Viscoelastic relaxations in poly(dimethylphenyl methacrylates)

Summary Dynamic mechanical properties of poly(dimethylphenyl methacrylátes) were studied considering the different positions of the methyl groups on the phenyl ring. In all cases a clear relaxation can be observed which is associated to the polymer glass transition temperature (Tg). Nevertheless, at lower temperatures, viscoelastic activity is negligible. A correlation between the steric hindrance due to the methyl groups and the temperature at which the relaxation is detected, was established.     

Ultraviolet irradiation of poly(alkyl acrylates) and poly(alkyl methacrylates)

Acrylic and methacrylic homopolymers containing different side groups were irradiated with ultraviolet light in the presence of air. The changes of molecular weight distributions of the irradiated polymers were analyzed by means of gel permeation chromatography (GPC), and the rates of chain scission and crosslinking were estimated. As the result of this study, it was found that chain scission takes place more easily in polyalkyl methacrylates than in polyalkyl acrylates.     

Ultrasonic studies of solid poly(alkyl methacrylates)

The attenuation and velocity of ultrasonic longitudinal waves of frequencies 5–35 MHz in poly (methyl methacrylate), poly(ethyl methacrylate), poly (n-butyl methacylate) and poly(isobutyl methacrylate) between 233 and 363K are reported. The methyl and ethyl polymers showed evidence of a single relaxation process (associated with cooperative main chain and ester group motions), but the butyl polymers showed also a second relaxation at about 200–230K. This is associated with conformational rearrangement of the alkyl group, and the acoustic energetics are in line with theoretical predications for this process.The velocity data show the expected decreases due to the main glass transition (and cooperative processes) and to reduction of the intermolecular interaction force constant with increasing size of the alkyl group. Attempts to calculate an acoustic low temperature specific heat yielded values lower than expected from calorimetric observations, showing that the acoustic modes are capable of greater energy storage than is involved in the longitudinal perturbation, and/or that calculation based on a Debye T³ law are invalid for these glassy polymers.     

Metallographic characterization of rubber-modified poly(methyl methacrylates)

The microstructure of rubber-modified samples of poly(methyl methacrylates) was characterized by depositing a thin layer of gold on a polished surface and then applying the conventional techniques of metalography. Samples were prepared with a known volume fraction of rubber comprising particles of known size. It was shown that the methods of quantitative microscopy were successful in estimating these parameters. The method was also shown to provide information about crazing or cracking, which was viewed near the tip of an arrested crack. It is recommended that adoption of the metallographic method be extended to characterize other polymeric systems.     

Glass transition temperatures Tg of poly(tolyl methacrylates) and poly(di-xylenyl itaconates)

Summary Glass transition temperatures of poly(phenyl methacrylates) and poly(diphenyl itaconats) with one and two methyl substituents in the phenyl ring were determined by DSC. Within the group of 17 investigated polymers it was attempted to correlate the T_g values obtained with the polymer repeat unit structure, considering steric effects and dipole/dipole interactions, inherent to various modes of (di)substitution. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

Crystallization and morphology of isotactic poly(methyl methacrylates)

Several isotactic poly (methyl methacrylates) (iPMMA), with isotactic triad contents ranging from 46 to 100%, have been investigated after crystallization in the melt at different temperatures by differential scanning calorimetry, polarizing microscopy and small-angle light scattering. It was found that the crystallization of iPMMA, even of samples with high isotactic content, is slow. It never gives high degrees of crystallinity, but nevertheless leads to a spherulitic structure.     

Characterization of blends of naphthalene-containing polymers with poly(alkyl methacrylates) by combined steady-state fluorescence spectroscopy and fluorescence decay measurements

The extent of mixing in two-component solution-cast films of poly(2-vinyl naphthalene) (P2VN) and poly(2-iso-propenyl naphthalene) (P2IPN) with poly(methyl methacrylate) and poly(n-butyl methacrylate) was studied by steady-state and time-resolved fluorescence spectroscopy. The steady-state fluorescence spectrum of 1% P2IPN in the two poly(alkyl methacrylates) evolves from 100% monomer emission (λ_max = 340 nm) to >70% excimer emission (λ_max = 390 nm) as its molecular weight increases from 1900 to 278000. Despite such clear-cut changes in the steady-state spectra on phase separation, the fluorescence decays were nonexponential for all mixed films. Triple-exponential decay functions were necessary to describe excimer decays at 430 nm and monomer decays at 340 nm. Moreover, the fluorescence decays varied slightly across the excimer emission band, and changed significantly when the polymer films were annealed. Studies on blends containing from 1 to 100% of P2VN and P2IPN established that this multicomppnent fluorescence decay behavior is intrinsicto the naphthalene-containing polymer phase, it is proposed that excimers formed between chromophores in meso and racemic dyads have different mean decay times and that imperfectly aligned chromophore pairs lead to an additional short-lived excimer decay component.     

Synthesis and molecular weights of metal poly(methyl methacrylates)

Summary Methyl methacrylate colloids were obtained by codeposition at 77K of the monomer with several metals such as: Au, Pd, Cu, Ge, Ga, In, Sn, Sb and Bi. The colloids were polymerized with different amounts of initiator (AIBN) at 60°C and a wide range of viscosity average molecular weights (Mv; 10⁴–10⁵) were obtained depending upon the metal used. The metal colloid concentrations are reported. The thermal stability and metal composition are also described. The polymers are stable even at 350°C and the metal content is 0.7 to 3.1%.     

Autoadhesion of high density polyethylene (HDPE) to HDPE by ultraviolet grafting of methacrylates and acrylates

A study has been made on the effect of the presence of grafted acrylic layers on the autoadhesion of polyethylene. Methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA), and butyl methacrylate (BMA) were grafted onto high density polyethylene (HDPE). The grafting reaction was faster at higher temperature and methacrylates graft more easily than acrylates. For methacrylates and acrylates, the grafted amount increases with increasing length of the pendant alkyl chain. The grafting temperature is a crucial factor affecting the adhesion of grafted PE samples. For the samples grafted at lower temperature (in a room temperature water bath), the adhesion is very low (less than 50 N/m), even for very thick grafted layers. But for the samples grafted at higher temperature, much higher adhesion can be obtained. The presence of homopolymer was another factor affecting the adhesion of PE samples. When homopolymer is removed from the surface of the grafted sample, higher adhesion can be obtained. For some samples, the highest peel strength of more than 1000 N/m has been obtained. The low adhesion of the samples grafted at low temperature is attributed to the high branching of grafted chains.     

A novel method for preparing poly(alkyl methacrylates) and poly(methacrylic acids) of varying tacticity

In order to synthesize poly(methacrylic acid) and poly(alkyl methacrylates) over a wide range of polymer tacticity, the anionic polymerization of the following alkyl methacrylates (ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-amyl, n-hexyl, n-octyl, n-decyl, n-lauryl, and n-octadecyl) in toluene using phenylmagnesium bromide initiation was studied. It was found that the amount of isotactic polymer structure generally decreased as the size of the ester group increased. In all cases, the polymers had greater than 50% isotactic triad structure. Whether the polymerization was carried out at 0° or ?78°C had little or no effect on the tacticity of the polymer produced. It was found that the poly(alkyl methacrylates) produced could be hydrolyzed in concentrated sulfuric acid to poly(methacrylic acid). The poly(methacrylic acid) produced in the hydrolysis could be esterified with diazomethane to give poly(methyl methacrylate) or with diazoethane to give poly(ethyl methacrylate) with the same tacticity as the poly(alkyl methacrylate) from which the poly(methacrylic acid) was derived. It is possible, therefore, to produce poly(alkyl methacrylates) of a desired tacticity by polymerizing the appropriate monomer, hydrolyzing, and reesterifying the resultant poly(methacrylic acid) with a diazoalkane to give the desired poly(alkyl methacrylate).     

Studies on semiinterpenetrating polymer networks based on poly(vinyl chloride-co-vinyl acetate) and poly(alkyl methacrylates)

A number of semi-interpenetrating polymer networks (IPNs) based on linear poly(vinyl chloride-co-vinyl acetate) and poly(alkyl methacrylates) were synthesized. The semi-IPNs were found to be transparent, high strength materials. The IPNs show only one glass-transition temperature and it is dependent on the composition as studied by differential scanning calorimetry and dynamic mechanical analysis. These IPNs are also characterized by high tan δ values. The tensile strength of the IPNs were found to be higher compared to the starting polymers. In order to compare the properties of these IPNs with the corresponding homopolymers and blends, the latter were synthesized and the properties were studied. © 1994 John Wiley & Sons, Inc.     

Low-frequency thermomechanical spectrometry of polymeric materials: Tactic poly(methyl methacrylates)

A computerized and automated torsional pendulum has been used to characterize amorphous poly(methyl methacrylates) at about 1 Hz in the temperature sequence 473° → 93° → 473°K. The effects of thermal prehistory, temperature cycling, water content, and tacticity are demonstrated. In particular, a comparison of the out-of-phase shear modulus (G″) versus temperature for “syndiotactic,” “atactic,” and “isotactic” polymer specimens shows that the intensity of the glassy-state β loss peak decreases with increasing isotactic content while the temperature of its location remains the same. Extrapolation suggests that completely isotactic polymer would not display a β loss peak. The shape and location of the G″ data at low temperatures indicate that the basic mechanism of the β process is the same for the three polymer samples and support the validity of the extrapolation. The effect of tacticity is reflected also in the glass transition region; the isotactic sample has its T_g about 65°C lower with greater intensity than the syndiotactic polymer.     

Study of miscibility of poly(vinyl acetate) and poly(vinyl alcohol) blends by fluorescence spectroscopy

Secondary relaxation of poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), and their blends in different proportions (9 : 1, 1 : 1, and 1 : 9) were studied by photoluminescence of anthracene, fluorescein, and both probes dissolved in the polymer blends. The temperature of the glass transition in the homopolymers was determined by the radiationless deactivation of anthracene as T_g(PVAc) ? 304 K and the photobleaching of fluorescein as T_g(PVA) ? 350 K. The relaxation processes of the different phases of the polymer blends occur at temperatures close to the homopolymers, which may be explained by the localization of each molecular probe within the matrix. These deactivation curves, however, are not similar to those of the individual homopolymers, suggesting a partial miscibility between these polymers. © 1995 John Wiley & Sons, Inc.     

Correlations between alkyl side chain length and dynamic mechanical properties of poly(n-alkyl acrylates) and poly(n-alkyl methacrylates)

In the present paper, dynamic mechanical properties of poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) with different alkyl side chain length were studied. The results show that with the increase of alkyl side chain length, the storage modulus changes more steadily, and the loss modulus peak and the tanδ peak become broader for PnAA and PnAMA. At the same time, the tanδ peak is more and more apart from the loss modulus peak and the point where the storage modulus begins to drop. For quantitative discussion, three variables, the steepness index (S), the transition wideness (W) of storage modulus and the integration area (A) of tanδ were defined to investigate the potential correlation between the dynamic mechanical properties and alkyl side chain length. It can be observed that S decreases while W and A increase with increasing alkyl side chain length. Moreover, the relaxation spectra of the two series of polymers are calculated from the corresponding mechanical spectra. The shapes of the relaxation spectra are broader and broader with the increase of the alkyl side chain length. These phenomena are interpreted by the perspective of fragility, molecular packing efficiency and intermolecular coupling.     

Accelerated degradation of poly(vinyl chloride) (PVC) monitored by photoacoustic spectroscopy

Poly(vinyl chloride) film shows substantial changes in its photoacoustic absorption spectra (PAS) on either irradiation or heating in the presence of O₂ or N₂. These spectral changes are due to the conjugation structures and carbonyl (group formation), formed during photo and thermal degradation. In this paper interpretations of the PAS and of the decomposition mechanism of PVC are presented.     

Degradation of respirable fibrils of poly(p-phenylene terephthalamide) by solar ultraviolet radiation

After ～ 160 days in the environment, the polymer in a respirable-size poly(p-phenylene terephthalamide) fibril (diameter = 0.3 μm) is expected to degrade, due to solar ultraviolet radiation, from an initial molecular weight of ～ 20,000 to less than 400. This estimate is based on ultraviolet absorption characteristics, photolytic degradation kinetics, and judgments regarding how these translate into actual time in the environment. Degradation to this molecular weight level will cause the fibril tensile strength and modulus to decrease to ～ 1% of their initial values. Mechanically, such a degraded fibril will be weak and brittle with properties similar to those of uncooked spaghetti. © 1994 John Wiley & Sons, Inc.     

Vibrational spectra and structure of stereoregular poly(methyl methacrylates) and of the stereocomplex

Infra-red and Raman spectra of films and solutions of syndiotactic and isotactic poly(methyl methacrylate) (PMMA) and of the stereocomplex of PMMA were measured. Vibrational bands sensitive to conformational transitions were determined. Differences of band intensities in spectra of stereoregular PMMA and of the stereocomplex indicate changes of populations of conformational forms of polymer chains accompanying stereocomplex formation. For syndiotactic PMMA in the stereocomplex, the extended chain conformation predominates.     

Preparation of functional poly(acrylates and methacrylates) and block copolymers formation based on polystyrene macroinitiator by ATRP

The polymerization by ATRP of hydroxy and amino functional acrylates and methacrylates with tert-butyldimethylsilyl (TBDMS) or tert-butyloxycarbonyl (BOC) protective groups has been studied for the first time achieving high control over molecular weight and polydispersity. Detailed investigation of the ATRP of 2-{[tert-butyl(dimethyl)silyl]oxy}ethyl acrylate (M2b) in bulk and 2-[(tert-butoxycarbonyl)amino]ethyl 2-methylacrylate (M3a) in diphenyl ether (DPE) showed that the type of ligand plays an important role on either the polymerization rate or the degree of control of the polymerization. Among the ligands used, N,N,N,′N″N″-pentamethyl diethylenetriamine (PMDETA) was the most suitable ligand for ATRP of all functional acrylates and methacrylates. The kinetics of M2b and M3a polymerization using PMDETA as a ligand was reported and proved the living character of the polymerization. Well-defined block copolymers based on a halogen terminated polystyrene (Pst) macroinitiator and the functional acrylate and methacrylate monomers were successfully synthesized by ATRP, and subsequent deprotection of the protective groups from the acrylate or methacrylate segment afforded amphiphilic block copolymers with a specific solubility behavior.     

Molecular relaxation in cross-linked poly(ethylene glycol) and poly(propylene glycol) diacrylate networks by dielectric spectroscopy

The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-T_g relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.