Allyl sulfides and α‐substituted acrylates as addition–fragmentation chain transfer agents for methacrylate polymer networks

Abstract

The rapid and uncontrolled nature of network formation from di(meth)acrylate monomers produces high shrinkage stress and results in polymers with oftentimes brittle mechanical properties. Methods for regulating polymerization and network formation are sought. One option is the use of addition–fragmentation chain transfer (AFCT) agents, which are well known to control molecular weight and molecular weight distribution of monofunctional (meth)acrylates. A series of novel and previously described AFCT reagents were synthesized and screened with laser flash photolysis to determine reactivity. Well‐performing AFCT reagents were then tested in polymerizations with monofunctional and difunctional methacrylates. With monofunctional monomers, the molecular weight and polydispersity of the resultant linear polymers tend to decrease with the addition of AFCT agent. In copolymerization with dimethacrylate monomers, the AFCT agents were found to substantially lower and sharpen the glass transition. Sharpness of the glass transition is here indicative of a more regular and homogenous network. After coupling of the instruments, photorheology was performed simultaneously with real‐time IR to show an increase in monomer conversion at the time of gelation, which appears to have a positive effect on reducing shrinkage stress. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 394–406

Toughness enhancers for bone scaffold materials based on biocompatible photopolymers

“…This restrains chain mobility and results in high shrinkage stress as the polymerization continues in a gel‐like state. Directly connected with t g is DBC g , which can be increased by delaying the gel point (e.g., by employing thiols as network modifier) in order to reduce shrinkage stress . DBC should be as high as possible to achieve good mechanical properties.…”

“…Directly connected with t g is DBC g , which can be increased by delaying the gel point (e.g., by employing thiols as network modifier) in order to reduce shrinkage stress. 36,37 DBC should be as high as possible to achieve good mechanical properties. t 95 helps characterizing the suitability of a resin for additive manufacturing.…”

The influence of vinyl activating groups on β-allyl sulfone-based chain transfer agents for tough methacrylate networks

“…BMA is a monofunctional monomer which does not gel but does solidify when polymerized neat. Auto‐acceleration is much less pronounced with BMA than with typical difunctional monomers and thus t max is reached much later . While CTAs moderate auto‐acceleration of difunctional monomers and thus delay t max , the effect is different with BMA.…”

“…In comparison to the previously investigated ester 2‐ethyl‐2‐(tosylmethyl)acrylate ( ASEE ), the other CTAs all have activating groups with different capability of stabilizing the intermediate radical, which should influence the rate of addition to the CTA and possibly allow better control of the network structure. Furthermore, the fairly high concentration of ASEE required to illicit an effect (typically 10–20 wt %) may limit its use in real world formulations . Therefore, we concluded to also investigate the newly synthesized compounds at lower concentrations.…”

Photo-induced Polymerization and Degradation of Formulations Containing Photolabile Crosslinkers Monitored in a Rheometer

“…For example, the analysis of photopolymerization and photo-induced gelation [6][7][8] by using the rheometer were reported in recent years.…”