DOI: 10.14457/tu.the.2017.206
title: Development of poly(lactide-co-acrylamide) copolymers for use in environmental and biomedical applications

description: UV-C induced surface grafting has been performed on bio-degradable/bio-compatible polylactide (PLA) films, and poly(lactide-co-glycidyl methacrylate) and partially crosslinked poly(lactide-co-glycidyl methacrylate), P(LA-co-GMA) copolymer powders by employing a hydrophilic vinyl monomer, acrylamide (Am), and a crosslinker, N,Nˈ-methylene bisacrylamide (MBAm) to form a partial crosslinked structure among PAm graft chains. Three separate photo-initiators (with/without coinitiator, and thermal initiator to speed up photo-grafting reaction); riboflavin (RF) photo-initiator/ammonium persulfate (APS) thermal-initiator/N,N,Nˈ,Nˈ-tetramethylethylenediamine co-initiator (TEMED), camphorquinone (CQ) photo-initiator/N,Nˈ-dimethylaminoethyl methacrylate (DMAEMA) co-initiator, and benzophenone (BP) photo-initiator are deployed in methanol solutions of monomer-crosslinker, independently. The surface-grafted poly(lactide-graft-acrylamide-co-N,Nˈ-methylene bisacrylamide) copolymer films, P(LA-g-Am-co-MBAm) and poly(lactide-co-glycidyl methacrylate-graft-acrylamide-co-N,Nˈ-methylene bisacrylamide) copolymers particles, P(LA-co-GMA-g-Am-co-MBAm) possess a combination of unique properties of biodegradable PLA, PAm, and PGMA (only in powder samples) polymers. The success of the surface photo-grafting process on both films and powders was verified by FTIR (transmission and/or ATR mode) and 1H NMR spectroscopy. The characteristics FTIR absorption bands at around 1680 and 1599 cm−1 in the grafted copolymers’ spectra, accounted for amide I and amide II bands, respectively, confirm the presence of PAm as P(Am-co-MBAm) graft chains. Two characteristics 1H NMR signals of PAm appear at around 2.0-2.1 and 1.5-1.6 ppm (overlap with PLA methine proton) in the grafted copolymer spectra, further ensuring the existence of polyacrylamide. The evidence of grafting reaction on the PLA films is also confirmed by XPS analysis. Physicochemical changes of the blank PLA and grafted PLA films are evaluated in terms of chemical structures, radiation-induced degradation followed by crystallization, morphology, thermal properties and mechanical behavior by applying analytical techniques GPC, DSC, XRD, SEM, contact angle (θ) measurements, and Tensile Testing along with FTIR and 1H NMR. The results reveal that a low degree of PLA degradation through chain scission is observed in both blank and grafted PLA films. This generates more polar chain ends that can further induce crystallization. Results from contact angle measurements indicate that the grafted films have higher hydrophilicity and pH-responsive behavior. The incorporation of PAm on the film’s surface and the induced crystallization lead to improvements in certain aspects of mechanical properties of the films.  Standard techniques for quantitative measurement of PAm contents grafted on PLA film substrates, P(LA-g-Am-co-MBAm) and P(LA-co-GMA) powder substrates, P(LA-co-GMA-g-Am-co-MBAm), have been developed with 1H-NMR, FTIR, and XPS (only for film samples) spectroscopy. The techniques are then applied to examine P(LA-g-Am-co-MBAm) and P(LA-co-GMA-g-Am-co-MBAm) samples prepared from RF/APS/TEMED and CQ/DMAEMA photoinitiator/coinitiator systems. Efficiency and accuracy of the techniques are compared. The results from all techniques are in good agreements, indicating high analysis precisions, although FTIR technique provides additional advantages, in terms of short analysis time, ease of sample preparation, and accessibility of a machine.  The results indicate that the riboflavin (RF) initiator system has higher grafting efficiency than its camphorquinone (CQ) counterpart in the measurements of both the films and powder copolymers. These standard techniques can be applied in the analysis of these materials, and further modified for quantitative analysis of other grafting systems. The materials have high potential for use in biomedical and environmental applications, such as cell culture substrates or scaffolds or pH-sensitive absorbents.