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The Importance of Minor Sequence Alterations on the Hydrolysis Behaviors of Degradable Polyesters

Nowalk, Jamie A. (2019) The Importance of Minor Sequence Alterations on the Hydrolysis Behaviors of Degradable Polyesters. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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The extent to which small changes in monomer sequence affect the behaviors of biological macromolecules is studied regularly, yet the dependence of bulk properties on small sequence alterations is underexplored for synthetic copolymers. Investigations of this type are limited by the arduous syntheses required, lack of scalability, and scarcity of examples of polymer systems that are known to exhibit sensitive sequence/property dependencies. Our group has previously explored the hydrolysis behaviors of a library of sequenced poly-(lactic-co-glycolic acid)s (PLGAs) and found a strong correlation with the L-G sequence. To investigate the degree to which properties are dominated in this system by relatively minor sequence changes, L-G sequences were incorporated into cyclic macromonomers, and these macromonomers were subjected to entropy-driven ring-opening metathesis polymerization. This polymerization method produces polymers with molecular weight control and sequence preservation, both being required for studies in which subtle sequence changes are compared.
Two hydrolysis studies were performed in which a precisely sequenced polymer containing a base alternating sequenced segment, LGLGL, was compared against 1) a copolymer in which the LGLGL segment was randomized, i.e., L3G2, thus confining disorder within this short segment, and 2) the base sequence doped with varying, small quantities of LGGGL “error” segments. In this first hydrolysis study, molecular weight decrease, mass loss, thermal behaviors, and film/surface characteristics were monitored to reveal stark differences in degradation behaviors despite the confinement of errors within a short segment. In the second hydrolysis study, degradation rate proved tolerant to substitutions up to 1% of the monomers but accelerated significantly when the error population was larger.
In instances where copolymer properties are dependent on monomer order, sequence engineering expands the functional capabilities of a given set of monomers. Investigations of how localized, property-dominating sequence segments affect behavior may aid researchers in establishing synthetic methods to either incorporate or eliminate such sequences for the preparation of materials for advanced function.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Nowalk, Jamie A.jan66@pitt.edujan66
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMeyer, Tara
Committee MemberHorne, W.
Committee MemberLiu,
Committee MemberMarra,
Date: 27 September 2019
Date Type: Publication
Defense Date: 31 May 2019
Approval Date: 27 September 2019
Submission Date: 7 June 2019
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 264
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: sequence controlled polymers, polyester, polymer, synthesis, polymer microstructure, sequence engineering, PLGA, poly-(lactic-co-glycolic acid)
Date Deposited: 27 Sep 2019 17:25
Last Modified: 27 Sep 2019 17:25

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