Shielding effects in polymer-polymer reactions, 1 -: Z-RAFT star polymerization of four-arm stars

Shielding effects of the surrounding arms and chains on the reactive centers taking part in RAFT four-arm star polymerization following the Z-group approach are calculated by means of exact enumeration of star/chain samples prepared by Monte Carlo techniques. The shielding effect, which can be relieved when using expanded core moieties, increases with increasing chain (arm) lengths. This leads to a reduction of the contact probability according to a power law with an exponent of -0.4 to -0.45. Additionally, characteristic chain properties and shape parameters are calculated as a function of the distance between the center of the star and the end of the linear chain in order to gain deeper insight into the mechanism of contact formation preceding the actual reaction.