Thermoset Blends of an Epoxy Resin and Polydicyclopentadiene

Transcription

1 SUPPORTING INFORMATION FOR: Thermoset Blends of an Epoxy Resin and Polydicyclopentadiene Brian J. Rohde, Kim Mai Le, Ramanan Krishnamoorti,* and Megan L. Robertson* Department of Chemical and Biomolecular Engineering, University of Houston *Corresponding authors 4726 Calhoun Road S222 Engineering Building 1 University of Houston Houston, TX Krishnamoorti: ramanan@uh.edu, Robertson: mlrobertson@uh.edu Krishnamoorti: , Robertson: S1

2 BLEND NOMENCLATURE Blends are labeled as xxe, where xx corresponds to the volume % of epoxy resin (consisting of DGEBA, NMA, and K54). The remain volume % corresponds to the DCPD precentage. For example, a 30E sample is 30 volume % epoxy resin and 70 volume % DCPD. TABLE OF CONTENTS Section 1: Optical Microscopy Images of Partially Cured Blends of Epoxy Resin and PDCPD Figure S1: Raw images of 95E, 90E, 80E, 70E, 50E, 30E, and 20E Section 2: Ultra-Small Angle X-ray Scattering of Fully Cured Blends (Reduced to Absolute Scale) (all data are slit smeared with slit length of Å -1 ) Figure S2: Neat epoxy resin and PDCPD Figure S3: 95E Figure S4: 90E plus Guinier-Porod fit Figure S5: 80E plus Guinier-Porod fit Figure S6: 70E plus Guinier-Porod fit Figure S7: 50E plus Guinier-Porod fit Figure S8: 30E plus Guinier-Porod fit Figure S9: 20E plus Guinier-Porod fit Figure S10: All data sets combined plus model fits Section 3: Differential Scanning Calorimetry of Neat Components and Fully Cured Blends Figure S11: Neat epoxy resin and PDCPD Figure S12: 20E, 30E, 90E, 95E Figure S13: 50E, 70E, 80E Figure S14: Derivative heat flow for 20E Figure S15: Derivative heat flow for 30E Figure S16: Derivative heat flow for 50E Figure S17: Derivative heat flow for 70E Section 4: Scanning Electron Microscopy of Tensile and SENB Fracture Surfaces Figure S18: Tensile bar fracture surfaces at 80X magnification Figure S19: Tensile bar fracture surfaces at 600X magnification Figure S20: SENB specimen fracture surfaces at 600X magnification Figure S21: Fracture surfaces of PDCPD at 40X and 80X magnification Section 5: Critical Stress Intensity Calculations Equation S1: Critical Stress Intensity Factor Figure S22: Determination of PQ S2

3 Equation S2: Plane strain criteria Table S1: Fracture testing parameters Section 6: Optimization of Neat PDCPD Curing Schedule Figure S23: DSC Total Heat of PDCPD/G2 Figure S24: Stress versus strain of PDCPD under various curing conditions Section 7: Attenuated Total Reflection - Fourier Transform Infrared Spectroscopy of Fully Cured Blends Equation S3: Conversion of FTIR absorbance peaks Figure S25: Baseline corrected FTIR spectrum of fully cured blends Table S2: Characteristic peak heights and conversions of fully cured blends. S3

4 Section 1: Optical Microscopy Images of Partially Cured Blends of Epoxy Resin and PDCPD Figure S1: Optical micrographs at 20X magnification of blends containing uncured epoxy resin components (DGEBA and NMA) and DCPD cured with G2 at 30 C. The scale is the same for all images. S4

5 Section 2: Ultra-small and small angle X-ray scattering of Fully Cured Blends Figure S2: USAXS/SAXS measurements of neat epoxy resin and PDCPD. Every 7 th point shown. Since the data were undistibguishable from background scattering, these data were not further analyzed. Figure S3: USAXS/SAXS measurements of blend 95E. S5

6 Figure S4: USAXS/SAXS measurements of blend 90E. The solid line in the figure was obtained using the generalized Guinier-Porod model. Figure S5: USAXS/SAXS measurements of blend 80E. The solid line in the figure was obtained using the generalized Guinier-Porod model. S6

7 Figure S6: USAXS/SAXS measurements of blend 70E. The solid line in the figure was obtained using the generalized Guinier-Porod model. Figure S7: USAXS/SAXS measurements of blend 50E. The solid line in the figure was obtained using the generalized Guinier-Porod model. S7

8 Figure S8: USAXS/SAXS measurements of blend 30E. The solid line in the figure was obtained using the generalized Guinier-Porod model. Figure S9: USAXS/SAXS measurements of blend 20E. The solid line in the figure was obtained using the generalized Guinier-Porod model. S8

9 Figure S10: Combined USAXS/SAXS scattering plots of all samples. The solid lines in the figure were obtained using the generalized Guinier-Porod model. S9

10 Section 3: Differential Scanning Calorimetry of Neat Components and Fully Cured Blends a) b) Figure S11: DSC data obtained from a) neat epoxy resin and b) neat PDCPD. S10

11 a) b) c) d) Figure S12: DSC data obtained from blends a) 20E, b) 30E, c) 90E, d) 95E. S11

12 a) b) c) Figure S13: DSC data obtained from blends a) 50E, b) 70E, and c) 80E. The black arrows indicate the location of a possible Tg only clearly present on the first heating ramp. S12

13 Figure S14: Derivative heat flow with respect to temperature for blend 20E. Two Voigt peaks were fitt to the data in order to determine the individual Tg locations. Figure S15: Derivative heat flow with respect to temperature for blend 30E. Two Voigt peaks were fit to the data in order to determine the individual Tg locations. S13

14 Figure S16: Derivative heat flow with respect to temperature for blend 50E. Two Voigt peaks were fit to the data in order to determine the individual Tg locations. Figure S17: Derivative heat flow with respect to temperature for blend 70E. Two Voigt peaks were fit to the data in order to determine the individual Tg locations. S14

15 Section 4: Scanning Electron Microscopy of Tensile and SENB Fracture Surfaces Figure S18: SEM micrographs of the tensile bar fracture surfaces at 15kV and 80X magnification of neat epoxy resin, 95E, 90E, 80E, 70E, 50E, 30E, and 20E. The scale applies to all images. S15

16 Figure S19: SEM micrographs of the tensile bar fracture surface at 15kV and 600X magnification of neat epoxy resin, 95E, 90E, 80E, 70E, 50E, 30E, and 20E. The scale applies to all images. S16

17 Figure S20: SEM micrographs of the fracture specimen fracture surface at 15kV and 600X magnification of neat epoxy resin, 95E, 90E, 80E, 70E, 50E, 30E, and 20E. Neat epoxy and 95E were smooth relative to their tensile bar fracture surface. The scale applies to all images. S17

18 Figure S21: SEM micrographs of fracture surface at 15kV and 40X/80X magnification of neat PDCPD tensile and SENB specimens. 40X and 80X are of different locations on the fracture surface. S18

19 Section 5: Critical Stress Intensity Calculations The critical stress intensity factor, KIC, determined from ASTM standard D5045 is defined as (assuming a valid test) K IC = ( P Q BW1/2) f(x) (S1) where for 0 < x <1, f(x) = 6x 1/2 [1.99 x(1 x)( x + 2.7x2 )] (1 + 2x)(1 x) 3/2 P Q = The peak load determined from testing (see Figure S22), kn B = specimen thickness, cm W = specimen width, cm a eff = effective crack length (average of the length both sides a1 and a2), cm x = a eff W The peak load, P Q, is determined from analysis of the load (kn) versus deflection plot as shown in Figure S22, where a line following the slope of the linear region is determined ( in Figure S22) to establish the initial compliance and used to create a secondary compliance line (- - - in Figure S22) with a slope that is of the initial compliance slope. The max load, PMax, differs from PQ and represents the maximum in the raw data. The intersection of the secondary compliance (- - -) and the raw data is the peak load, PQ. If PMax < PQ, PMax is used as PQ in the calculation of KIC. If PMax/PQ < 1.1, PQ in the calculation of KIC. If PMax/PQ > 1.1, the test is not valid. S19

20 Figure S22: Raw load versus displacement data for a neat epoxy SENB specimen. The solid black line ( ) is the initial compliance used to determine the secondary compliance with 5% great compliance than the initial (- - -). The maximum in the raw data is PMax and the intersection of the raw data and the secondary compliance is PQ. In order to maintain the validity of the testing, the samples must satisfy the plane strain criteria expresses by B, a, (W a) > 2.5 ( K 2 IC ) σ y (S2) where KIC is the critical stress intensity factor determined above and σ y is the yield stress of the material determined from tensile testing. Should this criteria not be satisfied (i.e., the lefthand side needs to be greater than the right), plane strain does not occur and the test is not valid. All samples satisfied this criterion. All relevant fracture testing parameters are included in Table S1. S20

21 Table S1: Testing parameters for SENB specimens. Sample W (cm) B (cm) aeff (cm) W-aeff (cm) σy x PQ f(x) KIC (Mpa-m 1/2 ) Neat Epoxy Neat Epoxy Neat Epoxy Neat Epoxy E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E Neat PDCPD Neat PDCPD Neat PDCPD Neat PDCPD S21

22 Section 6: Optimization of Neat PDCPD Curing Schedule Previous literature indicated a wide range of values for the elongation % of PDCPD, ranging from ~10% to over 100%. [1-5] In order to properly predict the mechanical behavior of the blended systems, it was paramount that the mechanical properties of the PDCPD be well explored and reproducible. It must also be considered that the epoxy phase requires high temperatures for complete conversion (greater than 160 C) in the blended systems the two components must follow the same curing schedule. Differentially scanning calorimetry (Figure S23) of dicyclopentadiene (DCPD) mixed with second generation Grubbs catalyst (G2) at a 5000:1 molar ratio of DCPD to G2, showed that the peak in the exotherm was around 50 C and the primary exotherm was completed by 60 C with a long tail to 110 C. Based on this result and in conjuntion with prior FTIR work, [6] the ring opening metathesis polymerization (ROMP) of DCPD stagnates at about 60 C with ~70% conversion (i.e. the total heat measured is not a true total heat of a sample with 100% conversion). Figure S23: DSC heat flow curve given off during the ROMP reaction of DCPD at a 5000:1 ratio of DCPD to G2. The reaction mixture was prepared by mixing G2 and DCPD at the specified ratio, violently mixing for 10 second and syringing drops in to liquid nitrogen to stop the reaction. The frozen drops were then transferred to the DSC (precooled to -90 C) and then heated at 10 C/min. The endothermic peak (down) at 30 C is the melting of DCPD. S22

23 Initially, tensile bars were cured at 30 C for 1 hour and 70 C for 2 hours to drive the ROMP reaction to relative completion. However, doing so presumably leaves ~30% of unreacted DCPD in the system based on FTIR results. [6] Mechanical testing of PDCPD following that curing schedule are represented in Figure S24 ( ). Curing at 30 C and 70 C results in elongation at break of near 100%. Adding a post curing step at 200 C (which was emloyed in the blends), results in much lower elongation % (consistent with Jeong and Kessler s work, which also use a high temperature curing stage of 170 C [5] ), but similar modulus and tensile strength as the blends that did not undergo this high temperature curing stage (Figure S24 ( )). Since PDCPD is composed of a large number of unsaturated olefins, it is possible that oxidation and not lack of plasticization is the source of the change of the mechanical properties when the high tempeature curing schedule was used. To prevent oxidation, two curing proctols were used: 1) curing in the convection oven at 30/70 C as done previously and then post curing at 200 C under vacuum (~50 mtorr) for two hours ( ), and 2) curing in the convection oven at 30 C and then post curing at 70 C and 200 C in the vacuum oven ( ). Figure S24 shows that these additional measures to prevent oxidation had very little impact on the mechanical properties of PDCPD, leading us to believe that the high elongation % observed without the high temperature curing stage is from the plasticization of PDCPD with unreacted DCPD. S23

24 Figure S24: Stress versus stain curves of PDCPD following four different curing protocols: ( ) Protocol A, ( ) Protocol B, ( ) Protocol C, and ( ) Protocol D. Figure (a) highlights the much longer extension that the PDCPD cured with Protocol A (which omits the 200 C step) achieves relative to the other samples. Figure (b) shows that Protocols B, C and D result in comparable mechanical properties. Protocol A: 1) convection oven at 30 C for 1 h, 2) convection oven at 70 C for 2 h. Protocol B: 1) convection oven at 30 C for 1 h, 2) convection oven at 70 C for 2 h, 3) convection oven at 200 C for 2 h. Protocol C: 1) convection oven at 30 C for 1 h, 2) convection oven at 70 C for 2 h, 3) vacuum oven at 200 C for 2 h. Protocol D: 1) convection oven at 30 C for 1 h, 2) vacuum oven at 70 C for 2 h, 3) vacuum oven at 200 C for 2 h. S24

25 Section 7: Attenuated Total Reflection - Fourier Transform Infared (ATR-FTIR) Spectroscopy of Fully Cured Blends ATR- FTIR was performed on a Thermo Nicolete 6700 with a SmartiTR ATR sampling accessory and a single reflection diamond crystal. The bottom edges of fully cured tensile bars were used for testing (the mold release was scraped off). A spectrum with the baseline corrected (for only the 1855 cm -1 and 1508 cm -1 peaks) is shown in Figure S25 for wavenumbers between 1900 cm -1 and 600 cm -1. Peak assignment is described in more detail elsewhere, [6] but the peak located at 1855 cm -1 is related to the stretching of the anhydride ring and that located at 1508 cm - 1 is related to the stretching of the aromatic ring in the diglycidyl ether of bisphenol-a (DGEBA). By taking the ratio of 1855 cm -1 and 1508 cm -1 the conversion, α, of anhydride was determined with the following expression: α = A 0 A t A 0 (3) where A o is the ratio of the 1855 cm -1 and 1508 cm -1 absorbance at the beginning of the reaction (at time = 0) taken to be here based on prior publications [6] (this ratio is specific to a 1:1 molar ratio of DGEBA to NMA) and A t is the ratio of the 1855 cm -1 and 1508 cm -1 absorbance at time t, which in this case is after a complete curing cycle. Tabulated results are shown in Table S2. The epoxy conversion was consistent for all blends and around 90%, in-line with previous FTIR work on these blended systems. [6] S25

26 Figure S25: ATR-FTIR spectra of fully cured tensile bars of neat epoxy resin and blends: (a) the entire fingerprint region from 1900 cm -1 to 650 cm -1 (the cut off for diamond crystals), (b) 1900 cm -1 to 1400 cm -1 showing key features such as the 1508 cm -1 peak associated with the aromatic ring of DBEGA that remains constant throughout the reaction, ester creation at 1740 cm -1, and the anhydride peaks at 1780 cm -1 and 1855 cm -1 that decrease as the reaction progresses, and (c) 1900 cm -1 to 1800 cm -1 highlighting the 1855 cm -1 peak of the anhydride. S26

27 Table S2: Peak heights, ratios, and conversions of fully cured tensile bars as determined from ATR-FTIR analysis. Peak Heights 1508 cm cm cm -1 /1508 cm -1 Conversion Neat Epoxy Resin E E E E E E E S27

28 REFERENCES 1. Constable, G.S., A.J. Lesser, and E.B. Coughlin, Morphological and Mechanical Evaluation of Hybrid Organic Inorganic Thermoset Copolymers of Dicyclopentadiene and Mono- or Tris(norbornenyl)-Substituted Polyhedral Oligomeric Silsesquioxanes. Macromolecules, (4): p Li, H., Z. Wang, Y. Wang, and B. He, Ring-opening metathesis polymerization of dicyclopentadiene catalyzed by a polymer-supported tungsten catalyst. Reactive and Functional Polymers, (2 3): p Yang, G. and J.K. Lee, Curing Kinetics and Mechanical Properties of endo- Dicyclopentadiene Synthesized Using Different Grubbs Catalysts. Industrial & Engineering Chemistry Research, (8): p Kirk-Othmer Encyclopedia of Chemical Technology. 5. Jeong, W. and M.R. Kessler, Toughness Enhancement in ROMP Functionalized Carbon Nanotube/Polydicyclopentadiene Composites. Chemistry of Materials, (22): p Rohde, B.J., M.L. Robertson, and R. Krishnamoorti, Concurrent curing kinetics of an anhydride-cured epoxy resin and polydicyclopentadiene. Polymer, : p S28