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Lamellar Thickness Dependence of Crystal Modification Selection in the Syndiotactic Polystyrene γ-to-α/β Phase Transition Process
Macromolecules ( IF 5.5 ) Pub Date : 2018-01-05 00:00:00 , DOI: 10.1021/acs.macromol.7b01943
Hai Wang 1 , Chunji Wu 1 , Dongmei Cui 1 , Yongfeng Men 1
Affiliation  

The syndiotactic polystyrene (sPS) γ-to-α/β phase transition was investigated using temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurement. The sPS γ form samples, which were obtained from acetone solvent induced crystallization followed by annealing at various temperatures (Ta), exhibited a regular manner on the selection of the α or β crystal modification during the phase transition process. As the Ta was increased from 25 to 150 °C, the weight fraction of β form in bulk sPS decreased from 55% to 0%, but that of the α form increased from 45% to 100%. In other words, the α form became the dominating crystalline modification at higher Ta. The lamellar thickness (dc) of the γ form at the initial state (before heating) ranged from 4.4 to 5.8 nm, and the weight crystallinity (Xc) was between 0.52 and 0.64. However, the dc values of the γ form at the final state (before γ-to-α/β phase transition) were very close for the samples pretreated at different Tas, which were in the range 7.0–7.4 nm. Therefore, the most plausible interpretation for the crystal modification selection during the γ-to-α/β phase transition was that the nucleation of β form was suppressed totally in the γ form with higher initial dc value (>5.8 nm). With the elevated Ta and increase of initial dc, the promoted nucleation of α form in the γ form resulted in the enhanced growth of the α crystalline phase during the γ-to-α/β phase transition. As a result, after the phase transition the crystalline phase in bulk sPS had a gradually increased weight fraction of the α form and turned out to be pure α form when Ta was increased from 25 to 150 °C.

中文翻译:

间规聚苯乙烯γ-α/β相变过程中晶体变型选择的层厚厚度依赖性

使用与温度有关的同步加速器广角X射线衍射(WAXD)和小角X射线散射(SAXS)测量,研究了间规聚苯乙烯(sPS)的γ至α/β相变。sPSγ形式的样品是由丙酮溶剂诱导的结晶,然后在不同的温度(T a)下退火得到的,在相变过程中选择α或β晶型时表现出规律的方式。随着T a从25℃增加到150℃,散装sPS中β形式的重量分数从55%降低到0%,而α形式的重量分数从45%增加到100%。换句话说,α形式在较高的T a下成为主要的晶体修饰。初始状态(加热之前)的γ形式的层状厚度(d c)在4.4至5.8nm的范围内,并且重量结晶度(X c)在0.52至0.64之间。然而,在7.0至7.4 nm范围内以不同的T a s预处理的样品,最终状态(在γ至α/β相变之前)的γ形式的d c值非常接近。因此,最合理的解释是在γ到α/β相变过程中的晶体变型选择是:以较高的初始d c值(> 5.8 nm)在γ形式中完全抑制了β形式的成核。随着T a的升高随着初始d c的增加,γ形式的α形式的成核作用增强,从而导致了γ到α/β相变过程中α晶相的增长。结果,在相变之后,本体sPS中的结晶相具有逐渐增加的α形式的重量分数,并且当T a从25℃增加至150℃时变成纯α形式。
更新日期:2018-01-05
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