Synthesis and characterization of polystyrene-b-poly(ethylene oxide)-b-poly(ε-caprolactone) block copolymers

被引:81
作者
Arnal, ML
Balsamo, V
López-Carrasquero, F
Contreras, J
Carrillo, M
Schmalz, H
Abetz, V
Laredo, E
Müller, AJ
机构
[1] Univ Simon Bolivar, Dept Ciencia Mat, Grp Polimeros USB, Caracas 1080A, Venezuela
[2] Univ Los Andes, Fac Ciencias, Dept Quim, Grp Polimeros ULA, Merida 5101A, Venezuela
[3] Univ Bayreuth, D-95440 Bayreuth, Germany
[4] Univ Simon Bolivar, Dept Fis, Grp Fis Solidos USB, Caracas 1080A, Venezuela
关键词
D O I
10.1021/ma011058g
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
The preparation of polystyrene-b-poly(ethylene oxide)-b-poly(epsilon -caprolactone) triblock copolymers using three different strategies is described. Experimentally, a method we have called "thermal" is the simplest one of the three employed. However, it presents serious limitations for the preparation of high molecular weight triblock copolymers with low polydispersity. The titration method is a more elegant alternative to prepare the PS-b-PEO-b-PCL triblock copolymers. Nevertheless, the stoichiometric titration of the precursor terminal hydroxyl groups requires much expertise, and it becomes more difficult as the concentration of such terminal groups decreases when the precursor molecular weight increases. Finally, the sequential method may be regarded as the most convenient one. However, the experimental steps involved a solvent exchange during polymerization that must be performed under conditions of strict purity and high vacuum. Several triblock and pentablock copolymers of varying compositions and molecular weights were successfully prepared. The fact that these copolymers contain two crystallizable blocks, i.e., PEO and PCL, makes them very interesting from a structural point of view. The copolymers were found to be phase segregated according to evidence provided by DSC and WAXS. The crystallization and melting behavior of both PEO and PCL blocks is greatly affected by composition. Fractionated crystallization phenomena were detected when either one or both blocks constituted the minor components within the block copolymers.
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页码:7973 / 7982
页数:10
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