PLLA-PEO Copolymers

PLLA-Z)-PEO diblock copolymers were initially studied by Younes and Cohn in 1987 and are probably one of the most studied systems. In these copolymers, the PEO block is expected to improve the physical properties of PLA, as well as to enhance its degradation resistance and improve drug release properties.The PLA-Z)-PEO-Z)-PLA triblock copolymer has also been much studied. -  

These block copolymers are usually miscible or weakly segregated in the melt (depending on their segregation strength, a function of the average molecular weight of each block time the Flory-Huggins interaction 

Microphase separation takes place during crystallization. ° ° Miscibility in the melt has also been reported for some high-molecular-weight blends of PLLA and PEO. The miscibility has been explored by changes in Tg of one or both blocks by and 

° However, as the Tg of PLA and the of PEO nearly overlap in many cases, it is difficult to evaluate miscibilities from simple Tg measurements. Nevertheless, if data published by different groups are ana-lyzed, ° ° both the Tg of PLA and that of PEO blocks are a function of the PEO composition and exhibit trends close to the predietions of the Fox equation for miseible systems. 

Sun et al. studied the erystallization of PLLA-Zj-PEO dibloek copolymers with different compositions (i.e. 68, 44 and 29 wt% of PEO) hy DSC, WAXS, PLOM and AFM. A PEO block length of 5 kg mol was constant for all the block copolymers studied. The of the PLLA block increased with its content. However, for contents of PEO lower than 44 wt% values higher 

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