Abstract
The influence of reaction rate on the evolving polymer structure of photo-activated dimethacrylate biomedical resins was investigated using neutron and in situ synchrotron X-ray scattering with simultaneous Fourier-transform-near-infrared spectroscopy. Previous studies have correlated the degree of reactive group conversion with mechanical properties, but the impact of polymerization rate on the resultant polymer structure is unknown. Here, we demonstrate that the medium-range structural order at the functional end groups of these materials is dependent on the reaction rate. Accelerating polymerization increases correlation lengths in the methacrylate end groups but reduces the medium-range structural order per converted vinyl bond when compared with more slowly polymerized systems. At faster rates of polymerization, the conformation of atoms at the reacting end group can become fixed into the polymer structure at the onset of autodeceleration, storing residual strain. Neutron scattering confirms that the structural differences observed are reproduced at longer length scales. This effect is not as prominent in systems polymerized at slower rates despite similar final degrees of reactive group conversion. Results suggest that current interpretations of these materials, which extrapolate mechanical properties from conversion, may be incomplete. Accelerating polymerization can introduce structural differences, which will dictate residual strain and may ultimately explain the discrepancies in the predictive modeling of the mechanical behavior of these materials using conventional techniques.
Highlights
IntroductionThis work explores for the first time the effects of polymerization rate on the development of the medium-range (∼4−15 Å) polymer structure of the most commonly encountered photo-initiated biomedical resin polymers based on methacrylate chemistry, which are used ubiquitously in contemporary dental care
The physiochemical properties of these materials are highly sensitive to photopolymerization variables which impact on the degree of reactive group conversion and the development of transient and residual stresses, which affect clinical performance.[1−3] The degree of reactive group conversion is typically measured using Fourier-transform infrared (FTIR) or Raman spectroscopy but fails to provide insight into the architecture of the cross-linked polymer structure and the development of Received: January 18, 2019
The shift to lower q is indicative of a net length increase of the correlation length, while a narrowing of the peak demonstrates an increase in the medium-range (
Summary
This work explores for the first time the effects of polymerization rate on the development of the medium-range (∼4−15 Å) polymer structure of the most commonly encountered photo-initiated biomedical resin polymers based on methacrylate chemistry, which are used ubiquitously in contemporary dental care. The majority of contemporary dental resin-composite filling materials are composed of a dimethacrylate polymer matrix that consist of a viscous monomer and reactive low molecular weight diluent monomer(s), combined with nanoscale and/or micron-scale inorganic filler particles.
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