Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 12: Polymerizing inorganic monomers dissolved in organic polymers

Key concepts Reasons for making an inorganic filled organic polymer hybrid: improve strength, abrasion resistance, modulus, hardness, inflammability, Metal oxide inorganic particles can be made by sol-gel, flame synthesis Organic phase: organic polymers Inorganic particles increase viscosity Particle aggregation ruins hybrid effects smaller the particle, the greater the strength and modulus of the hybrid the higher the particle concentration, the greater the strength and modulus of the hybrid

Making Hybrid Materials: Class 1B (in situ particle growth) Ideally, no Solvent except for monomer(s) No solvent with low t g organic polymers or in polymer melts (< 100 °C) or if monomer will is soluble in polymer. Otherwise solvent may be used to mix before casting.

Preparation by dissolving inorganic monomer in solid organic polymer then polymerizing to form particles Solid Organic Polymer Monomer must be soluble in polymer Polymerization by: 1) hydrolysis & condensation of M(OR) n Water diffuses into membrane from air 2) Reduction of metal compound. H 2 or polymer itself as reducing agent 3) sulfidation of cations (H 2 S) 4) photochemical or thermal decomposition Inorganic Monomer (liquid) & catalyst Organic Polymer Inorganic Monomer Monomer polymerizes & forms particles

Preparation by mixing inorganic monomer with liquid organic polymer & hydrolysis & condensation Physical mixing Very few liquid polymers, save some elastomers like polydimethylsiloxane and low molecular weight polybutadiene or polyisoprene Organic Polymer Inorganic Monomer Liquid Organic Polymer Inorganic Monomer (liquid) & catalyst 1) Water diffuses in from outside 2) Monomer polymerizes 3) Particles phase separate Silica-PMS materials are looked at later in lecture

Preparation by mixing inorganic monomer with solid organic polymer and allowing particles to form Solid Organic Polymer Physical mixing Solvent must be removed before polymerization Water for hydrolysis and condensation would be diffused into dry film from air. Organic Polymer Inorganic Monomer in solvent Organic Polymer Inorganic Monomer in solvent Dissolve Organic Polymer in solvent Evaporate solvent Inorganic Monomer (liquid) Organic Polymer Inorganic Monomer Monomer polymerizes & forms particles Silica-Nafion materialsmade this way are looked at later in lecture Spherical particles

Polymers used Elastomers: silicone, polybutadiene, polyisoprene Thermoplastics: polyurethanes, polycarbonates, polyvinylalcohol, polyacrylates, polysulfones, polyethylene oxide (PEO), polypropylene oxide (PPO) Thermosets: epoxies Polyionomers: Nafion

Review of polymerizations 1) hydrolysis & condensation of M(OR) n or RSi(OR’) 3 2) Reduction of metal compound 3) sulfidation of cations 4) photochemical or thermal decomposition

Hydrolysis & condensation of M(OR) n : the monomers Silicon: Si(OR) 4 or R’Si(OR) 3 Aluminum: Al(OR) 3 or AlCl 3 6H 2 O Transition metals: M z (OR) n or M z Cl n hH 2 O z = oxidation number for metal n = number of alkoxide or halide in monomer h = number of coordinating waters

Hydrolysis & condensation of Si(OR) 4 Catalyzed by acids (HCl,HNO 3 ) or bases (NH 3 aq, NaOH) or fluoride.

Particles from hydrolysis & condensation of Si(OR) 4 Typically leads to amorphous spherical particles (not quartz) Can template particles with ordered mesopores with surfactants Stober synthesis from TEOS with NH 3 and water gives monodisperse particles Emulsion polymerization (water in oil) gives monodisperse particles Other preps give polydisperse particles

Hydrolysis & condensation of RSi(OR) 3

Particles from hydrolysis & condensation of RSi(OR) 3 Typically leads to amorphous spherical particles Not as easy to prepare particles as with silica Can template particles with ordered mesopores with surfactants Stober synthesis from TEOS with NH 3 and water affords polydisperse particles Emulsion polymerization (two step) gives monodisperse particles

Hydrolysis & Condensation of M z (OR) n to form MO n/2 Hydrolysis: formation of monomeric MOH species higher charge & higher pH More reactive, but too high shuts down condensation Condensation: formation of “oxo” (neutral) M-O-M M = Al, B, Ti, Zr, Cr, Fe…..

Hydrolysis & Condensation of M z (OR) n to form MO n/2 Olation: formation of “oxo” (neutral) M-O-M olation >> oxolation

Particles from hydrolysis & condensation of M(OR) n Particles may be amorphous or crystalline Some amorphous particles will crystallize with time. Stober synthesis from TEOS with NH 3 and water does not work Emulsion polymerization (water in oil) gives monodisperse particles Many more molecular clusters are available through olation chemistry

Reduction of metals

Metal and Semiconducting Sulfides

in situ Silica-Nafion Nanocomposite Solid Nafion Physical mixing Nafion & TEOS in ethanol Nafion & TEOS in ethanol Dissolve Nafion in Ethanol Evaporate solvent Si(OEt) 4 (liquid) Nafion & TEOS Silica particles form in membrane Nafion TM Spherical particles

5 weight percent ex situ silica in Nafion in situ Silica-Nafion Nanocomposite In situ Silica particles Class 1B Class 1A

In situ filled Silica in polydimethylsiloxanes Journal of Polymer Science Part B: Polymer Physics, 2003, 41, 16 Solid Organic Polymer Inorganic Monomer (liquid) & catalyst Organic Polymer Inorganic Monomer Spherical particles

In situ filled Silica in polydimethylsiloxanes Highly transparent Does not require mechanical blending Journal of Polymer Science Part B: Polymer Physics, 2003, 41, 16

In situ filled Silica in polydimethylsiloxanes Journal of Polymer Science Part B: Polymer Physics, 2003, 41, 16

Silver particles made in situ polydimethylsiloxanes

Templating with triblock copolymer is formally a Class 1B material Polymer is template. After removal, silica remains

Summary: In situ formation of inorganic phases in polymers Method for mixing at nanoscale without mechanical blending required-less chance for aggregation and segregation to occur (steric stabilization) Raises modulus and strength of materials In situ polymerization of inorganics selectively in blocks of block copolymers-first step to biomimetic mineralization.