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Introduction to Chain Molecules
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
Next let us consider a few specific examples of these classes of polymers. The addition polymerization of a vinyl monomer CH2 = CHX involves three distinctly different steps. First, the reactive center must be initiated by a suitable reaction to produce a free radical, anionic, or cationic reaction site. Next, this reactive entity adds consecutive monomer units to propagate the polymer chain. Finally, the active site is capped off, terminating the polymer formation. If one assumes that the polymer produced is truly a high molecular weight substance, the lack of uniformity at the two ends of the chain – arising in one case from the initiation and in the other from the termination – can be neglected. Accordingly, the overall reaction can be written
HEMA and alginate-based chondrogenic semi-interpenetrated hydrogels: synthesis and biological characterization
Published in Journal of Biomaterials Science, Polymer Edition, 2020
María Luz Torres, Tamara Gisela Oberti, Juan Manuel Fernández
Semi-interpenetrating hydrogels were synthesized employing various compositions of EGDMA or AIBN and the obtained membranes were denoted as SEMI 1, SEMI 2, SEMI 3 and SEMI 4. The variation in the amount of crosslinker (EGDMA) produces networks with different crosslinking density, so the properties (like mechanical, swelling) of the hydrogels obtained depend on the proportion of reagents used. Thus, more rigid hydrogels will be obtained by using a greater amount of crosslinker. In addition, the lesser quantities of initiator would imply a decrease in the amount of reactive species available to initiate polymerization, which would cause each reactive center to produce polymer chains of higher molecular weight; therefore the hydrogels synthesized under this condition will be less rigid. Furthermore, the influence of the different synthesis conditions of the hydrogels on the cellular response was analyzed. The sample designated as HEMA acted as control material which was prepared using distilled water instead of the alginate solution (Table 1). The selected reaction conditions and the experimental procedure carried out were based on bibliographic research [9–11]. In particular, 3.5 ml of HEMA were added under stirring to the aqueous solution of sodium alginate 1% w/v (pH 7-8) in a 1:1 volume ratio. EGDMA (1%, 0.5% and 0.25%v/v with respect to HEMA + sodium alginate volume) and AIBN (1% and 0.5%w/v with respect to HEMA + sodium alginate volume) were added later. After dissolution of AIBN, dissolved oxygen of the reaction mixtures was removed by purging with nitrogen gas for half an hour. Then, each mixture was poured between two glass plates spaced by a 1 mm-thick Teflon cast to obtain uniform rectangular membranes. The reaction was performed at 60 °C for 1 h. Scheme 1 shows a representation of the semi-IPN hydrogels synthesized in this study.