Modification of stable and degradable polymers by heterogeneous grafting (1998)

This thesis summarizes the investigations of the electronbeam initiated grafting of a hydrophilic monomer, acrylamide(AAm), onto three polymers; linear low density poly(ethylene)(LLDPE), poly(&-caprolactone) (PCL) and chemicallycrosslinked poly( 1,5-dioxepan-2-one) (PDXO-X). LLDPE and PCLare semicrystalline and PDXO-X is fully amorphous. Both PCL andPDXO-X contain a hydrolysis sensitive ester bond in therepeating unit and are considered as biodegradable substrateswhile LLDPE is stable. The solid polymeric substrates areelectron beam irradiated prior to immersion in a liquid phasecontaining the monomer. Graft initiation, propagation andterrnination Will then occur in a heterogeneous phase system.The main goal with this work is to obtain new knowledge of somefundamental properties and potential applications for theheterogeneous grafting.The first part concems the influence of EB radiation onLLDPE, PCL and PDXO-X. The aim was to identify the initiatingspecies in the polymers using electron spin resonance andluminescence analyses. The cross linking and/or chain scissionin the polymer matrix, as a result of the EB irradiation, wasanalyzed. It was found that EB irradiation of PCL in inertatmosphere (argon) generated secondary alkylether radieals.This type of radieal was also found in PCL irradiated in airtogether with peroxy radieals. Chain scission was found to bethe dominating reaction in PCL as a result of the irradiation.The EB irradiation of PDXO-X in argon and air generatedtertiary carbon centered radieals. However, no peroxy radiealscould be detected for PDXO-X irradiated in air. Swellingmeasurements and SEC analysis of the soluble fraction suggeststhat chain scission is the main reaction in PDXO-X as a resultof the EB irradiation.The second part investigates the morphology of the graftedpolymer matrix, using LLDPE as model material. It also coversthe AAm grafting onto PCL, mainly evaluating the effect of doseand added inhibitor (Mohr's salt) upon gti yield (GY), andchain length of the grafted poly(acry1 amide) (PAAm). In thecase of the grafting of AAm onto LLDPE it is suggested that theinitiation occurs mainly in the semi-ordered interphase alongwith a decrease in crystallinity, due to solubilization of theordered crystalline domains. The grafted PAAm chains were foundto be more branthed than that of a ungrafted PAAm referencematerial. This is explained by that the chain growth of PAAmoccurs in the interphase where the toncentration of radieals,originating from the crystalline phase and from growing chainends, is high, hence promoting chain transfer reactions.The third part investigates the degradation of a system witha hydrophilic polymer (AAm) surface grafted onto the morehydrophobic PCL and PDXO-X. For PCL, no differente indegradation behavior could be obset-ved between irradiatedmaterials and irradiated and grafted materials. In the case ofPDXO-X, a significant decrease in degradation time was observedfor theirradiated and surface grafted sarnple as compared tothe irradiated sample.In the fourth part, derivatization of grafted PAArn topoly(viny1 amine) by the Hofmann degradation is examined. Theprimary amines were used for the coupling of heparin onto LLDPEand the surface activity towards arttimrombin III (AT III) wastested. The heparinized surfaces had a low but significantuptake of AT III and no activation of FXTI could bedetected.