Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3283
標題: Metastability Studies of Syndiotactic Polystyrene Polymorphism
對位聚苯乙烯多形結構之介穩定性探討
作者: 林建邦
Lin, Chien-Pang
關鍵字: Polymorphism;多形結構;structural metastability;morphological metastability;equilibrium melting temperature;stability inversion phase;結構介穩定性;形態介穩定性;平衡熔點;相穩定性轉換
出版社: 化學工程學系
摘要: 
ABSTRACT
Syndiotactic polystyrene (sPS) exhibits a very complex polymorphic behavior in crystal structure. Two types of melt-crystallized crystal structures have been identified, and described in terms of αand β, both containing the planar-zigzag conformation of backbone chain. The crystalline βform is characterized by orthorhombic chain packing, whereas the crystalline αform is characterized by trigonal chain packing. Two types of solvent-induced crystal structures have also been found. They are γ and δ both containing the helical conformation of backbone chains. In this study, the development of α and β forms of melt-crystallized syndiotactic polystyrene, sPS, has been examined by structure analysis of FTIR (Fourier transform infrared spectroscopy), WAXD (wide angle X-ray diffraction) and ED (electron diffraction) as well as thermal analysis of DSC (differential scanning calorimetry). Significant factors, such as the maximum annealing temperature (Tmax), crystallization temperature (Tc), crystallization time (tc) that influence the formation of polymorphism, were examined and described. According to the experimental results, it was noted that the Tmax for melt crystallization seems the primary factor to determine the formed structure. The probability for formation of α crystals becomes greater for samples treated at lower Tmax. It was also interesting to discover that the formation of mixed forms is dependent upon the crystallization temperature and time. The shorter the crystallization time or the lower the crystallization temperature, the larger the fraction of α crystals. When the crystallization time is long enough, there is only β form crystals left. However, the effect of crystallization time on the population of mixed forms become insignificant while the Tmax is above 340oC. Isolated α crystals and β crystals of sPS crystallized at different crystallization temperatures from the melt were thus obtained. The equilibrium melting temperatures, Tmo, of both forms were determined by using linear Hoffman-Weeks (H-W) extrapolation and non-linear H-W treatment. The Tmo (i.e., structural metastability) of β form in sPS was found to be higher than that of α form. The occurrence of phase stability inversion with lamellar size (i.e., morphological metastability) in sPS was recognized. Transformations from α to β phase in the stage of crystal growth or in the heating scanning process have been evidenced. The interlinkage of structural metastability and morphological metastability in sPS polymorphism was examined. The behavior of phase transformation has been successfully interpreted in terms of the stability inversion phase diagram. The formation of the α form is indeed a kinetic result of crystallization.

摘要
對位聚苯乙烯(syndiotactic polystyrene, sPS)為一具有多形結構之結晶性高分子,其結晶構造極為複雜,隨結晶環境的不同而有四種不同的結晶結構α、β、γ及δ,其中α及β又因其排列完整性之不同而細分為α’ 及α”、β’及β”。α和β的結晶構造為平面之zig-zag結構,其分子鏈之排列方式(chain packing)分別為三角柱體排列之三方晶(trigonal) 結晶及長方體排列長方晶(orthorhombic)結晶,一般於熔融結晶時形成,而γ及δ的結晶構造為立體之螺旋結構僅在溶劑誘導(solvent-induced)下形成。本實驗針對α及β兩種結晶結構進行其結晶相介穩定性(metastability)之探討,由於形成此多形結構的因素相當複雜,研究重點在於首先利用廣角X光繞射圖譜(wide angle X-ray diffraction, WAXD)、傅立葉轉換紅外線光譜(Fourier transform infrared spectroscopy, FTIR)以及穿透式電子顯微鏡(Transmission Electron Microscope, TEM)之電子單晶繞射圖譜(electron diffraction, ED)分析不同熔融結晶條件下所形成之結晶結構,並結合微差掃瞄熱卡(differential scanning calorimetry, DSC)之結晶及熔融行為的分析,探討多形結構之形成條件及控制因子,歸納形成多形結構的成因,以期獲得在不同結晶溫度下以熔融等溫結晶方式所形成之單一α結晶結構及單一β結晶結構之熔解行為,依等溫結晶溫度對應熔解溫度的相關性,利用線性Hoffman-Weeks外插圖形法及非線性Hoffman-Weeks之數據處理方式,決定α結晶結構及β結晶結構之平衡熔點(Tmo),依據平衡熔點的差異推論多形結構之結構介穩定性(structural metastability)的高低。實驗結果發現,β結晶結構之平衡熔點不論以線性或非線性Hoffman-Weeks方式求得之結果皆高於α結晶結構之平衡熔點。
由於結晶相之介穩定性包括結構介穩定性與形態介穩定性(morphological metastability),藉由平衡熔點之測定結果,將可鑑定α相與β相之結晶結構介穩定性,由本次實驗結果發現β相之結構介穩定性較α相之結構介穩定性高,但熔解實驗結果卻發現相同等溫結晶下成長之β相熔點較α相之熔點低,此結果顯示結構介穩定性高的β將可能因形態介穩定性的影響而成為較不穩定的結晶相,此一有趣之結晶相介穩定性變換行為與Keller及Cheng利用熱力學所推演提出,“相穩定性之反轉 (phase stability inversion)模型”完全吻合。由實驗結果結合相穩定性反轉行為的分析,本研究提出另一造成多晶結構的機制,有別於結晶核之記憶效應,α結晶相的形成乃是由於結晶動力的因素所造成。
另外,本研究亦由穿透式電子顯微鏡之電子繞射圖譜、傅立葉轉換紅外線光譜及廣角X光繞射圖譜之結構鑑定結果發現α結晶結構(三角柱體排列之三方晶)可進行轉換而成為β結晶結構(長方體排列之斜方晶),且由實驗結果中發現,此一結構上之轉換機構包括:熔融等溫結晶後升溫過程中所產生之結構上轉換以及等溫結晶時之固態-固態結構轉換,實驗結果亦證實此種相轉換的行為乃是一不可逆相轉換的現象。
URI: http://hdl.handle.net/11455/3283
Appears in Collections:化學工程學系所

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