臺灣博碩士論文加值系統

本實驗係利用固定分子量5000的聚乙二醇單甲基醚(MePEG)，藉由加入不同比例的左旋乳酸單體(L-Lactide)，合成出不同鏈段長度的PLLA—MePEG雙結晶性共聚合物，並與PLLA均聚物比較於不同等溫結晶溫度結晶完成樣品之結晶熱力學、動力學性質與結構差異。
首先使用微差掃描熱卡計(DSC)將3種PLLA—MePEG共聚合物與PLLA均聚物於不同的溫度使PLLA鏈段結晶，根據Hoffman-Weeks方程式得到樣品之平衡熔點，發現到PLLA鏈段愈長的樣品，平衡熔點愈高。而利用樣品於各溫度下結晶之熔融曲線，可計算出樣品於該結晶溫度時的絕對結晶度，發現到PLLA鏈段於中過冷度時，因遠離樣品的玻璃轉換溫度與熔點，故結晶度會達到一極大值。接著由樣品的結晶放熱曲線計算出樣品結晶完成比例與時間的關係，將此曲線以Avrami方程式進行模擬配置，可得之樣品的結晶速率(G)與Avrami指數(n)，由G值可知PLLA均聚物與PLLA—MePEG共聚物隨著結晶溫度的提高，結晶速率會提高而後降低，由此可證明結晶的成核成長機制，而由n值得知，本實驗中的樣品，其結晶形態皆為球晶。而在樣品的熔融過程中，發現到PLLA有雙重熔融峰的存在，為了證明此雙重熔融峰為PLLA的再結晶行為所造成，嘗試改變結晶溫度與升溫速率，發現在高結晶溫度及高速升溫的情況下，PLLA的高溫熔融峰會逐漸減弱甚至消失，由此可證明PLLA再結晶的現象。
由DSC實驗中以模擬配置得知樣品的結晶形態為三維球晶，接著使用偏光顯微鏡(POM)直接觀察樣品的球晶形態，在實驗中除了證明PLLA結晶確實為球晶，且發現不同的結晶—非晶比例與結晶溫度會導致球晶內部形態產生變化，形成標準、同心圓環狀與樹枝狀球晶，而於25℃時，得知MePEG鏈段受到PLLA鏈段共價鍵的束縛，並不會生成獨立球晶，僅能於PLLA球晶間隙形成散亂的結晶。
研究PLLA均聚物與PLLA—MePEG共聚合物之結構，首先使用廣角X光繞射儀(WAXD)，討論PLLA分子鏈排列的結晶繞射平面分析與晶格常數計算，發現受到MePEG鏈段結晶的影響，共聚合物中PLLA的分子鏈間距較PLLA均聚物為大，且隨著MePEG的含量提高，MePEG鏈段造成的結晶繞射峰更加明顯，因此若利用模擬配置的方式分析樣品各成份之結晶度，則可知樣品中MePEG含量愈高，MePEG所貢獻的結晶度愈高。
為了得知PLLA均聚物層狀結構，使用小角X光散射(SAXS)並搭配一維相關函數轉換，利用圖形中的切線值，可得到PLLA非晶層的厚度，而圖形中的極大值則為PLLA的長週期，兩者相較之下，可得到PLLA均聚物在不同結晶溫度下結晶層與非晶層厚度，因此可計算出樣品的線性結晶度(XCL)與結晶層於樣品中比例(XL)，接著使用兩種層狀結構模型計算散射不變量的理論值，與由實驗所得之散射不變量進行比較，可確定樣品接近何種模型描述之結晶形態。而在共聚合物方面，則是自行建立出一結晶模型，將所有由一維相關圖形中所得之尺寸代入模型中，可得到各層尺寸與兩成份之線性結晶度與結晶層比例，發現共聚合物中PLLA完全形成層狀形態，無獨立之非晶區域存在，最後將兩種散射不變量模型公式分別改寫，並與實驗值相比可確定適合的層狀結構模型為少量MePEG非晶區域夾雜於共聚合物的層狀結構中。

We study the crystallztation behavior and analyze the structures of crystalline diblock PLLA-MePEG copolymers. In particular, we employ Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM), Wide-Angle X-ray Diffraction (WAXD), Small-Angle X-ray Scattering (SAXS) experiments.
With DSC, we observe that the equilibrium melting point of PLLA decreases with decreasing PLLA molecular weight. This is due to the fact that as PLLA molecular weight increases, the thickness of formed lamellar stacks increases and therefore it is necessary to meet the lamellar stacks at a higher temperature.As crystallization temperature (Tc) increases, the crystal growth rate (G) of pure PLLA first increases and reaches a maximum at Tc~105℃, and then decreases. This is not surprising due to the competition between nucleation and growth mechanisms. With decreasing the composition of PLLA (fPLLA) to the value of 0.61, the crystal growth rate of PLLA reaches a maximum at Tc~95℃. However, as fPLLA<0.61, G keeps decreasing with increasing Tc, which manifests the fact that the PLLA crystallization is determined by the nucleation mechanism. Similar behavior is observed for PLLA crystallinity (Xc) v.s. crystallization temperature (Tc). It is worthy to note that the relative crystallinity of PLLA, i.e., , is close to fPLLA in the region of high crystal growth rates.
With POM, weobserve that with decreasing the PLLA molecular weight (i.e., increasing the amount of amorphous MePEG), the crystal morphology of PLLA transforms from Spherulites→Ringed spherulites→Dendrite spherulite.
With WAXD, we examine the effects of MePEG on the crystal system as well as the unit cell parameters and PLLA crystallinity. As expected, the crystalline PLLA forms orthohombic system for both pure homopolymer and copolymer system. However, in the percent of MePEG, the value of a,b which are characteristic of distance between PLLA chains, increases about 2%, and the value of c decreases about 1%. The PLLA crystallinity determined by WAXD shows similar trends by DSC.
With SAXS, we successfully determined the long period (L) and each crystalline and amorphous layer thickness of both PLLA and MePEG components. As Tc increases, all values of lc, la and L for pure PLLA increases; while they remain constants for PLLA-MePEG copolymer systems with fPLLA=0.61. At a fixed Tc, when fPLLA decreases, both L and LMePEG increases and LPLLA decreases. This is due to the fact that PLLA molecular decreases. Therefore, lc,PLLA decreases and la,PLLA increases. Also XCL,PLLA decreases with fPLLA decreasing; however, the volume fration of PLLA lamellar stacks XL,PLLA increases from 0.8 to 1. Similarly, both XCL,MEPEG and XL,PEG decrease with increasing fPLLA. Finally, we compared a larger amorphous regions scattering model and a smaller amorphous regions model from invariant Q with r(0), and discovered the trends of smaller amorphous regions model is very closed to r(0). It is easily to determine the crystallization model of pure PLLA. In PLLA-MePEG copolymer system, we extend two theory models of invariant Q. As pure PLLA, compared two models with r(0), and determined the crystallization model of PLLA-MePEG copolymer is the smaller amorphous regions model.

中文摘要…………………………………………………………………….I
英文摘要…………………………………………………………………..III
誌謝…………………………………………………………………………V
目錄………………………………………………………………………..VI
圖目錄……………………………………………………………….…..VIII
表目錄……………………………………………………………….…....XV
第一章 緒論……………………………………………………..................1
1.1 前言………………………………………………………….........1
1.2 研究背景與動機………………………………………………….4
第二章 實驗部分………………………………………………………….11
2.1 聚合反應…………………………………………………………11
2.2 光譜與分子量分析………………………………………….…...14
2.2.1 核磁共振光譜分析……………………………………….…..14
2.2.2 凝膠滲透層析儀………………………………………….…..16
2.3 微差掃描熱卡計…………………………………………………20
2.3.1平衡熔點與絕對結晶化度……………………………….…...20
2.3.2 結晶動力學與相對結晶化度…………………………….…..22
2.3.3 再結晶行為……………………………………………….…..25
2.4 偏光顯微鏡………………………………………………………28
2.4.1 球晶型態觀察………………………………………….……..28
2.4.2 平衡熔點………………………………………………….…..29
2.5 廣角度X光繞射…………………………………………….…...30
2.5.1 結晶平面與晶格常數………………………………………...30
2.5.2 結晶化度……………………………………………………...31
2.6 小角度X光散射…………………………………………………37
2.6.1小角度X光散射基本理論…………………………………..37
2.6.2結晶層狀結構的小角度X光散射分析……………………..38
第三章 結果與討論………………………………………………………46
3.1微差掃描熱卡計………………………………………………….46
3.1.1 結晶動力學與平衡熔點之分析與量測………………...…....46
3.1.2 結晶度分析…………………………………………………...73
3.1.3 再結晶行為之研究…………………………………………...81
3.2 偏光顯微鏡………………………………………………………85
3.2.1 球晶型態分析………………………………………………...85
3.2.2 平衡熔點量測………………………………………………...96
3.3 廣角度X光繞射…………………………………………………99
3.3.1 結晶平面與晶格常數分析…………………………………...99
3.3.2結晶度分析…………………………………………………..112
3.4 小角度X光散射………………………………………………..116
3.4.1 長週期與結晶層厚度分析………………………………….116
第四章 結論……………………………………………………………...139
第五章 參考文獻……………………………………………………...…145
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