ISSN:
0360-6376
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Homogeneous condensation of a symmetrical diacyl monomer T with two symmetrical diols D1 and D2 has been studied under low-temperature, nonequilibrium conditions, using the diol sequence in the product as a probe. For terephthalate copolyesters of diols such as bisphenol A and neopentyl glycol the alternation frequency f12 has been related to the rate parameters by measurement [using nuclear magnetic resonance (NMR) and other methods] and calculation.It is usually assumed that all functionalities attached to the same residue have the same reactivity, that is, that all steps of type \documentclass{article}\pagestyle{empty}\begin{document}$$ \cdots {\rm T + D}_{\rm 1} \cdots \to \cdots {\rm TD}_{\rm 1} \cdots + {\rm eliminant (HC1)} $$\end{document} have the same specific rate; this assumption leads to a random, high-molecular-weight copolyester. If the diacyl species shows a large penultimate group effect, as in phosgene, chloroformate [see M. Matzner et al., Chem. Rev., 64, 645 (1964)], and phthalates, this assumption must be discarded.After simplification the alternation can be calculated exactly in terms of two parameters: r, the relative reactivity of the diacyl functionalities, and δ, the relative reactivity of the two diols. A nonrandom copolyester results only when neither r nor δ is unity. The maximum nonrandomness (for fixed r) occurs when δ → ∞ (sequential reaction).
Zusätzliches Material:
1 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1978.170161111
