한국섬유공학회지, Vol. 53, No. 5, 340-346 http://dx.doi.org/10.12772/tse.2016.53.340 ISSN 1225-1089 (Print) ISSN 2288-6419 (Online) 폴리히드록시아미드공중합체의열고리화거동에대한연구 강찬솔 민재호 남민우 서무송 지민호 백두현 충남대학교유기소재 섬유시스템공학과 Thermal Cyclization Behavior of Polyhydroxyamide Copolymers Chan Sol Kang, Jae Ho Min, Min Woo Nam, Moo Song Seo, Min Ho Jee, and Doo Hyun Baik Department of Advanced Organic Materials and Textile System Engineering, Chungnam National University, Daejeon 34134, Korea Corresponding Author: Doo Hyun Baik E-mail: dhbaik@cnu.ac.kr Received October 1, 2016 Revised October 20, 2016 Accepted October 20, 2016 c 2016 The Korean Fiber Society Abstract: A series of polyhydroxyamide copolymers (Co-PHAs) containing 2,2-bis(3-amino- 4-hydroxyphenyl)hexafluoropropane (BAHHFP) and/or bis(3-amino-4-hydroxyphenyl) sulfone (BAHS) were synthesized via a low-temperature solution polymerization method. The synthesized Co-PHAs were characterized by Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). All the Co- PHAs were found to be soluble in organic solvents with or without LiCl. The chemical structures of the Co-PHAs were identified using FT-IR spectroscopic analysis. The DSC and TGA results showed that the inclusion of BAHHFP and/or BAHS in the Co-PHAs reduced the thermal cyclization temperatures as compared to DHB, which is due to the difference in the rotational energy of the diamine monomers. Keywords: polyhydroxyamide copolymers, BAHHFP, BAHS, thermal cyclization, thermal stability 1. 서론 폴리히드록시아미드 (polyhydroxyamide, PHA) 는방향족 diamine과 diacyl chloride를반응시켜얻을수있는방향족폴리아미드계고분자로서, 일정온도이상에서열고리화 (thermal cyclization) 반응에의해폴리벤즈옥사졸 (polybenzoxazole, PBO) 과매우유사한구조로전환된다고알려져있다. 이러한 PHA는 PBO와달리극성유기용제에잘용해되어성형성이우수하고내열특성및기계적물성이뛰어나기때문에강산을사용하지않고도고온에서 PBO 를제조할수있는강점이있어많은연구가진행되어왔다 [1 10]. 그러나 PHA는 350 o C 이상의높은온도에서 PBO로전환되기때문에에너지소비에대한문제가대두되고있으며, 이를해결하기위해 PHA의주쇄에유연한그룹또는벌키 (bulky) 한그룹을도입하거나측쇄에치환체를도입하여용해특성과열고리화온도를상당한수준으로낮춘연구결과도보고된바있다 [11 20]. 특히, Baik 등 [21] 은 diamine 성분으로서 3,3'-dihydroxybenzidine(DHB) 과 2,2- bis(3-amino-4-hydroxyphenyl)hexafluoropropane(bahhfp), 그리고 diacyl chloride 성분으로서 terephthaloyl chloride (TPC) 및 isophthaloyl chloride(ipc) 를단량체로하여네종류의 PHA homopolymer를제조하였고, 그에따른열고리화거동및열적특성에관한연구결과를보고하였다. 그러나 PHA 내공단량체를도입해서용해성을향상시키고열고리화온도를낮추려는시도는많이있었지만 diamine 및 diacyl chloride 성분의함량을달리하여 PHA 공중합체를제조하고, 그에따른용해성과고리화거동및 PBO 공중합체로전환된후열분해특성이어떻게달라지는지체계적인연구는필요할것으로판단된다. 따라서이러한다양한구조를갖는 PHA 공중합체연구는최종분자구조형태에따라그물성이결정되고이는궁극적으로섬유고분자재료로서의다양한용도전개를위한유용한정보를제공하기때문에 PHA 공중합체제조및물성분석에대한기초연구가반드시필요하다고할수있다. 본연구에서는 diamine 성분으로서 DHB와 BAHHFP 및 340
폴리히드록시아미드공중합체의열고리화거동에대한연구 341 bis(3-amino-4-hydroxyphenyl)sulfone(bahs) 를사용하고, diacyl chloride 성분으로서 TPC 및 IPC를사용하여저온용액축합중합법을통해일곱종류의 Co-PHAs를합성하였다. 또한, 각각의단량체구조에따른 PHA 분자구조제어가최종 PHA 공중합체의열고리화거동및물성에미치는영향을체계적으로고찰하였다. 2. 실험 2.1. 재료및시약 PHA 중합에사용한단량체는 3,3'-dihydroxybenzidine (DHB, 99.0%, Tokyo Chemical Industry) 와 2,2-bis(3-amino- 4-hydoxyphenyl)hexafluoropropane(BAHHFP, 98.0%, Tokyo Chemical Industry) 및 bis(3-amino-4-hydroxyphenyl)sulfone (BAHS, 98.0%, Tokyo Chemical Industry) 의 diamine 성분과 terephthaloyl chloride(tpc, 99.0%, Tokyo Chemical Industry) 와 isophthaloyl chloride(ipc, 99.0%, Sigma Aldrich) 의 diacyl chloride 성분을구입하여사용하였으며, 중합용매로는무수 N,N-dimethylacetamide(DMAc, 99.8%, Sigma- Aldrich) 와 1-methyl-2-pyrrolidone(NMP, 99.5%, Sigma Aldrich) 를구입하여사용하였다. 또한, PHA 공중합체중합시용해성향상을위해무기금속염인 lithium chloride (LiCl, Junsei Chemical) 과 calcium chloride(cacl 2, Sigma Aldrich) 를구입하여사용하였으며, 합성된 PHA 공중합체의용해도를확인하기위하여상기 DMAc와 NMP를비롯하여 dimethyl formamide(dmf, 99.5%, Samchun Chemical), dimethyl sulfoxide(dmso, 99.0%, Samchun Chemical), tetrahydrofuran(thf, 99.5%, Samchun Chemical) 및 sulfuric acid(h 2 SO 4, 95.0%, Samchun Chemical) 를구입하여사용하였다. Table 1. Sample identification of Co-PHAs Monomer feed ratio Sample Diamine part Diacyl chloride part code DHB BAHHFP BAHS TPC IPC Co-PHA 1 50 50 0 100 0 Co-PHA 2 50 50 0 0 100 Co-PHA 3 50 0 50 100 0 Co-PHA 4 50 0 50 0 100 Co-PHA 5 100 0 0 50 50 Co-PHA 6 0 100 0 50 50 Co-PHA 7 0 0 100 50 50 2.2. Co-PHA 및 Co-PBO의제조일곱종류 Co-PHAs의합성은각단량체를용매에용해시킨후질소기류하에서저온용액축합중합법을이용하여진행하였으며, 각공중합체별투입량 (feed ratio) 은 Table 1에정리하여나타내었다. 먼저, diamine 성분으로 BAHHFP 가도입된 Co-PHA 1, 2, 6의경우용매시스템인 NMP/ LiCl에 DHB와 BAHHFP를 5:5로용해시킨용액을 ice bath 를이용해냉각하고추가적으로같은당량의 TPC 또는 IPC 를투입하여 0 2 o C에서 1시간교반한후상온에서 24시간반응을진행하였다. Diamine 성분으로 BAHS가도입된 Co- PHA 3, 4, 7의경우용매시스템만 NMP/LiCl 대신 NMP/ CaCl 2 로사용한것외에는앞서언급한 Co-PHA 1, 2, 6의합성과정과유사하게진행하였다. Diacyl chloride 성분으로 TPC 및 IPC가도입된 Co-PHA 5의경우용매시스템만 DMAc/LiCl로사용한것외에는앞서언급한 Co-PHAs 의합성과정과유사하게진행하였다. 반응종료후합성된 Co-PHAs를증류수에석출한후수세하여 80 o C에서 24시간건조를실시하였다. 건조된 Co-PHAs는실험실규모열처리장치를이용하여질소기류하에서 350 o C, 1시간 Scheme 1. Reaction scheme for the synthesis of the Co-PHAs and the conversion into Co-PBOs on heating.
342 강찬솔 민재호 남민우 서무송 지민호 백두현 Textile Science and Engineering, 2016, 53, 340-346 열처리를실시하여 Co-PBOs를제조하였다. Scheme 1은각각의 Co-PHAs의합성및 Co-PBOs로의전환과정을나타낸모식도이다. 2.3. Co-PHA 및 Co-PBO의특성분석합성된 Co-PHAs의고유점도는 Co-PHAs를 0.5 g/dl의농도로 sulfuric acid에용해시킨후 30±0.1 o C의항온수조에서 Ubbelohode 점도계를사용하여측정하였다. 합성된 Co- PHAs의화학구조및특성밴드를관찰하기위해적외선분광분석기 (FT-IR, Nicolet is50, Thermo) 를이용하였으며, Co-PHAs의열고리화거동은시차주사열량계 (DSC, Q100, TA Instrument) 를이용하여질소기류하에서승온속도 20 o C/min로 30 o C에서 500 o C까지승온시켜열고리화반응에따른흡열피크를비교하였다. 또한 Co-PHAs의열고리화거동및열안정성은열중량분석기 (TGA, Q50, TA Instrument) 를이용하여질소기류하에서승온속도 10 o C/ min으로상온에서 900 o C까지측정하여분석하였다. 3. 결과및고찰 3.1. 합성된 Co-PHA의특성분석 Figure 1은합성된 Co-PHAs의 FT-IR 스펙트럼분석결과를나타낸것이다. Figure 1(A) 의스펙트럼에서공통적으로 PHA의구조에해당하는 3410 cm -1 (N-H stretching), 3500 3000 cm -1 (O-H stretching), 1646 cm -1 (C=0 stretching), 1605 cm -1 (C-C vibration), 1526 cm -1 (coupling of C-N stretching and N-H bending) 및 1407 cm -1 (C-O-H bending) 의특성밴드를확인할수있다 [22]. 특히, Figure 1(B) 의확대스펙트럼에서알수있듯이, BAHHFP와 BAHS가각각도입된 Co- PHA 1, 2와 Co-PHA 3, 4의스펙트럼의경우도입되지않은 Co-PHA 5와비교시 1191 cm -1 (CF 3, C-F stretching) 와 1145 cm -1 (O=S=O symmetric stretching) 에해당하는특성밴드를관찰할수있다 [21,23]. 전반적으로 FT-IR 구조분석 을통해모든 Co-PHAs가잘합성되었음을알수있다. Table 2는합성된 Co-PHAs의용해도를평가한결과를정리한표이다. Table 2에서알수있듯이, Co-PHA 5의 I.V. 가 1.52인반면에 BAHHFP 및 BAHS 단량체를포함하는 Co-PHAs의 I.V. 가 0.31 0.93의범위로낮게나타났는데이러한결과로부터분자량이상당히낮을것으로예상할수있다. 그러나 I.V. 는희박용액에서고분자사슬이차지하는부피및흐름저항에비례하기때문에용매및고분자의구조에영향을많이받으므로 I.V. 를직접적으로분자량과연관짓기는곤란하다. 따라서, BAHHFP 및 BAHS 단량체를포함하는 Co-PHAs의분자량이상대적으로낮은것을예상할수있으나본연구에서와같이열고리화거동을주로고찰하는경우에는열고리화거동에미치는분자량의효과가크지않을것으로가정하였다. 전반적으로 THF 용매를제외하고는모든 Co-PHAs 는 LiCl 존재하에서 DMAc, DMF, NMP, DMSO 등의극성용매에서잘용해되는것을알수있으며, 특히단량체로 DHB와 TPC를 100% 도입한 Co-PHA 1, 3, 5를제외하고는 BAHHFP와 BAHS 투입만으로 diacyl chloride 조성및 LiCl의존재와는관계없이유기용매및 sulfuric acid에서모두용해가되는것을확인할수있다. 이러한용해도차이는단량체의입체구조적특성으로설명할수있으며반복단위내 bulky한구조를갖는플 Table 2. Solubility and the intrinsic viscosities of Co-PHAs Sample code DMAc DMF NMP DMSO THF H 2 SO 4 I.V (dl/g) Co-PHA1 ++ + ++ + ++ 0.93 Co-PHA2 ++ ++ ++ ++ ++ ++ 0.31 Co-PHA3 ++ + ++ + ++ 0.88 Co-PHA4 ++ ++ ++ ++ ++ ++ 0.70 Co-PHA5 ++ + ++ + ++ 1.52 Co-PHA6 ++ ++ ++ ++ + ++ 0.48 Co-PHA7 ++ ++ ++ ++ ++ ++ 0.60 ++ : soluble without LiCl, + : soluble with LiCl, : insoluble. Figure 1. FT-IR spectra of Co-PHAs (A) and their expansion spectra between 1300 and 600 cm -1 (B).
폴리히드록시아미드공중합체의열고리화거동에대한연구 343 루오르기와술폰기의도입, 주쇄에벤젠고리의결합위치에따른분자사슬의유연성과자유부피 (free volume) 증가그리고사슬패킹효율과수소결합력감소등다양한연구결과를통해얻어진고찰로해석가능하며 [10,21,24], 결과적으로 BAHHFP와 BAHS를이용하여공중합한 Co-PHAs가기존 PHA homopolymer보다용해성이더뛰어나성형과가공에있어더큰장점을지닌다고볼수있다. 3.2. Co-PHA의열고리화거동분석 Figure 2는 Co-PHAs의 DSC 승온곡선을나타낸그래프이고, Table 3은 DSC 및 TGA 결과값을정리하여나타낸것이다. Figure 2를보면알수있듯이, Co-PHA 1, 2 및 Co- PHA 3, 4의경우, TPC 보다대칭성이낮은 IPC 사용시 kink 구조의도입으로인하여더유연한분자구조를형성하게되고, 그구조가덜치밀해져서열고리화피크온도가각각 321.3 o C에서 286.9 o C로 349.4 o C에서 292.5 o C로크게감소한것을확인할수있다. 또한 Co-PHA 5-7의경 우, diacyl chloride 성분을 TPC(50):IPC(50) 으로고정하고 diamine 성분을각각 DHB, BAHHFP 및 BAHS로달리하여 DSC를관찰한결과, 열고리화피크온도가 DHB(Co- PHA 5) > BAHS(Co-PHA 7) > BAHHFP(Co-PHA 6) > 순으로낮아지는것을확인할수있다. 따라서, DHB 대신에 BAHHFP와 BAHS를투입하여공중합할경우열고리화온도를더낮출수있기때문에에너지절감측면에서의미하는바가크다고할수있다. 이는 diamine 성분의입체구조적특성으로설명할수있는데반복단위내 bulky한구조를갖는술폰기및플루오르기의도입으로인해 Co-PHA 에서 Co-PBO 구조로전환시회전에너지가증가하여열고리화반응이용이한것으로판단된다. 또한, Co-PHA 내 BAHHFP의도입이 BAHS가도입된것보다열고리화피크온도가더낮은것을확인할수있는데이는 BAHS보다 BAHHFP가유연한분자쇄와약한극성 (polarity) 을지니고있어보다더우수한회전력으로인해열고리화가촉진된것으로해석된다 [25]. 특히, 크게주목할부분은 BAHS가도입된공중합체 Co-PHA 3, 4, 7의열고리화개시및종료온도범위가다른 Co-PHAs에비해좁은것을알수있는데, 이는열고리화반응이신속하게일어나는것으로해석가능하다. 다만, 열고리화반응은분자쇄의구조적차이및입체효과 (steric hinderance effect) 등에영향을받는것으로알려져있지만, BAHS가도입된 Co-PHAs는어떠한메카니즘으로열고리화반응이진행되어 Co-PBO 구조로전환될수있는지는향후분자동역학시뮬레이션을이용한전산모사측정방법을기반으로원인규명을진행할예정이다. Figure 2. DSC thermograms of seven different Co-PHAs at a heating rated of 20 o C/min under nitrogen atmosphere. Table 3. DSC and TGA results of Co-PHAs DSC results Sample code T c a) ( o C) T c.r b) ( o C) T d c) ( o C) TGA results Char d) (%) Co-PHA 1 321.3 202.4 382.1 538.1 56.1 Co-PHA 2 286.9 181.4 369.9 525.3 39.0 Co-PHA 3 349.4 256.1 374.8 560.4 60.4 Co-PHA 4 292.5 247.7 359.9 538.1 55.8 Co-PHA 5 319.5 246.6 424.1 620.4 64.5 Co-PHA 6 309.6 199.7 379.9 514.7 54.6 Co-PHA 7 287.5 229.4 347.3 537.0 62.5 a) Thermal cyclization peak temperature, b) the range of thermal cyclization temperature, c) thermal decomposition temperature, and d) residue at 800 o C. 3.3. Co-PHA 및 Co-PBO의열안정성분석 Figure 3은일곱종류 Co-PHA의 TGA 곡선을나타낸것이고, 그결과값을 Table 3에정리하여나타내었다. 전반적으로두개의큰중량감소를관찰할수있는데이는각각 PHA의열고리화반응과 PBO의열분해거동에기인한다 [10,16,21]. Table 3에서알수있듯이, 모든 Co-PHAs의초기분해온도가 514.7 620.4 o C인것을관찰할수있으며, 전반적으로우수한열안정성을지니고있는것으로판단된다. 또한, TGA 분석결과 Co-PHA 2를제외한다른 Co-PHAs 모두실제중량감소율이이론적중량감소율에매우근접한수치를나타낸반면, Co-PHA 2의경우열고리화반응과함께분해가동반된것으로보인다. Diamine 성분인 DHB base에 BAHHFP와 BAHS가각각 50:50으로도입된 Co-PHA 1, 2와 Co-PHA 3, 4의경우를비교해볼때 (Figure 3(A)), BAHHFP가도입된 Co-PHA 1, 2 보다 BAHS가도입된 Co-PHA 3, 4가더우수한열안정성을갖는것을확인할수있으며, 특히 diacyl chloride 성분으로서 IPC(Co-PHA 1, 3) 보다는 TPC(Co-PHA 2, 4) 가더우수한열안정성을갖는것을관찰할수있는데이는 TPC의
344 강찬솔 민재호 남민우 서무송 지민호 백두현 Textile Science and Engineering, 2016, 53, 340-346 Table 4. TGA results of Co-PBOs Sample code T a) d ( o C) Char b) (%) Co-PBO 1 548 63.6 Co-PBO 2 535 62.8 Co-PBO 3 570 65.3 Co-PBO 4 544 64.7 Co-PBO 5 630 68.5 Co-PBO 6 524 60.6 Co-PBO 7 547 64.1 a) Thermal cyclization peak temperature and b) residue at 800 o C. 재인 Zylon (68%) 과 Kevlar 49(39%) 및 polyetheretherketone (PEEK)(48%) 등 [10,27 29] 열안정성이뛰어난소재들과비교시상당히우수한것을확인할수있다. 결과적으로이러한공중합방법을이용한 Co-PHA의제조는저온열고리화를통해 Co-PBO로전환시사용되는에너지소비의절감과동시에신규내열성고분자소재로적용가능성이있다는것을의미한다고볼수있다. 4. 결론 Figure 3. TGA curves obtained under nitrogen atmosphere for seven different Co-PHAs; (A) Co-PHA 1 4 and (B) Co-PHA 5 7. 강직한구조에기인한것이라고충분히예상된다. 또한 Co- PHA 5, 6, 7의경우 (Figure 3(B)), diacyl chloride 성분을 TPC(50):IPC(50) 로고정하고 diamine 성분을각각 DHB, BAHHFP 및 BAHS로달리하여 TGA를관찰한결과, 열안정성이 DHB(Co-PHA 5) > BAHS(Co-PHA 7) > BAHHFP (Co-PHA 6) 순으로높은것을확인할수있는데이는상기언급한용해도및 DSC 결과와마찬가지로 diamine 성분의입체구조적특성으로해석가능하다. Table 4는 Co-PHAs에서 Co-PBOs로전환된후의열적특성결과를정리하여나타낸것으로, Co-PBO 5의경우, 약 630 o C 부근에서열분해가시작되는반면플루오르기및술폰기가도입된 Co-PBOs의경우 524 570 o C로약 60 105 o C 낮은범위에서열분해가시작되는것을관찰할수있다. 이러한결과는주쇄내플루오르기및술폰기가도입된 Co- PBOs의경우, 가열시두벤젠링사이에서열적으로불안정한 CF 3 단일결합과 SO 2 이중결합 chain이먼저절단되면서상당수의라디칼을발생시키기때문에 Co-PBOs의열분해가가속화되는것으로판단된다 [26]. 반면모든 Co- PBOs의 char 함량이약 60.6 68.5% 수준으로고내열성소 본연구에서는 diamine 성분으로서 DHB, BAHHFP 및 BAHS를사용하고, diacyl chloride 성분으로 TPC 및 IPC를사용하여저온용액축합중합법을통해일곱종류 Co-PHA 를합성하였고, 단량체종류에따른화학구조, 열고리화거동및열분해특성을평가하였다. FT-IR 분석결과, BAHHFP 및 BAHS가도입된 Co-PHAs의특성밴드확인을통해합성이잘된것을확인하였다. 용해도평가결과는 THF 용매를제외하고는모든 Co-PHAs는 LiCl 존재하에 DMAc, DMF, NMP, DMSO 등의극성용매에서잘용해됨을알수있었으며, Co-PHA 2, 4, 7의경우염첨가없이도유기용매에용해가능한것을확인하였다. DSC 결과를통해 Co-PHAs 내 BAHHFP의도입이 BAHS의도입보다열고리화피크온도가더낮은것을알수있었다. TGA 결과로는모든 Co-PHAs 의초기분해온도가 514.7 620.4 o C 인것으로보아 Co-PHAs 모두열안정성이우수한것을확인하였다. 또한, BAHHFP가도입된 Co-PHA 1, 2 보다 BAHS가도입된 Co-PHA 3, 4가더우수한열안정성을갖는것을확인할수있었으며, Co-PHA 5, 6, 7의경우열안정성이 DHB(Co-PHA 5) > BAHS(Co-PHA 7) > BAHHFP (Co-PHA 6) 순으로높은것을관찰할수있었는데, 이는 diamine 성분의입체구조적특성에기인한다. 종합하면본연구에서진행한일곱종류 Co-PHA는전구체상태에서기존 PHA homopolymer보다다양한유기용매에용해가가능하기때문에성형성및가공성이더용이할뿐만아니라보다낮은온도에서고리화반응을통해 PBO 구조로전환이가능한것을확인하였다. 또한 diamine
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