Hyperbranched Polymers in Cationic UV Curing

Abstract

Summary: A wide range of hyperbranched polymers (HBP) was synthesized and investigated as additives in cationic photopolymerization of epoxy systems. The HBP were inserted into the polymeric network either by a copolymerization or through a chain transfer reaction involving the phenolic hydroxyl groups. By varying the type and concentration of HBP a modification of the bulk properties of photocured films was induced. An increase of toughness properties together with a flexibilization was obtained without affecting the processability and the viscosity of the photocurable mixture. In the presence of fluorine-containing HBP, a surface modification was induced.

Enhancement of Epoxy Thermosets with Hyperbranched and Multiarm Star Polymers: A Review

“…For instance, epoxy groups are reactive in amine curing systems while hydroxyl groups are not, at least at conventional curing temperatures (<250 °C). However, when hydroxyl-ended HBPs are used under cationic conditions, they become incorporated into the network structure through hydroxyl-induced chain transfer reactions that occur, via monomer-activated mechanism, in the cationic ring-opening polymerization of epoxy groups [ 50 , 51 , 52 ].…”

Synthesis of a New Hyperbranched Polyaminoester and Its Use as a Reactive Modifier in Anionic Curing of DGEBA Thermosets

“…Cationic initiators have been used to cure mixtures of epoxy resins and hydroxyl ended HBPs in both thermal and photochemical conditions. [17,20] In these systems, homogeneous materials have usually been obtained by the chemical incorporation of hydroxyl groups by the monomer activated mechanism. [37] However, in our case, the presence of amines in the PAE structure deactivates the ring-opening polymerization process when it is initiated by Lewis acids such as lanthanide triflates, which does not happen when these basic groups are not present.…”

“…The chemical incorporation of hydroxyl-terminated HBPs to the epoxy matrix has been accomplished by cationic curing by a ring opening mechanism under photochemical [20] and thermal [17] conditions, but, until now, the modification of anionic ring-opening cured epoxy materials with hydroxyl terminated HBPs has not been reported. The ring opening mechanism is most suitable from the point of view of shrinkage because it does not eliminate small molecules and, for every bond that goes from a van der Waals to a covalent distance, another bond goes from a covalent to a van der Waals distance.…”

Ethylene–propylene‐α‐olefin terpolymers thermal and mechanical properties

“…The highly branched structure gives further access to a large number of reactive end groups and thus, hb polymers have been successfully used as multifunctional cross linkers in various coating and resin applications including epoxy systems to improve their properties like reduced shrinkage, and increase in gel content, thermal stability, modulus, toughness, and reworkability, which is a matter of industrial interest 5–10. By use of the aliphatic hb polymer, Boltorn H30, reduced shrinkage and improved flexibilization was achieved 11.…”