Simon Champ

Observations on some copolymerisations involving N-isopropylacrylamide

Abstract Free radical copolymerisations of N -isopropylacrylamide (NIPA) with acrylic acid (AA), methacrylic acid (MAA) and 2-methyl-2-acrylamidopropane sulphonic acid (AMPS) have been conducted over a range of conversions in ethanol, ethanol and water respectively. It was necessary to devise special methods for isolating the copolymers, since the common device of precipitation into a non-solvent could not be adopted here. Experimental procedures necessary to overcome rapid attainment of high conversion, crosslinking and irreproducibility for the systems containing AA and MAA as comonomers are discussed. For all three systems compositions of linear copolymers were determined by conductometric titration vs. aq. NaOH. The monomer reactivity ratios ( r ) were calculated from the initial monomer feed composition, the fractional conversion and the copolymer composition, by means of the extended Kelen-Tudős method. The 95% confidence ellipses were also computed. The results are: r 1 =14.0±1.9 and r 2 =0.07±0.09 for NIPA(1)/AA(2), r 1 =10.2±1.4 and r 2 =0.01±0.03 for NIPA(1)/MAA(2) and r 1 =2.4±0.8 and r 2 =0.03±0.02 for NIPA(1)/AMPS(2). Hence none of these systems undergoes azeotropic copolymerisation. The extent of compositional heterogeneity has been demonstrated by computed curves of instantaneous copolymer composition at different stages of conversion. Examination of the rather limited literature on linear copolymerisations involving NIPA discloses possible flaws and uncertainties in some of the procedures employed.

Hydrogen‐Bonded Molecular Ribbons as Templates for the Synthesis of Modified Mineral Phases

The combination of two important organizational principles, that is surfactant monolayer assembly and the triazinetriamine - triazinetrione hydrogen-bonding molecular ribbon, produces a hybrid assembly which is used as a novel template to control the orientation and morphology in the crystallization of calcium carbonate.

New superabsorbent thermoreversible hydrogels

Abstract The novel octafunctional crosslinker glyoxal bis(diallylacetal) (GLY) was employed in the synthesis of thermosensitive hydrogels of ( N -isopropylacrylamide- co -acrylic acid). The resultant chemically crosslinked networks show levels of swellability in water significantly higher than those previously reported for such copolymers crosslinked by N , N ′-methylene bisacrylamide (BIS) whilst retaining the ability to deswell at temperatures above the lower critical temperature ( T c ). Additionally, the replacement of BIS by GLY yielded a decrease in the T c of the hydrogels, indicating that incorporation of GLY into the polymer network increases the hydrophobicity of the network; this is consistent with the structure of GLY and its sparing solubility in water.

The ion-pair reinforced, hydrogen-bonding molecular ribbon

A hydrogen transfer potential is programmed into the components of a self-organising system, and cocrystallisation gives a molecular ribbon in which a triple hydrogen-bonding motif is reinforced by ion pairing.