Jumat, 16 Maret 2012

Produk Alami 6 - Natural Product - 天然产物化学 - 天然產物化學 - Polimer 4



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Polymers
Introduction:
Polymers are long chain giant organic molecules are assembled from many smaller molecules called monomersPolymers consist of many repeating monomer units in long chains. A polymer is analogous to a necklace made from many small beads (monomers).  
Another common name for many synthetic polymers is plastic which comes from the Greek word "plastikos", suitable for molding or shaping. Many objects in daily use from packing, wrapping, and building materials include half of all polymers synthesized. Other uses include textiles, TV's, CD's, automobiles, and many other all are made from polymers.
A quarter of the solid waste from homes is plastic materials - some of which may be recycled as shown in the table on the left.
Types of Polymers: There are many types of polymers including synthetic and natural polymers.
Natural polymers are discussed in other web pages and include:
Other Natural polymers: 
  • Rubber (hydrocarbon base).
  • Silicones (alternating silicon and oxygen).





Classification of Polymers:
Homopolymers - consist of chains with identical bonding linkages to each monomer unit. This usually implies that the polymer is made from all identical monomer molecules. 

These may be represented as : -[A-A-A-A-A-A]-
Copolymers - consist of chains with two or more linkages usually implying two or more different types of monomer units.

These may be represented as : -[A-B-A-B-A-B]-
A separate kind of chain structure arises when more that one type of monomer is involved in the synthesis reaction. These polymers that incorporate more than one kind of monomer into their chain are called copolymers. There are three important types of copolymers. A random copolymer contains a random arrangement of the multiple monomers. A block copolymer contains blocks of monomers of the same type. Finally, a graft copolymer contains a main chain polymer consisting of one type of monomer with branches made up of other monomers. The following diagram displays the different types of copolymers.
Polymers are further classified by the reaction mode of polymerization, these include:
Addition Polymers - the monomer molecules bond to each other without the loss of any other atoms. Alkene monomers are the biggest groups of polymers in this class.
There are three significant reactions that take place in addition polymerization: initiation (birth), propagation (growth), and termination (death)
Condensation Polymers - usually two different monomer combine with the loss of a small molecule, usually water. Polyesters and polyamides (nylon) are in this class of polymers. Polyurethane Foam in graphic.
Classification based upon the physical property related to heating:
Thermoplastics - plastics that soften when heated and become firm again when cooled. This is the more popular type of plastic because the heating and cooling may be repeated. Thermosets - plastics that soften when heated and can be molded, but harden permanently. They will decompose when reheated. An example is Bakelite, which is used in toasters, handles for pots and pans, dishes, electrical outlets and billiard balls.
Makromolekul adalah molekul yang sangat besar. Polimer baik itu alami maupun sintetik merupakan makromolekul, misalnya hemoglobin. Beberapa senyawa non-polimer juga ada yang termasuk ke dalam makromolekul, misalnya lipid. Bagaimanapun juga, sistem jaringan atom besar lainnya seperti ikatan kovalen logam tidak dapat dikatakan sebagai makromolekul. Istilah makromolekul ini pertama kali diperkenalkan oleh pemenang hadiah nobel Hermann Staudinger sekitar tahun 1920an.

Biopolimer, juga dikenal sebagai polimer organik, ialah polimer alami. Pati, protein dan peptida, serta DNA dan RNA ialah contoh biopolimer, di mana unit monomernya berturut-turut adalah glukosa, asam amino, serta asam nukleat. Komposisi kimia tepat dan urutan di mana unit-unit disusun dinamakan struktur utama polimer. Banyak biopolimer "berlipat" menjadi bentuk-bentuk tertentu, yang dapat menentukan fungsi biologi biopolimer. Biologi struktural adalah bidang penyelidikan bentuk-bentuk biopolimer.

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