Peter F. W. Simon

Molecular Parameters of Hyperbranched Copolymers Obtained by Self-Condensing Vinyl Copolymerization, 2. † Non-Equal Rate Constants

The kinetics, molecular weight averages, and the average degree of branching, DB, are calculated for the self-condensing vinyl copolymerization (SCVCP) of a vinyl monomer M with an “inimer” AB* in the case of different reactivities of active species. Emphasis is given to two limiting cases: formation of “macroinimers” occurs if the monomer M is more reactive than the vinyl groups of inimers or polymer, and “hyperstars” are formed in the opposite case. It is shown that the kinetics, the molecular weight averages, and the average degree of branching strongly depend on the relative reactivities of monomer and inimer. Comparison with experimental data shows that consistent fits of the reactivity ratios can be

Synthesis of hyperbranched poly(tert-butyl acrylate) by self-condensing atom transfer radical polymerization of a macroinimer

Using 2-hydroxyethyl α-bromoisobuty-rate as initiator, atom transfer radical polymerization (ATRP) of tert-butyl acrylate leads to poly(tert-butyl acrylate) (PtBA) with a hydroxyl group at one and a bromine atom at the other end. Esterification of the hydroxyl group of these heterotelechelic polymers with acryloyl chloride yields PtBA (M n = 3060) with a polymerizable double bond at one end and a bromine atom at the other end which can act as an initiator in ATRP (macroinimer). Self-condensing ATRP of such a macroinimer leads to hyperbranched or highly branched PtBA. The polymer was characterized by GPC viscosity measurements. Even at M w = 78800, a rather low polydispersity index of M w M n = 2.6 was obtained. A significantly lower value for the Mark-Houwink exponent (α = 0.47 compared to α = 0.80 for linear PtBA) indicates the compact nature of the branched macromolecules.

Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization of macroinimers

The molecular weight averages and the degree of branching, DB, of a hyperbranched polymer obtained by self-condensing vinyl polymerization (SCVP) of a macroinimer A-(m)γ-B* is calculated by modifying the existing equations for SCVP. The polydispersity is lowered by a factor (γ + 1), where γ is the degree of polymerization of the macroinimer. DB decreases with γ, however, at full conversion the DB of the polymacroinimer is approximately 60% higher than expected from the “dilution” of an AB* inimer with linear m units. This is the result of the existence of a new kind of branched units. The structure of polymacroinimers is similar to the pattern of a highly branched copolymer obtained by self-condensing vinyl copolymerization. However, the polydispersity index and the DB of these two processes are different, for a given molecular weight the polydispersity and the DB of the macroinimer is lower than the corresponding parameters for SCVCP at the same value of γ.

Synthesis and large scale fractionation of non-linear polymers: brushes and hyperbranched polymers

Polymer brushes with poly(methyl methacrylate) (PMMA) backbone and polystyrene side chains were synthesized by radical polymerization of ω-methacryloyl-polystyrene macromonomers. Hyperbranched PMMA was obtained by means of self-condensing group transfer copolymerization of methyl methacrylate with an initiator-monomer containing a polymerizable methacryloyl moiety and an initiating silylketeneacetal function. Both non-linear products were fractionated using the method of continuous polymer fractionation, consisting in a particular type of continuous countercurrent extraction. The combination of methyl ethyl ketone (solvent) with acetone (AC) (precipitant) turned out to be suitable for the fractionation of the polymer brushes; in case of the hyperbranched material AC served as the solvent component and methanol as the precipitant. The achieved fractionation was checked by means of GPC measurements and in case of the polymer brushes also by AFM, where the differences in the size of the macromolecules became clearly visible.