Die polymerisation der lactame XI. Die copolymerisation von 6-caprolactam mit 12-laurolactam

The course of the incorporation of 6-caprolactam and 12-laurolactam into polymer chains during the hydrolytic, cationic and anionic copolymerization for an equimolar ratio of the monomers was studied. During the hydrolytic copolymerization 6-caprolactam is incorporated more rapidly at 260, 230 or 200°C at the beginning of the polymerization process; the differences between incorporation rates of the lactams into the copolymer increase with decreasing temperature. During the cationic copolymerization the incorporation of 12-laurolactam is more rapid by orders of magnitude for the above temperatures at the beginning of the process. Changes in the composition of cationic copolymers as compared to the hydrolytic copolymers are independent of the temperature during the copolymerization. The anionic copolymerization is characterized by a more rapid incorporation of 6-caprolactam into the polymer chain. The differences in the polymerization activity of the two lactams decrease with increasing temperature of the anionic copolymerization. The described course of incorporation of individual monomers, with the various mechanisms of the polymerization, also corresponds to melting points of copolymers in accordance with their composition.     

Die Polymerisation von Lactamen. IV. Die anionische Copolymerisation von 6-Caprolactam mit 8-Caprylolactam

Conditions were defined for preparing homogeneous castings based on copolymers of 6-caprolactam and 8-caprylolactam under conditions of the low-temperature adiabatic copolymerization of the two lactams below the melting point of polymeric products (catalyst: sodium salt of lactams, activator: N-acetyl-6-caprolactam). The content of 8-caprylolactam in the copolymer cannot exceed 30 mole-% owing to its high polymerization heat and to the dependence of the copolymer melting point on the concentrations of the two lactams; the homopolymerization of the 8-caprylolactam cannot be accomplished under these conditions. The copolymer melting point exhibits a minimum in the region of the equimolar ratio of the two lactams. Further, the temperature dependence of the 8-caprylolactam specific heat was determined over an interval of 100 to 226°C (C_p = 0.2543 + 0.0007 T). The copolymerization rate of the anionic process increases with increasing content of 8-caprylolactarn, in accordance with differences of several orders existing between homopolymerization rates of the two lactams. The content of water extractable portions in the copolymers drops proportionally to increasing content of 8-caprylolactam, similarly as in equilibrium copolymers prepared by the hydrolytic copolymerization.     

Clay mineral/polyamide nanocomposites obtained by in-situ polymerization or melt intercalation

Series of so far undescribed clay mineral polyamide nanocomposites (CPN) were prepared by hydrolytic polymerizations of η-capryllactam (L8), ω-laurolactam (L12) and N-methyl-ω-laurolactam (ML12) initiated with 12-aminododecanoic acid (ADA) in the presence of a organomontmorillonite (OMt). Polymerization process was markedly accelerated due to a contribution of acidolytic and cationic polymerization on the intercalated ADA and its hydrochloride. Simple kinetics of polymerization with constant number of growth centers is valid up to a high polymer yield for all the lactams under study. For the sake of comparison, polyamide 6 nanocomposites were synthesized both by the method of the in-situ ε-caprolactam (L6) polymerization and by polyamide 6 melt blending. Structures of the CPN were analyzed by X-ray diffraction.     

Polymerization of lactams, 48. Autocopolymerization of 6-caprolactam with 12-dodecanelactam

The homo- and copolymerization of 6-caprolactam and 12-dodecanelactam was studied in the absence of an intentionally added initator. Both the polymerization and the copolymerization of an equimolar mixture of the monomers exhibited an induction period, the length of which was reduced with increasing temperature. Above 260°C, the polymers and copolymers of 6-caprolactam were not stable and their intrinsic viscosities as well as the polymer content decreased during long polymerization periods. On the other hand, insoluble products were formed in the homopolymerization of 12-dodecanelactam at temperatures of 300°C and higher. As much as 35 wt.-% of oligomers, predominantly cyclic ones, were formed in the initial stage of polymerization and copolymerization.     

Polymerization of lactams, 49. Hydrolytic polymerization of 6-caprolactam in the presence of its cyclic dimer

The hydrolytic polymerization of 6-caprolactam has been studied at 260–280°C in the presence of 5, 10 and 15 mol-% of cyclic dimer of 6-caprolactam and 2 mol-% of 6-aminocaproic acid as an initiator. The content of monomer and cyclic oligomers, including pentamer, was determined by HPLC. It has been proved that the rate of polymerization decreases with increasing content of cyclic dimer in the initial mixture and the time required to attain the equilibrium content of polymer increases as much as by an order of magnitude. The cyclic dimer is incorporated into the polymer above all in the final reaction stage.     

Die Polymerisation der Lactame. XV. Die Polymerisation der Lactame in Gegenwart von N-Benzoyllactamen und Pentamethylguanidin

The catalytic system pentamethylguanidine/N-acyllactam is able to induce the polymerization of lactams. Whereas in the case of 2-pyrrolidone the course or the process is similar to polymerizations initiated with alkali salts of this lactam, except for that it is remarkably more moderate, in the case of 6-caprolactam and 8-caprylolactam it is characterized by an induction period that is not typical for activated anionic polymerizations of these lactams. At 175°C the rate of polymerization of 8-caprylolactam is by more than one order of magnitude higher than that for 6-caprolactam, and in both of them the process is more moderate than in case of activated polymerizations of these lactams initiated by their alkali salts. On the basis of conductivity measurements in the case of 2-pyrrolidone it is possible to assume an anionic mechanism of the polymerization.     

ε-Caprolactam polymerization in presence of polyhedral oligomeric silsesquioxanes (POSS)

Polyhedral oligomeric silsesquioxanes (POSS) have been covalently linked to polyamide 6 (PA6) chains with the aim of synthesizing hybrid organic/inorganic polymer materials. The synthesis has been achieved by in situ polymerization of ε-caprolactam (CL) in presence of increasing amounts of POSS molecules, using two polymerization mechanisms (hydrolytic and anionic). The latter method has been carried out by three different approaches, in order to get PA6 samples characterized by various morphologies and content of structural defects: (i) quasi-adiabatic bulk polymerization; (ii) isothermal bulk polymerization; (iii) quasi-isothermal suspension polymerization. The products obtained have been characterized in term of structure, morphology, thermal properties and molecular mass.     

Tough,self-recovery and self-healing polyampholyte hydrogels

This article reviews the recently developed tough, self-recovery, and self-healing polyampholyte hydrogels. Polyampholyte hydrogels are synthesized using one-step radical copolymerization of cationic and anionic monomers with equal charges at high monomer concentration. The random copolymerization process makes the ionic monomers randomly distributing along the backbones, resulting in the formation of ionic bonds with a wide strength distribution via inter and intra chain complexation in the polymer network, weak bond and strong bonds. The strong bonds serve as permanent cross-linking, integrating the hydrogels to impart the elastic behavior, while the weak bonds can break upon the loading, dissipating energy to give the toughness, and re-form again after unloading to enable the self-recovery behavior. Accordingly, polyampholyte hydrogels have condensed polymers in water (ca 40?50 wt %). They are strongly viscoelastic and have a high toughness (fracture energy of 4000 J/m²), a wide range of tuning modulus (0.01 to 8 MPa), 100% self-recovery, and a high self-healing efficiency after cutting.     

Die Polymerisation von Lactamen. VII. Die Autopolymerisation von 8-Capryllactam

By heating of anhydrous 8-capryllactam to 240–280°C in the absence of catalysts polymerization takes place. The polymerization is characterized by a short induction period which decreases with increasing temperature. The degree of polymerization remains almost constant in the region of 40 to 90 percent of polymer content, in the region of high content of polymer the degree of polymerization increases rapidly. At higher temperatures insoluble, crosslinked products are formed. The possible mechanism of autopolymerization of lactames is discussed.     

Effects of cationic and anionic clays on the hydrolytic degradation of polylactides

Polylactide (PLA)/montmorillonite (MMT) cationic clay and PLA/hydrotalcite (HT) anionic clay composites at 5wt% clay were melt compounded and characterized for morphology before and after hydrolytic degradation. Semicrystalline and amorphous polymers were used as well as noncalcined and calcined clays. The addition of cationic clays led to the formation of microcomposites, whereas the addition of anionic clays produced a much finer dispersion and enhanced polymer intercalation corresponding to that found in nanocomposites. Hydrolytic degradation rate constants of cationic microcomposites and, particularly, of anionic nanocomposites are lower than those of the unfilled polymers, possibly due to the reduction of the carboxylic group catalytic effect through neutralization with the hydrophilic alkaline filler. Comparison of calcined MMT and HT clays vs. their noncalcined counterparts suggest that calcination can further reduce hydrolytic degradation rates, particularly for semicrystalline PLA. Based on the calculated activation energies, the degradation kinetics did not differ significantly above and below the assumed T_g of 58–60°C. The results of this work would be applicable to controlled release pharmaceutical formulations containing clay/drug combinations produced by melt compounding with a biodegradable polymer matrix. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Ionic graft copolymerization. VI. Graft copolymerization of β-propiolactone and N-vinylcarbazole onto trunk polymer containing carboxylic acid,sulfonic acid,and their salts

It was pointed out in previous papers that both cationic and anionic polymerization might be involved simultaneously in grafting onto trunk polymers containing ? COOH or ? SO₃Na. The graft copolymerization of β-Propiolactone (βPL)–N-vinylcarbazole (NVCZ) onto styrene-divinylbenzene copolymers containing carboxylic acid, sulfonic acid, and their salts was carried out in order to distinguish between the polymers produced by anionic and cationic mechanisms. The polymer obtained by the polymerization of βPL–NVCZ with BF₃·OEt₂, a typical cationic catalyst, consisted mainly of NVCZ units, but the polymer obtained with BuLi, a typical anionic catalyst, consisted mainly of βPL units. In the graft copolymerization of NVCZ–βPL onto trunk polymer containing ? COOH, the NVCZ contents of the branch polymer and the tolueneinsoluble fraction were estimated to be ca. 50 mole-%; therefore these polymers were produced by both cationic and anionic mechanisms. In the case of graft copolymerization onto the trunk polymer containing SO₃Na, it was found that both cationic and anionic polymerization also occurred simultaneously.     

Polymerization of Lactams: 57. G.l.c. and n.m.r. analysis of the anionic copolymers of 2-pyrrolidone with 6-caprolactam and 8-octanelactam

The activated anionic copolymerization of 2-pyrrolidone (PD) with 6-caprolactam (CL) or 8-octanelactam (OL) proceeds even above the ceiling temperature for PD homopolymerization. At high temperatures, the copolymerizations are accompanied by the depolymerization of PD sequences, which is more pronounced with the copolymers with CL. The copolymers obtained probably exhibit a constitutional heterogeneity and contain considerable amounts of low-molecular weight fractions. This may be the reason why the content of comonomers in the prepared copolymers determined by g.l.c. did not agree with that found by ¹H n.m.r. or ¹³C n.m.r. spectroscopy. The copolymers with CL had in part a block structure and also an alternating character, depending on temperature and polymerization time, while random copolymers were obtained at high temperatures. The copolymers with OL tended mostly to alternation.     

Determination of the residual monomer concentration of ε-caprolactam in polyamide-6 using thermogravimetric analysis coupled with Fourier transform infrared spectroscopy gas analysis

For the anionic polymerization of ε-caprolactam to polyamide-6 the residual monomer concentration in the final polymer is an important characteristic. To determine this residual ε-caprolactam monomer concentration, a fast and fail-safe method was developed, which couples thermogravimetric analysis (TGA) with Fourier transform infrared spectroscopy (FTIR) gas analysis. FTIR allows an identification of the types of gasses released during heat treatment. Calibration of the infrared absorbance of ε-caprolactam and the corresponding mass loss in TGA allows a quantitative evaluation of the ε-caprolactam monomer release. Low-heating rates and powdery samples guarantee high-precision measurements.     

Polymerization of lactams, 38. Copolymerization of 6-caprolactam with some of its non-homopolymerizing derivatives

It was demonstrated that non-homopolymerizing derivatives of 6-caprolactam: 7-cyclohexyl-1-aza-2-cycloheptanone (I) and 7-isopropyl-5-methyl-1-aza-2-cycloheptanone (II) were polymerizing with 6-caprolactam under conditions of the socalled hydrolytic polymerization. With its increasing content in the initial reaction mixture the copolymerization rate, the equilibrium content of the copolymer, and the reduced viscosity decreased. Lactam (I) was a more reactive comonomer in comparison with lactam (II).     

Controlled synthesis of crosslinked polyamide 6 using a bis-monomer derived from cyclized lysine

The controlled synthesis of polyamide 6 chemical networks by anionic ring-opening copolymerization of ε-caprolactam (CL) with synthesized bis-ε-caprolactam derived from α-amino-ε-caprolactam, i.e. N-functionalized α-amino-ε-caprolactam bis-monomers, using sodium ε-caprolactamate as an initiator and hexamethylene-1,6-dicarbamoylcaprolactam as di-functional fast activator was examined in bulk at 140 °C. An urea-based bis-monomer and CL were first shown to copolymerize with a decreasing polymerization rate due to side reactions. On the contrary, quantitative copolymerization of CL with various amounts of bis-N(2-oxo-3-azepanyl)-1,6-tetramethylenediamide, an amide-based bis-monomer, leads to fast kinetics similar to the homopolymerization of CL. Crosslinked PA6 with network exhibiting elastic or viscoelastic behaviors, depending on the amount of crosslinker, were observed and characterized by swelling in hexafluoroisopropanol, dynamic mechanical analysis and rheology measurements. Crystallinity and swelling were shown to decrease with the increasing content of the crosslinking agent.     

AM_nBS_SSS三元疏水缔合聚合物PAnBS的合成及溶液性能研究

以对正丁基苯乙烯(nBS)、对乙烯基苯磺酸钠(SSS)和丙烯酰胺(AM)为原料,采用自由基胶束聚合法合成了阴离子型三元疏水缔合聚合物PAnBS,用红外光谱法、紫外光谱法以及核磁共振氢谱法对共聚物的结构进行了表征;考察了不同反应条件对共聚物溶液表观黏度的影响,得到了具有较强增黏能力的聚合物合成工艺条件:nBS、SSS和引发剂用量分别为总单体摩尔分数的1.5%、9%和0.1%,总单体和表面活性剂十二烷基硫酸钠(SDS)在溶液中的质量分数分别为25%和6%,反应温度50℃,反应时间10 h。与相对分子质量(简称分子量,下同)1 970万、水解度19.43%的超高分子量部分水解聚丙烯酰胺(HPAM)相比,所得PAnBS在NaCl或CaCl2水溶液中具有更强的增黏能力;PAnBS在淡水或盐水溶液中于80℃下的耐老化性能优于超高分子量HPAM,表现出优良的耐温抗盐性能。     

丙烯酰氧乙基三甲基氯化铵-丙烯酰胺共聚物的制备研究

以丙烯酰氧乙基三甲基氯化铵(DAC)和丙烯酰胺(AM)为单体,过硫酸铵和亚硫酸氢钠为引发剂,采用水溶液聚合合成阳离子高分子聚合物P(DAC-AM)。讨论了单体质量比、引发剂用量、温度等因素对聚合反应的影响,得到了合适的制备参数:反应温度55℃,引发剂0.035g,单体质量比m(AM):m(DAC)=3:14;并对产物进行了红外光谱和热失重分析,确定了聚合物为P(DAC-AM),热分解温度为230℃。     

疏水缔合改性丙烯酰胺共聚物的合成

采用自由基胶束聚合法合成了丙烯酰胺（AM）/丁基苯乙烯（BS）/2-甲基-2-丙烯酰胺基丙磺酸钠（NaAMPS）疏水缔合水溶性共聚物PASA,PASA避免了目前疏水缔合聚合物溶液热稳定性差的问题.研究得到了适宜的反应条件,包括NaAMPS、BS和引发剂加量相对于单体总量的摩尔分数分别为10%、2.5%和0.07%,总单体在水里的质量分数为10%,SDS在水里的质量分数为6.0%,反应温度50℃,pH=6～7,反应时间12 h.采用以上反应条件得到PASA的临界缔合质量浓度为0.05 g·dL^-1,对应的水溶液表观黏度为283 mPa·s,质量浓度为0.1 g·dL^-1的水溶液表观黏度为1020 mPa·s.采用元素分析、UV、FT-IR和¹HNMR证实了共聚物的分子结构;DSC分析表明了共聚物分子链中存在疏水嵌段.     

Graft copolymers of poly(methyl methacrylate) and polyamide-6 via in situ anionic polymerization of ε-caprolactam and their properties

Graft copolymers of poly(methyl methacrylate) and polyamide-6 (PMMA-g–PA6) were investigated via in situ anionic polymerization of ε-caprolactam, using PMMA precursors with N-carbamated caprolactam pendants (PMMA–CCL) as macroactivators and sodium caprolactamate as catalyst. Three grades of PMMA–CCLs obtained by free radical copolymerization were used for synthesizing the PMMA-g–PA6 copolymers with different PMMA content. The resulting graft copolymer was characterized by Fourier-transform infrared spectroscopy and selective extraction. Scanning electron microscopy is used to clarify the phase morphology of obtained polymer by fracture surface. The thermal property, crystallinity and dimensional stability of graft copolymer were studied using differential scanning calorimetry, X-ray diffraction and water absorption measurement. The results show the T_g of graft copolymer is higher than that of neat PA6, but the onset and peak points of graft copolymer melting point are shifted to lower temperature. The percentage crystallinity and water absorption of PMMA-g–PA6 copolymer decrease with increasing PMMA content, but the crystal structure of PA6 is scarcely affected by the presence of PMMA. Graft copolymers have improved dimensional stabilities relative to neat PA6. Upon the incorporation of 19.9 wt% PMMA into PA6, the water absorption of PMMA-g–PA6 copolymer has been reduced from 4.8 for neat PA6 to 2.1%.     

Die polymerisation der lactame XIV. Einfluß des hexamethylguanidiniumchlorides auf die aktivierte anionische polymerisation der lactame

It was proved that hexamethylguanidiniumchloride (HMGC) exhibited a pronounced accelerating effect on the activated anionic polymerization of 2-pyrrolidone (40°C) and 6-caprolactam initiated by alkali metal salts of the corresponding lactams. The accelerating effect of HMGC was not specific for a certain type of alkali metal salt of lactams as initiator, it was proved that the effect is operative for polymerization of 6-caprolactam when using sodium or cesium salt of 6-caprolactam. It was proved that HMGC does not form growing centers under reaction conditions studied. The initial polymerization rate in the homogeneous phase is a linear function of square root of HMGC concentration at constant concentrations of initiator and activator. On the basis of this finding it was possible to suggest a plausible mechanism of HMGC influence on the polymerization process.