Toshiichi Soen

Domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide and isoprene cast from solutions

Abstract The domain structure and crystalline morphology of AB and ABA type block copolymers of ethylene oxide (EO) and isoprene (Ip) were investigated by using two kinds of casting solvents, non-selective (benzene) and selective (ethyl benzene) solvents. The domain structures of both types of block copolymers are identical, as in the case of amorphous block copolymers, depending mostly on the fractional compositions of each block segment but hardly on the sequence arrangements. When benzene is used as a cast solvent, the change of domain structure with increase of Ip fraction follows, in general, a role established for amorphous block copolymers, except for the fact that the EO segment is crystallizable so that the above role is considerably modified, especially when the EO fraction is dominant, to form spherulitic crystalline texture. The domain structure of mixed system of block copolymer with homo-PEO, cast from benzene solution, also follows the above role, simply depending on fractional composition as a whole, of each component, unless the molecular weight of the homopolymer is much larger than that of corresponding block segment. On the other hand, when ethyl benzene is used as a cast solvent, the domain structure is quite different from that cast from benzene solution, giving single crystal-like texture of EO segments on which Ip segments are segregated to form Ip layer even for a copolymer having an EO fraction as small as 20%. The above contrast of domain formation mechanism between the two kinds of casting solvents is interpreted in terms of an interrelation of two binodal surfaces, critical concentration of crystallization of EO segments and critical concentration of micelle formation of EO and Ip segments, in the phase diagram of the system at a given temperature.

Grain boundary relaxation phenomena in block and graft copolymers

SummaryThe grain boundary relaxation phenomena, which have been found in the mechanical relaxation of the cast films of a series ofgraft copolymers ofpoly(methyl acrylate) with styrene, are examined again, in order to understand its relaxation mechanism, by using some particular series of heterogeneous systems of two components having different interaction between the two phases and, subsequently, different grain boundary structure; i. e., two series of poly(vinyl acetate) filled with two types of carbon blacks having relatively high and low surface activities, respectively, a series ofmechanical mixtures ofpoly(vinyl acetate) with polystyrene, and a series of styrene-isoprene-styrene tri-block copolymers.The grain boundary relaxation phenomena are again detected for the series of the tri-block copolymers but definitely not for the series of the mechanical mixtures, suggesting that the grain boundary relaxation phenomena must arise not from the heterogeneous structures themselves but from characteristic arrangements of molecular chains at the boundary of the two phases. That is, there must be a considerably strong interaction between the two phases, and there exists an intermediate phase in which the polymer segments of soft component are rigidified while the other polymer segments of hard component are softened. In other words, there must be a cooperative motions of chain segments of the two components to produce a mechanical relaxation under a certain environmental condition, such as temperature and time scale of observation.ZusammenfassungDie Korngrenzenrelaxationsphänomene, die in der mechanischen Relaxation einer Serie von aus Graft-Copolymeren von Polymethylacrylat mit Styrol gefunden wurden, wurden erneut geprüft, um den Relaxations-mechanismus zu verstehen, unter Verwendung einer besonderen Serie von heterogenen Systemen zweier Komponenten, die verschiedene Wechselwirkungen zwischen den zwie Phasen besitzen und deshalb verschiedene Korgrenzenstrukturen. Das heißt, wir verwendeten zwei Serien von Polyvinylacetaten, gefüllt mit zwei Rußtypen von vergleichsweise hoher und niedriger Oberflächenaktivität, eine Serie von mechanischen Mischungen aus Polyvinylacetat mit Polystyrol und eine Serie von Styrol-Isopren-Dreiblockcopolymeren. Die Korngrenzenrelaxationsphänomene, wurden für die Serie der Dreiblockcopolymeren wiederum festgestellt, aber definitiv nicht für die Serie der mechanischen Mischungen. Das läßt vermuten, daß Korngrenzenrelaxation nicht von heterogenen Strukturen selbst, sondern von charakteristischen Anordnungen der molekularen Kette an der Grenze von zwei Phasen herrührt. Das heißt, es muß eine beträchtlich strenge Wechselwirkung zwischen den zwei Phasen bestehen, und es muß eine Zwischenphase existieren, in welcher die Polymersegmente der weichen Komponente versteift werden, während die anderen Polymersegmente der harten Komponente erweicht werden. Mit anderen Worten, es müssen cooperative Bewegungen von Kettensegmenten der zwei Komponenten vorhanden sein, um eine mechannische Relaxation unter gewissen Umgebungsbedingungenzuerzeugen, Umgebungsbedingungen wie Temperatur und Zeitskala der Beobachtungen.

Studies on Domain Formation Mechanism of A-B Type Block Copolymer from its Solution

Recent development in anionic polymerization technique have made it possible to synthesize A-B-A as well as A-B type block copolymer, and some characteristic mechanical properties of the copolymers consisting of hard and soft block segments, such as high-elasticity without crosslinking process, have attracted attention (1). The dynamic mechanical properties, such as two distinct peaks in the loss modulus-temperature relation and a two step character of the dynamic modulus-temperature relation including the high-elasticity, have been explained in terms of a two- phase structure originating from the microphase separation of the block segments into respective domains (1–12).