Cyclizations in hyperbranched aliphatic polyesters and polyamides

Hyperbranched aliphatic polyesters of 2,2′-bis-(hydroxymethyl) propanoic acid and hyperbranched aliphatic polyamides obtained from new carboxy- and amino-functionalized caprolactams were studied by NMR spectroscopy and MALDI-TOF mass spectrometry. Ring-chain equilibria taking place through intramolecular hydroxy-ester, carboxy-amide or amine-amide interchanges and leading to the formation of cyclic branches or end-groups were found to exert a predominant influence on the molar mass of these hyperbranched polymers. A number of intra- or intermolecular side reactions, such as the formation of ethers in polyesters and the formation of anhydrides, imides, amidines and secondary amines in polyamides were also detected and resulted in polymer crosslinking on prolonged heating. The existence of such ring-chain equilibria and side-reactions make the control of hyperbranched polymer structure much more difficult than generally accepted.     

Structural study of Mg‐bearing sodosilicate glasses by Raman spectroscopy

The presence of magnesium in glasses of geological, medical, and technological interests influences their physicochemical and durability properties. However, the understanding of the role of magnesium is dependent on the combined knowledge of the structural environment of magnesium in the glass or melt and of the silicate network connectivity of the studied systems. In this article, we present a Raman spectroscopic study of the network connectivity of 10 ternary silicate glasses in the system Na₂O MgO SiO₂ and one Mg‐free binary silicate glass Na₂O SiO₂. Results obtained at constant polymerization suggest the existence of various Qⁿ units according to the nature of the modifying cation. As polymerization decreases for Na₂O MgO αSiO₂ glasses (labeled as NMSα with α decreasing from 10 to 2), the band associated with Si O Si bending in fully polymerized region disappears being gradually replaced by a band attributed to Si O Si bending in region containing mainly Q² and Q³ species. For highly polymerized glasses (NMS10‐NMS4), the coexistence of these two bands suggests the presence of two interconnected networks. Concomitantly, the signal associated with Q³ species first increases. For a further decrease of the polymerization, the high wavenumber part of the signal associated with Q³ species decreases, while the intensity of the high wavenumber part of the band related to Q² species increases. This result strongly suggests that magnesium charge‐balances preferentially Q² species rather than Q³ species. Copyright © 2010 John Wiley & Sons, Ltd.