Glass transition and exclusion model in crystallization of polyether±polyester block copolymers with amide linkages Rong-Ming Ho * , Chih-Wei Chi, Chi-Chun Tsai, Jiang-Jen Lin Department of Chemical Engineering, National Chung Hsing University, Taichung 40227, Taiwan, ROC Received 2 July 2001; received in revised form 24 September 2001; accepted 26 September 2001 Abstract Polyether±polyesterblockcopolymershavingvariouspolyetheramidecontentsweresynthesized.Singleglasstransitionintermediatedin temperature between the glass transition temperatures of polyester and polyetheramide components was found for all of polyether±polye- sters.Thecompositionalvariationofglasstransitionexhibitedasimilartrendtothepredictedresultofthermodynamictheoryforcompatible polymer blends. The incompatible pair of homopolyester and homopolyether was forced to be compatible after copolymerization. A modi®ed theoretical prediction for the glass transition of copolymers based on the thermodynamic theory is proposed. Consistent results between theoretical prediction and experimental measurements were found. Unlike homopolyesters, the glass transition temperature of copolymer amorphous domains gradually decreases with crystallization time. An exclusion model for the crystallization of polyester segments in copolymers is proposed. The temperature width of the glass transition increases with crystallization time. The broadening towardsthelowtemperaturesideinglasstransitionisinterpretedastheevidenceofcrystallization-inducedpartialphaseseparation.Instead of forming macroscopic segregation, the excluded polyether segments resided in-between crystalline polyester lamellae and mix with amorphous polyesters to generate amorphous domains exhibiting concentration gradient along the lamellar basal surface normal. Further increasing the polyetheramide segment content brings the excluded polyetheramide segments to form domains among the crystallized polyester spherulites so as to inhibit the occurrence of spherulitic impingement. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Exclusion model; Polyether±polyester; Crystallization 1. Introduction Thecopolymerizationoflowmolecularweightpolyether, such as polyethyleneoxide) PEO), with terephthalic polyesters to form segmented copolymers has been used to prepare thermoplastic elastomers TPE) [1]. Polyether acts like a soft segment to provide rubber-like properties for the terephthalic polyester [2±14]. Polyether±polyesters have been identi®ed to be semicrystalline-like materials, possessing crystalline polyester domains and well-mixed amorphous polyether and polyester domains [4±7,11]. More recently, the polyether±polyesters have drawn attention for their hydrophilic properties. A small amount of PEO usually below 10 wt%) is introduced to PET by copolymerization in order to increase their hydrophilicity [15]. Crystallization kinetics of the low ether content poly- ether±polyesters has been analyzed via Avrami treatment combined with morphological observations by polarized light microscopy PLM) and transmission electron micro- scopy TEM). A crystallization mechanism through the heterogeneousnucleationprocesswithhomogeneouslamel- larbranchingwasproposed[16].PEOhomopolymerisalso a crystallizable polymer. However, the crystallizability of PEO segments in polyether±polyesters is strongly affected by the molecular weight of PEO segment. At molecular weights below 4000gmol 21 , PEO segments become non-crystallizable because of too short blockiness for crystallization. The crystallizability is thus restricted by the blocking effect of polyester segments [1]. In general, polyether±polyesters are prepared by copolymerization of ethylene glycol, dimethyl terephthalate or terephthalic acid) and PEO having molecular weights ranging from 1000 to 4000 g mol 21 . A variety of copolymer properties canthusbetailoredthroughthecontrolofnon-crystallizable PEO content. In this study, a variety of polyether±polyesters with amide linkage has been synthesized. For terephthalic polyesters, there is always a problem about transesteri®ca- tion and/or degradation such as hydrolysis on polymer molecules after high temperature treatment. Furthermore, Polymer 43 2002) 1365±1373 0032-3861/02/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII:S0032-386101)00680-2 www.elsevier.com/locate/polymer * Corresponding author. Tel.: 1886-4-2285-7471; fax: 1884-4-2285- 4734. E-mail address: rmho@dragon.nchu.edu.tw R.-M. Ho).