Semiaromatic Polyamides Research Articles

The condensation kinetics of polyphthalamides. I. Diamines and diacids or dimethylesters

AbstractSemiaromatic polyamides are high‐performance thermoplastics with a huge potential but also a high price. In this study, the condensation kinetics of aliphatic diamines with aromatic diacids, diesters, and polyesters were investigated, to find ways of producing semiaromatic polyamides at lower costs. The condensation of hexamethylene diamine with phthalic acids and their dimethylesters are discussed in this Part I. The amidation of phthalic acids turned out to proceed like the amidation of adipic acid leading to PA66, only more slowly. The amidation of dimethylphthalates proved to be difficult. It is accompanied by a side reaction of amino alkylation which prevents the growth of long polyamide chains. This side reaction was investigated kinetically in detail, using model compounds that were unable to polymerize. The aim was to provide a basis for attempts to amidate polyesters, in particular, PET, which will be reported in Part II. POLYM. ENG. SCI., 47:1589–1599, 2007. © 2007 Society of Plastics Engineers

Hysteretic thermal behavior of amorphous semi-aromatic polyamides

The hysteretic thermal behavior of two amorphous semi-aromatic polyamides, subjected to cyclic loading at high stress levels, has been investigated. The two polymers, called 1I and 1.8T, were selected with regards to chain mobility and plastic deformability considerations. This work reports the exothermal response of these materials to high level cyclic stress (of the order of σ y), with emphasis on the initial thermal peak, normally observed in commercial polycarbonate (PC) and not in commercial polymethylmethacrylate (PMMA). The investigated materials exhibit noticeable initial thermal peaks, which are similar, to some extent, to those observed in PC. The present results suggest that chain mobility may indeed be partially responsible for the initial exothermal peak, thus supporting the hypothesis that it may be related to the transition from shear deformation zones to chain disentanglement crazing.

N‐chloro amides, lactams, carbamates, and imides. New classes of initiators for the metal‐catalyzed living radical polymerization of methacrylates

AbstractMetal‐catalyzed living radical polymerization of methyl methacrylate initiated with N‐chloro amides (N‐chloro N‐ethyl propionamide, N‐chloro benzanilide, N‐chloro methylbenzamide, and N‐chloro acetanilide), lactams (N‐chloro caprolactam and N‐chloro 2‐pyrrolidinone), carbamates or urethanes (N‐chloro ethylcarbamate or N‐chlorourethane), imides (N‐chloro phtalimide, N‐chloro succinimide, trichloroisocyanuric acid, and N‐chloro saccharin) and catalyzed with the self‐regulated catalytic system Cu2S/2,2′‐bipyridine is reported. The initiation efficiency of these initiators is determined by their structure. Regardless of the initiator efficiency, in all cases, poly (methyl methacrylate) with narrow molecular weight distribution and functionalized chain‐ends was obtained. These new classes of initiators open new strategies for the functionalization of polymer chain‐ends and for the synthesis of complex architectures by graft copolymerization initiated from N‐chloro proteins, aliphatic, aromatic and semiaromatic polyamides, and polyurethanes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5283–5299, 2005

Influence of moisture on the viscoelastic relaxations in long aliphatic chain contained semiaromatic polyamide, (PA9-T) fiber

The effect of moisture on the mechanical relaxation processes of semiaromatic semicrystalline polyamides synthesized by a long-chain aliphatic diamine and terephthalic acid was investigated by dynamic viscoelastic analysis (DVA) and differential scanning calorimetry (DSC). Moreover, the implication of moisture with the amorphous and crystalline domains was also examined by temperature-dependent wide-angle X-ray diffraction and Fourier transform infrared spectra. The characteristics of the relaxations such as α, β, γ, and the pronounced peak shoulder appeared at 25–100 °C in DVA tan δ curves were found to be strongly susceptible to the presence of moisture. With moisture evaporation, the peak shoulder of 25–100 °C and the β-relaxation disappeared. The former is anticipated to originate from to the side group motion of hydrogen-bonded water, whereas the later one is from the motions of the amide–water complex units. With the disappearance of the β-relaxation, the γ-relaxation appeared simultaneously in much lower temperatures and ultimately coupled with the δ-relaxation. The γ-relaxation is attributed to be associated with the molecular motion of the amide group and δ-relaxation with for the motion of the methylene units. The existence of two types of water was identified in the polymer, namely, tightly bound and loosely bound. The tightly bound water is believed to be directly connected by hydrogen bonding with the strong polar groups and the loosely bound water weakly links with those connected water making hydrogen bridges. The moisture acts as a plasticizer in the polymer matrix, which causes quite a large depression in its glass transition temperature (Tg). WAXD and FTIR studies corroborated the existence of water solely in amorphous regions, i.e., no rapport of water with the crystalline parts. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2878–2891, 2003

Microdeformation mechanisms in thin films of amorphous semi-aromatic polyamides

Optical and transmission electron microscopy have been used to investigate the microdeformation mechanisms in thin films of amorphous semi-aromatic polyamides with different chemical structures and chain lengths. In the chosen range of test temperatures (between −120 °C and the principal mechanical relaxation temperature, T α), three successive microdeformation mechanisms were identified: chain scission crazing (CSC) at the lowest temperatures, shear deformation zones (SDZs) at intermediate temperatures and chain disentanglement crazing (CDC) at the highest temperatures. The critical stress for SDZ formation was identified with the experimental yield stress, whereas the critical stresses for CSC and CDC were derived from model expressions, using experimental data for the molecular mass between entanglements, the monomeric friction coefficient and the plastic flow stress. Variations in the transition temperatures among the different polymers were attributed to differences in the temperature dependence of the yield stress, and hence to variations in chain mobility, which could be accounted for in terms of the chemical structure.

Macrocycles. 17. The Role of Cyclization in Kinetically Controlled Polycondensations. 2. Polyamides

Two series of kinetically controlled polycondensations were conducted yielding polyamides of aliphatic dicarboxylic acids. First, the bis(trimethylsilyl) derivatives of 1,3-diaminobenzene, 4,4‘-diaminodiphenylmethane, 1,12-diamino-4,9-dioxadodecane, and 1,12-diaminododecane were polycondensed with dicarboxylic acid dichlorides in N-methylpyrrodidone below 0 °C. After optimization of the reaction conditions mainly cyclic polyamides were detectable in the MALDI−TOF mass spectra (up to 13 000 Da) of the semiaromatic polyamides in contrast to the Carothers−Flory theory. In the case of silylated aliphatic diamines, side reactions of the acid chlorides prevented a complete conversion of the amino groups, so that the reaction products mainly consisted of cycles and linear chains having two amino end groups. Second, normal interfacial polycondensations were performed either with 1,6-diaminohexane and adipoyl chloride or with 1,12-diaminododecane and decane-1,10-dicarbonyl chloride. When the loss of acid chloride ...

Molecular analysis of the plastic deformation of amorphous semi-aromatic polyamides

The plastic behavior of a series of amorphous semi-aromatic polyamides (SAPA-A) was investigated in compression mode at temperatures ranging from −100°C to their glass transition temperatures. Data analysis was mainly based on the inspection of the temperature dependence of yield stress, σy, plastic flow stress, σpf, and strain softening, SSA=σy−σpf. The activation volumes, V0, and the index of non-elastic behavior, I, were also determined, to account for the sensitivity of plastic deformation to strain rate and for the relative easiness of elastic and non-elastic processes, respectively. Some connections have been established between the nature of the molecular motions and the values of σy, σpf, SSA, V0, and I, thanks to the knowledge of the relaxation behavior of these materials. The role played by the secondary relaxation motions (and especially by those presenting a cooperative character) was highlighted, in agreement with our conclusions in earlier reports on the subject. In addition, the molecular analysis proposed for describing the plastic deformation of the SAPA-A materials was shown to hold for other polymers also bearing phenylene rings in the main chain, namely some semi-aromatic polyamides of another series (SAPA-R) and aromatic polycarbonates. Interestingly, the line of reasoning proposed here proved to be suitable also to account for the plastic deformation characteristics of various vinyl polymers and copolymers.

On the viscoelastic and plastic behavior of semiaromatic polyamides

Different semiaromatic polyamides (SAPA) have been synthesized by step-growth polymerization of an aliphatic diamine, M (the 2-methyl 1,5-pentanediamine), and isophthalic acid, I, or terephthalic acid, T, or mixtures of these two diacids. The influence of the relative amount of randomly distributed MT units on the viscoelastic properties of the materials was investigated. It was shown that the glass transition T g , as deduced from DSC thermograms, and the relevant mechanical relaxation T α raise when the content of MT units increases. In contrast, the broad low-temperature secondary relaxation, called y, does not markedly depend on the MT content. Samples systematically studied in the absence of any moisture did not exhibit the intermediate-temperature secondary relaxation, called β, which is characteristic of the wet polyamides. The study of the plastic behavior was focused on the samples MI and I5, which are strictly amorphous, and contain 0% and 50 mol % of MT units, respectively. Mechanical experiments were carried out in both the compression and traction modes, at temperatures ranging from -80°C to T g . Analysis of the compression data was based on the inspection of the temperature dependence of elastic modulus, E(T), yield stress, σ y , plastic flow stress, σ pf , and strain softening σ y - σ pf . Whereas the plots of σ y as a function of temperature, T, reveal some differences between MI and I5 behavior, a unique master curve was obtained by plotting σ y /E(T) vs. T - T g , which means that the plastic behavior of these materials is controlled by their chain packing in the glassy state. The strain softening profile of MI and I5 is similar to that already reported in the case of brittle vinyl polymers. This observation is consistent with the traction data, which give evidence for the occurrence of the tensile yielding of MI and I5 at temperatures rather close to T g .

Phase behaviour of polyamide—polyester blends: the influence of aromaticity

Miscibility in blends of semi-aromatic polyamides and random aliphatic co-polyesteramides, derived from ϵ-caprolactam, ϵ-caprolactone and laurolactam has been investigated by calorimetric methods. Dilution of ϵ-caprolactam by ϵ-caprolactone in PA-6 transforms miscible blends based on PA-6I and PA-TMDT, respectively, to immiscible mixtures at approximately 35 and 46 mol%, respectively, of ϵ-caprolactone in the copolymer. The data have been found to conform to an analysis provided by a binary interaction model incorporating segmental interaction parameters, χ ij , derived from related blends. Extension of the treatment to polyamide/polyester blends whose constituents contain aromaticity, e.g. PA-66/poly(ethylene terephthalate), PET and PA-6I/polyarylate, PAr, has also been explored. The results confirm the gross immiscibility, indicated by a large unfavourable interaction parameter, typically encountered in these blends.

Moisture effects on the glass transition and the low temperature relaxations in semiaromatic polyamides

The influence of moisture absorption on the primary (glass) transition (Ta or Tg) and the low temperature relaxations of semiaromatic amorphous polyamides synthesized by isomeric aliphatic diamine and metha or para oriented phthalicdiacids has been investigated by means of differential scanning calorimeter (DSC) and dynamic mechanical thermal analyser (DMTA). The glass transition of semiaromatic polyamides was lowered due to the water absorption, and the β and the γ relaxations were as well. From the observed Tg and the difference in the heat capacity, the calculated Tg depression per 1 wt % water content was 12.3 K and the result was in good agreement with the experimental data. The depression of the glass transition may be expressed by the same manner as the plasticization of nylon 6 by water. The depressed β relaxation observed in the specimen containing a few percent of moisture was splitted into two transitions due to the reduction of water content, of which one was the elevation of the Tβ and another was the simultaneous appearance of the Tγ, and then the single Tγ solely was observed for the completely dried specimen. The Tγ seemed to be merged into or not to be observed by the large and broad Tβ transition when the sample was governed by a few percent of water, then it was emerged from the Tβ due to water desorption. Thus, the Tβ is believed to arise from the intermolecular hydrogen bonding between water molecules or between water and amide groups in wet polyamides. In addition, the γ relaxation originated from the peptide groups is attributable to the inter- and intramolecular hydrogen bonding between amide groups. © 1997 John Wiley & Sons, Inc. J Polyn Sci B: Polym Phys 35: 807–815, 1997

Design, Preparation and Characterization of Thermotropic Liquid Crystal Polyamides

There are few examples of thermotropic polyamides reported in the literature due to the strong tendency for hydrogen bonding between polymer chains. The vast majority of reported liquid crystalline (LC) polyamides are aromatic, highly crystalline and consequently infusible— and can only exhibit LC behaviour in solution (lyotropic behaviour). In this paper, the authors set out to synthesize novel amorphous wholly aromatic and semi-aromatic thermotropic polyamides. As crystalline aromatic polyamides are normally infusible, it was necessary to ensure that the target polyamides were amorphous with a definable softening point below their temperature of decomposition. The ‘Symmetry Index’ approach first developed by Dolden was used to ensure that the chosen monomer compositions were able to produce amorphous polyamides. Aharoni has reported that three amide linked aromatic rings is the minimum unit size needed to obtain mesogenic polyamides. Building on this principle, a new empirical predictive technique called the ‘Mesogenic Index’ is introduced and combined with the Symmetry Index to predict polyamides which are both amorphous and thermotropic. This approach was validated by the preparation of a whole new series of thermotropic amorphous polyamides which were based on 3,3′-dimethoxy benzidine, and the acid chlorides of terephthalic, isophthalic and adipic acids. Furthermore, this led on to the preparation of two more series of amorphous polyamides, believed by the authors to be the first wholly aromatic thermotropic polyamides to be reported, based on 3,3′-dimethoxy and 3,3′-dimethyl benzidine in conjunction with a variety of aromatic and cyclic diacids.

Photochemical behaviour of semi-aromatic polyamides

Semi-aromatic polyamides were irradiated with monochromatic light of short wavelength ( λ = 254 nm) or polychromatic light of long wavelength ( λ > 300 nm), in the presence or the absence of oxygen. The changes of the irradiated samples were characterized by both UV-visible and FTIR spectroscopies. It was observed that in short wavelength irradiation, a direct homolysis of the NHCO bond of the amide function occurred, leading to the formation of the amine and aldehyde. The crotonization of the aldehydes led to unsaturated aldehydes, which were responsible for the reversible discoloration phenomena observed. The long-wavelength irradiation in the presence of oxygen was shown to provoke a photoinduced oxidation of the methylene adjacent to the aromatic ring. The determination of the photooxidation profiles showed that the oxidation was limited to the superficial layers of the samples. The formation of imide groups and thermally unstable N-1 hydroxyl-acid groups was observed. The photooxidation as well as the hydrolysis of imide groups was shown to produce primary aliphatic or aromatic amides and carboxylic acid functions.

Syntheses and thermal properties of aromatic and semi-aromatic polythioetheramides containing oligo(thio-1,4-phenylene) segments

A family of aromatic and semi-aromatic polythioetheramides was prepared from well-defined diamine-terminated oligo(thio-1,4-phenylene)s (PPS-DA) containing n=1,2,3,4,5,6 thio-1,4-phenylene units. Polycondensation reactions with adipic, sebacic, terephthalic and isophthalic acid chlorides were carried out in N-methyl-2-pyrrolidone solution at room temperature to yield amorphous and semi-crystalline polythioetheramides. The influence of the oligo(thio-1,4-phenylene) segment lengths on phase transitions and thermal degradation of the polythioetheramides was investigated. As a function of the PPS segment lengths, glass transition temperatures vary between 120°C and 300°C, and melting temperatures between 290°C and 500°C. The thermal stabilities determined by thermogravimetric analysis under nitrogen increase with increasing PPS segment lengths. In the case of the higher molecular weight PPS segments, the resulting semi-aromatic polyamides exhibit two crystalline phase transitions.

Synthesis and Properties of Polyamides of 2,2′-[Isopropylidenebis-(p-phenyleneoxy)] diacetic Acid

Abstract A group of six semiaromatic polyamides of 2,2′-[isopropylidenebis-(p-phenyleneoxy)]diacetic acid (Bisacid A2) were synthesized by low-temperature solution polycondensation techniques. Six different diamines were condensed independently with Bisacid A2 chloride in a mixture of N-methylpyrrolidone (NMP and hexamethylhosphoramide (HMPA). The polymers were obtained in 82–95% yield and possessed inherent viscosities in the range from 0.32 to 0.63 dL/g. The polyamides were characterized by IR and 'H-NMR spectra. The molecular weight and molecular weight distribution of the polyamides were determined by gel-permeation chromatography. The thermal stability, thermal degradation kinetics, crystallinity, density, and solubility were also determined. A model diamide (MDA) was synthesized from aniline and Bisacid A2 chloride to confirm the formation of polyamides from diamines.

Preparation of polymers and reactive prepolymers by the aminolysis of acylbis(hexanelactams)

The aminolysis of N,N'-isophthaloyl and N,N'-terephthaloyl-bis(6-hexanelactam) with aliphatic diamines was used in the preparation of semiaromatic polyamides, in the extension of polymer chains and in the preparation of N,N'-[poly(oxyethylene)di(carbamoylbenzoyl)]bis(6-hexanelactams) under mild conditions (50-80 °C).