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Polymer Classification: Architecture

Polymer Classification: Architecture

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...

Radical Chain-Growth Polymerization: Overview

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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...

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The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...

Step-Growth Polymerization: Overview

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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...

Types of Step-Growth Polymers: Polyesters

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The introduction of polyesters has brought major development to the textile industry. The wrinkle-free behavior of polyester blends has eliminated the need for starching and ironing clothes.
Polyesters are commonly prepared from terephthalic acid and ethylene glycol; the crude product is known as poly(ethylene terephthalate) or PET. However, polyesters are synthesized industrially by transesterification of dimethyl terephthalate with ethylene glycol at 150 °C. The two reactants and the polymer...

Polymers

Polymers

The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the properties that they exhibit. Additionally,...

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

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Universal tree structures in directed polymers and models of evolving populations.

Eric Brunet¹, Bernard Derrida, Damien Simon

¹Laboratoire de Physique Statistique, Ecole Normale Supérieure, 24, rue Lhomond, 75231 Paris Cedex 05, France. Eric.Brunet@lps.ens.fr

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics

|March 5, 2009

Summary

Coalescence time ratios become universal in large populations, revealing distinct universality classes regardless of selection. This finding simplifies understanding evolutionary dynamics across different models.

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Area of Science:

Population genetics
Theoretical biology
Statistical mechanics

Background:

Understanding the timescale of genetic coalescence is crucial for inferring population history.
Previous models often incorporated selection, complicating universal predictions.
The behavior of coalescence in the large population size limit remains an active area of research.

Purpose of the Study:

To investigate the universality of coalescence times across various evolutionary models.
To determine if selection influences these universal properties.
To identify distinct classes of universal behavior in large populations.

Main Methods:

Calculating coalescence times for multiple theoretical models.
Comparing models with and without the influence of natural selection.
Analyzing the behavior of coalescence time ratios in the limit of large population sizes.

Main Results:

Ratios of coalescence times exhibit universal behavior as population size increases.
This universality holds true irrespective of whether selection is included in the model.
Several distinct universality classes were identified based on model parameters.

Conclusions:

Coalescence time ratios offer a universal metric for population genetics.
The identified universality classes provide a simplified framework for analyzing evolutionary dynamics.
These findings have implications for inferring demographic history from genetic data.