半结晶聚酯的两相分离及其可靠性分析

联用Rietveld方法、Fourier过滤技术和径向分布函数(RDF)研究了半结晶聚酯(PET)粉末样的结晶相和非晶相两相分离及结构分析问题，得到合理的结晶相和非晶相的结构参数，表明这种方法对分析半结晶高聚物的两相结构是可行的.文中提出，判断半结晶高聚物二相分离和结构分析是否可靠，除需考虑分辩结晶相结构参数是否正确的三个判据之外，还需加上二个物理判据.还指出 ,若要获得合理的两相分离结果，提供纯非晶试样的散射曲线作为拟合时本底强度初始值是必要的.

Two Phases Separation and Its Reliability Analysis of Semicrystalline Polyethylene Terephthalate

The X ray diffraction whole pattern (XDWP) data of semicrystalline poly(ethylene terephthalate) PET2 sample were collected in the symmetric reflection geometry on a diffractometer employing a copper target (Kα wavelength 0.15418 nm )(see Fig.1 ).The XDWP was fitted by combining the Rietveld method and Fourier filtering technique,Rietveld structure refinement for PET2 crystalline phase was performed,the unit cell parameters obtained are a =0.445 nm,b=0.592 nm,c =1.072 nm,α= 99.6(°),β= 116.9(°),γ= 111.9 (°),the density of the crystals is dc = 1.495 g•cm－3(see Table 1) .Meanwhile the XDWP was separated into two parts,CR2 crystalline region and AM2 non crystalline region in PET2 (see Fig.2).The reduced radial distribution function G2(r) was calculated from AM2 and lead to three main peaks,G21(r) = 0.150 nm,G22(r) = 0.254 nm,G23(r)=0.460 nm which characterize the structure of the non crystalline phase in PET2 (see Fig.3).The result shows that this combination of techniques is feasible.The auther suggests that the reliability of evaluation on two phases separation and structure analysis in semicrystalline polymer,besides the three criteria to estimate the parameters of the crystalline phase,also depends on other two new physical criteria.Effect of various fitting plans on the results of structure refinement and phase separation were discussed.It is shown that in order to get reliable results it is necessary to have scattering pattern of pure amorphous sample as initial values of background intensity in fitting process.　　This work discusses how to deal with the difficulties and its possible solutions in applying Rietveld method to polymer structure analysis.