ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTDynamic NMR Determination of the Barrier for Interconversion of the Left- and Right-Handed Helical Conformations in a PolyisocyanateKoichi Ute, Yoichi Fukunishi, Salil K. Jha, Kap-Soo Cheon, Beth Muñoz, Koichi Hatada, and Mark M. GreenView Author Information Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan, and Herman F. Mark Polymer Research Institute, Polytechnic University, 6 Metrotech Center, Brooklyn, New York 11201 Cite this: Macromolecules 1999, 32, 4, 1304–1307Publication Date (Web):February 4, 1999Publication History Received9 September 1998Revised30 December 1998Published online4 February 1999Published inissue 1 February 1999https://doi.org/10.1021/ma981427hCopyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views318Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (108 KB) Get e-AlertsSUBJECTS:Energy,Hydrogen,Nuclear magnetic resonance spectroscopy,Polymers,Thermodynamics Get e-Alerts

The microstructure of copolymers generated from enantiomeric 2,6-dimethylheptyl isocyanate monomers was determined by desorption chemical ionization mass Spectrometry (DCI-MS). (R)-2,6-Dimethylheptyl isocyanate and (S)-2,6-dimethyl-5,6-dideuteroheptyl isocyanate were prepared with the deuterium label incorporated into the (S)-monomer so that the (R)- and (S)-enantiomers could be distinguished by mass spectrometry. Homo- and copolymers of these enantiomers were prepared and examined by desorption chemical ionization, a method which causes depolymerization and generates protonated 1,3,5-tris(2,6-dimethylheptyl)cyanuric acids. The degree of deuterium incorporation into the (S)-monomer was determined by a tandem mass spectrometry procedure which avoids the errors associated with signals due to adventitious ions present in the single-stage mass spectra. The experiment involved mass selection and collision-induced dissociation of the entire isotopic envelope representing the (S)-trimer. This information was used to simulate the trimer region of the mass spectra of two copolymers, one containing 27% (R)-enantiomer and the other containing 74% (R)-enantiomer. Random and block structures were considered, and comparison with experiment revealed that the monomers are randomly distributed in the original copolymers. This analysis sets the stage for understanding the unusual nonlinearity between enantiomeric excess and optical activity in these copolymers and provides the first experimental correlation between the microstructure and the optical properties of synthetic D,L-copolymers.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMajority Rules in the Copolymerization of Mirror Image IsomersMark M. Green, Bruce A. Garetz, Beth Munoz, HePing Chang, Steven Hoke, and R. Graham CooksCite this: J. Am. Chem. Soc. 1995, 117, 14, 4181–4182Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://pubs.acs.org/doi/10.1021/ja00119a039https://doi.org/10.1021/ja00119a039research-articleACS PublicationsRequest reuse permissionsArticle Views1638Altmetric-Citations348LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Homopolymers and copolymers of alkylisocyanates having n-hexyl, 2,6-dimethylheptyl, 3,7-dimethyloctyl, and (2,2-dimethyl-1,3-dioxolan-4-yl)methyl substituents underwent thermal degradation in the course of desorption electron ionization to yield trimers and monomers that were characterized in situ by tandem mass spectrometry. The trimers were trisubstituted cyanuric acids, the protonated molecules displaying a characteristic series of alkene eliminations on collision-induced dissociation to yield protonated cyanuric acid, m/ z 130. Confirmation of the identity of the pyrolysates was obtained by using two types of MS3 experiments: the reaction intermediate scan and the two-dimensional familial scan. The ion chemistry of the trimers and of the protonated monomer, the alkylisocyanate, was elucidated. Among the many interesting fragmentation processes undergone by the ionized trimers were a and 3 C-C bond cleavages and charge-remote fragmentations, which provided information on branching in the alkyl substituent. The dioxolane-containing substituent showed unique ion chemistry. The monomer distribution in the copolymers was deduced from the abundances of the various protonated trimers. The distribution was found to be random in all copolymers except that containing the dioxolane substituent.

AbstractPolymer (II) exhibits a surprisingly high, temp.‐dependent (α)D ‐258° (47 °C), ‐367° (25 °C), ‐450° (10 °C), whereas the polymer (IV) has (α)D ‐480° (47 °C), ‐485° (21 °C), and ‐498° (10 °C).