Preparation and Characterization of Polymer/Dendrimer Blends Progress Report Eric J. Amis Barry J. Bauer Franziska Grohn Ty J. Prosa Dawei Liu Kathleen A. Barnes Catheryn J. Jackson Brent D. Viers Alamgir Karim Jack F. Douglas U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Polymers Division Gaithersburg, MD 20899, U.S.A NIST luu NISTIR 6353 Preparation and Characterization of Polymer/Dendrimer Blends Progress Report Eric J. Amis Barry J. Bauer Franziska Grohn Ty J. Prosa Dawei Liu Kathleen A. Barnes Catheryn J. Jackson Brent D. Viers Alamgir Karim Jack F. Douglas U.S. DEPARTMENT OF COMMERCE Technology Administration National Institute of Standards and Technology Polymers Division Gaithersburg, MD 20899, U.S.A July 1999 U.S. DEPARTMENT OF COMMERCE William M. Daley, Secretary TECHNOLOGY ADMINISTRATION Gary R. Bachula, Acting Under Secretary for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Raymond G. Kammer, Director Table of Contents General Information 3 Dendrimer Interpenetrating Polymer Networks 4 Ternary Dendrimer Blends 7 SANS of Polystyrene Hypergrafts 11 Fatty Acid Modified Dendrimer Blends and Solutions 15 SAXS of Dendrimer Internal Structure 19 Dendrimers as Crosslink Points in Networks 23 SANS of PAMAM-Deuterated Benzoic Acid Solutions 26 SANS of PAMAM-PEG Solutions 30 Dendrimer Gold Colloids 33 Gold Filled Fatty Acid Modified Dendrimers 36 Dewetting of Hypergraft Thin Films 38 2 General Information Throughout this report certain conventions will be used when describing uncertainties in measurements. Plots of small angle scattering data have been calculated from circular averaging of two dimensional files. The uncertainties are calculated as the estimated standard deviation of the mean and the total combined uncertainty is not given as comparisons are made with data obtained under the same conditions. In cases where the limits are smaller then the plotted symbols, the limits are left out for clarity. In data plots with uncertainties larger than the symbols, representative confidence limits are plotted at appropriate places. Fits of the scattering data are made by a least squares fit of the data giving an average and a standard deviation to the fit, this is true for fit values such as radius of gyration and exponents. Temperatures are given as expected ranges of values based on previous work. All concentrations are calculated from weighed samples and are reported as mass fractions and are nominal values for naming purposes. The range of the concentrations calculated from mass are within one percent of the reported value. The conventional notation “molecular weight” has been replaced by “relative molecular mass” in most cases. Rarely, the conventional notation is used to conform to previous publications. Certain commercial materials and equipment are identified in this paper in order to specify adequately the experimental procedure. In no case does such identification imply recommendation by the National Institute of Standards and Technology nor does it imply that the material or equipment identified is necessarily the best available for this purpose. This work is supported in part by the U.S. Army Research Office under contract number 35109-CH. 3 Dendrimer Interpenetrating Polymer Networks NIST: Barry J. Bauer, Ty J. Prosa, Dawei Liu, and Eric J. Amis Outside Collaborators: Donald Tomalia, MMI, Rolf Scherrenberg, DSM Objectives: To synthesize and characterize interpenetrating polymer networks (IPNs) containing dendrimers that are molecularly dispersed. Technical Description: Use IPN techniques to prepare molecularly dispersed moderate to large size poly(amido amine) (PAMAM) and polypropyleneimine (PPI) dendrimers in a polymeric matrix. Use small angle xray scattering (SAXS) to measure the radius of gyration of dendrimers and the correlations between dendrimers. Summary Report: The EPNs were prepared by dissolving the dendrimers in 2-hydroxyethylmethacrylate (HEMA) containing approximately mass fraction 1 % ethylene glycol dimethacrylate with AIBN as an initiator. They were polymerized at 35 °C for 72 h and at 70 °C for an additional hour. Figure la shows the scattering from solutions and IPNs of PAMAM dendrimers. All SAXS curves show higher order features in the scattering, characteristic of their sphere- like shapes. The positions of these features can be used to estimate the size of the dendrimers, even at high concentration. In going from mass fraction 1 % to mass fraction ~ 1 26 % in methanol, a peak at low q (q 0.04 A' ) appears. This is due to the correlation formed between the positions of the dendrimers. It has been shown that this is due to the tendency of the dendrimers to avoid overlapping. The positions of the higher order features do not shift, however. This suggests that the dendrimer size remains constant in this concentration range. This has been seen before in polypropylene imine) dendrimers For the IPNs, the mass fraction 1 % dendrimer sample is quite similar to that of the solution. The second higher order feature of the IPN is difficult to distinguish due to the weak scattering of this sample. As one goes to a mass fraction 10 % dendrimer IPN, the higher order features are shifted to higher q. This indicates that the dendrimer size has decreased. This shifting is also present for mass fraction 10 % and mass fraction 25 % IPNs of G6 and Gil. These concentrations are below the overlap concentration of the dendrimers themselves, suggesting that the presence of polymer instead of solvent promotes the shrinkage of the dendrimers. 4 Figure lb is a plot of the of in in Rg dendrimers solution and IPNs for G6 through Gil dendrimers. fraction 1 dendrimer concentration, the for solutions At mass % Rg values IPNs are nearly identical, there is significant in of at and but a decrease Rg the dendrimers mass fraction 10 % loading of the IPNs. The dendrimers in IPNs at high concentrations have segment density near that of a bulk PAMAM dendrimer without solvent. IPNs made by polymerizing a network around linear chains are strongly pushed towards phase separation. It has been shown that when the network size becomes smaller than the linear chain size, the linear chains contract in size and eventually form large clusters. The difference may be related to the very compact, spherical size of the dendrimers. They seem to shrink in size, but remain molecularly dispersed in the polymeric matrix. Future Plans: To further investigate these IPN’s by synthesizing the PHEMA type with metals incorporated inside the dendrimers by doing the synthesis with metal containing dendrimers and by taking preformed IPNs and exposing them to aqueous metal solutions. To synthesize networks with chains attached to dendrimer crosslink points. 5 Ternary Dendrimer Blends NIST: Barry J. Bauer, Dawei Liu, Catheryn L. Jackson, and Eric J. Amis Outside Collaborators: Aissa Ramzi, DSM, Rolf Scherrenberg, DSM Objectives: To measure the effect of hydrophobically modified dendrimers on the miscibility of a polymer blend. To measure the dispersion of the dendrimer in the blend. Technical Description: Ternary blends of polystyrene-d (PSD) and poly(vinylmethyl ether) PVME are modified by incorporation of between mass fraction 1 % and mass fraction 10 % dendrimer. SANS is used to locate the phase boundaries and TEM is used to measure the size and dispersion of the dendrimer. Summary: As reported previously, hydrophobically modified dendrimers were synthesized from a G5 polypropylene imine) (PPI) dendrimer with -NH2 terminal groups by 80 fold mass excess 1,2-epoxy octane in vacuum at 140°C for 8 h. Blends of PSD and PVME were made by mixing in toluene. Solid samples suitable for scattering were prepared by pressing the vacuum dried, powdered blend into disks. SANS from blends with and without added dendrimer demonstrate that the presence of the dendrimer gives the sample stability, causing it to remain miscible when blends without the dendrimer phase separate. Experiments were continued with G5 PPI dendrimers that were modified by reaction with stearic acid, forming amide bonds on all 64 terminal amino groups. Figure 2a shows the SANS from PSD/PVME = 1/9 (mass ratio) blends with and without mass fraction 1 % of the dendrimer added. Two types of dendrimer were used, one with deuterated stearic acid (-<135 ) and one with hydrogenated stearic acid (-h3 6). At 140 °C, all three samples have scattering typical of a miscible blend. At 150 °C, however, the blend without dendrimer showed increased scattering at low q indicating phase separation is taking place. The blends with the dendrimer still showed scattering typical of micibility at 150 °C. These results are qualitatively similar to previous results of PSD/PVME blends with 1 ,2-epoxy octane modified dendrimers. Experiments were repeated under experimental conditions that gave results extending to lower values of q. Figure 2b shows SANS of blends of PSD/PVME = 1/9 (mass ratio) and PSD/PVME = 3/7 (mass ratio) containing mass fraction 1 % of dendrimer. The data were taken at 70 °C which is well within the range of miscbility for the blend without dendrimer. At lower q there is an upturn in the scattering which is typical of a large dispersed phase. The q range shown in figure 2a gives a linear relationship, but when 7 lower q is probed, the 2 phase structure is evident. The PSD/PVME 1/9 (mass ratio) samples, ED-1 and ED-4 (containing mass fraction 1 % to 10 % epoxy octane modified G5 DSM dendrimer), were ultramicrotomed to a thickness of ~60 nm to 80 nm at -70 °C and transferred to 200-mesh, carbon coated Cu grids. The sections were stained with OsC>4 vapors by exposing the grids to a mass fraction 0.04 % aqueous solution of OsCMt room temperature for 2 h. The blend samples were imaged by transmission electron microscopy (TEM) at 120 kV in a Philips 400T using low-dose conditions. Figure 2c is the TEM result of ED-1. It shows dark domains of sizes <100 nm, presumed to be aggregates of the dendrimers in the single phase, PS/PVME blend.