Policloropreno

Polychloroprene (CR), chloroprene rubber
Applications Among the speciality elastomers polychloroprene [poly(2-chloro-1,3butadiene)] is one of the most important with an annual consumption of nearly 300 000 tons worldwide. First production was in 1932 by DuPont (“Duprene”, later “Neoprene”) and since then CR has an outstanding position due to its favourable combination of technical properties. CRis used in different technical areas, mainly in the rubber industry (ca.61%), but is also important as a raw material for adhesives (both solvent based and water based, ca.33%) and has different latex applications (ca.6%) such as dipped articles (e.g. gloves), moulded foam and improvement of bitumen. The typical delivery form of CR is “chips” (picture 1), a consequence of the special productionprocess (see below).

Picture 1: Typical polychloroprene “chips”

Picture 2 : Rubber applications (belts, hoses)

Application areas in the elastomer field are widely spread, such as moulded goods, cables, transmission belts, conveyor belts, profiles etc. (See picture 2) . Rubber Properties CR is not characterised by one outstanding property, but its balance of properties is unique among thesynthetic elastomers. It has: Good mechanical strength High ozone and weather resistance Good aging resistance Low flammability Good resistance toward chemicals Moderate oil and fuel resistance Adhesion to many substrates Polychloroprene can be vulcanized by using various accelerator systems over a wide temperature range.

Chemistry and Manufacture From the beginning until the 1960s, chloroprenewas produced by the older “acetylene process”. This process has the disadvantages of being very energyintensive and having high investment costs. The modern chloroprene process, which is now used by nearly all producers, is based on butadiene, which is readily available. Butadiene is converted into the monomer 2-chlorobutadiene-1,3 (chloroprene) via 3,4-dichlorobutene-1. In principle it ispossible to polymerize chloroprene by anionic, cationic and ZieglerNatta catalysis techniques. However, because of product properties and economic considerations, free radical emulsion polymerization is used exclusively today. It is carried out in a commercial scale using both batch and continuous processes. A production flow diagram is shown in Picture 3 :

Schematic of the production ofpolychloroprene
Sulfur Acid

Emulsifier

C D

F

Modifier unreacted Chloroprene monomer

G

M

Water

B
M M

L E H J I K

A

A) Polymerization reactor; B) Stripper; C) Purification; D) Neutralization; E) Peptization; F) Rotating cooling drum; G) Coagulation by freezing H) Latex concentration; I) Chopping machine; J) Dusting machine; K) Roping machine; L) Dryer; M) Washing

Picture 3: Production scheme With the aid of radical initiators, chloroprene in the form of an aqueous emulsion is converted into homopolymers or, in the presence of comonomers into copolymers. The polymerization is stopped at the desired conversion by the addition of a short stopping agent. The latex is freeze-coagulated on large, refrigerated revolving drums, from which it is drawn as a thin sheet. Afterwashing and drying, the sheet is formed into a rope and then chopped to form the familiar chips (Picture 1) or granules.

Cl n H 2C C C H CH 2

R

.
C H2

Cl C C H

H2 C
n

1

H2 C

C C

2

3

H C H2
4

1

H2 C

C C

2

3

H2 C H

4

Cl

Cl 1,4 -cis

1,4 -trans

H H 2 3C C 4 C 2
1CH 2

1

H 2 Cl C C2
3CH 4

Cl

CH 2 1,2

3,4

Structureand structural units The basic polymerization scheme leads to incorporation of the monomer into a polymer consisting of different structural units (Picture 4) : Picture 4 : Basic polymerization scheme and structural units The physical, chemical and rheological properties of the different grades of commercial polychloroprene are dependent on the ability to change the molecular structure by...