| Polyamides(PA)have been commercialized and developed for nearly 100 years,and they have become one of the five most widely used engineering plastics in the world.However,the raw materials used for preparation of monomers which are used to synthesize polyamides are mainly derived from petrochemical products.With the shortage of petrochemical resources and the increasing pressure on environmental protection,the synthesis of green,high-efficiency and novel biobased polyamides from renewable biobased monomers have become a hot topic in the field.Currently,due to the restriction of biobased monomers,commercially available biobased polyamide 410(PA410),polyamide 610(PA610),polyamide 1010(PA1010),polyamide 11(PA11)and polyamide 10T(PA10T)are mainly synthesized from monomers prepared using castor as a starting material.The biobased azelaic acid monomer prepared from vegetable oil has been industrialized.If the industrialization of related polymer materials can be successfully realized,it will help to broaden the product line of bio-based polyamide.Hence,biobased azelaic acid with 1,6-hexamethylenediamine,1,10-diaminodecane and 1,12-diaminododecane,respectively,were selected as monomers to synthesize polyamide 69(PA69),polyamide(PA109)and polyamide 129(PA129),respectively,and structure and properties of them were also studied,in order to provide basic data for polymerization and processing.In this paper,the main contents of studies are as follows:(1)Biobased PA69,PA109 and PA129 were synthesized respectively by biobased azelaic acid with 1,6-hexamethylenediamine,1,10-diaminodecane and 1,12-diaminododecane monomers,respectively,by the monomer salt formation and polycondensation reaction which included prepolymerization reaction and melt polycondensation reaction stage.The effects of experimental conditions on the preparation of ammonium salts formation reaction using water as solvent and synthetic experimental conditions on the degree of reaction and relative viscosity of PA69,PA109 and PA129 was investigated,in order to optimize experiment plan.Fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance(NMR),and elemental analysis(EA)were used to characterize the chemical structures of ammonium salts and PA69,PA109 and PA129.It is concluded that the optimum temperatures of ammonium salts formation reaction of them were 60 °C,70 °C and 60 °C,respectively.The optimum time of ammonium salts formation reaction of them was 1 h and the monomer ratio(the monomer molar ratio of diamine to diacid)of ammonium salts formation reaction of them were 1.02:1,1.01:1 and 1.01:1,respectively.The optimum temperatures of prepolymerization reaction of them were 210 °C,220 °C and 190 °C,respectively,and the optimum pressures of prepolymerization reaction of them were 1.6 MPa,1.9 MPa and 0.9 MPa,respectively.The optimum times of prepolymerization reaction of them were 2.5 h,2.5 h and 3 h respectively.The optimum temperature ranges of melt polycondensation reaction of them were 240~250 °C,250~260 °C and 220~230 °C,respectively.The optimum pressure(vacuum degree)of melt polycondensation reaction of them was-0.09 MPa,and the optimum time ranges of melt polycondensation reaction of them were 1.5~2 h,1~1.5 h and 2.5-3 h,respectively.The maximum relative viscosities of them which were synthesized under the obtained optimized conditions determined by experiments could reach to 2.3~2.4,2.2~2.3 and 2.0~2.1,respectively.(2)High molecular weight PA69,PA109 and PA129 were synthesized by salt formation-polycondensation method under the obtained optimized conditions,and physical and chemical properties of them were characterized and studied deeply by gel permeation chromatography(GPC),differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),dynamic mechanical analysis(DMA),X-ray diffraction(XRD),mechanical properties test,solubility test and water absorption test.The results showed that the number average molecular weights of them were determined to be 51300,38900 and 35500,respectively,which could meet the processing requirements.It showed that with an increase of the content of methylene in the polymer backbone,the melting temperature,crystallization temperature and glass transition temperature of them decreased,while the thermal stability of them were outstanding.They were proved to be partially crystalline polymers and their crystalline phase consisted of ? and ? crystalline forms.The mechanical properties of them were excellent,and the toughness of them was better than biobased PA610,PA1010 and PA11.They could not be dissolved in non-polar solvents and conventional organic solvents except strong polar solvents such as concentrated sulfuric acid.Water put a plasticizing effect on them under room temperature,which could lower the glass transition temperature and improve the elongation at break of them,while they showed lower water absorption and better dimensional stability properties than PA6 and PA66.(3)The law of changes in the structural and properties of PA69,PA109 and PA129 after treatment under the condition of different temperatures of isothermal crystallization were investigated by XRD,FTIR and DSC.It indicated that PA69,PA109 and PA129 belonged to a homogeneous polycrystalline polymer,and isothermal crystallization treatment put an annealing effect on them.With an increase in the temperature of isothermal crystallization,the crystalline form of melt-quenched PA69,PA109 and PA129 were transformed from ? to ? form,this phenomenon was called Brill transition of crystalline form which was ascribed to the mechanism of thermal expansion.With an increase in the temperature of isothermal crystallization,the crystallinity,the degree of perfection of crystal,crystallite size perpendicular to different crystal plane of them increased,and they were close to the state of thermodynamic equilibrium.Moreover,with an increase in the temperature of isothermal crystallization,the movement of molecular chain of melt PA69,PA109 and PA129 was improved,the internal stress and defects of structure of them was eliminated,and the recrystallization effect on them was more significant.(4)Both the effects of different hydrothermal treatment condition on the mechanism of annealing,dissolution and hydrolysis,and the structure and properties of PA69,PA109 and PA129 were studied by DSC,XRD,FTIR and small-angle X-ray scattering(SAXS).In the range of 140~165 °C,hydrothermal treatment exerted an annealing effect on them,and under the same temperature,hydrothermal annealing treatment was superior to isothermal crystallization annealing treatment for improving the properties of crystallization and melting.With an increase in the temperature of hydrothermal treatment,all of the crystallinity,the degree of perfection of crystal,the thickness and the order of lamellar crystals of them were increased,which led to an increase in melting temperature.The dissolution temperatures of them were 170 °C and the dissolution mechanism was mainly attributed to that the increase in the diffusion and permeability ability of water molecules under hydrothermal conditions could break hydrogen bonds between amide groups of polymer main chain of them to destroy the crystallization of PA69,PA109 and PA129,resulted in the occurrence of dissolution of them.In the range of 170~280 °C,the complete dissolution of them occurred with different degrees of hydrolysis.With an increase in the temperature of hydrothermal treatment,hydrolytic degradation was more prominent,and all of the degree of ordered arrangement of lamellar crystals,the degree of perfection and regularity of crystal,and the crystallinity of them were significantly decreased,which resulted in an decrease in melting temperature and the scission reaction of molecular chain of them occurred.The hydrolytic degradation reaction could be considered as a typical nucleophilic substitution reaction which took place when the carboxyl groups of polymer chains were attacked by H+ which was produced by water molecules and hydrolysis ionization reaction,and the scission of C-N bonds of O=C-N-H groups was generated.Eventually,amine-ended and carboxyl-ended oligomers were generated by the above hydrothermal effect.(5)The possible pyrolysis products and mechanism of PA69,PA109 and PA129 were studied by high temperature pyrolysis-gas chromatography/mass spectrometry.The reasonable pyrolysis mechanism(reaction)of them could be expressed as follows: the C-N bond of the N-alkyl amide bond of the molecular chain of PA69,PA109 and PA129 was cleaved and simultaneously C-H transfer reaction was initiated by the H of methylene group(position ?)jumping N of C-N bond to form products such as 1,9-nonanedinitrile,di-olefin,olefin,alkane and cyano dimer.The cleavage of the C-N bond(position ?)of the amide group of molecular chain of PA69,PA109 and PA129 generated and simultaneously the recombination reaction of free radical was initiated to generate diamine monomer and diazacyclo-alkyl-dione diazacyclo-alkyl-diketone products.The random scission of C-C bond consisted of carbonyl carbon atom of polymer chain of PA69,PA109 and PA129 was generated to form alkenyl nitriles,alkyl nitriles,alkenes and alkanes.Due to the hydrolysis reaction of polymer chain of PA69,PA109 and PA129 under high temperature condition,cyano-carboxylic acid,amino olefin and amino alkane could be produced. |
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