JianCheng Liu1, Jeffrey W Stansbury2. 1. Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA. 2. Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO, USA; Department of Craniofacial Biology, School of Dental Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, USA. Electronic address: jeffrey.stansbury@ucdenver.edu.
Abstract
OBJECTIVE: This study examines how nanogel structure correlates with photopolymerization and key polymer properties upon addition of nanogels with latent reactivity into a monomer dispersant to produce polymer/polymer composites. METHODS: Two nanogels that retained RAFT functionality based on the synthetic approach were prepared to have different branching densities. These reactive nanogels were dispersed in triethylene glycol dimethacrylate at 0-40 wt%. Reaction kinetics, volumetric shrinkage and shrinkage stress associated with the photopolymerization of nanogel-modified formulations were measured in real time with mechanical properties of the polymers also evaluated. The basic structure of RAFT-derived nanogel particles was examined by the preparation of a separate nanogel constructed with degradable disulfide crosslinking groups. The model nanogel molecular weight and polydispersity were compared before and after degradation. RESULTS: Despite the controlled radical synthetic approach, the nanogels, which are composed of multiple interconnected, short primary chains, presented relatively high polydispersity. Through addition of the reactive nanogels to a monomer that both infiltrates and disperses the nanogels, the photopolymerization rate was moderately reduced with the increase of nanogel loading levels. Volumetric shrinkage decreased proportionally with nanogel concentration; however, a greater than proportional reduction of polymerization-induced stress was observed. Mechanical properties, such as flexural strength, storage modulus were maintained at the same levels as the control resin for nanogel systems up to 40 wt%. SIGNIFICANCE: This study demonstrated that beyond the use of RAFT functionality to produce discrete nano-polymeric structures, the residual chain end groups are important to maintain reactivity and mechanical properties of nanogel-modified resin materials.
OBJECTIVE: This study examines how nanogel structure correlates with photopolymerization and key polymer properties upon addition of nanogels with latent reactivity into a monomer dispersant to produce polymer/polymer composites. METHODS: Two nanogels that retained RAFT functionality based on the synthetic approach were prepared to have different branching densities. These reactive nanogels were dispersed in triethylene glycol dimethacrylate at 0-40 wt%. Reaction kinetics, volumetric shrinkage and shrinkage stress associated with the photopolymerization of nanogel-modified formulations were measured in real time with mechanical properties of the polymers also evaluated. The basic structure of RAFT-derived nanogel particles was examined by the preparation of a separate nanogel constructed with degradable disulfide crosslinking groups. The model nanogel molecular weight and polydispersity were compared before and after degradation. RESULTS: Despite the controlled radical synthetic approach, the nanogels, which are composed of multiple interconnected, short primary chains, presented relatively high polydispersity. Through addition of the reactive nanogels to a monomer that both infiltrates and disperses the nanogels, the photopolymerization rate was moderately reduced with the increase of nanogel loading levels. Volumetric shrinkage decreased proportionally with nanogel concentration; however, a greater than proportional reduction of polymerization-induced stress was observed. Mechanical properties, such as flexural strength, storage modulus were maintained at the same levels as the control resin for nanogel systems up to 40 wt%. SIGNIFICANCE: This study demonstrated that beyond the use of RAFT functionality to produce discrete nano-polymeric structures, the residual chain end groups are important to maintain reactivity and mechanical properties of nanogel-modified resin materials.
Authors: Rafael R Moraes; Jeffrey W Garcia; Matthew D Barros; Steven H Lewis; Carmem S Pfeifer; JianCheng Liu; Jeffrey W Stansbury Journal: Dent Mater Date: 2011-03-08 Impact factor: 5.304
Authors: Francoise Isaure; Peter A G Cormack; Susan Graham; David C Sherrington; Steven P Armes; Vural Bütun Journal: Chem Commun (Camb) Date: 2004-03-25 Impact factor: 6.222