Improving glass transition temperature of unsaturated polyester thermosets: Conventional unsaturated polyester resins

Abstract

Highly crosslinkable unsaturated polyester resins (UPR) have attracted many interests in the application as reinforced matrix materials. Here, we present a systematical study of the influence of different curing conditions and styrene concentrations on resin viscosity and dynamic-mechanical properties of the thermoset. The pure maleic Palapreg® P18-03 was selected as model UPR because of its broad industrial use. By applying newly developed thermal curing profiles (without thermal initiators) and by raising the styrene content, the T g of the network could be increased up to 206/215 C (1/10 Hz). For the first time, a fast curable UPR based on propylene glycol and neopentyl glycol with a T g of up to 215 C is described. A partial substitution of problematic styrene with methylmethacrylate, tert-butylacrylate, and maleic anhydride (MA) was studied as well. MA leads to significantly improved resin reactivity. A resin containing 42 wt% styrene and 8 wt% MA yields thermosets with remarkably improved mechanical properties and with a narrower glass transition range compared to the original P18-03.

Phase distribution changes of neat unsaturated polyester resin and their effects on both thermal stability and dynamic‐mechanical properties

“…It was possible to observe that, as the curing temperature increases domains size tended to be smaller, and phase distribution was more homogeneous and more compact. These novel information about nanostructure of UPR achieved after different curing conditions could be explained taking into account both domains showed in AFM images are a consequence of the microgel formation, 34 and higher curing temperatures generate smaller microgels 7,17,36 …”

“…Basically, this mechanism suggests the generation of a microgels rich in UP (UP rich ) that are surrounded by a phase rich in ST (ST rich ), 9 which are differentiated by variation in the crosslinking density 16 . Moreover, the literature reports show that the UP rich size depends on the variation of intramicrogel reaction between UP and ST 17 . Huang and Chen, 18,19 studied the effect of the variation of the cure temperature of a UPR on the reaction kinetics concluding that at high reaction temperatures there is a greater conversion of UP and diffusion of ST into the microgel generated more homogeneous conversions.…”

Study on Microwave Curing of Unsaturated Polyester Resin and Its Composites Containing Calcium Carbonate

“…The curing of UPR usually requires to be initiated by an initiator, such as methyl ethyl ketone peroxide and cyclohexanone peroxide. Then, a free-radical copolymerization reaction between the C=C in the unsaturated polyester molecular chain and vinyl monomers occurs, forming a polymer with a stable three-dimensional network structure [7][8][9]. However, the initiators must be decomposed and activated under the conditions of heating or accelerator induction.…”

Enhanced performance of a bio‐based diluent with both vinyl and epoxide groups for unsaturated polyester resin applications

“…Particularly, bio‐based thermosetting resins like benzoxazine resins, 5–10 epoxy resins, 3,11–18 and unsaturated polyesters resins (UPRs) 19,20 have gained great attention due to their excellent mechanical properties, outstanding dimensional stability, and low cost 21,22 . Of these, UPRs was highly desirable for a diversity of applications such as boat hulls, automobile parts, and building components 23–26 . Among with the simple synthesis route, molecular design flexibility of UPRs enabled a wide availability from renewable raw materials.…”

“…21,22 Of these, UPRs was highly desirable for a diversity of applications such as boat hulls, automobile parts, and building components. [23][24][25][26] Among with the simple synthesis route, molecular design flexibility of UPRs enabled a wide availability from renewable raw materials.…”