BROADBAND DIELECTRIC STUDY OF THE RELAXATION DYNAMICS OF AMORPHOUS AND SEMI-CRYSTALLINE POLYMER BLENDS

Open Access
Author:
Jin, Xing
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 27, 2004
Committee Members:
  • James Patrick Runt, Committee Chair
  • Ian Roland Harrison, Committee Member
  • Ralph H Colby, Committee Member
  • Qiming Zhang, Committee Member
Keywords:
  • Dielectric
  • Relaxation
  • Dynamics
  • Semi-crystalline
  • Polymer Blends.
Abstract:
ABSTRACT In order to elucidate the complex relaxation dynamics in polymer blends containing a crystallizable component and having a large Tg difference between the components, a series of systems were investigated principally via dielectric relaxation spectroscopy, with the aid of differential scanning calorimetry, infrared spectroscopy and wide-angle X-ray diffraction experiments. For neat semi-crystalline poly(ethylene oxide) (PEO), a dielectric relaxation (labeled as g0„4) faster than the cooperative segmental relaxation is observed for the first time, and it is assigned to a segmental relaxation with reduced cooperatvity in the order - disorder interphase regions. Poly(styrene-co-p-hydroxystyrene) (SHS) and poly(methyl methacrylate) (PMMA) were selected to investigate the dynamics of blends of crystallizable PEO with relatively high Tg components, with and without strong intercomponent interactions. For amorphous SHS/PEO blends (0…6 60wt% SHS), hydrogen bonding is capable of suppressing concentration fluctuations and leads to a single cooperative segmental process involving both components. In addition, a fast PEO segmental process is observed in the dielectric spectra of blends with 0…680 wt% SHS, due to reduced intermolecular hydrogen bonding and repulsion between SHS styrene units and PEO segments. For amorphous PMMA/PEO blends, after room-temperature aging, a dielectric relaxation becomes apparent at approximately the same frequency-temperature location as that of the PEO g0„4 process. It is assigned to nanoscale PEO regions possessing a degree of partial order comparable to that of an order ¨C disorder interphase. Thermorheological simplicity is observed for amorphous mixtures of dihydroxyl naphthalene (DHN) and poly(vinyl ethyl ether) (PVEE), where DHN is a model small molecule with two functional groups capable of forming hydrogen bonds with PVEE, a non-crystallizable analog of PEO. The absence of chain connectivity in DHN and the presence of a suitable degree of intercomponent interactions is proposed to enable DHN molecules to closely contact PVEE segments and distribute uniformly in the PVEE matrix, thereby having the same effect on all PVEE local environments.