Abstract
In this paper, chemical functionalization of poly(lactic acid) (PLA) was carried out by using of salicyl aldehyde (SAl) and salicylic acid (SAc) as co-initiators of ring opening polymerization (ROP). Two factorial designs (22) were performed to evaluate the effects of the lactide/catalyst and co-initiator/catalyst molar ratios on the content of aldehyde or carboxylic acid end groups, thermal properties and molecular weight (Mw) of PLA. Tin(II) 2-ethylhexanoate was used as a catalyst. The co-initiator/catalyst molar ratio has a statistically significant influence on the polymer functionalization. The highest co-initiator/catalyst molar ratio of 12/1 allows the best aldehyde or carboxylic acid functionalization, independent on the lactide/catalyst molar ratio. On the other hand, the used lactide/catalyst and co-initiator/catalyst molar ratios did not show a statistically significant influence on the polymer thermal properties. Besides, co-initiator/catalyst molar ratio has a statistically significant influence on the polymer molecular weight. So, the highest co-initiator/catalyst molar ratio used (12/1) in combination with the highest lactide/catalyst ratio (125/1) produced functionalized PLA with higher molecular weights.
Highlights
The use of two co-initiators, salicylic acid and salicyl aldehyde, for the synthesis of the aldehyde or carboxylic acid end functionalized poly(lactic acid) (PLA) by ring opening polymerization (ROP) in the presence of Sn(Oct)[2] as a catalyst was reported in a previous work of our group at a specific reaction condition.[22]
The two experimental designs used in this work made possible the identification of the best ROP condition to assure maximum aldehyde and carboxylic acid functionalization of PLA
[lactide]/[Sn] molar ratio shows the expected behavior regarding to molecular weight, i.e., the Mw is higher as [lactide]/[Sn] increases, co‐initiators/catalyst molar ratios ([salicyl aldehyde (SAl)]/[Sn] and [salicylic acid (SAc)]/[Sn]) showed no statistically significant effect on Mw
Summary
Bioresorbable polymers are those capable of being completely degraded in an aqueous environment in their corresponding monomers, which, in turn, undergo metabolic action of living organisms.[1,2,3,4,5,6,7,8] Among these polymers, poly(lactic acid) (PLA), poly(glycolic acid) and their copolymers have been widely used in biomedical applications, especially in orthopedics and controlled drug release due to characteristics such as, biodegradation and biocompatibility.[9,10,11,12]PLA can be synthesized in a wide range of molecular weights using two procedures: (i) direct polycondensationRing opening polymerization (ROP) allows the synthesis of end functionalized polylactones and polylactides of high molecular weight.[6]. Two 22 factorial designs with replicates at central point were developed to evaluate the effects of lactide/catalyst and co-initiator/catalyst molar ratios as independent variables on the aldehyde or carboxyl acid end functionalized PLA.
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