臺灣博碩士論文加值系統

本篇論文是利用多重結晶性嵌段共聚物PEO-PCL-PLLA，經由控制結晶溫度和溶劑誘導時間來研究在薄膜狀態下的結晶行為，由DSC和in-situ WAXD結果確定PEO、PCL、PLLA鏈段都會結晶，再藉由TEM及SAED來探討薄膜狀態下的形態和繞射分析。在溫度誘導的過程中，都只能得到單一結晶層板，無法獲得雙層或三層的結晶層板，亦即在高溫結晶可以得到PLLA的單晶，室溫可以得到PCL的單晶，而在低溫結晶則可以得到PEO的單晶，然而，只要其中一個鏈段先結晶，之後不管怎麼調控溫度都無法再讓另外兩個鏈段結晶，這是因為先結晶的鏈段會形成一個堅固的結晶層板，而這個結晶層板會對其他鏈段造成局限效應，使另外兩個鏈段在溫度的控制下也無法結晶，所以在溫度誘導的製程最終只能得到單一鏈段結晶所形成的單晶。從SAED中可以分析結晶方向性，PLLA和PCL兩個結晶方向性的方向都是垂直基材表面的；在較低溫成長的PEO則是出現平行基材表面的現象。
此外，我們利用溶劑誘導的方法，選用不同的溶劑和誘導的時間來製備單晶，然而在溫度調控下無法得到的雙層和三層的結晶層板，在溶劑誘導的製程中可以利用時間的調控來得到。我們選用三種溶劑，分別是chlorobenzene，toluene和n-hexanol，其中chloobenzene對PEO和PCL都是相容性很好的溶劑；toluene則是較偏PCL選擇性溶劑，但是chlorobenzene和toluene對PLLA都是溶解度很差的溶劑；n-hexanol則是PLLA選擇性溶劑且對PCL是溶解度很差的溶劑。在chlorobenzene和toluene溶劑誘導結晶的過程中，結晶的順序是由PLLA先聚集結晶誘導PCL結晶，PCL再誘導PEO結晶，即PLLA→PCL→PEO，而在n-hexanol誘導結晶的過程中則是PCL先結晶在誘導PLLA結晶，即PCL→PLLA，這邊PEO不會結晶是因為PEO和n-hexanol都具有極性，n-hexanol對PEO溶解性很好使得PEO無法結晶，此結晶順序在另一個PLLA分子鏈較短不會結晶的樣品PEO-PCL-PLLA也可以得到，由此可知，在溶劑誘導結晶的過程中，結晶的順序性和溶劑的相容性有很大的關係。和前段溫度控制不同，利用溶劑誘導出來的單晶，單層、雙層、三層結晶層板中的PLLA，PCL和PEO的結晶方向性都是垂直於基材表面。
最後，我們發現PLLA和PCL有磊晶的現象，兩個結晶的a軸互相夾0o和90o的磊晶，還有夾角是30o的”soft epitaxy”，這是利用PLLA的(110)結晶面和PCL的b軸相互平行而磊晶；PCL和PEO也有磊晶的現象，互相夾20o，利用PEO的(120)結晶面平行PCL的(110)結晶面磊晶，稱作”soft epitaxy”。

In this study, crystal growths of multiple-crystalline poly(ethylene oxide)-block-poly(ε-caprolactone)-block-poly(L-lactide) (PEO-PCL-PLLA) triblock copolymers in thin films are investigated by melt and solvent-induced crystallizations. Differential scanning calorimetry (DSC) and in-situ wide angle X-ray diffraction (WAXD) results indicate that the PEO, PCL, and PLLA blocks are able to sequentially crystallize in bulk state. The crystalline morphologies of the PEO-PCL-PLLA in thin films were explored using transmission electron microscopy (TEM) associated with selected-area electron diffraction (SAED). Only single crystallization of PLLA, PCL or PEO, i.e., one of the blocks is crystallizable and the others are non-crystalline, can be found in the melt-crystallized PEO-PCL-PLLA thin films. This might be due to a crystalline template driven by the first-crystallized block, giving a robust confined environment for the subsequent crystallization. Notably, the PLLA and PCL single crystals with flat-on orientation (i.e., c-axis is perpendicular to substrate surface) can be observed, whereas the PEO single crystal possess edge-on (i.e., c-axis is parallel to substrate surface) orientation due to low crystallization temperature. Most interestingly, single- double- or/and triple-crystalline morphologies can be observed in the PEO-PCL-PLLA thin films by solvent-induced crystallization. After solvent annealing by neutral chlorobenzene and PCL-selective toluene, the development of crystalline morphologies from single to double and to triple crystallization in sequence, that is PLLA → PCL → PEO, is carried out due to solvent selectivity. By contrast, after solvent annealing by n-hexanol, the evolution of crystalline morphologies from single to double crystallization in sequence, that is PCL → PLLA, is accomplished. The non-crystalline PEO block is attributed to strong polar interaction between PEO and n-hexanol, giving rise to dissolution of the PEO. Similar crystalline tendency can be observed in the PEO-PCL-PLLA BCP thin film having non-crystalline PLLA block due to short chain length. In contrast to melt crystallization, the solvent-induced formation of single crystals all exhibit flat-on chain orientation consistent to that obtained from solution crystallization. Most interestingly, these solvent-induced crystalline morphologies exhibit epitaxial crystallization associated with the crystallization sequence. In the double-crystalline morphologies, i.e., PLLA → PCL or PCL → PLLA, two cases with the angle θ = 0o or 90o between aPLLA and aPCL are found, indicating the lattice matching between the PLLA and PCL crystals. In addition, the angle θ = 30o between the aPLLA and aPCL, in which the dimension of (110)PLLA is almost identical to bPCL, is obtained, namely, “soft epitaxy”. In the triple-crystalline morphologies, the third-crystallized PEO exhibits soft epitaxy with the preformed second-crystallized PCL crystal, in which the growth plane of (120)PEO is parallel to that of (110)PCL. As a result, the control of crystalline morphologies associated with different crystallization sequences and chain orientations can be achieved in the multiple-crystalline PEO-PCL-PLLA thin films by melt and solvent-induced crystallizations.

摘要...................................................................................................................................I
Abstract...........................................................................................................................III
Table of Contents...........................................................................................................VI
List of Tables..................................................................................................................IX
List of Figures..................................................................................................................X
Chapter 1. Introduction....................................................................................................1
1.1 Self-assembly............................................................................................................1
1.2 Self-assembly of Block Copolymers..........................................................................2
1.3 Crystalline Diblock Coplymers...................................................................................4
1.3.1 Microphase-Separated Morphology of Semicrystalline BCPs................................4
1.3.2 Double Crystalline BCPs.........................................................................................7
1.4 Polymeric Single Crystal............................................................................................8
1.4.1 Single Crystals from Self-assembly of Homopolymers...........................................8
1.4.2 Single Crystals from Self-assembly of Block Coplymers......................................14
Chapter 2. Objectives....................................................................................................21
Chapter 3. Materials and Experimental Methods...........................................................23
3.1 Materials..................................................................................................................23
3.1.1 Synthesis of Poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(L-lactide) (PEO-PCL-PLLA).....................................................................................................................23
3.1.2 Sample Preparation..............................................................................................24
3.1.2.1 Bulk Samples Prepared by Solution Casting.....................................................24
3.1.2.2 Thin Films Prepared by Spin Coating ................................................................25
3.2 Characterization of Multiple-Crystalline Block Copolymers.....................................25
3.2.1 Differential Scanning Calorimetry (DSC)..............................................................25
3.2.2 Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Diffraction (WAXD)..........................................................................................................................26
3.2.3 Transmission Electron Microscopy (TEM)............................................................27
Chapter 4. Results and Discussion................................................................................29
4.1 Crystallization Behaviors of PEO-PCL and PEO-PCL-PLLA...................................29
4.1.1 Crystallization Sequence......................................................................................29
4.1.2 Isothermal Crystallization......................................................................................36
4.2 Self-assembled Morphology....................................................................................38
4.3 Melt-Crystallized Morphology in Thin Film...............................................................42
4.3.1 Crystallization of PEO5-PCL3 in Thin Film...........................................................42
4.3.2 Crystallization of PEO5-PCL3-PLLA6 in Thin Film...............................................44
4.4 Solvent-Induced Crystallization in BCP Thin Film....................................................54
4.4.1 As-spun Thin Film Morphologies..........................................................................55
4.4.2 Morphologies after Solvent Annealing by Neutral Solvent for PEO and PCL blocks.............................................................................................................................56
4.4.3 Morphologies after Solvent Annealing by PCL-selective Solvent.........................62
4.4.4 Morphologies after Solvent Annealing by PLLA-selective Solvent.......................66
4.5 Epitaxial Crystallization............................................................................................72
Chapter 5. Conclusions..................................................................................................79
Chapter 6. References...................................................................................................82

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