我們發現如使用芳香族CDI及脂肪族CDI，分別與有機酸反應，有截然不同的結果。脂肪族CDI與有機酸反應，其主要產物為尿素（urea）及酸酐（anhydride）；而芳香族CDI與有機酸反應，其主要產物為一反應途徑生成之Acylurea（>90％）。我們也發現使用芳香族有機酸與芳香族CDI反應，反應有極高選擇率朝向Aacylurea。然而在短鏈脂肪族有機酸與芳香族CDI的反應系列，例如甲酸（formic acid）及乙酸（acetic acid），由初期中間體acylisourea轉換生成acylurea之速度較慢，使此系列之acylurea產率明顯較低。
我們進一步證實Acylurea 在高溫下會裂解成異氫酸鹽（ioscyanate）及醯胺（amide），而生成的isocyanate可進一步與alcohol反應生成carbamate。而由起始反應物isocayanate反應生成之acylurea，如適當的加熱及在催化劑（phospohlene oxide）的作用下，會進一步與過量酸反應生成最後產物amide。由此結果得知，acylurea可作為生成amide及isocyanate之中間體。
本實驗室也成功合成出具備imide官能基的聚醚二元酸（POP2000 diacids），POP2000 diacids的合成是利用Jeffamine® D2000(and ED2001)與TMA製備出高分子主鏈為POP之聚醚酸(而聚醚鏈段之分子量可為2000或200)，而利用TMA合成之POP2000 diacid因主鏈當中帶有imide官能基，因此可有效改善POP鏈段在高溫下不穩定之缺點，另外末端所帶之羧酸官能基可作為下一步反應之鏈延長劑。
我們將上述二元酸經由P-CDI途徑來製備聚醯胺（polyamide）。例如以POP 2000-diacid與PCDI（由MDI製備），於60℃反應生成網狀結構之polyacylurea（PACU）中間體，再加熱至160℃熱處理將PACU轉化成poly-amide-imide-ether（PAIE）。我們並可將上述反應進一步簡化成一步驟，在180℃時以4,4-MDI慢速進料至POP 2000-diacid。此方法的優點為POP2000 diacid本身為液體，故在進料時，不需溶劑溶解，故省略了溶解及去除溶劑的問題，而本身在生成PACU及熱裂解形成PAIE，由於反應條件是在180℃，故其生成PACU及瞬間熱裂解形成PAIE，是幾乎同時發生的，所以在此系統下可以視為一步驟（one-step）反應。在此研究中，其製備PAIE的優點，具有不需溶劑、一步驟反應……等較傳統製備法的優勢，對於在產品應用及生產製裎上，具有相當大的應用性及優勢。
An extensive study on reaction between carbodiimides (CDI) and carboxylic acids were carried out in this research aiming to isolate and enhance yields of acylurea (ACU) intermediates. In the meantime, the condition and mechanism for converting ACUs into amides also were investigated. Based on those understandings, we have attempted to prepare polyamideimideethers (PAIE) directly from methylene diphenylene diisocyanate (MDI) and a liquid polyether diacid via P-CDI and P-ACU routes.
We found that there are substantial differences in the reaction direction between aryl-CDI and aliphatic-CDI when they are treated with carboxylic acids. Aliphatic CDI reacted with carboxylic acid rapidly and formed anhydrides and aliphatic urea as the major products. Whereas, High yields (>90%) of acylureas (ACU) could generally be isolated under ambient condition from aryl—CDI and acids. The selectivity and yield of ACUs were highest when aryl-CDI was reacted with an aryl carboxylic acid. However, when aryl-CDI and short-chained acids such as formic or acetic acid were similarly reacted, the rearrangement of initial isoacylureas (IACU) into ACU became substantial slower. This could lead to lowering of ACU yields and other complication in overall chemistries,
ACU are found to be an excellent blocked-isocyanate candidate. At a temperature greater than 100 C, ACU dissociates to form isocyanate and amide where isocyanate could be trapped by alcohols. With appropriate heating and addition of phospohlene oxide as the catalyst in ACU, the formation of initial isocyanate could be further reacted by additional acid to form amide as the final product. In essence, ACU was served as the intermediary between isocyanate and amide.
In this research, we have prepared a high molecular-weight diacid prepolymer (POP 2000-diacid) by the condensation reaction of Jeffamine 2000 (polyether diamine of about 2000 molecular-weight) with trimellitic anhydride (TMA). This diacid was used for our trial preparation of polyamides through P-CDI chemistry. For example, when the prepolymer, POP2000 diacid, was reacted with P-CDI (prepared from MDI) at 60 C, a highly crosslinked polyamideimideether (PAIE) was obtained. This crosslinked material could be converted into liner soluble polymers simply by heating at 160 C. Furthermore, preparation of PAIE by a one-step process also was tried by slowly addition of MDI into POP2000 diacid in the presence of methyl phospolyene oxide. In these manners, a series of PAIE with varied molecular-weight have been prepared. However, there are indications of other chemical complications resulting from the instability of PAEI, which had to be addressed before the one-step process can be satisfactorily adapted.