SYNOPSISThe purpose of this study is to reinforce the flexible nylon-6 by using Poly (p-diphenyl methyl terephthalamide) (PMA) using MDI as a chain extender. Observation by scanning election microscopy showed that the multiblock copolymer had a homogeneous texture. From the differential scanning calorimetry measurements, the multiblock copolymers were shown to have only one melting point, Tm, which is higher than that of nylon-6. The wideangle X-ray diffraction pattern shows that nylon-6 has two diffraction peaks at 20 = 20" and 23.8". However, the multiblock copolymer has only one peak at 20 = 20°, indicating a different crystal structure of multiblock copolymers. The copolymers appears to have a significant reinforcing effect on the mechanical properties. 0 1994 John Wiley & Sons, Inc.
INTRODUCTIONRecently, a number of attempts have been made to improve the mechanical properties of the aliphatic nylons by using physical blending and chemical modification with aromatic polyamides such as Kevlar, polybenzamide (PBA) , '-' and poly (4,4'-diphenylsulfone terephthalamide) (PSA) .7-9 As shown in our previous p a p e~,~.~ the aliphatic nylon-6 was modified by the semirigid PSA, exhibiting better thermal and mechanical properties. In our studies, we used semirigid polyamide poly ( p -diphenyl methyl terephalamide) (PMA) with (4,4'-diphenylene methane diisocyanate) (MDI) as a chain extender to reinforce the aliphatic nylon-6. The chemical structure of PMA is shown below.The semirigid PMA has the same monoclinic crystal structure as that of nylon-6.* To whom correspondence should be addressed.
EXPERIMENTAL MaterialsNylon-6 is made by Formosa Chemical and Fiber Corporation. Nylon-6 was first dissolved in formic acid and then poured into an excess amount of water. Samples are refluxed with methanol and hot water for 16 h then dried under vacuum at 100°C for 8 h.The inherent viscosity ( vinh = 1.24) and= (21,500) of nylon-6 are obtained from the 1iterat~re.I~ c-Caprolactam, 6-aminohexanoic acid, hexamethylene diamine, 4,4'-diphenylene methane diisocyanate ( MDI ) , 4,4'-diaminodiphenyl methane (DDM ) , and terephthaloyl dichloride (TPC ) were the products from Merck Co., and used as received.N-Methyl-2-pyrrolidone (NMP) was first distilled over CaH2 at 92"-94"C/14 mmHg and then stored in the molecular sieves. The moisture content of a 5% LiCl solution in NMP was 0.018 w t %, determined with a Karl-Fischer Moisture Meter, MK A-3, and Kyoto Electronic. Lithium chloride (LiC1) was dried under vacuum at 160°C for 5 h.
Preparation for Polyamides and Their PrepolymersLow molecular weight diamine-terminated PMA is polymerized by low-temperature solution polymerization in N M P containing 5% LiCl at -10°C for 30 min. The reaction is shown below.Low molecular weight diamine-terminated nylon-6 prepolymer was prepared by using an excess of hexamethylene diamine (HMDA) described in the l i t e r a t~r e . '~. '~
Synthesis of Nylon-6-MDI-PMA Block CopolymersThe copolymers were synthesized by reacting nylon-6 prepolymer and PMA prepoly...
