavior. Furthermore, this polymerization system permits the production of controlled and specific variations in molecular weight distribution and degree of branching. n-Butyllithium catalyzed 1, 4-polybutadiene with its mixed microstructure and high cis-1, 4-polybutadiene have both shown outstanding abrasion resistance, especially under conditions of severe tire service. There is as yet no generally clear molecular interpretation for the outstanding abrasion resistance of the 1, 4-polybutadienes. For reasons of both improved processing and increased wet traction, these 1, 4-polybutadienes are seldom used alone but are blended with either natural rubber or SBR plus large amounts of extending oils. As a start, using as few fundamental concepts as possible, attempts were made to relate the industrial processing, heat build up, traction, and abrasion resistance characteristics of amorphous elastomers to two features measurable in terms of molecular parameters. The macrostructure (molecular weight distribution and branching) of the polymer is especially related to processing behavior. The glass temperature, Tg, of a polymer characterizes both the temperature and rate of deformation conditions in which the polymer exhibits rubbery behavior. Hence, the polymer Tg is directly related to both heat build-up and failure characteristics of an elastomer. Thus we shall be mostly discussing polymer structure in just two terms (i) macrostructure and (ii) Tg.

The Gordon—Taylor—Wood relationship between composition and glass temperature has been used as the basis of a DTA method for block styrene analysis in butadiene styrene copolymers having the same microstructure and a similar compositional distribution. The determined K value of the Gordon—Taylor—Wood equation for these polymers prepared with a butyllithium catalyst is in fair agreement with values previously determined for emulsion butadiene styrene copolymers. The total styrene content of the copolymer was determined using the refractive index method, and the composition of the “non-block” segment of the copolymer was obtained from DTA measurement using a Tg as a function of composition graph The amount of block styrene can then be obtained by difference. Evidence is presented supporting the validity of the method, and the results are compared with those obtained by a chemical method which involved polymer degradation by a hydroperoxide in the presence of osmium tetroxide. The thermal analysis requires approximately one-half hour. All measurements are made on the dry polymer eliminating the necessity of redissolving the polymer as required by most other methods of analysis.