Runsheng Mao

A new linear method to calculate monomer reactivity ratios by using high conversion copolymerization data: terminal model

Abstract A new linear method of calculation of monomer reactivity ratios is presented for copolymerizations up to very high conversion. It is a linear least-squares method involving several interations. The basis of calculation is the differential copolymerization equation and the Kelen-Tudős (K-T) method. The principle and the calculation of computer-simulated data indicate that this new method can correct completely the systematic errors due to high conversion. Calculation using data in the literature shows that this method can be applied in any real systems. The comparison of K-T and extended K-T methods is also discussed.

Reactivity ratios in copolymerizations involving allyl methacrylate

Abstract The copolymerizations of allyl methacrylate (AMA) with methyl methacrylate (MMA) and of AMA with N-vinyl-2-pyrrolidone (VP) have been effected in bulk by γ-irradiation to various stages of fractional conversion θ extending over a wide span of θ. Addition of n-heptane isolated the crosslinked copolymer. FT i.r. analysis on the supernatant solution yielded the composition of unreacted monomer mixture, which was used in conjunction with θ and the composition of initial feed to determine the reactivity ratios (r) via an iterative procedure involving a simplex algorithm, yielding AMA(1) MMA(2) r1 = 1.55 ± 0.16, r2 = 0.99 ± 0.19 and AMA(1) VP(2) r1 = 1.408 ± 0.074, r2 = 0.401 ± 0.044. For the system AMA VP , analysis of crosslinked copolymer (via nitrogen analysis) was also possible and manipulation of the data by three modern procedures afforded good agreement with the values of r1 and r2 obtained by analysis of monomer mixture alone.

Quantitative analysis of copolymers by FTIR

Quantitative analysis of copolymers is described in detail for a series of copolymers of 2-[(phenylamino)carbonyl]oxyethyl methacrylate and 1-methyl-2-phenoxyethyl methacrylate. Particular emphasis is placed on aspects optimising the accuracy of the technique. Thus the irreproducibility resulting from the use of cast films is overcome when using solutions. The criteria of most appropriate solvent are established. Very satisfactory calibration is afforded by blends of the two homopolymers in solution, thus providing an absolute calibration and obviating the use of model compounds or copolymers of known composition.

A new linear method to calculate monomer reactivity ratios by using high-conversion copolymerization data: penultimate model with r2=0

Abstract The new iterative linear least-squares method for calculation of monomer reactivity ratios for the terminal model, proposed by Mao and Huglin, is applied to the penultimate model system with r 2 =0. The principle and the calculation procedure are similar for the two different models. All advantages of the new method when applied to the terminal model, i.e. fast convergence, exact calculation and the fact that any initial estimation of reactivity ratios always leads to the same correct results, remain valid when applied to the penultimate model. The superiority of the new method over the Kelen-Tudos and extended Kelen-Tudos procedures is even more evident for the penultimate model than for the terminal model.

Characteristics of copolymerizations involving dimethylacrylamide and swelling behaviour of the copolymers in water

Abstract The free radical copolymerizations of dimethylacrylamide (DMA) with ethylene dimethacrylate (EDMA) and of DMA with methyl methacrylate (MMA) have been conducted over a wide range of conversion. Compositions of resultant crosslinked poly(DMA- co -EDMA) and of linear poly(DMA- co -MMA) were determined by nitrogen analysis and FT i.r., respectively. Appropriate modern procedures applied to the data yielded reactivity ratios of r DMA = 0.51 ± 0.15, r MMA = 2.07 ± 0.19 and r DMA = 0.9 ± 0.2, r EDMA = 1.8 ± 0.6, the latter pair being obtained neglecting possible reactivity of pendant double bonds. γ-Irradiation of DMA/MMA mixtures both in the absence and presence of EDMA yielded highly swellable crosslinked xerogels. The equilibrium water content of the hydrogels increased with increase of DMA in copolymer and with decreasing content of EDMA. Over the range of swelling temperature examined, 280–338 K, the swelling was found to be exothermic. At comparable molar compositions, these materials exhibited higher water contents than the corresponding hydrogels containing N -vinyl-2-pyrrolidone in place of DMA.

Dynamic light scattering from polymer gels: spring-rotor model

Dynamic light scattering behaviour in the form of periodic oscillating correlation functions has been found from measurements on both physically and chemically crosslinked hydrogels. The former were aqueous methyl cellulose at the thermal gelation temperature and the latter were poly(N,N-dimethylacrylamide-co-methyl methacrylate-co-ethylene dimethacrylate) at swelling equilibrium in water. In order to explain the oscillating behaviour, a spring-rotor model is proposed in which the molecular motions inside a gel are modelled as vibrations of springs having various frequencies. These frequencies are equivalent to the rotational frequencies when the free rotor theory was used to process the oscillating correlation functions by a modified CONTIN computer program. The validity of this model is supported by experimental data in three ways. (1) The model fits the experimental data almost perfectly. (2) The main peak positions of the obtained frequency distribution are not affected by the scattering angle. (3) For the chemically crosslinked hydrogels differing only in content of ethylene dimethacrylate, the mean vibrational frequency of the gel spring is higher the shorter the spring, i.e. the lower the average molecular mass between crosslinks.

Some aspects of the copolymerization of glyceryl methacrylate with methyl methacrylate

Abstract Free radical polymerization of glyceryl methacrylate (GMA) has been conducted (i) in bulk, (ii) in moderately concentrated aqueous solution and (iii) in dilute aqueous solution. For (i) and (ii) the resultant poly(glyceryl methacrylate) (PGMA) was either insoluble or only swelled in a wide range of common solvents, whereas for (iii) solubility occurred in three polar liquids of which only one (2-methoxyethanol) was capable of dissolving poly[GMA-co-methyl methacrylate (MMA)] over the whole range of copolymer composition. The γ-ray initiated copolymerization of GMA with MMA in bulk has been effected to various conversions. On addition of di-isopropyl ether (DPE) the copolymer was isolated, and carefully calibrated Fourier transform infra-red measurements on the resultant solutions of unreacted monomer mixture in DPE afforded the composition of unreacted monomer mixture. This quantity, in conjunction with the initial feed composition and the value of the fractional conversion, was employed to calculate the monomer reactivity ratios by a specially devised non-linear least-squares program using simplex algorithm, yielding rMMA = 0.53 and rGMA = 1.61.

Synthesis and properties of poly(β-acryloxypropionic acid) hydrogels

Abstract Poly(β-acryloxypropionic acid) (PAOPA) hydrogels crosslinked by ethylene glycol dimethacrylate (EDMA) have been prepared by using both a chemical initiator and by γ-irradiation. Polymerizations were conducted in bulk and also in the presence of water. Characterizations were made by swelling, compression-strain measurements and differential scanning calorimetry (d.s.c.). The findings show the following: (a) that γ-irradiation is the preferred preparative procedure, (b) the equilibrium water content is affected by the concentration of crosslinker, but not by the content of water in the feed mixture, (c) the equilibrium water content increases with increase in the swelling temperature, and (d) there is considerable heterogeneity of crosslinking, as evidenced by calculated curves of instantaneous copolymer composition vs. fractional conversion during the crosslinking copolymerization. Similarities with and significant differences from the properties of poly(2-hydroxyethyl methacrylate) hydrogels are indicated and discussed.