Quang-Tho Pham

Microstructure of acrylamide-acrylic acid copolymers: 1. As obtained by alkaline hydrolysis

Abstract Kinetics of alkaline hydrolysis of high molecular weight commercial polyacrylamide were studied by two different methods proposed by Fuoss and Higuchi. Compositional triad distributions and cotacticity parameters are determined from results obtained by 13C (1H) nuclear magnetic resonance of carbonyl and methine resonance patterns of partially hydrolysed polyacrylamides. It is established that acrylate monomers tend to occur as isolated groups along the molecular chain but it is not possible to assert whether there is racemization or not during the reaction.

Acrylonitrile copolymerization—IX. Synthesis and characterization of copolymers with methacrylic acid

Abstract In the emulsion copolymerization of acrylonitrile (AN) with methacrylic acid (MA) at 35°, the reactivity ratios are: r AN =0.128 r MA =2.40 Constant composition copolymers in the range of 0–10% of methacrylic acid units have been prepared and characterized with respect to composition and sequence distribution using mostly 1H and 13C NMR spectroscopy. The observed sequence distribution from triads is Markovian first order and corresponds quite well to the computed values. The stereopropagation is nearly Bemouillian.

Copolymerization reactions of vinylidene cyanide with styrenes carrying a fluorocarbon segment: preliminary studies of their microstructure

In order to prepare piezoelectric copolymers, vinylidene cyanide has been copolymerized with two styrenes bearing a fluorinated chain in the para position of the aromatic nucleus, The microstructure of the resulting copolymers has been studied by 13 C NMR, with decoupling of fluorine and hydrogen. These copolymers are perfectly altemating and for one copolymer, a partial cristallinity is observed, due to the side fluorinated chain.

A 1H and 13C n.m.r. study of the products from direct polyesterification of ethylene glycol and terephthalic acid

Abstract Low molecular weight samples of poly(ethylene terephthalate), obtained by direct bulk polyesterification of terephthalic acid and ethylene glycol, were studied by 1H and 13C n.m.r. It was possible to determine degrees of conversions of acid and alcohol groups, distributions of free, monoesterified and diesterified terephthalic acid and ethylene glycol and to identify the dimer, trimer and tetramer. Side reactions were also studied.

Copolymers of Cyano Compounds with Captodative Monomers. Studies of Their Microstructures

Abstract Copolymers of vinylidene cyanide, methacrylonitrile, and acrylonitrile with various captodative monomers such as cyanovinyl acetate, methyl α-acetoxyacrylate or methyl 1-(methoxy carbonyl) vinyl carbonate were synthesized by radical copolymerization. The microstructures of these copolymers were studied by means of 13C NMR. The copolymers of vinylidene cyanide are rich in alternating structure, and the copolymers of methacrylonitrile and acrylonitrile are rather statistical than alternating. The measurements of reactivity ratios for three copolymerization reactions, vinylidene cyanide, methacrylonitrile, and acrylonitrile with methyl α-acetoxyacrylate, confirm these conclusions.

Mechanisms of the bulk copolyesterification of azelaic acid, o-phthalic anhydride and trimethylolpropane studied by 13C nuclear magnetic resonance

Abstract Polyesterifications in bulk of trimethylolpropane (T) with azelaic acid (Z) and o -phthalic anhydride (P) and copolyesterification of a (Z + P + T) ternary mixture have been studied by 13 C nuclear magnetic resonance (n.m.r.) before and after gelation. It has been found that Z is more able than P to give covalent gels. 13 C n.m.r. allows quantitative determinations of the conversions of acid functions of Z and P and alcohol functions of T as well as the distributions of monoester and diester of P and those of free, mono-, di- and triesterified T. In all cases, the actual critical conversions are larger than the theoretical ones calculated due to the Flory-Stockmeyer statistics because (i) 3–5% of free T and P are trapped and (ii) the two acid functions of P or Z and the three alcohol functions of T do not have the same reactivities. For the ternary system, four types of T triesters have been identified and quantitatively determined, and finally, reticulation should only occur if more than one-third of T are triesterified. In the copolyesterification in bulk of the (0.5Z + 0.5P + 0.8T) mixture, the distributions of Z and P on the mono-, di- and triesterified T follow Bernoullian statistics.

Microstructure of copolymers of vinylidene cyanide, methacrylonitrile and acrylonitrile with methyl α acetoxyacrylate, a captodative monomer

SummaryCopolymers of vinylidene cyanide (1a) methacrylonitrile (1b) and acrylonitrile (1c) with a captodative monomer, methyl α acetoxyacrylate were synthesized by radical copolymerization and their microstructures were studied by 13C NMR spectroscopy.The copolymer of 1a with methyl α-acetoxyacrylate (2) has mostly an alternating structure but the copolymers of 1b and 1c with 2 are rather statistical. The measurement of their reactivity ratios for these two reactions is in agreement with the proposed structures.

Vinyl Chloride-Vinylidene Chloride Copolymerization: Kinetic Deviations and Structural Defects

Abstract The penultimate effect in the radical copolymerization of vinyl chloride (C) and vinylidene chloride (V), described in a previous paper, is interpreted in terms of head-to-head addition of a V molecule to a C-ended radical. The later is estimated from NMR analysis of the copolymer. It occurs about three times faster than the corresponding head-to-tail addition. It is shown that both the penultimate effect model and the “head-to-head assumption” lead to the same values for either the copolymer composition or several functions of the sequence distribution. It is further suggested that the head-to-head addition is possible owing to the propagation-depropagation equilibrium for the V-ended radical and to the very high reactivity of the tail radical produced.

Copolymerization of Olefins by Ziegler-Natta Catalyst. The Copolymerization of 1-Hexene and Propylene. Kinetic Study

Abstract The copolymerization of 1-hexene and propylene in the presence of a Ziegler-Natta type catalyst (AlEt2 Cl-TiCl3) has been studied. The gas chromatography method used for the kinetic study allowed determination of reactivity ratios of both monomers from the classical copolymerization equation which was found to be followed. The copolymers composition has been confirmed by NMR analyses and the theoretical sequence distribution computerized, thus giving an a priori description of the macromolecules useful for further studies of the properties of these copolymers. The drift in copolymer composition and thus in the distribution of monomer units occurring with conversion has been found important, and to avoid this heterogeneity in composition, some copolymers were prepared at constant monomer feed composition using a very simple manometric device.

Internal Transfer Reactions in the Copolymerization of Vinyl Acetate with Chlorinated Monomers

Abstract In the copolymerization of vinyl acetate (A) with either vinyl chloride (C) or vinylidene chloride (V), an internal transfer (backbiting) reaction—of the C- or V-ended radi-cals on an antepenultimate A unit—is proposed to be responsible for the deviation of the copolymerization kinetics from the Lewis and Mayo theory. The deviations disappear if A is replaced by isopropenylacetate [Ip], Then one gets, for the Ip -C copolymerization. rI p =0.35 and :rc=2.4, and for I -V copolymerization, rI p=0.13 and rv=5.9. The internal transfer reaction causes the formation of branches which may be evidenced by NMR analysis of constant composition suspension A-C copolymers. A kinetic scheme is proposed and the corresponding reactivity ratios derived rA=0.29, rc=1.60, r=0.3 (radical resulting from the transfer reaction), and kT=1500 (rate constant of the transfer reaction at 50°C). The distribution of branches is calculated together with the sequence distribution functions for the .A. or Cunits.