Identifier

etd-04142013-223923

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

This dissertation presents the first experimental efforts for synthesizing a new class of peptidomimetic polymers, cyclic block copolypeptoids, studying their self-assembly in dilute solution, and examining their macroscopic properties. Cyclic poly(N-methyl-glycine)-b-poly(N-decyl-glycine) (PNMG-b-PNDG) diblock copolymers were synthesized via sequential, N-heterocyclic carbene (NHC)-mediated ring-opening polymerization of NCA monomers with controlled chain length and compositions. Cryo-TEM shows that PNMG105-b-PNDG10 copolymers in methanol (1 mg/mL) form spherical micelles that organize to form cylindrical micelles over time. The formation of cylindrical micelles is attributed to the crystallization of PNDG chains, as revealed by SAED and microDSC analyses. Cyclic PNMG100-b-PNDG10 copolymers form thermo-reversible, free-standing gels at a concentration of 5 wt %. Rheological measurements of the gels reveal that cyclic copolymers produce harder gels than their linear counterparts. Variable-temperature 1H NMR suggests that thermo-reversible gelation is related to any transitions of morphologies formed from the copolymers upon heating and cooling. Analyses by WAXS and SAXS suggest that the cyclic copolymers favor to form cylindrical micelles more than the linear copolymers, leading to formation of harder gels due to more transient networking among the cylindrical micelles. The second part focuses on the synthesis of cyclic triblock terpolypeptoids and their self-assembly in solution. Cyclic poly(N-methyl-glycine)-b-poly(N-allyl-glycine)-b-poly(N-benzyl-glycine) triblock terpolypeptoids were synthesized via sequential addition of monomers. Studies by SEC and NMR suggest block copolymer compositions can be controlled by varying molar ratios of each monomer to NHC. Similarly, cyclic [poly(N-ethyl-glycine)-ran-poly(N-butyl-glycine)]-b-poly(N-methyl-glycine)-b-poly(N-decyl-glycine) triblock terpolypeptoids were synthesized. Analysis by DLS suggests that this terpolymer forms micelles with broad size distributions below the cloud point temperature (Tcp) of PNEG-ran-PNBG blocks, and it may form well-defined, larger micellar aggregates above the Tcp. The third part presents systematic studies of the melting and crystallization of cyclic or linear polypeptoids with various n-alkyl side groups. Studies by DSC show that polypeptoids with butyl or longer side groups have two endothermic melting transitions (Tm,1 < Tm,2). Tm,1 increases and Tm,2 decreases, as the length of n-alkyl side groups increases. Studies by WAXS show that polypeptoids with butyl or longer side groups are well ordered. Tm,1 is attributed to side chain packing and Tm,2 to main polypeptoid packing.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Zhang, Donghui

Included in

Chemistry Commons

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