Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydr ophilic random and model networks. Cationic random networks were prepared b oth in bulk and in tetrahydrofuran (THF) using a monofunctional initiator a nd simultaneous polymerization of monomer and branch units, while a bifunct ional initiator was employed in THF for the synthesis of model networks com prising basic or acidic chains. Upon polymerization of the monomer, the lat ter initiator gives linear polymer chains with two "living" ends, which are subsequently interconnected to a polymer network by the addition of a bran ch unit. Homopolymer network star polymers were also synthesized in THF by a one-pot procedure. The synthesis involved the use of a monofunctional ini tiator and the four-step addition of the following reagents: (i) monomer, t o give linear homopolymers; (ii) branch unit, to form "arm-first" star poly mers; (iii) monomer, to form secondary arms and give "in-out" star polymers ; and, finally (iv) branch unit again, to interconnect the "in-out" stars t o networks. Different networks were prepared for which the degree of polyme rization (DP) of the linear chains between junction points was varied syste matically. For all networks synthesized, the linear segments, the "arm-firs t" and the "in-out" stars were characterized in terms of their molecular we ight (MW) and molecular weight distribution (MWD) using gel permeation chro matography (GPC). The degrees of swelling of both the random and model netw orks in water were measured and the effects of DP, pH, and monomer type wer e investigated.