SYNTHESIS AND CHARACTERIZATION OF MACROCYCLIC POLYSTYRENE BLOCK-COPOLYMERS

The synthesis of macrocyclic polystyrene-block-poly(2-vinylpyridine) a nd macrocyclic polystyrene-block-poly(dimethylsiloxane) was carried ou t by initiation of 2-vinylpyridine (2VP) and hexamethylcyclotrisiloxan e (D3) by difunctional living polystyryllithium followed by coupling w ith 1,4-bis(bromethyl)benzene (1,4-DBX) and dichlorodimethylsilane ( C l2SiMe2), respectively. A small portion of the living ABA precursors w ere protonated to serve as isobaric linear precursors.The linear and m acrocyclic block copolymers were characterized by size-exclusion chrom atography (SEC). The ratios of apparent cyclic/linear SEC molecular-we ight maxima versus,degree of polymerization (DP) show increases with d ecreasing DP varying from 0.70 +/- 0.03 at high DP greater-than-or-equ al-to 200 to 0.78 +/- 0.044 at low DP (less-than-or-equal-to 60) where as that of the linear ABA block copolymers decreased. Increases in gla ss transition temperature (Tg) were also observed for the cyclic PS-b- PDMS copolymers with respect to the isobaric linear precursors.The mac rocycles were characterized by H-1 and C-13 NMR and in the case of mac rocyclic PS-b-PDMS by Si-29 NMR as well. Broadening in the NMR absorpt ions of the macrocyclic block copolymers is general and is similar to that observed for the homopolymers. Differential scanning calorimetry (DSC) analysis of the PS-b-P2VP macrocycles shows increases in Tg at l ower molecular weight as was observed for the PS and P2VP macrocycles.