Accession Number:
AD1016838
Title:
Organic Crystal Engineering of Thermosetting Cyanate Ester Monomers: Influence of Structure on Melting Point
Corporate Author:
Air Force Research Laboratory (AFMC) AFRL/RQRP Edwards AFB United States
Report Date:
2016-05-27
Abstract:
Key principles needed for the rational design of thermosetting monomer crystals, in order to control the melting point, have been elucidated using both theoretical and experimental investigations of cyanate esters. A determination of the thermodynamic properties associated with melting showed that the substitution of silicon for the central quaternary carbon in the dicyanate ester, 2,2-bis4-cyanatophenylpropane, resulted in an increase in the entropy of melting along with a decrease in the enthalpy of melting, leading to a decrease in the melting temperature of 21.8 or - 0.2 K. In contrast, the analogous silicon substitution in the tricyanate ester, 1,1,1-tris4- cyanatophenylethane, resulted in no significant changes to the enthalpy and entropy of melting, accompanied by a small increase of 1.5 or - 0.3 K in the melting point. The crystal structure of 1,1,1-tris4-cyanatophenylethane was determined via single crystal X-ray diffraction, and the structures of these four dicyanate esters and tricyanate esters were examined. Although both the empirical models of Lian and Yalkowsky, as well as Chickos and Acree, provided reasonable estimates of the entropy of melting of 2,2-bis4-cyanatophenylpropane, they successfully predicted only certain effects of silicon substitution, and did not capture the difference in behavior between the dicyanate esters and the tricyanate esters. Semi-empirical molecular modeling, however, helped to validate an explanation of the mechanism for the increase in the entropy of melting of the silicon-containing dicyanate ester, while providing insight into the reason for the difference in behavior between the dicyanate esters and tricyanate esters. Taken together, the results assist in understanding how freedom of molecular motions in the liquid state may control the entropy of melting, and can be utilized to guide the development of compounds with optimal melting characteristics for high-performance applications.
Descriptive Note:
Journal Article
Supplementary Note:
Crystal Growth and Design , 16, 7, 01 Jan 0001, 01 Jan 0001, Journal article published in the Crystal Growth and Design Vol. 16, Issue 7, May 2016 Crystal Growth Des., 2016, 16 (7), pp 40824093; DOI: 10.1021/acs.cgd.6b00612; Received 21 April 2016; Publication Date (Web): 27 May 2016; Published in print 06 July 2016 Copyright 2016 American Chemical Society The U.S. Government is joint author of the work and has the right to use, modify, reproduce, release, perform, display, or disclose the work.
Pages:
0058
Distribution Statement:
Approved For Public Release;
File Size:
1.29MB
