Weight change of polymers

Effect of the Treatment Conditions on the Weight Changes of Polymers. From the data shown in Tables 3 and 4, the effect of pressures and temperatures on observed weight change of polymeric... 

Polymer-Fluid Equilibria and the Glass Transition Most polymer systems fall in the Class HI or Class V phase diagrams, and the same system can often change from one class into the other as the polymer s molecular weight changes. Most polymers are insoluble in CO9 below 100°C, yet CO9 can be quite sohible in the polymer. For example, the sorption of CO9 into silicone rubber is highly dependent upon temperature and pressure, since these properties have a large influence on the density and activity of CO9. 

Thermogravimetric analysis In thermogravimetric analysis (TGA) a sensitive balance is used to follow the weight change of the sample as a function of temperature. Its applications include the assessment of thermal stability and decomposition temperature, extent of cure in condensation polymers, composition and some information on sequence distribution in copolymers, and composition of filled polymers, among many others. 

It was observed elsewhere that plasma treatment of polymer macromolecules results in their cleavage, ablation, alterations of chemical structure and thus affects surface properties e.g. solubility [75]. The effects of the treatment in Ar plasma on the surface properties of PE were examined in [72]. The parameters of the plasma discharge (240 s, 8.3 W power) were chosen, on the basis of our previous experiments [70-74,78], to guarantee the most pronounced changes of polymer surface. Mean thickness of the ablated PE layer was calculated from the weight difference measured by gravimetry. By Ar plasma (8.3 W, 240 s) 30 8 nm thick surface layer is ablated and thickness of the surface layer removed from plasma-modified PE by 24 hour water etching is 21 5 nm [78]. 

Figure 8.10 Structure of polyester bearing the alkoxyamine unit and change on molecular weight and molecular weight distribution of polymer 43 in the radical...

When products of low molecular weight are obtained from a chemical reaction process, it is often possible to separate these products after they have left the reactor. Thus, the choice of reactor conditions can be taken from a wide range of options. With polymerisation processes, the results of reaction selectivity (i.e. the molecular weight distribution of polymer molecules) cannot be changed easily once the material has left the reactor. Since polymer properties depend on the molecular weight distribution, the relative yields of polymers with particular sizes must be matched to a required specification. Therefore, the choice of reactor type is very important. 

In TGA, a sensitive balance is used to follow the weight change of a polymer as a function of time or temperature. In making both TGA and thermocalorimetric measurements, the same heating rate and flow of gas should be employed to give the most comparable thermograms. TGA and DTA can be used to determine (1) the sample purity, (2) the material identity,... 

Thermogravimetry is a technique that measures the weight change of a sample as a function of temperature or time (time is suitable only when thermal analysis is performed at specified constant temperature increments). The solid or liquid sample is heated or cooled at a selected rate or isothermally maintained at a fixed temperature. TG is used to measure degradation, oxidation, reduction, evaporation, sublimation, and other heat-related changes occurring in polymers. 

Table 3. Observed Weight Change for Polymers Treated with Carbon Dioxide at 40°C for 1 Hour as a Function of Treatment Pressure ...

R. L. Miller, R. W Seymour, and L. W Branseome, The application of size-exclusion chromatography to study molecular-weight changes of flame-retardant fiber-reinforced polyesters, Polym. Eng. ScL 592 31-38 (1991). 

A mathematical model for styrene polymerization, based on free-radical kinetics, accounts for changes in termination coefficient with increasing conversion by an empirical function of viscosity at the polymerization temperature. Solution of the differential equations results in an expression that calculates the weight fraction of polymer of selected chain lengths. Conversions, and number, weight, and Z molecular-weight averages are also predicted as a function of time. The model was tested on peroxide-initiated suspension polymerizations and also on batch and continuous thermally initiated bulk polymerizations. 

Breaks of the main chain of macromolecules are the main reasons for the loss of PCA service properties at photooxidative destruction therefore definition of the change of polymer molecular weight before and after photooxidation is one of the methods of evaluating such important characteristic as the number of breaks. There were investigated PCA samples... 

The number-average molecular weight (MJ of polymers can be easily determined from methods based on colligative properties, which are dependent on the number of molecules in the solution [28]. Thus, the addition of a number of solute molecules to a solvent produces a change in the chemical potential (A/Ui) of the solvent from which the molecular and interactional parameters can be deduced. 

Thus, we can conclude that the shrinking of the hypercrosslinked polymers at temperatures in the range of250-300°C is caused by oxidation, with the rupture of a certain portion of the stressed carbon—carbon bonds. Under the permanent tendency for reducing the free volume of the material, the scission of the most stressed bonds leads unavoidably to the formation of a more compact structure and to the decrease of the beads volume and their inner specific surface area. The rupture of bonds can then be followed by their partial recombination or termination with oxygen. The latter process seems to proceed to a lower extent, since no noticeable weight change of the air-exposed samples was observed. 

Reactions of fp-Polvstvrylmethvlltriphenvlphosphonium Ions. In these reactions the polymer-bound phosphorane reacts with an aldehyde or ketone to produce an alkene substituent on the polymer and leave the by-product triphenylphosphine oxide in solution, where it can be washed away from the polymer. The results are in Table II. Many of the same methods of phosphorane generation used to produce soluble alkenes were used. The yields in Table II are less accurate than the yields of micromolecular alkenes in Table 1 because of the difficulty of analysis of insoluble polymers. The yields have been based on weight changes of the polymer, analysis of the polymer for an element introduced during the reaction, the yield of triphenylphosphine oxide, or the amount of bromine consumed by the modified polymer. 

Various organic solvents were used as reactionary medium at nonequilibrium polycondensation in solution realization [96]. The solvent type influence on the synthesis reaction main characteristics (conversion degree Q and molecular weight MM) is well known and is explained usually by solvent various characteristics (dielectric constant, solubility parameter, heat of dissolution and so on) [96]. However, up to now the indicated effects general theoretical explanation is not obtained. Besides, at the solvent type influence analysis its correlation with polycondensation process quantitative characteristics (the same Q and MM) is usually considered, but any changes of polymer structure or reaction mechanism are not assumed, although the possibility of side reactions is noted repeatedly [96]. The authors [71, 127] studied the solvent influence on the enumerated above characteristics on die example of the rules of chloranhydride of terephthalic acid and phenolfthaleine low-temperature polycondensation (polyarylate F-2), performed in 8 different solvents [128]. 

The results of the weight changes of the polymer samples studied during biodegradation in compost and in sea water are presented in Table 3 and Table 4, respectively. 

Let us consider the kinetics of DMDAACh initial polymerization in more details. The autoacceleration effect in radical polymerization (the so-called gel-effect) plays an important role in polymers synthesis processes and during years number was a topic of intensive studies [20,29-32]. At present it is assumed, that the autoacceleration realization is due to a stmctural changes in polymer solution [31, 32]. The detailed interpretation of this point of view is adduced in the indicated above works. However, it should be noted, that polymerization autoacceleration beginning is accompanied by a number of other important effects, which get much less attention. Let us indicate the some from them. The attention is paid to very high molecular weights MM of polymer, which are realized on polymerization initial section at low reaction rates, small conversion degrees (up to 5%) and small reaction durations (of order of 5 min) [32], Secondly, as it... 

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