Synthesis and solution properties of comb polystyrenes

A new method for the synthesis of comb shaped polystyrenes of predetermined structure is described. Silicon-chlorine bonds are introduced into the backbone polystyrene by reaction of SiMe2Cl2 with hydrolysed styrene/vinyl acetate copolymers and coupled with polystyryl-lithium in benzene. From a common backbone polymer a series of comb polymers are prepared that have a constant number of branches but vary in branch length. The MwMn of the whole comb polymers is about 1.3. The comb polymers with high branch density show θ (A2) temperatures lower than that for linear polystyrene. The radius of gyration at θ (A2) [〈S2〉θ (A2)] is always larger than calculated from random flight statistics. For comb polymers with 20–30 branches 〈S2〉θ (A2)〈S2〉0,bb increases with λ−0.46 where λ is the fraction of polymer in the backbone. The intrinsic viscosities of the comb polystyrenes at θ (A2) are equal to that of the parent backbone polymer when λ > 0.25 and increase only little when λ becomes equal to 0.1. Similar behaviour is found in toluene. Intrinsic viscosities in cyclohexane at 35°C show a complex pattern because of the θ-temperature variation.