How to improve the heat and cold resistance of rubber, that is, to expand the range of its service temperature:

Above a certain temperature, rubber loses elasticity due to aging; Below a certain temperature, rubber loses elasticity due to vitrification.

1. Improve high temperature aging resistance and heat resistance

(1) Change the main chain structure of rubber

(a) The main chain does not contain double bonds;

(b) Butyl rubber (isobutylene and isoprene) with less double bonds in the main chain;

(c) Polysulfide rubber containing S atoms in the main chain;

(d) Polyether rubber containing O atom in the main chain;

(e) Dimethylsilicone rubber with non carbon atoms on the main chain;

(2) Change substituent structure

*Rubber with electron donor substituents is easy to oxidize: natural rubber, styrene butadiene rubber

*Rubber with electron absorbing substituents is not easy to oxidize: neoprene and fluororubber

(3) Change the structure of cross-linked chain

Principle: the crosslinking chain with less sulfur has greater bond energy and good heat resistance. If the crosslinking bond is C-C or C-O, the bond energy is greater and the heat resistance is better. (ZnO vulcanization crosslinking bond for neoprene is - C-O-C -, peroxide or radiation crosslinking for natural rubber is - C-C -)

2. Reduce glass transition temperature and improve cold resistance

Any measure to increase the activity of molecular chains and weaken the interaction between molecules will reduce the glass transition temperature,

Any measure to reduce the crystallization ability and crystallization speed of polymer will increase the elasticity and cold resistance of polymer (because crystallization is the regular arrangement of polymer chains or segments, which will greatly increase the intermolecular interaction, increase the strength and decrease the elasticity of polymer)

(1) Add plasticizer: weaken the intermolecular force

For example, the tg-62 ℃ of chloroprene gum can be increased by adding dibutyl kuilate TG (- 80 ℃);

If Trimethylphenol phosphate (- 64 ℃) is used, tg-57 ℃ can be made.

It can be seen that the plasticizing effect is not only related to the structure of plasticizer, but also related to its own TG. The lower the of plasticizer, the lower the of plasticized polymer.

(2) Copolymerization

Polystyrene has large side groups, so it is difficult and rigid to rotate in the main chain. TG is higher than room temperature, but styrene butadiene rubber after copolymerization is - 53 ℃, polypropylene fine has polarity, so it is difficult and rigid to rotate in the main chain. TG is higher than room temperature. Nitrile rubber after copolymerization with butadiene and acrylonitrile is - 42 ℃

(3) Reduce polymer crystallinity

Linear polyethylene molecular chain is very flexible and TG is very low, but due to its high regularity, it is difficult for polyethylene to be used as rubber. A small non-polar substituent methyl group is introduced to destroy the regularity of polyethylene molecular chain and its crystallinity, which is ethylene propylene copolymer rubber, TG = - 60 ℃.

By destroying the regularity of the chain, the crystallinity of the polymer is reduced and the elasticity is improved, but the side effect is to damage the strength.