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(methoxypoly(ethylene glycol)-poly(L-lactide))(mPEG-PLLA)雙團聯共聚物。將其中親水段mPEG聚合度固定為113，並合成三種PLLA疏水段(聚合度為35、60和98)的共聚物，利用凝膠滲透層析儀(GPC)對共聚物進行分子量的分析。使用翻轉試管法觀察不同疏水長度共聚物在水中的水溶性並測量臨界成膠濃度，利用流變儀量測共聚物不同濃度下之凝膠溶體相變化溫度，將相變化之實驗數據加上Flory-Huggins均場理論模型建立預測的相圖。使用螢光探針法量測臨界微胞濃度，證明在本研究共聚物濃度範圍內有微胞相的存在，並以動態光散射儀(DLS)測量共聚物在水中不同濃度、溫度下的相關長度變化，討論標準焓對相變化行為的影響。實驗結果發現當共聚物的親水段聚合度與疏水段聚合度之比值小於1.15時，在水中無法溶解而沉澱，不形成凝膠態，當疏水鏈段上升時，臨界成膠濃度愈低。以均場理論計算共聚物在水中之交互作用參數值隨疏水鏈段聚合度上升而增加，表示疏水段長度上升時共聚物與水之作用力下降。將古典的交互作用參數進一步考慮溶液混合前後的比熱差及θ溫度所造成的影響，預測之相圖都能與兩性團聯共聚物之實驗數據相符。流變法及翻轉試管法以力學方法觀測到在大尺度下共聚物高濃度時之相變化，均場理論預測到在相圖低濃度時仍有相變化的發生，但無法預測到共聚物在高溫時的沉澱相。利用螢光激發光譜量測臨界微胞濃度，發現在極低濃度下時已有微胞相形成，以動態光散射觀察濃度與溫度對相行為的影響，發現在相圖高濃度時，相關長度隨共聚物濃度上升而增加，隨溫度上升而下降。在相圖低濃度時，則隨共聚物濃度上升而下降，隨溫度上升而下降。綜合以上結果，推論共聚物在小尺度下存在著以力學方法觀測不到的相，相圖低濃度為以微胞聚集行為為主的相，相圖高濃度則為以膠體粒子聚集為主的相。

Monomethoxy Poly(ethyl glycol)-Poly(L-lactic acid)(mPEG-PLLA) diblock copolymers with fixed mPEG length with degree of polymerization 113 and various PLLA with degree of polymerization from 35 to 98 were synthesized. The molecular weights were determined by gel permeation chromatography (GPC). The critical gelation concentration (CGC) was measured by tube-inverting method. We calculated the power-law exponents for the CGC versus the degree of polymerization. The phase transition temperatures were determined by rheological measurement. We used Flory-Huggins mean field theory and phase transition data to predict the phase diagrams. The exponent n of power relationship of degree of polymerization can be calculated according to the critical gel temperatures on the phase diagrams. The critical micelle concentration (CMC) of diblock copolymer can be measured by fluorescent probe to assess the existence of the micelle phase and we used dynamic light scattering (DLS) to analyze the phase behavior in water solutions.
The experimental results showed that when the degree of polymerization ratio of hydrophilic chain to hydrophobic chain was less than 1.15, the diblock polymer couldn’t exist a gel state but precipitated. There was an exponential relationship, with a negative exponent, between the critical gel concentration and degree of polymerization. It meant the critical gel concentration decreased with increasing the hydrophilic length. We used mean field theory to calculate the interaction parameters between copolymers and water. The values increased with increasing hydrophobic segment length. It meant the interaction of copolymers and water decreased with increasing hydrophobic segment length. We found the experimental results were fit well with the predicted phase diagrams. When it was applied on some higher ratio of the hydrophobic segment length to the hydrophilic segment length copolymers, the predicted phase boundary fit poorly for the experimental data around the critical point.
Rheological measurement and tube-inverting method couldn’t be used to measure the phase transition at low copolymer concentrations. We used mean field theory to predict the phase boundary even if at low concentrations, but couldn’t predict the precipitated state at high temperatures. This work found that the micelle phase formed at extremely low concentrations. We observed the effect of concentrations and temperatures on the phase behavior by DLS. The correlation length at high concentrations increased with increasing concentrations and decreased with increasing temperatures. By contrast, the correlation length at low concentrations decreased with increasing concentrations and decreased with increasing temperatures. We calculated the enthalpy of phase transition and the enthalpy decreased with increasing the degree of polymerization of hydrophobic segment. In conclusion, we suggest that the phase behavior at low concentrations was controlled by micelles aggregation and the phase behavior at high concentrations was controlled by colloidal particle clusters.

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