Influence of (1,3-phenylene)bis(3-methyl-1-phenyl pentylidene)dilithium initiator concentration on the modality of polybutadiene
KAUST DepartmentKAUST Catalysis Center (KCC)
Physical Sciences and Engineering (PSE) Division
Chemical Science Program
Polymer Synthesis Laboratory
Permanent link to this recordhttp://hdl.handle.net/10754/562422
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AbstractThe strong influence of (1,3-phenylene)bis(3-methyl-1-phenyl pentylidene)dilithium initiator (DLI) concentration on the modality of polybutadiene (PBd) in the presence of lithium s-butoxide (s-BuOLi) in benzene, at room temperature, has been studied. The quality of DLI has been evaluated by gas chromatography-mass spectrometry (GC-MS) and 1H NMR. Keeping s-BuOLi/C-Li ratio (R) close to unity, at relatively high DLI concentrations (C > 7 × 10-4 M), monomodal high 1,4-PBds with polydispersity index less than 1.07 were obtained, whereas bimodal ones at lower concentrations (C < 6 × 10-4 M). The effect of C-Li concentration on the modality of PBd has been evaluated using size exclusion chromatography on samples taken during and at the end of the polymerization. Viscosity observations have also been used to further support the results. The bimodality of PBd has been attributed to partially terminated difunctional species because of the inevitable presence of protic impurities in the polymerization solution, although high vacuum technique was used, which becomes more significant at low initiator concentrations. Moreover, the strong influence of s-BuOLi on the microstructure of PBd has been demonstrated by 1H NMR. © 2012 Wiley Periodicals, Inc.
SponsorsThe authors thank J. Roovers for the invaluable suggestions and comments. Stavroula Batistatou, University of Athens, is acknowledged for the GC/MS measurements. Douglas Adamson, University of Connecticut, is greatly acknowledged for PEB supply. The financial support of the Ministry of Education through the HRAKLITOS II program, co-financed from the Operational Program and Initial Educational Vocational Training-EPEAEK and the European Social Funds, is greatly appreciated.