Study On Relationship Between Sequence Distribution And Properties Of PES/PEES Copolymers

PES is aromatic engineering plastics with balanced properties as excellentthermal stability widely applied in aerospace, automobile and electrical industries.Because it has a relatively high melt viscosity and low ultimate elongation, thereare some difficulties in the process and the application. To improve the toughnessof PES, U.K. ICI company introduces the means of copolymerization to synthesisa series of PES/PEES random copolymers which have been applied in a lot ofscopes. In the period of my Ph.D. degree, I design and prepare five kinds ofPES/PEES copolymer samples with almost equal in mol composition but differentin sequence distribution, and deal with the relationships between their internalstructure factors and the external characteristics.Chemical structures of five kinds of copolymers were characterized byinverse gated decoupling 13C NMR. The research results show that copolymerssamples, almost equal in composition but different in number-average sequentiallength and the degree of randomness. Their thermal properties were studied bymeans of DSC and TGA. The glass transition temperature of the samples fit theFOX equation well and is equal to 215℃. The studys of thermal decompositionkinetics of five kinds of copolymers showed that sequence distribution hadprodigious effects on thermal decomposition process. The results of X-raydiffraction radial distribution function (RDF) showd that five quenched copolymersamples existed the short range order in the scope of 15 ?, and the appearance oftwo wide peaks at ~ 5 ? periodic suggested the existence of more or less parallelchain segments in the copolymers. Five more highly annealed sample at 200℃were examined to assess the sensitivity of the X-RDF method to short rangeintermolecular ordering. The RDF plots of five samples showed a markedperiodicity peaking at intervals of ~5? which were attributed to intermolecularordering, and the short range order scope of alternative copolymer A50 reached35?, correspondingly, the short range order scope of random copolymer R50reached 21?. The results of electron-microscopy investigation of five copolymerssample, heat treated at 200 ℃ for 7 days indicate that copolymers molecularaggregation is changed from a randomly coiled amorphous phase to an orderedone, and the order structure of alternative copolymer is more distinct than randomone. The experimental results of the present work suggest that the motion ofsegments is affected by different molecular chain sequence distribution. Asystematic study of the influence of sequence distribution on the dynamicmechanical properties of PES/PEES copolymer has also been made. Three distinctloss maxima are observed and named as, β, β' and α relaxation peaks from low tohigh temperature. Thereinto, β' transition temperature changes a lot, but the α andβ transition temperature almost keep stable. The study of fluorescence spectrumproved that excited phenylene-rings of alternative copolymer A50 with high orderstructure in its main chain could form excimer with the surrounding unexcitedphenylene-rings, and the emission peak intensity of excimer strengthens with theincrease of dichloromethane solution concentration. Effects of sequencedistribution on the tensile properties were studied by stress-strain curve. Theresults show that its initial modulus and yield stress increase while the elongationdecreases when five copolymer samples are heat treated 96 hour at 200℃, and theyield stress of alternative copolymer A50 increases more distinct than random one.The result of rheological behavior proved that the melt viscosity of five copolymersamples is lower than PES, and the sequence distribution has some effects onrheological properties.Through above we give the relationship between the internal constructionfactor and the external properties, so as to give a fully theoretic foundation for thelater studies and application.