Oligomer, defined

The 4,4 -MDA is sold commercially with a diamine assay of 98 —99%. The major impurity is the 2,4 -MDA isomer, which can be present in amounts up to 3%. PMDA products are normally defined by hydrogen equivalent weight and viscosity. Typical products exhibit a 50 hydrogen equivalent weight and a viscosity of 80 140 mPa-s(=cP) at 70°C. PMDA products normally contain, in addition to the isomers and oligomers of MDA, small amounts of aniline, water, chlorides, and various alkylated amines. AH MDA products should be stored in sealed containers in a cool dry area. 

UF solutions are clear water solutions. They contain only very low molecular-weight, water-soluble UF reaction products plus unreacted urea. Various combinations of UF solutions are found. They contain a maximum of 55% unreacted urea with the remainder as one or more of methylolureas, methylolurea ethers, MDU, DMTU, or triazone, a cycHcal oligomer. AAPFCO has defined this class of compounds as urea—formaldehyde products (water- s oluble). 

The synthesis-driven approach towards material science can be applied to create oligomers and polymers with optimized properties, e.g. maximized carrier mobilities and electrical conductivities or high photo- and electroluminescence quantum yields. It becomes obvious, however, that the ability to synthesize structurally defined -architectures is the key to these high performance materials. 

The authors developed two general concepts for the synthesis of these mono-disperse, defined oligomers. The oligomers can be built up in a stepwise fashion, e.g. via addition of organomelallic species to cyclohexane-1,4-dione followed by aromatization to the oligo(arylene) (e.g. for 25). 

Feldman et a .210 211 and Wulff et ul v have examined other forms of template controlled oligomerization of acrylic monomers. The template (23) has initiator and transfer agent groups attached to a rigid template of precisely defined structure.210 "11 Polymerization of MMA in the presence of 23 gave a 3 unit oligo(MMA) as ca 66% of the polymeric product. The stereochemistry of the oligomer was reported to be different" from that of atactic PMMA. 

Detailed procedures for the synthesis ofa,o>-organofunctionally terminated siloxane oligomers with well defined structures have been given 50,66-67). Tables 6 and 7 provide the data on the synthesis and characteristics of aminopropyl and hydroxybutyl terminated polydimethylsiloxane oligomers prepared via anionic and cationic ringopening polymerization of octamethylcyclotetrasiloxane (D in the presence of appropriate disiloxanes, respectively. 

Interestingly, the first example of a macromonomer, long before the names Macro-mer or macromonomer have been coined 94), is a styrene terminated polydimethyl-siloxane synthesized by the reaction of a Grignard derivative of p-ch loro styrene and an co-chlorodimethylsiloxane oligomer 90) as shown in Reaction Scheme IX. Later, these macromonomers have been reacted with different vinyl monomers such as styrene and acrylates, and relatively well defined graft copolymers have been synthesized. 

Synthesis of hydrolytically stable siloxane-urethanes by the melt reaction of organo-hydroxy terminated siloxane oligomers with various diisocyanates have been reported i97,i98) -yhg polymers obtained by this route are reported to be soluble in cresol and displayed rubber-like properties. However the molecular weights obtained were not very high. A later report56) described the use of hydroxybutyl terminated disiloxanes in the synthesis of poly(urethane-siloxanes). No data on the characterization of the copolymers have been given. However, from our independent kinetic and synthetic studies on the same system 199), unfortunately, it is clear that these types of materials do not result in well defined multiphase copolymers. The use of low molecular weight hydroxypropyl-terminated siloxanes in the synthesis of siloxane-urethane type structures has also been reported 198). 

As a simplification, it was assumed that the interactions between charged oligomeric segments were negligible. These redox data correlate well with potential values obtained by extrapolation from quantum ma hanical calculations and redox potential measurements on oligomers of defined chain length. As expected,... 

Voltammetric measurements on defined soluble oligomers in the homologous series of the p-phenylenevinylenes and the p-phenylenes have finally ended specu-... 

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