高分子英语

• The repeat units can all be identical（同样 的）, in which case the compound is a homopolymer（均聚物）.
• If the repeat units are different, the result is a
5.3 自动加速作用 Autoaccelaeration
Autoaccelaeration: For the major duration of a chain polymerization the reaction is first-order (一级）in monomer concentration。 However, at high conversions of monomer to polymer using either undiluted monomer or concentrated solutions there is a significant deviation from first-order kinetics, under such circumstances the rate

本体聚合的缺点：The disadvantage of the bulk polymerization: 1. 聚合热不易扩散，the dissipation of the heat is not easy 2. 产物分子量分布宽。The distribution of the molecular weight is wide.
5.3 自动加速作用 Autoaccelaeration
Reason of autoaccerleration As polymerization proceeds there is an increase in the viscosity of the reaction mixture which reduces the mobility of the reacting species. Hence termination reaction show down, while initiation and propagation reactions still continue. Such a decrease in the rate of the termination steps leads to the observed increase in the overall rate of polymerization.
Processability
加工性
Thermoplastics（热塑性塑料）
• Some polymers can be readily melted and then molded into any shape.
• they usually have linear or branched architectures.
Crystalline and Amorphous Polymers
结晶和无定形聚合物 • Solid organic compounds consisting of ordinary small molecules tend to be crystalline, that is, the molecules pack themselves in regular three-dimensional arrays.
• Most thermoplastics can also be dissolved in suitable solvents.
Processability.
Thermosets（热固性材料）
• Some other polymers decompose（分解） on heating before they can melt. • and they are usually crosslinked and therefore insoluble. • To form a part out of a thermoset, one usually synthesizes the polymer in the mold itself. • Once the polymer has cured, the only way to reshape the part is by machining (e.Baidu Nhomakorabea., grinding, drilling, etc.)
Crystalline and Amorphous Polymers
结晶和无定形聚合物
• Polymers are different; they can be amorphous （无定形的）(totally lacking positional order on the molecular scale) or semicrystalline（半结晶的） (containing both crystalline and amorphous regions in the same sample). The semicrystalline case can be pictured according to the "fringed micelle" model 樱状微束模型. Here is a two-dimensional representation
Fundamentals of Chain Structure
链结构的基础
• Polymers are large molecules. Fortunately, they are not random collections of atoms; if this were the case, they would be impossible to study. Polymers are built up from smaller molecules (monomers), and therefore possess a characteristic chain structure consisting of multiple repeat units that are related chemically, as for the example of polystyrene.
10 聚合反应实施方法
Practical Methods of Chain Polymerization
• 本体聚合－－只有单体本身在引发剂作用下进行的聚合反应。 • Bulk Polymerization—the starting material consists mainly of pure polymer, with traces of initiator and possible chain transfer agent present. 本体聚合的优点: The advantage of the bulk polymerization: 1. 聚合物较为纯净 the polymer is more pure 2. 聚合设备简单 the facilities of the polymerization is simple
Polymer Molecular Weight
The ratio of Mw to Mn is known as the polydispersity index (PDI)（多分散指 数）, and provides a rough indication of the breadth of the distribution. The PDI approaches 1.0 (the lower limit) for special polymers with very narrow MW distributions, but, for typical commercial polymers, is typically greater than 2 (occasionally much greater). Here is a typical MW distribution curve.
Classifications
• Again looking at the chains in decreasing detail, there is an infinite variety of chain architectures • linear, 线性的， • branched支化的, • crosslinked交联的).
Physical performance
物理性能.
• Polymers that stretch and rebound are called rubbers or elastomers（弹性体）. These materials are usually crosslinked, either by covalent bonds, or, in several modern cases, by noncovalent forces such as H-bonds. • Other solid polymers are known simply as plastics（塑料）, adhesives（粘合剂）, or fibers（纤维）, depending on their application. • The word resin is a generic(专业） term for polymer, although occasionally it indicates a thermoset.
聚合反应实施方法
Practical Methods of Chain Polymerization
溶液聚合－－将单体和引发剂溶于适当溶剂中的聚合反应。 Solution polymerization—that is to dissolve the monomer and initiator in an appropriate solvent. 优点：反应热易传出，聚合温度易控制，反应后物料易传出。低 分子物质易除去，能消除自动加速现象 Advantage: The exotherm on polymerization can be dissipated, temperature can be readily controlled, the reaction materials can come out, the autoacceleration can be eliminated. 缺点：单体浓度低，聚合速率慢；设备利用率低；聚合物分子量 低；溶剂回收难。 Disadvantage: the concentration of the monomers are lower, the rate of the polymerization is slow, the using rate of the facilities is also lower, the molecular weight is lower, the solvent is difficult to recover.
copolymer（共聚物）
structures of chain
• The chain itself can take many different overall structures, among them:
• Most polymers consist of linear chains • but branched systems have important uses • and highly branched polymers with fractal structures are a current hot topic of research