The oligomer structure

This chapter is a preliminary report of our results. We found a procedure by which PHBA can be reacted with pre-formed amorphous oligoester diols at 230°C with minimal formation of phenol, an undesirable by-product. The products of such reactions are oligomers containing amorphous and ordered phases. They appear liquid crystalline. While the oligomer structures formed in the procedure described here differ from those of the previous paper, they form baked enamel films of exceptional hardness, toughness, and adhesion. 

The basis for the EEW determination is the size of the oligomer structure, number of bridging carbons and the number of terminal epoxide groups. As n increases the number of bridging carbons increases but the number of epoxide groups stay the... 

DNA, where very little control of the cleavage pattern by the oligomer structure would be expected—i.e., the reactivity should largely control the extent of cleavage at each site. From the data in Table I, an average augar r TMP, dCMP, and dAMP of 1.2 M s can be calculated. Using the value of /jq = 9 M s" obtained from the analysis in Fig. 9, the ratio calculated from the kinetic data is = 7.5, which is... 

Fig. 7. Room-temperature optical absorption spectra of PPV oligomers (a) in KBr pellets and (b) in chloroform solution. The oligomer structure is represented in (c). Reprinted, by permission of Elsevier Science from H. S. Woo, O. Lhost, S. C. Graham, D. D. C. Bradley, R. H. Friend, C. Quat-trocchi, J. L. Bredas, R. Schenk, and K. Miiiien, Synth. Met. 59,13 (1993). Copyright 1993 Elsevier Science.

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. 

In these reactions the system is tuned, for example by adjustment of the reaction temperature and time and modification of the catalyst structure to maximize the quantity of the desired dimers produced, and to minimize the production of higher molecular weight oligomers and polymers. In other reactions it is the opposite... 

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

In a complementary study of the interaction between polyanilinc and ITO, oligomeric polyaniline model compounds, namely phenyl-capped amino (PC2) and imino (PC20X) dimers [113, 114] have been used. The chemical structures of the polyaniline oligomers are displayed in Figure 5-20. Both substances are soluble in... 

Stoicescu and Dimonie103 studied the polymerization of 2-vinylfuran with iodine in methylene chloride between 20 and 50 °C. The time-conversion curves were not analysed for internal orders but external orders with respect to catalyst and monomer were both unity. Together with an overall activation energy of 2.5 kcal/mole for the polymerization process, these were the only data obtained. Observations about the low DP s of the products, their dark colour, their lack of bound iodine and the presence of furan rings in the oligomers, inferred by infrared spectra (not reported), completed the experimental evidence. The authors proposed a linear, vinylic structure for the polymer, and a true cationic mechanism for its formation and discussed the occurrence of an initial charge-transfer complex on the... 

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. 

---