Copolyarnides, based on 1,12-dodecanedicarboxylic acid and different ratios of 1,2-ethylenediamine and piperazine, i.e., PA2,14-co-pip,14 as well as the homopolymers PA2,14 and PApip,14 are Studied. Incorporation of the piperazine component in the homopolymer PA2.14 reduces the number of hydrogen bonds. This provides a unique opportunity to investigate the influence of hydrogen bonding on the origin of the Brill transition and chain mobility within polymer crystals. Time-resolved conformational. structural, and morphological changes during heating are followed by FTIR spectroscopy, WAXD, and SAXS. The findings are that from 0 to 62 mol % of piperazine the Brill transition occurs in the same temperature region. The transformation is triggered by the conformational changes in the methylene sequences of the main chain, followed by twisting in the methylene sequences next to the amide group. This results in enhanced chain mobility along the c-axis, causing lamellar thickening. For 80 mol % of piperazine and higher, no Brill transition is observed. However, conformational changes in the methylene sequences of the main chain occurs, triggering lamellar thickening.

Copolyamides, based on 1,12-dodecanedicarboxylic acid and different ratios of 1,2-ethylenediamine and piperazine, i.e., PA-(2.14-co-pip.14), as well as the corresponding homopolymers PA-2.14 and PA-pip.14, were studied by SAXS and WAXS. Up to a pip mole ratio of 0.62, the 2.14 and pip.14 units cocrystallize in a common crystal lattice, slightly deviating from the structure of homopolyamide 2.14. The hydrogen bonds obviously tolerate significant amounts of comonomer before the crystal structure is changed significantly. For pip mole percentages of 0.90 and higher, both repeating units cocrystallize in a slightly distorted PA-pip.14 crystal structure. For pip mole percentages of 0.70 and 0.82, however, the X-ray patterns show peaks that stem from both the PA-2.14- and the PA-pip.14-like crystalline structure, indicating that the two structures coexist in this composition range. Since the intersheet distance practically remains unaffected upon incorporation of the piperazine rings, it is concluded that these rings are oriented parallel to the hydrogen-bonded sheets. Furthermore, from the composition dependency of the experimentally determined lattice spacings, keeping in mind that the intersheet distance is constant, it is concluded that the hydrogen-bonded sheets are shifted parallel to one another.

Following our previous study on the stereoselective cocrystallization of linear and cyclic dicarboxylic acid residues in copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid (12.6/12.1,4-CHDA, Vanhaecht et al., Macromolecules 2004, 37, 421), we have now investigated a series of copolyamides containing trans or cis isomers of 1,4-diaminocyclohexane (1,4-DACH), viz. 4.14/1,4-DACH.14. Solidstate NMR studies and WAXD experiments demonstrate that the cis isomer is present in the amorphous regions of the copolyamide, whereas the trans isomer is located in both the crystalline and the amorphous phase. Similar to the results for the trans-1,4-CHDA-based copolyamides, trans-1,4-DACH moieties are probably built into the crystalline structure with the cycloaliphatic ring oriented perpendicular to the hydrogen-bonded crystal sheets. Temperature-dependent WAXD patterns show that, unlike in the homopolyamide 4.14, a pseudohexagonal phase is not formed at the Brill temperature in the copolyamide. Instead, crossing rather than merging of the (100) and the combined (010)-(110) WAXD reflections occurs upon heating of the copolyamides containing trans-1,4-DACH. In contrast to the cis isomer, introduction of trans-1,4-DACH into polyamide 4.14 raises the melting temperature, confirming the findings by solid-state NMR and WAXD analysis. Unlike 1,4-CHDA moieties, 1,4-DACH residues do not undergo thermal isomerization. Therefore, at the same amount of initially trans isomers, the copolyamides 4.14/1,4-DACH. 14 exhibit higher second heating end melting points than the corresponding isomeric copolyamides 12.6/12.1,4-1,4-CHDA.

Copolyamides 2.14/piperazine.14 with variable built-in ratios of 1,2-ethyl-enediamine (1,2-EDA) and piperazine (pip) were synthesized by solution polycondensation. The built-in ratio of both diamine comonomers was determined with solution C-13 NMR analysis. The gradual replacement of 1,2-EDA units by cycloaliphatic pip units in polyamide 2.14 resulted in a progressively decreased melting (T.) and crystallization temperature of the obtained copolyamides. Apparently, the T-m raising effect of the incorporation of rigid cycloaliphatic moieties is overruled by the simultaneous T. reduction caused by a decreasing hydrogen-bond density. Indications for cocrystallization of 2.14 and pip.14 repeating units were obtained by the thermal analysis of copolyamides 2.14/pip.14 and of a blend of both homopolyamides. A preliminary wide-angle X-ray diffraction study pointed to the same conclusion. Solid-state NMR spectroscopy was used to investigate the influence of the composition on the percentage of the rigid phase of the copolyamides and delivered additional indications for cocrystallization. (C) 2003 Wiley Periodicals, Inc.

The aim of this work is to investigate whether or not both the cis and the trans isomers of either 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) and 1,4-diaminocyclohexane (1,4-DACH) are participating in the formation of cryst. domains in copolyamides based thereon. Two isomeric series of partially cycloaliph. copolyamides were synthesized. In the series based on polyamide 12.6, the adipic acid residues were partially replaced by cis/trans mixts. of 1,4-CHDA, and in the series based on polyamide 4.14, the 1,4-diaminobutane residues were partially replaced by cis/trans mixts. of 1,4-DACH. By submitting these series of copolyamides to careful DSC and WAXS analyses, it could unambiguously be concluded that only the trans isomers of both 1,4-CHDA and 1,4-DACH residues are cocrystg. with the adipic acid based residues. Such evidence was not yet available in literature.

Two series of isomeric copolyamides were synthesised, viz. polyamides 12.6 for which the adipic acid residues were partially replaced by cis/trans-1,4-cyclohexanedicarboxylic acid (1,4-CHDA), and polyamides 4.14 for which the 1,4-diaminobutane residues were partially replaced by cis/trans-1,4-diaminocyclohexane (1,4-DACH). A careful DSC and WAXS analysis learned that only the trans isomers of both 1,4-DACH and 1,4-CHDA are incorporated into the crystalline phase. During DSC analysis, an intitial high trans content is preserved in the case of the non-isomerising 1,4-DACH, whereas the 1,4-CHDA residues gradually isomerise from a high initial trans content to a significanly lower trans content. Since these cis residues are not incorporated into the crystalline domains, the lower second heating melting points of the 1,4-CHDA-based copolyamides in comparison with 1,4-DACH-based copolyamides, having similar cycloaliphatic monomer contents, can be understood.

To study the influence of the stereochemistry on the possibility of cocrystallization of linear and cyclic aliphatic residues in copolyamides, a series of copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid with variable compositions were synthesized. From solid-state NMR studies it could be deduced that cis-1,4-CHDA is present in the amorphous regions whereas the trans residues are located in both the crystalline and the amorphous phase. WAXD patterns confirm the presence of trans-1,4-CHDA inside the crystals and reveal that the cycloaliphatic ring is most likely oriented in a direction perpendicular to the crystal sheets that contain the hydrogen bonds. As a result, the intersheet distance is increased compared to that of polyamide 12.6. Furthermore, the rings prevent the genesis of a pseudohexagonal phase above the Brill temperature. Exceptionally, crossing rather than merging of the (100) and the combined (010)-(110) WAXD reflections is observed with increasing temperature, indicating that the intersheet distances increase and become larger than the interchain distances within the hydrogen-bonded sheets before the crystals start to melt. Incorporation of trans-1,4-CHDA residues into polyamide 12.6 leads to higher melting temperatures, pointing at cocrystallization in terms of a solid solution rather than as defects. In contrast, a slight melting point depression is observed for copolymers with predominately cis-1,4-CHDA residues.

High molecular weight poly(styrene-co-N-substituted-maleimide)-block-poly(tetrahydrofuran) multiblock copolymers with an excellent thermal stability were synthesized using the polymeric iniferter technique. Evidence for the existence of these multiblock copolymers was obtained by submitting them to gradient polymer elution chromatography and by snipping the chemical bonds between the SMI blocks and the PTHF blocks, after which the molecular weight distribution of the remaining SMI blocks was determined. Only one glass transition temperature was observed in a modulated temperature DSC scan of the segmented copolymers, typical for a homogeneous material. The T-g of these flexibilized, single-phase multiblock copolymers is still high enough to qualify them as engineering plastics. The entanglement density, which is closely related to the toughness of materials, of a styrene-N-phenylmaleimide copolymer flexibilized by 12 wt % PTHF was raised by a factor 1.6 as compared to the unflexibilized styrene-N-phenylmaleimide copolymer. These entanglement densities were deduced from the respective rubber plateau moduli, which were corrected for the nonentangled low molar mass fraction by applying the Wasserman-Graessley model.

The effects of the partial substitution of 1,4-disubstituted cyclohexano monomers for linear aliphatic monomers in polyamides are discussed. More specifically, the relation between the stereochemistry of the cycloaliphatic residues and the thermal properties [melting temperature (T-m) and crystallization temperature (T-cr)] was investigated. For this purpose, two different types of copolyamides were synthesized: in polyamides 12.6, the adipic acid residues were partially replaced by cis/trans-1,4-cyclohexanedicarboxylic acid (1,4-CHDA), whereas in polyamides 4.14, the 1,4-diaminobutane residues were partially substituted with cis/trans-1,4-diaminocyclohexan((1,4-DACH). For both systems, increasing the degree of substitution of cycloaliphatic residues for linear aliphatic residues resulted in a rise of both T. and T, This points to the isomorphous crystallization of the linear and cycloaliphatic residues. In contrast to the use of 1,4-DACH as a comonomer, 1,4-CHDA residues showed isomerization upon thermal treatment of the polyamides. This isomerization. of the cyclohexane residues influenced the thermal properties of the copolyamides. The use of a nonisomerizing cis-trans mixture of 1,4-DACH exhibited the large influence of the stereochemistry of the cycloaliphatic residues on the T-m of the copolyamides. For both the 1,4-CHDA- and 1,4-DACH-based copolyamides, differential scanning calorimetry analysis revealed that recrystallization occurs during melting. This exothermal effect becomes less pronounced with an increasing content of rigid cycloaliphatic residues. (C) 2002 Wiley Periodicals, Inc.

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) residue, or a mixture of both. The influence of the synthetic route of 1,4-CHDA containing polyamides on the obtained cis-trans ratio of the incorporated 1,4-CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis-trans ratio of the 1,4-CHDA residue during synthesis, whereas synthesis at elevated pressure and temperature caused isomerization. The content and cis-trans ratio of 1,4-CHDA in the copolyamides were determined by solution C-13 NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4-CHDA resulted in an increase in T-m, even for low molar precentages of 1,4-CHDA. This phenomenon points to isomorphous crystallization of both the 12.6 and 12.CHDA repeating units. The mps of the synthesized polyamides were independent of the initial cis-trans ratio of 1,4-CHDA, provided that the samples were annealed at 300 degreesC before DSC analysis. The polyamides exhibited a different melting pattern depending on the 1,4-CHDA content. At a low a 1,4-CHDA content a net exothermic recrystallization occurred during melting, whereas at higher contents of 1,4-CHDA this recrystallization occurs to a lesser extent, and two separate melting areas are observed. (C) 2001 John Wiley & Sons, Inc.

This article describes the synthesis and molecular characterization of thermal polymeric iniferters, based on hydroxy-terminated poly(tetrahydrofuran) (PTHF), bearing thiuram disulfide groups along the chain. Thermal polymerization after the addition of styrene (S) and N-methylmaleimide (MI) to these PTHF-based polymeric iniferters yielded segmented PTHF (SMI-block-PTHF)(n) block copolymers that proved to have a single T-g. The multiblock copolymers were molecularly characterized by elemental analysis, IR, and NMR. The thermal stability, as checked by thermogravimetric analysis, proved to be good up to about 350 degrees C. A size exclusion chromatography/differential viscosity (DV) analysis showed that the molecular weights of the synthesized single-phase multiblock copolymers were sufficiently high (several times the estimated molecular weight between two adjacent entanglements) to determine the entanglement density from the rubbery plateau modulus, for which the method developed by S. Wu (J Polym Sci Part B: Polym Phys 1989, 27, 723-741) was applied. The entanglement density of flexibilized SMI proved to be about 20-25% higher than that of the nonflexibilized SMI. This increase is disappointing, and more work, based on the described concept, is required to achieve the desired enhancement of the toughness. (C) 2000 John Wiley & Sons, Inc.

We investigated the use of dicyclohexylcarbodiimide (DCC) as an activating agent in the synthesis of aliphatic polyesters. Butylhexanoate was synthesized in order to optimize the reaction conditions. The reactions were carried out in methylene chloride at room temperature. It was shown that nearly complete conversion is achieved if 4-(dimethylamino)pyridinium 4-toluenesulfonate (DPTS) is used as the catalyst. DPTS is a complex formed from 4-(dimethylamino)pyridine (DMAP) and p-toluenesulfonic acid (PTSA). The polyesters based on 1,10-octanedicarboxylic acid and 1,4-butanediol, synthesized in this way, had degrees of polymerization up to 67.