플루오르화 가소제와의 아자이드-알카인 클릭반응을 적용한 폴리우레탄 결합제의 합성 및 물성 : Synthesis of Polyurethane Binders Utilizing Azide-Alkyne Click Modification with Fluorinated Plasticizers and Their Properties

다국어 초록 (Multilingual Abstract)

In development of energetic materials, energetic plasticizer as an additive is facing lots of challenges such as high and secure energy output, efficient plasticizing ability and long sustained service life. The way to meet the requirements about providing high energy is to modify plasticizer by using energetic functional groups. But the energetic functional groups, such as nitrate, nitro, nitrite and azido groups, show high impact sensitivity, instability at high temperature or easy oxidation under air atmosphere, and these properties cause the safety problem during the process of manufacture, transportation, usage and storage. So plasticizers with new concept was studied in this research. The energy output was by the reaction between the new concept of plasticizer and other material, such as thermite reaction.
Thermite reaction is used to describe exothermic reactions involving reduction of oxides with aluminum (Al) to form aluminum oxide and reduction of element. The use of fluorine or its derivatives as oxidizers in various propellants and explosives has been recognized for many years. The reaction of fluorine and its derivatives with metals and metal hydrides is of interest in various pyrotechnics. Al reacts with decomposition products of fluorine containing polymers to produce metal fluorides, generally in the gaseous state yielding comparatively high flame temperature and enthalpy release. Therefore the fluorine-containing group was proposed to use as new concept of energetic functional group.
The problem of leaching, migrating and evaporating could be solved by strengthening the force between plasticizer and polymer. By referencing the idea of reactive plasticizer, a new form of reactive plasticizer with suitable molecular weight (MW) was designed to resist leaching, migrating and evaporating while had excellent plasticization. Efficient and effective “click” reaction was used to form a chemical bond between plasticizer and polymer.
Hence three types of six different reactive plasticizers (RPs), long fluorinated ester linkage RPs, short fluorinated ester linkage RPs and short fluorinated formal linkage RPs, have been synthesized by combining fluorine-containing groups and clickable alkyne groups. As well as, the ability of RPs on improving processability of prepolymer and the effect on thermal and mechanical property after being incorporated with polyurethane (PU) binders were investigated. RPs present low viscosity (20 cP to 30 cP at 30 °C and 6 cP to 10 cP at 60 °C), low glass transition temperature (below -100 °C) and acceptable thermal stability, as well as high reactivity with azide groups of poly(glycidyl azide-co-tetramethylene glycol) (PGT) polymers. The four short fluorinated ester and formal linkage RPs showed good miscibility with PGT polyols and decreased the viscosity of PGT polyols. The viscosity of PGT polyol dramatically decreased after mixing 50 wt% of RPs.
The extent of azide-alkyne click reaction between RP and PGT prepolymer could reach 100%. The reactivity of RP was proportional to electrophilic ability of alkynyl group. The ester linkage RPs and shorter intramolecular distance between EWG and alkynyl (d=1) RPs showed higher reactivity.
The thermite reaction between PGT-RP and n-Al was assessed by DSC (Al crucible) and DSC (high pressure crucible). 20 wt% n-Al mass loading was selected to apply into PU binders. The investigation of energetic performance about long fluorinated ester linkage RP, E-15F-2, proved the high content of fluorine made a contribution to higher energetic performance.
RP was incorporated in PGT-based PU binder with aluminum nanopowder (n-Al) by in-situ "click" reaction during PU reaction. After getting PU binder, mechanical properties of RP-incorporated PGT-based PU binders with n-Al were investigated by means of measuring the tensile strength and strain. The mechanical properties were changed after incorporating with RPs. The glass transition temperature (Tg) of RP-incorporated PGT-based PU binders with n-Al was measured by differential scanning calorimetry (DSC). The triazole groups which were formed by “click” reaction appeared to affect on the thermal property, presenting higher Tg than PGT base PU binder. As well as, the thermal stability was analysed by thermogravimetric analysis (TGA) with temperature from 50 °C to 900 °C. Compared to thermal maximum decomposition temperature (Td,max) of PGT-based PU binder with n-Al aroud 240.0 °C, the Td,maxs of RP-incorporated PGT-based PU binders with n-Al were around 380 °C, implying that the incorporating of RPs could enhance the thermal stability of PU binders. The energetic performance of RP-incorporated PGT-based PU binder and n-Al was assessed by DSC (Al crucible) and DSC (high pressure crucible). The PGT(5/5) PU binder system exhibited more excellent energrtic performance than PGT(3/7) PU binder system because the larger fluorine content.

국문 초록 (Abstract)

가소제는 낮은 유리전이온도, 낮은 점도, 낮은 누출특성 및 높은 열 안정성을 가져서 고분자의 유연성 및 가공성 향상에 기여한다. 이러한 요구 특성들은 일반적으로 많은 경우에 상충되므로, 최적의 가소제를 적용하는데 어려움을 가진다. 최근 고에너지 물질 분야에서 에너지화 가소제에 대한 연구가 많이 진행되고 있으며, 다양한 구조의 에너지화 가소제가 현재 합성 및 적용되고 있다. 현재까지 합성된 에너지화 가소제들은 가소제로서의 특성을 충족시켜주고 있을 뿐 만 아니라, 높은 에너지 공급에 기여하고 있다. 그러나, 에너지화 가소제는 물리적으로 고에너지 물질에 분산되어 있으므로, 시간이 지남에 따라 에너지화 가소제의 누출이 발생함으로써 장기적인 저장 및 안정성에 큰 문제점을 지니고 있는 단점이 있다. 또한 에너지화 가소제에서 에너지 증대에 기여하는 에너지 그룹은 열 안정성의 감소, 충격감도의 증가 등 고에너지 물질의 민감도를 증가시키는 단점도 지니고 있다.
본 연구에서는 이러한 단점들을 보완하기 위한 새로운 반응형 가소제를 디자인하고 합성하고자 하였다. 신규 반응형 가소제의 구조적 특징으로는, 첫째 뛰어난 가소화 효과를 부여하기 위해서는 고분자 결합제와의 혼화성이 중요하므로 에스터 또는 에테르 화학구조를 도입하였다. 둘째 반응형 관능기인 알카인 구조를 가소제에 도입하여 고분자 결합제의 곁가지에 클릭반응을 통하여 도입됨으로서 시간에 따른 가소제의 누출 문제를 해결하고자 하였다. 셋째 기존 에너지화 가소제에 도입되는 에너지화 그룹을 대체하여 일상적인 조건에서는 inert한 물질로 존재하지만 고에너지 물질이 작동하는 조건에서 추가적인 에너지를 공급할 수 있는 관능기를 도입하였다. 이러한 잠재적 에너지화 반응으로 thermite 반응을 이용하고자 하였으며 이를 위하여 반응형 가소제에 플루오르기를 도입하였다.
기본적으로 3가지 형태로 분류될 수 있는 6종류의 반응형 가소제를 합성하였다. Long fluorinated ester linkage 반응형 가소제, short fluorinated ester linkage 반응형 가소제와 short fluorinated formal linkage 반응형 가소제를 합성하였다. 이들 반응형 가소제들은 낮은 점도 (20~30 cP at 30 oC,6~10 cP at 60 oC),낮은 유리전이온도 (-100 oC이하), 적합한 열 안정성 및 poly(glycidyl azide-co-tetramethylene glycol) (PGT)의 아자이드 그룹과의 매우 높은 클릭반응성을 가지고 있음이 확인되었다. Short fluorinated ester linkage 반응형 가소제와 short fluorinated formal linkage 반응형 가소제는 PGT prepolymer와 뛰어난 상용성을 나타내었으며, 50 중량 퍼센트의 이들 반응형 가소제를 혼합했을 때 PGT prepolymer의 점도가 급격히 하락됨을 확인하였다.
반응형 가소제와 PGT prepolymer의 아자이드-알카인 클릭반응도는 100%에 도달하였다. 이때 반응형 가소제의 반응성은 alkynyl group의 친전자성에 비례하였다. 반응형 가소제 구조내에 있는 EWG와 alkynyl group 사이에 1개의 methylene spacer가 있는 반응형 가소제가 높은 반응성을 나타내었다.
반응형 가소제와 반응한 PGT와 나노 알루미늄과의 thermite 반응은 일반 Al crucible을 사용한 DSC와 고압 crucible을 사용한 DSC를 사용하여 각각 평가하였다. 이 평가에서 20 중량 퍼센트의 나노 알루미늄 함량을 폴리우레탄 바인더에 적용하기로 결정하였다.
PGT-based 폴리우레탄 결합제 합성하는 폴리우레탄 반응에 반응형 가소제와 나노 알루미늄을 혼합하여 in-situ 클릭반응을 수행하였다. 합성된 폴리우레탄 결합제의 기계적 물성은 반응형 가소제의 첨가에 의해 변화하였으며, 유리전이온도도 합성된 폴리우레탄 결합제내에 생성된 triazole group에 의해 증가함이 관찰되었다. 열 안정성은 TGA를 이용하여 평가하였으며, 합성된 폴리우레탄 결합제의 열 분해온도는 반응 전의 PGT prepolymer의 240 oC에서 380 oC로서 증가하였으며 이는 반응형 가소제의 도입에 의해 생성된 triazole 관능기에 의한 증가효과로 판단되었다. 나노 알루미늄과 혼합된 RP-incorporated PGT-based 폴리우레탄 결합제의 에너지 성능을 평가한 결과에 의하면, fluorine 함량과 보다 많은 반응을 할 수 있는 PGT(5/5) prepolymer를 사용하여 합성한 폴리우레탄 결합제가 PGT(3/7)을 적용한 시스템보다 높은 에너지 성능을 나타냄을 확인하였다.

목차 (Table of Contents)

• List of Tables iv
• List of Schemes vi
• List of Figures vii
• Abstract xiii
• Ⅰ. Introduction 1
• 1. Normal Plasticizers 1
• 1) Definition and function of plasticizers 1
• 2) Plasticization of plasticizers 1
• 3) Development of plasticizers 3
• 2. Plasticizers in energetic field 6
• 1) General plasticizers in energetic field 6
• 2) Energetic plasticizers in energetic field 6
• 3) New concept for energetic plasticizers in energetic field 10
• (1) Reactive plasticizers 10
• (2) New concept for energetic functional groups 13
• a. Ring strain energy (RSE) 13
• b. Thermite reaction 14
• 3. Objective 21
• Ⅱ. Experimental 24
• 1. Materials 24
• 2. Instruments and methods 26
• 3. Synthesis and characterization of RPs 28
• 1) Prop-2-yn-1-yl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoate (E-15F-1) 28
• 2) But-3-yn-1-yl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoate (E-15F-2) 29
• 3) Prop-2-yn-1-yl 4,4,5,5,6,6,6-heptafluorohexanoate (E-7F-1) 30
• 4) But-3-yn-1-yl 4,4,5,5,6,6,6-heptafluorohexanoate (E-7F-2) 31
• 5) 1,1,2,2,3,3,4,4-Octafluoro-5-((prop-2-yn-1-yloxy)methoxy)pentane (F-8F-1) 32
• 6) 5-((But-3-yn-1-yloxy)methoxy)-1,1,2,2,3,3,4,4-octafluoropentane (F-8F-2) 33
• 4. Preparation of mixtures of RP-incorporated PGT with n-Al 34
• 5. Preparation of PGT-based PU binder with n-Al 35
• 6. Preparation of RP-incorporated PGT-based PU binder with n-Al 36
• Ⅲ. Results and Discussion 37
• 1. Design concept for RP 37
• 2. Synthesis and characterization of RPs 41
• 1) Synthesis and characterization of ester linkage RPs 41
• 2) Synthesis and characterization of formal linkage RPs 44
• 3) Thermal properties of RPs 46
• 3. Plasticizing performance of RPs 52
• 1) Miscibility of RP with PGT polyols 52
• 2) Plasticization of RPs on lowering viscosity of PGT polyol 65
• 4. Reactivity of click reaction between RP and PGT polyol in bulk condition 76
• 1) Reaction rate of click reaction between RP and PGT polyol 76
• 2) Ea of click reaction between RP and PGT polyol 84
• 5. Assessment of thermite reaction between RP-incorporated PGT and n-Al 88
• 6. Preparation and properties of RP-incorporated PGT-based PU binders with n-Al 101
• 1) Preparation of RP-incorporated PGT-based PU binders with n-Al 101
• 2) Mechanical properties of RP-incorporated PGT-based PU binders with n-Al 102
• 3) Thermal properties of RP-incorporated PGT-based PU binders with n-Al 105
• 4) Assessment of thermite reaction of RP-incorporated PGT-based PU binders with n-Al 111
• Ⅳ. Conclusions 116
• References 118
• 초록 125
• Acknowledgments 127