Study On Synthesis,Crystallization Behavior And Properties Of Semi-Crystalline Biphenyl Poly(Arylene Ether Sulfone Ketone) Copolymers

Poly（arylene ether sulfone）resin（PAESs）are thermoplastic polymers with high glass transition temperature and excellent thermal stability,which is composed of the benzene ring,sulfone group,and ether bond in the backbone.Meanwhile,they have good mechanical and processing properties,which make them widely used in electronic and electrical,mechanical industry,aerospace,biomedical,and other fields.However,there is a large difference in bond angles between the phenyl sulfone bond and the phenyl ether bond in the backbone of PAESs,which makes it difficult for the molecular chains to be stacked in an orderly manner.As a result,the aggregation structure of most PAESs is amorphous.Due to the lack of protection from crystal domains,PAESs have deficiencies in solvent resistance,weather resistance,wear resistance,heat resistance,and other aspects,which greatly limits their application and development as structural materials.Considering the above background,based on the high glass transition temperature of PAESs,this paper is committed to changing the aggregate structure of PAESs resin through molecular structure regulation,design,and synthesis of semi-crystalline PAESs（BD-PESKs）with high crystallinity.By studying their crystallization behavior and unique memory effect（self-nucleation effect）,the self-nucleation crystal regulation method was developed,which significantly improved the heat resistance level and mechanical properties of the BD-PESKs,so that they have good prospects for application and development in aerospace,precision machinery,and other high-tech fields.As the ancient saying goes,"Learning about what is forthcoming by observing tiny clues",in the contemporary polymer field,it can be understood as learning the changing trend of micro structure will bring to the macro properties of materials.This requires a large amount of experimental data and summaries to obtain the influence law of its micro structure and macro properties,which has important guiding significance for the molecular structure design of high-performance polymers.In this paper,from the perspective of molecular structure design,based on the understanding of the relationship between micro structure,aggregation structure,and macro properties,rigid biphenyl structures were introduced on both sides of the sulfone group of PAESs,and relatively flexible ether ketone units were added to adjust the rigid and flexible balance of the segment,to modify the molecular backbone structure of PAESs.Based on this structure,a series of semi-crystalline BD-PESKs were synthesized.By optimizing the melting processing parameters to improve the aggregation structure,the advantages of BD-PESKs as structural materials in thermal conductivity and mechanical strength were explored,and the influence of ether-ketone chain structure on the crystallization behavior and macro properties of the polymer was studied and obtained.The following section focuses on the main research results:Firstly,through the polymerization of 4,4’-bis（4-hydroxyphenyl）diphenyl sulfone monomer（BDS）containing biphenyl structure and 4,4’-difluorophenone monomer,rigid biphenyl groups and ether ketone units were successfully introduced into the backbone of PAESs,and by controlling the ratio of monomer feeding during polymerization,the semi-crystalline biphenyl poly（arylene ether sulfone ketone）resin（BD-PESK）with different molecular weight were prepared.BD-PESK has excellent thermal stability and solvent resistance.The 5%thermal weight loss temperature of the high molecular weight polymer is higher than 548°C.The glass transition temperature（T_g）and the annealing melting point（T_m）can reach 241 and 352°C,respectively.Unlike aliphatic semi-crystalline polymers,the highly rigid molecular segment structure gives BD-PESK a unique and persistent self-nucleation（memory）effect（350～370°C）,which persists at temperatures above the equilibrium melting point（T_m⁰=394°C）.Aiming at the problem that it is difficult for high molecular weight BD-PESK to crystallize again after melting,based on the guidance of its memory effect temperature domains,this paper developed a self-nucleation crystal control method.A series of semi-crystalline BD-PESK（A-BD-PESK）with different crystallinities（10～23%）were successfully prepared.The crystallinity of high molecular weight A-BD-PESK can reach 10%,and it shows excellent mechanical properties.The tensile strength of A-BD-PESK at room temperature（25°C）and200°C can reach 85.8 and 45.5 MPa,the elongation at break is 23.3%and 30.5%,and the storage modulus at 240°C can still maintain 71%initial storage modulus.Meanwhile,the influence of molecular weight on the mechanical properties was also investigated,and the principle of melting recrystallization to improve the mechanical properties was analyzed.In addition,the intrinsic thermal conductivity of A-BD-PESK increased 55%higher than PPSU up to 0.293 W·（m·K）^-1due to the crystal structure and high proportion of biphenyl groups,which fully demonstrated the advantage of crystal structure.In order to improve the crystallinity and crystallization rate of the poly（arylene ether sulfone ketone）resin（PAESKs）,a series of semi-crystalline biphenyl poly（arylene ether sulfone ketone ketone）resin（BD-PESKK）with different molecular weights were successfully prepared by increasing the length of the ether ketone unit through the molecular structure design.The T_gand annealed T_mare 230 and 359°C,respectively.Compared with BD-PESK,the chain flexibility of BD-PESKK was increased,the crystallization rate and crystallinity were significantly improved,and the memory effect domain was narrowed（365～380°C）.In view of the slow recrystallization of high molecular weight resin samples after melting,semi-crystalline A-BD-PESKK samples with different crystallinity（12～30%）were successfully prepared by following the above self-nucleation crystal regulation method,and the crystallinity of high molecular weight sample could be increased to21%.Compared with A-BD-PESK,A-BD-PESKK with significantly improved crystallinity has better mechanical properties.The tensile strength at room temperature and 200°C increases to 90.0 and 48.5 MPa,respectively,and the storage modulus at 300°C is 142%higher than that of A-BD-PESK.Moreover,the rigid biphenyl unit and more crystal structures jointly improve the intrinsic thermal conductivity of A-BD-PESKK up to 0.304 W·（m·K）^-1.In addition,the influence of crystal structure on the mechanical properties was studied by optimizing melting temperature,molecular weight,and other factors.To further solve the problem of crystallization difficulty of high molecular weight BD-PESKs after melting,two semi-crystalline biphenyl poly（arylene ether sulfone ketone）copolymers（b-BD-PESK-m and b-BD-PESK-h）with different sequence distribution ratios were prepared by introducing longer ether ketone segments in the backbone by step polymerization.As the chain flexibility of the two copolymers increased sequentially,their T_gdecreased to 190 and 178°C,respectively,compared with BD-PESK and BD-PESKK.What’s more,the increase in the length of the ether ketone segment broadens the memory effect domain（DII）and melt processing temperature range of the copolymer,which promotes the crystallization behavior.The melting crystallization ability of the copolymer is significantly improved,so the original b-BD-PESK samples prepared by conventional melting processing can achieve high crystallinity.After annealing,the crystallinity of high molecular weight A-b-BD-PESK-m and A-b-BD-PESK-h can be increased to 24%and 37%,respectively,and the T_mwas 340°C in all cases.High crystallinity of A-b-BD-PESK-h increases its thermal conductivity to 0.310 W·（m·K）^-1,as well as the tensile strength at room temperature and 150°C to 102.3 and 52.6 MPa,the elongation at break to 23%and 39.3%,respectively,and the storage modulus retention rate at240°C is still 42%.Compared with A-BD-PESKK,the tensile strength and elongation at break of A-b-BD-PESK-h are significantly improved,and the storage modulus at300°C is 58%higher than that of A-BD-PESKK.However,more flexible segments lead to a significant decrease in the tensile strength at 200°C（higher than T_g）to 27.9MPa.Therefore,the trade-off of segment stiffness and flexibility is necessary for the molecular design of semi-crystalline BD-PESKs.In addition,by comparing the thermal conductivity and mechanical properties of BD-PESK,BD-PESKK and b-BD-PESK,it is found that the molecular chain stiffness,molecular weight,melting processing temperature,thermal treatment,and other factors affect the crystal parameters and macro properties of BD-PESKs.Therefore,the regulation of crystal and mechanical properties of BD-PESKs can be realized.In summary,effective regulation of BD-PESKs crystal structure,melting recrystallization behavior and memory effect temperature domains can be achieved through reasonable molecular design and precise preparation of molecular structure,as well as regulation of polymer molecular weight,rigid segment proportion,and flexible chain segment sequence distribution.Therefore,the high-temperature mechanical strength and intrinsic thermal conductivity of semi-crystalline BD-PESKs achieve a significant improvement.It is hoped that this work can broaden the application prospect of semi-crystalline PAESKs and provide theoretical guidance and reference for the development of novel high-temperature resistant semi-crystalline polymers in the future.