Papers by Keyword: Glass Transition Temperature

Abstract: The glass transition temperaure Tg of amorphous polymer thin film was investigated. The opposite experimental results, the increase or decrease in Tg of thin film with decreasing film thickness, were found. It was believed that the free surface near the polymer-air interface has a smaller chain ends density, leading to the decrease in Tg; while the polymer-substrate interface has a larger chain ends density, resulting in the increase in Tg. However, there are a competition between the both, and the interaction of polymer and substrate is a dominant factor to affect Tg of thin film. In addition, the multilayer model of thin film was proposed to explain the effect of the free surface and the interface on the Tg of thin film.

Abstract: A novel Tin-functionalized integrated rubber of styrene-isoprene-butadiene (St-Ip-Bd) tri-copolymer (Sn-SIBR) was prepared by anionic polymerization using self-made tin-containing organolithium (SnLi) as initiator, tetrahydrofuran (THF) as polar modifier, and cyclohexane as solvent. The microstructure and the glass-transition temperature (Tg) of tri-copolymers were characterized by 1H NMR and differential scanning calorimetry (DSC), respectively. The result shows that the non-1,4-structure content and the Tg of tri-copolymers increased with the increase of THF dosage and the initiator concentration or the decrease of polymerization temperature. We also obtained the relationships between the ln(T/Li)( THF/ SnLi, mole ratio) and the non-1,4-structure content, the non-1,4-structure content and the Tg of copolymers, respectively.

Abstract: . Based on two quantum chemical descriptors (the thermal energy Ethermal and the total energy of the whole system EHF) calculated from the structures of the repeat units of polyacrylamides by density functional theory (DFT), the support vector regression (SVR) approach combined with particle swarm optimization (PSO), is proposed to establish a model for prediction of the glass transition temperature (Tg) of polyacrylamides. The prediction performance of SVR was compared with that of multivariate linear regression (MLR). The results show that the mean absolute error (MAE=4.65K), mean absolute percentage error (MAPE=1.28%) and correlation coefficient (R2=0.9818) calculated by leave-one–out cross validation (LOOCV) via SVR models are superior to those achieved by QSPR (MAE=14.25K, MAPE=4.39% and R2=0.9211) and QSPR-LOO (MAE=17.01K, MAPE=5.66% and R2=0.8823) models for the identical samples, respectively. The prediction results strongly demonstrate that the modeling and generalization abilities of SVR model consistently surpass those of QSPR and QSPR-LOO models. It is revealed that the established SVR model is more suitable to be used for prediction of the Tg values for unknown polymers possessing similar structure than the conventional MLR approach. These suggest that SVR is a promising and practical methodology to predict the glass transition temperature of polyacrylamides.

Abstract: . This study introduces support vector regression (SVR) approach to model the relationship between the glass transition temperature (Tg) and multipole moments for polymers. SVR was trained and tested via 60 samples by using two quantum chemical descriptors including the molecular traceless quadrupole moment and the molecular average hexadecapole moment Φ. The prediction performance of SVR was compared with that of reported quantitative structure property relationship (QSPR) model. The results show that the mean absolute error (MAE), mean absolute percentage error (MAPE) and root mean square error (RMSE) of training samples and test samples achieved by SVR model, are smaller than those achieved by the QSPR model, respectively. This investigation reveals that SVR-based modeling is a practically useful tool in prediction of the glass transition temperature of polymers.

Abstract: Polyurethane/poly (methylacrylate-butylmethacrylate-2-Hydroxyethylmethacrylate) Interpenetrating polymernetworks (IPNs) were prepared by sequential polymerization. Their glass transition performance was measured by using differential scanning calorimetry (DSC). DSC results revealed there are three glass transition temperatures (Tg) for both IPNs samples. Their damping properties were evaluated according to ASTM E756-05. Their loss factor (tan δ>0.3) from 10-1300Hz displays a wide temperature range of 94°C.

Abstract: One of the primary applications of polymer based cellular solids is to act as an energy absorbing material during impact where compressive strain rates may reach 500-800/s. In reality, impacts occur over a wide range of temperatures and velocities at different angles of incidence. Understanding and modelling the behaviour of the polymer foams requires characterisation of the material response in detail. The stress-strain response that covers both compressive and tensile behaviour for a wide range of strain rates and temperatures are needed to characterize the mechanical performance of polymer foams as polymeric foams are highly nonlinear materials that undergo large deformation in crashworthiness related cases. It is reported in literature that any increase or decrease in temperature over the glass transition region can cause changes by order of magnitude in elastic modulus of polymeric foams. However, creation of cross linking at high temperature can affect the elastic modulus. In this work, the behaviour of two, polyamide-6 (PA-6) based closed cell foams at elevated temperatures were investigated covering the glass transition temperature. This work presents the variation of elastic and tangent modulus of two low densities PA-6 and PA-6/polyolefin (Nylon alloy) based foams. Empirical equations have been proposed to allow the prediction of modulus over a temperature range of 23°C to 120°C for these materials.

Abstract: For better understanding on adhesive ability and action mechanism of asphalt mortar, a series of mortar based on Zhong-hai asphalt were prepared and evaluated by the method used in high molecule composite materials. Some influencing factors including temperature, filler-binder ratio and asphalt type were discussed on interface adhesive ability. And some conclusions were conducted. The interface adhesive ability between asphalt and mineral filler will decline as temperature fall, until the glass transition or interface phase break appears in mortar system. To the same mineral filler and asphalt, interface adhesive ability of mortar will declines as filler-binder-ratio increases under a certain temperature, and beyond this temperature, high filler-binder-ratio will upgrade the interface adhesive ability and the whole binding performance of mortar.

Abstract: Microwave heating technology is a cost-effective alternative way for heating and curing of used in polymer processing of various alternate materials. The work presented in this paper addresses the attempts made by the authors to study the glass transition temperature and curing of materials such as casting resins R2512, R2515 and laminating resin GPR 2516 in combination with two hardeners ADH 2403 and ADH 2409. The magnetron microwave generator used in this research is operating at a frequency of 2.45 GHz with a hollow rectangular waveguide. During this investigation it has been noted that microwave heated mould materials resulted with higher glass transition temperatures and better microstructure. It also noted that Microwave curing resulted in a shorter curing time to reach the maximum percentage cure. From this study it can be concluded that microwave technology can be efficiently and effectively used to cure new generation alternate polymer materials for manufacture of injection moulds in a rapid and efficient manner. Microwave curing resulted in a shorter curing time to reach the maximum percentage cure.

Abstract: Polysiloxanes with cyanoethyl groups (PDMS-CN) is a useful functional polysiloxanes. In this paper, the polysiloxane with various number average molecular weight (Mn) and cyanoethyl groups were prepared. Mns of PDMS-CN were determined by GPC. The contents of cyanoethyl groups were determined by 1H NMR. The dynamic mechanical properties and thermal stability of PDMS-CN were investigated by DSC and TGA respectively. The hydrolysis of PDMS-CNs give the polysiloxanes with carboxyl groups. The factors influencing the hydrolysis of cyanoethyl groups were discussed by orthogonal array and the optimal reaction conditions were confirmed. This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text

Abstract: The viscoelastic property of the CTC composite cores was investigated through dynamic mechanical thermal analysis (DMTA) in single cantilever mode. The effect of the frequency on the glass transition temperature (T_g) was studied. The results show that the peaks were shifted to higher temperatures with increasing frequencies. T_g of CTC was approximately 180 ^°C, much higher than that of a home-made composite core (Composite I). The activation energy ΔH of CTC is also greater than that of Composite I. The CTC sample exhibit better stiffness and toughness.