ABSTRACT
A dithiocarbamate chain transfer agent (CTA) based on Z-group substituted with a diphenyl amine (-NPh2 ) moiety is selected for the synthesis of statistical and diblock copolymers of ethylene and vinyl acetate via reversible addition-fragmentation chain transfer polymerization. Benefiting from the good chain growth control of polyethylene (PE), poly(vinyl acetate) (PVAc), and poly(ethylene-co-vinyl acetate) (EVA) achieved with this CTA, linear diblock copolymers of the type EVA-b-PE, EVA-b-EVA, and PVAc-b-EVA are successfully synthesized. A three-arm EVA star is additionally obtained starting from a trifunctional dithiocarbamate CTA.
Subject(s)
Ethylenes , Polymers , Polyethylene , Polymerization , Vinyl CompoundsABSTRACT
Poly(ethylene oxide) (PEO) with dithiocarbamate chain ends (PEO-SC(=S)-N(CH3 )Ph and PEO-SC(=S)-NPh2 , named PEO-1 and PEO-2, respectively) were used as macromolecular chain-transfer agents (macro-CTAs) to mediate the reversible addition-fragmentation chain transfer (RAFT) polymerization of ethylene in dimethyl carbonate (DMC) under relatively mild conditions (80 °C, 80â bar). While only a slow consumption of PEO-1 was observed, the rapid consumption of PEO-2 led to a clean chain extension and the formation of a polyethylene (PE) segment. Upon polymerization, the resulting block copolymers PEO-b-PE self-assembled into nanometric objects according to a polymerization-induced self-assembly (PISA).
ABSTRACT
Aromatic xanthates and dithiocarbamates were used as chain-transfer agents (CTAs) in reversible addition-fragmentation chain-transfer (RAFT) polymerizations of ethylene under milder conditions (≤80 °C, ≤200â bar). While detrimental side fragmentation of the intermediate radical leading to loss of living chain-ends was observed before with alkyl xanthate CTAs, this was absent for the aromatic CTAs. The loss of living chain-ends was nevertheless detected for the aromatic xanthates via a different mechanism based on cross-termination. Narrow molar-mass distributions with dispersities between 1.2 and 1.3 were still obtained up to number average molar masses Mn of 1000â g mol-1 . The loss of chain-ends was minor for dithiocarbamates, yielding polyethylene up to Mn =3000â g mol-1 with dispersities between 1.4 and 1.8. While systems investigated showed significant rate retardation, the dithiocarbamates are the first CTAs giving polyethylene with a high livingness via RAFT polymerization.
ABSTRACT
The first successfully controlled radical polymerization (CRP) of ethylene is reported using several organotellurium chain-transfer agents (CTAs) under mild conditions (70 °C, 200â bar of ethylene) within the concept of organotellurium-mediated radical polymerization (TERP). In contrast to preceding works on CRPs of ethylene applying reversible addition-fragmentation chain-transfer (RAFT), the TERP system provided a high livingness and chain-end functionalization of polyethylene chains. Molar-mass distributions with dispersities between 1.3 and 2.1 were obtained up to average molar masses of 5000â g mol-1 . As in the RAFT system, the high reactivity of the growing polyethylenyl radical led to an inherent side reaction. For the presented TERP systems, however, this side reaction did not result in dead chains, while it could even be effectively suppressed by a good choice of the CTA.
ABSTRACT
The impact of band-broadening (BB) on the molar-mass determination of synthetic polymers via size-exclusion chromatography (SEC) is systematically studied. BB is simulated using the exponentially modified Gaussian (EMG) model, which combines the two inherent and distinct characteristics contributing to BB in SEC: symmetric Gaussian broadening and asymmetric skewing. It is demonstrated that BB both during the measurement of the analyte itself and during the calibration process has an individual impact on molar-mass determination. In this context, particularly skewing leads to a chain-length-dependent underestimation of molar masses, with deviations of the apparent from the true ones of only a few percent for low molar masses to up to 20% for high ones for reasonable extents of BB. The impact is shown to be independent of the shape of the analyte⬢s molar-mass distribution (MMD) and affects broad and multimodal MMDs similarly to narrow and unimodal ones. As a consequence, strategies are presented for a comprehensive quantitative correction of the observed effects, which may find their application in refined SEC software packages. The potential impact of the findings on general conceptions of repeatability and reproducibility within SEC experiments is discussed.
