In Situ Quantitative ¹H NMR Monitoring of Monomer Consumption:  A Simple and Fast Way of Estimating Reactivity Ratios

Abstract

The copolymerization reactions of acrylic systems of biomedical interest, 2-hydroxyethyl methacrylate (HEMA)/2-acrylamido-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide (DMAA)/AMPS, have been analyzed by 1H NMR. A new methodology is described for the determination of the reactivity ratios based on the quantitative in situ NMR analysis in the course of the copolymerization reaction. The methodology uses the continuous change of the intensity of resonance signals assigned unambiguously to the monomers participating in the polymerization reaction with the reaction time at a given temperature. The evaluation of the monomer concentrations leads to the determination of the instantaneous feed molar fractions and the reactivity ratios, by using a solution of the differential copolymerization equation which describes the terminal model described by Mayo and Lewis. Two approaches to obtain the reactivity ratios by nonlinear fitting of the experimental data to this integrated form are described. The first incorporates the initial conditions as third parameter in the optimization (the values obtained are r HEMA = 6.81 and r AMPS = 0.116 for the HEMA−AMPS system and r DMAA = 1.50 and r AMPS = 0.40 for DMAA−AMPS), and the second uses different points as initial conditions in the integrated equation (obtaining r DMAA = 1.53 and r AMPS = 0.36, in very good agreement with the obtained by the first method). These values are in good agreement with those described in the literature and with data for copolymers prepared at low conversion analyzed by standard methods.

Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity

“…From the conversion of the monomer, we determined the reactivity ratios using the integrated form of the copolymerization equation (terminal model) for the three reactions 38 , as described in Supplementary Fig. 1b.…”

Copolymers of N-(4-bromophenyl)-2-methacrylamide with 2-hydroxyethyl methacrylate

“…The r 1 and r 2 values from methods such as F-R, K-T, EKT and RREVM are presented in Table 2. The microstructure of a polymeric material plays an important role in the behavior of the material toward a variety of biological systems and could be especially important in copolymerizations with monomers of different reactivities [18]. This implies that the type of copolymer prepared (i. e., random, alternating, or block) may affect the response elicited by the material in a biological environment.…”

“…This implies that the type of copolymer prepared (i. e., random, alternating, or block) may affect the response elicited by the material in a biological environment. Monomer reactivity ratios provide a tool for estimating the average compositions of copolymers and the relative placement of reactive or functional monomers along the polymer chain [18]. The reactivity ratio values are also valuable because the final composition of a copolymer is not simply dependent on the amounts of the two monomers present; this is especially true for monomers displaying substantial differences in the copolymerization rates.…”

“…The first weight loss region appears around 50-150°C associated with dehydration of partially degradated of amide groups; secondary weight loss occurring around 150-300°C can be related to possible decarboxylation and/or other reactions of side-chain units. At last weight loss around 315-450°C indicates the main-chain degradation reactions and breakdown of the polymer backbone [18]. Copolymers show a high thermal stability which increases with increasing HEMA content in copolymers.…”

Reactivity ratios and copolymer composition evolution during styrene/dimethacrylate free‐radical crosslinking copolymerization

“…(10)]. For this purpose, the methodology proposed by Aguilar and co-workers 27 was employed. Feed composition values (f 1 , f 2 ) obtained in the range of overall conversions (P) between 0 and 0.08 were fitted to eq.…”