New Thermosets Obtained by Thermal and UV‐Induced Cationic Copolymerization of DGEBA with 4‐Phenyl‐γ‐butyrolactone

Abstract

Mixtures of DGEBA with 4‐phenyl‐γ‐butyrolactone (PhBL) were cationically copolymerized in the presence of ytterbium triflate or triarylsulfonium hexafluoroantimoniate as thermal or photo initiator respectively. Changes during curing and final properties of the cured materials were studied by means of DSC, FT‐IR/ATR, TMA, DMTA, TGA and densitometric measurements. The formation of a network containing polyether and poly(ether‐ester) moieties was demonstrated to take place through the ring‐opening polymerization of a spiroorthoester intermediate (SOE) formed during the copolymerization. An increase in the proportion of lactone resulted in an increase in the curing rate, a decrease in the shrinkage after gelation and in the thermal stability and glass transition temperature (Tg). A strong influence of the initiator on the curing mechanism was observed. As a consequence, the photocured materials exhibited superior thermal stability and Tg than those obtained thermally.magnified image

Unexpected differences between thermal and photoinitiated cationic curing of a diglycidyl ether of bisphenol A modified with a multiarm star poly(styrene)-b-poly(ε-caprolactone) polymer

“…Although the reason of this behaviour can be rationalized in a similar way to 5% PS-10 formulation, the fact that some part of PS-10 phase separates during curing, (as it will be seen later by scanning electron microscopy) can probably have an influence on the T g# value. The values of T g# found after photocuring are higher than those found after thermal curing (Table 1), because ytterbium triflates are able to induce reorganization, cyclization and/or degradation reactions when the curing reaches too high temperatures, which results in a network structure with a lower degree of crosslinking and consequently with a lower T g# [43,44].…”

Cationic copolymerization behavior of epoxide and 3-isochromanone

“…Another possible mechanism involves formation of a spiroorthoester (SOE) by 1:1 reaction of BGE and ICM and its acid‐catalyzed double ring‐opening reaction . Nevertheless, some spectroscopic investigation on the copolymerization did not give any clear evidence for the formation of SOE: According to our experiments during the previous SOE‐related studies, SOEs can be detected by their characteristic signals attributable to the orthoester carbon (R‐C(OR) 3 ) in a range from 135 to 145 ppm.…”

“…These copolymerizations have several advantages such as: (1) introduction of comonomer‐derived functions into the resulting copolymers, (2) formation of main chain structures that are totally different from that of the homopolymers of epoxides, leading to the drastic changes in physical properties, and (3) reduced volume shrinkage. Several examples of copolymerizations with photo‐induced initiation systems have been also reported …”

Development and Dental Applications of Spiro Expanding Monomers as Antishrinkage Additives

“…[56] The same EM under different initiators and reaction conditions undergoes different degrees of ring-opening polymerization and can produce different effects of expansion. [57][58][59] Initial studies involving the homopolymerization of spiro EMs were initiated by cationic initiators at high temperatures. [60][61][62][63] Reaction temperature and curing time directly affect the polymerization degree and expansion.…”