Mechanism and kinetics for homo- and copolymerization of cyclic acetals.
Item
-
Title
-
Mechanism and kinetics for homo- and copolymerization of cyclic acetals.
-
Identifier
-
AAI9618082
-
identifier
-
9618082
-
Creator
-
Lu, Na.
-
Contributor
-
Advisers: Nan-Loh Yang | George L. Collins
-
Date
-
1996
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Chemistry, Polymer | Chemistry, Analytical
-
Abstract
-
Bulk homo- and copolymerization of trioxane and dioxolane initiated with boron trifluoride etherate was studied through the application of {dollar}\sp1{dollar}H and {dollar}\sp{13}{dollar}C NMR. The results confirmed that trioxane homopolymerization is characterized by an "induction period", during which steady state concentrations of formaldehyde and tetraoxane are built up. Rapid propagation will not occur until the concentration of these two generated "monomeric" species reach their maximum. The formation of tetraoxane in trioxane polymerization is understood through insertion of formaldehyde into monomer trioxane. In contrast to polymerization of trioxane, polymerization of dioxolane involves an equilibrium of polymer and monomer only, without generation of formaldehyde and any other small cyclic compounds.;It was concluded that water acts as coinitiator and inactivator in both dioxolane and trioxane polymerizations. Time-conversion curves for both polymerization systems display a similar feature. That is, for the polymerization system with high water concentration, consumption of monomers is faster initially and then levels off. For the system with a low concentration of water, the initial rate of polymerization is slower but propagation increases rapidly. For trioxane polymerization, {dollar}\sp1{dollar}H NMR spectra show that significant levels of formaldehyde cannot be formed and polymerization cannot proceed when the water content is undetectable by NMR. There is no direct evidence to exclude direct initiation in dioxolane polymerization. But from the concentration of propagation species measured through the ion-trapping method, it seems that direct initiation through self-ionization also occurs together with a coinitiation mechanism. The different behavior for trioxane and dioxolane polymerization may be attributed to the fact that trioxane is a weaker base and has a stable six-member ring structure.;Formaldehyde plays an important role in copolymerization of trioxane and other cyclic acetals. Again, trioxane is not directly incorporated into the copolymer chain before formaldehyde reaches its steady state concentration. Instead, trioxane decomposes into formaldehyde. The insertion of formaldehyde into dioxolane leads to formation of trioxepane. This generated trioxepane is able to participate in copolymerization, leading to a shift in the equilibrium of propagation {dollar}\rightleftharpoons{dollar} depropagation to the direction of generation of more trioxepane. These processes occur repeatedly until a stable microstructure of copolymer is formed. Of course, occurrence of transacetalization during copolymerization of cyclic acetals may also contribute to sequence redistribution of microstructure.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
