Class 1E Interpenetrating Networks Lecture 8 Hybrid POSS Class 1E Interpenetrating Networks

Optional make-up homework for Quiz 3 Another powerpoint slide This time on a polysilsesquioxane or POSS research paper Due Saturday October 20th at 6 PM to my email address: daloy@email.arizona.edu Format: Title Your name & student number Chemdraw graphic (please make it legible) One bullet describing hypothesis in paper One bullet saying why this research was important One bullet describing summarizing how they tested hyothesis One bullet describing their results One bullet indicating if hypothesis was proven or disproven Citation for paper: Journal, year, volume, page No duplicate papers!

Ancient Humans also made Hybrid organic-inorganic materials: Maya Blue Indigo + white clay palygorskite (Mg,Al)2Si4O10(OH)·4(H2O) (also called Fullers Earth) Last time we talked about class D materials where small molecules were encapsulated into inorganic matrices. This includes natural dyes such as Maya blue which is an indigo in a clay. L. A. Polette, N. Ugarte, M. José Yacamán and R. Chianelli, Sci. Am. Discovering Archaeology, 2000, July–August, 46

Making Hybrid Materials: Class 1E (Interpenetrating network or IPN) Two lightly crosslinked networks Cannot be untangled. Each network has different mechanical Properties. Class 1E materials are called interpenetrating networks. These were a very popular research topic twenty years ago, because having two networks interwoven, but not connected through covalent bonds was calculated to give superior strength and toughness to other materials. The two networks can be prepared simultaneously or one after the other. Very important: if you have an IPN, the mechanical properties should be better than rule of averages. There should be a synergistic effect that makes the sum greater than its parts. • Together they are stronger, tougher than sum of the individual polymers = synergistic All organic IPN adhesives & coatings

Simultaneous Interpenetrating networks Simultaneous network forming in an IPN means the reaction rates are similar. In the example above the inorganic is a copolymer of dimethoxydimethyl silane and either methyltrimethoxysilane or a silica precursor like TEOS. About the only two organic polymerization chemistries that can stand sol-gel conditions used to make the inorganic phase are free radical polymerizations and ring opening metathesis using RuCl3 hydrate as catalyst. The organic network is a mixture of linear monomer:styrene (bottom left) or acrylamide (bottom, right) or hydroxyethylmethacrylate (middle of the bottom) and a crosslinker (top row of organic monomers), divinyl benzene (left top), the bisacrylate (middle top) and the bis acrylamide (right top). People generally assume that the networks don’t phase separate and that true polymer gels are gormed without any particulate structure. While this is not usually the case unless the crosslinking level is very low and the gels very soluble in the solvent. Separation of hard particles would still afford a hybrid material, but it would not have enhanced properties. Rule of averages would dictate the properties. •The two networks assembled at the same time •Phase separation of hard colloidal particles would ruin IPN

Sequential Interpenetrating networks •The two networks are not assembled at the same time •In this case the inorganic network is assembled before the organic Sequential polymerizations are more how IPNs form-either intentionally or unintentionally due to differences in polymerization rates. You must determine the polymerization rates. In this case the inorganic network (red) forms first, followed by the organic (blue). The sequence could be due to relative rates or due to the need for UV or heat to start the second network formation.

If phase separation of particles occurs, it is not an IPN This is just an example of what would happen if a nice hard collloid resulted from say teos polymerization. What you would get is a Class 1C material, silica in an organic polymer. Not interpenetrating networks. This is a hybrid, inorganic filled polymer, an extreme case of Class 1C. However, many publications refer to similar hybrids as IPN’s

Synthesis of poly(methylphenylsiloxane)/phenylene-silica hybrid material with interpenetrating networks and its performance as thermal resistant coating This is an example from the literature of what is thought of as an IPN. In this case it’s a linear siloxane “organic” and silica siloxane inorganic IPN. The abstract and experimental from the paper are below if you want more details. In this study, poly(methylphenylsiloxane) (PMPS) and phenylene-silica based hybrid material with interpenetrating networks was prepared by a two-step sol–gel process. Firstly, in the presence of H2SO4, the phenylene-silica was formed as sol particles with high branching degree by cohydrolysis and condensation of phenylene-bridged monomer, tetraethoxysilane (TEOS), and hexamethyldisiloxane (MM). Then, the intermediate transformed into gel framework in polymer matrix using alkali catalyst, in order to produce a homogenous hybrid material with interpenetrating networks. The structure of prepared hybrid material was characterized by FTIR and NMR, suggesting that phenylene-silica framework was imported into polymer matrix and the hybrid products have a much higher network chain density than neat PMPS. The thermogravimetric analysis (TGA) shows that the prepared materials start to degrade at around 490°C. The results of tensile test indicate that the typical PMPS/phenylene-silica hybrid material has a tensile strength up to 26 MPa and demonstrate a certain degree of flexibility. An increase of phenylene content in phenylene-silica particles tends to produce hybrid materials with improved thermal stability and tensile strength. The hybrid coating films after calcinating at 350 and 400°C for 2 h exhibit a good mechanical performance on adhesion, impact strength and flexibility. Electrochemical impedance spectroscopy (EIS) measurements show that the investigated films have an extremely high electric resistance (1010 Ohm·cm2) and a satisfied impermeability to 3.5 wt % sodium chloride solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012 Preparation of Poly(methylphenylsiloxane), PMPS The tetra-necked 1000 mL round-bottomed flask was equipped with a dropping funnel and a condenser. To this flask was added a mixture of the chlorosilanes monomers: methyltrichlorosilane (11.8 g, 79.0 mmol), dimethyldichlorosilane (19.1 g, 148 mmol), phenyltrichlorosilane (36.2 g, 171 mmol) and diphenyldichlorosilane (25.8 g, 102 mmol), and xylene (212 mL). The flask was immersed into a water bath heated to 60°C. A mixture of water (158 mL) and acetone (118 mL) were dropped slowly into the mixture within 1.5 h under stirring. The reaction mixture was stirred at 60°C for another 2.5 h and was placed for a phase separation, in which the organic layer was washed with an aqueous solution of NaHCO3 (0.400 g in 100 g) and water (2 × 100 g). This procedure yielded silanol solution in xylene. The silanol solution was placed in three-necked bottomed equipped with vacuum system and mechanical stirrer. After most of solvent was distilled at 2.0-3.0 kPa, the temperature was raised up to 160°C and the slow stirring rate was maintained for 6–8 h. Then a resin-like product (95%) was obtained, which was soon dissolved in a mixture of xylene and ethanol (1 : 1, v : v). The number average molecular weight (Mn) and polydiversity (PDI), measured by Gel Permeation Chromatography (GPC), was 1800 and 6.4, respectively. Preparation of Phenylene-Silica Sol TEOS and 1,4-bis(diethoxymethylsilyl)benzene (0.050 mol in total), hexamethyldisiloxane were mixed in a tetra-necked 100 mL round-bottomed flask with a dropping funnel, a condenser, a thermometer and a mechanical stirrer. The mixture was immersed into water bath of 15–20°C. Sulfuric acid (0.125 g, 1.25 mmol) was slowly dropped to the flask within 20 s. Deionized water (1.80 g, 0.100 mol) was fitted in dropping funnel, and was introduced into the reaction mixture within 20 min, while the temperature of the reactants was maintained below 20°C. Then the reaction mixture was heated to 78°C, stirred for 2.5 h. The system was neutralized by excessive amount of NaHCO3 (0.500 g). After injecting xylene (15.0 mL), the mixture was centrifuged to yield a clear sol. The molar ratios of TEOS and 1,4-bis(diethoxymethylsilyl)benzene were set to 1 : 10 and 1 : 8, to obtain Sol A and Sol B, respectively. The molar ratio under 1 : 8, which induce gelation within several hours, should be avoided. Preparation for PMPS/Phenylene-Silica Hybrid Materials The PMPS solution was placed in three-necked round bottom equipped with mechanical stirrer and vacuum system. The aqueous solution of Et4NOH (35 wt %) was added into the PMPS solution, and the sol of prepared phenylene-silica was dropped slowly at 30°C within 1 h. Then the mixture was continued to stir for 0.5 h. At a pressure of 29.3 kPa, the mixture was heated to 70°C to distill most of solvent within 0.5 h. A viscous hybrid sol was obtained via the process. The hybrid sol was placed at ambient temperature for 48 h and was heated at 120°C for 1 h. After the complete gelation, the samples were heated at 180°C for crosslinking of PMPS. Gao, D. and Jia, M. J. Appl. Polym. Sci. 2012. doi: 10.1002/app.38372

Synthesis of poly(methylphenylsiloxane)/phenylene-silica hybrid material with interpenetrating networks and its performance as thermal resistant coating Here is the data for the IPN from the proceeding vugraph. No baseline numbers were provided for stress strain curves for the pure inorganic and pure organic phases. Always run control or baseline experiments. If you don’t you will have no basis for comparison. Stable > 300 °C Tensile 10-20 MPa Gao, D. and Jia, M. J. Appl. Polym. Sci. 2012. doi: 10.1002/app.38372

Organic–inorganic polymer hybrids based on unsaturated polyester This is a very clever IPN where the linear organic polymer with maleate ester groups is made first, then the silsesquioxane is polymerized and the organic polymer is photochemically crosslinked to a network by 2 + 2 cycloadditions of the maleate groups on different macromolecules. The polyphenylsilsesquioxane is not very network like so it may even plasticize the composite. Maleic anhydride (MA) and ethylene glycol (EG) were fed in a molar ratio of 1:1 and condensation polymerization was carried out at 195 °C for 20 h, and then at 215 °C for 2.5 h to obtain PME. Another polyester PMPE was prepared in a similar manner using a molar ratio of MA:phthalic anhydride (PA):EG of 1:1:2. 1H NMR spectra of the UPEs were taken on a Varian Gemini 300-MHz spectrometer in methyl sulfoxide-d6 using tetramethylsilane as an internal standard. An alkoxysilane was added to an acetone solution of a UPE and benzoin methyl ether, and then aqueous HCl was added as catalyst to the resulting solution. The benzoin methyl ether, a typical photoinitiator in free radical photocure systems [5], was employed to initiate photocross-linking. The mixture was heated at 60 °C for one week. The hybrids obtained were dried and exposed to UV light to initiate cross-linking of UPE. Exposure of the hybrid samples was made on an exposure system of Spectra Energy Co. equipped with a 500 W high-pressure mercury lamp (light intensity: 72 mW/cm2). The measurement of cross-linking conversion was carried out with a Genisis FT-IR spectrophotometer (Mattson Instrument Co.) by a KBr-pellet technique. The ratios of calculated areas of the two absorption bands (1644 cm−1 for C=C and 1724 cm−1 for C=O) before and after exposure were compared to determine the degree of conversion of the C=C bonds [6]. The absorption band at 1724 cm−1 was used as an internal standard for the conversion determination. Each hybrid sample, unexposed or exposed, was ground in a mortar, and then was stirred in methanol for preliminary examination of its solvent-resistant property. •Sol-gel polymerization of phenyltriethoxysilane in presence of Linear organic polymer •Photochemical cure of organic network Journal of Non-Crystalline Solids, 2002, 311, 195–198

What about a forming a particle based gel in a monomer as solvent, then polymerize it Having the precipitation occur to form an inorganic gel in an organic monomer as the solvent isn’t necessarily bad. By definition the gel is a percolating network of particles that makes the gel feel like a solid to the touch. Since the length scale for the particles and their aggregates are nanometers to hundreds of nanometers, the length scales are not perfectly matched with the organic network, but the material properties should be good. But how is it different from a class 1c. Well it was made in the monomer as opposed to adding the monomer to a gel that’s already been made.

Simultaneous Interpenetrating networks: "Inverse" organic-inorganic composite materials. Monomer containing both silica and organic components splits apart This vugraph describes one of the more successful IPN hybrid systems made by eliminating the ethoxide groups from the inorganic silica precursor and replacing them with hydroxyethylacrylate groups. The polymerization itself was conducted in more of the hydroxyethylacrylate. Fluoride catlyzed hydrolysis with added water coupled with free radical polymerization generated true IPN’s. The silica content was relatively low, between 5-15wt% but better than in situ polymerization of TEOS in many organic polymers would be like. Macromolecules, 1991, 24 (19), pp 5481–5483

Simultaneous Interpenetrating networks: "Inverse" organic-inorganic composite materials. For a hybrid to be an IPN, there must be a non-linear, synergistic effect on the mechanical properties This is the plot of development of storage modulus in the IPN from the previous slide in comparison to that of the silica or free radical polymer by themselves. You can clearly see a non additive improvement in properties that is indicative of an IPN. Macromolecules, 1991, 24 (19), pp 5481–5483

Now onto covalent bonded class 2 hybrids