4 research outputs found
Improved Characterization of Polyoxazolidinones by Incorporating Solubilizing Side Chains
Carbon dioxide-based polyoxazolidinones
(POxa) are an
emerging
subclass of non-isocyanate polyurethanes for high temperature applications.
Current POxa with rigid linkers suffer from limited solubility that
hinders synthesis and characterization. Herein, we report the addition
of alkyl and alkoxy solubilizing groups to rigid spirocyclic POxa
and their poly(hydroxyÂoxazolidinone) (PHO) precursors. The modified
polymers were soluble in up to six organic solvents, enabling characterization
of key properties (e.g., molar mass and polymer structure) using solution-state
methods. Dehydration of PHO to POxa changed solubility from highly
polar to less polar solvents and improved thermal stability by 76–102
°C. The POxa had relatively high glass transition (85–119
°C) and melting (190–238 °C) temperatures tuned by
solubilizing group structure. The improved understanding of factors
affecting solubility, structure–property relationships, and
degradation pathways gained in this study broadens the scope of soluble
POxa and enables more rational design of this promising class of materials
Improved Characterization of Polyoxazolidinones by Incorporating Solubilizing Side Chains
Carbon dioxide-based polyoxazolidinones
(POxa) are an
emerging
subclass of non-isocyanate polyurethanes for high temperature applications.
Current POxa with rigid linkers suffer from limited solubility that
hinders synthesis and characterization. Herein, we report the addition
of alkyl and alkoxy solubilizing groups to rigid spirocyclic POxa
and their poly(hydroxyÂoxazolidinone) (PHO) precursors. The modified
polymers were soluble in up to six organic solvents, enabling characterization
of key properties (e.g., molar mass and polymer structure) using solution-state
methods. Dehydration of PHO to POxa changed solubility from highly
polar to less polar solvents and improved thermal stability by 76–102
°C. The POxa had relatively high glass transition (85–119
°C) and melting (190–238 °C) temperatures tuned by
solubilizing group structure. The improved understanding of factors
affecting solubility, structure–property relationships, and
degradation pathways gained in this study broadens the scope of soluble
POxa and enables more rational design of this promising class of materials
Understanding the Insertion Pathways and Chain Walking Mechanisms of α‑Diimine Nickel Catalysts for α‑Olefin Polymerization: A <sup>13</sup>C NMR Spectroscopic Investigation
Nickel α-diimine
catalysts have been previously shown to
perform the chain straightening polymerization of α-olefins
to produce materials with melting temperatures (<i>T</i><sub>m</sub>) similar to linear low density polyethylene (<i>T</i><sub>m</sub> = 100–113 °C). Branching defects
due to mechanistic errors during the polymerization currently hinder
access to high density polyethylene (<i>T</i><sub>m</sub> = 135 °C) from α-olefins. Understanding the intricacies
of nickel α-diimine catalyzed α-olefin polymerization
can lead to improved ligand designs that should allow production of
chain-straightened polymers. We report a <sup>13</sup>C NMR study
of polyÂ(α-olefins) produced from monomers with <sup>13</sup>C-labeled carbonsî—¸specifically 1-decene with a <sup>13</sup>C-label in the 2-position and 1-dodecene with a <sup>13</sup>C-label
in the ω-positionusing a series of α-diimine nickel
catalysts. Furthermore, we developed a mathematical model capable
of quantifying the resulting <sup>13</sup>C NMR data into eight unique
insertion pathways: 2,1- or 1,2- insertion from the primary chain
end position (1°), the penultimate chain end position (2<sub>p</sub><sup>°</sup>), secondary
positions on the polymer backbone (2°), and previously installed
methyl groups (1<sub>m</sub><sup>°</sup>). With this model, we accurately determined overall regiochemistry
of insertion and overall preference for primary versus secondary insertion
pathways using nickel catalysts under various conditions. Beyond this,
our model provides the tools necessary for determining how ligand
structure and polymerization conditions affect catalyst behavior for
α-olefin polymerizations
Understanding the Insertion Pathways and Chain Walking Mechanisms of α‑Diimine Nickel Catalysts for α‑Olefin Polymerization: A <sup>13</sup>C NMR Spectroscopic Investigation
Nickel α-diimine
catalysts have been previously shown to
perform the chain straightening polymerization of α-olefins
to produce materials with melting temperatures (<i>T</i><sub>m</sub>) similar to linear low density polyethylene (<i>T</i><sub>m</sub> = 100–113 °C). Branching defects
due to mechanistic errors during the polymerization currently hinder
access to high density polyethylene (<i>T</i><sub>m</sub> = 135 °C) from α-olefins. Understanding the intricacies
of nickel α-diimine catalyzed α-olefin polymerization
can lead to improved ligand designs that should allow production of
chain-straightened polymers. We report a <sup>13</sup>C NMR study
of polyÂ(α-olefins) produced from monomers with <sup>13</sup>C-labeled carbonsî—¸specifically 1-decene with a <sup>13</sup>C-label in the 2-position and 1-dodecene with a <sup>13</sup>C-label
in the ω-positionusing a series of α-diimine nickel
catalysts. Furthermore, we developed a mathematical model capable
of quantifying the resulting <sup>13</sup>C NMR data into eight unique
insertion pathways: 2,1- or 1,2- insertion from the primary chain
end position (1°), the penultimate chain end position (2<sub>p</sub><sup>°</sup>), secondary
positions on the polymer backbone (2°), and previously installed
methyl groups (1<sub>m</sub><sup>°</sup>). With this model, we accurately determined overall regiochemistry
of insertion and overall preference for primary versus secondary insertion
pathways using nickel catalysts under various conditions. Beyond this,
our model provides the tools necessary for determining how ligand
structure and polymerization conditions affect catalyst behavior for
α-olefin polymerizations