Synthesis and characterization of non shrinking nanocomposites for dental applications 1

SYNTHESIS AND CHARACTERIZATION OF “NON-SHRINKING” NANOCOMPOSITES FOR DENTAL APPLICATIONS SOH MUI SIANG (BSC, BSc(Hons), MSC), NUS A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF RESTORATIVE DENTISTRY NATIONAL UNIVERSITY OF SINGAPORE 2006 ACKNOWLEDGEMENTS Interdependence is a higher value than independence. This thesis is the result of multi-disciplinary collaboration that involved people from the Department of Restorative Dentistry, Faculty of Dentistry and the Institute of Materials and Research Engineering (IMRE) whom I would like to express my sincere gratitude. I would like to thank Associate Professor Jennifer Neo Chew Lian, Head of Restorative Dentistry, National University of Singapore for the opportunity and support given to me throughout the course of my postgraduate study. I would also like to thank and express my sincere gratitude to my supervisors, Associate Professor Adrian Yap U Jin and Dr. Alan Sellinger for giving me the opportunity to undertake this research. It is indeed my great honor to work and learn from them. Despite their heavy work duties, they never fail to make time for sharing research knowledge, for invaluable discussions and for giving scientific advice. Their patience, constant guidance, encouragement, support and motivation contribute much to the success of this research project. I would also like to thank Research Scientist, Dr. Low Hong Yee for help and invaluable discussions throughout the course of this project. Her patience and time is most appreciated. i I would also like to thank Dr. Sundarraj Sudhakar whom has been such a great mentor and friend. His advice, guidance, help and encouragement have been of great value in fulfilling this thesis. Special thanks are also extended to Senior Laboratory Officer, Mr Chan Swee Heng for his kind assistance, generous help and time. It is indeed a great pleasure to work with him. His resourcefulness never fails to impress me. I would also like to thank “big brother” Mr Chung Sew Meng for his guidance on the use of the Instron machine. His generous help and assistance has been most invaluable. Heartfelt thank is also extended to Ms Jane Ong Lay Hoon, Ms Ng Bee Wee and Mdm Ek Ben Lai for their constant administrative help and support. Without their help, administrative work would not have been that smooth and easy. Special appreciation is also extended to all my friends especially to Xiaoyan, Mee Yoon, Thelese, Elaine, Christine, Zien, Wahab, Xiuwen, Soon Yee, Vicky, Yuan Yuan, Dr. Sum Chee Peng, Saji and those countless others who have helped me in every little way. I would also like to show my appreciation to my sister, Mingjuan for help and suggestions given in the completion of this thesis. Finally, I am deeply grateful to my family, especially my parents, for raising me to believe that with determination, dedication and enthusiasm you can achieve any goal you can dream of. Their kind understanding, encouragement, support and love throughout the years of my education have made this possible. ii TABLE oF CONTENTS Foreword Chapter Acknowledgements i Table of Contents iii Summary vi List of Tables viii List of Figures xi List of Publications xix INTRODUCTION 1.1 Composite Resins – An Alternative to Dental Amalgam 1.2 Research Objectives Chapter LITERATURE REVIEW 2.1 Chemically Cured Composite Resins 2.2 Light-activated Composite Resins 2.3 Organic Matrix 2.4 Inorganic Fillers 10 2.5 Silane Coupling Agent 11 2.6 Limitations of Current Dental Composites 12 2.6.1 Polymerization Shrinkage 2.7 New Resin Technology 12 15 2.7.1 Ring-opening Monomers 15 2.7.2 Liquid Crystalline Monomers 18 2.7.3 Branched and Dendritic Monomers 20 2.7.4 Ormocers 20 2.8 Nanotechnology with Dental Composites 21 iii Chapter Chapter Chapter Chapter Chapter RESEARCH PROGRAMME 3.1 Research Overview 32 3.2 Research Programme 33 INORGANIC-ORGANIC SSQ AS SYNTHETIC PLATFORMS 4.1 Introduction 39 4.2 Materials and Methods 42 4.3 Results and Discussions 45 4.4. Conclusions 51 SYNTHESIS AND CHARACTERIZATION OF SSQ-BASED MONOMERS: DI(PROPYLENE GLYCOL) ALLYL ETHER METHACRYLATE SIDE CHAINS 5.1 Introduction 52 5.2 Materials and Methods 53 5.3 Results and Discussions 68 5.4. Conclusions 99 SYNTHESIS AND CHARACTERIZATION OF SSQ-BASED MONOMERS: PROPARGYL METHACRYLATE SIDE CHAINS 6.1 Introduction 101 6.2 Materials and Methods 102 6.3 Results and Discussions 110 6.4. Conclusions 142 SSQ-BASED MONOMERS AS COPOLYMERS 7.1 Introduction 143 7.2 Materials and Methods 144 7.3 Results and Discussions 145 7.4. Conclusions 181 iv Chapter Chapter References EXPERIMENTAL SSQ-BASED NANOCOMPOSITES 8.1 Introduction 182 8.2 Materials and Methods 183 8.3 Results and Discussions 189 8.4. Conclusions 211 GENERAL CONCLUSIONS AND FUTURE PERSPECTIVES 9.1 General Conclusions 212 9.2 Future Perspectives 215 220 v SUMMARY The aim of this study was to design and develop novel low shrinkage nanocomposites based on SSQ (Polyhedral Silsesquioxane) for dental applications. SSQ based nanocomposites with various types of methacrylate and/or epoxide functionalities were synthesized based on inexpensive starting materials. The synthesized SSQ compounds obtained in high yield were viscous liquids at room temperature and formed soluble hybrids when formulated with existing dental-based monomers in different proportions. The synthesized materials were characterized chemically using FTIR, NMR, DSC, TGA and SEC to confirm polymer structure and purity. Physico-mechanical properties such as post-gel polymerization shrinkage, indentation hardness and modulus of the synthesized materials and their formulated neat resins were then investigated and compared with unfilled 1:1 (control) Bis-GMA / TEGDMA materials (typical monomers used in dental composites). All samples investigated were cured using a dental light-curing unit at 500mW/cm2 for 40 seconds. At all time intervals, shrinkage associated with the control was found to be significantly higher than all SSQ based materials and their formulated neat resins. However, both hardness and modulus of the control were found to be significantly higher than all SSQ based materials and most of the formulated neat resins. It was observed that the addition of as little as wt% SSQ nanocomposites into the control monomers significantly reduced polymerization shrinkage while maintaining useful mechanical properties. Based on the study results, four promising materials were selected and developed into experimental nanocomposites (S1 – S4) by reinforcing with 63 wt% of commercial fillers. The experimental nanocomposites (S1 – S4) were then vi characterized for their physico-mechanical properties such as polymerization shrinkage, hardness, modulus, depth of cure, degree of conversion and water sorption. Results obtained were compared with various commercial dental composites (Filtek Supreme [FS], Filtek Flow [FF] and Filtek A110 [A110]). At 60 minutes post-gel polymerization, shrinkage associated with the experimental nanocomposites and commercial products ranged from (0.31 ± 0.03) to (0.42 ± 0.03)% and (0.54 ± 0.03) to (0.84 ± 0.07)% respectively. At all time intervals, shrinkage associated with the experimental materials was found to be significantly lower than the commercial products with depth of cure greater than 2mm obtained for all materials. No significant difference in hardness was observed between S1, A110 and FF. Modulus associated with S1 and S4 was found to be higher if not equal to A110 and FF. The degree of conversion of S4 was also found to be higher than A110. Water sorption obtained for all experimental nanocomposites was found to be significantly lower than the commercial products and met the ISO requirement of less than 40 μg/mm3. With the results obtained, we conclude that SSQ based nanocomposites show potential for use as dental restoratives and present a promising approach to achieve novel low/non–shrinking nanocomposite based dental materials. vii LIST OF TABLES Table 2.1 Classification of dental composites by filler particle size. 10 Table 5.1 Size Exclusion Chromatography synthesized SSQ compounds. of 83 Table 5.2 Thermogravimetric Analysis (TGA) data of synthesized compounds. 86 Table 5.3 Differential Scanning Calorimetry (DSC) data. 89 Table 5.4 Mean linear percent polymerization shrinkage at the various post-light polymerization time intervals. 93 Table 5.5 Results of statistical analysis. 94 Table 5.6 Hardness values of synthesized compounds. 96 Table 5.7 Modulus values of control and synthesized SSQ compounds. 97 Table 5.8 Comparison of mean hardness values of the various synthesized compounds to control. 98 Table 5.9 Comparison of mean modulus values of the various synthesized compounds to control. 98 Table 6.1 SEC data of compounds E - H. 127 Table 6.2 Thermogravimetric analysis data of compounds E - H. 130 Table 6.3 DSC data for compounds E - H. 133 Table 6.4 Mean linear percent polymerization shrinkage at the various post-light polymerization time intervals. 135 Table 6.5 Results of statistical analysis. 136 Table 6.6 Hardness values of synthesized compounds. 138 Table 6.7 Modulus values of control and synthesized SSQ compounds. 139 Table 6.8 Comparison of mean hardness values of the various synthesized compounds to control. 140 (SEC) data viii Table 6.9 Comparison of mean modulus values of the various synthesized compounds to control. 140 Table 7.1 Mean linear percent polymerization shrinkage at the various post-light polymerization time intervals of control and binary blend of compounds A - D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios respectively. 149 Table 7.2 Results of statistical analysis of post-gel linear shrinkage. 152 Table 7.3 Hardness values of the control and binary blend of compounds A - D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 155 Table 7.4 Elastic modulus of the control and binary blend of compounds A - D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 158 Table 7.5 Results of statistical analysis of mean hardness data. 161 Table 7.6 Results of statistical analysis of mean modulus data. 161 Table 7.7 Mean linear percent shrinkage of control and binary blend of compounds E - H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios respectively. 167 Table 7.8 Results of statistical analysis of post-gel linear shrinkage. 170 Table 7.9 Hardness values of the control and binary blend of compounds E - H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 172 Table 7.10 Elastic modulus of the control and binary blend of compounds E - H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 175 Table 7.11 Results of statistical analysis of mean hardness data. 178 Table 7.12 Results of statistical analysis of mean modulus data. 178 Table 8.1 The experimental and composite materials evaluated. 185 Table 8.2 Mean linear percent polymerization shrinkage at the various post-light polymerization time intervals. 191 Table 8.3 Results of statistical analysis. 192 ix Table 8.4 Mean hardness of the different materials. 197 Table 8.5 Mean modulus of the different materials. 198 Table 8.6 Statistical comparison of hardness between materials. 199 Table 8.7 Statistical comparison of modulus between materials. 200 Table 8.8 Mean degree of conversion of the different materials. 202 Table 8.9 Results of statistical analysis of the mean degree of conversion. 202 Table 8.10 Depth of cure of the different materials. 206 Table 8.11 Statistical comparison of depth of cure between materials. 206 Table 8.12 Results of water sorption obtained for the different materials. 209 Table 8.13 Results of statistical analysis. 209 x LIST OF FIGURES Figure 2.1 Chemical activation of dibenzoyl peroxide to produce free radical for polymerization. Figure 2.2 Chemical structure of Bis-GMA monomers. Figure 2.3 Light activation mechanism. Figure 2.4 Chemical structures of common base monomers used in dental composites. Figure 2.5 Structure of MPTS, a typical silane coupling agent used in dental composites. 11 Figure 2.6 Chemical structures of SOCs containing methylene groups. 16 Figure 2.7 Chemical structures of SOC-substituted methacrylate. 16 Figure 2.8 Cationic polymerizable SOC. 17 Figure 2.9 Chemical structures of cycloaliphatic diepoxide and polyol. 18 Figure 2.10 One example of near room temperature liquid crystalline dimethacrylate. 19 Figure 2.11 Branched liquid crystalline bismethacrylates. 20 Figure 2.12 Synthesis of SiO2 nanostructures. 21 Figure 2.13 Transmission electron micrographs of a hybrid, nanomer and nanocluster (Courtesy of 3M ESPE). 24 Figure 2.14 The Stöber process. 26 Figure 2.15 Example of commercially available methacrylate silanes. 28 Figure 2.16 Mono-methacrylate functionalized POSSTM. 29 Figure 2.17 POSSTM-MA. 30 Figure 2.18 Epoxy functionalized POSSTM structure. 30 Figure 2.19 Siloxane dendrimers. 31 xi Figure 3.1 Example of SSQ-based monomers synthesized using Ptcatalyzed hydrosilylation reaction. 34 Figure 4.1 Some common structures of silsesquioxane. 40 Figure 4.2 Silsesquioxanes produced by hydrolysis and condensation of trialkoxy- or trichlorosilanes. 40 Figure 4.3 Synthesis of hydridosilsesquioxane, (HSiO1.5)n. 41 Figure 4.4 Synthesis of “Octaanion”. 43 Figure 4.5 Synthesis of Octa(hydridodimethylsiloxy)silsesquioxane, (HMe2SiOSiO1.5)8. 44 29 46 Figure 4.6 Si NMR for the “octaanion” silsesquioxane. H NMR of Octa(hydridodimethylsiloxy)silsesquioxane, (HMe2SiOSiO1.5)8. 47 13 C NMR of Octa(hydridodimethylsiloxy)silsesquioxane, (HMe2SiOSiO1.5)8. 48 29 Si NMR of Octa(hydridodimethylsiloxy)silsesquioxane, (HMe2SiOSiO1.5)8. 49 Figure 4.10 FTIR spectrum of octa(hydridodimethylsiloxy)silsesquioxane. 50 Figure 5.1 Synthesis of compound A (SSQ with equivalents of DPGAEM). 54 Figure 5.2 Synthesis of compound B (SSQ with equivalents of DPGAEM and equivalents of VCE). 55 Figure 5.3 Synthesis of compound C (SSQ with equivalents of DPGAEM and equivalents of VCE). 57 Figure 5.4 Synthesis of compound D (SSQ with equivalents of DPGAEM and equivalents of VCE). 59 Figure 5.5 VIP light-curing unit. 61 Figure 5.6 Diagrammatic representation of the experimental set-up for the assessment of polymerization shrinkage. 63 Figure 5.7 Strain-monitoring device. 64 Figure 4.7 Figure 4.8 Figure 4.9 xii Figure 5.8 Figure 5.9 Figure 5.10 Figure 5.11 Figure 5.12 Figure 5.13 Figure 5.14 Figure 5.15 Figure 5.16 Figure 5.17 Figure 5.18 Figure 5.19 Figure 5.20 Depth-sensing microindentation test set-up. 67 71 H NMR of compound A. 13 C NMR of compound A. 72 29 Si NMR of compound A. 73 H NMR of compound B. 74 13 C NMR of compound B. 75 29 Si NMR of compound B. 76 H NMR of compound C. 77 13 C NMR of compound C. 78 29 Si NMR of compound C. 79 H NMR of compound D. 80 13 C NMR of compound D. 81 29 Si NMR of compound D. 82 Figure 5.21 α and β-trans isomer arising from Pt-catalyzed hydrosilylation of epoxy substituents on the cube. 83 Figure 5.22 SEC chromatogram for compound A. 84 Figure 5.23 SEC chromatogram for compound B. 84 Figure 5.24 SEC chromatogram for compound C. 85 Figure 5.25 SEC chromatogram for compound D. 85 Figure 5.26 TGA profile of compound A. 87 Figure 5.27 TGA profile of compound B. 87 Figure 5.28 TGA profile of compound C. 88 Figure 5.29 TGA profile of compound D. 88 Figure 5.30 Representative DSC plot for compound A. 90 Figure 5.31 Mean shrinkage during light polymerization. 92 xiii Figure 5.32 Mean linear shrinkage at various post-light polymerization time intervals. 93 Figure 5.33 Mean hardness values of control and synthesized SSQ compounds. 96 Figure 5.34 Elastic modulus of control and synthesized SSQ compounds. 97 Figure 6.1 Synthesis of compound E (SSQ with equivalents of PM). 103 Figure 6.2 Synthesis of compound F (SSQ with equivalents of PM and equivalents of VCE). 104 Figure 6.3 Synthesis of compound G (SSQ with equivalents of PM and equivalents of VCE). 106 Figure 6.4 Synthesis of compound H (SSQ with equivalents of PM and equivalents of VCE). 108 Figure 6.5 Oxysilylation reaction associated with allyloxy chemistry. 111 113 Figure 6.6 Figure 6.7 Figure 6.8 Figure 6.9 Figure 6.10 Figure 6.11 Figure 6.12 Figure 6.13 Figure 6.14 Figure 6.15 Figure 6.16 Figure 6.17 Figure 6.18 H NMR of compound E. 13 C NMR of compound E. 114 29 Si NMR of compound E. 115 H NMR of compound F. 116 13 C NMR of compound F. 117 29 Si NMR of compound F. 118 H NMR of compound G. 119 13 C NMR of compound G. 120 29 Si NMR of compound G. 121 H NMR of compound H. 122 13 C NMR of compound H. 123 29 Si NMR of compound H. 124 α and β-trans isomer arising from Pt-catalyzed hydrosilylation of propargyl and epoxy substituents on the cube. 126 xiv Figure 6.19 SEC chromatogram for compound E. 127 Figure 6.20 SEC chromatogram for compound F. 128 Figure 6.21 SEC chromatogram for compound G. 128 Figure 6.22 SEC chromatogram for compound H. 129 Figure 6.23 TGA profile of compound E. 130 Figure 6.24 TGA profile of compound F. 131 Figure 6.25 TGA profile of compound G. 131 Figure 6.26 TGA profile of compound H. 132 Figure 6.27 Representative DSC plot for compound F. 133 Figure 6.28 Mean shrinkage during light polymerization. 135 Figure 6.29 Mean linear shrinkage at various post-light polymerization time intervals. 136 Figure 6.30 Mean hardness values of control and synthesized SSQ compounds. 138 Figure 6.31 Elastic modulus of control and synthesized SSQ compounds. 139 Figure 7.1 Mean shrinkage of control and binary blend of compound A with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 146 Figure 7.2 Mean shrinkage of control and binary blend of compound B with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 147 Figure 7.3 Mean shrinkage of control and binary blend of compound C with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 147 Figure 7.4 Mean shrinkage of control and binary blend of compound D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 148 Figure 7.5 Mean linear shrinkage of control and binary blend of compound A with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 150 xv Figure 7.6 Mean linear shrinkage of control and binary blend of compound B with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 150 Figure 7.7 Mean linear shrinkage of control and binary blend of compound C with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 151 Figure 7.8 Mean linear shrinkage of control and binary blend of compound D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 151 Figure 7.9 Mean hardness values of control and binary blend of compound A with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 156 Figure 7.10 Mean hardness values of control and binary blend of compound B with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 156 Figure 7.11 Mean hardness values of control and binary blend of compound C with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 157 Figure 7.12 Mean hardness values of control and binary blend of compound D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 157 Figure 7.13 Mean elastic modulus of control and binary blend of compound A with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 159 Figure 7.14 Mean elastic modulus of control and binary blend of compound B with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 159 Figure 7.15 Mean elastic modulus of control and binary blend of compound C with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 160 Figure 7.16 Mean elastic modulus of control and binary blend of compound D with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 160 Figure 7.17 Mean shrinkage of control and binary blend of compound E with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 164 xvi Figure 7.18 Mean shrinkage of control and binary blend of compound F with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 165 Figure 7.19 Mean shrinkage of control and binary blend of compound G with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 165 Figure 7.20 Mean shrinkage of control and binary blend of compound H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization. 166 Figure 7.21 Mean linear shrinkage of control and binary blend of compound E with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 168 Figure 7.22 Mean linear shrinkage of control and binary blend of compound F with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 168 Figure 7.23 Mean linear shrinkage of control and binary blend of compound G with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 169 Figure 7.24 Mean linear shrinkage of control and binary blend of compound H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals. 169 Figure 7.25 Mean hardness values of control and binary blend of compound E with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 173 Figure 7.26 Mean hardness values of control and binary blend of compound F with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 173 Figure 7.27 Mean hardness values of control and binary blend of compound G with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 174 Figure 7.28 Mean hardness values of control and binary blend of compound H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 174 xvii Figure 7.29 Mean elastic modulus of control and binary blend of compound E with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 176 Figure 7.30 Mean elastic modulus of control and binary blend of compound F with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 176 Figure 7.31 Mean elastic modulus of control and binary blend of compound G with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 177 Figure 7.32 Mean elastic modulus of control and binary blend of compound H with control in 5, 10, 20 and 50 wt% of SSQ nanocomposite ratios. 177 Figure 8.1 Diagrammatic representation of the experimental set-up for the assessment of polymerization shrinkage. 186 Figure 8.2 Mean shrinkage during light polymerization. 191 Figure 8.3 Mean shrinkage post-light polymerization. 192 Figure 8.4 Mean hardness of the different materials. 198 Figure 8.5 Mean modulus of the different materials 199 Figure 8.6 Mean degree of conversion of the different materials. 203 Figure 8.7 Depth of cure of the different materials. 207 Figure 8.8 Mean water sorption obtained for the different materials. 209 Figure 9.1 Polymerization of the epoxy groups using the component initiating system. 216 Figure 9.2 Synthesis of cyclohexyl BZO. 217 Figure 9.3 Hydrosilylation reaction of SSQ with equivalents of cyclohexyl BZO. 218 Figure 9.4 Ring-opening of cyclohexyl BZO upon polymerization. 218 xviii LIST OF PUBLICATIONS Sections of the results/ related research in this thesis have been presented, published, accepted for publication or are submitted. International Papers 1. Soh MS, AUJ Yap and A Sellinger, Dental Nanocomposites. Current Nanoscience, 2, (2006) 373 -381. (United States). 2. Soh MS, AUJ Yap and A Sellinger, Methacrylate and Epoxy Functionalized Nanocomposites based on Silsesquioxane Cores for use in Dental Applications. European Polymer Journal, 43 (2007) 315-327. (Europe). 3. Soh MS, AUJ Yap and A Sellinger, Physicomechanical Evaluation of Low-shrink Dental Nanocomposites based on Silsesquioxane Cores. European Journal of Oral Science (Accepted for publication). 4. Soh MS, AUJ Yap and A Sellinger, Effect of Chain Modifications on the Physico-mechanical Properties of Silsesquioxane-based Dental Nanocomposites. Journal of Biomedical Research Part B. Applied Biomaterials (Submitted for publication). 5. Soh MS, AUJ Yap and A Sellinger, Silsesquioxanes-based Nanocomposites as Copolymers for Low Shrinkage Dental Composite. Biomacromolecules (Submitted for publication). 6. Soh MS, AUJ Yap and A Sellinger, Synthesis and Characterization of Low Shrinking Silsesquioxanes-based Experimental Nanocomposites for Dental Applications. Biomacromolecules (To be submitted for publication pending invention disclosure). xix Conference Papers 1. Soh MS, Sellinger A and Yap AUJ, Synthesis and Characterization of New Nanocomposite Monomers for use in Low Shrinkage Dental Restorations. Paper presented at 2nd IMRE Poster competition, 21 July 2004, Singapore. 2. Soh MS, Sellinger A and Yap AUJ, Synthesis and characterization of new monomers for dental restorations. Paper presented at 19th International Association for Dental Research (South-East Asian Division) Annual Meeting, 3-6 September 2004, Koh Samui, Thailand. 3. Soh MS, Yap AUJ and Sellinger A, Mechanical characterization of new monomers synthesized for dental restorations. Paper presented at 3rd Scientific NHG Congress, 9-11 October 2004, Singapore. 4. Soh MS, Sellinger A and Yap AUJ, Low Shrinkage Nanocomposites based on Silsesquioxane Cores for Applications in Dental Composites. Paper presented at 3rd International Conference on Materials for Advanced Technologies (ICMAT) 2005, Singapore. 5. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low Shrinkage POSS based Nanocomposites. Paper presented at 20th International Association for Dental Research (South-East Asian Division) Annual Meeting, 1-4 September 2005, Malacca, Malaysia. 6. Soh MS, Yap AUJ and Sellinger A, Mechanical Properties of Novel Nanocomposites Developed for Dental Restorations. Paper presented at Combined Scientific Meeting (CSM) 2005, Singapore. 7. Soh MS, Sellinger A and Yap AUJ, Low-shrinking Novel POSS Based Nanocomposites Developed for Dental Applications. Paper presented at Combined Scientific Meeting (CSM) 2005, Singapore. xx 8. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low Shrinkage POSS based Nanocomposites. Paper presented at SERC InterRI Poster Symposium, 19 September 2005, Singapore. 9. Soh MS, Sellinger A and Yap AUJ, Post-gel Polymerization Shrinkage of Novel Low-shrinking POSS Based Nanocomposites. Paper presented at 84th Annual General Session of the International Association for Dental Research, 28-1 July 2006, Brisbane, Australia. Awards 1. Soh MS, Sellinger A and Yap AUJ, The Development of Novel Low Shrinkage POSS Based Nanocomposites. Awarded Best paper in Dental Materials Research Category in 20th International Association for Dental Research (South-East Asian Division) Annual Scientific Meeting, 1-4 September 2005, Malacca, Malaysia. 2. Soh MS, Sellinger A and Yap AUJ, Synthesis and Characterization of New Nanocomposite Monomers For Use In Low Shrinkage Dental Restorations. Awarded IMRE Poster Competition 2004 3rd Prize. xxi [...]... Figure 6 .11 Figure 6 .12 Figure 6 .13 Figure 6 .14 Figure 6 .15 Figure 6 .16 Figure 6 .17 Figure 6 .18 H NMR of compound E 13 C NMR of compound E 11 4 29 Si NMR of compound E 11 5 1 H NMR of compound F 11 6 13 C NMR of compound F 11 7 29 Si NMR of compound F 11 8 H NMR of compound G 11 9 1 13 C NMR of compound G 12 0 29 Si NMR of compound G 12 1 1 H NMR of compound H 12 2 13 C NMR of compound H 12 3 29 Si NMR of compound... Figure 5 .19 Figure 5.20 Depth-sensing microindentation test set-up 67 1 71 H NMR of compound A 13 C NMR of compound A 72 29 Si NMR of compound A 73 1 H NMR of compound B 74 13 C NMR of compound B 75 29 Si NMR of compound B 76 1 H NMR of compound C 77 13 C NMR of compound C 78 29 Si NMR of compound C 79 1 H NMR of compound D 80 13 C NMR of compound D 81 29 Si NMR of compound D 82 Figure 5. 21 α and β-trans... Synthesis of compound F (SSQ with 6 equivalents of PM and 2 equivalents of VCE) 10 4 Figure 6.3 Synthesis of compound G (SSQ with 4 equivalents of PM and 2 equivalents of VCE) 10 6 Figure 6.4 Synthesis of compound H (SSQ with 2 equivalents of PM and 6 equivalents of VCE) 10 8 Figure 6.5 Oxysilylation reaction associated with allyloxy chemistry 11 1 1 113 Figure 6.6 Figure 6.7 Figure 6.8 Figure 6.9 Figure 6 .10 ... 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 6 Figure 7 .11 Mean hardness values of control and binary blend of compound C with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 7 Figure 7 .12 Mean hardness values of control and binary blend of compound D with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 7 Figure 7 .13 Mean elastic modulus of control and binary blend of compound... 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 9 Figure 7 .14 Mean elastic modulus of control and binary blend of compound B with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 9 Figure 7 .15 Mean elastic modulus of control and binary blend of compound C with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 16 0 Figure 7 .16 Mean elastic modulus of control and binary blend of. .. H 12 4 α and β-trans isomer arising from Pt-catalyzed hydrosilylation of propargyl and epoxy substituents on the cube 12 6 xiv Figure 6 .19 SEC chromatogram for compound E 12 7 Figure 6.20 SEC chromatogram for compound F 12 8 Figure 6. 21 SEC chromatogram for compound G 12 8 Figure 6.22 SEC chromatogram for compound H 12 9 Figure 6.23 TGA profile of compound E 13 0 Figure 6.24 TGA profile of compound F 13 1... 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 16 0 Figure 7 .17 Mean shrinkage of control and binary blend of compound E with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization 16 4 xvi Figure 7 .18 Mean shrinkage of control and binary blend of compound F with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios during light polymerization 16 5 Figure 7 .19 ... of control and binary blend of compound D with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios at various post-light polymerization time intervals 15 1 Figure 7.9 Mean hardness values of control and binary blend of compound A with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 15 6 Figure 7 .10 Mean hardness values of control and binary blend of compound B with control in 5, 10 ,... ratios 17 3 Figure 7.26 Mean hardness values of control and binary blend of compound F with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 17 3 Figure 7.27 Mean hardness values of control and binary blend of compound G with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 17 4 Figure 7.28 Mean hardness values of control and binary blend of compound H with control in 5, 10 , 20 and. .. 50 wt% of SSQ nanocomposite ratios 17 4 xvii Figure 7.29 Mean elastic modulus of control and binary blend of compound E with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 17 6 Figure 7.30 Mean elastic modulus of control and binary blend of compound F with control in 5, 10 , 20 and 50 wt% of SSQ nanocomposite ratios 17 6 Figure 7. 31 Mean elastic modulus of control and binary blend of compound . compound E. 11 3 Figure 6.7 13 C NMR of compound E. 11 4 Figure 6.8 29 Si NMR of compound E. 11 5 Figure 6.9 1 H NMR of compound F. 11 6 Figure 6 .10 13 C NMR of compound F. 11 7 Figure 6 .11 29 Si. NMR of compound F. 11 8 Figure 6 .12 1 H NMR of compound G. 11 9 Figure 6 .13 13 C NMR of compound G. 12 0 Figure 6 .14 29 Si NMR of compound G. 12 1 Figure 6 .15 1 H NMR of compound H. 12 2 Figure. 71 Figure 5 .10 13 C NMR of compound A. 72 Figure 5 .11 29 Si NMR of compound A. 73 Figure 5 .12 1 H NMR of compound B. 74 Figure 5 .13 13 C NMR of compound B. 75 Figure 5 .14 29 Si NMR of