The Synthesis And Structure-properties Of High Performance Random And Multiblock Copolymers Based On Biobased Poly(ethylene 2,5-furandicarboxylate)

In comparison with petroleum-based polyester poly(ethylene terephthalate)(PET),bio-based poly(ethylene 2,5-furandicarboxylate)(PEF)possesses superior mechanical strength and gas barrier properties,which makes PEF a broad application prospect in engineering plastics and high gas barrier packaging materials.Moreover,its production and application will bring huge environmental benefits.However,PEF has inherent shortcoming that it has poor tensile ductility and impact toughness,namely low elongation at break and impact strength,which limits its processing and applications.At present,the toughness modification of PEF focused on copolymerization with flexible components,however,the toughness improvement was achieved at the expense of incorporating with high content of comonomers,which leads to sharp drop of tensile strength,gas barrier properties,bio-based carbon content and high increase of product costs.In this work,a series of high molecular weight random and multiblock copolymers based on bio-based PEF were synthesized by the copolymerization with different flexible units through transesterification/esterification-melt polycondensation and chain extension method,and their structure-properties relationship were discussed.We mainly focused on the influence of copolymer composition and structure on thermo-mechanical properties and gas barrier properties of PEF copolymers,in order to obtain high performance materials based on PEF with practical value.First,poly(ethylene-co-1,5-pentylene 2,5-furandicarboxylate)(PEPeF)and poly(ethylene-co-hexamethylene 2,5-furandicarboxylate)(PEHF)were synthesized via melt polycondensation in the presence of bio-based odd-carbon 1,5-pentanediol(PeDO)and petro-based even-carbon 1,6-hexanediol(HDO),respectively.The molar fraction of copolyester composition(?PeF and ?HF)in PEPeF and PEHF were high than feeding diol composition(?PeDO and ?HDO),and the Mayo-Lewis equation can be used as an empirical equation to correlate the copolyester composition with feeding diol composition.PEPeFs proved nearly amorphous copolyester having excellent thermal stability,and HF-rich(?HF?88 mol%)PEHFs are semicrystalline but the others are almost amorphous,both of them has good thermal stability.The effect of PeDO on the toughness modification of PEF is better than HDO.Brittle-ductile transition of PEPeF and PEHF copolyesters was achieved at ?PeF of 9 mol%and ?HF of 28 mol%,respectively.In comparison with PEF,PEF-rich PEPeFs(?PeF 9-47%)not only showed greatly improved elongation at break(29-265%vs.4%)and slightly enhanced impact strength(2.2-3.9 vs.2.1 kJ/m2),and at the same time retained very high Young's modulus(2.8-3.3 vs.3.3 GPa)and strength(72-83 vs.82 MPa).This result is better than poly(ethylene-co-1,4-cyclohexamethylene 2,5-furandicarboxylate)(PECF)reported by literauture.In addition,mechanical properties of PEHF copolyester is comparable to PECF.Although increasing ?PeF and ?HF led to decrease in O2 barrier performance,a high level is maintained for PEPeFs and PEHFs.Particularly,when compared with bottle-grade PET,PE82Pe18F possessed comparable Tg(75?)and elongation at break(115%),but greatly improved tensile modulus(3.3 GPa)and strength(83 MPa)as well as O2 and CO2 barrier property(BIFo2=1.8,BIFCO2=8.6).Second,a series of poly(ethylene 2,5-furandicarboxylate-co-1,4-butylene carbonate)(PEFBC)and poly(ethylene 2,5-furandicarboxylate-co-l,5-pentylene carbonate)(PEFPeC)were synthesized by melt polycondesation in the presence of dimethyl carbonate(DMC),1,4-butanediol(BDO)or 1,5-pentanediol(PeDO).Due to ester-carbonate exchange reaction during melt polycondensation,there may be EF,EC,BF or PeF,BC or PeC units in the PEFBC or PEFPeC copolyesters.The synthesized copolyesters are amorphous,and their Tg and thermal stability decreases with the increasing of the copolyester composition,but it is enough to meet the requirements of processing.With the increasing of copolyester composition,the tensile ductility of PEFBC and PEFPeC copolyesters are improved.By contrast,brittle-ductile transition of PEFPeC copolyester was achieved at lower copolyester composition,while higher tensile modulus and strength were maintained in PEFBC copolyester.The elongation at break of PEFBC with ?BC of 43-52 mol%and PEFPeC with ?Pec of 29-40 mol%copolyesters were improved to 33-284%and 125-206%,respectively,while the tensile strength decreased to 66-61 MPa and 45-34 MPa respectively.The tensile ductility of PEFBC and PEFPeC are improved,at the same time their O2 barrier property are comparable to PET and CO2 barrier property are better than PET.However,in comparison with PEF,no improvement in impact toughness of PEFBC and PEFPeC copolyesters was observed,and the effect of toughening and maintaining gas barrier property is not as good as PEPeF copolyesters.Third,considering that the limited improvement of impact toughness was achieved by random copolymerization,a series of poly(ethylene 2,5-furandicarboxylate)-mb-poly(tetramethylene glycol)(PEF-mb-PTMG)multiblock copolymers with high molecular weight were successfully synthesized via melt polycondensation in the presence of PTMG oligomer diols with different moleculer weight.The PTMG flexible segments showed chain length dependent partial miscibility with PEF hard segments,and its presence also plasticized and promoted cold crystallization of PEF segments but unchanged the crystal structure of PEF segments.The incorporation of PTMG resulted in a greatly improvement in tensile and impact toughness of PEF-mb-PTMG,but the decrease in tensile modulus and strength was higher than that of random copolymers,and the gas barrier property was also significantly sacrificed.The effect of PTVG1K on the toughness modification of PEF was better PTMG2K,and with tuning the PTMG content,high performance PEF-based materials can be tailor-made from high tough thermoplastics with excellent ductility and impact toughness to thermoplastic elastomers with high strength.Particularly,PEF-mb-PTMG1K20 showed excellent ductility(elongation at break of 252%)while retaining high modulus(3.0 GPa)and yielding strength(74 MPa),and its Tg(68?)and CO2 barrier property were comparable with the bottle-grade PET,however,its O2 barrier property was inferior to PET.PEF-mb-PTMG1K35 showed an impact strength of>50 kJ/m2,which is the first reported PEF-based super-tough thermoplastic.PEF-mb-PTMG1K50-60 are thermoplastic elastomer with excellent performance.Finally,in order to simultaneously improve the tensile and impact toughness of PEF and maintain good gas barrier property.Two aliphatic polycarbonate diols(APC-diol),namely,commercial amorphous hydroxyl terminated poly(pentylene-hexamethylene carbonate)(PPeHC2K-diol)and self-made crystalline hydroxyl terminated poly(1,6-hexamthylene carbonate)(PHC4K-diol),were used with hydroxyl terminated PEF to synthesized a series of high molecular weight PEF-mb-PPeHC2K16-42 and PEF-mb-PHC4K15 multiblock copolymers via isocyanate chain extension.The synthesized copolymers are weakly crystalline polymers,and PPeHC2K or PHC4K segment showed partially miscible with PEF segments.The APC segment can both plasticize PEF hard segment and form microphase separation structure with PEF hard segment.The incorporation of APC segment resulted in a great improvement in impact strength of PEF-mb-APC copolymers.In comparison with PEF-mb-PTMG,PEF-mb-APC possessed better impact toughness and comparable tensile modulus and strength.However,the improvement in tensile ductility was inferior to that in PEF-PTMG.Moreover,it is currently known that PEF-mb-APC copolymers has significantly improved gas barrier property than PEF-mb-PTMG copolymers at low copolymer composition.Among them,PEF-mb-PHC4K15 copolymer showed good elongation at break(55%)and impact strength(4.0 kJ/m2),while possessing high tensile modulus(2.8 GPa)and strength(65 MPa),and its O2 barrier property was comparable to PET and CO2 barrier property was superior to PET.PEF-mb-PPeHC2K29-42 copolymers are super tough PEF-based thermoplastic with high impact strength of 15-80 kJ/m2.In comparison with PEF,the designed PEPeF random copolyester has significantly improved tensile ductility,while retaining good gas barrier property,tensile strength and rigidity.The designed PEF-mb-PTMG copolymers showed greatly enhanced tensile ductility and impact toughness,at the same time possessed good tensile modulus and strength,and the super tough PEF-based materials was obtained.The designed PEF-mb-APC copolymers showed better impact toughness and gas barrier properties than PEF-mb-PTMG copolymers,which is the PEF-based materials possessed excellent tensile and impact toughness and retained good gas barrier property,tensile strength and modulus.