Hydroxy-telechelic aliphatic (co)polyesters are important building blocks of biodegradable multiblock copolymers which can be used as biodegradable elastomers and biodegradable shape memory polymers (BSMPs).For BSMPs

the transition or switch temperature at which the shape memory effect takes place is determined by the thermal trasition temperature of the reversible phase or soft segments

and the shape memory properties and mechanical properties are maily affected by the condensed state of the fixed phase or hard segments.Therefore

the thermal transition temperatures of hydroxy-telechelic aliphatic (co)polyesters are critical parameters for successful design of BSMPs.This article aims to report the relationship among the thermal transition temperature of two important hydroxy-telechelic aliphatic copolyesters

poly(L-lactide-co-glycolide) (PLLGA) and poly(ε-caprolactone-co-glycolide) (PCG)

and their molecular weight and copolymer composition. Hydroxy-telechelic PLLGA and PCG are synthesized via ringopening copolymerization of L-lactide and glycolide (LLA/GA) and ε-caprolactone and glycolide (CL/GA) using 1

4-butanediol as initiator and stannous octoate as catalyst at 140℃.After dissolving in chloroform

precipitated from methanol and drying under vacuum at 75℃ for 48 h

purified PLLGA and PCG were obtained and characterized by FTIR

1H-NMR

GPC and DSC. The polymerization took place in a living/controlled manner

and the molecular weight was adjusted by the monomer/initiator ratio in the range of 2000～14000.The polydispersity index ranged from 1.1 to 1.3.The GA content in the copolymers is of 0～0.22 for PLLGA and 0～0.32 for PCG and can be adjusted by the GA content in monomer feed (GA

0～0.2).The contents of GA in copolymers are higher than GA because of higher reactivity ratio of GA than LLA and CL.For convenience，GA was used to denote the copolymer composition.The FTIR and 1H-NMR spectra indicate that the copolymers are hydroxy-telechelic. The DSC results indicate that the copolymers with above mentioned copolymer composition and molecular weight are all semicrystalline polymers.The melt temperatures (Tm) of both PLLGA and PCG were determined from the second scan.The Tm ranged from 37℃ to 58℃ for PCG and from 80℃ to 162℃ for PLLA.They increased with increasing the molecular weight but decreased with increasing the copolymer composition.The glass transition temperature (Tg) of PLLGA was obtained from the second scan and ranged from 35℃ to 54℃.It also increased with increasing the molecular weight but decreased with increasing the copolymer composition.By ploting Tg and Tms with the reciprocal of number average molecular weight (Mn)

linear relationships

Tg＝Tg(∞)-K/Mn and Tm＝Tm(∞)-K′/Mn

are observed.For Tm

the interceptions Tm(∞) are linearly decreased with increasing GA

but the slope K′ is independent of GA.Therefore

experiential linear equations Tm＝Tm(H)-AGA-K′/Mn have been established to describe their relationship

in which Tm(H) is the melt temperature of PLLA and PCL homopolymers.For PLLGA

the values of Tm(H)

A and K′ are 166.9

129.5 and 1.48×105

respectively.For PCG

they are 60.4

82.0 and 2.92×104

respectively.From these results

one can design and synthesize hydroxytelechelic PLLGA and PCG copolymers and corresponding shape memory multiblock copolymers with desired transition temperatures.