Alan Tonelli

Bio

Professor Tonelli’s research interests include the conformations, configurations, and structures of synthetic and biological polymers, their determination by NMR, and establishing their effects on the physical properties of polymers.

The formation and study of molecular composites formed by the embedding of inclusion compounds (ICs) formed between the host cyclic starches (cyclodextrins, CDs) containing 6 (α), 7 (β), and 8 (γ) glucose units and polymer or small molecule guests into polymer fibers and films followed by the release and coalesence of the guest into the carrier polymer phase has been persued. We hope this new method of fabrication will permit the delivery of various additives to polymer fibers and films which is superior to the current technologies. We and several other research groups have recently reported the ability of CDs to act as hosts in the formation of inclusion compounds with guest polymers. Polymer-CD-ICs are crystalline materials formed by the close packing of host CD stacks, which results in a continuous channel of ~5-8Ǻ in diameter running down the interior of the CD stacks. The guest polymers are confined to the narrow, continuous CD channels, and so are necessarily highly extended and segregated from neighboring polymer chains by the walls of the CD stacks. Our 13C and 1H NMR studies of polymer-CD-ICs have yielded motional parameters (relaxation times and resonance line widths) that, when compared to the same motional parameters observed on their bulk samples, reveal the inherent contribution made by single (α-CD-ICs) and pairs of side-by-side (γ-CD-ICs), extended polymer chains to the necessarily cooperative motions occurring in bulk polymer samples. We are expanding these studies to additional polymer-CD-ICs and by employing 2-D exchange NMR experiments designed to probe the specific angular distributions of conformational reorientations observed for polymer chains when segregated in their CD-IC channels and in their bulk samples.

Additionally and more importantly, we have shown that coalescence of guest polymers from their CD-IC crystals can result in a significant reorganization of the structures, morphologies, and even conformations that are normally observed in their bulk samples. For example, when polycarbonate (PC) is coalesced from its γ-CD-IC, we obtain a semicryst-alline sample with a Tm elevated ~15° C above the melting temperature observed in solution-cast or high temperature annealed PC samples. This suggests a chain-extended crystalline morphol-ogy in the PC sample coalesced from its γ-CD-IC. On the other hand, when poly(ethylene terephthalate) (PET) is coalesced from its γ-CD-IC, we find that in the non-crystalline regions of the sample the PET chains are adopting highly extended kink conformations, which result in their rapid recrystallization from the melt. Unlike normal PET samples, we have been unable to quench the coalesced PET rapidly from above Tm to achieve an amorphous sample. When a poly(ε-caprolactone) (PCL)-poly(L-lactic acid) (PLLA) diblock copolymer was coalesced from its α-CD-IC, we found a significant reduction in the phase-separated morphology normally produced in solution-cast samples, as indicated by 50 and 80% reductions in the crystallinities observed for the PCL and PLLA phases, respectively, in the coalesced diblock sample. We have also created well-mixed blends of normally incompatible polymers by coalescing them from CD-ICs containing both polymer pairs. Coalescence of polymer pairs from their common CD-ICs, where chemically distinct polymers are spatially proximal, results in molecularly intimate blends, which have been demonstrated for both crystallizable polymer pairs, such as PCL/PLLA and PET/PEN (poly(ethylene-2,6-naphthalate), and the amorphous pairs PC/PS (polystyrene) and PC/PMMA [poly(methyl methacrylate)]. Finally we have found the unique morphologies created by the coalescence of homopolymers, diblock copolymer, and homopolymer pairs from their CD-ICs are stable to heat treatment for prolonged periods above their Tm‘s and/or Tg‘s. Thus we can create polymer materials with unique morphologies that are retained during normal melt processing. As a consequence, we are beginning to more fully characterize these unique and newly created, coalesced polymer samples principally by solid state NMR techniques, such as 2-D HETCOR, WIM-WISE, variable temperature 1D and 2D exchange, and CODEX experiments, which will provide measures of both the scale of mixing and the motions of their constituent polymer chains at the molecular level.

Scale-up of the production of these CD-IC-coalesced polymer materials will eventually enable the determination of their bulk properties, such as permeabilities and strengths, which are presumably distinct from and hopefully better than those of their normally produced solid samples, such as their phase-segregated blends. Achievement of molecularily well-mixed blends composed of any two or more chemically distinct polymers, or between additives and polymers, would permit a virtually unlimited expansion of useable polymer materials. More recently we have found polymers coalesced from their CD-ICs can be used in very small amounts as nucleants for the same bulk polymers. Such nucleated polymers behave essentially like their neat CD-IC coalesced samples, so they can then be used to nucleate the melt crystallization of additional bulk samples of the same polymers. We have called such nucleating polymer samples “Stealth” nucleants, because they contain no other material than the bulk polymer they are nucleating. This means such samples are more recycled and may potentially be usable in animal and humansI. In addition to the obvious commercial significance, which would have important consequences for US industry, this development could greatly benefit society at large.

Most recently we have demonstrated the ability to characterize the types, amounts, and locations of microstructural elements contained in synthetic polymers. For the first time this permits determination of the complete molecular architectures or macrostructures of synthetic polymers. This is achieved by employing 13C-NMR to determine the types and quantities of short-range polymer microstructures, followed by Kerr-Effect examination to locate these microstructural elements along the polymer backbone. This is made possible, because the Kerr-Effect or birefringence contributed by polymer solutes when their dilute solutions are subjected to strong electric fields is highly sensitive to polymer macrostructures. As an example, small molecules (~ the size of monomers), exhibit molar Kerr constants that range over nearly five orders of magnitude and can be either positive or negative.

Just as the behaviors of proteins are determined by their primary structures, i.e., their sequences of amino acids, so too must the behaviors and properties of materials made of synthetic polymers be determined by their macrostructures.

Organizations

• American Chemical Society – National Counselor
• American Chemical (Polymer Chemistry Div.), American Physical (Polymer Physics Div.) and Fiber Societies. – Member
• American Chemical Society – Tour speaker
• North Carolina Polymer Group of the American Chemical Society – Chairman
• NC local ACS Section 2008 – Chair
• Research programs of 50 High School and undergraduate, 30 graduate, and 12 Post-Doctoral Students. – Supervisor
• Editorial Boards of Macromolecules(1984-1986) and Comp. and Theor. Polym. Sci.(1991-2001) – Supervisor

Teaching

• TC 203
• TC 441
• TC 442
• TC 461
• TC 561
• TC 771

Students

Yavuz Caydamli – FPS

Alper Gurarslan – FPS

Rana Gurarslan – FPS

Abhay Joijode – FPS

Shanshan Li – FPS

Ganesh Narayanan – FPS

Jialong Shen – FPS

Hui (Cathy) Yang – PhD (Shanghai University)

Area(s) of Expertise

Fiber Science
Polymer Science

Publications

• External Stimuli Responsive Nanofibers in Biomedical Engineering , ELECTROSPUN POLYMERIC NANOFIBERS (2023)
• Chitosan based bioadhesives for biomedical applications: A review , CARBOHYDRATE POLYMERS (2022)
• Cyclodextrin-based nanostructures , PROGRESS IN MATERIALS SCIENCE (2022)
• Chitosan/Graphene Oxide Composite Films and Their Biomedical and Drug Delivery Applications: A Review , APPLIED SCIENCES-BASEL (2021)
• Effect of clinoptilolite on structure and drug release behavior of chitosan/thyme oil gamma-Cyclodextrininclusion compound hydrogels , JOURNAL OF APPLIED POLYMER SCIENCE (2021)
• A New Two-Step Strategy for Encapsulating Amorphous Polymer Chains in Thiourea Crystals , MACROMOLECULAR CHEMISTRY AND PHYSICS (2020)
• Are poly(p-phenylene terephthalamide) (Kevlar (R)) and other liquid crystalline polymers conformationally rigid? , POLYMER (2020)
• Chitosan-based hydrogels loading with thyme oil cyclodextrin inclusion compounds: From preparation to characterization , EUROPEAN POLYMER JOURNAL (2020)
• Conformations , (2020)
• Delivery of pharmaceuticals and other active ingredients with their crystalline cyclodextrin inclusion compounds , INTERNATIONAL JOURNAL OF PHARMACEUTICS (2020)

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