(17)--4.10 问题与解答（双语）.ppt

《(17)--4.10 问题与解答（双语）.ppt》由会员分享，可在线阅读，更多相关《(17)--4.10 问题与解答（双语）.ppt（21页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、4.10 Problem examples and solutions问题与解答Problem 1Define and differentiate polymers,plastics,and elastomers.A polymer is the long-chain molecule formed from monomer units.Plastics are a large and varied group of synthetic materials which are produced through forming and molding processes and are clas

2、sified as either thermoplastic or thermosetting.Elastomers(rubbers)are highly flexible plastics:when subjected to stress,they are capable of withstanding large elastic deformation;once the stress is removed,these plastics regain,or nearly regain,their original shape and dimensions.Problem 2What type

3、 of bonding exists within the molecular chains of thermoplastics?What type of bonding exists between the molecular chains of thermoplastics?Within thermoplastic molecular chains,covalent bonds exist.Between thermoplastic chains,permanent dipole bonds provide weak secondary bonding.Problem 3(a)Define

4、 thermosetting plastics.(b)Describe the atomic structural arrangement of thermosetting plastics.(a)Thermosetting plastics are plastics which can be formed into a shape and permanently cured or“set”by a chemical reaction.The cured product can not be melted and reused because these materials degrade a

5、t high temperatures.(b)Most thermosetting plastics consist of three-dimensional networks of covalently bonded atoms,as compared to the long chain-like molecules of thermoplastics.Problem 4Define the following terms:chain polymerization,monomer,and polymer.Chain polymerization is the process by which

6、 monomers are chemically combined into long-chain molecular polymers.A monomer is the simple molecule that is covalently bonded with other monomers to form long molecular chains.A polymer is the long-chain molecule formed from monomer units.Problem 5Describe the bonding structure within an ethylene

7、molecule by using(a)the electron-dot-cross notation and(b)straight-line notation for the bonding electrons.Problem 6(a)What is a free radical?Write a chemical equation for the formation of two free radicals from a hydrogen peroxide molecule by using(b)the electron-dot-cross notation and(c)straight-l

8、ine notation for the bonding electrons.Problem 7What is the functionality of a monomer?Distinguish between a bifunctional and trifunctional monomer.The functionality of a monomer is the number of active bonds the monomer has.A bifunctional monomer uses two active bonds for long-chain polymerization

9、while a trifunctional monomer utilizes three active bonds.Problem 8Distinguish between a homopolymer and a copolymer.A homopolymer consists of polymer chains made up of a single repeating unit;whereas a copolymer consists of polymer chains containing two or more repeating units,of dissimilar chemica

10、l structure,that can form a variety of sequences.Problem 9What materials are used in the compounding of rubber and what is the function of each?Fillers,plasticizers,accelerators and antioxidants are used in the compounding of rubber.Fillers,such as carbon black and silicas,lower the cost of producti

11、on and increase the materials strength.Plasticizers impart greater flexibility while accelerators shorten the cure time at elevated temperatures.Antioxidants are added to retard oxidation and thus reduce brittleness.Problem 10If 3 kg of sulfur is added to 300 kg of butadiene rubber,what fraction of

12、the cross-links are joined?Assuming one sulfur atom is involved in cross-linking each butadiene mer,the fraction of cross-link sites is simply the ratio of the moles of sulfur to the moles of butadiene.What weight percent sulfur must be added to polybutadiene to cross-link 20 percent of the possible cross-link sites?If 15 percent of the cross-link sites in isoprene rubber are to be bonded,what weight percent sulfur must the rubber contain?