本研究使用聚乙二醇單甲醚與左旋-丙交酯以開環聚合方法合成聚乙二醇單甲醚-聚乳酸(mPEG-PLLA)雙團聯共聚物。將其中親水段mPEG聚合度固定為113，並合成兩種PLLA疏水段(聚合度為308及96)的共聚物。首先利用凝膠滲透層析儀(GPC)和質子核磁共振儀(1H-NMR)對共聚物進行分子量與特徵結構的分析。
共聚物加入去離子水和電解質(NaCl或NaI)水溶液中，並改變電解質濃度及溶液的環境溫度，使用螢光探針法量測臨界微胞濃度，利用臨界微胞濃度計算其微胞化熱力學參數。接著以動態光散射儀(DLS)、穿透式電子顯微鏡(TEM)測量微胞粒徑。探討溫度、電解質濃度、電解質物種及高分子疏水鏈段聚合度對臨界微胞濃度、微胞化熱力學性質及微胞粒徑之影響。
實驗發現臨界微胞濃度隨著溫度上升而增加；隨著疏水鏈段聚合度愈大而下降。當電解質濃度增加時，臨界微胞濃度下降，其中最特別的是，在低濃度(0~ 0.005 M)的NaI水溶液中，臨界微胞濃度已有較大量降低，至0.1~ 0.5 M，下降則較不明顯。利用salting係數(ks)來比較不同共聚物在不同的電解質溶液中salting效果，得知ks隨著溫度上升而增加；共聚物的疏水鏈段聚合度減小，salting係數會增加，鹽析(salting out)效果愈明顯。共聚物在NaI溶液測得ks較大，對臨界微胞濃度有明顯影響。
微胞化熱力學參數的計算結果得知，隨著電解質濃度上升，微胞化自由能(負值)之絕對值及微胞化熵(正值)增加，而微胞化焓(負值)之絕對值會減少。微胞化自由能為負值，表示共聚物在水溶液中的微胞化為自發性過程，且是由微胞化熵所主導。共聚物中PLLA鏈段聚合度愈大，微胞化自由能及微胞化焓之絕對值隨之愈大。且微胞化自由能和熵受到碘化鈉的影響較氯化鈉明顯；△Hmic值在NaCl溶液中的變化較明顯。
DLS測得微胞平均粒徑隨電解質濃度上升；電解質濃度較高時，微胞產生聚集。由於TEM測量經乾燥脫水而收縮的微胞，得到小於DLS測得微胞粒徑。接著分析微胞標度關係後，得知共聚物在純水中的標度指數(a)為0.23，介於0.16 ≤ a ≤ 0.67的極限範圍；標度指數隨著NaCl濃度上升而增加，表示共聚物鏈段在溶液中傾向於crew-cut。

This study is methoxypoly(ethylene glycol)-poly(L-lactide) (mPEG-PLLA) diblock copolymers were synthesized by ring-opening polymerization of L -lactide in the presence of mPEG. Copolymers with fixed mPEG length (degree of polymerization= 113) and various PLLA segment lengths (degree of polymerization= 308 and 96). Above all, the copolymers were characterized by using gel permeation chromatography (GPC) and 1H-NMR.
We use fluorescent probe to determine the critical micelle concentration (CMC) of diblock copolymer solutions with various concentrations of sodium chloride or sodium iodide at 25 to 45℃, and calculate subsequently thermodynamic parameters of micellization. Also, the micelle size is measured with dynamic light scattering (DLS) and transmission electron microscopy (TEM). We research the effects of degree of polymerization, electrolyte species and concentrations on the critical micelle concentration, thermodynamic properties of micellization and the particle size of micelles.
Experimental results show that critical micelle concentration increase with rising temperature, and decrease with increasing the degree of polymerization of hydrophobic block chain. The CMC value is lower with the higher concentration of electrolyte solution. It should not be neglected that various CMC are dramatically in the range from 0 to 0.005 M NaI solutions, and CMC tend to be less significant in the range from 0.1 to 0.5 M NaI solutions.
The salting coefficient (ks) is used to signify the effect of salting in solutions of various electrolytes and diblock copolymers. It is indicated that the salting out effect is pronounced as the salting coefficient increases with rising temperature, decreasing the degree of polymerization of hydrophobic block in copolymer. The greater value of salting coefficient on NaI solution means the electrolyte effect on CMC is more pronounced.
Calculated thermodynamic parameters of micellization show that the absolute values of Gibbs energy of micellization (△Gmic, negative value), entropy of micellization (△Smic, positive value) increase but enthalpy of micellization (△Hmic, negative value) decreases with electrolyte concentration. The negative Gibbs energy indicates that micellization process is spontaneous and the micellization is driven by entropy. There are absolute values of △Gmic and △Hmic increasing with increasing the degree of polymerization of PLLA chain. Moreover, △Gmic and △Smic are affected more significantly by sodium iodide than sodium chloride. △Hmic is affected in the opposite way.
DLS experiment reveals the mean size of micelle increases with increasing the electrolyte concentration. The micelle size determined by TEM is smaller than by DLS due to dehydration and shrinkage during drying. The index (a) of scaling in pure water is 0.23 by analyzing scaling relation of micelle size against hydrophobic segment length, which is in the limiting range of 0.16 to 0.67. The effect of NaCl concentration on the micelle size makes the index of scaling increase, indicating the chain of polymer in electrolyte solution tends to be the crew-cut.

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