Synthesis of next-generation polystyrene derivatives and their application for orientation layer of anisotropic materials

다국어 초록 (Multilingual Abstract)

Firstly, we synthesized a series of polystyrene derivatives that were modified with precursors of liquid crystal (LC) molecules, such as 4-ethyloxyphenol (homopolymer PEOP and copolymer PEOP#; # = 20, 40, 60, and 80, where # indicates the molar fraction of 4-ethyloxyphenoxymethyl in the side chain), 4-n-butyloxyphenol (PBOP), 4-n-hexyloxyphenol (PHOP), and 4-n-octyloxyphenol (POOP), via polymer modification reaction to investigate the orientation of LC molecules on polymer films, exhibiting part of the LC molecular structure. LC molecules showed a stable and uniform vertical orientation in LC cells fabricated with polymers that have 4-ethyloxyphenoxymethyl in the range of 40–100 mol%. In addition, similar results were obtained in LC cells fabricated with homopolymers of PEOP, PBOP, PHOP, and POOP. The vertical orientation of LC molecules in LC cells fabricated with polymer films correlated to the surface energy of polymer films. For example, vertical LC orientation was observed when the total surface energies of the polymer films were lower than approximately 43.2 mJ/m2. Good alignment stabilities were observed at 150 °C and 20 J/cm2 of ultraviolet irradiation for LC cells fabricated with PEOP film.
Secondly, we synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules, including 4-(trans-4-ethylcyclohexyl)phenol (homopolymer PECH and copolymer PECH#; # = 5, 10, 15, 20, 40, 60, and 80, where # indicates the molar fraction of 4-(trans-4-ethylcyclohexyl)phenoxymethyl in the side chain), 4-(trans-4-propylcyclohexyl)phenol (PPCH), 4-(trans-4-butylcyclohexyl)phenol (PBCH), and 4-(trans-4-amylcyclohexyl)phenol (PAmCH) via polymer modification reactions in order to investigate the orientation of LC molecules on polymer films exhibiting part of the LC molecular structure. A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with PECH#, having 15 mol% or more of 4-(trans-4-ethylcyclohexyl)phenoxymethyl side groups. In addition, the vertical orientation of LC molecules was observed in LC cells fabricated with homopolymers of PECH, PPCH, PBCH, and PAmCH. The water contact angle on the polymer films could be associated with the vertical orientation of the LC molecules in the LC cells fabricated with polymer films. For example, a vertical LC orientation was observed when the water contact angle of the polymer films was higher than ~81°. Good orientation stability was observed at 200 °C and 15 mW/cm2 of UV irradiation for LC cells fabricated with PECH films.
Finally, we synthesized a series of polystyrene derivatives modified with precursors of liquid crystal (LC) molecules via polymer modification reactions. Thereafter, the orientation of the LC molecules on the polymer films, which possess part of the corresponding LC molecular structure, was investigated systematically. The precursors and the corresponding derivatives used in this study include ethyl-p-hydroxybenzoate (homopolymer P2BO and copolymer P2BO#, where # indicates the molar fraction of ethylbenzoate-p-oxymethyl in the side chain (# = 20, 40, 60, and 80)), n-butyl-p-hydroxybenzoate (P4BO), n-hexyl-p-hydroxybenzoate (P6BO), and n-octyl-p-hydroxybenzoate (P8BO). A stable and uniform vertical orientation of LC molecules was observed in LC cells fabricated with P2BO#, with 40 mol% or more ethylbenzoate-p-oxymethyl side groups. In addition, the LC molecules were oriented vertically in LC cells fabricated with homopolymers of P2BO, P4BO, P6BO, and P8BO. The water contact angle on the polymer films can be associated with the vertical orientation of the LC molecules in the LC cells fabricated with the polymer films. For example, vertical LC orientation was observed when the water contact angle of the polymer films was greater than ~86°. Good orientation stability was observed at 150 °C and with 20 J/cm2 of UV irradiation for LC cells fabricated with the P2BO film.
The results of this research can provide a new perspective for the design and synthesis of orientation material to align the anisotropic materials, such as liquid crystals, using the similarity between the chemical structure of the orientation layer and LC molecules.

국문 초록 (Abstract)

우리는 액정 분자와 배향제 간 화학구조의 유사성이 액정 분자의 초기 배향에 미치는 영향을 체계적으로 연구하기 위해 액정 전구체를 포함하는 폴리스티렌 유도체들을 합성하였다.
첫째, 단일중합체 PAOP(4-n-alkyloxyphenoxymethyl-substituted polystyrene)와 공중합체 PEOP#(# = 20, 40, 60, 및 80)를 합성한 뒤 박막 형태로 액정 셀에 도입하여, 액정 분자와 배향막 간 화학구조의 유사성이 액정 분자의 초기 배향에 미치는 영향을 체계적으로 연구하였다. 여기서 #은 고분자의 측쇄에 치환된 4-ethyloxyphenoxymethyl group의 몰 비율이다. PEOP40, PEOP60, PEOP80, 그리고 PAOP(PEOP, PBOP, PHOP, 및 POOP)로 제작한 액정 셀에서 액정분자 5CB(4-cyano-4'-pentylbiphenyl)의 초기배향이 수직으로 유도됨을 관찰하였다. 액정의 수직 배향은 고분자 필름의 표면에너지가 43.2 mJ/m2 이하일 때 관찰되었으며, 상온에서 150 °C 에 이르는 온도범위 그리고 20 J/cm2 에너지에 달하는 자외선 노출에 대해 액정 분자의 배향이 안정하게 유지됨을 확인하였다.
둘째, 단일중합체 PACH(4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted polystyrene)와 공중합체 PECH#(# = 5, 10, 15, 20, 40, 60, 및 80)를 합성한 뒤 박막 형태로 액정 셀에 도입하여, 액정 분자와 배향막 간 화학구조의 유사성이 액정 분자의 초기 배향에 미치는 영향을 체계적으로 연구하였다. 여기서 #은 고분자의 측쇄에 치환된 4-(trans-4-ethylcyclohexyl)phenoxymethyl의 몰 비율이다. PECH 15, PECH20, PECH40, PECH 60, PECH 80, 그리고 PACH(PECH, PPCH, PBCH, 및 PAmCH)로 제작한 액정 셀에서 액정분자 5CB의 초기배향이 수직으로 유도됨을 관찰하였다. 액정의 수직 배향은 고분자 필름의 물 접촉각이 81° 이상일 때 관찰되었으며, 상온에서 200 °C 에 이르는 온도범위 그리고 15 mW/cm2 세기의 자외선 노출에 대하여 액정 분자의 배향이 안정하게 유지됨을 확인하였다.
셋째, 단일중합체 PABO(n-alkylbenzoate-p-oxymethyl-substituted polystyrene)와 공중합체 P2BO#(# = 20, 40, 60, 및 80)를 합성한 뒤 박막 형태로 액정 셀에 도입하여, 액정 분자와 배향막 간 화학구조의 유사성이 액정 분자의 초기 배향에 미치는 영향을 체계적으로 연구하였다. 여기서 #은 고분자의 측쇄에 치환된 ethyl-p-hydroxybenzoate group의 몰 비율이다. P2BO40, P2BO60, P2OP80, 그리고 PABO(P2BO, P4BO, P6BO, 및 P8BO)로 제작한 액정 셀에서 액정분자 5CB의 초기배향이 수직으로 유도됨을 관찰하였다. 액정의 수직 배향은 고분자 필름의 물 접촉각이 86° 이상일 때 관찰되었으며, 상온에서 150 °C 에 이르는 온도범위 그리고 20 J/cm2 에너지에 달하는 자외선 노출에 대해 액정 분자의 배향이 안정하게 유지됨을 확인하였다.
본 연구의 결과는 액정 분자와 배향제 간 화학 구조적 유사성이 액정 분자의 수직 배향을 유도하도록 영향을 미칠 수 있음을 보여줌으로써 수직전계방식 액정표시장치 배향제의 개발에 영감을 제공할 수 있다.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• 1. Chemical structures and compositions of liquid crystals 1
• 2. Classification of liquid crystals: lyotropic and thermotropic liquid crystals 1
• 3. Orientational order 3
• 4. Initial orientation of liquid crystals 3
• References 4
• Ⅱ. Part 1 – Vertical orientation of liquid crystal on 4-n-alkyloxyphe-noxymethyl-substituted polystyrene containing liquid crystal precursor 7
• 1. Introduction 7
• 2. Experimental 10
• 2.1 Materials 10
• 2.2 Preparations of 4-n-alkyloxyphenoxymethyl modified polystyrene 11
• 2.3 Film preparation and liquid crystal cell assembly 14
• 2.4 Instrumentation 15
• 3. Results and discussion 16
• 3.1 Synthesis and characterization of 4-n-alkyloxyphenoxymethyl modified polystyrene 16
• 3.2 Liquid crystal orientation behavior of the liquid crystal cell fabricated with PAOP films 32
• 3.3 Liquid crystal orientation behavior of the liquid crystal cell fabricated with PEOP# films 33
• 3.4 Surface properties of PEOP# and PAOP films 37
• 3.5 Reliability of the liquid crystal cells fabricated with PEOP films 40
• 4. Conclusions 42
• References 43
• Ⅲ. Part 2 – Vertical orientation of liquid crystal on comb-Like 4-(trans-4-alkylcyclohexyl)phenoxymethyl-substituted polystyrene containing liquid crystal precursor 53
• 1. Introduction 53
• 2. Experimental 57
• 2.1 Materials 57
• 2.2 Preparations of 4-(trans-4-alkylcyclohexyl)phenoxymethyl modified polystyrene 58
• 2.3 Film preparation and liquid crystal cell assembly 60
• 2.4 Instrumentation 61
• 3. Results and discussion 62
• 3.1 Synthesis and characterization of 4-(trans-4-alkylcyclohexyl)phenoxymethyl modified polystyrene 62
• 3.2 Liquid crystal orientation behavior of the liquid crystal cell fabricated with PACH films 68
• 3.3 Liquid crystal orientation behavior of the liquid crystal cell fabricated PECH# films 70
• 3.4 Surface properties of PECH# and PACH films 73
• 3.5 Reliability of the liquid crystal cells fabricated with PECH films 76
• 4. Conclusions 79
• References 80
• Ⅳ. Part 3 – Vertical orientation of liquid crystal on polystyrene substi-tuted with n-alkylbenzoate-p-oxymethyl pendant group as a liquid crystal precursor 90
• 1. Introduction 90
• 2. Experimental 93
• 2.1 Materials 93
• 2.2 Preparations of n-alkylbenzoate-p-oxymethyl modified polystyrene 95
• 2.3 Film preparation and liquid crystal cell assembly 98
• 2.4 Instrumentation 99
• 3. Results and discussion 99
• 3.1 Synthesis and characterization of n-alkylbenzoate-p-oxymethyl modified polystyrene 100
• 3.2 Liquid crystal orientation behavior of the liquid crystal cell fabricated with PABO modified polystyrene 125
• 3.3 Liquid crystal orientation behavior of the liquid crystal cell fabricated with P2BO# modified polystyrene 128
• 3.4 Surface properties of P2BO# and PABO films 131
• 3.5 Reliability of the liquid crystal cells fabricated with P2BO films 134
• 4. Conclusions 136
• References 137
• 국문초록 149
• 감사의 글 152