Thermal analysis of complex relaxation processes in poly(desaminotyrosyl-tyrosine arylates) George Collins a, * , Seung-uk Yoo b , Ali Recber a , Michael Jaffe a a Medical Device Concept Laboratory, New Jersey Institute of Technology, Department of Biomedical Engineering, 111 Lock Street, Newark, NJ 07040, United States b Medical Device Concept Laboratory, New Jersey Institute of Technology, Department of Material Science and Engineering, 111 Lock Street, Newark, NJ 07040, United States Received 10 July 2006; received in revised form 5 November 2006; accepted 9 November 2006 Available online 12 January 2007 Abstract The goal of this study is to better understand the thermal characteristics and molecular behavior of two poly(desaminotyrosyl-tyrosine ar- ylates). These two polymers were chosen from a combinatorial library of polymers developed by changing the type and size of the two sub- stitutable chain locations. The objective of this work was to describe the origin of the complex relaxation processes that have been observed by thermal analysis methods. DSC, TMA and TSC studies were conducted on poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate), poly(DT 12,10), and poly(desaminotyrosyl-tyrosine ethyl succinate), poly(DT 2,2), in film and fiber form. DSC experiments on poly(DT 2,2) show only a glass transition at about 80  C which is characteristic of an amorphous polymer. The DSC of poly(DT 12,10) shows multiple thermal events indicative of a more complex internal structure. The thermally stimulated current (TSC) analysis results for poly(DT 2,2) indicate a region of molecular mobility at about 80  C consistent with the T g from DSC. For poly(DT 12,10) there is a dipole relaxation process observed at about 40  C. An additional region of mobility at 60  C for poly(DT 12,10) fibers is observed. The comparison of conventional TSC with a modified TSC procedure suggests that this process represents a spontaneous reorganization of the internal structure of the solid. The comparison of DSC and TSC results suggests that poly(DT 12,10) has two distinct modes of organization with a transition between these modes at about 60  C. Previously published results indicate that solid state structure formation is related to two different modes of hydrogen bonding in the internal structure of the solid. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Biodegradable polyesteramide; Hydrogen bonding; Polyamorphism 1. Introduction 1.1. Objective Biomaterials are synthetic materials that are used in medical devices in order to replace, support or heal tissue. A biomaterials’ ability to achieve success depends on its proper- ties and the body’s acceptance of the material. As the implant is placed in the body it must not invoke immunological and toxic responses. How the material is placed in the body and what its properties and functions are must be predetermined. The biological acceptability of an implant material and its ability to perform the desired function are dependent on the bulk and surface properties of the implant. Thus before a mate- rial is implanted in the body, an extensive characterization of its physical properties must be conducted. These properties in- clude mechanical and thermal behavior, biodegradability as well as the changes of these properties as the material ages un- der biological conditions. This characterization process is an important step in understanding the initial and long-term be- havior of the material. This study involves the thermal charac- terization of two specific polymers synthesized by Kohn for biomedical applications [1e3]. The two polymers that have been chosen for study are repre- sentative of desaminotyrosyl-tyrosine monomers incorporated * Corresponding author. Tel.: þ1 973 596 6496; fax: þ1 973 802 1545. E-mail address: collins@adm.njit.edu (G. Collins). 0032-3861/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.11.049 Polymer 48 (2007) 975e988 www.elsevier.com/locate/polymer