scholarly journals Effect of Temperature and Pressure on Segmental Relaxation in Polymethylphenylsiloxane

2003 ◽  
Vol 76 (5) ◽  
pp. 1106-1115 ◽  
Author(s):  
S. Pawlus ◽  
S. J. Rzoska ◽  
J. Ziolo ◽  
M. Paluch ◽  
C. M. Roland
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Pressure Dependence ◽  
Activation Volume ◽  
Relaxation Times ◽  
Effect Of Temperature ◽  
Loss Peak ◽  
Glass Transition Temperatures ◽  
Segmental Relaxation ◽  
Temperature And Pressure

Abstract Segmental relaxation in a series of polymethylphenylsiloxanes (PMPS) was studied using dielectric spectroscopy. The measurements covered a temperature range of more than 40 deg at pressures from ambient to 115 MPa. The results confirmed that the shape of the loss peak is independent of temperature, pressure and molecular weight. Consequently, the Tg -scaled dependence of the relaxation times was also independent of molecular weight. The pressure dependence of the relaxation times was characterized by means of the activation volume. This quantity changes markedly with pressure at a given temperature. However, the activation volume at the respective glass transition temperatures of the PMPS are essentially invariant to molecular weight. Finally, we measured the dependence of Tg on pressure, with the results well-described by the Andersson equation.

The effect of methyl and methoxy substituents on dianilines for a thermosetting polyimide system

2020 ◽  
Vol 32 (7) ◽  
pp. 801-822 ◽  
Author(s):  
John J La Scala ◽  
Greg Yandek ◽  
Jason Lamb ◽  
Craig M Paquette ◽  
William S Eck ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Molecular Weight ◽  
Glass Transition ◽  
Elevated Temperature ◽  
Methyl Substituent ◽  
Glass Transition Temperatures ◽  
High Performing ◽  
Methoxy Substituent ◽  
Acidic Conditions ◽  
Thermal Stability Of

4,4′-Methylenedianiline (MDA) is widely used in high-temperature polyimide resins, including polymerization of monomer reactants-15. The toxicity of MDA significantly limits the manufacturability using this resin. Modifying the substitution and electronics of MDA could allow for the reduction of toxicity while maintaining the high-performing properties of the materials derived from the modified MDA. The addition of a single methyl substituent, methoxy substituent, location of these substituents, and location of the amine relative to the phenolic bridge were modified as were other non-aniline diamines. Various anilines were condensed with paraformaldehyde under acidic conditions to yield dianilines. These dianilines and diamines were reacted with nadic anhydride and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in methanol to form the polyamic acid oligomers and heated at elevated temperature to form polyimide oligomers. It was found that the molecular weight of the oligomers derived from MDA alternatives was generally lower than that of MDA oligomers resulting in lower glass transition temperatures ( T gs) and degradation temperatures. Additionally, methoxy substituents further reduce the T g of the polymers versus methyl substituents and reduce the thermal stability of the resin. Methyl-substituted alternatives produced polyimides with similar T gs and degradation temperatures. The toxicity of the MDA alternatives was examined. Although a few were identified with reduced toxicities, the alternatives with properties similar to that of MDA also had high toxicities.

scholarly journals Glass Transition and Interfacial Segmental Dynamics in Polymer-Particle Composites

2008 ◽  
Vol 81 (3) ◽  
pp. 506-522 ◽  
Author(s):  
C. G. Robertson ◽  
C. M. Roland
Keyword(s):  
Glass Transition ◽  
Relaxation Times ◽  
Polymer Particle ◽  
Polymer Chains ◽  
Nano Particle ◽  
Segmental Mobility ◽  
Segmental Dynamics ◽  
Reinforcing Fillers ◽  
Segmental Relaxation ◽  
Polymer Interaction

Abstract We review the literature concerned with the effect of proximity to a filler surface on the local segmental mobility of polymer chains. This mobility is commonly assessed from either the glass transition temperature, Tg, or the segmental relaxation times measured by mechanical, dielectric, or NMR spectroscopy. Published studies report increases, decreases, or no change in Tg upon the addition of carbon black, silica, and other reinforcing fillers. Similarly, the segmental relaxation times have been found to increase or be invariant to the presence of nanometer-sized particles. Some of these discrepancies can be ascribed to ambiguous methods of data analysis; others likely reflect the variation in filler-polymer interaction among different systems. There are unequivocal examples of polymers that have segmental dynamics and glass transitions unaffected by nano-particle reinforcement. However, the general principles governing the behavior remain to be clarified, with further work, focusing on the micromechanics at the particle interface, required for resolution of this important aspect of rubber science and technology.

The dynamics of freestanding films: predictions for poly(2-chlorostyrene) based on bulk pressure dependence and thoughtful sample averaging

Soft Matter ◽  
2021 ◽  
Author(s):  
Ronald P. White ◽  
Jane E. G. Lipson
Keyword(s):  
Pressure Dependence ◽  
Relaxation Times ◽  
Quantitative Agreement ◽  
Segmental Relaxation

We model the segmental relaxation in poly(2-chlorostyrene) 18 nm freestanding films, using only data on bulk samples to characterize the system, and predict film relaxation times that are in semi-quantitative agreement with film data.

Functionalized Polyesters via Stereoselective Electrochemical Ring-Opening Polymerization of O-Carboxyanhydrides

2020 ◽  
Author(s):  
Yongliang Zhong ◽  
quanyou feng ◽  
xiaoqian wang ◽  
jia chen ◽  
wenjun cai ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Catalytic System ◽  
Ring Opening ◽  
Electrical Current ◽  
Ring Opening Polymerization ◽  
Glass Transition Temperatures ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions

Ring-opening polymerization is used to prepare polyesters with precisely controlled molecular weights, molecular weight distributions, and tacticities. Herein, we report a newly developed Co/Zn catalytic system that can be activated by an electrical current to mediate efficient ring-opening polymerization of enantiopure <i>O</i>-carboxyanhydrides, allowing for the synthesis of isotactic functionalized polyesters with high molecular weights (>140 kDa) and narrow molecular weight distributions (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> < 1.1). We also demonstrate that these catalysts can be used for stereoselective ring-opening polymerization of racemic <i>O</i>-carboxyanhydrides to synthesize syndiotactic or stereoblock copolymers with different glass transition temperatures compared with their atactic counterparts.

High Pressure Dielectric Studies of 8CB in the Isotropic, Nematic, and Smectic A Phases

1999 ◽  
Vol 54 (5) ◽  
pp. 275-280 ◽  
Author(s):  
Phineus Markwick ◽  
Stanislaw Urban ◽  
Albert Würflinger
Keyword(s):  
Activation Energy ◽  
Complex Permittivity ◽  
Activation Volume ◽  
Activation Enthalpy ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Retardation Factor ◽  
Smectic A ◽  
Parallel Component ◽  
Temperature And Pressure

The static and complex permittivity of 4-n-octyl-4'-cyanobiphenyl (8CB) has been measured for the isotropic, nematic and smectic A phases as functions of temperature and pressure. The ranges of 297 - 361 K, 0.1 - 220 MPa, and 0.1 - 13 MHz, were covered. Only the parallel component of the complex permittivity, ɛ*( f ) = ɛ' ( f ) - iɛ"(f), was measured. The relaxation times T||(p, T) as well as Tis(p, T) were analysed at constant temperature, pressure and volumes yielding the activation volume, Δ ≠V(T), activation enthalpy Δ≠H(p), and activation energy Δ≠U(V), respectively. All activation parameters calculated for the smectic A phase of 8CB are smaller than those obtained for the nematic phase. The activation energy constitutes approximately half of the activation enthalpy value in all three phases studied. The pressure study allowed to calculate the pressure dependence of the retardation factor g|| (p, T), from which the nematic potential q(p,T) can be derived. Using the relationships between g\\ and q/ RT proposed by Kalmykov and Coffey, the order parameter (P2(p, T)) was calculated as a function of pressure.

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