Synthesis and Properties of Copolymers of Diphenylsiloxane with Other Organosiloxanes

Abstract

We describe the synthesis, characterization and properties of various types of siloxane polymers containing diphenylsiloxane (P) as a component. The polymer types include di-and tri-block copolymers with dimethylsiloxane (M) as the second component, and random and statistical copolymers with dimethylsiloxane or methylphenylsiloxane (P/M) as the second component. Such copolymers combine siloxane units whose polymers have very different properties. The polydiphenylsiloxane chain is rigid and inflexible, and the polymer is a highly crystalline solid with a liquid crystalline or condis crystalline state and a very high melting (clearing) temperature. In contrast, the polydimethylsiloxane or polymethylphenylsiloxane chains are very flexible and the polymers have very low glass transition temperatures.Polymers of controlled molecular composition, size and architecture were prepared by anionic polymerization of the "cyclic trimers", using lithium-based initiators.The physical properties of the copolymers vary dramatically with composition and architecture. Two types of "random" copolymers can be prepared. In one type, siloxane units of a given type are randomly placed in the chain in groups of three, i.e., the minimum sequence length of a given siloxane type is three siloxane units. In the other type of random copolymer, individual siloxane units are randomly distributed so that the minimum sequence length is a single siloxane unit. The properties of the two types are quite different, showing that subtle changes in sequence distribution can have major effects on physical properties. At molar ratios near 1/1 and with molecular weights of -105 , the first type of "random" copolymer is an elastic solid with appreciable mechanical properties, whereas the latter type is a sticky gum.Diblock copolymer (P-M) with dimethylsiloxane as the major component are paste-like, whereas the triblock (P-M-P) and star-block copolymers of the same composition are tough elastomers. The block copolymers are molecular composites, in which the polydiphenylsiloxane component separates into crystalline microphases with very uniform fibrillar or lamellar morphologies, and with widths or thicknesses comparable to the length of the polydiphenylsiloxane block, i.e, typically of the order of 100 A.

Anionic block copolymerization of cyclotetrasiloxanes initiated by 4,4'‐bis(dimethyllithiioxylsilyl)diphenyl ether

“…Therefore, we consider that the copolymers should belong to block copolymers mainly. Compared with previous results,3, 4 which indicate that block copolymers were only dissolved at very high temperature in a few selective solvents (e.g., diphenyl ether), our results suggest that our block copolymers were probably disturbed to some extent during the copolymerization process and should not belong to perfect triblock polymers. Instead, they should be approximately expressed as PMP and PMVP according to the different order of feeding in raw materials.…”

“…However, the block copolymers do not have good mechanical properties and have to be used by means of chemical crosslinks. As late as the 1980s, Ibemesi3 and Gvozdic4 obtained the desired copolymers, which are only soluble at high temperature in a few selective solvents (e.g., diphenyl ether), do not need chemical crosslinks, and can be used as thermoplastic elastomers. In these references, the anionic living copolymerization was carried out in diphenyl ether with n ‐BuLi and diphenyl silandiol (DLS) as initiators, tetrahydrofuran (THF) or dimethyl sulfoxide (DMSO) as activating agent, and the trimers of dimethyl and diphenyl siloxane as monomers.…”

Synthesis and characterization of alt‐copoly(carbosiloxane)s containing oligodiphenylsiloxane segments

“…The observation of a single T g for each copolymer was consistent with a homogeneous material. The absence of phase separation may be due to the short length of the alternating segments because two distinct thermal transitions have been observed for block copolymers of PDMS and PDPS 40–42. Copolymer XII had a higher T g than XI .…”

Facile Synthesis of Cx(AB)yCx Triblock Silicone Copolymers Utilizing Moisture Mediated Living‐End Chain Extension

“…Living ring‐opening polymerization employs a highly reactive initiator (typically BuLi) combined with a strained cyclic siloxane (most commonly hexamethylcyclotetrasiloxane (D 3 ), D = Me 2 SiO) at low temperatures, in solvents, and under an inert atmosphere; the use of difunctional initiators has also been reported . Blocks are formed by the sequential addition of different types of cyclic siloxanes that are added to the reactive chain end of the growing polymer . Chains are typically terminated with reactive silicone species such as chlorosilanes.…”