Physical-Chemical Investigations of Artificial Rubber

1942 ◽  
Vol 15 (4) ◽  
pp. 854-859
Author(s):  
A. Springer
Keyword(s):  
Degree Of Polymerization ◽  
Polymerization Process ◽  
Chemical Transformations ◽  
Thermal Methods ◽  
Chain Molecules ◽  
Physical Chemical ◽  
Thermal Measurements ◽  
Heats Of Combustion ◽  
The Difference ◽  
Energy Relations

Abstract Among the physical methods of which use has been made to explain the structure of organic compounds, thermal measurements, particularly measurements of heats of combustion, have played a particularly important part. With the aid of data on heats of combustion, it is possible to draw conclusions on the energy relations within molecules and on the heat tones of chemical transformations. Such measurements have been carried out on highly polymeric substances. In some cases, the object was to study the reactions of formation. e.g., polymerization; in other cases it was to explain the transformations which high polymers themselves undergo. Studies of polymerization reactions by thermal methods have shown that, in distinction to monomers, a decrease in the heat of combustion with increase in the degree of polymerization is to be expected. The polymerization process is accordingly exothermic, and the difference between the heats of combustion represents the heat of polymerization which is liberated. A direct comparison of heats of polymerization found experimentally by different investigators is, however, not possible because, in most cases, no information on the degree of polymerization, branching of the chain molecules, or other significant properties of the polymers are given.

Degree of Conversion of Light Cured Resin Cements Polymerized under Two Thicknesses of Different Lithium Silicate Ceramics

2020 ◽  
Author(s):  
Mohamed Abdel Rahman Maraghy
Keyword(s):  
Degree Of Polymerization ◽  
Resin Cement ◽  
Lithium Silicate ◽  
Resin Cements ◽  
Ceramic Disc ◽  
Ceramic Disk ◽  
The Difference ◽  
Light Cure Unit ◽  
Glass Slab ◽  
Finger Pressure

Objective: To show the consequence of two thicknesses of ceramic on the polymerization of resin cement light cured when three different lithium silicate ceramics were used. Materials and Methods: 42 ceramic slices were prepared from three types of ceramics, Emax CAD, Celtra Duo CAD and Vita suprinity CAD (n=14). They were further divided into two subgroups according to thicknesses into sub group thickness 0.5mm and sub group thickness 1mm (n=7). Teflon moulds were fabricated with specific dimensions, where the ceramic disc was placed followed by light cured resin cement Bisco choice 2 veneer and a glass slab with finger pressure applied. Curing with Ascent® PX LED light cure unit for 20 seconds took place, where the tip placed over the ceramic sample directly. Cement film was then separated from the ceramic disk and subjected to analysis by Fourier Transform Infrared Spectroscope. Uncured cement samples were also subjected to analysis. Results: Celtra DUO CAD ceramic showed higher degree of polymerization that of Emax and Vita suprinity while the difference between Emax and Suprinity on the degree of polymerization was not significant. Also, ceramic thicknesses had a significant effect on the degree of polymerization of the resin cement. Conclusion: Thickness of ceramics up to 1mm affects the polymerization of resin cement significantly.

scholarly journals Physiological regulation of total tubulin and polymerized tubulin in tissues.

1977 ◽  
Vol 74 (2) ◽  
pp. 351-357 ◽  
Author(s):  
D G Pipeleers ◽  
M A Pipeleers-Marichal ◽  
D M Kipnis
Keyword(s):  
Mouse Liver ◽  
Marked Decrease ◽  
Human Lymphocytes ◽  
Fold Increase ◽  
Human Platelets ◽  
Degree Of Polymerization ◽  
Polymerization Process ◽  
Physiological Factors ◽  
Physiological Regulation ◽  
Tubulin Content

Polymerized and depolymerized forms of tubulin were measured in rat and mouse liver, rat islets, human lymphocytes, and platelets. The percent of the total tubulin present in the polymerized form varied from 30.3 +/- 1.5% in the liver of the fed rat to 89.2 +/- 0.2% in human platelets. Fasting decreased the total tubulin and to a greater extent the polymerized form of tubulin in both rat and mouse liver. Glucose feeding increased the polymerized tubulin without affecting the total tubulin content in rat liver. Phytohemagglutinin-stimulated lymphocytes exhibited at least a three-fold increase in total tubulin (expressed in terms of DNA content), which during the initial 48 h of incubation was accounted for in toto by an increase in polymerized tubulin. It is suggested that the lectin not only accelerates tubulin synthesis but also stimulated the polymerization process. Storage of platelets at 4 degrees C for 6 days resulted in a marked decrease in total tubulin and an even greater reduction in the polymerized form. It is concluded that both the total tubulin content and its degree of polymerization can be modulated independently by a wide variety of physiological factors.

Synthesis of Polyurethane Dendrimers and Transfer Properties of Dye

2013 ◽  
Vol 457-458 ◽  
pp. 65-71
Author(s):  
Jing Ru Jia
Keyword(s):  
Methyl Orange ◽  
Phase Transfer ◽  
Raw Materials ◽  
Toluene Diisocyanate ◽  
Polymerization Process ◽  
Process Conditions ◽  
Addition Polymerization ◽  
Different Temperatures ◽  
The Difference ◽  
Transfer Properties

The polyfunctional organic compounds 2- hydroxymethyl -1,4- butanediol (trihydric alcohol) and toluene diisocyanate -2, 4- diisocyanate (TDI) were taken as the raw materials in this study. A polyurethane dendrimer was synthesized by utilizing the difference in the reaction activity of two isocyanate groups of TDI at different temperatures. The polymerization process conditions were studied. The addition polymerization of para-position NCO groups occurred at 50 °C, and that of ortho NCO groups occurred at 90 °C. According to the structure of the dendrimer synthesized, methyl orange was used as the guest molecule. Consequently, the aqueous methyl orange showed a phase transfer. With the increase of dendrimer concentration, the transfer rate of methyl orange increased.

Thermogravimetric Analysis of Glucose-Based and Fructose-Based Carbohydrates

2013 ◽  
Vol 805-806 ◽  
pp. 265-268 ◽  
Author(s):  
Fang Ming Cui ◽  
Xiao Yuan Zhang ◽  
Li Min Shang
Keyword(s):  
Activation Energy ◽  
Thermogravimetric Analysis ◽  
Kinetic Parameters ◽  
Degree Of Polymerization ◽  
Experiment Data ◽  
Pyrolysis Characteristics ◽  
The Difference ◽  
Kinetic Calculations

Thermogravimetric analysis (TGA) was employed to study the pyrolysis characteristics of four glucose-based and three fructose-based carbohydrates. Kinetic parameters were calculated based on the experiment data. The results indicated that the starting and maximal pyrolysis temperatures of the glucose-based carbohydrates were increased steadily as the rising of their degree of polymerization (DP). The fructose-based carbohydrates exhibited similar pyrolysis behaviors as the glucose-based carbohydrates, but the difference was smaller. Kinetic calculations revealed that the activation energy values of the glucose-based carbohydrates were higher than those of the fructose-based carbohydrates, indicating the glucose-based carbohydrates were more difficult to decompose than the fructose-based carbohydrates.

scholarly journals Influence of Dimethacrylate Monomer on the Polymerization Efficacy of Resin-Based Dental Cements—FTIR Analysis

Polymers ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 247
Author(s):  
Aleksandra Maletin ◽  
Ivan Ristic ◽  
Tanja Veljovic ◽  
Bojana Ramic ◽  
Tatjana Puskar ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Clinical Practice ◽  
Chemical Structure ◽  
Cementitious Materials ◽  
Degree Of Polymerization ◽  
Cementitious Material ◽  
Ftir Analysis ◽  
Dental Cement ◽  
Polymerization Mechanism ◽  
The Difference

The degree of polymerization for dimethacrylate resin-based materials (BisGMA, TEGDMA, UDMA, HEMA) ranges from 55 to 75%. Literature data indicate that polymerization efficacy depends, among other factors, on the type of methacrylate resin comprising the material. The aim of this study was to evaluate the polymerization efficacy of four dental cement materials characterized by different polymerization mechanisms using FTIR analysis. In the present study, the FTIR method was adopted to analyze the degree of polymerization efficacy of four resin-based dental cement materials, two of which were self-cured and two were dual-cured cements. The IR spectral analysis was performed 24 h after the polymerization of the cementitious material. RelyX ARC cement exhibits the lowest polymerization efficacy (61.3%), while that of Variolink II (85.8%) and Maxcem Elite is the highest (90.1%). Although the efficacy of self-cured cements appears to be superior, the difference is not statistically significant (p = 0.280). Polymerization efficacy largely depends on the chemical structure of the material in terms of the presence of a particular methacrylate resin and less on the polymerization mechanism itself, i.e., whether it is a self-cured or dually cured dental cement. Thus, in clinical practice, cementitious materials with a higher proportion of TEGDMA compared with BisGMA are recommended.

scholarly journals The effect of sorbitol and white sweet potatoes (Ipomea batatas L.) inulin extract application on marshmallow physical, chemical and organoleptic properties

Food Research ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 298-305
Author(s):  
B. Yudhistira ◽  
A.K. Putri ◽  
S. Prabawa
Keyword(s):  
Sweet Potato ◽  
Design Method ◽  
Sweet Potatoes ◽  
Physical Chemical ◽  
Organoleptic Characteristics ◽  
Randomized Design ◽  
Ipomea Batatas ◽  
The Difference ◽  
The One ◽  
High Calorie

Marshmallow belongs to a high-calorie food that requires a low-calorie substitute for sucrose, one of which is sorbitol. Marshmallow has the potential to become a functional food with the addition of inulin contained within white sweet potatoes. Inulin refers to a type of fructan carbohydrate which contains fiber and has the potential as a prebiotic that is beneficial for the human’s body. This study aims to determine the effect of the addition of white sweet potato (Ipomea batatas L.) inulin extract and sorbitol on the physical, chemical and organoleptic characteristic of marshmallows and to obtain the best marshmallow’s formula through white sweet potato (Ipomea batatas L.) inulin extract and sorbitol addition. The completely randomized design method (CRD) applied in this study consisted of one factor, namely the difference in formulation between the concentration of white sweet potato inulin extract (2% and 3%) and the concentration of sorbitol (25%, 50%, and 75%). The statistical analysis utilized the One Way Analysis of Variance (ANOVA) method using SPSS. The results of this study indicated that the addition of white sweet potato inulin extract and sorbitol had a significant effect on tensile strength, density, moisture content, ash content, total calories, dietary fiber, and organoleptic characteristics of marshmallows. The best formula for marshmallows was formula 4 with the addition of 2% white sweet potato inulin extract and 50% sorbitol.

scholarly journals Dynamics of physical-chemical transformations at Eastern Donbass siltstones firing

2019 ◽  
Author(s):  
Kh. S. Yavruyan ◽  
V. D. Kotlyar ◽  
E. S. Gayshun ◽  
A. S. Okhotnaya ◽  
G. O. Budagyants ◽  
...  
Keyword(s):  
Chemical Transformations ◽  
Physical Chemical

The statistics of stiff chain molecules I. The particle scattering factor

1970 ◽  
Vol 316 (1525) ◽  
pp. 185-199 ◽  
Keyword(s):  
Distribution Functions ◽  
Chain Model ◽  
Particle Scattering ◽  
Hindered Rotation ◽  
Chain Molecules ◽  
Chain Stiffness ◽  
Angle Scattering ◽  
Analytic Expressions ◽  
Scattering Factor ◽  
The Difference

Analytic expressions for the particle scattering factor of stiff chains have been derived, both for the wormlike and a discrete chain model with an axial symmetric potential of hindered rotation. The angular distribution functions agree well with the results of Monte Carlo calculations by Heine, Kratky & Roeppert (1962), if the chains are longer than five persistence lengths. The particle scattering factor of short chains can be well represented by the simple Guinier approximation. A transition point from the behaviour of a coil to that of the rod-like short chain sections has been determined by graphical extrapolation and appears at X a = 2.87 ± 0.05. The difference between the wormlike and the discrete chain models turned out to be smaller than 14% even for an alkane type chain with free rotation of the chain elements and decreases with increasing chain stiffness. The influence of the cross-section has been taken into account by representing the chain by a pearl necklace. Comparison with X -ray small angle scattering measurements of a cellulosetricarbanilate reveals close similarities between calculated and experimental curves.

STUDIES ON THERMAL METHODS OF MEASURING THE HOLDING TIME IN HIGH-TEMPERATURE SHORT-TIME PASTEURIZERS

1953 ◽  
Vol 16 (1) ◽  
pp. 15-25 ◽  
Author(s):  
W. K. Jordan ◽  
R. F. Holland
Keyword(s):  
High Temperature ◽  
Correction Factor ◽  
Holding Time ◽  
Thermal Waves ◽  
Thermal Methods ◽  
Thermal Test ◽  
High Temperature Short Time ◽  
The Difference ◽  
Short Time

Data are presented on the properties of thermal waves produced by several means of suddenly increasing or decreasing the temperature of the fluid moving through the holding tube of a high-temperature short-time pasteurizer. Thermal holding-time measurements made with eight instruments or methods are compared with the holding time measured by the 3-A standard salt test. The reasons for variation in the correction factor, the difference beween the holding times measured by the salt test and a thermal test, are discussed.

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