Abstract The thermal decomposition and the glass transition temperature of poly(p-chlorostyrene) (PpCIS) were studied with a Model 2 differential scanning calorimeter (DSC). The undecom-posed and decomposed polymers were analyzed by gel permeation chromatography for molecular weight distributions and by DSC for changes in the polymer glass transition temperature. The decomposition of PpCIS under isothermal conditions during 50 min intervals at various temperatures or at a fixed temperature (320°C) but for different periods is characterized by the disappearance of increasing quantities of high molecular weight polymer and the appearance of low molecular weight products. Random scissions have been shown to break down the polymer chains which depolymerize into volatile products. Activation energy (72 kcal/mole) for the decomposition of PpCIS is lower than that (103 kcal/mole) for the decomposition of polystyrene. 相似文献
The thermal decomposition and the glass transition temperature Tg of poly(phenyl methacrylate) (PPhMA) and poly(cyclohexyl methacrylate) (PcHU) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties, e.g., Tg. For all values of weight-loss α, the thermal stability of the polymers follows the order: Poly-(methyl methacrylate) (PMMA) = PcHMA > poly(ethyl methacrylate) (PEMA) > PPhMA > poly(n-butyl methacrylate) (PnBuMA) > poly(isobutyl methacrylate) (PiBuMA). In the depolymerization reactions that occur during the isothermal decomposition of PPhMA, there is no specific preference for longer or shorter chains although a minor fraction of the volatilized fraction with an [Mbar]w 10?5 of 2.5 and an [Mbar] n |MX 10.?5 of 1.5 does undergo chain recombination yielding high molecular weight products with an Mw × 10?6 of 1.35 and an Mn × 10?6 of 1.0 to 1.23. In the case of PcHMA, depolymerizations did show a preference for longer chains. No chain recombination, however, was found to take place. Activation energy of decomposition for substituted poly-methacrylates follows the order: PnBuMA = PiBuMA >; PEMA >; PcHMA >; PMMA >; PPhMA. Tge values of PPhMA samples varied from 362 K for undecomposed polymers to 396 K for a polymer treated at 300° C. The literature value of 383 K does fall within this range. In the case of PcHMA, an average Tge of 356 f 6.0 ± is not far removed from the reported value of 359 K. 相似文献
Abstract The thermal decomposition and the glass transition temperatures of poly(methyl methacrylate) (PMMA) and poly(isobutyl methacrylate) (PiBuMA) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties and glass transition temperatures, T. In the isothermal decomposition of PMMA and PiBuMA, depolymerization reactions exclusively are operative. During low temperature decompositions, longer PMMA chains depolymerize first. These are followed by the shorter chains. In the case of PiBuMA, the shorter chains depolymerize first. Some of these undergo chain recombinations to yield very high molecular weight products. For identical values of weight loss, the respective decomposition temperatures for PiBuMA are 40 to 70 K lower than those for PMMA. The activation energies of decomposition (42 kJ/mol for PMMA and 67 kJ/mol for PiBuMA) have been found to be lower than those reported in the literature. Although Tg∞ of PiBuMA (331 K) agrees well with the literature value (326 K), Tg∞ of atactic PMMA (394 K) is higher than the reported value (378 K). 相似文献
A novel and straightforward one‐pot multicomponent polycondensation method was established in this work. The Biginelli reaction is a versatile multicomponent reaction of an aldehyde, a β‐ketoester (acetoacetate) and urea, which can all be obtained from renewable resources, yielding diversely substituted 3,4‐dihydropyrimidin‐2(1H)‐ones (DHMPs). In this study, renewable diacetoacetate monomers with different spacer chain lengths (C3, C6, C10, C20) were prepared via simple transesterification of renewable diols and commercial acetoacetates. The diacetoacetate monomers were then reacted with renewable dialdehydes, i.e., terephthalaldehyde and divanillin in a Biginelli type step‐growth polymerization. The obtained DHMP polymers (polyDHMPs) displayed high molar masses, high glass transition temperatures (Tg) up to 203 °C and good thermal stability (Td5%) of 280 °C. The Tg of the polyDHMPs could be tuned by variation of the structure of the dialdehyde or the diacetoacetate component.
Polymethyl methacrylate (PMMA) polymer chains were grafted on neoprene W (NW) by a one-step ATRP reaction. The thermal properties of the products were analyzed by DSC. Improvement of Tg was a result of the PMMA grafted chains. Also, the melting point (Tm) changed from 42°C for NW to 142°C for modified NW. Using different solvents for the resulting copolymers, aggregates were obtained. Phase separation was influenced by the grafting degree of PMMA and the employed solvent. The copolymers were analyzed by GPC, FT-IR, DSC, and SEM. 相似文献
On the basis of results of kinetic investigates of many compounds general temperature dependence of Gibbs free energy of activated
complexes created in thermal decomposition processes and the reaction rate constant were calculated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
The pressure exponent (γ) equation of the burning rate (u) of the title propellant is u=apγ=4.350p0.192 at 4-10 MPa, having very good combustion characteristics. It has the potential for possible use as solid rocket propellant from the point of view of … 相似文献
