Chain extension reactions of unsaturated polyesters with bis(2‐oxazoline)s

Two different bisoxazolines, 2,2′‐(1,3‐phenylene) bis(2‐oxazoline) (1,3‐PBO) and 2,2′‐bis(2‐oxazoline) (BO) were investigated as chain extenders for short chain unsaturated polyesters (UPEs). These extenders reacted readily with carboxyl ends of unsaturated polyesters, leading to rapid molecular weight increase through coupling of oligomeric chains. Commercially available unsaturated polyesters commonly have molecular weights around 1500, usually reached after a 20‐h polyesterification reaction. When bisoxazolines were reacted with short UPE chains obtained at the 6th hour of a commercial polyesterification reaction, the molecular weight of UPE reached 1500 within 5–30 min, which provides economies and prevents the glycol loss and yellowing which are associated with extended reaction times. Styrene solubility, gel time, and thermal and mechanical properties of the chain extended polyesters remained comparable to the commercial UPE, with 8–10 min of gel time and a storage modulus about 3000 MPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Blocked isocyanates and isocyanated soybean oil as new chain extenders for unsaturated polyesters

Two different blocked isocyanates, diphenylmethane–bis‐4,4′‐ethyleneurea and diphenylmethane–bis‐4,4′‐carbamoil–ϵ‐caprolactam, and isocyanated soybean oil were used as chain extenders for low‐molecular‐weight unsaturated polyesters. Oligomeric polyesters (molecular weight = 600–700), taken from a manufacturing process in the sixth hour of a 16‐h polyesterification reaction, were reacted with these chain extenders, and the desired chain lengths (molecular weight = 1000–1500) were obtained in a very short time through the reaction of the chain extenders with the polyester end groups. The increase in the molecular weight was monitored with gel permeation chromatography. The obtained polymers were characterized with Fourier transform infrared and ¹H‐NMR and with styrene solubility and gel time measurements. After dilution with styrene, the polyesters were cured with a radical initiator. The thermal and mechanical properties of the cured polyesters were examined with dynamic mechanical analysis and thermogravimetric analysis tests and then compared to those of a commercially available reference unsaturated polyester. The results show that unsaturated polyesters can be chain‐extended with these compounds to shorten the polyesterification time substantially without alterations of the styrene solubility or gel time of the polyesters. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and mechanical behavior of unsaturated polyesters filled with phase change material

Samples of commercial unsaturated polyester (UPE) resin, filled with phase‐changeable fillers (PCMs), were prepared, and the thermal and mechanical properties of the cured samples were examined. Fillers chosen were paraffin and Wood's metal. Samples were prepared by making dispersions of these fillers in liquid unsaturated polyester followed by curing with methyl ethyl ketone peroxide (MEKP) and conaphtanate and rigid thermoset samples filled with PCM particles were obtained. The thermal and mechanical behaviors of such a filled composite around the melting points of fillers are very interesting. Effects of varying proportions of PCM on mechanical and thermal properties of final products were examined. The samples show thermal melting behavior without undergoing a change in physical state. Decreases in the maximum working temperature from 75 to 53°C for metal‐filled samples and from 75 to 43°C for paraffin‐filled samples were observed by using dynamic mechanical thermal analysis. Differential scanning calorimetry indicated that heat absorption of paraffin samples were higher than that of metal‐filled samples. For paraffin‐filled samples, heats of fusion were 3.44 cal/g for 10% filled sample and 6.35 cal/g for 20% filled sample. For Wood's metal‐filled samples, heats of fusion were 1.18 cal/g for 10% metal‐filled sample and 1.54 cal/g for 20% metal‐filled sample. Surface hardness was tested with Shormeter D. Surface hardness of metal‐filled composites varied from 86 to 34 shore D at 21°C and 80.6 to 35 shore D at 80°C. For paraffin‐filled samples, surface hardness changed from 86 to 42 shore D at 21°C and from 80.6 to 13 shore D. Morphology of the samples was determined by scanning electron microscopy, of the crack surfaces. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 832–838, 2006     

Chain extension and mechanical properties of unsaturated aliphatic copolyesters based on poly(L‐lactic acid)

Chain extension of poly(L ‐lactic acid) (PLLA) with unsaturated groups (PLBM) was attempted using benzoyl peroxide (BPO) and the resulting variation in molecular weight and mechanical properties was explored. Bulk copolymerization of L ‐lactic acid (LA)/1,4‐butanediol (BD)/maleic acid (MA) (100/1/1) isomerized some of the cis‐structured maleate units into trans‐structured fumarate units. The optically active LA promoted isomerization during the condensation polymerization. Chain extension of PLBM with BPO did not bring about a discernible increase in the molecular weight when the chain extension was carried out in various solvents with different radical abstraction abilities. In contrast, the hot pressing of PLBM containing BPO increased the molecular weight and sometimes produced chloroform‐insoluble gels depending on the BPO concentration and temperature. The chain extension at low temperatures increased the flexibility of PLBM considerably. However, PLBM lost the flexibility precipitously as the chain‐extension temperature increased above 120°C. The biodegradation rate of PLBM was much slower than that of PLLA. The biodegradation rate was further lowered by the chain extension. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1802–1807, 2003     

Preparation of waterborne elastic polyesters by chain extension with isophorone diisocyanate as a chain extender

Isophorone diisocyanate was used as a chain extender to coupling the soft segment water-borne polyester with the hard segment water-borne polyester, to overcome the disadvantages of low molar mass and poor mechanical properties of waterborne sulfonate-containing polyesters. The molecular structure of the extended polyester was confirmed by FTIR and ¹H NMR, and the increased molar mass of the resultant was characterized by SEC. The extended products could be dispersed in water with the emulsion particle size less than 50 nm in diameter, slightly larger than that of precursors of soft- and hard-segment polyesters. The emulsion viscosity of polyesters after the chain extension was lower when the emulsion concentration was not larger than 25 wt%, which is conducive to the spraying application of the polyester for coating. DSC analysis indicated that the polyester after chain extension had two different glass temperatures, suggesting that the polyester bulk had a microphase separation structure. The mechanical performance of the coupled polyester manifested an obviously improved elongation at break and had a feature of higher elastic recovery rate. The results of this study indicate that the chain extension is an effective method to increase the molar mass and improve mechanical properties of waterborne polyesters. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48453.     

Molecular weight averages and distributions of unsaturated polyesters: Their effect on the properties of styrene-crosslinked networks

Unsaturated polyesters have been synthesised and modified to determine the effect of number-average molecular weight (M̄_n) and molecular weight distribution (MWD) on the following properties of the polyesters after crosslinking with styrene: (i) water absorption, (ii) initial mechanical properties and (iii) property retention after immersion The most important factor was found to be the very low molecular weight ‘tail’ which adversely affected behaviour in several respects. Above a certain M̄_n, initial mechanical properties were insensitive to the variables mentioned, but mechanical property retention after immersion closely reflected the water absorption behaviour by its dependence on the average chain length and the low molecular weight constituents. The importance of removing such constituents is apparent.     

Vinyl methyl oxazolidinone as reactive diluent to overcome the solubility limitations of highly polar unsaturated polyesters

Vinyl methyl oxazolidinone (VMOX®) is studied as a new reactive diluent (RD) for highly polar unsaturated polyesters (UPs). Molecules with special structure properties are extensively investigated as components for unsaturated polyester resins (UPRs) and thermosets, particularly for high-temperature applications. Special diols with a cyclic structure like isosorbide and tricyclodecanedimethanol or special diols with side groups like 2-methyl-2-propyl-1,3-propanediol and 2-ethyl-2-butyl-1,3-propanediol can provide interesting properties. Bio-based diols such as isosorbide and 1,3-butanediol improve the sustainability profile. However, UPs based on such special diols have a higher polarity, limiting their solubility in styrene. This demands a RD, which provides adequate solubility and is suitable for high-temperature applications. Therefore, our study compares the solubility of highly polar UPs based on special diols in styrene and VMOX®. UPs with different formulations, polarities, and Hansen parameters were synthesized and characterized. The solubility sphere of styrene was determined experimentally with the synthesized UPs. The influence of the special diols on the thermoset properties was investigated in dynamic mechanical analysis measurements. In conclusion, VMOX® as a RD enables full utilization of special diols properties due to the wide solubility window. Moreover, a new class of high-temperature styrene-free UP resin was developed.     

Effect of the epoxy molecular weight on the properties of a cyanate ester/epoxy resin system

Bisphenol A dicyanate (BADCy) was modified by diglycidyl ether of bisphenol A epoxy resins with different molecular weights [E20 (weight‐average molecular weight = 1000) and E51 (weight‐average molecular weight = 400)] to investigate the effects of the epoxy molecular weight on the properties of the modified systems. The reactions were monitored with differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy, and the results showed that more pentacyclic oxazolidinone rings were formed in BADCy/E51 than in BADCy/E20 with the same epoxy resin weight content. DSC showed that BADCy/E20 had a lower curing temperature than BADCy/E51 because of the higher concentration of hydroxyl groups (? OH) in E20. Thermal, moisture absorption, and mechanical testing showed that E51‐modified BADCy performed better because of its lower molecular weight. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1744–1750, 2006     

Radiation‐induced crosslinking of acetylene‐impregnated polyesters. II. Effects of preirradiation crystallinity,molecular structure,and postirradiation crosslinking on mechanical properties

Electron beam‐irradiated crosslinking has been studied in a series of acetylene‐impregnated polyesters and amorphous copolyesters, including poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(cyclohexane dimethylene terephthalate) (PCDT), and poly(cyclohexane dimethylene terephthalate‐co‐ethylene terephthalate) (P(CDT‐co‐ET)) having 29 and 60 wt % ethylene terephthalate (ET). The extent of crosslinking was observed by gel fraction measurements and was found to be significantly influenced by the aliphatic chain content of the polyesters (PET < PBT < PCDT). In addition, as the preirradiation crystallinity of the polyesters was reduced, the extent of acetylene‐enhanced crosslinking was greatly raised. Decreases in the postirradiation crystalline melting temperature and degree of crystallinity were observed in all the polyesters, using differential scanning calorimetry measurements. Particularly significant findings have been the shift in the glass‐transition temperatures (Tg) to higher temperatures and the decrease in loss tangents at higher temperatures, both of which confirm that crosslinking has taken place. The storage moduli (E′) in the rubbery plateau region of PCDT and P(CDT‐co‐ET) were significantly affected by irradiation dose. Increased network tightness in postirradiated PBT and PCDT films was also inferred from melt‐rheology measurements, in which stress relaxed more slowly following a stepped strain. Improvements in the mechanical properties of the irradiated polyesters and copolyesters were clearly evidenced by the increased modulus at higher temperatures, observed using dynamic mechanical thermal analysis and melt‐rheology methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4476–4490, 2006     

Synthesis of unsaturated polyesters of increased solubility in styrene

The present study presents the synthesis of unsaturated polyester resins using only one glycol i.e., ethylene glycol. Polyesters of inorganic solubility in styrene were prepared. Properties of the resins in the noncrosslinked state in the process of crosslinking and after curing were studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3143–3150, 2006     

Tensile properties of kenaf/unsaturated polyester composites filled with a montmorillonite filler

Kenaf/unsaturated polyester composites filled with montmorillonite (MMT) filler were produced. Overall, the study showed that, for samples with kenaf filler only, the strength properties decreased as the kenaf filler loading was increased from 40 to 60%. The increase in the kenaf filler loading reduced the amount of matrix material. This subsequently lowered the ability of the sample to absorb energy or distribute stress efficiently. However, with MMT, the tensile properties improved because of the high aspect ratio and surface area of the MMT. The study of the effect of kenaf filler size on the tensile properties showed that the samples with the smallest size (74 μm) displayed the lowest tensile properties compared to the larger ones. This was attributed to the agglomeration of the kenaf fillers. The addition of MMT resulted in an overall increase in the tensile strength of the composites compared to those without MMT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Chemical modification of unsaturated polyesters influence of polyester's structure on thermal and viscoelastic properties of low styrene content copolymers

In this study, the chemical modification of unsaturated polyesters and the influence of polyester's structure on thermal and viscoelastic properties have been presented. The structure of unsaturated polyesters obtained in polycondensation of cyclohex‐4‐ene‐1,2‐dicarboxylic anhydride (THPA), maleic anhydride and only one suitable symmetrical glycol: ethylene glycol or 1,4‐butanediol (BDO) or 1,6‐hexanediol has been modified by peracetic acid. The selective oxidation of unsaturated polyesters conducted in mild time and temperature conditions was a successful and effective method to prepare new materials/unsaturated epoxy polyesters/containing epoxy groups in cycloaliphatic rings and carbon–carbon double bonds in polyester chain. The unsaturated epoxy polyesters were capable of both copolymerization with vinyl monomer and polyaddition reactions with suitable curing agent. Therefore, they were successfully used as a component of low styrene content copolymers. As was confirmed by DSC, DMA, and TGA analyses, polyester's structure had significant influence on thermal and viscoelastic properties of styrene copolymers. The properties of styrene copolymers prepared from unsaturated epoxy polyesters were considerably better compared with those obtained for styrene copolymers from unsaturated polyesters.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal and mechanical properties of poly(butylene terephthalate)/epoxy blends

In this study, melt blends of poly(butylene terephthalate) (PBT) with epoxy resin were characterized by dynamic mechanical analysis, differential scanning calorimetry, tensile testing, Fourier transform infrared spectroscopy, and wide‐angle X‐ray diffraction. The results indicate that the presence of epoxy resin influenced either the mechanical properties of the PBT/epoxy blends or the crystallization of PBT. The epoxy resin was completely miscible with the PBT matrix. This was beneficial to the improvement of the impact performance of the PBT/epoxy blends. The modification of the PBT/epoxy blends were achieved at epoxy resin contents from 1 to 7%. The maximum increase of the notched Izod impact strength (≈ 20%) of the PBT/epoxy blends was obtained at 1 wt % epoxy resin content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ageing of poly(ethylene terephthalate) and poly(ethylene naphthalate) under moderately accelerated conditions

PEN is thought to have increased thermal and hydrolytic resistance in comparison to PET. However, due to a lack of research, few studies have been published on the degradation of PEN. In our research, we report on the extent of degradation in PET and PEN after ageing under contrasting environments (dry nitrogen, dry air, wet nitrogen, and wet air) at temperatures between 140°C and 190°C. A combination of analysis techniques were employed in order to characterize and track the physical and chemical changes in the aged polyester samples, enabling the effects of temperature, water, and oxygen to be mapped onto the resultant property changes of PET and PEN. The extent of degradation has been shown to differ between both polymers and the dominant degradation mechanism in PET was shown to differ with ageing temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Six‐arm star‐shaped polymer with cyclophosphazene core and poly(ε‐caprolactone) arms as modifier of epoxy thermosets

A six‐arm star‐shaped poly(ε‐caprolactone) (s‐PCL) based on cyclophosphazene core was obtained by presynthesis of a hydroxy‐teminated cyclophosphazene derivative and subsequent initiation of the ring‐opening polymerization of ε‐caprolactone, and its use in different proportions as toughening modifier of diglycidylether of bisphenol A/anhydride thermosets was studied. The star‐shaped polymer was characterized to have approximately 30 caprolactone units per arm. Differential scanning calorimetry revealed a nonsignificant influence on the curing process of the epoxy‐anhydride formulation by the addition of s‐PCL. The s‐PCL‐modified epoxy thermosets exhibited a great improvement in both toughness and strength compared with the neat resin, as the result of a joint effort by the internal rigid core and the external ductile polyester chains of s‐PCL. When the addition of the modifier was 3 wt %, an optimal mechanical and thermomechanical performance was achieved. The impact resistance and tensile strength of the cured epoxy resin were enhanced by 150% and 30%, respectively. The glass transition temperature was also increased slightly. Moreover, the addition of the star‐shaped modifier had little harmful effect on the thermal stability of the material. Thus s‐PCL was proved to be a superior toughening agent without sacrificing thermal and mechanical properties of the thermosets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44384.     

Polymerization of epoxidized soybean oil with maleinized polybutadiene

Epoxidized soybean oil (ESO) triglycerides were reacted with maleinized polybutadiene (MMPBD) to give plant‐oil‐based thermoset polymers. MMPBD samples were of two different molecular weights [high‐molecular‐weight maleinized polybutadiene (MMPBD‐H), maleate content = 10%, number‐average molecular weight (M_n) = 9000, and low‐molecular‐weight maleinized polybutadiene (MMPBD‐L), maleate content = 15%, M_n = 5000]. To increase the crosslink density of the product, a free‐radical initiator, benzoyl peroxide, was added to this mixture to further crosslink MMPBD through its double bonds. The characterizations of the products were done by dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and IR spectroscopy. The ESO–MMPBD polymers were crosslinked rigid infusible polymers. ESO–MMPBD‐H–1 : 1 and ESO–MMPBD‐L–1 : 1 showed glass‐transition temperature values at −23, 78 and −17, 64°C, respectively, whereas the storage moduli of the two polymers at 25°C were 13 and 16 MPa, respectively. The storage moduli of the polymers remained the same or decreased with the addition of a free‐radical initiator. The storage moduli also decreased with increasing ESO concentration above a 1 : 1 epoxy‐to‐anhydride molar ratio. The surface hardness increased dramatically, and the equilibrium swelling ratio decreased with the addition of free‐radical initiator. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Peroxide crosslinking of a styrene‐free unsaturated polyester

Thermoset unsaturated polyesters are usually obtained by the crosslinking of unsaturated polyester chains dissolved in an unsaturated, reactive, monomeric diluent, which is usually styrene. This article describes a new approach in which styrene‐free unsaturated polyester chains are intrinsically cured into a crosslinked matrix. The gel time, gel content, swelling degree, glass‐transition temperature, dynamic mechanical properties, tensile properties, and molecular weight between crosslinks (calculated according to both the Flory–Rehner equation and the theory of rubber elasticity) of the crosslinked polymer are studied as a function of the peroxide concentration. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2 wt %) and change to a lesser extent with higher peroxide concentrations (up to 6 wt %). The thermal properties of the isolated gel fraction are studied as a function of the peroxide concentration. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the glass‐transition temperature and stress–strain behavior of the crosslinked polymer. In light of the crosslink densities derived from swelling experiments, a molecular structure and crosslinking mechanism are suggested for the gel fractions of 1 and 6 wt % peroxide crosslinked unsaturated polyester chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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     

Molecular dynamics simulation of crosslinking process and mechanical properties of epoxy under the accelerator

To simulate the crosslinking process of epoxy resin under the accelerator action, the crosslinking system of bisphenol-A diglycidyl ether (DGEBA) as a monomer, methyl tetrahydro-phthalic anhydride (MTHPA) as a thermal curing agent and 2,4,6-tris (dimethylaminomethyl) phenol (DMP-30) as a thermal curing accelerator has been studied using molecular dynamics (MD) simulation. An algorithm that can construct the high-crosslinked system with different crosslinking density is completed based on the Perl language, and the subsequent properties are simulated. The results of molecular dynamics simulation show that modulus have an increasing trend, and glass transition temperature (Tg) raises from 325 K to 480 K when crosslinking density is from 0% to 95.5%. Conversely, cohesive energy density lessens from 620 J/cm³ to 170 J/cm³, solubility and Poisson's ratio decrease, and the tensile strength firstly increases and then diminishes. The friction coefficient decreases firstly and then increases, meanwhile, the temperature suddenly adds by 20 K and the relative concentration distribution (RCD) grows by 1.58 times at the contact surface. This study predicts for the crosslinking process and micro mechanical properties in the DGEBA/MTHPA/DMP-30 system.     

Mechanical,thermal, and morphological properties of bismaleimide/unsaturated polyester copolymers

An unsaturated polyester (UP) resin was modified by the addition of a thermosetting bismaleimide (BMD) as a second coreactive monomer. The copolymers were characterized in terms of mechanical, thermal, and morphological properties by tensile, bend, and impact testing; thermogravimetric analysis; heat deforming temperature analysis; dynamic mechanical analysis; and scanning electron microscopy. In addition, Fourier transform infrared spectroscopy of modified resin indicated that crosslinking networks were formed between BMD and UP. The properties of the modified resins were compared with those of unmodified resins. The results indicate that the addition of BMD not only improved the thermal decomposition temperature and heat deforming temperature but also caused small changes in the mechanical properties. The effect of the construct of BMD and the reactions among BMD, UP, and styrene were analyzed. The results show that BMD has great potential to improve the properties of UP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 593–598, 2006