Question

Answer about anionic ‘living’ polymerization:
(a) What number-average molecular weight (Mn) polystyrene would be formed by polymerization of 10 g styrene with 0.1 g of butyl lithium, under complete living polymer system?

(b) Suggest three different ways to synthesize polystyrene-b-polybutadiene-b-polystyrene (SBS) tri-block copolymer with controlled block length.

Answer 1

Solution (a) :

In this experiment styrene will be polymerized anionically by using Bu-Li+ as the initiator.

For an initiator such as butyl lithium which initiates a polymer growing from one end, the number average molecular weight (or Xn, the number average degree of polymerization) is a linear function of conversion for a living polymerization,

= gram of monomer / moles of initiator

,

Solution (B)

Method's for synthesis of  polystyrene-b-polybutadiene-b-polystyrene (SBS) tri-block copolymer with controlled block length:

(1) Anionic copolymerization ( Polar monomers, nonpolar cyclohexane was used as solvent and only trace amounts tetrahydrofuran (THF) was used as a polar regulator.the produce of tri-block copolymers with PMMA block of different lengths confirmed this synthesis method controlled for definite structures, fewer side reactions and a appropriate temperature.And ths method is also useful for commocial scale).

(2) Group transfer polymerization

(3) Metal-free anionic polymerization

Last two methods are not economcal as industry point of view, because of high cost, inherent termination reaction, incomplete initiation efficiency, etc.

For Detailed Knowledge,

Li, Zheng, et al. "A controlled synthesis method of polystyrene-b-polyisoprene-b-poly (methyl methacrylate) copolymer via anionic polymerization with trace amounts of THF having potential of a commercial scale." RSC advances 7.16 (2017): 9933-9940.