Copolymers of Styrene with Aziridines

Polymerization of styrene in the presence of HC104 at ambient temperatures proceeds with considerable transfer i.e., several tens of macromolecules are formed from one initiator molecule 103). Therefore, there remains a small proportion of chains with reactive end-groups. 

At a sufficiently low temperature (e.g. —78 °C) polymerization proceeds differently after an initial fast period to limited conversions, the polymerization proceeds slowly ( 2 hrs) to completion. This behaviour was explained assuming that polystyryl cations are the growing species during the initial fast period of polymerization. Combination with the perchlorate anions converts the macrocations to polystyryl esters that are unable to further react with styrene in line with Szwarc we may 

Styrene (2-5vol% in CH2C12) was polymerized with HC104 (0.01 mole l-1) and the system was kept at —78 °C a few minutes. Then, the second monomer 1 -/-butyl aziridine (TBA) or l(2-phenylethyl)-2-methyl aziridine (PEMA) was added to the solution 104). The mixture was stored at —78 °C for several hours and then warmed up to room temperature. A sample of polystyrene solution was taken before the addition of aziridine and its Mn was determined. A block copolymer was isolated and its Mn was determined separately. GPC traces of both products showed unimodal molecular weight distributions. The GPC trace of the copolymer indicated a considerable molecular weight increase, as compared to the homopolymer. Two block copolymers were obtained with Mn = 4,100 (starting from polystyrene of Mn = 800) and Mn = 7,100 (from polystyrene of Mn = 1,800). 

Copolymers with high (e.g., 88 %) TBA content were water soluble and homopolystyrene could not be extracted by CCl or CH2C12. 

When the polymerization mixture was heated for a few minutes after the addition of TBA, a bimodal molecular weight distribution was obtained. Part of the polystyrene remained unreacted probably as a result of incomplete initiation of aziridine. The polystyryl ester may decompose e g. by proton transfer before it can initiate TBA polymerization. Copolymer formation may proceed by the following route  

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