UNDERSTANDING THE VIBRATIONAL STRUCTURE, RING- OPENING KINETICS OF OXAZINE RING AND HYDROGEN BONDING EFFECTS ON FAST POLYMERIZATION OF 1,3- BENZOXAZINES by LU HAN Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Dissertation Advisor: Dr. Hatsuo Ishida Department of Macromolecular Science and Engineering CASE WESTERN RESERVE UNIVERSITY May, 2018 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Lu Han Candidate for the degree of Doctor of Philosophy. * Committee Chair Dr. Hatsuo Ishida Dr. Gary Wnek Dr. Lei Zhu Dr. Daniel Lacks Date of Defense Nov. 2nd, 2017 *We also certify that written approval has been obtained for any proprietary material contained therein. DEDICATION To my parents, Jianjun Han and Jinyan Zhang TABLES OF CONTENTS TABLE OF CONTENTS i LIST OF TABLES iv LIST OF SCHEMES v LIST OF FIGURES vi ACKNOWLEDGEMENTS xiii ABSTRACT xv CHAPTER 1: Introduction 1 1.1 Review of benzoxazine 2 1.2 Oxazine ring related modes 3 1.3 Intrinsic ring opening of oxazine ring 3 1.4 Hydrogen bonding in amide-containing benzoxazine 4 1.5 References 4 CHAPTER 2: Study of oxazine ring-related vibrational modes of benzoxazine monomers 8 2.1 Introduction 8 2.2 Experimental 13 i 2.3 Results and Discussion 25 2.4 Conclusions 51 2.5 References 51 CHAPTER 3: Investigation of intrinsic self-initiating thermal ring-opening polymerization of 1,3-benzoxazines 55 3.1 Introduction 56 3.2 Experimental 60 3.3 Results and Discussion 65 3.4 Conclusions 91 3.5 References 92 CHAPTER 4: Study of the effects of intramolecular and intermolecular hydrogen- bonding of amide-containing benzoxazines 96 4.1 Introduction 97 4.2 Experimental 99 4.3 Results and Discussion 102 4.4 Conclusions 120 4.5 References 120 ii CHAPTER 5: Conclusion 125 5.1 Oxazine ring related modes 126 5.2 Intrinsic ring opening of oxazine ring 126 5.3 Hydrogen bonding in amide-containing benzoxazine 126 SUPPORTING INFORMATION 128 iii LIST OF TABLES Table 2.1 Potential energy distribution for the oxazine ring-related modes of PH-a which is calculated using Gaussian 09 with B3LYP/6-31G** theory and basis and VEDA4 software. 43 Table 2.2 Frequency of the characteristic band in experimental FT-IR and Raman and theoretical model for PH-a, PH-a-phenol-d4, PH-a-2oxazine-d2, PH-a-4oxazine-d2, PH- 15 a-oxazine-d4, PH-d-a and PH-a- N. 46 Table 3.1 Elemental Analysis Results of PH-a. 71 Table 3.2 Weight of 4-methoxyphenol and PH-a of different phenolic content mixture sample. 72 Table 3.3 Phenolic content in each PH-a/4-metoxyphenol mixture and the specific weight of every sample studied by DSC. 73 Table 3.4 Polymerization temperature of mixture samples measured by DSC. 76 Table 4.1 Maxima of the N-H stretching absorption bands observed by FT-IR. Spectra were recorded in solution using CHCl3 as solvent. 107 Table 4.2 Examples of reported results on secondary amide N-H stretching band positions determined by FT-IR. 111 Table 4.3 Chemical shifts of the –O–CH2–N= and =N–CH2–Ar in CDCl3 and DMSO-d6 as solvent. 113 iv LIST OF SCHEMES Scheme 2.1 Synthesis scheme of all substituted benzoxazine. 26 Scheme 2.2 Synthesis scheme of isotopes of PH-x, PH-x-phenol-d4, PH-x-oxazine-d4 and PH-d-a. 30 Scheme 2.3 Synthesis scheme of isotopes of PH-x-2oxazine-d2 and PH-x-4oxazine-d2. 31 Scheme 3.1 Solvent-less PH-a synthesis. 65 Scheme 4.1. Synthesis of benzoxazine monomers PH-a, pHBA-a, and oHBA-a. 104 v LIST OF FIGURES Figure 2.1 Chemical structure of all-substituted benzoxazines. 10 Figure 2.2 Chemical structure of PH-a series. 12 Figure 2.3 Chemical structure of PH-t series. 12 Figure 2.4 Chemical structure of methyl group substituted benzoxazine series. 13 1 Figure 2.5 H-NMR spectra for (a)25DMR-h, (b)PG-a and (c)PG-anis in CDCl3 at room temperature. 27 Figure 2.6 Comparison of FT-IR spectra of all-substituted benzoxazine monomer (top) and its corresponding polymer obtained by heating the monomer at 180oC for 2 h (bottom): (a) 25DMR-h and its polymer; (b) PG-a and its polymer; (c) PG-anis and its polymer. 28 Figure 2.7 1H-NMR spectra for PH-a isotopes (left) and PH-t isotopes (right). (a) PH-a, (b) PH-a-phenol-d4, (c) PH-a-2oxazine-d2, (d) PH-a-4oxazine-d2, (e) PH-a-oxazine-d4, (f) PH-d-a, (g) PH-t, (h) PH-t-phenol-d4, (i) PH-t-2oxazine-d2, (j) PH-t-oxazine-d4 in CDCl3 at room temperature. 33 Figure 2.8 FT-IR spectra of PH-a isotopes (left) and PH-t isotopes (right). (a) PH-a, (b) PH-a-phenol-d4, (c) PH-a-2oxazine-d2, (d) PH-a-4oxazine-d2, (e) PH-a-oxazine-d4, (f) PH-d-a, (g) PH-t, (h) PH-t-phenol-d4, (i) PH-t-2oxazine-d2, (j) PH-t-oxazine-d4. 34 Figure 2.9 FT-IR spectra of (a) PH-a, (b) PH-a-15N. 36 vi 1 Figure 2.10 H-NMR spectra for PH-a-4oxazine and PH-a-2oxazine in CDCl3 at room temperature. 38 Figure 2.11 FT-IR spectra of oxazine ring substituted PH-a. (a) PH-a-4oxazine, (b) PH- a-2oxazine. 39 Figure 2.12 The crystal structure and optimized structure of PH-a. 40 Figure 2.13 Experimental and theoretical FT-IR results for PH-a. 41 Figure 2.14 Comparison of experimental FT-IR results and theoretical results for FT-IR spectra of PH-a isotopes (a) PH-a, (b) PH-a-phenol-d4, (c) PH-a-2oxazine-d2, (d) PH-a- 4oxazine-d2, (e) PH-a-oxazine-d4, (f) PH-d-a. 43 Figure 2.15 Characteristic band fitting of FT-IR spectrum of PH-a. 48 Figure 3.1 FT-IR spectrum of benzoxazine monomer, PH-a. 67 1 Figure 3.2 H NMR spectrum of PH-a. Satellites of each –CH2– peak corresponding to H2 and H4 can be better observed in the inset of the figure, which shows a close look near the baseline within the region between 4 and 6 ppm. Spectrum recorded at 25 °C, using DMSO- d6 as solvent. 68 Figure 3.3 a) DSC thermograms showing the change in the polymerization temperature of PH-a after successive recrystallization processes. b) Crystals of PH-a after all recrystallization processes. 70 Figure 3.4 DSC thermograms, region between 240 and 190 oC showing the exothermic polymerization peaks of different mixturesamples with increasing percentages of 4- methoxyphenol: (a) 0.00% of 4-methoxyphenol (pure PH-a), (b) 0.23 mol% of 4-methoxy- vii phenol, (c) 0.44 mol% of 4-methoxyphenol, (d) 0.56 mol% of 4-methoxyphenol, (e) 0.88 mol% of 4-methoxyphenol, and (f) 1.05mol% of 4-methoxyphenol. 75 Figure 3.5 Polymerization temperature as a function of the concentration of a phenol- containing compound (4-methoxypheonol). 77 Figure 3.6 DSC thermogram of PH-a from 30 to 300 °C. The endothermic peak at 59 °C is assigned to the melting while the exothermic one at 272 °C to the polymerization of PH- a. 79 Figure 3.7 Resonance structures of the unsubstituted benzoxazine PH-a. Structures in involving the aromatic ring that was adjacent to the oxazine ring (a) and the aniline moiety (b). 81 Figure 3.8 Simplified mechanisms for the polymerization of benzoxazines. a) The classically accepted thermally accelerated (or activated) polymerization mechanism, where in addition to heat impurities must participate in the initiation step; and b), thermal polymerization mechanism, induced only by heat. 83 Figure 3.9 Ring-chain tautomeric equilibrium of the unsubstituted benzoxazine PH-a. 84 Figure 3.10 Resonance structures of the chain-like tautomer of the unsubstituted benzoxazine PH-a involving the aromatic ring that was adjacent to the oxazine ring. 85 Figure 3.11 Plots to graphically calculate the activation energy (Ea) of the polymerization reaction of PH-a applying the Kissinger and Ozawa methods. In the plots, β is the constant heating rate and Tp is the maximum value of the exothermic polymerization peak. Linear viii regression obtained for each method are: R2 = 0.996 for the Kissinger method and R2 = 0.997 for the Ozawa method. 87 Figure 3.12 TGA thermogram of the highly purified poly(PH-a). 89 Figure 4.1 (a) 1H and (b) 13C NMR spectra of pHBA-a, (c) 1H and (d) 13C NMR spectra of oHBA-a. 105 Figure 4.2 FT-IR spectra showing the region between 3500 and 3380 cm-1 for (a) pHBA- a, and (b) oHBA-a. Spectra were recorded in solution at different concentrations using CHCl3 as solvent. 107 Figure 4.3 pHBA-a, and oHBA-a N-H stretching wavenumber vs. concentration. 109 Figure 4.4 1H NMR spectra of pHBA-a at different concentrations. All spectra were recorded at 25 °C using CDCl3 as solvent. 112 Figure 4.5 DSC thermograms comparing oHBA-a, pHBA-a with PH-a. 115 Figure 4.6 DSC thermograms comparing poly(PH-a) (blue), poly(pHBA-a) (red), and poly(oHBA-a) (black). 119 Figure S.1 NMR Spectrum of 25DMR-h 129 Figure S.2 NMR Spectrum of PG-a 130 Figure S.3 NMR Spectrum of PG-anis 131 Figure S.4 NMR Spectrum of PH-a 132 Figure S.5 NMR Spectrum of PH-a-phenol-d4 133 Figure S.6 NMR Spectrum of PH-a-2oxazine-d2 134 ix Figure S.7 NMR Spectrum of PH-a-4oxazine-d2 135 Figure S.8 NMR Spectrum of PH-a-oxazine-d4 136 Figure S.9 NMR Spectrum of PH-d-a 137 Figure S.10 NMR Spectrum of PH-t 138 Figure S.11 NMR Spectrum of PH-t-phenol-d4 139 Figure S.12 NMR Spectrum of PH-t-2oxazine-d2 140 Figure S.13 NMR Spectrum of PH-t-oxazine-d4 141 Figure S.14 NMR Spectrum of PH-a-4oxazine 142 Figure S.15 NMR Spectrum of PH-a-2oxazine 143 Figure S.16 FT-IR Spectrum of 25DMR-h 144 Figure S.17 FT-IR Spectrum of PG-a 145 Figure S.18 FT-IR Spectrum of PG-anis 146 Figure S.19 FT-IR Spectrum of PH-a 147 Figure S.20 FT-IR Spectrum of PH-a-phenol-d4 148 Figure S.21 FT-IR Spectrum of PH-a-2oxazine-d2 149 Figure S.22 FT-IR Spectrum of PH-a-4oxazine-d2 150 Figure S.23 FT-IR Spectrum of PH-a-oxazine-d4 151 Figure S.24 FT-IR Spectrum of PH-d-a 152 Figure S.25 FT-IR Spectrum of PH-t 153 x Figure S.26 FT-IR Spectrum of PH-t-phenol-d4