不同構形嵌段共聚高分子poly(styrene)-block- poly(4-vinyl pyridine)之合成及其形態之研究

Abstract

雙親嵌段性共聚高分子本身為具有可調控形態與特殊性質的奈米材料，於許多領域都有很好的應用前景。過去數十年中，化學合成的技術廣泛地被拓展，特別是離子聚合及自由基聚合，我們可藉由這些技術合成出特定組成、分子量及構形的共聚物。在本論文中，依照文獻裡的活性陰離子聚合結合連續單體添加法可成功製備線性嵌段型、異相條型星狀以及嵌段型星狀三種不同構形之嵌段性共聚物polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP)。但是對於此種利用DVB當作交聯劑來合成出星狀嵌段共聚物的方法，如何控制共聚物分枝數是一大課題，因此我們將藉由調控(1)活性PSLi聚合物的長度（2）反應溫度（3）[PSLi]/[DVB]莫耳比例三個方向以製備出高分枝數的PS-b-P4VP星狀嵌段共聚物。根據實驗結果我們可以知道當活性PSLi聚合物分子量越長，所造成的立體障礙越大，則接著要加入的DVB單體越不易和活性PSLi聚合物反應，因此分枝數明顯地較小。對於反應溫度而言，當溫度越高，使得反應速率也提升，因此可以使分枝數迅速提升。最後，藉由控制[PSLi]/[DVB]的莫耳比例也可以達到我們控制分枝數的目的，當每條高分子鏈之陰離子末端具有較多的DVB時，也就是當[PSLi]/[DVB]的莫耳比例較高時，將反應機率增加，進而使其分枝數增加。而當反應溫度的提升，由於其副反應，導致產物之分子量分佈變得很寬，因此須經藉由GPC將其分離。 所製備不同構形的PS-b-P4VP共聚物配製成微胞溶液，並進行下列研究：（1）改變微胞溶液其選擇溶劑品質對於微胞形態轉變之探討：當選擇溶劑濃度越高，表示溶劑品質越差導致聚集產生，但對於不同構形之PS-b-P4VP而言，線性會比星狀共聚物聚集得快，原因就是構形影響分子移動的速度，也影響了聚集的快慢。(2)在改變共同溶劑系統中，利用DMF、1,4-Dioxane和THF三種對於PS鏈段溶解度不同做微胞形態轉變之探討：在改變共同溶劑的系統中，因為共同溶劑對於PS鏈段溶解度的不同也造成了微胞形態的轉變，而由穿透式電子顯微鏡結果得知L-PS159-b-P4VP50、H-(PS158)4-b-(P4VP48)4及B-(PS172-b-P4VP37)25在不同的選擇溶劑濃度下所呈現的微胞形態皆為球型微胞，隨著選擇溶劑的加入，則其聚集尺寸及形態皆會顯著改變，所觀察之形態包括球狀微胞、囊泡狀微胞、相連球狀微胞、囊泡狀微胞、Large compound micelles等等。（3）加入酸或鹼去改變DMF/MeOH微胞溶液的pH值後，微胞形態將隨pH值不同而改變，例如微胞形態在pH=8為囊泡型;而在pH=6則為互穿網狀。且在鹼性下，微胞都會因為P4VP分子鏈和溶劑斥力的緣故使得尺寸下降。這些趨勢不論是在哪種構形下都一樣的。

Amphiphilic block copolymers have stimulated significant scientific interest since they offer the possibilities to nanoscale materials with tunable morphology and properties. Living polymerization, such as living ionic and controlled free radical methods are generally employed to synthesize block copolymers with well defined compositions, molecular weights and structures of very elaborate architectures. In this study, the synthesis of amphiphilic block copolymers of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) and polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) with different architectures were explored. Then, the morphologies of linear, heteroarm, and blockarm PS-b-P4VP were studied with different solvent quality. In the synthesis of polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP), the issues of controlling arm numbers was investigated by the following three factors: (1) the chain length of living PSLi; (2)reaction temperature; (3)[PSLi]/[DVB] molar ratio. The experimental results suggested that the larger chain length of living PSLi led to the low arm number of heteroarm PS-b-P2VP due to the steric effect. The arm numbers was elevated rapidly at a high temperature. The higher [PSLi]/[DVB] molar ratio results in high probability of living PSLi chains reacted with the DVB monomers, which led to the enhancement of arm numbers of star copolymers. The control on the arm number of star PS-b-P4VP had a similar conclusion as that of PS-b-P2VP. Relatively low PDI on the synthesized block copolymers could be obtained through the GPC fractionation. The morphology of the prepared PS-b-P4VP copolymers was studied on the following issues: (1) the effect of selective solvent (MeOH or H2O)on crew-cut aggregates：The results of static light scattering (SLS) showed that linear PS-b-P4VP copolymers aggregated easier than the heteroarm analog since the linear architecture moved faster; (2) the effect of the common solvent (DMF, dioxane, or THF) on the micelle morphology: The experimental results suggested that spherical micelles were observed in all three architectures of PS-b-P4VP regardless on the variation of the DMF/methanol. Aggregation morphology could also be changed with different common solvent quality based on their solubility with PS. The observed morphology include sphere、vesicle、connected sphere、Large compound micelles. The morphology transformation for the linear architecture is faster than that of the star architecture. (3) The effect of pH value on the aggregation morphology: the TEM images showed that the aggregation morphology of the PS-b-P4VP copolymers changed with different pH condition. For example, vesicle morphology was observed at pH=8 but interpenetrating morphology was shown at pH equal to 6. Reduced aggregation size was exhibited fro all three kinds of block copolymers due to the increased repulsion between P4VP chain and solvent.