The anionic polymerization of caprolactam

1999

Angew. Makromol. Chem.

One‐step preparation of composites of alkaline poly(6‐hexanelactam) (PCL) with solid lubricants (SL), such as graphite and molybdenum disulfide, is an energy‐saving process as additional polymer fusion and melt mixing are not necessary. The initiator/activator system used were: (i) sodium dihydrido‐bis(2‐methoxyethoxo) aluminate (SYN)/cyclic trimer of phenyl isocyanate (PIC); (ii) sodium/hexamethylene‐1,6‐diisocyanate (HMDIC); (iii) SYN/HMDIC. These systems have been found suitable for the composite synthesis since they are relatively insensitive to traces of humidity and other low‐molar‐mass compounds which may be adsorbed on lubricant surfaces. Incorporated graphite (up to 20 wt.‐%) and MoS2 (up to 40 wt.‐%) do not perceptibly affect glass transition temperature, melting temperature and crystallization temperature while polymer yield, polymerization degree and rate decrease. The crystallinity assessed by DSC passes through a maximum at 20% of MoS2 in contrast to that detected by X‐ray diffraction (XR) measurements. As expected, the mean spherulite diameter drops profoundly. Both SL affect mechanical properties of produced composites: (i) increase the modulus; (ii) decrease the compliance, the time dependence of which remains close to that observed for the matrix; (iii) reduce the yield strength; (iv) slightly lower the impact strength of composites. A tentative hybrid composite containing 15 wt.‐% of graphite, 5 wt.‐% of MoS2, and 5 wt.‐% of mineral oil (as a liquid lubricant) shows a modulus high enough and its propensity to creep is not enhanced. The observed changes in mechanical properties of PCL caused by the incorporation of SL do not preclude applications analogous to those of unfilled PCL. Friction properties of the composites were beyond the scope of this work.

Section: Synthesismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Composites of alkaline poly(6-hexanelactam) with solid lubricants: one-step synthesis, structure, and mechanical properties

Horský¹,

1999

Angew. Makromol. Chem.

“…The adiabatic conditions of the polymerization process were achieved by additional heating of the jacket, which maintained the jacket temperature identical with that inside the reactor. Sodium as the initiating agent was added to the molten monomer at temperatures ranging from 95 to 100 °C to prevent its inhibiting effect occurring if added at higher temperatures 19. Fillers were added afterwards within 5 minutes and the mixture stirred under nitrogen atmosphere was heated to the initial polymerization temperature T 0 ; activator was applied at T 0 stabilized for at least 2 minutes.…”

Section: Experimental Partmentioning

confidence: 99%

One‐Step Synthesis of Hybrid Composites of Poly(6‐hexanelactam) Combining Solid Tribological Additives and Reinforcing Components

Horský

2003

Macro Materials & Eng

Four types of composites of polyamide 6 with hybrid tribological additives were synthesized via anionic adiabatic “in situ” polymerization of 6‐hexanelactam (ε‐caprolactam) initiated with metallic sodium and activated with cyclic trimer of phenyl isocyanate or diphenylmethane 4,4′‐diisocyanate. The optimization of the initiator/activator systems in the range of 0.3 to 1.2 mol‐% and of the initial polymerization temperatures from 125 to 150 °C preceded the composite preparation. Combinations of fillers and their maximum applied concentrations (in wt.‐%) were the following: MoS2/graphite/oil (5/16/9), carbon fibers/graphite/oil (5/20/10), copper phthalocyanine (7), and B2O3 (11). Analysis of selected composites encompassed water extraction, DSC, and DMTA measurements. All tested fillers decreased the polymerization rate, polymer yield, melting temperature and crystalline fraction. Polymerization rate constants of the neat polyamide 6 obtained for various initial temperatures obeyed the Arrhenius plot giving an average activation energy value of 78.6 kJ · mol−1.Rate of polymerization as a function of the total fillers content in adiabatic anionic polymerization of 6‐hexanelactam (A: MoS2 + G/O, Na/PIC, B: CPC, Na/MDI, C: MoS2 + G/O, Na/MDI, D: CF + G/O Na/MDI).magnified imageRate of polymerization as a function of the total fillers content in adiabatic anionic polymerization of 6‐hexanelactam (A: MoS2 + G/O, Na/PIC, B: CPC, Na/MDI, C: MoS2 + G/O, Na/MDI, D: CF + G/O Na/MDI).

“…Although a number of practical findings about the bulk polymerization of 6-caprolactam in the presence of various reinforcements have been collected 13) , the effect of preparation conditions on the structure and properties of the produced composites still remains an intriguing task, especially when alternative catalytic systems or fillers are attempted. As generally known, the anionic polymerization of caprolactam is initiated with strong bases able to form free lactam anions whose addition to N-acyllactam growth centers (created due to the action of suitable activators) brings about propagation of the polymer chain [13][14][15][16][17] . Frequently, sodium caprolactam is prepared by using sodium dihydridobis(2-methoxyethoxo)aluminate and sodium tetra(6-caprolactamo)aluminate.…”

Section: Introductionmentioning

confidence: 99%

Composites of alkaline poly(6-caprolactam) and short glass fibers: one-step synthesis, structure and mechanical properties

Horský¹,

1999

Angew. Makromol. Chem.

If incorporation of short fibers precedes the polymerization process, their damage is reduced because the viscosity of a monomer is much lower than that of a corresponding polymer. One‐step preparation of composites also leads to essential energy savings since polymer fusion and melt mixing are eliminated. Structure and properties of poly(6‐caprolactam) matrix polymerized with the initiator/activator systems sodium dihydridobis(2‐methoxyethoxo)aluminate/cyclic trimer of phenyl isocyanate are affected by rising concentration of (γ‐aminopropyl)triethoxysilane sizing agent: polymerization is slower, but polymerization degree rises; yield strength and notched impact strength decrease, while crystallinity and modulus remain unaffected. When the initiation system sodium tetra(6‐caprolactamo)aluminate/cyclic trimer of phenyl isocyanate is alternatively used, the polymerization is somewhat faster, but the polymer is insoluble in m‐cresol due to side crosslinking reactions. Incorporated short glass fibers (SGF) (up to 13.2 vol.‐%) do not markedly affect the matrix properties. As expected, SGF decrease the compliance (increase the moduli) of composites, but do not affect the time dependence of the creep. Increasing the fraction of SGF also decreases the yield strength of composites, which indicates poor interfacial adhesion; the latter is only slightly improved by fiber sizing. Impact strength decreases with the fraction of as‐received SGF, while a moderate opposite trend can be seen for the composites containing silane treated fibers.