Telechelic Ionomers:  Molecular Structure and Kinetics of Physical Gelation of Unsaturated Polyester as Studied by Solid State NMR and X-ray

Abstract

The kinetics of physical gelation and the structure of telechelic ionomers have been studied by 1 H and 13 C solid-state NMR, SAXS, and WAXD. The reaction of MgO with unsaturated polyesters containing carboxylic and hydroxyl end groups leads to about a 10 3 -10 4 -fold viscosity increase in the initial solution of polymer in styrene. The results of the present study suggest that the main mechanism, involved in the viscosity increase, is determined by strong electrostatic interactions between Mg 2+ ions and the charged carboxylato chain ends, resulting in the formation of immobilized ionic multiplets and their aggregates or clusters. Molecular diffusion is the limiting step for cluster formation. SAXS, WAXD, and NMR results suggest a lamella-like structure of the clusters, which are composed of crystalline carboxylato-Mg-aqua complexes in the core part surrounded by a glassy polymer layer with a thickness of a few nanometers. Polyester chains interconnect multiplets, resulting in the formation of a physical network. The estimated distance between neighboring lamella is comparable with the end-to-end distance of network chains. The increase in the content of network chains and immobilized domains causes a large increase in viscosity and storage modulus. The effect of temperature and of ionic and hydroxyl containing additives on the thickening is discussed.

Local Molecular Dynamics and Heterogeneity in PEO–NiCl2 Supramolecular Networks

“…16 As the effective spin-diffusion coefficient cannot be accurately determined for polymers with disordered complex structures or materials with undetermined morphologies, we use a typical value of 0.7 nm 2 /ms for D eff . 19 Assuming spherical shape for the hindered domains and also considering there is presumably no long-range regularity in the systems, Figure 5 shows the minimum diameter of those domains in the systems which exhibit biexponential recovery of T 1 , for different molecular weights and ion concentrations.…”

Melting-Induced Evolution of Morphology, Entanglement Density, and Ultradrawability of Solution-Crystallized Ultrahigh-Molecular-Weight Polyethylene

“…The presence of network junctions, either chemical cross-links, physical junctions, or both, increases the anisotropy of chain motions, which causes an increase in the strength of interactions between nuclear spins. These internuclear interactions are quantified by different NMR experiments and are used for calculating the molecular weight of network chains. − The T 2 relaxation method is a simple and robust way for such analysis providing quantitative data on the molecular weight of network chains in polymers with chemical cross-links, (quasi)­permanent physical junctions, or both. − In polymer melts, the fluctuation of entanglement nodes (in the discrete binary entanglements model) or the tube diameter (in the tube model) at the time scale of the NMR T 2 relaxation experiment (∼ T 2 value) causes an overestimation of molecular weight between apparent chain entanglements, M e . The effect is small for UHMWPE, as was shown by a theoretical analysis of T 2 decay for a series of HDPE melts with a large range of molecular weight .…”

“…49,50,51 The T 2 relaxation method is a simple and robust way for such analysis providing quantitative data on molecular weight of network chains in polymers with chemical crosslinks, (quasi)permanent physical junctions, or both. 52,53,54 In polymer melts, the fluctuation of entanglement nodes (in the discrete binary entanglements model) or the tube diameter (in the tube model) at the time scale of the NMR T 2 relaxation experiment ( T 2 value) causes an overestimation of molecular weight between apparent chain entanglements, M e . The effect is small for UHMWPE as was shown by a theoretical analysis of T 2 decay for a series of HDPE melts with a large range of molecular weight.…”

Effect of covalent cross-links on the network structure of thermo-reversible ionic elastomers

“…NMR spectroscopy, and especially multiple-quantum NMR experiments, 5,32,37 could be considered the most direct and reliable methodology to determine the molecular weight between constraints by measuring the residual dipolar couplings. Although NMR spectroscopy has been used to study the complex structure and phase separation of ionic elastomers, 38,39 the exact analysis of NMR data (based on advanced 1 H MQ-NMR experiments) need to include the development of new fitting strategies that can deal with such large heterogeneity, since the current state-of-the-art approach 32,37 produces systematic errors related to the fact that the sub-populations exhibit very different relaxation behaviour (detailed investigations supporting this issue are being performed and will be the subject of an upcoming publication).…”