Low-Temperature Thermochromic Polydiacetylenes

Abstract

The majority of polydiacetylenes (PDAs) described to date display thermochromic transitions above room temperature. The key of controlling the colorimetric transition temperature of PDAs is to manipulate headgroup interactions in the PDA supramolecules. A variety of studies have been explored for the manipulation of headgroup interactions such as hydrogen bonding, arene−arene and ionic interactions, that affect for the colorimetric transition temperature of PDAs. By employing a strategy that allows weak headgroup interactions, we have designed and prepared liquid DA monomers that solidify below room temperature. UV irradiation of these solidified DA monomers brings about an instantaneous formation of blue colored PDAs. The low-temperature polymerized PDAs were found to display thermochromic transition below room temperature. In this dissertation research, two important studies of low-temperature thermochromic PDAs, covering topics including thermal properties, spectroscopic analysis, as well as the practical applications, are described. Firstly, PDA-NCOs prepared from the isocyanate containing DA monomers were found to display a sharp blue-to-red color transition at the low-temperature. By taking advantage of its room temperature liquid phase property, we were able to readily transfer the DA monomer to solid substrates by using common stamping and writing methods used for creating patterned PDA images. In addition, the isocyanate moieties present in PDA-NCO have been utilized to differentiate 1o amines from 2o and 3o amines. This was achieved by the fact that PDA-NCO undergoes a rapid yellow-to-red color change in chloroform solution, which is associated with an insoluble urea forming reaction with primary amines. Secondly, we have focused rational design of low-temperature thermochromic PDAs derived from six liquid DA monomers which have different chain lengths and head groups. Based on the results of thermal analysis of DA monomers and thermochromic temperature of PDAs, we identified the relationship between the monomer structure and the thermochromic temperature. When the carbon chain length decreases by two units, the thermochromic temperature decreases by about 10 oC. One meritorious feature of the low temperature thermochromic PDA is that the colorimetric transition temperature can be readily manipulated by proper choice of the monomers. Thus, we were able to fabricate PDA sensors that display color transition in the range between 5 and 30 oC. The soluble nature of PDA allowed a straightforward approach for the preparation of PDA nanofibers by employing nanoporous template. |공액고분자의 한 종류인 폴리다이아세틸렌은 다양한 자극에 의해 변색성을 지니고 있어 센서분야에서 주목 받고 있는 고분자이다. 특히 폴리다이아세틸렌의 열변색성은 단량체의 헤드 그룹의 작용기를 변화하여 열변색 온도나 가역성을 조절 할 수 있어 다양한 온도센서에 관한 연구가 진행되고 있다. 폴리다이아세틸렌은 단량체의 자가조립을 유도하기 위해서 수소결합, 방향족 그룹간의 결합, 이온결합을 할 수 있는 말단기들이 주로 사용되고 있다. 하지만 이러한 단량체들로 중합된 폴리다이아세틸렌들은 강한 헤드그룹간의 결합 때문에 약 40도 이상에서 색전이 현상이 발생한다. 저온에서 색전이 현상을 유도하기 위해서 강한 분자간 결합을 하는 헤드그룹을 제거하여 저온에서 자발적으로 자가조립이 유도되는 단량체들을 합성하였다. 본 연구논문에서는 저온 색전이 폴리다이아세틸렌에 관련된 두 종류의 연구를 기술하고 있다. 첫 번째로 반응성을 지니는 이소시아네이트 그룹이 치환된 단량체인 DA-NCO 1과 DA-NCO 2를 합성하여 11도와 -3도에서 청색에서 적색으로 색전이를 지니는 폴리다이아세틸렌들을 개발하였다. 그리고 상온에서 액체상태인 단량체를 도장이나 볼펜의 잉크로 사용하여 종이 위에 손쉽게 이미지를 제작하는 방법을 개발하였다. 또한 마이크로 컨택 프린팅 기법을 이용하여 폴리다이아세틸렌 마이크로 패턴을 제작하였다. 마지막으로 이소시아네이트와 아민과의 반응성을 이용하여 이소시아네이트를 지니는 폴리다이아세틸렌 고분자를 1차 아민 검출센서로 응용하였다. 두 번째로 분자의 탄소길이와 헤드그룹을 조절한 6개의 다이아세틸렌 단량체를 합성하였고 이를 이용하여 폴리다이아세틸렌의 색전이 온도를 0~30도의 범위까지 세밀하게 조절하였다. 다이아세틸렌 단량체의 열 분석결과와 폴리다이아세틸렌 색전이 온도를 비교하였을때 단량체의 탄소길이가 2개씩 줄어들 때마다 약 10도씩 색전이 온도가 감소하였고 헤드그룹에 에틸렌글리콜 그룹이 포함되면 평균적으로 약 5도씩 색전이 온도가 감소하였다. 우리는 실용적인 응용을 위해 단량체가 내포된 잉크를 제작하여 잉크젯 프린팅 기법을 이용하여 손쉽게 저온 변색성 이미지를 종이 위에 인쇄하였다. 또한 합성한 6종의 단량체를 고체상 중합하여 6종의 적색 폴리다이아세틸렌을 분리하였다. 중합한 6종의 고분자를 필터종이에 흡착시켜 리트머스 타입의 센서를 제작하였고 각 고분자의 용해도를 이용하여 기존의 방법으로 구별이 힘든 메틸렌클로라이드와 클로로포름을 구별하였다. 마지막으로 낮은 녹는점을 지니는 폴리다이아세틸렌을 AAO 맴브레인 틀 위에서 녹여내어 손쉽게 폴리다이아세틸렌 나노 섬유를 제조하였다.; The majority of polydiacetylenes (PDAs) described to date display thermochromic transitions above room temperature. The key of controlling the colorimetric transition temperature of PDAs is to manipulate headgroup interactions in the PDA supramolecules. A variety of studies have been explored for the manipulation of headgroup interactions such as hydrogen bonding, arene−arene and ionic interactions, that affect for the colorimetric transition temperature of PDAs. By employing a strategy that allows weak headgroup interactions, we have designed and prepared liquid DA monomers that solidify below room temperature. UV irradiation of these solidified DA monomers brings about an instantaneous formation of blue colored PDAs. The low-temperature polymerized PDAs were found to display thermochromic transition below room temperature. In this dissertation research, two important studies of low-temperature thermochromic PDAs, covering topics including thermal properties, spectroscopic analysis, as well as the practical applications, are described. Firstly, PDA-NCOs prepared from the isocyanate containing DA monomers were found to display a sharp blue-to-red color transition at the low-temperature. By taking advantage of its room temperature liquid phase property, we were able to readily transfer the DA monomer to solid substrates by using common stamping and writing methods used for creating patterned PDA images. In addition, the isocyanate moieties present in PDA-NCO have been utilized to differentiate 1o amines from 2o and 3o amines. This was achieved by the fact that PDA-NCO undergoes a rapid yellow-to-red color change in chloroform solution, which is associated with an insoluble urea forming reaction with primary amines. Secondly, we have focused rational design of low-temperature thermochromic PDAs derived from six liquid DA monomers which have different chain lengths and head groups. Based on the results of thermal analysis of DA monomers and thermochromic temperature of PDAs, we identified the relationship between the monomer structure and the thermochromic temperature. When the carbon chain length decreases by two units, the thermochromic temperature decreases by about 10 oC. One meritorious feature of the low temperature thermochromic PDA is that the colorimetric transition temperature can be readily manipulated by proper choice of the monomers. Thus, we were able to fabricate PDA sensors that display color transition in the range between 5 and 30 oC. The soluble nature of PDA allowed a straightforward approach for the preparation of PDA nanofibers by employing nanoporous template.