Date of Award

Summer 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

Committee Chair

Robson F. Storey

Committee Chair Department

Polymers and High Performance Materials

Committee Member 2

Jeffrey S. Wiggins

Committee Member 2 Department

Polymers and High Performance Materials

Committee Member 3

Derek L. Patton

Committee Member 3 Department

Polymers and High Performance Materials

Committee Member 4

Sergei I. Nazarenko

Committee Member 4 Department

Polymers and High Performance Materials

Committee Member 5

Xiaodan Gu

Committee Member 5 Department

Polymers and High Performance Materials

Abstract

This dissertation exploits properties inherent to azide-alkyne cycloaddition and applies practical solutions to difficult problems. Chapter II addresses structure-property relationships in glassy azido-alkyne matrices by varying the identity of the central linkage within tetrapropargyl bis-aniline-type crosslinkers, and by the addition or omission of Cu(I) catalyst. This systematic study showed that an ether or methylene linkage yielded lower melting tetrapropargyl crosslinkers that were soluble in, and produced homogeneous, networks when cured with, a standard azido resin, di(3-azido-2-hydroxypropyl) ether of bisphenol-A; in contrast, a sulfone linkage yielded a relatively insoluble crosslinker and poorly dispersed, heterogeneous networks when reacted with the same resin. The study also showed that the presence of Cu(I) and the concomitant network regularity afforded by a single triazole regioisomer increased compression modulus and Tg. However, due to increased kinetics of reaction the catalyzed system was much harder to process.

Chapter III introduces the use of azide-alkyne cycloaddition as an alternative curing mechanism in non-isocyanate polyurethanes (NIPU). Several commercial polyisocyanate resins derived from hexamethylene diisocyanate were converted to propargyl carbamates by reaction with propargyl alcohol; azidated co-reactants were synthesized from several different commercial polyols including polyether, polyester, and polyacrylic types. Each resin/coreactant combination was rendered into a two-component coating system and cured in the presence and absence of Cu(I) catalyst. Coating properties were compared to the precursor polyisocyanate/polyol coating systems, and the best-performing NIPU coating was found to result from a propargylated allophanate resin, XP2580, and an azidated polyacrylic resin, Setalux DA870. The latter coatings met or exceeded the properties of the precursor polyurethane coatings except for uncatalyzed rate of cure at ambient temperature.

Chapter IV focused on increasing the sluggish curing kinetics observed for the azide-propargyl systems. In Chapter III, this was overcome by the addition of Cu(I). However, this also caused discoloration to the coating. This chapter focused on making an aesthetically pleasing coating that cured similarly to the as received material. This was achieved by the synthesis of 2-hydroxyethyl propiolate (2-HEP) and its subsequent reaction with XP2580 to form a propiolate modified polyurethane resin. Incorporation of the propiolate functionality increased the rate of reaction with the azidated Setalux DA870, such that the observed curing kinetics were approximately the same as that of the as-received resin pairs.

Chapter V, the final chapter, addressed problem that plagued the carbamates synthesized in the previous two chapters. Upon propargylation, the viscosity increased dramatically, making the resins difficult to work with unless diluted by an appreciable amount of organic solvents. This was overcome by sacrificing a fraction of the isocyanate functionality to attach internal plasticizing moieties consisting of a monoalkyl ether of either ethylene glycol (EG) or diethylene glycol (DEG). This approach was successful in reducing coating system viscosity, and created a softer and more flexible coating with a lower glass transition. This study showed that the length of alkyl chain, rather than the choice of EG or DEG, produced the larger effect on viscosity and coating properties, i.e., butyl provided a much greater plasticizing effect than ethyl.

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