We are Yixing Wencheng Chemical Co., Ltd., a manufacturer specializing in polyols—including diethylene glycol (DEG)—with over 40 years of experience in the production and sales of polyols and their derivatives. DEG is a diol featuring two hydroxyl groups and a flexible ether linkage in its molecular structure, making it a crucial comonomer for the synthesis of unsaturated polyester resins (UPR). During the UPR condensation polymerization stage, DEG can undergo esterification condensation reactions with dicarboxylic acids such as phthalic anhydride and maleic anhydride. The hydroxyl groups in its molecule dehydrate and condense with the carboxyl groups of the carboxylic acid to form ester bonds, which are stably integrated into the main chain of the polyester molecule, while the ether bonds inherent in the molecule are completely retained inside the polyester chain segment. Meanwhile, the dihydroxy structure of DEG can ensure the regular construction of the linear long chain of polyester, and it can synergistically participate in the polymerization with conventional polyols such as ethylene glycol (EG) and propylene glycol (PG).
Diethylene glycol (DEG) is a commonly used modified diol for general unsaturated polyester resins (UPR). Compared with ethylene glycol (EG) and propylene glycol (PG), it can optimize the UPR system from multiple dimensions such as product performance, production process, compatibility and cost due to its unique molecular structure. DEG molecules contain internally rotatable ether bonds, resulting in longer chain segments and greater flexibility than EG. This effectively improves the elongation at break after UPR curing, addresses the shortcomings of pure EG resin being hard and brittle, and enhances the impact and crack resistance of products. It is suitable for products such as artificial stone, ordinary fiberglass, and resin coatings. At the same time, it can weaken the rigidity of the molecular chain, improve the low-temperature resistance of the resin, prevent outdoor FRP products from cracking during hot and cold cycles, and improve weather resistance. For the same molecular weight, DEG-modified UPR has a lower melt viscosity. This facilitates smoother discharge during resin synthesis, reduces residue buildup on reactor walls, and boosts both production efficiency and raw material utilization. Furthermore, the lower viscosity of the styrene-diluted system improves glass fiber wetting, effectively optimizing molding processes like hand lay-up and spray-up while simplifying fabrication. DEG is priced lower than propylene glycol (PG) in the market and can partially replace PG in general UPR formulations. While ensuring the basic mechanical and performance properties of the resin, it can effectively reduce raw material costs and improve the cost-effectiveness of the product.
UPR modification using DEG has obvious formulation shortcomings and production control risks, the most critical of which is the deterioration of hydrolysis resistance. The ether bonds in DEG molecules are easily broken under high temperature, humid heat, and alkaline environments. Adding too much DEG will significantly reduce the water and alkali resistance of the cured product. Long-term immersion in water can easily lead to problems such as whitening, bubbling, and strength reduction. Therefore, DEG should not be used extensively in corrosion-resistant and highly water-resistant UPRs. Only general-purpose UPRs can use DEG to partially replace polyols, and it is not recommended to replace all alcohol components with DEG. Due to its inherent flexible segments, DEG lowers the resin's glass transition temperature (Tg) and heat deflection temperature (HDT); high dosage levels result in insufficient heat resistance, causing the product to soften and deform at elevated temperatures, rendering it unsuitable for high-temperature FRP components. Although DEG-modified systems exhibit slightly lower curing shrinkage than propylene glycol (PG) systems, excessive addition reduces cross-link density, thereby diminishing surface hardness and abrasion resistance. The production and synthesis stage requires precise control of process conditions: DEG has a high boiling point, so strict temperature control is needed during the polycondensation and dehydration stage to prevent excessive evaporation and to avoid imbalance in the alcohol-acid ratio and loss of molecular weight control; DEG is easily oxidized at high temperatures, which will generate colored aldehyde impurities that affect the color of the resin, so nitrogen protection must be implemented in the reaction vessel during the reaction process; at the same time, the moisture content of DEG raw materials must be strictly controlled, as excessive moisture will prolong the esterification cycle, increase energy consumption, cause molecular weight fluctuations, and reduce the storage stability of the finished product. During the storage stage, DEG system resins are quite sensitive to acid value. Improper acid value control can cause the viscosity to rise rapidly during long-term storage. It is necessary to adjust the amount of polymerization inhibitor added accordingly to stabilize the storage performance of the finished product.
The UPR esterification polycondensation process generates process wastewater containing small amounts of free alcohol, low molecular weight polyester, and organic acids. When DEG is used in copolymerization, the distillate wastewater will also carry some unreacted DEG. During production, esterification wastewater can be purified by vacuum distillation. Water is removed by relying on the difference in boiling points of the materials, and polyols such as DEG and EG in the wastewater are enriched and recovered. The purified materials can be returned to the UPR synthesis reactor for recycling. This process combines economic and environmental benefits. It can replace some fresh raw materials, reduce the consumption of polyols and raw material costs, and effectively reduce the COD of wastewater, reduce wastewater treatment agents and energy consumption, thus meeting the requirements for energy conservation and emission reduction in production. In practical applications, there are certain limitations to the use of recycled DEG: because it contains trace amounts of organic acids, oligomers and colored impurities, it is only suitable for blending and producing general-purpose UPR products and cannot be used for high-end UPR products. Before recycling materials are reused, their acid value, moisture content, and color index must be tested, and the blending ratio must be strictly controlled to ensure stable product quality. Meanwhile, the distillation process incurs energy costs, and the recovery revenue fluctuates with the DEG market price. It is necessary to calculate the economic break-even point and flexibly adjust the operation plan according to market conditions. Finally, the wastewater requires pretreatment to remove suspended oligomers before entering the distillation system; this prevents column packing blockages and equipment scaling, ensuring the system's stable operation.
Our company's diethylene glycol (DEG) has been widely and long-term used in the process of preparing unsaturated polyester resin (UPR). Our DEG products are known for their stable performance, superior quality, and consistent supply. They are exported to many countries worldwide. With over four decades of experience in the industry, we remain committed to quality and stable production capacity. We sincerely welcome customers from all walks of life to inquire, discuss, and cooperate with us!
