Calorimetric Characterization of the Heterogeneities Produced by the Radiation-Induced Cross-Linking Polymerization of Aromatic Diacrylates

Abstract

The structural heterogeneities in networks produced by UV-and by electron beam-initiated polymerization of aromatic diacrylates were unambiguously revealed by AFM imaging and studied by means of temperature-modulated differential scanning calorimetry. Two main second-order thermodynamic transitions were observed during the analysis of diacrylate networks exhibiting a fractional degree of conversion ranging from 0.1 to 0.8. The bimodal distribution of transition temperatures observed as fused peaks in the diagrams representing the differential quantity associated with the reversing heat capacity, dC p,rev /dT, was satisfactorily resolved by a two-component numerical fitting method allowing a quantitative exploitation of the data in terms of Gaussian contributions with particular central relaxation temperature and peak width affected by the gradual polymerization of the sample. The dual relaxation phenomenon was assigned to a biphasic-like structure consisting of clusters with a high cross-link density formed in continuous domain of lower monomer conversion. The evolution of the calorimetric data in the samples affords detailed information on the gradual formation of the network, with the initial broadening and final narrowing of the transition peak at high temperature related to the densely cross-linked clusters, whereas the low-temperature transition vanishes in intensity with an increasing broadening of the associated transition range. The analyses carried out in this work did not point out any influence of the UV-or EB-induced initiation mechanism of the time scale and thermal conditions of the polymerization process on the calorimetric features of the observed heterogeneities.

A structural interpretation of the two components governing the kinetic fragility from the example of interpenetrated polymer networks

“…Similar results can be found in the literature. Krzeminski et al, for instance, reported a bimodal distribution of the transition temperatures during the radiation‐induced crosslinking of aromatic diacrylates. In the case of poly(caprolactone)/polylactide copolymer networks, Serra and coworkers concluded about microphase separation due to blending.…”

A Guide through the Dental Dimethacrylate Polymer Network Structural Characterization and Interpretation of Physico-Mechanical Properties

“…At the same time, in the literature, it had been suggested, that the presence of microgel agglomerates may adversely affect mechanical properties of poly(dimethacrylate)s, primarily the impact resistance [21,[24][25][26][27][28]. In recent years, with advances in characterization techniques, substantial efforts have been made to precisely describe the polymer network spatial heterogeneity, especially the morphology [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. All of this has resulted in many studies on structure-property relationships.…”

“…It is only in recent years that methodologies for quantitatively characterizing the morphology of dimethacrylate polymer networks have been developed. They utilize AFM supported with advanced mathematical tools [33,34,38,148], X-ray powder diffractometry (XRPD) [32,35,45,136] as well as techniques of thermal analysis: dynamic-mechanical analysis (DMA) [1,42,52,[69][70][71][149][150][151][152][153], differential scanning calorimetry (DSC) [39] and thermogravimetry (TG) [154][155][156].…”

“…The AFM morphology was quantified by using the phase imaging AFM of local viscoelasticity of the Bis-GMA and Bis-EMA acrylate analogue polymers [37][38][39]. The results provided valuable information about the kinetics of diacrylate radical polymerization, which can be transformed into dimethacrylates.…”

Influence of an oxidation of the carbon fiber surface by boiling nitric acid on the adhesion strength in carbon fiber‐acrylate composites cured by electron beam

“…The values of IFSS were systematically lower in the case of EB curing, and it is assumed that the little difference in the fraction conversion (0.03) and homogeneity of curing in the sample cannot be the only parameter responsible for it. Indeed, Krzeminski et al . characterized the mechanisms influencing the structure of Ebecryl 600® polymer network and showed that, for the same value of the fraction conversion, it did not depend on the initiation mechanism, the curing temperature and the polymerization timescale.…”