TEMPERATURE DEPENDENT MICROPHASE MIXING OF MODEL POLYURETHANES

Open Access
Author:
Pongkitwitoon, Suphannee
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 14, 2010
Committee Members:
  • Joan Marie Redwing, Thesis Advisor
  • Paul C Painter, Thesis Advisor
Keywords:
  • PDMS/PHMO-PUs
  • Synchrotron small angle x-ray scattering
  • microphase separation transition
  • microphase mixing
  • segmented polyurethane block copolymers
Abstract:
In this thesis I explore the temperature dependence of segregation of hard and soft segments of selected segmented polyurethane copolymers using synchrotron small-angle X-ray scattering (SAXS). The copolymers are composed of the same hard segments but three different soft segment chemistries, of particular interest in biomedical device applications. Hard segments are formed from 4,4Œ-methylenediphenyl diisocyanate and 1,4-butanediol, and soft segments from an aliphatic polycarbonate (i.e. poly(1,6-hexyl 1,2-ethyl carbonate), [PHEC]), poly(tetramethylenoxide) [PTMO], or a mixed soft segment synthesized from hydroxyl-terminated poly(dimethylsiloxane) [PDMS] and poly(hexamethylenoxide) macrodiols [PHMO]. The changes in SAXS relative invariants and interdomain spacings are indicative of gradual dissolution of phase separated hard and soft segments with increasing temperature. All copolymers investigated herein, even those containing PDMS soft segments, transform to the single-phase state at a temperature determined by the soft segment chemistry (and hard segment content). The SAXS findings, along with those from parallel temperature controlled Fourier Transform infrared spectroscopy measurements, also facilitate assignment of the origin of the thermal events observed in the DSC thermograms of these materials.