Prediction Of Glass Teansition Temperatures Of Linear Aromatic Polyamides On Group Contribution Method And Molecular Dynamics

The glass transition temperature is one of the most important properties of polymeric materials.It affects the performance of polymeric materials directly,which is of great significance to the selection and design of new materials.In this paper group contribution method was used to study the glass transition temperatures of Poly(m-phenylene isophthalamide)(MPDI)and Poly(p-phenylene terephthamide)(PPTA)with different chain length.It was found that there is a rapid increase in the glass transition temperatures as their degree of polymerization increases and this effect will level off at still higher molecular weights.Then the glass transition temperatures of MPDI and PPTA were acquired based upon molecular dynamics simulation method combined with analysis from charts of density-temperature,Specific volume-temperature,the radial distribution function-temperature,radius of gyration-temperature,non-bond energy-temperature,with these calculation results being very close.Both results from the group contribution method and molecular dynamics simulation method were compared with the reported experimental data.Results show that the glass transition temperature from group contribution method was lower than the experimental value while the glass transition temperature from the molecular dynamics simulation method was higher than the experimental value,but both were close to the data in the literature,which concludes that the group contributionmethod and molecular dynamics simulation could be exploited to study the glass transition temperature of wholly aromatic polyamides.The above methods were extended to predict the glass transition temperature of three new aromatic polyamide polymers,i.e.Poly(p-phenylene isophthalamide)(PPIA),Poly(p-phenylenediamine-alt-2,6-diformyl quaterphenyl)(Auxe a)and Poly(p-phenylenediamine-4'''-aminocarbonyl-alt-2,6-diformyl quaterphenyl)(Auxe b).The glass transition temperatures of these three kinds of aromatic polyamides with different chain lengths were studied based on the group contribution method.Similar laws about the relation between glass transition temperature and the degree of polymerization were observed in these three aromatic polyamides.Then the glass transition temperatures of PPIA,Auxe a and Auex b were acquired based upon molecular dynamics simulation method combined with analysis from charts of density-temperature,Specific volume-temperature,the radial distribution function-temperature,radius of gyration-temperature,non-bond energy-temperature,with these calculation results being very close.For PPIA,the glass transition temperature calculated on group contribution method is 554.4 K.And the glass transition temperature obtained from the analysis of density-temperature,Specific volume-temperature,the radial distribution function-temperature,radius of gyration-temperature,non-bond energy-temperature are 593.6 K,594.1K,592.2 K,594.3 K,592.5 K respectively.For Auxe a,the glass transition temperature calculated on group contribution method is 498.6 K.And the glass transition temperature obtained from the analysis of density-temperature,Specific volume-temperature,the radial distribution function-temperature,radius of gyration-temperature,non-bond energy-temperature are 521.2 K,522.0K,523.2 K,522.3 K,523.7 K respectively.For Auxe b,the glass transition temperature calculated on group contribution method is 498.4 K.And the glass transition temperature obtained from the analysis of density-temperature,Specific volume-temperature,the radial distribution function-temperature,radius of gyration-temperature,non-bond energy-temperature are 518.1 K,517.9K,519.4 K,519.3 K,519.2 K respectively.It can be concluded from the above results that the glass transition temperature of PPIA lies between those of PPTA and MPDI,and so PPIA has the potential to be developed into a new type of aromatic polyamide fiber with its performance lying between those of PPTA and MPDI.The glass transition temperatures of Auxe a and Auxe b are lower than that of PPIA due to the introduction of the quarterphenyl structure on the main chains of Auxe a and Auxe b,leading to the increase of the intermolecular distance.At the same time,the glass transition temperature of Auxe b is slightly lower than that of Auxe a because of the influence of the amide groups on the quarterphenyl structure.