Xianmei Wan

Biobased Polyols Using Thiol-Ene Chemistry for Rigid Polyurethane Foams with Enhanced Flame-Retardant Properties

Biobased polyol was synthesized using 1-thioglycerol and limonene, an extract of orange peel, via thiol-ene chemistry as an alternative to petrochemical-based polyol for preparation of rigid polyurethane foams (RPFs). Fire-retardant polyurethane foams were prepared by addition of different amounts of dimethyl methyl phosphonate (DMMP) in the polyol. The effect of DMMP on the properties of RPFs was studied. All the biobased RPFs maintained a regular cell structure with uniform cell distribution and over 90% of closed cell. The RPFs showed excellent compressive strength of ~230 kPa without addition of DMMP. These RPFs almost retained their specific compressive strength even when 2 parts by weight (pbw) of DMMP was added but with significant improvement in fire retardancy. Horizontal burning test of RPFs containing only 2 pbw of DMMP showed reduction in burning time by ~83% compared to the neat sample. Weight loss during the burning test for the control sample was nearly 50% and this was reduced significantly by addition of 2 pbw of DMMP to merely 7%. TGA analysis indicated that the improved flame retardancy could be attributed to the release of DMMP at the temperature range of 100 °C to 250 °C.

Polymercaptan-based polyurethane foams

Rigid thiourethane foams were prepared from vegetable oil-based polythiols (polymercaptans) and compared with soy- and castor oil-based polyurethane reference foams. Three types of polymercaptans were tested, soybean oil-based one with thiol groups only, epoxidized soybean oil-based with vicinal thiol and hydroxyl groups and castor oil-based with hydroxyl and thiol groups separated with several methylene units. Physical, mechanical, and thermal characteristics of polyol- and thiol based foams were similar to petrochemical foams used as heat insulation materials in construction, appliances, etc.

New polyols with isocyanuric structure by thiol-ene “click” chemistry reactions:

New polyols with isocyanuric structure were synthesized by thiol-ene “click” chemistry of triallyl isocyanurate with 1-thioglycerol and 2-mercaptoethanol. The synthesized polyols, prepared with high reaction rates and in very high yields, were chemically and structurally characterized. These polyols were used for the preparation of rigid polyurethane foams with excellent physical–mechanical properties and inherent flame retardancy. By alkoxylation of isocyanuric polyols with propylene oxide and/or ethylene oxide in a self-catalytic process, odorless polyols with lower hydroxyl numbers and lower viscosities were obtained, leading to PU foams with good properties, but without inherent flame retardancy. The synthesized polyols with isocyanuric structure are suitable for the preparation of all types of rigid polyurethane foams, including thermoinsulation of freezers, buildings, storage tanks and pipes for the food and chemical industry, for packaging, and as wood substitutes.