Milan Maric

Research

The ability of block copolymers to self-assemble into ordered, periodic structures at the nanometer length scale is of keen interest for next-generation electronic devices, porous materials for catalysts and separations media. Using the ordered block copolymer morphology as a template for such materials is extremely attractive due to the wide variety of synthetic techniques currently available to produce well-defined block copolymers and the facile tuning of the copolymer structure and properties by altering the respective block lengths and the choice of monomer sequences.

Our projects use novel controlled radical polymerization methods developed over the last decade such as nitroxide mediated polymerization (NMP) and atom transfer radical polymerization (ATRP) to synthesize the block copolymers. Such controlled radical polymerization methods are performed under similar conditions as conventional radical polymerization but produce polymers with much narrower molecular weight distributions which allows for precise control of the segment lengths. Previously, such control could only be attained using ionic polymerization methods which require extensive purification of reagents and protection of functional groups. Further, controlled radical polymerization allows combinations of monomer sequences which may not be necessarily possible with ionic polymerization. Our research projects are thus focused on block copolymer synthesis by controlled radical polymerization and the use of such block copolymers as templates for next-generation organic electronic devices and separations media.

Projects

One thrust of our research is to develop facile methods to produce block copolymers using controlled radical polymerization. Our general strategy has been to produce AC diblock copolymers and ABC triblock copolymers where A is a selectively degradable segment, B is a segment containing a functional group and C is a tough matrix material. We are developing several approaches focused on using functional initiators and/or polymers to link the various segments together. Using NMP, we have been using functional end-groups and macro-initiators based on poly(lactide) (PLA), poly(caprolactone) (PCL) and poly(ethylene oxide) (PEO) to produce various block copolymers with matrix phases such as poly(styrene) and various methacrylates. We are using gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) and other techniques to characterize the tailored block copolymers. Once characterized, we can apply methods to order the material and process the materials for several projects outlined below.

A strong impetus currently is to develop smaller, more flexible materials for next generation electronic devices and sensors. Many efforts currently exist that are attempting to develop objects such as nano-rods, nano-wires and periodic arrays of such objects. We have started examining poly(vinylcarbazole) (PVCz) containing block copolymers where the photoconductive PVCz serves as the functional segment. We are planning to extend this work to other block copolymers containing functional sequences such as poly(vinyldiphenylquinoline) (PVQ) which has garnered interest as a organic light emitting diode (OLED) for display technologies.

Due to the nanometer scale of their structures, ordered block copolymers offer a route to extremely high surface area/volume separations membranes. For example, ordering the AC or ABC block copolymer into a cylindrical morphology followed by selective etching of the cylindrical phase results in a nanoporous material. We are focusing our efforts in two areas: 1) incorporation of ionic functional segments such as sulfonate or pyridine on the cylindrical walls; 2) producing more robust matrix materials to improve mechanical properties. We have been doing this by altering the matrix material from a rather brittle poly(styrene) to incorporation of methacrylic monomers for alteration of the glass transition temperature and by cross-linking of the matrix phase.

Our main research projects above have used selective degradation to produce a structure. In collaboration with researchers in Chemical Engineering and Civil Engineering and Applied Mechanics, we are involved the development of environmentally friendly plasticizers. Plasticizers are additives used in polymer formulations to improve processing and mechanical properties. Once the finished article is disposed of in the environment, the plasticizer can leach out and transform into potentially harmful metabolites. Our collaborators have found evidence of metabolites from common plasticizers in several sites. We are involved in processing and mechanical property testing of plasticizer/resin blends where the plasticizer structure can allow them to degrade into harmless metabolites while still serving as a cost-effective mechanical property enhancer in plastic formulations.

Collaborators

"Green" Plasticizers with David Cooper (Chemical Engineering) & Jim Nicell (Civil Engineering)

Rheology of Branched Polymers: with John Dealy (Chemical Engineering)

Micro-Injection Molding: with Musa Kamal (Chemical Engineering) and Andrew Hrymak (Chemical Engineering, McMaster University)

Equipment

Gel permeation chromatography (organic phase)

Miniature conical twin screw extruder

Miniature injection molder

Particle sizer and zeta potential analyzer

Vacuum manifold and polymerization reactors

Courses

Polymer Processing (CHEE-584 - graduate/undergraduate course): This course is a survey into engineering properties of polymers an processing operations. Polymer rheology, constitutive equations and transport equations are used to model polymer processing operations. Topics include: die forming and extrusion, mixing, injection molding, fiber spinning, film blowing, compression molding, and thermoforming.

Polymer Engineering and Science (CHEE-582 - graduate/undergraduate course) : The application fo enignieering fundamentals to the preparation and processing of polymers emphasizing the relationship between polymer structure and properties. Topics include: polymer synthesis techniques, characterization of molecular weight (GPC, light scattering, osmometry), crystallinity, glass transition, phase behaviour, mechanical properties, visco-elasticity and rheology, and polymer processing for use in blends and composite materials.

Materials Engineering (CHEE-484 - undergraduate course): Processes for forming and producing engineering materials such as amorphous, semicrystalline, textured and crystal-oriented substances and composites. Effect of processing variables on the properties of the finished article. Process of blending and alloying. Shaping and joining operations. Vessel equipment design for chemical engineering applications.

Design Projects (CHEE-456 Design I; CHEE-457 Design II - undergraduate course): Design I: Introduction to a process design and economic evaluation project, including environmental and safety aspects, for a major industrial operation. Student work in small groups under an experienced plant design supervisor. Design II: A process plan design and economic evaluation, including environmental and safety aspects, for a major industrial operation. Students work in small groups, under an experienced plant design supervisor. Plant visit.