Chain transfer of polymer in radical polymerization

Abstract

Chain transfer with polymethylacrylate was determined by measuring chain transfer constants with model substances resembling part of polymer chain with P = 1–3 and extrapolating to higher P. The found value, 5 × 10−5, is much less than expected for an explanation of gel formation in the polymerization of methyl acrylate.

Measurement of Chain Transfer Constants to Polymer Using Oligomers and Model Compounds: Chain Transfer to Poly[11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl acrylate] in Radical Polymerization

“…However, the fact that the chain transfer constants to both model compounds and the oligomer are essentially equal demonstrates that the chain transfer event cannot be occurring by abstraction of the methine hydrogens from the polymer backbone as in nonmesogenic polyacrylates; i.e., if chain transfer involved the polymer backbone, the chain transfer constant to the oligomer and to 11-(4‘-cyanophenyl-4‘ ‘-phenoxy)undecyl isobutyrate would be greater than that to the propionate since the latter cannot generate a tertiary radical. In addition, the chain transfer constants are at least 1 order of magnitude higher than values of C P for nonmesogenic polyacrylates. ,, Chain transfer must therefore involve the mesogenic side chains, although we have not been able to identify the chain transfer event by NMR spectroscopy.…”

“…Alternatively, since the chain transfer constants to polymer are per repeat unit of the polymer, rather than per polymer chain, one can estimate C P using eq 3 and model compounds corresponding to one ( C p = C X ) or more repeat units of the polymer. For example, Lím and Wichterle measured the chain transfer constants to methyl isobutyrate ( C X = 1.4 × 10 -4 ), dimethyl 2,4-dimethylglutarate ( C X = 4.5 × 10 -5 ), and trimethyl heptane-2,4,6-tricarboxylate ( C X = 5.4 × 10 -5 ) as model compounds of poly(methyl acrylate) (PMA). In their experiments, the chain transfer constant to the model unimer was greater than those of the model dimer and trimer, and they therefore assumed that the chain transfer constant to PMA is similar to that of the trimer, i.e., C P = 5 × 10 -5 , although this is an order of magnitude lower than accepted values of C P for polyacrylates. , …”

Superlubricity of pH-responsive hydrogels in extreme environments

“…Hydrogels, a network of crosslinked hydrophilic polymer chains swollen in water, are often used as synthetic analogues of living tissue due to their comparable mechanical properties and inherent tunability. Since the first hydrogel was synthesized by Wichterle and Lím in their seminal work ( Lím and Wichterle, 1958 ; Wichterle and Lím, 1960 ), there has been significant interest in potential tribological applications. Hydrogels are often used as anti-biofouling materials and coatings for biomedical devices that require low friction interfaces such as catheters ( Yong et al, 2019 ).…”