Thermal stability and degradation studies of polyester resins

Thermal behavior and degradation mechanisms of three polyester resins, namely bisphenol A based, isophthalic acid based, and general purpose were studied. These resins were cured with styrene in the presence of benzoyl peroxide (BPO) and methyl ethyl ketone peroxide (MEKP) as initiators. The cured resins were studied by thermogravimetric analysis and mass spectrometry. From the thermogravimetric data it was observed that the cured bisphenol-A-based polyester resin was thermally more stable than the cured isophthalic acid-based and general purpose polyester resins. It was also observed that polyester resins cured with MEKP are thermally more stable than benzoyl peroxide-cured products. Thermogravimetric analysis data shows that there are two first-order degradation reactions during thermal degradation in nitrogen atmosphere. The first degradation step involves the scission of cross-links/weak links with the liberation of free linear chains. The second step involves a random scission of the free linear chains into smaller fragments. The framentation patterns of the polyester resins were identified by mass spectrometery. Possible mechanisms for the degradation of the cured polyesters accounting for the experimental observations are discussed.     

Physical properties of unsaturated polyester resin from glycolyzed pet fabrics

Physical properties of unsaturated polyester resins (UPE resins) prepared from glycolyzed poly (ethylene terephthalate) (PET) and PET/cotton blended fabrics were investigated. Initially, PET and PET/cotton blended fabrics were chemically recycled by glycolysis. The depolymerizations were carried out in propylene glycol with the presence of zinc acetate as a catalyst. The reaction time was varied at 4, 6, and 8 h. The glycolyzed products were then esterified using maleic anhydride to obtain UPE resins. The prepared resins were cured using styrene monomer, methyl ethyl ketone peroxide, and cobalt octoate as a crosslinking agent, an initiator and an accelerator, respectively. The cured resin products were tested for their mechanical properties and thermal stability. The results indicated that, among the fabric based resins, one prepared from the 8‐h glycolyzed product possessed the highest mechanical properties those are tensile strength, tensile modulus, flexural strength, impact strength, and hardness. The highest thermal stability was also found in the cured resin prepared from the 8‐h glycolyzed product. The mechanical properties of fabric based resins were slightly lower than those of the bottle based resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2536–2541, 2007     

Curable resins based on recycled poly(ethylene terephthalate) for coating applications

Poly(ethylene terephthalate) waste was depolymerised in the presence of diethylene- or tetraethylene glycol and manganese acetate as a catalyst. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. The produced oligomers were condensed with maleic anhydride and ethylene glycol to produce unsaturated polyester. The chemical structures of the resulting epoxy and unsaturated polyester resins were confirmed by ¹HNMR. The vinyl ester resins were used as cross-linking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The 2-amino ethyl piprazine was used as hardener for epoxy resins. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at different temperatures ranged from 25 to 55 °C to calculate the curing activation energy of the system. The cured epoxy and unsaturated polyester resins were evaluated in coating application of steel.     

Mechanical characterization and chemical resistances of cured unsaturated polyester resins modified with vinyl ester resins based on recycled poly(ethylene terephthalate)

Unsaturated polyester resin (UP) was prepared from glycolyzed oligomer of poly(ethylene terephthalate) (PET) waste based on diethylene glycol (DEG). New diacrylate and dimethacrylate vinyl ester resins prepared from glycolysis of PET with tetraethylene glycol were blended with UP to study the mechanical characteristics of the cured UP. The vinyl ester resins were used as crosslinking agents for unsaturated polyester resin diluted with styrene, using free‐radical initiator and accelerator. The mechanical properties of the cured UP resins were evaluated. The compressive properties of the cured UP/styrene resins in the presence of different vinyl ester concentrations were evaluated. Increasing the vinyl ester content led to a pronounced improvement in the compression strength. The chemical resistances of the cured resins were evaluated through hot water, solvents, acid, and alkali resistance measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3175–3182, 2007     

Structure and properties of o-carboxymaleanilic polyester resins

Polyester resins were prepared by the reaction of o-carboxymaleanilic acid with ethylene trimethylene, propylene, hexamethylene, diethylene, or 1,4-butenediol. All the polyester resins obtained have been characterized and were found to cure with styrene, except the polyester from diethylene glycol. The properties of the cured products in the form of films were determined. Infrared. UV, and NMR spectroscopy were used for both qualitative and quantitative analyses of the polyester resins and their hydrolyzate products, after curing with styrene.     

Structure and properties of p-carboxysuccinanilic polyester resins

Polyester resins were prepared by the reaction of p-carboxysuccinanilic acid ethyl ester with ethylene glycol and 1,4-butenediol. Also, unsaturated polyester resins were prepared by the copolymerization of p-carboxysuccinanilic acid ethyl ester and maleic anhydride with ethylene glycol, 1,6-hexanediol, 1,4-butenediol, and 2-butyne-1,4-diol. All the polyester resins and the copolyesters have been characterized and were found to cure with styrene, except those prepared in the absence of maleic anhydride. The properties of the cured products in the form of films were determined. Infrared and nuclear magnetic resonance (NMR) spectroscopy were used for both qualitative and quantitative analyses of the polyester resins and their hydrolyzate products after curing with styrene.     

Synthesis of unsaturated polyester resin from postconsumer PET bottles: Effect of type of glycol on characteristics of unsaturated polyester resin

Postconsumer PET bottles including water and soft‐drink bottles were depolymerized by glycolysis in excess glycols, such as ethylene glycol, propylene glycol, and diethylene glycol, in the presence of a zinc acetate catalyst. The obtained glycolyzed products were reacted with maleic anhydride and mixed with a styrene monomer to prepare unsaturated polyester (UPE) resins. These resins were cured using methyl ethyl ketone peroxide (MEKPO) as an initiator and cobalt octoate as an accelerator. The physical and mechanical properties of the cured samples were investigated. It was found that the type of glycol used in glycolysis had a significant effect on the characteristics of the uncured and cured UPE resins. Uncured EG‐based UPE resin was a soft solid at room temperature, whereas uncured PG‐ and DEG‐based resins were viscous liquids. In the case of the cured resins, the EG‐based product exhibited characteristics of a hard and brittle plastic, while the PG‐based product did not. The DEG‐based product exhibited characteristics of hard and brittle plastic after strain‐induced crystallization had occurred. In addition, it was also found that no separation of the type of bottles was needed before glycolysis, since UPE resins prepared from water bottles, soft‐drink bottles, and a mixture of both bottles showed the same characteristics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 788–792, 2003     

含乳酸酯链节的不饱和聚酯

用丙交酯（由乳酸脱水得到）与顺丁烯二酸酐及1，2-丙二醇含成了不饱和聚酯树脂，树脂能与苯乙烯、甲基丙烯酸甲酯相溶混，能用一般不饱合聚酯的交联方法固化，固化后的拉伸强度与普通不饱和聚酯相当，且透明性良好。树脂的合成机理在文中进行了讨论。此研究着眼于树脂的环境降解及资源可再生性考虑。     

Epoxy resins VIII. Thermal properties of 4,4′-sulfonyldiphenol and bisphenol a epoxy resins

Epoxy resins of different molecular weights were prepared from epichlorohydrin and 4,4′-sulfonyldiphenol (SDP) and from epicholorohydrin and bisphenol A (BA). They were cured at high temperatures with four different crosslinking agents, including aliphatic and aromatic amines. The thermal behaviour of these cured epoxy resins was studied. From the IPDT and IDT data it was observed that sulfone epoxy resins were thermally more stable than bisphenol A epoxy resins. The activation energies of thermal degradation of the resins were calculated and the implications of these results are discussed.     

Vinyl ester resins. II. Effect of styrene on electrical properties

Bisglycidyl methacrylate of bisphenol A (vinyl ester resin) having systematically varying styrene content was cured by using benzoyl peroxide as a initiator. Thermally stimulated discharge current (TSDC) and ac dielectric measurements of the cured resins were carried out. The polarization of these resins depended on the presence of polar groups and space charge. The lowest dielectric constant was observed with the resin having 30% styrene.     

Compressive Properties and Curing Behaviour of Unsaturated Polyester Resins in the Presence of Vinyl Ester Resins Derived from Recycled Poly(ethylene terephthalate)

Poly(ethylene terephthalate) waste was depolymerised in the presence of tetraethylene glycol and manganese acetate as a catalyst, so as to produce oligomers. An epoxy resin was then prepared by the reaction of these oligomers with epichlorohydrin in presence of NaOH as a catalyst. New diacrylate and dimethacrylate vinylester resins were then synthesized by reaction of the terminal epoxy groups with acrylic and methacrylic acid in the presence of triphenyl phosphite as a catalyst. The chemical structures of the resulting vinyl ester resins were confirmed by ¹HNMR. The vinyl ester resins were used as crosslinking agents for unsaturated polyester resin diluted with styrene, using free radical initiator and accelerator. The curing behaviour of the unsaturated polyester resin, vinyl ester resins and styrene was evaluated at temperatures from 25 to 55 ^○C. The compression properties of the cured resins, having different vinyl ester contents and different cure temperatures, were evaluated. Increasing the cure temperature and the vinyl ester content led to a pronounced improvement in the compression strength and Young’s modulus.     

Synthesis of polymers by using divalent metal salts of mono(hydroxyethyl) phthalate: Unsaturated polyesters from metal salts,glycol, anhydrides,and epoxides

Syntheses of unsaturated polyesters were investigated by the divalent metal salts of mono(hydroxyethyl) phthalate–ethylene glycol–anhydrides–epoxide reactions. As anhydrides, phthalic anhydride and maleic anhydride were used, and propylene oxide and 1,2-butylene oxide were the epoxides used. The metal carboxylate groups of the above metal salts catalyzed the reaction. Viscosities of styrene solutions of the polyesters obtained showed a tendency to increase with increase in metal content. The styrene solutions could be cured to give metal-containing cured polyester resins. The cured resins were evaluated for physical properties. Generally, Mg was more effective than Ca in improving the physical properties. Further, resistance to chemical attack and boiling water and thermal behavior were also discussed.     

Unsaturated polyester resins based on rosin maleic anhydride adduct as corrosion protections of steel

Unsaturated polyester resin (UP), based on 1 mol maleopimaric adduct (MPA), 1 mol maleic anhydride, 1 mol isophthalic acid, 1 mol adipic acid, 1 mol propylene glycol, and 1 mol diethylene glycol, were obtained at various times during polyesterification. They were characterized by ¹H NMR and chemical titration. Increasing the reaction time to 8 h led to an increase in (a) the number-average molar mass (Mn), (b) the glass transition temperature (T_g) and (c) the compatibility with styrene. Several of these fractions were cured with styrene, in amount of UP/ST = 2.5 (weight of styrene, ST, and unsaturated polyester, UP), using initiator and activator. The curing behaviors of cured UP resins with styrene were evaluated by DSC measurements. The prepared UP curable resins were evaluated in the field of steel coating by measuring their mechanical properties and chemical resistance. The corrosion resistance of cured films was evaluated using salt fog resistance test.     

Metal-containing cured resins based on divalent metal salts of ethylene glycol-methacrylate-maleate

Divalent metal salts of ethylene glycol-methacrylate-maleate in the amorphous state were easily soluble in styrene, methyl methacrylate and ethyl acrylate, to give homogeneous, curable mixtures with high metal content. The viscosities of the mixtures varied depending on the metal present. The mixtures were copolymerized to give metal-containing cured resins of increased compressive strength and Rockwell hardness. Moreover, heat distortion temperature could be improved by introducing Mg or Ca. Of the cured resins studied, the Mg-containing resin showed the best physical properties. Resistance of the metal-containing resins to attack by organic solvents was generally high, whereas greater degradation by aqueous reagents was noted. The thermal behavior of the resins is discussed.     

不饱和聚酯改性丙烯酸树脂及其涂料的研制

合成了低相对分子质量不饱和聚酯树脂,再与甲基丙烯酸甲酯、苯乙烯等单体进行自由基聚合,制得含羟基的不饱和聚酯改性丙烯酸树脂。由该改性树脂与异氰酸酯制得的涂层,其干性、丰满度、光泽、硬度等综合性能优于一般羟基丙烯酸树脂制得的涂层。讨论了各种合成因素对树脂及涂膜性能的影响。     

Methacrylate monomer as an alternative to styrene in typical polyester–styrene copolymers

This study presents the research on the influence of crosslinking monomers [styrene and diethylene glycol dimethacrylate (DEGDMA)] on the properties of unsaturated polyester resins (UPRs). Syntheses of the unsaturated polyesters (UPs) modified with benzyl alcohol were carried out. Then, each polyester was used in preparation of five resin solutions with different amounts of crosslinking monomers acting as reactive diluents. These diluents improve the processability of UPs reducing their viscosities. They also take part in crosslinking of resins during copolymerization process. The properties of the prepared UPRs systems were investigated before and after the curing process. The measurements of their viscosity, reactivity, mechanical properties, thermal stability (thermogravimetry), and dynamic mechanical analysis were performed. Resins where DEGDMA was used as reactive diluent were characterized by the largest viscosities in comparison to styrene ones. The type of the used monomer influenced also degree of the resin crosslinking. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47735.     

Thermal stability of substituted phenol-formaldehyde resins

A variety of crosslinked phenol-, or derivatized phenol-formaldehyde polymers have been synthesized. The phenol derivatives included o- and p-cresol, p-nonylphenol, m-pentadecylphenol, and raw and distilled cashew nutshell liquid. The derivatives were copolymerized with phenol and formaldehyde using sulfuric acid as catalyst to yield novolak-type prepolymers, which were then cured with hexamethylenetetramine. Thermogravimetric analysis was used to evaluate the thermal stability of the cured resins. It was found that the thermal stability of the resins decreased with increasing amounts of cashew nutshell liquid, with distilled cashew resins being slightly more thermally stable than raw cashew resins. The thermal stability of resins containing substituted phenols with alkyl chains was observed to increase from n-pentadecylphenol to cresol to phenol. The trend in thermal stability of the resins may be explained on the basis of alkyl groups being less thermally stable than aromatic rings. The amount of hexamethylenetetramine used to cure the prepolymers also influences the thermal stability of the resins. It appears that a level of 10 to 15% hexamethylenetetramine maximizes the thermal stability of the resin.     

A comparative study of structure-property relationships in low-profile polyester matrices

Structure-property relationships of polyester matrices containing various low profile additives such as poly(vinylacetate), polyurethane, poly(methyl methacrylate), polystyrene, and polycaprolactone were studied. The morphology and particle size of the dispersed phases in the polyester matrices are very dependent upon the type of low profile additives incorporated in the cured resins. Microvoids which are responsible for the degradation of physical properties of resin matrices are usually observed in the polyester phase and/or the dispersed phase of the low-profile resin matrices. Low profile additives, in general, lower the glass transition temperatures of polyester matrices, slightly increase the loss moduli and the loss factors, and slightly decrease the storage moduli. These polymeric additives also degrade tensile properties and improve the fracture toughness of polyester matrices, but do not have significant effects on the thermal stability.     

Effect of adding feldspar on free volume properties of crosslinked polyester studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PAL) was applied to study the feldspar effect on the free volume properties of crosslinked polyester based on neopentyl glycol, succinic acid, phthalic anhydride, and maleic anhydride. The measurements have been carried on the polyester resin samples cured with three crosslinking agents namely styrene (SS) or styrene/methyl methacrylate (SM) or styrene/acrylonitrile (SA) comonomers mixtures in the ratios of 2 : 1 and loaded with different concentrations of feldspar in the range from 0 to 80 wt %. The free volume parameters (size and fractions of holes) depend on type of the crosslinking agent as well as the feldspar content added to the polyester. The results are supported by a significant variation in the nanoscale free volume hole size distributions. Moreover, the correlation between positron annihilation parameters and electrical parameters was discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Wood-polyester composite materials II. Dependence of the processing parameters on the initiation rate

Optimum processing parameters were searched for pilot scale production of woodpolyester composite materials by studying the effect of initiation rate on the curing process. The radiation initiation of the following systems were examined: methyl methacrylate, mixture of styrene and acrylonitrile, and their combinations with unsaturated polyester. In the most cases, the over-all rate of the whole process of polymerization in wood matrix is proportional to the square root of the initiation rate. The most favourable composite was made from a ternary resin based on styrene, acrylonitrile, and unsaturated polyester, which can be cured in the wood with a very low dose.