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Related Concept Videos

Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

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Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
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Polymers: Molecular Weight Distribution01:10

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For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
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Polymers: Defining Molecular Weight01:01

Polymers: Defining Molecular Weight

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Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight.  So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
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Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
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Step-Growth Polymerization: Overview01:03

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Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
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Polymer Classification: Architecture01:14

Polymer Classification: Architecture

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Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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Temperature-Controlled Cyclic Polyester Molecular Weights in Ring-Expansion Polymerization.

Jinxing Jiang1, Ge Yao2, Yaqin Cui1

  • 1Key Laboratory of Advanced Optoelectronic Functional Materials of Gansu Province, Key Laboratory for New Molecule Materials Design and Function of Gansu Universities, College of Chemical Engineering and Technology, Tianshui Normal University, Tianshui 741001, China.

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Summary

This study demonstrates precise control over cyclic polyester molecular weights by adjusting polymerization temperature. This method allows for tunable synthesis of poly(salicylic phenyl glycolide) with high glass transition temperatures.

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Area of Science:

  • Polymer Chemistry
  • Materials Science

Background:

  • Synthesizing cyclic polyesters via ring-expansion polymerization is challenging, particularly in controlling molecular weight.
  • Precise molecular weight control is crucial for tailoring polymer properties.

Purpose of the Study:

  • To develop a method for easily controlling the molecular weight of cyclic polyesters.
  • To investigate the relationship between polymerization temperature and molecular weight control.
  • To synthesize poly(salicylic phenyl glycolide) with tunable molecular weights and high glass transition temperatures.

Main Methods:

  • Chain-growth polymerization of cyclic esters was employed.
  • Polymerization temperature was adjusted to regulate polymerization and cyclization rates.
  • Molecular weights were characterized using gel permeation chromatography, mass spectrometry, and atomic force microscopy.

Main Results:

  • Molecular weights of poly(salicylic phenyl glycolide) were successfully controlled, ranging from 32.2 to 189.0 kg/mol.
  • An inverse relationship was observed between the natural logarithm of molecular weights and polymerization temperatures.
  • The glass transition temperature reached 116.6 °C due to phenyl group incorporation.

Conclusions:

  • Adjusting polymerization temperature offers an effective strategy for controlling cyclic polyester molecular weights.
  • This approach facilitates the synthesis of tailored cyclic polyesters with desirable thermal properties.