Recent advances in flame retardant epoxy systems containing non-reactive DOPO based phosphorus additives

The synthesis and processing of most thermoplastics and thermoset polymeric materials rely on energy-inefficient and environmentally burdensome manufacturing methods. Frontal polymerization is an attractive, scalable alternative due to its exploitation of polymerization heat that is generally wasted and unutilized. The only external energy needed for frontal polymerization is an initial thermal (or photo) stimulus that locally ignites the reaction. The subsequent reaction exothermicity provides local heating; the transport of this thermal energy to neighboring monomers in either a liquid or gel-like state results in a self-perpetuating reaction zone that provides fully cured thermosets and thermoplastics. Propagation of this polymerization front continues through the unreacted monomer media until either all reactants are consumed or sufficient heat loss stalls further reaction. Several different polymerization mechanisms support frontal processes, including free-radical, cat- or anionic, amine-cure epoxides, and ring-opening metathesis polymerization. The choice of monomer, initiator/catalyst, and additives dictates how fast the polymer front traverses the reactant medium, as well as the maximum temperature achievable. Numerous applications of frontally generated materials exist, ranging from porous substrate reinforcement to fabrication of patterned composites. In this review, we examine in detail the physical and chemical phenomena that govern frontal polymerization, as well as outline the existing applications.

Frontal Polymerizations: From Chemical Perspectives to Macroscopic Properties and Applications

Synthesis of a novel reactive type flame retardant composed of phenophosphazine ring and maleimide for epoxy resin

Commonly, volumetric shrinkage occurs during polymerizations due to the shortening of the equilibrium Van der Waals distance of two molecules to the length of a (significantly shorter) covalent bond. This volumetric shrinkage can have severe influence on the materials’ properties. One strategy to overcome this volumetric shrinkage is the use of expanding monomers that show volumetric expansion during polymerization reactions. Such monomers exhibit cyclic or even oligocyclic structural motifs with a correspondingly dense atomic packing. During the ring-opening reaction of such monomers, linear structures with atomic packing of lower density are formed, which results in volumetric expansion or at least reduced volumetric shrinkage. This review provides a concise overview of expanding monomers with a focus on the elucidation of structure-property relationships. Preceded by a brief introduction of measuring techniques for the quantification of volumetric changes, the most prominent classes of expanding monomers will be presented and discussed, namely cycloalkanes and cycloalkenes, oxacycles, benzoxazines, as well as thiocyclic compounds. Spiroorthoesters, spiroorthocarbonates, cyclic carbonates, and benzoxazines are particularly highlighted.

https://www.mdpi.com/2073-4360/13/5/806/pdf

Expanding Monomers as Anti-Shrinkage Additives.

Improving thermal and flame‐retardant properties of epoxy resins by a new imine linkage phosphorous‐containing curing agent

In this work, a novel DOPO-based spiroorthocarbonate (DSOC), 6,6ʹ-((3,9-diethyl-1,5,7,11-tetraoxaspiro[5.5]undecane-3,9-diyl)bis(hydroxymethylene))bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide) was synthesized and confirmed with 1H, 31P, 13C NMR, and FT-IR spectra. It was used as anti-shrinkage additive and flame retardant in the cationic polymerization of epoxy resin. The shrinkage of the cured epoxy resin containing DSOC was investigated by measuring the density of the system before and after curing. It was found that the shrinkage of epoxy resin changed from −1.49 to 1.43% with the content of DSOC increased to 20 wt%, not only the shrinkage of epoxy resin was eliminated, but also a slight expansion was achieved. The flame retardancy and thermal stability of the cured epoxy resins were tested by limiting oxygen index (LOI), vertical burning test (UL-94), and thermogravimetric analysis (TGA). LOI values increased from 19.9% for pure E-51 to 30.9% for modified epoxy resins, UL-94 V-0 rating can be obtain...

https://www.tandfonline.com/doi/pdf/10.1080/15685551.2015.1070501

Synthesis of DOPO-based spiroorthocarbonate and its application in epoxy resin

A novel copolymer containing a double spiro orthocarbonate structure, poly 3-methylene-9-methyleneoxy-3,9-Bis(hydroxymethyl)-1,5,7,11-tetraoxaspiro[5.5] undecane (SOC), was synthesized. The structure of SOC was confirmed by 1H, 13C NMR and FTIR spectra. Prepolymer (SOCP) reacting from SOC and 2,4-toluene diisocynate (TDI) was prepared and used as anti-shrinkage additives in the cationic polymerization of epoxy resin (EP-51). The volume changes of the cured epoxy resin containing SOCP were investigated by density measurements with an electronic hydrometer. The mechanical properties of the modified epoxy resin were investigated by adhesive strength, impact strength and flexural strength, while thermal properties were investigated by thermal gravimetric analysis (TGA).

Synthesis of Copolymers Containing Double Spiro Orthocarbonate and Used as Anti-shrinkage Additives in Epoxy Resin Composite

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Synthesis of DOPO-based spiroorthocarbonate and its application in epoxy resin

Synthesis of Copolymers Containing Double Spiro Orthocarbonate and Used as Anti-shrinkage Additives in Epoxy Resin Composite