Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3462
標題: Crystallization Effects on the Morphology of PS-PLLA: from Hard Confinement to Soft Confinement
結晶效應對於PS-PLLA形態的影響:從硬相侷限至軟相侷限之探討
作者: 林芳禾
Lin, Fang-Ho
關鍵字: crystallizable block copolymer;結晶性團聯共聚合物;crystallization;spatial confinement;hard confinement and soft confinement;large scale orientation;結晶;空間侷限;硬相侷限與軟相侷限;大範圍排整
出版社: 化學工程學系
摘要: 
摘要
本研究成功合成結晶性高分子團聯共聚合物聚苯乙烯與聚左旋乳酸之雙團聯共聚合物(Polystyrene-block-poly(L-lactide),PS-PLLA)
,利用溶劑塗佈方式及升溫除核步驟形成微觀相分離,經由體積分率的調控可製備出具有有序層板微結構,並且藉由熱分析的測定而逐漸建構出結晶性團聯共聚合物PS-PLLA的相圖。對照文獻中PS-PLA之間的作用參數(χ)與溫度(T)的關係,推導其TODT相對地高於結晶性團聯PLLA結晶溫度範圍,且結晶溫度範圍跨越非結晶團聯PS的玻璃轉化溫度,同時涵蓋硬相侷限(hard confinement)與軟相侷限(soft confinement)的結晶環境。然而由於邊界的存在會造成結晶驅動力對於最終形態變化的變因增加,本實驗乃針對此一系統比較在無規則性的排整與具有大範圍排整之PS-PLLA的層板微結構,從硬相侷限到軟相侷限時其非結晶團聯鏈段玻璃轉化溫度對於結晶驅動力侷限作用的影響,而導致最終形態上的差異。
首先將無序排整的PS-PLLA團聯共聚合物於硬相侷限 (Tc,PLLA< Tg,PS) 環境下進行結晶時,結晶性團聯PLLA受到非結晶團鏈PS的牽制效應,固有的相分離層板微結構其最終形態將不受影響,反之在軟相侷限(Tc,PLLA≧Tg,PS)環境時因非結晶團聯PS的牽制效應降低,結晶性團聯PLLA結晶造成層板微結構的扭曲變形而導致特殊的波動形態,然而有別於一般文獻之觀察結晶後微結構形態完全受到破壞,此時結晶仍處於侷限環境,但相對於具有大範圍排整的層板微結構中,在硬相侷限系統下進行結晶後仍呈現一侷限的形態,而由於具有完全延伸的一維空間侷限,使得在軟相侷限下結晶驅動力對於層板微結構界面的影響減少,而導致僅在界面上形成扭曲形態。另一方面,將具有大範圍排整的試片配合同步輻射的小角度散射與廣角度繞射實驗,推導相對於PS-PLLA層板微結構的界面之PLLA結晶分子鏈的排列方式,進而瞭解結晶成長延伸方向與形態變化上的幾何關係,而在實驗結果中,於結晶性團聯共聚合物PS-PLLA所形成的層板微結構,其PLLA結晶分子鏈從硬相侷限至軟相侷限時皆是呈現垂直層板界面,顯示在熱力學上具有較穩定的排列方式。綜合實驗結果,我們推論在進行結晶時的核種來自於邊界且其成長延伸的方向為平行層板界面,以致於層板界面受到結晶所產生的內應力推擠,使得層板微結構必須調整其界面以消除應力,但由於強偏析的限制而無法造成破壞,而形成具有特殊波動形態。
而在不同的溫度下進行等溫結晶時,結晶性團聯共聚合物PS- PLLA所對應的熔點會遠低於均聚合物PLLA,意味著結晶層板形成受到奈米空間侷限的影響,造成厚度成長的侷限,但就PS-PLLA的系統中可發現到經過PS團聯鏈段的玻璃轉換溫度時,其熔點之變化並非以線性上升的方式,表示非結晶團聯鏈段的牽制程度的不同,亦會反映在結晶層板厚度的形成。經由傳統的Avrami的分析法進行均聚合物PLLA與具有大範圍排整的PS-PLLA層板微結構的結晶機構的模擬,對於均聚合物PLLA的Avrami Index和偏光顯微鏡的形態觀察可得知其結晶機構為異質成核(heterogeneous nucleation)機制。對於較低溫的硬相侷限的成核機制偏向於均質成核,而當等溫結晶的溫度越過非結晶團聯鏈段PS的玻璃轉換溫度時,由於結晶造成層板界面產生扭曲而形成界面上的缺陷,而此缺陷的存在進而形成結晶所需的核種,使得在高溫的軟相侷限下之結晶轉而趨向於異質成核機制。

Abstract
Crystallizable diblock copolymers, polystyrene-b-poly(L-lactide)) (PS- PLLA), have been synthesized by living free radical polymerization and ring opening polymerization in sequence. Microphase-separated lamellar morphology was identified by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The predicted order-disorder transition temperature (TODT) is relatively higher than crystallization temperature for PLLA block (TC,PLLA); crystallization of PLLA blocks thus carries out under strong segregated microdomains so as to encounter spatial confinement. Owing to the glassy transition of PS block (Tg,PS) occurring in the range of PLLA crystallization window, PLLA crystallization might conduct from hard confinement (Tc,PLLA As evidenced in our pervious results, confined morphology for crystallized PS-PLLA was observed while Tc,PLLA To prove the suggested mechanism, crystallization and melting behavior of PLLA from hard confinement to soft confinement were studied. The crystallization mechanisms of PLLA under 1-D spatial confinement were analyzed in accordant with Avrami treatment of exothermic response. Crystallization under hard confinement tends toward homogenous nucleation, whereas heterogeneous nucleation gradually dominates under soft confinement due to the increase of chain mobility; leading to undulation of morphology.
Because of the growth of PLLA crystals under confinement, the melting point of PS-PLLA copolymer is lower than that of PLLA homopolymer. Also, Tm exhibits an increase when TC passes over the glass transition temperature of PS block. This observation further confirms that the growth of PLLA crystals is strongly dependent upon the glass transition temperature of PS.
URI: http://hdl.handle.net/11455/3462
Appears in Collections:化學工程學系所

Show full item record
 

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.