聚酯多元醇合成及其性質與水解探討

Abstract

聚氨酯為用途最多樣化的高分子材料之一，其中聚酯型聚氨酯具有較好的機械性質與易於水解特質。水解的性質雖可為分解材料，但同時也限制了材料的耐用度和操作環境。而在聚酯型聚氨酯結構上，最容易水解的部分為聚酯多元醇端，因此探討如何藉由改變觸媒以及原料來改善聚酯多元醇為本論文重點。 在第2章中，使用己二酸與丁二醇聚合得到 poly(1,4-butylene adipate)，透過改變進料比例以及不同催化劑而得耐水解性佳與適當分子量(Mn=2000~4000)的聚酯多元醇的條件。從GPC和羥價滴定數據發現，丁二醇與己二酸進料比為1.2的poly(1,4-butylene adipate ) 能達成我們所需的分子量。而在反應速率上，主要藉由分子量大小推斷，以蒐集1莫耳水量時間為輔。藉由GPC發現分子量大小依序為Ti-(OBu)4 (3.76 kg/mol) > Ti-iso (3.38 kg/mol) > Zr-iso (3.21 kg/mol) >Al-tert (3.04 kg/mol) >Zr-pro (2.73 kg/mol) >Al-iso (2.63 kg/mol)。此反應屬於親核取代反應。在相同配位基結構的催化劑中，像是Al-iso, Zr-iso 與 Ti-iso，影響其催化效率有兩項原因。第一項因素為金屬原子的電負度，電負度大小依序為Al (1.61) > Ti (1.54) > Zr (1.33) ;第二項因素為配位基的個數，配位基個數依序為Ti (4) = Zr (4) > Al (3)。從這兩項原因可以發現，雖然Al的電負度最大，但因配位基數少於Zr、Ti，造成催化效率最慢。而Ti則因為與Zr有相同配位基數，但電負度略大於Zr，因此催化效率為最好。最後，配位基結構的差異也會影響催化效率。若比較Al-tert 與Al-iso，Al-tert因為立體障礙較大，而阻礙逆反應，因此可有較大分子量。而Zr-iso同樣也因立體障礙大，而在反應速率上略快於Zr-pro。水解速率可藉由觀察各樣品經過水解30小時後的酸價變化量得知，依序為: Al-tert > Al-iso > Ti-iso > Zr-pro > Zr-iso > Ti-(OBu)4。因為水解為合成的逆反應，參考合成的反應機制後可以發現催化劑的立體障礙性會影響水解反應速率。而立體障礙會因金屬原子的大小以及配位基的結構有所差異。金屬原子大小依序為Zr (155皮米) > Ti (140皮米) > Al (125皮米)，因此Zr的立體障礙會最大，使得樣品不易與水反應;而Al的立體障礙最小，使得樣品容易與水產生反應。在配位基的結構上，以Zr-pro與Zr-iso為比較，因為isopropoxide的支鏈結構使得立體障礙比propoxide的結構大，因此在水解速率上呈現Zr-pro > Zr-iso。 在第3章中，我們使用十二烷二酸與丁二醇聚合得到 poly(1,4-butylene dodecanedioate)。其中十二烷二酸可以藉由生物方法製備，且其與己二酸同為直鏈二酸並帶有更長的碳鏈，因此藉由改變進料比例與不同催化劑而得不同分子量的poly(1,4-butylene dodecanedioate)和poly(1,4-butylene adipate)，來探討長碳鏈對分子量以及水解穩定性的影響。藉由改變進料比例與不同催化劑來得到不同分子量的poly(1,4-butylene dodecanedioate)並與第2章的結果比較。從實驗結果發現，分子量都會比poly(1,4 butylene adipate)來得大，而比較水解後的酸價改變量，可以發現水解速率大小依序為: Al-iso >Ti-iso > Zr-iso，與poly(1,4-butylene adipate)的水解速率之結果是一致。而與poly(1,4-butylene adipate)的酸價改變量數值進行比較，可以發現poly(1,4-butylene dodecanedioate) 的酸價改變量較低，因此在二酸上的長碳鏈不僅可以幫助分子量提升也能提升耐水解性。 本研究為聚酯多元醇的耐水解性提升提供新方向，並期望藉由較好耐水解性的聚酯多元醇聚合而得的聚氨酯亦能具有良好的耐水解性。

Polyurethane is one of the important polymeric materials, which has versatile applications. Polyester-based polyurethanes have better mechanical properties but are easily hydrolyzed. The degradability due to hydrolysis also restricts the operating environment and its endurance. The easily hydrolyzed part of polyester-based polyurethane is the polyester polyol block. Hence, the important issue in this thesis is how to improve the hydrolytic stability of polyester polyol. In chapter 2, adipic acid (AA) and 1,4-butanediol (BDO) were used to synthesize poly(1,4-butylene adipate)s. By changing different reactant ratio and different catalysts, we optimized the reaction parameter for producing polyester polyol with a better hydrolytic stability and a suitable molecular weight (Mn=2000~4000). From the results of GPC and hydroxyl values, the desired molecular weight could be obtained by using the molar ratio of BDO/AA =1.2. The comparison on the reaction rate of preparing polyester polyol was from the molecular weight by GPC and the time for collecting 1 mole H2O. The order on the GPC molecular weight is Ti-(OBu)4 (3.76 kg/mol) > Ti-iso (3.38 kg/mol) > Zr-iso (3.21 kg/mol) >Al-tert (3.04 kg/mol) >Zr-pro (2.73 kg/mol) >Al-iso (2.63 kg/mol). The reaction is one kind of nucleophilic substitute reactions. There are two factors to explain the efficiency when compare the catalyst efficiency with same structure of coordination ligands, such as Al-iso, Zr-iso and Ti-iso. The first is the electronegativity of metal atom with the order of Al (1.61) > Ti (1.54) > Zr (1.33). The second is the number of the coordination ligands in the order of Ti (4) = Zr (4) > Al (3). Though Al has the largest electronegativity, it has the least amount of coordinate ligands. Therefore, Al-iso has the worst catalytic efficiency among the studied catalysts. Ti-iso has a better catalytic efficiency than Zr-iso due to its higher electronegativity. The steric hindrance of Al-tert is larger than that of Al-iso and thus promotes the forward reaction to have a higher molecular weight. A similar conclusion is obtained for the comparison between Zr-iso and Zr-pro. The hydrolysis rate of the prepared polyester polyol is in the following order: Al-tert > Al-iso > Ti-iso > Zr-pro > Zr-iso > Ti-(OBu)4, suggesting the effect of the steric hindrance from the chemical structure. The size of metal atom is in the order of Zr (155 pm) > Ti (140 pm) > Al (125 pm) and it explains the order of hydrolysis of Al-iso, Ti-iso, and Zr-iso. The isopropoxide ligand makes a higher steric hindrance than the propoxide structure and thus the hydrolysis rate is in the order of Zr-pro > Zr-iso. In chapter 3, dodecanedioic acid (DA) and 1,4-butanediol were used to synthesize poly(1,4-butylene dodecanedioate)s. The DA can be obtained from bio-resources and is a linear dicarboxylic acid, which can be used to compare the effect of the chain length on molecular weight and hydrolytic stability. From the GPC and hydroxyl value results, the molecular weights of poly(1,4-butylene dodecanedioate)s are all larger than those of poly(1,4-butylene adipate)s. The results of acid value change suggests that the hydrolysis rate is in the order of Al-iso > Ti-iso > Zr-iso, which is the same as the hydrolysis rate of poly(1,4-butylene adipate). However, the amount of acid value change on poly(1,4-butylene dodecanedioate)s is smaller than poly(1,4-butylene adipate). Hence, a longer chain length in the dicarboxylic acid probably increases the molecular weight and the hydrolytic stability of the prepared polyester polyol, if it does not affect the reaction rate significantly. This work provides an approach for improving the hydrolytic stability of polyester polyol. It is hoped that the polyurethane from the above polyester polyol could have a good hydrolytic stability.