Microstructure in copolymers. II. Analysis of tetrad sequences in vinylidene chloride‐isobutylene copolymers by NMR spectroscopy

Macromolecules

“…7.13 60 MHz proton NMR spectra of the homopolymers (a) and (b) are shown. [19][20][21] The homopolymer of vinylidene chloride gives a single resonance for the methylene protons (a); the homopolymer of isobutylene (which can be prepared with cationic but not with free radical initiators) gives singlet resonances of 3:1 intensity for the methyl and methylene protons. The spectrum of a copolymer, prepared 1 é é I é é é é I ι é é é I é é é é I é U (The upfield isobutylene peaks show considerable overlap and assignments here are less certain, but these resonances are not required for the analysis.)…”

High resolution NMR studies on sequence distribution of vinylidene chloride copolymers

“…Copolymer compositions P,{M] and P,{D}, where P,{M} + P,{D} = 1, were determined from the C1 analyses, and the monomer reactivity ratios were obtained as r~ = 2.5 2~ 0.3 and rD = 0.34 f 0.05 in fair accord with the reported valuesls).On the other hand, the above concentrations can be calculated according to the usual copolymerization theory (terminal model) as follows 10,12,19).PDM PMD + PDM P,{M} = 1-P,{D} = P,{MMM} = P,{M}PMM' The A's represent the respective specific peak areas, while Pl{.…”

“…However, in the isobutylene systems, JOHNSEN lo) and 12) and their coworkers have reported some deviations from the usual copolymerization theory The reason for this discrepancy is not clear at present, though the copolymerization of isobutylene might be expected t o be influenced by such abnormal effects as depropagation and penultimate monomer units of the growing chain as suggested12). However, in the isobutylene systems, JOHNSEN lo) and 12) and their coworkers have reported some deviations from the usual copolymerization theory The reason for this discrepancy is not clear at present, though the copolymerization of isobutylene might be expected t o be influenced by such abnormal effects as depropagation and penultimate monomer units of the growing chain as suggested12).…”

Theoretical Consideration of Phase Behavior of the Products of Free‐Radical Copolymerization Described by the Penultimate Model

“…Numerous examples of pairs of monomers are reported in literature for whose copolymerization a pronounced effect of the penultimate units on the reactivity of a macroradical is observed . Among reasons responsible for such an impact are steric, polar, and induction effects .…”

“…Quite typical is also the case when both monomers can polymerize individually, but the reactivity of the radical with terminal unit of only one of two types is controlled by the type of the penultimate unit. In this case, copolymerization is described by the three‐parametric kinetic model that along with the general penultimate model can be used to calculate the statistical characteristics of the chemical structure of particular copolymers …”