Mechanical, thermomechanical, and thermal properties of polystyrene crosslinked with a multifunctional zirconium oxo cluster

Abstract

Inorganic-organic hybrid materials were prepared by free radical polymerization of styrene in the presence of varying amounts of the cluster Zr 6 O 4 (OH) 4 (methacrylate) 12 . Stepwise polymerization allowed the preparation of bubble-and crack-free, transparent bulk samples on a 30 g scale with dimensions required for mechanical testing. Small-angle X-ray scattering investigations and transmission electron micrographs revealed that the clusters formed randomly distributed aggregates of random size. Solvent uptake in swelling experiments was related to the cluster proportion. Storage moduli in the glassy state were slightly increased when compared with neat polystyrene, but pronounced plateau moduli were observed above the glass transition temperature, which correlated to the cluster proportion. Plateau moduli were used to calculate network parameters such as network density. Onset temperatures of thermal decomposition and the glass transition temperatures of the cluster-crosslinked polymers were higher than that of neat polystyrene. Thermal expansion coefficients were unaffected in the glassy state, but were gradually reduced above the glass transition temperature with increasing cluster proportion. Both the tensile moduli at room temperature and the yield points increased when polystyrene was doped with the cluster. The strain hardening moduli, as determined in compression tests at large deformations, increased linearly with the cluster proportion.

Suppression of Crazing in Polystyrene Crosslinked with a Multifunctional Zirconium Oxo Cluster Observed In Situ during Tensile Tests

“…The stabilization of the polymer network is also indicated by the increase in the network density with increasing cluster proportion as determined from dynamical mechanical analysis. [11] Whereas the elastic properties are only very weakly affected [11] and still governed by the PS matrix, which is typical for small loading with an inorganic component, [21] the maximum stress and strain change by a factor of nearly three. The main structural cause is that the development of crazing is increasingly suppressed with increasing cluster proportion.…”

“…A detailed description of the synthesis can be found in ref. [11] A cluster-free PS sample was prepared under the same conditions for reference.…”

“…Though this new class of materials, the cluster-doped hybrid polymers, exhibits promising new features such as improved thermal properties, [9,10] the investigation of the mechanical properties was limited, because only small laboratory samples could be prepared. In a recent paper, [11] we reported for the first time the successful preparation of bubble-and crack-free samples of polystyrene (PS) crosslinked with different proportions of the transition metal oxo cluster Zr 6 O 4 (OH) 4 (methacrylate) 12 (denoted in the following by Zr 6 ) with dimensions sufficiently large for mechanical testing, which were investigated with focus on thermal, thermomechanical and mechanical properties and structural characterization. [11,12] During mechanical loading, polymers like PS exhibit significant crazing.…”

“…In a recent paper, [11] we reported for the first time the successful preparation of bubble-and crack-free samples of polystyrene (PS) crosslinked with different proportions of the transition metal oxo cluster Zr 6 O 4 (OH) 4 (methacrylate) 12 (denoted in the following by Zr 6 ) with dimensions sufficiently large for mechanical testing, which were investigated with focus on thermal, thermomechanical and mechanical properties and structural characterization. [11,12] During mechanical loading, polymers like PS exhibit significant crazing. For its characterization, small-angle X-ray scattering (SAXS) turned out to be one of the most useful tools because of two advantages: SAXS is a nonintrusive technique without the requirement of special sample preparation [13] and quantitative information from a statistically relevant large volume is obtained: [14] the craze fibrils are aligned in the direction of the applied stress, which gives rise to an oriented scattering intensity, from which the number and size of the craze fibrils are obtained.…”

Retro-crosslinking of cluster-based hybrid polymers

“…The obtained hybrid polymers are glassy, transparent materials which are insoluble in organic solvents but swell, the degree of swelling depending on the cluster proportion. Their properties can be traced back to an interplay between crosslinking and inorganic filler effects [6,7]. Furthermore, a stepwise polymerization protocol allowed optimizing the materials properties of the Zr6-based hybrid materials [8].…”