M. Valero

Quantitative evaluation of sequence distribution and stereoregularity in ethyl acrylate-methyl methacrylate copolymers by 13C n.m.r. spectroscopy

Abstract 13C n.m.r. spectra (75 MHz) of ethyl acrylate (A)-methyl methacrylate (M) copolymers prepared by free radical polymerization at 50°C, were analysed in terms of sequence distribution and stereoregularity of monomer units along the macromolecular chains. Ethyl acrylate and methyl methacrylate centred triad molar fractions were determined from the α-CH3, quaternary carbon and carbonyl group, resonance signals. The experimental sequence concentrations were in fairly good agreement with the values calculated from the terminal copolymerization model and Bernoullian statistics, with the statistical parameters Pij determined from the reactivity ratios and the feed composition and the coisotacticity parameters σMM = 0.24, σAA = 0.31, σ MA = σ AM = σ∗ = 0.41 .

Phenoxy blends: an approach to the miscibility by FTi.r. and chemical modification of the interacting sites

Abstract In this work, FTi.r. spectroscopy has been used in order to verify the proposed influence of the hydroxyl group, present in each monomeric unit of the phenoxy (PH) resin, in the observed miscibility of this polymer with a variety of other polymer families such as polyoxides or polyesters. Two different approaches have been used for this purpose. First, FTi.r. studies at different temperatures have been carried out on mixtures of PH with polyoxides, in order to demonstrate the higher strength of the hydrogen bonds in the mixture with respect to those existing between pure PH molecules. Second, chemical modification of the PH resin, with a controlled elimination of the repetitive hydroxyl, has been carried out intending to relate the percentage of hydroxyl substitution to the observed miscibility of PH. In the second approach, mixtures of PH and modified PH with poly(N-vinyl-2-pyrrolidone) have been studied.

Graft copolymerization of hydroxylic methacrylates and ethyl acrylate onto amylopectin

Abstract In order to achieve new biocompatible materials, graft copolymerization of mixtures of hydroxyethyl methacrylate/ethyl acrylate (HEMA/EA) and hydroxypropyl methacrylate/ethyl acrylate (HPMA/EA) onto amylopectin by ceric ammonium nitrate initiation was carried out. The influence of feed composition was studied with respect to the characteristic grafting reaction yields. Homopolymer formation decreases as the per cent of HEMA monomer increases in the feed and increases as the per cent of HPMA monomer increases in the feed. The values obtained for the percentage grafting were quite high for all the feed compositions.

Synthesis of graft copolymers of acrylic monomers on amylose: Effect of reaction time

Abstract A study has been carried out on the graft copolymerization of methyl acrylate, ethyl acrylate, ethyl methacrylate and n -butyl methacrylate on the linear fraction of starch (amylose), initiated by ceric ammonium nitrate; the results are compared with those obtained previously for methyl methacrylate and butyl acrylate. We obtained the following maximum grafting efficiency = 99% for poly(methyl acrylate), percent grafting = 338% for poly(ethyl methacrylate) and percent total conversion = 97% for poly( n -butyl methacrylate). The results are discussed.

Transesterification reactions between a polyarylate and poly(1,4-butylene terephthalate): identification of interchange units via model compounds

Abstract The reactions taking place during melt mixing of polyarylate (a copolyester of bisphenol A and an equimolar mixture of isophthalic and terephthalic acids) with poly(butylene terephthalate) (PBT) were studied by 1 H and 13 C nuclear magnetic resonance (n.m.r.). Model compounds whose structures match those of the polymers and possible interchange units were synthesized and characterized by 1 H and 13 C n.m.r. By means of this characterization, assignments of the absorptions appearing in the spectra of the soluble fraction were possible.

13C n.m.r. study of the graft copolymerization of a mixture of methyl methacrylate with ethyl acrylate on amylose

Abstract The study of the simultaneous grafting of ethyl acrylate with methyl methacrylate onto amylose with Ce(IV) ammonium nitrate as initiator was attempted. Grafting yields obtained using gravimetric and 13C n.m.r. spectroscopic methods were compared and similar results were obtained. A study of the microstructure of the grafted products obtained involving either the quantitative determination of the grafted copolymer composition or the qualitative study of the sequence distribution and the stereochemical configuration of grafted copolymer sequences has been carried out. The α-methyl group carbon, the quaternary carbon and the carbonyl group carbon have been found to be sensitive to the relative stereochemical configuration of the chain segments.

Stereoregularity of various polyacrylates obtained from graft copolymers onto starch

Abstract 13 C nuclear magnetic resonance spectra of poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA) and poly(butyl acrylate) (PBA), obtained from graft copolymers onto amylose or amylopectin, have been studied. The spectra of the polymers were recorded with a 75 MHz spectrometer and were analysed by triad, tetrad, pentad or hexad placements. All of them follow Bernoullian statistics, with an isotactic parameter of 0.51, 0.44 and 0.43 for PMA, PEA and PBA respectively. By comparison with other values found in the literature it can be asserted that the presence of the carbohydrate has no effect on the tacticity of the grafted polymer.

Graft copolymerization of ethyl acrylate with alkyl methacrylates onto amylose initiated by cerium (IV). Microstructure of graft copolymers with respect to statistical copolymers

Abstract The graft copolymerizations of ethyl acrylate (A) with ethyl methacrylate (E) and butyl methacrylate (B) via redox initiation with cerium(IV) in water at 30°C are described. The kinetic parameters of the grafting reaction such as yield of the graft copolymer, grafting efficiency and total conversion were evaluated comparatively and the microstructures of the graft copolymers were analysed by 13 C n.m.r. spectroscopy. The results obtained are compared with the microstructural characteristics of statistical A-E and A-B copolymers prepared by free radical copolymerization at low conversion using 2,2′-azobisisobutyronitrile as the initiator at 60°C.

Determination of the tacticity of polymethacrylates obtained from graft copolymers

Abstract 13 C n.m.r. spectroscopy has been used to analyse copolymers of hydrophobic and hydrophilic polymethacrylates on starch. The analysis was carried out after releasing the grafted chains by hydrolysis. They were all syndiotactic as expected from a radical initiation method. Triad, tetrad, pentad or hexad signals were resolved.

Synthesis of graft copolymers of hydrophobic and hydrophilic methacrylates onto amylopectin

Abstract Mixtures of hydrophilic and hydrophobic methacrylates were grafted onto amylopectin, using the ceric ion redox initiation system. The pairs hydroxyethyl methacrylate (HEMA)/methyl methacrylate (MMA), hydroxypropyl methacrylate (HPMA)/MMA, HEMA/ethyl methacrylate (EMA) and HPMA/EMA were grafted at different concentrations of the monomer feed. In all cases, a major formation of ungrafted acrylic polymer can be observed when the hydrophilic monomer used is HPMA. High yields were obtained with all the mixtures at certain concentrations of the monomer feed.