Synthesis and characterization of macrocyclic poly(.-methylstyrene)

Abstract

The synthesis is described of macrocyclic poly( -methylstyrene) (PAMS) by the lithium naphthalide initiated polymerization of AMS followed by high dilution end to end coupling with 1,4-bis(bromomethyl)benzene (DBX). The cyclization is carried out by simultaneous addition of tetrahydrofuran solutions of the PAMS dianion and DBX at about -100ºC. A sample of the matching linear PAMS is obtained by protonation of the PAMS dianion. The purified cycles are obtained by fractional precipitation that is monitored by size exclusion chromatograhy. A careful study of the coupling reactions carried out at high concentrations indicates that coupling is efficient and this is borne out by the ratios (<G>) of apparent molecular weights (MW's) of cycles and matching linear polymers. The <G> values of the cycles tend to vary with MW in the same manner as was demonstrated for polystyrene and other vinyl polymers and increase from around 0.74 at MW of about 30000 to values of around 0.82 at MW of about 2500. A higher apparent <G> value was observed for a very low MW PAMS but this sample could not be purified and analyzed adequately. As was also observed for other macrocyclic vinylpolymers, the glass transition temperatures of the cycles are MW independent above MW of about 5000 but decrease sharply at lower MW's.

Cyclic polymers: Synthetic strategies and physical properties

“…299 Therefore, the T g s of the cyclic species were higher than those of the linear analogues for M n s < 10 kDa. These findings were in agreement with the aforementioned properties of other cyclic polymers, [62][63][64][65][66]253,274 but surprisingly the T g s of cyclic oligosiloxanes (M n s < 4 kDa) increased above T g 1.…”

“…This combination of properties allowed for a separation of the quasi monomeric cycles (containing one PS chain) from the higher cyclic or linear polycondensation products by means of size-exclusion chromatography (SEC). [10][11][12][13][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] The optimum iMC was calculated via eq 5, 13 which correlates the molecular weight of the bifunctional polymer chains with a concentration (C eq ) where rates of cyclization and chain growth are equal C eq ¼ a ¼ 1 in eq 3. For bisanionic PS of M n 10 kDa a C eq value around 10 À3 mol/L was calculated.…”

“…[62][63][64][65][66][67][68][69][70] The formulas of these monomers are summarized in Scheme 14. However, in all cases, living anionic polymerizations were used to control the molecular weight and to keep the polydispersities low.…”

“…The bulk of cyclic polymers studied by numerous research groups [57][58][59][62][63][64][65][66]73,74,89,95,253, comprised glass transition temperatures (T g s), melting temperatures (T m s), morphologies, melt viscosities, thermostabilities, and compatibilities. Cyclic PS, cyclic PEOs, and cyclic polysiloxanes were again the most widely studied cyclic polymers.…”

“…At this point, it should also be mentioned that T g measurements were, of course, not limited to cyclic PS and T g data were reported for cyclic poly(a-methyl styrene), 62 for cyclic poly(2-vinyl naphthalene), 65 and for cyclic poly(9,9-methyl-2-vinyl fluorine). 63,66 All three polymers agreed with PS in that the T g s of the cyclic oligomers having DPs > 10 were almost as high as those of high molar mass polymers, and thus, considerably higher than the T g s of the linear oligomers.…”