Oligomer structure

Theoretically, there are three classes of structures cyclic, dihedral, and cubic. Cubic structures are only possible from 24 subimits upward. Only oligomers with an even number of subunits exhibit dihedral structures. Oligomers with an odd number of subunits have cyclic build. 

The sodium salt of methacrylic acid 2A has also been polymerized directly in aqueous media via ATRP employing a PEO macro-initiator (130). Short chain, controlled structure oligomers of PMAA may also be prepared by CCTP (131). 

Ah initio calculations of polymer properties are either simulations of oligomers or band-structure calculations. Properties often computed with ah initio methods are conformational energies, polarizability, hyperpolarizability, optical properties, dielectric properties, and charge distributions. Ah initio calculations are also used as a spot check to verify the accuracy of molecular mechanics methods for the polymer of interest. Such calculations are used to parameterize molecular mechanics force fields when existing methods are insulficient, which does not happen too often. 

In addition to this diester, di-2-hydroxyethyl terephthalate, some oligomers of general structure ... 

Linear polymers are the most commonly found, and consist of chains of D units endblocked by a variety of functionalized M units. Branched-chain silicones consist mainly of D units, with a D unit being replaced by a T or a Q unit at each point of branching. Cyclic PDMS oligomers are also common and can play a role in adhesion. They are usually found as mixtures of structures going from three siloxy units, to four, five, and higher siloxy units. A whole range of analytical techniques can determine the detailed molecular structures of these materials [20,21],... 

In the narrow sense, bis-maleimide resin means the thermosetting resin eom-posed of the bis-maleimide of methylene dianiline (BMI, bis(4-maleimidophenyl)-methane) and methylene dianiline (MDA, bis(4-aminophenyl)methane) (Fig. 1). Beeause of the addition meehanism, the resin is eured without elimination, whieh is a eharacteristic of this resin. Bis-maleimide resin is used as a thermally stable matrix up to 204°C (400 F) whieh typical epoxy resins may not normally be used. However, in spite of having an imide structure, bis-maleimides are classified as being moderately thermally stable resins. The aliphatic structure of the resin is not stable for long periods above 232°C (450°F.) If a highly aromatic thermally stable thermosetting resin is necessary, acetylene end-capped aromatic imide-based oligomers should be used. 

It is often the case that chemists involved or familiar with ethylene oxide (oxiran) chemistry refer to these cyclic oligomers as EO-4, EO-6 and EO-7 respectively. Such designations are informal if not colloquial but, like any name, are useful if they correctly convey an idea. The difficulty with these informalities, indeed with the crown nomenclature system is that it cannot adequately deal with complicated structures or even isomers of simple ones. 

Similar reactions lead to other oligomers depending on the size of the R groups and the conditions of the reaction, e.g. cyc/o-(Me2AlNMe2)2 (structure 1) and the imido-clusters (PhAlNPh)4, (HAlNPr )4 or 6,... 

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