Title

Multicomponent polymers containing poly(lactic acid)

Date of Completion

January 1996

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

Hydrophobic-hydrophilic copolymers containing poly(lactic acid) (PLA) were synthesized using three types of starting materials. The PLA macromonomers with methacrylate terminal functionality were synthesized from the cyclic dimer of lactic acid (lactide) with 2-hydroxyethyl methacrylate (HEMA) as initiator and stannous octoate as catalyst. The macromonomers were characterized with FTIR, NMR, DSC, TGA, WAXS, TEM, GPC, elemental analysis, circular dichroism (CD) and specific optical rotation measurements. CD and optical rotation measurements demonstrate that there is little racemization during polymerization. The properties of the macromonomers vary with the stereochemistry of the lactide and composition. Furthermore graft copolymers of various hydrophilic-hydrophobic balances and thermal properties can be prepared by copolymerization of the macromonomers with HEMA. Copolymers of L-lactide and HEMA synthesized using potassium tert butoxide also show compatibility in the amorphous phase. The T$\sb{\rm g}$ of the copolymers shifts to higher values with increasing HEMA content. Higher T$\sb{\rm g}$'s were also obtained for interpenetrating networks of PLLA-HEMA containing higher content of ethylene glycol dimethacrylate crosslinker.^ Polymerization of lactides with poly(ethylene glycol) (PEG) as initiator and stannous octoate as catalyst gives triblock copolymers in good yields. The results demonstrate that block copolymers of various hydrophilic-hydrophobic properties and exhibiting one, two, or three phase behavior can be prepared by varying the copolymer composition, PEG block (1,000 to 10,000) and stereochemistry of PLAs. All copolymers show compatibility in the amorphous phase. Furthermore, multicomponent polymers of L-lactide, HEMA and PEG can be prepared with T$\sb{\rm g}$ of the matrix above or below biological temperature (37$\sp\circ$C).^ The hydrophilic properties of poly(vinyl alcohol) were modified via the chemical grafting of DL-lactic acid to obtain tough rubbery materials. The materials were also characterized with DMTA, instron and swelling experiments. It is shown that various types of graft copolymers exhibiting improved mechanical properties can be synthesized using the new method developed in this study. The results demonstrate that different types of hydrophilic-hydrophobic hydrogels having high or low swelling characteristics can be synthesized. ^