In the past, there has been considerable interest in the production of new polymeric materials by the blending of existing polymers. However, it has become apparent over the past two decades that most of these polymer blends are not miscible, i.e. the component polymers (homopolymers) do not mix at a molecular level. Much research has been devoted to characterising the miscibility of polymer blends, although quantitative measurements of the level of mixing in polymer blends are still difficult to obtain, and to understanding the factors that affect the miscibility of polymer blends. The affects of miscibility on the molecular dynamics of the homopolymer chains in polymer blends and, therefore, the mechanical properties of the blends are, however, poorly understood.
In this thesis, two NMR techniques (13C T 1p relaxation time measurements and simulations of 1H spin diffusion) for investigating the molecular dynamics and quantifying the miscibility of the homopolymers in. polymer blends have been developed. These and a number of other NMR techniques (2H NMR, 1H NMR,13C NMR and 2D heteronuclear correlation NMR) and have been used to investigate molecular dynamics in, and to quantify the miscibility of a number of polymer blends. The relationships between the miscibility and molecular dynamics of the homopolymers in polymer blends are then discussed. The blends studied in this thesis, namely poly(styrene)-poly(vinyl methyl ether) (PSTY-PVME), poly(ethylene oxide)-poly(vinyl phenol) (PEO-PVPh), and PEO-poly(methyl methacrylate) (PMMA), were chosen because they represent a set of miscible blends• which display a range of different morphologies and types of specific interactions.
Measurements of 1H spin-lattice relaxation times (1H T1 and 1H T1ρ) combined with simulations of 1H spin diffusion were used to investigate the details of the morphology of, and quantify the level of miscibility in blends of PSTY-PVME and PEO-PMMA. The details of the morphology of the so-called 'miscible' blends of PS TY-PVME were shown to be complex. The size of domains in these blends were determined to be between 2 nm and 80 nm, depending on the composition of the blend. In addition, it was also shown that the so-called v blends of PSTY -PVME with ≤20 wt % PSTY are comprised of regions of intimately mixed PSTY-PVME. Blends of PEO-PMMA were shown to have a three-phase morphology. The size and composition of each of the phase were characterised by 1H NMR, and were found to be consistent with previously reported data.
lD 2H NMR measurements were used to investigate phenyl group dynamics in PSTY and 'miscible' PSTY -PVME blends. It was shown that the molecular dynamics of the phenyl groups of PSTY are sensitive to changes in free volume, the segmental dynamics of the PSTY main-chains and specific molecular interactions between PSTY and PVME. 2H NMR measurements above the Tg of PSTY suggest that the structure of pure PSTY is not homogeneous. Instead it is proposed that two regions of ordered and disordered phenyl groups exist in PSTY. In addition specific interactions between PSTY and PVME were shown to restrict the molecular motions of the phenyl groups of PSTY. A model for the nature of the specific interaction in PSTY -PVME blends is presented in this thesis.
13C T1P relaxation time measurements were shown to provide a simple, yet highly effective, technique for probing the molecular dynamics of the main-chains and side-groups of the individual homopolymers in polymer blends. Measurements of the 13C T1P relaxation times of PEO-PVPh and PEO-PMMA blends have shown that main-chain motions of the homopolymers are affected by intimate mixing in these blends. However, the segmental motions of the homopolymers in both of these blends are not concerted. In addition, from 13C T1ρ relaxation time measurements, two types of motion could be measured for the phenol groups of PVPh in these blends. It was shown that the rotational motions of the phenol groups of PVPh are liberated by blending with PEO.
From comparisons of the molecular dynamics in PSTY -PVME, PEO-PVPh and PEO-PMMA blends with the degree of miscibility of these blends, measured by 1H NMR, it was concluded that the molecular motions of the homopolymer main-chains and side-groups are affected by intimate mixing with dissimilar polymer chains. However, the molecular motions of the individual homopolymers in intimately mixed blends are not concerted. Furthermore, it was shown that strong specific interactions between the homopolymer chains enhance the degree of cooperativity between dissimilar chains.