Isomorphism phenomena in macromolecules

Abstract

Through x‐ray and infrared examinations of stereoregular polymers and copolymers of vinylaromatic monomers, the occurrence of chain isomorphism phenomena, together with many cases of a new type of isomorphism between monomeric units, have been proved. Isomorphism of macromolecules, allowing true solid solutions, has been observed when melting and crystallizing mixtures of homopolymers (i.e., isotactic polystyrene) and of crystalline copolymers (i.e., styrene‐p‐methylstyrene) having the same identity period and differing very little in lattice constants. Isomorphism among monomeric units occurs in copolymerizing monomers that have a chemical nature and shape slightly different one from the other, e.g., styrene and o‐fluorostyrene. This allows the formation of crystallizable copolymers in the entire composition range. They show physical properties (lattice constants, melting temperatures, etc.) continuously varying between those of the pure homopolymers. The occurrence of isodimorphism phenomena has been observed in crystalline copolymers obtained from monomers the homopolymers of which have different crystalline structures (e.g., styrene‐p‐fluorostyrene), and also in copolymerizing styrene with monomers (e.g., p‐methyl, p‐chlorostyrene) giving only amorphous homopolymers. In the latter case, of course, the copolymers show crystallinity only in a limited composition range.

Aliphatic copolyester with isomorphism in limited composition range

“…Random copolymerization is an easy and convenient way to randomly place different monomers on polymer chains, which benefits for the formation of isomorphism. Therefore, until now lots of random copolymer serials exhibiting isomorphism phenomena have been observed, such as styrene/p-fluorostyrene copolymer [7], ethylene/ a-olefin copolymers [9], polyhydroxyalkanoates [10,11], etc.…”

“…This phenomenon has been commonly observed in both small molecular and macromolecular system, which provides a unique view for studying the crystallization theory and fabricating functional structure [1e5]. The concept of isomorphism in polymer field was first arisen by Natta et al [6,7]. Later, Allegra and Bassi [8] stated two fundamental requirements for the formation of isomorphism in crystalline polymer system: first, different types of monomers must approximately have the same shape, occupy the similar volume; second, the conformation of the two types of monomers must be compatible with each other.…”

Chain Conformation, Crystal Structures, and Structural Disorder in Stereoregular Polymers

“…For instance, in the case of vinyl polymers it is possible to accommodate into the crystalline lattice different comonomeric units having lateral groups with different shape and dimensions. Copolymers of butene and 3-methylbutene 3 or copolymers of styrene and o-fluorostyrene 4 are crystalline in the whole range of composition, provided that the copolymers are isotactic, whereas propene and 1-butene comonomeric units are able to cocrystallize at any composition in syndiotactic copolymers. 5,6 Isomorphism of comonomeric units also occurs in copolymers of acetaldehyde and n-butyraldehyde, which are crystalline over the whole range of composition.…”

Sequence distribution and crystal structure of poly(ethylene/butylene terephthalate) copolyesters compared with poly(ethylene/trimethylene terephthalate) copolyesters

“…Loss of perfection of the crystal structure seems to be a general result for increasingly poorer isomorphism. Natta distinguishes two different types of repeating unit isomerism for crystallizable homopolymers 1, 2. Type 1: homopolymers of the two repeating units have crystals with similar structure.…”