Epimerization of vinyl polymers to stereochemical equilibrium. 1. Theory

Abstract

conventional PGC and PHGC with catalytic hydrogenation.The fact that there exists fairly good agreement between the relative yields before and after hydrogenation supports the validity of the presumption for the assignment of some peaks on the pyrogram in Figure 1A. Thus, the identified peaks in the monomer and the trimer regions on the pyrograms in Figures 1A and IB mostly reflect the H-H and/or the T-T structures. Although the monomer is still most abundant among the products on the pyrogram, its yield only amounts to 20.4%. On the other hand, the formation of a comparable size for the multiplets of the monomer, dimer, and trimer regions suggests that random scission type thermal degradation might be predominant for H-H PS.As was reported in the PMS work on H-H PS by Lüderwald,6 we can also find on the pyrogram in Figure IB a very minor PhCH2Ph peak (peak 10) and a fairly strong PhCH(CH3)Ph peak (peak 35). This suggests either that these structures were incorporated through minor byproducts at the stage of the monomer preparation or that thermal rearrangements took place during the pyrolysis. Furthermore, it is very interesting to note that, even though very minor, PhCH2CH2Ph and PhCH2CHPhCH3 peaks can be observed on the pyrogram of H-T PS (Figure 1C). This fact, which was also pointed out by Alajbeg et al.,13 could be indicative of the existence of H-H linkages even in H-T PS.

Segmental Dynamics of Atactic Polypropylene As Revealed by Molecular Simulations and Quasielastic Neutron Scattering

“…As in ref , the model system used in generating the MD trajectories with model II consisted of two parent chains having a degree of polymerization of 76 (molar mass 3208 g/mol) in a cubic cell of initial edge length 23.42 Å with three-dimensional periodic boundary conditions. The sequence of stereochemical configurations of the pseudoasymmetric carbon atoms along each parent chain was generated by assuming a Bernoullian distribution of meso and racemo diads with a probability of occurrence of a meso diad equal to 0.48, as observed experimentally in equilibrium epimerized aPP . The MD simulations were carried out in the isothermal−isobaric ( NPT ) ensemble at different temperatures, ranging from 260 to 600 K. Configurations from the production phase of each simulation were recorded every 1 ps during a total time of 1−5 ns, depending on the temperature.…”

Tacticity and Ionization Effects on Adsorption Behavior of Poly(acrylic acid) and Poly(methacrylic acid) at the CCl4–H2O Interface Revealed by MD Simulations

“…The experimentally measured dyad and triad fractions for a -PAA are f M = 0.483, f MM = 0.242, f MR = 0.482, and f RR = 0.274. The atactic chains of PAA and PMA were constructed according to the Bernoullian distribution − of dyads. The dyad sequences of atactic chains used in simulations are provided in Table S1 as Supporting Information.…”

Predicting Polyelectrolyte Coacervation from a Molecularly Informed Field-Theoretic Model

“…The last reference simulation is a solution of 10 weight % PEs (50:50 mol/mol PAA to PAH; 24-mers, fully ionized) and 0.3 M NaCl in the NPT ensemble. We model the PEs as atactic polymers; they are built with the target dyad composition of around 0.44 meso and 0.56 racemic as per the Bernoullian distribution, Figure S4. , We note that the CG force field is composed of soft interaction potentials that do not account for the bending stiffness that partially dictates the chain conformation in the reference model. Chain conformation embeds information about the bending rigidity, intramolecule interactions, volume exclusion effects, and solvent screening; thus, it is essential for the CG model to reproduce this characteristic of the reference system.…”