Thermal behaviour of dendritic methacrylated polyesters (original) (raw)
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Thermal and X-ray powder diffraction studies of aliphatic polyester dendrimers
Journal of Polymer Science Part A: Polymer Chemistry, 2004
The syntheses and thermal and X-ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2-bis(hydroxymethyl)propionic acid as a repeating unit and 2,2-dimethyl-1,3-propanediol, 1,5-pentanediol, and 1,1,1-tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250°C for the hydroxyl-ended dendrimers and around 150°C for the acetonide-protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X-ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first-generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass-transition temperatures were observed in subsequent heating scans.
Unsaturated Polyester Resins
The fact that some natural oils besides alkyd resins can be dried by certain additives and employed as coatings was realized long ago. This results from a polymerization reaction of the unsaturated moieties in ester molecules (Fig. 6.1). Carleton Ellis' original patents with regard to polyester resins egressesed in the 1930s. While profit-making production started in 1941 by now reinforced with glass fiber for radar domes, also known to as radomes. Unsaturated polyester resins (UPRs) consist of two polymers, that is, a short-chain polyester bearing, polymerizable double bonds and a vinyl monomer. The curing reaction involves the copolymerization of the vinyl monomer with the double bonds of the polyester. During the process of curing, a threedimensional network is formed. UPR is yielded in this process, belonging to the thermoset class. UPRs have interesting applications in compression molding (sheet molding compounds), injection molding (bulk molding compounds), filament winding, resin transfer molding (RTM), pultrusion, and the hand lay-up process [1]. 85% of fiber-reinforced polymer (FRP) products such as aircraft parts, motor covers, belt guards, water-cooling towers, boats, architectural parts, chairs in ducts and other process equipment in chemical plants and paper mills, water pipes, and chemical containers are manufactured using polyesters, and they are used in offshore applications, construction, and the paint industry [2,3]. The determination of the gel time and curing time is a very significant step in the processing of UPRs while manufacturing composite products. The curing reaction should be accomplished in a governable manner to attain a high-quality product [4]. On account of the enormous amount of applications where flammability does not matter, such as underground mine bolts, pipes, and in many marine applications, the percentage of flame-retardant resins relative to all UPRs is less than 153 Unsaturated Polyester Resins.
International Journal of Plastics Technology, 2010
Cyclohexanone-formaldehyde (CHF) resins with different hydroxyl value were treated with maleic anhydride (MA) stoichiometrically. The resultant carboxy unsaturated CHF resins were then polycondensated with various epoxy resins (i.e. diglycidylether of various bisphenols) in the presence of pyridine. The unsaturated CHF resins thus obtained and unsaturated polyesters (UPE's) were characterized by unsaturation, spectral studies, and by number average molecular weight (Mn) estimated by vapor pressure osmommetry (VPO). The curing of UPE's was carried out by using benzoyl peroxide (BPO) as catalyst and monitored on differential scanning calorimeter (DSC). Based on DSC data, glass fiber reinforced composites (i.e. laminates) of these UPE's were fabricated, maintaining 40/60 proportion of resin to glass fiber. The laminates thus formed were tested for chemical, mechanical, and electrical properties. The unreinforced cured samples of UPE's resins were also analyzed thermogravimetrically.
Macromolecules, 1998
The fourth generation tridendron dendrimer based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) with 48 hydroxyl groups was synthesized in high yields using N,N′-dicyclohexylcarbodiimide (DCC) for the coupling steps. A double-stage convergent approach reduced the number of synthetic and liquid chromatographic steps required in the synthesis and purification of the final dendrimers. The hydroxyl functional dendrimer was subjected to a variety of surface modifications by reaction with different acid chlorides. The acetonide, hydroxy, acetate, n-octanoate, n-palmitoate, and benzoate end-functionalized dendrimers showed large differences in thermal and solution behavior depending on the nature of their end groups. The glass transition temperature varied from -4°C for the acetate-terminated dendrimer to +57°C for the hydroxyl-functionalized dendrimer. Dendrimers terminated with long alkyl chains were highly soluble in hexane and dichloromethane and poorly soluble in water and methanol whereas the hydroxy-terminated dendrimer showed the opposite solution behavior. All surface modified dendrimers were amorphous according to differential scanning calorimetry (DSC) except for the n-palmitoateterminated dendrimer that showed a distinct melting transition at +28°C in its DSC trace due to the crystallization of the long alkyl chains.
Toward replacement of styrene by bio-based methacrylates in unsaturated polyester resins
European Polymer Journal, 2015
Several potentially bio-based methacrylate derivatives, namely (with mol. % of bio-based carbon), butanediol dimethacrylate (BDDMA) (33%), isobornyl methacrylate (IBOMA) (71%), lauryl methacrylate (LMA) (75%)) have been evaluated as alternatives to styrene as reactive diluent of unsaturated polyester (UPR). First the compatibility of these compounds with SMC/BMC processes has been studied in terms of volatility, miscibility with UPR and viscosity. Based on these preliminary experiments, butanediol dimethacrylate (BDDMA) was selected as sole reactive diluent. The thermomechanical and mechanical properties of the resulting network were found to be very different from the ones of a UPR/MMA network prepared as a reference. Consequently, mixtures constituted of BDDMA and one monomethacrylate derivative (MMA, IBOMA and LMA) were then used as reactive diluents to yield networks owning a large range of mechanical behaviours.
Polymers, 2021
Nowadays, unsaturated polyester resins (UPR) are mainly obtained from non-renewable resources. The ever-increasing regulations and the continuous demand for more sustainability have led to extensive research towards more environmentally suitable alternatives to petroleum-based materials. However, one of the main disadvantages of bio-based UPR is their relatively high viscosity compared to petrochemical ones. In order to overcome this drawback, in this work, we investigated the possibility to lower the resin viscosity utilizing a mixture of dimethyl itaconate (DMI) and methyl methacrylate (MMA) as a reactive diluent. The effect of the DMI and MMA ratio on resin rheological properties was investigated. The optimal curing parameters were determined and all UPRs had a high gel content, which was shown to be dependent on the DMI and MMA ratio in the formulation. Furthermore, thermomechanical and mechanical properties of the resulting network were also found to be affected by the used rea...
Polymer International, 2010
Unsaturated polyester resins (UPRs) are versatile compounds. However, their major drawback is the high shrinkage exhibited on curing. An attempt was made to reduce the shrinkage of UPRs without affecting other properties. In the present study a commonly used iso-reactive UPR was modified by the addition of ethylene–vinyl acetate (EVA; subjected to controlled depolymerisation to obtain samples of various molecular weights), and was cured at room temperature. The peak exotherm temperature and gel time were both observed to decrease with an increase in EVA content. The composition incorporating 0.5% of depolymerised EVA1 (highest degree of branching) showed maximum improvement in tensile and flexural properties with the heat deflection temperature and impact properties remaining almost unaffected. A uniform dispersion for the UPR containing 0.5% of EVA1 was observed. Addition of EVA reduced the percentage shrinkage in the modified matrix. Incorporation of depolymerised EVA can be an attractive option for the reduction of shrinkage in UPRs. The advantage of using depolymerised EVA is that generated waste EVA can be depolymerised and reused for this application making it cost effective. Copyright © 2010 Society of Chemical Industry
Fire Retardancy of Polymers
This paper discusses the effect of nanoclays on thermal degradation of unsaturated polyester resin with and without conventional flame retardants. Unsaturated polyester nanocomposites were prepared by in-situ polymerization with exfoliated structures. Simultaneous DTA-TGA analysis showed that nanoclays reduce thermal stability of the unsaturated polyester resin below 600 0 C and after that there was no change. Nanoclays also reduce the onset of degradation temperature of the resin. Above 600 0 C, char formation is enhanced but not to the same extent as reported in literature for other polymer (e.g., nylon, polystyrene, etc.)nanocomposite structures. The effect of conventional flame retardants-ammonium polyphosphate, melamine phosphate with and without dipentaeythritaol and alumina trihydrate on thermal degradation of resin was also studied. All these flame retardants enhance char formation of the resin above 400 0 C and presence of nanoclays promotes further increase. Analysis of the thermogravimetric data indicates that this enhancement in char formation is not as much as expected when compared with similar other polymernanocomposite structures.
Curing and thermal behaviour of epoxy resin in the presence of aromatic imide-amines
Indian Journal of Engineering and Materials Sciences, 2005
The paper describes the synthesis and characterization of aromatic imide-amines obtained by reacting pyromellitic dianhydride (P)/or benzophenone 3,3′, 4,4′-tetracarboxylic dianhydride (B) (1 mol) with excess of 4,4′-diaminodiphenyl ether [E]/or 4,4′-diaminodiphenyl methane [M]/or 4,4′-diaminodiphenyl sulfone [S] and their use as curing agents for diglycidyl ether of bisphenol-A (DGEBA). Structural characterization of imide-amines was done using FTIR, 1 H-NMR, 13 C-NMR spectroscopy and elemental analysis. These aromatic imide-amines were used as curing agents in order to investigate the effect of structure on the curing and thermal behaviour of diglycidyl ether of bisphenol-A (DGEBA). Curing behaviour of DGEBA in the presence of stoichiometric amounts of aromatic imide-amines was investigated by differential scanning calorimetry (DSC). A broad exothermic transition in the temperature range of 180-230°C was observed in all the samples. The peak exotherm temperature (T p) was lowest in case of imide-amines based on B and M and highest in case of imide-amines based on P/or B and S. Thermal stability of the isothermally cured resins was investigated using dynamic thermogravimetry in nitrogen atmosphere. The char yield was highest for resin cured with imide-amines based on B and E.