Poliamid modifikasyonu

Abstract

Bu çalışmada poliamide yumuşak bir segment sokul masıyla oluşan blok kopolimer modifikasyonu denenmiştir, üç bloklu kopolimer hazırlanmasında modifiye eden polimer olarak kullanılacak polimerler genellikle molekül ağırlı ğı az olan ve zincirlerinin sonunda reaktif uçlar bulunan polimerlerdir. Karboksil sonlu poli bütadienin uç grupları klorlandıktan sonra uçlarında pol i meri esmen in başlayacağı merkez molekül olarak kullanılmıştır. e-Kaprolaktamın anyon i k polimerizasyonu ile üç bloklu kopolimer oluştu rulması alkali katalizör olarak sodyum hidrür ve kokata- lizBr olarak N-pol ibütadieni 1 kaprolaktamın kullanılması ile gerçekleştirilmiştir. Ayrıca ikinci bir kokatalizör olarak asetil klorür kullanılarak e-kaprolaktamın aktive edilmiş monomer kondensasyonu ile anyonik polimerizasyonu da gerçekleştirilip, üçbloklu kopolimerle karşılaştırıl mak üzere naylon-6 hazırlanmıştır. Bu polimerizasyonu yürüten temel mekanizma e-kaprolaktam anyonunun imid bağına yaklaşıp kırmasına dayanmaktadır C1J Polimer i zasyonlarda katalizörün bozunmasına neden olabilecek nemi uzak tutmak için nemsiz ortam oluşturulup monomer, çözücü ve kokatalizörün azami derecede saf olma sına dikkat edilmiştir. Karboksil sonlu polibütadien (CTB- (CO2H)3) tionil klorür (S0C12) ile azot atmosferi al-tında klorlandıktan sonra piridin varlığında yine azot atmosfer altında E-kaprolaktam ile reaksiyona sokularak N- pol ibütadieni 1 kaprolaktam kokatalizörü elde edilmiş tir. Asetil klorür ile E-kaprolaktamın yine piridin varlığında reaksiyonu ile de N- asetil kaprolaktam kokatalizörü elde edilmiştir. Reaksiyon şartlarından, sıcaklık, katalizör ve kokatalizör konsantrasyonları değiştirilerek e-kapro laktam hazırlanıp azot atmosfer altında saklanan kokata- lizörler ile reaksiyona sokularak naylon- 6 ve üç bloklu kopolimer naylon- 6 - polibütadien - naylon- 6 hazırlanıp polimerleşme oranları incelenmiştir.

Owing to their properties polyamides belong to the most important commercially produced polymers. They have, however, a certain disadvantage in their low impact strength, and therefore modification by inserting a soft segment to form a block copolymer has often been considered. In this study preparation of block copolymer from e- caprolactam and a liquid carbonyl terminated butadiene having higher impact strength then ordinary poly (e-caprolactam) was concerned. Triblock copolymers with an elastomeric central sequence and terminal blocks as cohesive as nylon- 6 are indeed attractive materials. Block copolymers based on nylon might be considered in the solution of some problems due to hydrophilic character of polyamides The presence of hydrophobic blocks like polybutadiene in nylon-6 would reduce its sometimes detrimental character. The modifying polymers employed mostly possess relatively low molecular weight and their chains are terminated with reactive groups (-COOH, NH3, -NCO, etc.) Carbo>;yl terminated polybutadiene after chlorination is referred as the growth center of polymerization in this study. Anionic polymerisation of e- caprolactam is conducted with the aid of sodium hydride as alkaline catalyst and N- polybutadienyl caprolactam as cocatalyst. The mechanism of such a polymerization involves attack of an e-caprolactam anion at imide linkage til. The anionic polymerization of e- caprolactam was studied in 1939 by Joyce and Ritter £2], Anhydrous conditions must be strictly maintained during the course of the polymerization to prevent destruction of the catalyst. Further, monomer, solvent and cocatalyst must be purified.The following reaction mechanism is generally proposed for -this system. x- H,(CHa)8-N <1) C=Q HX,(CHa)es-N 6=0,(CHa)a-l)l c=o (2) 9 Ç~(CHa)Bi-NH 6=0 0 fc-(CHa> (3) TZ> «S -NH.ai-NHs Polymerisation occ induction period. The in fact that step 2 of the disproportionation reacti effects of adding N-acety mixture, Sabenda and Krai effect of certain imides Addition of these imides disproportionation reacti the polymerisation of e-c induction periods at lowe urs after a characteristic due t i on period results from the above scheme is a slow on. During their study of the 1 caprolactam to the reaction icek discovered the cocatalytic upon this polymerization [31. essentially eliminates the on. This modification allowed ap rol act am with shorter r temperatures.The polymerization of E-caprolactam in this system may be represented by the following mechanism: (1) 9 R-C-N-(CH2>ies 0=6 N-(CH 0= 2' C9 9 -*? (CH2)es-N-C-(CH2)l c=o -%-î (2) «CH2)0-lşi-C-<="" style="margin: 0px; padding: 0px; outline: 0px;"> a-bp =0 C=0 Many cocatalysts have been used to activate thö polymerization of caprolactam. Among the most successful are the acyl compounds. In lactam polymerization, according to Odian E 4 3, initiation may involve contributions from both the imide dimer and the N-acyl- lactam. In this system, polymer size increases with increasing concentration of catalyst and decreasing concentration of N- acyl lactam. In this study polymerization of e- caprolactam was achieved using sodium hydride as catalyst, N- acetyl caprolactam and N- polybutadienyl caprolactam as cocatalysts. Specifically, the effects of catalyst concentration, cocatalyst concentration and polymerization temperature on the conversion of initial monomer to the resultant polymer were studied. Carboxyl terminated polybutadiene was chlorinated by thionyl chloride under nitrogen atmosphere. Acylchlaride terminated polybutadiene reacted with e-caprolactam in the presence of pyridine to evaluate VI!N- polybutadienyl caprolactam, the second cocatalyst N-acetyl caprolactam was evaluated by reacting acetyl chloride with e- caprolactam. Reacting these two cocatalysts with e- caprolactam and polybutadiene at different temperatures nylon-6 and triblock copolymers were prepared. Results are given in the following table. Table 1. Polymerization of e-Caprolactam-" Using Acyl Lactams "e-Caprolactam taken as 100 mol percentage Conversion of polymers was decreased as the size of cocatalyst increased. N- acetyl caprolactam which has relatively small size gave higher yield than N- poly butadienyl caprolactam. The effects of temperature on polymerization of the small sized N-acyl lactams is known. In this study e-caprolactam polymerized with N-polybutadienyl caprolactam at different temperatures. They have an optimum polymerization temperature around 200°. Table 2. Temperature Effect on Conversion VIIICatalyst effect on triblock copolymerization was alsa dependent upon the activation amount of monomer. Increased number of activated monomers would react much more rapidly at both functional ends of the template molecule. The center molecule of polymerization process must easily meet and react with activated monomer. Therefore if, the concentration of this big molecule is kept high the probability of meeting its all functional ends with activated monomer is reduced, hence polymerisation rate becomes less.