Designing Useful Polymers | 设计有用的聚合物

📚 Designing Useful Polymers | 设计有用的聚合物

Polymers are long-chain molecules built from repeating monomer units. Designing a useful polymer is not just about choosing the right monomer; it involves controlling chain length, branching, cross-linking, functional groups and intermolecular forces so that the final material has the required strength, flexibility, thermal stability or biodegradability. This article examines how chemists design polymers for specific applications, linking structure to properties.

聚合物是由重复单体单元构成的长链分子。设计有用的聚合物不仅在于选择合适的单体，还涉及控制链长、支化、交联、官能团和分子间作用力，使最终材料具备所需的强度、柔韧性、热稳定性或生物降解性。本文探讨化学家如何为特定应用设计聚合物，并将结构与性质联系起来。

1. Polymer Design Principles | 聚合物设计原则

All useful polymers start from the relationship between molecular structure and bulk properties. The main structural variables include average chain length (molar mass), chain branching, cross-link density, crystallinity, and the nature of pendant groups. Changing any one of these can alter melting temperature, tensile strength, flexibility, solvent resistance and permeability.

所有有用的聚合物都始于分子结构与宏观性质之间的关系。主要结构变量包括平均链长（摩尔质量）、链支化、交联密度、结晶度以及侧基的性质。改变其中任何一项都会改变熔点、抗拉强度、柔韧性、耐溶剂性和渗透性。

For example, longer chains increase van der Waals forces between chains, raising strength and melting point. Introducing branches makes chains pack less closely, reducing density and crystallinity. Cross-links form covalent bridges between chains, preventing them from sliding past one another and therefore increasing rigidity and thermal resistance.

例如，较长的链增强链间范德华力，提高强度和熔点。引入支化使链堆积较不紧密，降低密度和结晶度。交联在链之间形成共价桥，阻止链彼此滑移，因此提高刚性和耐热性。

2. Addition and Condensation Polymerisation | 加成聚合与缩合聚合

Addition polymers are formed from unsaturated monomers, usually alkenes, by opening the double bond. No small molecule is lost. Poly(ethene), poly(chloroethene) (PVC) and poly(propene) are common examples. The empirical formula of the polymer is the same as that of the monomer.

加成聚合物由不饱和单体（通常为烯烃）通过打开双键形成，不失去小分子。聚乙烯、聚氯乙烯和聚丙烯是常见例子。聚合物的经验式与单体相同。

Condensation polymers are formed when monomers with two functional groups react together, eliminating a small molecule such as water or hydrogen chloride. Polyesters form from diols and dicarboxylic acids, while polyamides form from diamines and dicarboxylic acids or from amino acids. These polymers contain ester or amide links that can be hydrolysed.

缩合聚合物由带有两个官能团的单体相互反应形成，同时消去水或氯化氢等小分子。聚酯由二醇和二羧酸形成，聚酰胺由二胺和二羧酸或氨基酸形成。这些聚合物含有可水解的酯键或酰胺键。

3. Poly(ethene): HDPE versus LDPE | 聚乙烯：高密度与低密度聚乙烯

Poly(ethene) is the simplest and most widely used addition polymer, but its properties can be designed by controlling the polymerisation conditions. High-density poly(ethene) (HDPE) is made using Ziegler-Natta catalysts at low pressure, producing mostly linear chains that pack closely. It has high density, high tensile strength and a higher melting point, making it suitable for bottles, pipes and crates.

聚乙烯是最简单、应用最广的加成聚合物，但可以通过控制聚合条件设计其性质。高密度聚乙烯（HDPE）使用齐格勒-纳塔催化剂在低压下制备，生成大多为直链的链，堆积紧密。它具有高密度、高抗拉强度和较高熔点，适用于瓶子、管道和板条箱。

Low-density poly(ethene) (LDPE) is made at high pressure with a free-radical initiator. The chains contain many branches, so they cannot pack closely. LDPE is more flexible, transparent and has a lower melting point, which is why it is used for plastic bags and squeeze bottles.

低密度聚乙烯（LDPE）在高压下用自由基引发剂制备。链含有许多支链，因此无法紧密堆积。LDPE更柔韧、透明且熔点较低，因此用于塑料袋和挤压瓶。

4. PVC and Plasticisers | 聚氯乙烯与增塑剂

Poly(chloroethene), commonly called PVC, contains polar C–Cl bonds. The dipole-dipole interactions between chains make the pure polymer rigid and brittle. This is useful for drainpipes and window frames, where stiffness is needed.

聚氯乙烯（常称PVC）含有极性的C–Cl键。链间的偶极-偶极相互作用使纯聚合物刚硬且脆。这对于需要刚性的排水管和窗框很有用。

To make flexible PVC, chemists add plasticisers – small, non-volatile molecules that insert between polymer chains and weaken the intermolecular forces. This allows chains to slide more easily, lowering the glass transition temperature and producing flexible materials used in flooring, cables and clothing.

为了制造柔性PVC，化学家加入增塑剂——插入聚合物链之间并削弱分子间作用力的小分子非挥发性物质。这使链更容易滑动，降低玻璃化转变温度，从而产生用于地板、电缆和服装的柔性材料。

5. Designing Polyesters: PET | 设计聚酯：PET

Poly(ethylene terephthalate), PET, is a condensation polymer formed from ethane-1,2-diol and benzene-1,4-dicarboxylic acid (terephthalic acid). Each monomer has two functional groups, allowing long chains to form with ester links. The rigid benzene ring in the diacid contributes to chain stiffness and a high melting point.

聚对苯二甲酸乙二醇酯（PET）是由乙二醇和对苯二甲酸形成的缩合聚合物。每种单体有两个官能团，使长链得以形成并带有酯键。二酸中的刚性苯环有助于链的刚性和高熔点。

PET can be processed into fibres by drawing, where chains align and crystallise to give high tensile strength. It is also used for drinks bottles and food packaging because it is clear, tough and a good barrier to carbon dioxide. The same repeat unit can therefore be designed for very different products by controlling orientation and crystallinity.

PET可通过拉伸加工成纤维，使链取向并结晶，从而获得高抗拉强度。它也用于饮料瓶和食品包装，因为它透明、坚韧且对二氧化碳有良好阻隔性。因此，相同的重复单元可以通过控制取向和结晶度来设计用于截然不同的产品。

6. Polyamides: Nylon and Kevlar | 聚酰胺：尼龙与凯夫拉

Nylon-6,6 is made from hexane-1,6-diamine and hexanedioic acid. The repeating unit contains amide links, –CONH–. Hydrogen bonding between the N–H of one chain and the C=O of a neighbouring chain holds the chains together strongly. This gives nylon high tensile strength, toughness and resistance to wear, making it suitable for ropes, fabrics and engineering plastics.

尼龙-6,6由己二胺和己二酸制成。重复单元含有酰胺键–CONH–。一条链的N–H与相邻链的C=O之间的氢键将链牢固地结合在一起。这赋予尼龙高抗拉强度、韧性和耐磨性，使其适用于绳索、织物和工程塑料。

Kevlar is an aromatic polyamide made from benzene-1,4-diamine and benzene-1,4-dicarbonyl chloride. The rigid benzene rings and strong hydrogen bonds produce a highly ordered structure with exceptional strength per unit mass. Kevlar is used in bullet-proof vests and composites. The design principle is that stiff aromatic groups plus hydrogen bonding lead to high-performance fibres.

凯夫拉是由对苯二胺和对苯二甲酰氯

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

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