Name: polymer chains and their properties
Uploaded: 2023-04-30T18:28:47.000Z
Duration: 2 min 34 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.1

Polymers

Un polimero è una catena di piccole molecole, dette monomeri, che sono tenute insieme da legami covalenti. Gli organismi possono sintetizzare polimeri biologici, oppure gli scienziati possono sintetizzare polimeri in laboratorio. I polimeri naturali includono il DNA, il materiale genetico che si trova in tutti gli organismi viventi, e proteine, polisaccaridi e lipidi, i mattoni della vita.

Le materie plastiche sono alcuni dei polimeri sintetici più comuni e includono nylon, polietilene e teflon. Il processo dei monomeri che si collegano fra loro per formare una molecola più grande è detto polimerizzazione. I monomeri polimerizzano mediante due distinti meccanismi di reazione, condensazione e addizione.

La polimerizzazione per condensazione si verifica quando due monomeri con un atomo di idrogeno reattivo e un gruppo idrossile, rispettivamente, si legano fra loro, con il rilascio di acqua come sottoprodotto. La maggior parte dei polimeri naturali si forma attraverso reazioni di condensazione. In più, nella polimerizzazione, i monomeri con doppi legami carbonio-carbonio sono aggiunti fra loro per formare un polimero senza la generazione di alcun sottoprodotto, attraverso il rilascio di atomi.

I polimeri costituiti dallo stesso tipo di monomeri sono detti omopolimeri e quelli costituiti da diversi tipi di monomeri sono detti eteropolimeri. La cellulosa, il polimero naturale più abbondante, è un omopolimero del glucosio, laddove l'agarosio, un polimero di origine marina, è un eteropolimero del galattosio e del 3, 6-anidro-L-galattopiranosio. I polimeri hanno varie strutture a seconda del loro tipo di monomeri.

I polimeri lineari sono lunghe catene di monomeri. Per esempio, la cellulosa è un polimero lineare tenuto insieme da legami beta 1, 4-glicosidici. I polimeri ramificati hanno catene che si separano dalla catena principale, come l'amilopectina, un componente dell'amido che si ramifica dopo 24-30 monomeri attraverso legami alfa 1, 6-glicosidici.

I polimeri reticolati hanno due o più catene tenute insieme in diversi punti a forma di scala, come un polimero a scala di silicio costruito sinteticamente, o formano una complessa rete di catene interconnesse come il gel formato dalla pectine nelle gelatine e nelle marmellate.

polimeri

La parola polimero deriva dalle parole greche “poly” che significa “molti” e “mer” che significa “parti”. I polimeri sono lunghe catene di molecole composte da unità ripetitive di molecole più piccole, note come monomeri. Sono presenti in natura, come il DNA e le proteine, oppure possono essere costruiti sinteticamente, come la plastica. Hanno varie caratteristiche strutturali, come catene lineari, catene ramificate o reti complesse, che contribuiscono alle proprietà che esibiscono. Inoltre, i gruppi funzionali che possono essere presenti su un polimero ne definiscono ulteriormente le proprietà. Le singole unità di un polimero sono tenute insieme da legami covalenti stabili che si verificano attraverso la polimerizzazione per addizione o condensazione.

Polimerizzazione per addizione

Un'ulteriore polimerizzazione si verifica quando i monomeri che partecipano alla reazione hanno doppi legami. Questa reazione richiede la presenza di una molecola esterna che ha un elettrone di valenza spaiato per avviare la reazione. Questo elettrone spaiato è altamente reattivo e forma un legame con uno dei doppi legami in un monomero, che porta il monomero ad avere un elettrone di valenza spaiato. Questo elettrone di valenza spaiato si associa quindi ad un altro monomero con doppi legami portando ad una reazione a catena in cui la molecola continua ad aggiungere ad essa altri monomeri con doppi legami. Ciò si traduce nella formazione di una catena di monomeri, dove quello aggiunto più recentemente ha un elettrone di valenza spaiato. Questa reazione di addizione continua finché due catene con elettroni spaiati reagiscono tra loro per formare un legame. Ciò elimina eventuali elettroni di valenza spaiati, con conseguente interruzione della reazione.

Polimerizzazione per condensazione

La polimerizzazione per condensazione, nota anche come polimerizzazione a crescita graduale, richiede un catalizzatore, come un acido o un enzima, e i monomeri devono avere almeno due gruppi funzionali reattivi, come ammine o acidi carbossilici. I gruppi funzionali sui monomeri reagiscono tra loro per formare legami come legami estere o ammidici e sono accompagnati dalla perdita di una piccola molecola, come l'acqua. La polimerizzazione per condensazione è una reazione più lenta rispetto alla polimerizzazione per addizione e, in molti casi, richiede la presenza di calore.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/Hydrocarbons">Openstax, Chemistry 2e, Chapter 20.1: Hydrocarbons</a>.

Polimeri

La parola polimero deriva dalle parole greche "poly" che significa "molti" e "mer" che significa "parti". ...

Education

Didattica

JoVE Core

Cell Biology

Biologia cellulare

Unit 1

Unità 1

Biochemistry of the Cell

Biochimica della cellula

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

polymer chains and their properties

Polymers are large molecules made from repeating units called monomers. These long chains can form many common materials. Their structure helps explain why different polymers can behave in different ways.

Polymers can be built in more than one way. Some form by addition polymerization, where monomers join together directly. Others form by condensation polymerization, which releases a small molecule as the chain grows.

The type of polymer affects its properties and uses. Some polymers are strong and flexible, while others are more rigid. Many everyday materials are made from polymers, so understanding how they form helps explain the materials people use every day.

Polymer Chains and Their Properties

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polymers

Polymers are large molecules made from repeating units called monomers. These long chains can form many common materials. Their structure helps explain why different polymers can behave in different ways. Polymers can be built in more than one way. Some form by addition polymerization, where monomers join together directly. Others form by condensation polymerization, which releases a small molecule as the chain grows. The type of polymer affects its properties and uses. Some polymers are...

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Polymer Chains and Their Properties | JoVE K12

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SC.912.L.18.2

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SC.912.L.18.3

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SC.912.L.18.5

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SC.912.L.18.6

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SC.912.L.18.7

A. All living things are composed of four basic categories of macromolecules and share the same basic needs for life.

B. Living organisms acquire the energy they need for life processes through various metabolic pathways (primarily photosynthesis and cellular respiration).

C. Chemical reactions in living things follow basic rules of chemistry and are usually regulated by enzymes.

D. The unique chemical properties of carbon and water make life on Earth possible.

Polymer Chains and Their Properties

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