氮化硼原位聚合對聚亞醯胺/氮化硼複合材料之導熱增益

Abstract

本論文研究主要分為三個部份: (1) 探討不同溶劑下合成微米級氮化硼(Microsized boron nitride,μ-BN)/聚亞醯胺 (Polyimide,PI)複合材料薄膜導熱性質與使用溶劑之間的影響。(2) 討論不同比例下μ-BN/PI之間界面與導熱的關係，並利用BN原位聚合處理改善PI間之界面，進而增進導熱效果。(3) 比較不同比例奈米級氮化硼 (Nanosized boron nitride,n-BN)及μ-BN混入PI/BN複合材料薄膜之熱性質。其中PI由雙氨基單體4,4'-二氨基二苯醚 (4,4'-Oxydianiline,ODA)及雙酸酐單體苯均四酸酐 (Pyromellitic dianhydride,PMDA)於溶劑中合成聚醯胺酸(Polyamic acid,PAA)，經熱亞醯胺化後形成PI。

首先本研究發現BN分散在溶劑中時，會隨著溶劑PH值有顯著的分散性改變，在此使用的溶劑為二甲基乙醯胺 (Dimethyl acetamide,DMAc)、吡啶(Pyridine)以及甲基吡咯酮 (N-Methyl-2-pyrrolidone,NMP)隨著不同溶劑的PH值上升BN在溶液中分散性越佳，因此將此特性的BN溶液進一步加入聚亞醯胺前趨物聚醯胺中增加分散性，在合成PI後比較在不同溶劑中之導熱值，經測定由NMP中合成之13%μ-BN/PI有最佳導熱值0.62 W/(m•K)。

第二部份本研究利用滴定法測得μ-BN上有0.106 wt%氨基，並利用此官能基先與PI的雙酸酐單體PMDA反應，藉此改善BN與PI在介面聲子散射，並減少BN與BN粒子間縱向作用力吸引，導致BN互相聚集分散不均的影響，經由改進後30%μ-BN/PI導熱值有35%的提升。

為了更進一步增強BN原位聚合影響PI/BN的效果，加入經滴定測試表面有更多氨基的n-BN，藉調配不同比例的n-BN及μ-BN後得到最佳比例在BN 30%且n-BN/μ-BN為2~3.29倍時，導熱值提升至1.4~1.43 W/(m•K)。

最後測得BN/PI膜的熱性質，(20%n+10%μ)BN/PI的熱膨脹係數為 17.7 ppm/℃，玻璃轉移溫度為380.7℃，熱分解溫度為586℃，此結果證明在BN原位聚合可以對PI增進導熱效果，並且對熱性質不止負面影響不大，更可以增強其熱性質，所以讓此方法可以讓BN/PI利用在一些高溫環境下，進而使用在更多領域。

This study was divided into three parts: (1) researched the relationship between thermal coductivity and solvent effect of microsized boron nitride(μ-BN) disperse in polyamic acid(PAA)/BN to synthesizeμ-BN/PI composite films .(2) Discuss different ratios μ-BN/PI relationship between interface and thermal conductivity. Then, improve the interface between the PI and BN by in-situ polymerization on BN surface. (3) Compare thermal properties of different proportions μ-BN and n-BN in BN/PI composite film. Wherein PI from monomers that were 4,4 '- diaminodiphenyl ether (ODA) and pyromellitic anhydride(PMDA) in solvent to form PAA synthesized PI by thermal imidization process.

First, we found the solvent effect of BN disperse in solvent that would change with PH value obviously. We used dimethyl acetamide (DMAc), pyridine and n-methyl-2-pyrrolidone (NMP) that with the increasing in PH value dispersion of BN got better and better. Therefore, BN solution was further added in PAA that was PI precursor to increase dispersion. After synthesized 13% μ-BN/PI films from the BN/PAA in NMP, the thermal conductivity determined to 0.62 W / (m • K) which was the best value of this part.

Next, we measured μ-BN amono group by the titration method and got the value which is 0.106 wt%. This functional group would react with PMDA, so it could improve PI/BN phonon scattering at the interface and reduce BN-BN longitudinal forces between particles attracting each other that resulted BN gather together. The dispersed of BN/PI unevenly was improved, so thermal conductivity value of 30% μ-BN/PI increased 35%.

To further enhance the surface polymerization of BN/PI , we adding the n-BN that was more surface and more amino. Different ratios of n-BN and μ-BN were adjusted to give the best thermal conductivity at BN 30%.Then, the proportion was better at 2~3.3 of nm/μm and the value of thermal conductivity was 1.4~1.43 W / (m • K).

Finally, we measured to thermal properties of the BN / PI film. (20%n +10%μ) BN / PI were a better thermal property in the value 17.7 ppm/℃ of CTE, 380.7℃of Tg and 586℃of Td. The results show the PI/BN surface polymerization can improve thermal couducivity and no adverse effects on the thermal properties besides that enhanced the properties of thermal, so the high thermal conductivity PI/BN could be used in more and more area.