Polymeranalytik: Strukturbestimmung von Makromolekülen mit der Gelpermeations‐Chromatographie

2005

Comb-shaped polystyrenes with UV-labeled side chains were synthesized and analyzed by SEC with on-line light scattering and viscometry detection. The introduction of the UV label allows for a model-independent determination of the number of grafts within each SEC slice and therefore the calculation of the expected contraction factors, g = 〈R g , br 2〉/〈R g ,lin 2〉 and g ‘ = [η]br/[η]lin. Using molecular weight sensitive detectors, the contraction factors were determined experimentally and compared to the expected ones. It was found that the experimentally determined g values are larger than the ones calculated on the basis of the Gaussian chain assumption. Therefore, the calculation of the number of branches based on theoretically expected contraction factors is not feasible. Attempts to include corrections for excluded-volume effects failed. For the exponent ε of the relationship g‘ = g ε a value close to ε = 1 was found, in contradiction with the expectations from the Flory−Fox and Zimm−Kilb relations. It was observed that the intrinsic viscosities of the combs are close to the intrinsic viscosities of the parent backbone polymer itself, allowing to use this empirical relationship for the determination of the amounts of grafts present in the polymer.

Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Synthesis and Characterization of Comb-Shaped Polymers by SEC with On-Line Light Scattering and Viscometry Detection

Radke

2005

“…Raw data were processed using PSS WinGPC V4.02 software. Universal calibration curves − [η] M = f ( V e ) were constructed using narrow PMMA standards in THF. Since this universal calibration curve is valid for any polymer structure, absolute molecular weights can be determined within an error range of 10%.…”

Section: Methodsmentioning

confidence: 99%

Kinetic Investigation of Self-Condensing Group Transfer Polymerization

Simon

2004

Hyperbranched methacrylates were synthesized by self-condensing group transfer polymerization (SCGTP) of 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) and characterized by multidetector SEC and 13C NMR. Depending on the reaction conditions, molecular weights up to M w = 38 000 at a polydispersity of M w/M n ≈ 3.8 could be obtained. Kinetic measurements showed that cyclization, i.e., the intramolecular reaction of a functional group with the polymer's vinyl group, limits the molecular weights and lowers the polydispersity. A maximum degree of branching of DB ≈ 0.4 and a reactivity ratio of the propagating and initiating groups in the range of 13 < r < 23 were determined. Slow addition of MTSHEMA to the monofunctional initiator, 1-methoxy-3-(trimethylsilyloxy)-2-methyl-1-propene (MTS), enabled the control of molecular weights and decreased the polydispersity to M w/M n ≈ 2.8. The addition of methyl methacrylate (MMA) to a living MTSHEMA core yielded a “hyperstar” polymer.

“…Linear PIBHEMA as reference material for NMR studies 13 was prepared according to the literature. 12 Universal calibration curves, [36][37][38] [η]M ) f(Ve), were constructed using narrow PMMA standards of different molecular weights in THF. Since this universal calibration curve is valid for any polymer structure, absolute molecular weights can be determined by this method within an error range of 10%.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of Hyperbranched and Highly Branched Methacrylates by Self-Condensing Group Transfer Copolymerization

Simon

2001

We report a study of the self-condensing group transfer copolymerization of the initiator−monomer (“inimer”) 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) with methyl methacrylate (MMA). The highly branched polymethacrylates were characterized by multidetector SEC and NMR. Kinetic measurements show that cyclization, i.e., the intramolecular reaction of an active center with the vinyl group of the polymer, limits the molecular weights and lowers the polydispersity. Depending on the comonomer ratio, γ = [MMA]0/[MTSHEMA]0, molecular weights up to M w = 240 000 at a polydispersity of M w/M n ≈ 3 could be obtained. The Mark−Houwink exponent of these branched copolymers depends on the comonomer ratio and is significantly lower (0.45 ≥ α ≥ 0.23) than linear PMMA (α = 0.69). Only 4% of inimer are necessary to lower the Mark−Houwink exponent to half the value of linear PMMA. Using slow addition of the comonomer mixture to the monofunctional initiator 1-methoxy-3-(trimethylsilyloxy)-2-methyl-1-propene (MTS) enables control of the molecular weights and decreases the polydispersity to M w/M n ≈ 1.6. Copolymerization of MTSHEMA with tert-butyl methacrylate followed by acid-catalyzed hydrolysis of the tert-butyl groups yields highly branched poly(methacrylic acid).