Molar mass changes

With very few exceptions, polymers consist of macromolecules (or network chains) with a range of molar masses. Since the molar mass changes in intervals of M0, the distribution of molar mass is discontinuous. However, for most polymers these intervals are extremely small in comparison to the total range of molar mass and the distribution can be assumed to be continuous, as exemplified in the figure above. 

The borderline between chain and step polyadditions has never been strictly defined. In fact it is mobile, and if the molar mass change with time is accepted as a criterion, this borderline is expected to change with the development of experimental methods. Polymerizations proceeding on the multiple bonds of monomers or by opening of their rings need not be classified in this way ... 

One can consider that the kinetics carbonyl build-up is representative of the overall oxidation kinetics, at least when considered at the molecular scale (or monomer unit). It remains to establish a relationship between structural changes at this scale and molar mass changes. For the PE polymer understudy, random chain scission is predominant. It will be assumed that the main scission process is the rearrangement of alkoxyl radical (p scission). Then, every elementary reaction generating alkoxyl radicals will induce chain scission. In the chosen mechanistic scheme, both hydroperoxide decomposition processes and the nonterminating bimolecular peroxyl combination are alkoxyl sources. Thus, the number of moles of chain scissions per mass unit (s) is given by ... 

Fig. 2 CCD of a multireactor resin. Combination of a Ziegler-type resin reactor 1) with a single-site resin reactor 2) and possible combinations of comonomer incorporation and molar mass changes...

A typical resorption profile of a material consists of four steps, namely water sorption, reduction of mechanical properties, reduction of molar mass, and finally complete loss of weight, as shown in (Fig. 2.1) [1]. Initially, water and/or biological fluids diffuse into the material, followed by a reduction in the mechanical properties. Loss in strength and modulus is initially due to the plasticizing effect of the fluids and later due to the reduction in molar mass. Change in shape and weight loss are the final stages before the material is completely resorbed [2]. 

Compare relative values of v,ms, v ostprob/ 3Fid v. Will they always have the same relative values, or can variations in conditions like temperature or molar mass change their relative magnitudes ... 

During a homogenous (bulk or solution) polymerization reaction, both the concentration of polymer and molar mass change and hence viscosity should also change. Therefore, online monitoring of the viscosity could give... 

Molar Mass Changes during Degradation Analysed by Size Exclusion Chromatography and/or Matrix Assisted Laser Desorption Ionisation... 

MOLECULAR WEIGHT (MOLAR MASS) CHANGES BY SEC AND MALDI... 

Arrhenius plots for molar mass change (reproduced from Jakubowicz I, Polym. Deg. Stab., 80, 42 (2003) with permission). 

---