DESIGN AND REALIZATION OF STIMULI-RESPONSIVE REGIOREGULAR COPOLYMERS WITH TUNABLE ONSET OF RESPONSE
Open Access
- Author:
- Foley, Theresa
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 20, 2008
- Committee Members:
- Evangelos Manias, Committee Chair/Co-Chair
Ralph H Colby, Committee Member
Seong Han Kim, Committee Member
Qing Wang, Committee Member - Keywords:
- water-soluble polymer
stimuli-responsive - Abstract:
- A series of temperature-responsive polymers with tunable onset of water dissolution was synthesized and their aqueous phase behavior was explored. The applicability of temperature-sensitive polymers relies on their ability to phase separate from water abruptly at a specific temperature. A series of polyamides and polyesters was developed, where the lower critical solution temperature (LCST) in water is controlled by the balance of hydrophobic and hydrophilic segments in the polymer. Cloud point measurements were used to study the phase transition of the aqueous polymer solutions. It was shown that by changing the size of either the hydrophobic or hydrophilic component, the LCST in water can be shifted to higher or lower temperatures by design. In order to maintain a sharp LCST phase transition, the hydrophilic and hydrophobic segments were connected in an alternating manner. This avoids “blockyness” within the backbone, which would result in broader phase transitions due to micelle formation. PEO was chosen as the hydrophilic component in all of the copolymers because of its LCST behavior in water and its proven utility in many biological applications. The hydrophobic components consisted of either aliphatic hydrocarbons or aromatic groups. Aliphatic hydrocarbons are an ideal choice for tuning the LCST because they are readily available in many lengths. By selecting sequences of different lengths, the aqueous solution LCST was tuned. Additionally, altering the copolymer molecular weight as well as the hydrophilic or hydrophobic nature of the terminal sequences was used for fine tuning the LCST. The influence of the nature of the hydrophobic group was investigated by preparing copolymers with aromatic hydrophobic segments, including an aromatic group with a pendant carboxylic acid. The latter hydrophobic segment imparted more hydrophobicity to the copolymers than aliphatic units of similar molecular weight, and the addition of carboxylic acid groups to the copolymer resulted in a dual temperature- and pH-responsive macromolecule. Finally, by using the “grafting from” approach in conjunction with polycondensation synthesis, a method to end-tether temperature-sensitive polyamides to a silicon wafer was devised, rendering the substrates temperature-responsive. The surface was characterized with contact angle and atomic force microscopy (AFM).