Expansion upon polymerization

A sample of polymer B prepared by using sodium methoxlde as an additive had a nsp of 0.5 and a of 46,000 (9). The glass transition temperature was between 4 and 10°C and the crystalline melting point was between 140 and 160°C. The specific gravities of monomer II and polymer B are respectively 1.528 and 1.483 this would indicate an expansion upon polymerization. The mechanical properties of this sample of polymer B are shown in Table II (16). 

These dimers are of interest because they serve as model compounds for a new class of phenolic materials, the polybenzoxazines, whose synthesis and characterization has been described by Ishida and coworkers.146-149 These polybenzoxazine resins were found to have a number of unusual, but commercially favorable, properties, in particular a near-zero shrinkage or volumetric expansion upon curing (polymerization) as well as low water absorption. In addition, the resins have high glass-transition temperatures even though they have been shown to have low crosslink densities. Explanations for these properties have been hypothesised in terms of favorable hydrogenbonding interactions.150... 

According to these results expansion in volume during polymerization occurs only when both fused rings open upon polymerization. 

One of the more recently exploited forms of thermal analysis is the group of techniques known as thermomechanical analysis (TMA). These techniques are based on the measurement of mechanical properties such as expansion, contraction, extension or penetration of materials as a function of temperature. TMA curves obtained in this way are characteristic of the sample. The technique has obvious practical value in the study and assessment of the mechanical properties of materials. Measurements over the temperature range - 100°C to 1000°C may be made. Figure 11.19 shows a study of a polymeric material based upon linear expansion measurements. 

In GPC, the product [77] M, (or the hydrodynamic radius Re) has been widely accepted as a universal calibration parameter. In the Ptitsyn-Eizner modification of the Flory-Fox equation the quantity 4>, which relates the dimensional parameters to the above product, is taken as a variable. The value of < depends upon molecular expansion in solution as represented by a function f(e). Because of this dependence polymeric species having the same [77] M value cannot have the same statistical dimensions (radius of gyration or end-to-end distance) unless they have the same e value. Thus, if [77] M is a universal calibration parameter, the statistical parameters cannot be used as such. A method is presented for obtaining the Mw/Mn ratio from GPC data even though universal calibration is used. 

An early estimate, based upon the position of the optical absorption of TS-polymer at low conversion gave n(X = 0) 24 repeat units Although the conclusiveness of the procedure to derive this number is questionable — for n 10 the position of the lowest absorption band of the polymer backbone is almost independent of n yet sensitive to chain expansion, known to be important at low X — this number has turned out to be essentially correct. Analysing diffusive features in the X-ray diffraction pattern of partially polymerized TS crystals Albouy et al. recently... 

The conservation of the shape is a result of the balance between the osmotic forces originated by the water upon entering the polymer and the cohesive forces exerted by the polymeric chains that resist that expansion.f ... 

The polymerization is accompanied by approximately 6% shrinkage (calculated from densities of monomer and polymer at 25 °C). Upon heating the polymer solution in the presence of trifluoromethanesulfonic acid the substituted 1,3-dioxolane ring opens and linear polymer is formed. This is accompanied by a 9.7% expansion in volume. 

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