Size exclusion chromatography (SEC) with differential refractive index (RI), multiangle light scattering (MALS) and UV detectors has been used to obtain information about copolymers of styrene (S) and methyl methacrylate (MMA). Homopolymers PS and PMMA having broad molecular weight distributions, mixtures of PS and PMMA homopolymers, and copolymers containing different weight fractions of S and MMA units were studied. Molecular weight distributions, molecular dimensions and scaling laws are reported for these systems. The behavior of the random copolymers is very different from that exhibited by the heterogeneous mixtures of homopolymers. Thus, the results obtained for the copolymers can be explained by assuming that these molecules have homogeneous distributions of S and MMA units along their chains. On the contrary, the mixtures produce the results that would be expected from heterogeneous combinations of different molecules. The SEC technique offers the possibility of determining the composition of random copolymers and discriminating among random copolymers (having homogeneous distributions of units) and block copolymers.

Samples of poly(2,2‘-dioxybiphenylphosphazene) were prepared according to procedures previously reported in the literature and submitted to thermal degradation at temperatures between 100 and 200 °C during periods of time ranging from 6 to 250 h. Experimental characterization of the parent polymer and the degraded samples was performed employing DSC and double detector SEC techniques. Values of T g, molecular weight distributions and averages, molecular dimensions and scaling laws coefficients were thus obtained. THF solutions of this polymer at 25 °C are below ϑ conditions although the chain behaves as a random coil. Molecular dimensions of degraded samples are noticeably smaller than those of nondegraded samples of the same molecular weight. Extrapolation to unperturbed conditions gives values of C N = 12 and 7, respectively, for original and degraded samples. Molecular dynamics simulations were also carried out seeking for the conformational properties of the chain which allowed the formulation of a RIS model whose application provides theoretical values of the molecular dimensions in good agreement with experimental results measured for the nondegraded sample.

Poly(2,2′-dioxy-1,1′-biphenyl)phosphazene (I) is a weak base that can be reversibly protonated with HBF 4 in acetone. Acidic degradation of poly(2,2′-dioxy-1,1′-biphenyl)phosphazene was experimentally performed using HBF 4 , HCl, and H 2 SO 4 yielding the same polymer I with lower molecular weights. The reaction takes place through protonation of some of the skeletal bonds thus producing a protonated P + -NH bond, and posterior rupture of those bonds by reaction with water. The hydrolysis breaks only these protonated skeletal bonds, leaving unaffected the regular P-N bonds. The degree of hydrolysis is controlled by the amount of time during which the system was treated with the acid. Molecular dynamics simulations performed on systems containing protonated and unprotonated oligomers together with water and HCl molecules proved that Clions and water molecules get close enough to protonated P + -NH bonds as to produce a hydrolytical rupture, however, they do not get into such a proximity to the regular P-N bonds. The products of hydrolysis were characterized by (SEC-MALS) (i.e., size exclusion chromatography coupled with multiangle light scattering) and fluorescence. The results indicated that the parental polymer and all the degraded samples have the same chemical microstructure despite their very different molecular weight, i.e., they exhibit the same molecular calibration curve, unperturbed dimension, scaling law parameters, fluorescence emission, lack of cross-linking etc. It seems that the acidic degradation can be controlled to produce homogeneous samples in a much easier way than the thermal degradation used before.

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