The aim of this research was to modify polyamide 6 (PA6) either starting from low molecular weight end modified polymer or high molecular weight commercial grade by solution and/or solid-state polymerization (SSP) without destroying the crystalline phase. Synthetic approach consisted of first molecular mixing of all components in a common solvent preferably followed by SSP below the melting temperature of the PA6. By this way, modification of the backbone occurs in the amorphous phase which is the only mobile part of the polymer at those temperatures. By SSP reactions blocky microstructures are formed instead of random copolymers. In this study, modification of PA6 was mainly done for two purposes: for improved biodegradability and for better properties such as increased Tg. In the first part oligoesters were incorporated in the low molecular weight PA6 chain as hydrolyzable blocks which as a result provide degradability. For this aim two different synthetic routes were followed. The first one was done by making use of isocyanate and amine end groups which are highly reactive already at room temperature. Low molecular weight totally amine end-capped PA6 and totally isocyanate end-capped polycaprolactone diol were synthesized and reacted during the solution mixing in hexafluoroisopropanol (HFIP). High molecular weight multi-block copolymers of PA6-PCL were obtained which were susceptible to degradation either hydrolytically or enzymatically. The second route consisted of base-catalyzed diepoxide oligoester (DEPA)- and low molecular weight carboxyl end-capped PA6 reactions to obtain partially degradable polyesteramides by solution mixing in HFIP followed by complete removal of the solvent and finally SSP. Firstly, model reactions were performed by using polypropylene glycol diglycidyl ether to determine the optimum reaction conditions and later DEPA was used. Here, side reactions and crosslinking prevented obtaining high molecular weight multi-block copolymers as a result of very complicated nature of epoxide-carboxyl reactions. However, multi-block copolymers were achieved consisting of a few blocks of PA6 and oligoester. In the second part of the research, a commercial grade of PA6 was modified with a ‘Nylon salt’ of 1,5-diamino-2-methylpentane (Dytek A) and isophthalic acid (IPA). This modification was also done in the solid state after solution mixing of the salt and PA6. Different amounts of salt were used and melt polymerizations were also performed for comparison. Salt incorporation occurs via aminolysis and acidolysis of PA6. Therefore, in the first stages of the reaction a dramatic decrease in molecular weight is observed which later starts increasing. It was first observed that due to a loss of the volatile diamine mostly acidolysis was taking place which means chain scission by the incorporation of the diacid but not the diamine. This resulted in acid end groups and prevented further increase in molecular weight. For that reason another method was developed to keep the diamine in the mixture. Not only the reaction temperature was lowered but also the reaction was performed in a totally closed environment under Argon until all the diamine was incorporated via aminolysis. In the second stage the reaction temperature was increased and continuous Argon flow was applied to remove the condensation water produced by coupling of the broken chains. This method indeed provided higher molecular weights than before. Molecular and microstructural analysis was done in detail by SEC, 1H and 13C NMR whereas thermal analysis was done by TGA and DSC. Detailed comparison with melt-polymerized random polymer-salt copolymers was performed. It was observed that after SSP reactions the crystalline phase of the PA6 was kept intact while amorphous phase was modified. The degrees of randomness were calculated from NMR and blocky structures were confirmed. Melting points comparable to neat PA6 were achieved and higher Tg values were obtained.
|Qualification||Doctor of Philosophy|
|Award date||19 Mar 2012|
|Place of Publication||Eindhoven|
|Publication status||Published - 2012|