| Polyimides (PI) have been used in many advanced technologies and novel applications, such as aerospace, aeronautical, optical, electrical and microelectronics industry, because of their excellent thermal stability, high mechanical performance, and outstanding electrical properties. While as a widely used dielectric material, with dielectric constants from 3.1 to 3.5, conventional polyimides cannot meet the requirements of the future microelectronics with dielectric constant less than 2.5. While the applications of PIs are limited due to their high thermal stability and poor solubility in organic solvents, that make them hard to be manufactured. Accordingly, reducing the dielectric constant and increasing the solubility of PIs is highly focused in the research of this area.In this work, a soluble polyimide containing fluorine moiety in the main chain was synthesized by the conventional two-step method. Then the polyimide was modified by grafting side-chain via chloromethyl groups which we had successfully introduced into the main chain beforehand. The structure and properties of the polymer was characterized and analyzed. There are three parts to be included in this paper:1. Synthesis of rigid bulky pendant group that we have designed. Symmetric 1,n-diol was treated with stoichiometric equivalent of n-butyl lithium, followed by adding triphenylmethyl bromide to produce monotritylated symmetric 1,n-diol in situ. Products were separated and purified by column chromatography. The structure of products was characterized by FTIR, 1H NMR, UV-vis and elemental analysis measurements. The results indicated that good yields of the monotritylated derivative could be observed, as controlling the dripping velocity of n-butyl lithium and adjusting temperature and time of the reaction in the second step.2. The polyimide (6FOD-PI) containing fluorine moiety in the main chain was synthesized by the condense polymerization of 4,4'-(hexafluoroisopropylidene)- diphthalic anhydride (6FDA) and 4,4'-diaminodiphenylether (ODA) in the conventional two-step method. Then the chloromethylated polyimide (CMPI) was synthesized by the reaction of polyimide with chloromethyl methyl ether in the presence of tin (IV) chloride, and the chloromethyl group was successfully introduced into the repeat unit. The monotritylated symmetric 1,n-diol was then successfully grafted to the main chain with 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU) as catalyst, tetrabutylammonium bromide (TBAB) as phase transfer catalyst, and we have prepared several products with different grafting ratio. The structure of these products was characterized by FTIR and 1H NMR, their properties were investigated. The results of measurements showed that free volume of the polyimide with rigid bulky pendant group modification increased, dielectric constant reduced and the solubility was further improved, the polymer could be manufactured in ease.3. By using the same method above, we took chloromethyl group as a functional reactive group to graft poly(propylene glycol) (PPG) side-chain and attained polyimides with different grafting ratio of PPG side-chain modification, the structure of the product was identified by FTIR and 1H NMR. Dielectric Constant and BET characterizations revealed respectively that, after the polyimide had been modified by oligomer side chain which had large volume, the dielectric constant reduced from 2.577 to 2.475, the specific surface area and the pore volume increased. Besides, the polymer that we had prepared had good solubility, such property made the polyimide easy processing and well application in microelectronic industry. |
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