Synthesis, Characterization And Properties Of PBT-based Poly(Ether Ester) Block Copolymers

We present here the one pot, one feeding step synthesis of poly(ether-ester) blockcopolymers with poly(butylene terephthalate)(PBT) as one of the block segment. A seriesof PBT poly(ether ester) triblock and multiblock copolymers with various molecularweight were synthesized by solution and melting ring-opening polymerization (ROP) ofcyclic oligo(butylene terephthalate)s (COBTs), using dihydroxyl end-functionizedpolyethers as macroinitiator, including poly(ethylene glycol)(PEG), poly(tetramethyleneoxide)(PTMO) and poly(dimethyl siloxane)(PDMS). The structure of the multiblockcopolymers is well characterized by nuclear magnetic resonance (NMR) techniques,together with gel permeation chromatography (GPC), and matrix-assisted laser desorptionionization time-of-flight (MALDI-TOF) measurements. The behaviors of these multiblockcopolymers were measured by differential scanning calorimetry (DSC), thermogravimetricanalysis (TGA), wide-angle X-ray diffraction (WAXD), etc.The main contents are summarized as follows:(1) We demonstrated a facile synthesis method to novel double crystalline triblockcopolymers for confinement effect studies. Three PBT-b-PEO-b-PBT triblock copolymerswith same PEO but different PBT molecular weights were synthesized by solution ROP ofCOBTs using PEG as macroinitiator and titanium isopropyloxide as catalyst. The structureof copolymers was well characterized by1H NMR and GPC. TGA results revealed that thedecomposition temperature of PEO in triblock copolymers increased about30°C to thesame as PBT copolymers, after being end-capped with PBT polymers. These triblockcopolymers showed double crystalline properties from PBT and PEO blocks, observedfrom DSC and WAXD measurements. The crystallization of PBT blocks showed thestrong confinement effects on PEO blocks due to covalent linkage of PBT blocks withPEO blocks, where the melting and crystallization temperatures and enthalpiescorresponding to PEO blocks decreased significantly with increment of PBT content. Thecrystal morphology was observed by polarized optical microscopy (POM), andamorphous-like spherulites were observed during PBT crystallization. (2) The isothermal crystallization kineties and melting behaviors after isothermalcrystallization of PBT homopolymer and PBT-b-PEO-b-PBT triblock copolymers wereinvestigated by DSC. The equilibrium melting temperatures of PBT homopolymer andtriblock copolymers were determined by Hoffman-Weeks equation. The deduced Avramiexponent n varies in the range of3.0~4.0, from the analysis of the crystallization kineticdata using the Avrami equation, indicated that the addition of PEO did not alter the crystalgrowth mechanism. The crystallization rates of the PBT-b-PEO-b-PBT triblockcopolymers were decreased with increasing content of PEO.(3)(PBT-b-PEO-b-PBT)xmultiblock copolymers was were synthesized by the one potmelt polymerization of COBTs using dihydroxyl end group of PEG-1k as themacroinitiator. NMR techniques including1D-quantitative1H NMR、HSQC and1H-1HCOSY have been used to characterize the multiblock copolymer structures This wasfurther confirmed by MALDI-TOF. An improved quantitative1H NMR technique wasapplied to calculate the absolute molecular weights by the chain end and functional groupsestimation. It was found that the polymerization efficiency decreased when the molecularweight of PEO increased to4,000or10,000Da.(4) A novel method is utilized to synthesize (PBT-b-PTMO-b-PBT)xmultiblockcopolymers by the one pot melt polymerization of COBTs using PTMO as a macroinitiator.The NMR techniques (1D-quantitative1H NMR and1H-1H COSY) have been used tocharacterize and reveal the multiblock copolymer structures and absolute molecularweights. It was found the molecular weights of the multiblock copolymers increasedlinearly with reaction time. The structures of the multiblock copolymers are furthercharacterized by GPC. The polymerization kinetics is slightly affected and incresed withthe catalyst content. These multiblock copolymers show improved thermal stability whencompared to PTMO homopolymers. The mechanical properties test at room temperatureindicates the elongation of the multiblock copolymers increased with molecular weights. (5) A series of PBT-PDMS multiblock copolymer with different mass content ofPDMS were synthesized by using dihydroxyl end functioned group ofpoly(dimethylsiloxane) as macroinitiator, and their properties are measured.1H NMR andGPC analysis reveals the formation of block copolymers, with very low polymerizationefficiency and unknown block copolymer structure.