Enrique López Madruga

From classical to living/controlled statistical free-radical copolymerization

Abstract Solvent effects on monomer reactivity ratio values along with the determination of radical reactivity ratios, their possible origins as well as their importance in conventional free-radical copolymerization is described first. Predictions from data obtained at low conversion of cumulative composition and stereochemical distribution in copolymer chain along with glass transition temperature and the lumped overall copolymerization parameter k p / k t 1/2 at high conversion are described. Transfer reactions in free-radical copolymerization using classical chain transfer agent as well as the new catalytic chain transfer agent and the effect on the copolymer structure and properties are also studied. Finally the new living/controlled free-radical polymerization process and the preparation of well-controlled statistical copolymers are described to stand out the subtle mechanisms differences between living/controlled and conventional free-radical copolymerization.

The importance of solvent polar character on the synthesis of PMMA-b-PBA block copolymers by atom transfer radical polymerization

Abstract The synthesis of diblock copolymers using atom transfer radical polymerization (ATRP), of methyl methacrylate (MMA), and butyl acrylate (BA), is reported. These copolymers were prepared from bromo-terminated macroinitiators of poly(MMA) and poly(BA), using copper chloride, CuCl,/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), as catalyst system, at 100°C in bulk and in benzonitrile solution. The block copolymers were characterized by means of size exclusion chromatography (SEC), and 1H-NMR spectroscopy. The SEC analysis of the synthesized diblock copolymers confirmed the importance of solvent on the molecular weight control. In addition, differential scanning calorimetry (DSC), measurements were performed, showing for all the copolymers a phase separation.

Solvent effects on the synthesis of poly(methyl methacrylate) by atom-transfer radical polymerization (ATRP)

Methyl methacrylate has been polymerized by ATRP at 100°C in bulk, in toluene (50%, v/v) and benzonitrile (50% and 25%, v/v), using methyl 2-halopropionate as initiator (MeXPr, X = Cl or Br), copper halide (CuX) as catalyst and 2,2′-bipyridine (bpy) as ligand. The mixed halogen system MeBrPr/CuCl has also been used. For all initiator systems used, the bulk polymerizations showed linear first-order rate plots, a linear increase of the number-average molecular weight with conversion, and relatively low polydispersities, but low initiator efficiency. The polymerizations performed in toluene do not significantly increase the polymerization efficiency, but the molecular weight distribution is broadened. When the polymerizations are performed in benzonitrile, the polymerization efficiency increases considerably, but is independent of monomer dilution. The molecular weight distributions are narrowed when the polymerizations are performed in 25% (v/v) benzonitrile solution. Experimental number-average molecular weights match the theoretical values when the polymerizations are carried out using the mixed halogen initiator system in benzonitrile solution.

Solvent effects on the free-radical polymerization of methyl methacrylate

Abstract The radical polymerization of methyl methacrylate has been studied in toluene and benzonitrile at 30, 45 and 60°C using 2-2′ azobisisobutyronitrile as initiator. Under the conditions of our experiments both the rates of polymerization and the molecular weights of the polymer obtained are dependent on the nature of the solvent. Determination of the effective initiation rate and the coupled parameter k p /k t 1 2 (where kp and kt are the constants for propagation and termination reactions, respectively) show that the dependence of the rate of polymerization on the nature of solvent arises in part from the effects of viscosity, polymer chain extension and polymer chain lengths on the termination coefficient and in part from a dependence of the effective initiation rate on the nature of the solvent.

Polymers with pharmacological activity: synthesis and free-radical polymerization of P-methacryloyloxyacetanilide

The synthesis and free-radical polymerization of p-methacryloyloxyacetanilide (MOA), an acrylic monomer derived from paracetaminophen (p-hydroxyacetanilide, a non-prescription antipyretic analgesic widely used around the world), has been studied. The kinetic behaviour of MOA in the polymerization initiated by azobisisobutyronitrile in solution of dimethylformamide, at temperatures in the range 50–120°C, seems to indicate a ceiling temperature of polymerization of about 137°C, for a monomer concentration of 1.0 mol l−1. The polymers obtained (PMOA) are predominantly syndiotactic and the stereo-control of the propagation process fits well the Bernoullian statistics, with an isotacticity parameter Pm = 0.26, the 13C nuclear magnetic resonance spectrum of CO ester group being sensitive to the stereochemical configuration of pentads. The hydrolytic behaviour of PMOA at several temperatures in alkaline solution has been tested.

Viscoelastic and mechanical properties of poly(butyl acrylate-g-styrene) copolymers

Abstract Viscoelastic relaxations of four poly(butyl acrylate- g -styrene) copolymers were studied over a wide range of temperatures. The temperature location and apparent activation energy of the distinct relaxations found are discussed. A single relaxation associated with cooperative motion has been observed in the range of graft content analysed. In addition, the stress–strain behaviour of these graft copolymers was studied. Films of the copolymer samples were stretched at room temperature since the possible application as adhesives might take place at about room temperature. Some mechanical parameters have been estimated, such as elastic modulus, tensile strength and toughness. Moreover, microhardness has been measured and its relationship with other mechanical properties has been established.

Free-radical homopolymerization and copolymerization of di-n-butyl itaconate

Abstract Di-n-butyl itaconate (DBI) was polymerized at 50°C in a 3 mol l−1 benzene solution using 2,2′-azobisisobutyronitrile (AIBN) as a free-radical initiator. Kinetic constants for DBI were obtained as follows: k p k 1 2 t = 0.021 mol −1 2 l 1 2 s −1 2 , 2fkd = 3.62 × 10−6s−1. Copolymerization reaction between DBI and methyl methacrylate (MMA), under the same experimental conditions, was carried out and the values of rDBI = 0.717 ± 0.11 and rMMA = 1.329 ± 0.09 were found for the reactivity ratios. Applying the Q—e scheme led to Q = 0.61 and e = 0.62 for DBI. Overall copolymerization rate coefficients have been analysed on the basis of terminal and penultimate effects on the propagation reaction. These parameters as well as the copolymer composition are not affected by total monomer concentration.

Glass transition temperatures of butyl acrylate-methyl methacrylate copolymers

The glass transition temperatures Tg of butyl acrylate–methyl methacrylate copolymers obtained by free radical polymerization in 3 and 5 mol/L benzene solution have been measured using differential scanning calorimetry (DSC) and the values have been correlated using Johnstons equation with inter-intramolecular copolymer structure. From the data calculated with copolymer prepared at low conversion, the variation of glass transition temperature with copolymer conversion has been theoretically predicted.

Radical Copolymerization of Acrylic Monomers. II Effect of Solvent on Radical Copolymerization of Methyl Methacrylate and Styrene

Abstract The influence of various solvents on the copolymerization behavior of methyl methacrylate with styrene has been investigated. In these systems there is a significant solvent effect on both rS and rM which may be attributed to changes in the dielectric constant of the solvents used. The calculated relative reactivity of the polystyryl radical towards the methyl methacrylate monomer increases with increasing solvent polarity, whereas the reactivity of poly(methyl methacrylate) radical towards styrene monomer decreases. The results obtained are discussed taking into account the behavior of both monomers in homopolymerization with the same experimental conditions as in copolymerization.

Synthesis and microstructure of polymers from o-methacryloyloxybenzoic acid

The free radical polymerization of o-methacryloyloxybenzoic acid using acetone and benzene as solvents, in the interval 30–120°C, is investigated. The polymerization in benzene has a precipitant character. However, when acetone is used as solvent, at reaction temperatures higher than 60–70°C, the polymerization deviates from the classic free radical mechanism and, beside the addition of monomer molecules to growing chain ends, the release of salicylic acid and the formation of cyclic anhydride structures of glutaric type in the main chain has been detected. The microstructure of polymers obtained has also been studied by the transformation into the corresponding poly(methyl methacrylate)s.