聚乙烯-聚矽氧烷壓克力雙親性嵌段共聚物之合成及形態鑑定

Abstract

近年來，關於雙親性嵌段共聚物的研究蓬勃的發展；不但發展出許多的製備方法，更有許多研究是利用其親疏水鏈段在極性上的差異來形成特殊之型態結構。在本論文中，主要是對雙親性嵌段共聚物PS-b-PMSMA的合成做研究，並對其morphology做探討，並可將本論文分為兩大部分： (1) 以原子轉移自由基聚合法製備不同鏈段比例及分子量之雙親性嵌段共聚物。並藉由探討各製備條件對於共聚高分子分子量大小及分佈的影響來有效的控制其成長。 (2) 觀察PS-b-PMSMA在PS選擇性溶液與PMSMA選擇性溶液中的morphology。 在本研究中， PS、PMSMA及PS-b-PMSMA雙親性高分子共聚物都已成功的使用原子轉移自由基聚合法製備，反應主要是以有機鹵化物(MBrP)作為起始劑，溴化亞銅 / 烷基胺類(PMDETA)錯合物作為觸媒系統來合成。並對製備條件及反應組成做探討，如金屬觸媒/ 起始劑的莫耳比例、單體、配位基濃度及溫度等等，藉此找出最佳之反應參數來有效控制嵌段共聚物之分子量及其分佈。由實驗的結果得到以下的結論：(1) 增加溴化亞銅含量、增加單體的含量或是降低溶劑的含量都可以明顯的提升反應之速度並維持分子量的分佈。(2) 提高溴化銅的濃度雖然會降低反應之速度，但是能有效的縮小分子量的分佈。(3) 提升反應的溫度不但能增加反應之速度，也能藉由增進起始效率來縮小分子量的分佈。目前製備的PS巨起始劑之分子量分佈(PDI)可控制在1.1以下。而PMSMA及PS-b-PMSMA之分子量分佈也均能控制在1.4以下。然而當分子量大於30000時，過高的黏度及立體障礙會使PMSMA的成長不易，且分子量分佈容易失去控制。 以穿透式電子顯微鏡來研究PS-b-PMSMA 在不同溶液系統中的型態學得到以下的結論：(1) 由於在micelle外層PMSMA 鏈段間的斥力及micelle核心的PS鏈段Tg較高的緣故，在anisole/PMSMA選擇性溶劑系統中觀察到的型態都是實心球 (2) 在anisole/PS選擇性溶劑系統中觀察到的聚集形狀較anisole/PMSMA選擇性溶劑系統中觀察到的豐富。在體積混合比為50/50和25/75的anisole/EA的混合溶液中，我們分別觀察到實心球和柱狀micelle的共存態以微胞結構(vesicle)。我們認為在這個系統中，介於溶劑和micelle核心的表面能是決定聚集形狀及大小的主要驅動力。隨著選擇溶劑的增加，χ值增加，表面能隨之增加，而造成了單位表面積a0的縮小。在我們的系統中觀察到，隨著堆積常數P(=v/a0l)的增加，micelle的形狀由sphere (P=1/3), rod-like micelle (P=1/3~1/2), 轉變到 vesicle(P=1/2~1) (3) 鏈段長度改變造成的morphology影響比溶劑造成的影響小。兩個結果的差異唯有因PS鏈段長短不同造成兩者sphere大小的不一樣。例如 PS123-b-PMSMA42 sphere(60nm)， PS95-b-PMSMA42 sphere(40~50nm)。 (4) 我們發現PMSMA鏈段會自行水解。當鹼性的催化劑加到PS-b-PMSMA的溶液中，自組裝的vesicle中會產生交聯使形狀固定，且由TEM觀察到。用1HNMR和FT-IR鑑定可以發現其分子鏈間互相交聯。由目前研究的結果來看，不同比例和極性的溶液組成、不同長度的高分子鏈段和水解催化劑的添加都可對PS-b-PMSMA的morphology產生一定的影響與改變。

Amphiphilic block copolymers have been extensively studied in recent years. They can not only be prepared by versatile synthetic approaches but also have multiple morphologies generated from its different chemical interaction between two blocks or environment. In this thesis, the synthesis and morphologies of amphiphilic block copolymer, polystyrene-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PS-b-PMSMA), are reported. Two issues will be addressed in this thesis:： (1) Control of molecular weight and its distribution, chain length and its ratio by the reaction conditions of atom transfer radical polymerization (ATRP); (2) correlation of morphology of PS-b-PMSMA with PS/or PMSMA selective mixed solvent. In this study, the homopolymers of polystyrene(PS), poly[3-(trimethoxysilyl)propyl methacrylate](PMSMA), and diblock copolymer of PS-b-PMSMA were prepared by ATRP using alkyl bromide (MBrP) and CuBr/N,N,N’,N”,N”-pentamethyldiethylene -triamine (PMDETA) as initiator and catalyst, respectively. Various reaction composition and reaction condition were used to optimize the molecular weight and its distribution, including catalyst/initiator ratio, temperature, monomer and ligand concentration, and solvent content. The experimental results suggested the following conclusions for controlling the molecular weight and its distribution : (1)Increasing the concentration of CuBr and monomer or decreasing the content of solvent enhanced the polymerization rate and maintained the narrow molecular weight distribution; (2) Enhancing the concentration of CuBr2 would decrease polymerization rate but also decrease the molecular weight distribution; (3) enhancing reaction temperature could not only increase the polymerization rate but also enhance the initiation efficiency and obviously decrease the molecular weight distribution. The polydispersity indexes (PDI) of the obtained PS macroinitiators were controlled less than 1.1, and the PDI of both PMSMA and PS-b-PMSMA were controlled lower than 1.4. However, when the polymer molecular weight higher than 30000, the propagation of PMSMA would become difficult due to the high viscosity of polymerization reaction and steric hindrance from the polymer chain. Thus, the PDI would be out of control at such high molecular weight polymer.

The morphology of PS-b-PMSMA in different solvent systems was studied by TEM. The experimental results suggested various kinds morphology from the following solvent systems: (1) The morphology observed at anisole /PMSMA selective solvent (1-Methoxy-2-propanol, MOPO) system are mainly spheres due to the strong repulsion between PMSMA corona blocks or the high Tg PS blocks at the core of micelle. (2) The morphology observed in anisole/PS selective solvent( ethyl acetate, EA) system is more versatile than PMSMA solvent/anisole system. The coexistence of sphere and rod-like micelles was observed at the anisole/EA mixed solvent with volume ratio of 50/50, and vesicles are observed at 25/75, respectively. At this system, surface energy between solvent and core is considered as the major driving force to determine size and shape of micelles. The χ increases as the selective solvent content increases and results in an enhancing the surface energy, which leads to decrease the unit surface area (a0). Hence, with the increase of packing parameter P(=v/a0l), the micelle change form sphere (P=1/3), rod-like micelle(P=1/3~1/2), to vesicle(P=1/2~1) were observed in the mixed solvent system. (3) The effect of block length on the morphology was found less significant than the effect of selective solvent. The only difference observed is the morphology size, e.g., PS123-b-PMSMA42 spheres (60nm) are larger than the PS95-b-PMSMA42 spheres size (40~50nm) due to the longer PS chain length. (4) PMSMA block was found hydrolyzed spontaneously. When a basic catalyst was added into PS-b-PMSMA solution, the vesicles formed from self-assembly of hydrolyzed polymers would be fixed, as observed by TEM. 1HNMR and FTIR analysis also suggested the crosslink of PMSMA chains. The present study suggests that the morphologies of PS-b-PMSMA could be tuned by different solvent polarity, block length or the addition of hydrolysis catalyst.