Name: polymer chains and how they form
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 2 min 34 s
Channel: JoVE

聚合物是由小分子组成的链，称为单体，通过共价键结合在一起。生物体可以合成生物聚合物，或者科学家可以在实验室中合成聚合物。天然聚合物包括存在于所有活生物体中的 遗传物质 DNA，以及构成生命基本组成部分的 蛋白质、多糖和脂质。塑料是一些最常见的合成聚合物，包括尼龙、聚乙烯和聚四氟乙烯。单体相互连接，形成更大分子的过程称为聚合。单体通过两种不同的反应机理进行聚合，缩合和加成。缩聚反应是指 两个分别带有活泼氢原子 和羟基的单体 相互连接，同时释放出副产物水。大多数天然聚合物是通过缩合反应形成的。在加成聚合中，具有碳-碳双键的单体相互加成 形成聚合物，不会通过释放原子 产生任何副产物。由相同类型单体组成的聚合物 称为均聚物，由不同类型单体组成的聚合物 称为杂聚物。纤维素是最丰富的天然聚合物，是葡萄糖的均聚物，而琼脂糖 是一种来源于海洋的聚合物，是半乳糖和 3, 6-脱水-L-吡喃半乳糖的杂聚物。根据单体类型，聚合物有不同的结构。线性聚合物是单体的长链。例如，纤维素是由β1, 4-糖苷键 连接在一起的线性聚合物。支链聚合物的链从主链上分离出来，例如支链淀粉，它是淀粉的一种成分，在 24 到 30 个单体后，通过 1, 6-糖苷键分支出来。交联聚合物有两个或多个链连接在几个点上，就像一个梯子一样结合在一起，例如合成构建的硅梯聚合物，或形成复杂的交联网络-就像 果冻和果酱中的果胶形成的凝胶。

聚合物

聚合物一词源自希腊语“ poly ”，意思是“ many ”，而“ mer ”则意思是“ parts ”。 聚合物是由小分子的重复单位组成的长链分子，称为单体。 它们要么自然发生，如 脱氧核糖核酸（DNA） 和蛋白质，要么可以合成，如塑料。 它们具有多种结构特征，如线性链，分支链或化合物网络，这些特征对它们所展示的性质有着影响。 此外，聚合物上可能存在的官能团进一步定义了其性质。 聚合物的单个单位由稳定的共价键固定在一起，而稳定的凝结是通过添加或 聚合而产生的。 
 增加聚合 
 当参与反应的单体具有双键时，会出现额外的聚合。 这种反应需要存在一个具有未配对价电子的外部分子来启动反应。 这种未配对的电子产品反应非常灵敏，形成一个键，其中一个是单体中的双键，这会导致单体拥有一个未配对的价电子。 这种未配对的价电子随后与另一个单体与 双键相关联，导致链反应，该分子会不断增加其他单体并为其添加双键。 这导致形成了一组单体，其中最近添加的一组单体具有未配对的价电子。 这种添加反应将持续到两个带未配对电子的链相互反应形成键。 这可以消除任何未配对的价电子，从而导致反应终止。 
 凝结聚合 
 凝结聚合 (也称为步长聚合) 需要催化剂 (如酸或酶) ，单体必须至少有两个反应性官能团 (如胺或羧酸酸)。 单体上的官能团相互反应，形成链环，如酯或酰胺链环，并伴有水等小分子的流失。 与添加聚合相比，凝结聚合反应较慢，在许多情况下需要存在热量。 
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/Hydrocarbons"> Openstax, 化学 2e, 第 20.1 章：碳氢化合物</a>。

“聚合物”一词源于希腊语“poly”，意为“许多”，以及“mer”，意为“部分”。

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Chemistry

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Biochemistry

生物化学

KEY TERMS AND CONCEPTS

关键术语与概念

Polymers

polymer chains and how they form

Polymers are long chains of molecules made from repeating units called monomers. The word polymer comes from the Greek words &quot;poly,&quot; meaning many, and &quot;mer,&quot; meaning parts. Polymers can be found in nature, such as DNA and proteins, or made synthetically, such as plastics.

A polymer’s shape helps define its properties. Some polymers form linear chains, while others are branched or arranged in complex networks. Functional groups on a polymer also affect how it behaves. The repeating units in a polymer are held together by stable covalent bonds.

Polymers can form through addition polymerization or condensation polymerization. Addition polymerization happens when monomers with double bonds react in the presence of an external molecule with an unpaired valence electron. That unpaired electron starts a chain reaction as monomers keep joining one after another. The reaction ends when two chains with unpaired electrons bond together and no unpaired electrons remain.

Condensation polymerization is also called step-growth polymerization. It needs a catalyst, such as an acid or an enzyme, and monomers must have at least two reactive functional groups, such as amines or carboxylic acids. These groups react to make linkages like esters or amides, and a small molecule such as water is lost. This process is slower than addition polymerization and often requires heat.

Polymer Chains and How They Form

functional groups

Functional Groups in Organic Chemistry

Functional groups in organic chemistry are groups of atoms that give molecules specific properties. When these groups attach to a carbon skeleton, they can change how the molecule behaves. Some functional groups make a molecule hydrophilic, or water-attracting. Others make it hydrophobic, or water-repelling. Functional groups are a key part of organic chemistry and are also found in major biological molecules. They appear in carbohydrates, proteins, lipids, and nucleic acids. Each functional...

structure of lipids

Lipids, Fats, and Cell Membranes

Lipids are nonpolar molecules that do not mix well with water. They are hydrophobic, which means “water fearing,” because they contain mostly nonpolar carbon-carbon and carbon-hydrogen bonds. In cells, lipids store long-term energy as fats, help insulate plants and animals, and form protective water-repellent layers on feathers and fur. They are also part of cell membranes and serve as building blocks for many hormones. Common lipids include fats, oils, waxes, phospholipids, and steroids. A...

chemistry of the cell

Cell Chemistry: Water and Macromolecules

Cell chemistry includes water, organic molecules, and inorganic ions. These materials shape how cells store energy, build structures, and carry out life processes. Most cellular chemistry and metabolism happen in the watery cytoplasm. Water is a key part of the cell because it has special properties tied to its polarity. In a water molecule, hydrogen and oxygen form polar covalent bonds, so the molecule has no net charge but does have a slightly positive end and a slightly negative end. Oxygen...

dna base pairing

Chargaff’s Rules and DNA Pairing

Chargaff’s rules and DNA base pairing explain how DNA strands match up. In double-stranded DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Chargaff also found that A equals T, G equals C, and the total amount of purines (A and G) equals the total amount of pyrimidines (C and T). Watson and Crick later showed why these matches matter. A forms two hydrogen bonds with T, while G forms three hydrogen bonds with C. These pairings keep the DNA double helix a...

chemistry of carbohydrates

Carbohydrates as Energy and Storage Molecules

Carbohydrates are important energy sources in human and animal diets. Grains, fruits, and vegetables are natural sources of carbohydrates. They help provide energy to the body, especially through glucose, a simple sugar found in starch and many staple foods. Carbohydrates are identified by the stoichiometric formula (CH2O)n, where n is the number of carbons in the molecule. This means the ratio of carbon to hydrogen to oxygen is usually 1:2:1. The name carbohydrate comes from this pattern,...

protein and protein structure

How Protein Shape Controls Function

Proteins are a major class of organic molecules in living systems, and their shape helps determine what they do. They can act as structural, regulatory, contractile, or protective molecules. They also take part in transport, storage, membranes, toxins, and enzymes. All proteins are polymers of amino acids arranged in a linear sequence. A protein’s function depends on its three-dimensional form. For example, an enzyme works when its active site can bind a specific substrate. If local changes or...

amino acids

Amino Acids and Protein Building

Amino acids are the building blocks of proteins. Each amino acid has the same basic structure. A central carbon atom, called the alpha carbon, is bonded to an amino group, a carboxyl group, and a hydrogen atom. Each amino acid also has an R group, or side chain, attached to the central carbon. The R group is different for every amino acid. It helps determine whether an amino acid is acidic, basic, polar, or nonpolar. Scientists call these molecules amino acids because they contain both amino...

peptide bonds

Peptide Bond Formation and Shape

Peptide bonds join amino acids into peptides and polypeptides. They form when the carboxyl group of one amino acid reacts with the amino group of another. This dehydration reaction releases a water molecule and creates a covalent link. As more amino acids are added, the chain becomes a polypeptide. Each polypeptide has a free amino group at one end. This end is the N-terminal, or amino-terminal. The other end has a free carboxyl group. This end is the C-terminal, or carboxyl-terminal. The...

nucleic acids

DNA and RNA: Genetic Instructions

DNA and RNA are the nucleic acids that store genetic information and help direct cell activity. These macromolecules carry the cell’s genetic blueprint and the instructions it uses to function. DNA is the genetic material in all living organisms, from single-celled bacteria to multicellular mammals. In eukaryotic cells, DNA is found in the nucleus and also in organelles such as chloroplasts and mitochondria. In prokaryotes, DNA is not enclosed in a membrane. The full genetic content of a cell...

dna replication

DNA Copying: Leading and Lagging Strands

DNA replication copies genetic material before a cell divides. Each original DNA strand serves as a template for a new complementary strand. The result is semiconservative replication, which means each new DNA molecule contains one old strand and one new strand. The two daughter cells then receive DNA with the same sequence. Replication starts when helicase separates the two strands of the double helix. This creates a Y-shaped replication fork. Primase then adds short RNA primers that give DNA...

from dna to protein

The Genetic Code and Codons

The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis. Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand.

polymers

Polymers are long chains of molecules made from repeating units called monomers. The word polymer comes from the Greek words "poly," meaning many, and "mer," meaning parts. Polymers can be found in nature, such as DNA and proteins, or made synthetically, such as plastics. A polymer’s shape helps define its properties. Some polymers form linear chains, while others are branched or arranged in complex networks. Functional groups on a polymer also affect how it behaves. The repeating units in a...

key terms and concepts

Learn how polymers are built from monomers and how addition and condensation polymerization create natural and synthetic materials like DNA, proteins, and plastics.

Polymer Chains and How They Form | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

Polymer Chains and How They Form

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